THECONTROL OF MOISTUREMOVEMENT IN BUILDINGS USING THE DYNAYICB~ER ZONE
Paul Pasqualini
A thesis submitted in conformity with the requirements for the degree of Masters of Applied Science Department of Civil Engineering University of Toronto
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MASTERSOF APPLIEDSCIEXCE, 1999 PAULPASQUALINI Department of Civil Engineering University of Toronto
The performance and durability of building envelopes is significantly affected by
their ability to control moisture movement. This is especially true for intentionally
hurniditied buildings located in cold climates. Air esfiltration during winter months cm
cause serious damage to the building envelope. inevitable flaw-s in conventional air barrier
s>-stemsdue to workmanship and/or design deficiencies make the control of air Leakage a difficult task. The Dynamic Buffer Zone (DBZ) is an innovative air bamer system that can
elirninate the potential deleterious effects of air exfiltration.
The purpose of this research was to determine the influence of a DBZ systern on wall
surtàce temperatures. This \vas achieved by constmcting and exposing a DBZ \val1 assembly
to controiled temperature environrnents within a Iaboratory. The initial DBZ air temperature.
the DBZ air flow rate and the DBZ cavity width were the key characteristics OF the system
that il-ere investigated.
The ssperimental results obtained indicate that the influence of the DBZ system on
\vaIl surface temperatures is dependent on the tluid and therrnodynamic conditions of the
DBZ air Liithin the cavity. For the conditions investigated. it was found that the DBZ system
has a fairly insignifiant impact on wall surface temperatures. 1 should Iike to acknowledge the foliowing for their interest and assistance in the preparation of this thesis:
Mr. Renzo Basset of the Department of Civil Engineering, University of Toronto, for his invaluable assistance with the computer contrai system and data acquisition,
Mr. Peter DiLullo of Yolles Building Science Services, for providing the opportunity and the financial support to undertake this investigation,
The Natural Sciences and Engineering Research Council of Canada, for their financial support,
Dr. Kim Pressnail of the Department of Civil Engineering, University of Toronto, for his guidancet insight, and support throughout. List of Figures ...... vi
List of Tables ...... ix
1.0 Introduction ...... 1
2.0 Interaction of Moisture with Building Envelopes in Cold Regions ...... 4 2.1 The Effects of Moisture on Masonry Walls ...... 5 2.2 Condensation within the Building Envelope ...... ~~~~.~~~..~~~.~~~~..~~..~...... ~..~...~.7 2.2.1 Vapour Diffusion ...... 7 2.2.2 Air leakage ...... 8 2.2.2.1 Pressure Sources ...... 10 2.3 Quantity of Condensation due to Vapour Diffusion and Air leakage...... 13 2.3.1 Vapour Diffusion ...... 13 2.3 -2 Air Ieakage ...... 13 2.4 Limiting Condensation within the Building Envelope ...... 15 2.4.1 Vapour Retarder: Control of Vapow Diffkion ...... 16 2.4.2 Air Barrier: Control of Air Leakage ...... 16
3.0 The Dynamic Buffer Zone System...... 19 20 3.1 Building Envelope Retrofit:.. Control of Heat, Moisture and Air Flow ...... 3.2 Dynamic BuEer Zone Pnnciple ...... 24 3 -3 Dynamic Insulation ...... 29 3.3.1 Overview ...... 30 3 -3-2 DBZ - A Dynarnic lnsulation System ...... 31
4.0 DBZ Wall .Heat Triansfer Mechanisms ...... 33 ** 4.1 Thermal Energy Transfer ...... 33 4.1.1 Conduction ...... 33 4.1.2 Convection ...... 34 4.1.3 Radiation ...... 36 4.2 DBZ Wall .Heat Transfer Mechanisms ...... 37 4.3 Convection Heat Transfer Fundamentals ...... 43 4.3.1 Forced Convection Basics ...... 43 4.3.1.1 Velocity Boundary Layer ...... 44 Thermal Boundary Layer ...... 45 4.3.1 -3 Boundary Layer: Laminar or Turbulent Flow ...... 46 4.3.1.4 Convection Coefficients ...... 47 4.3.2 Interna1 Forced Convection Flow ...... 48 4.3 .2.1 Velocity Boundary Layer ...... 49 4.3.2.2 Thermai Boundary Layer ...... 51 4.3.3 Natural Convection ...... 52 9 4.3 .3.1 Natural Convection O Enclosures ...... -. ..53 4.3.3.2 Combined effects of Naturai Convection and Radiation ...... 55 4.3.4 Mixed Convection ...... -...... 56
5.0 Laboratory Research ...... 59 5-1 Method ...... 59 5.2 Apparatus ...... 64 5.2.1 TestingFacilityLayout ...... 64 5.2.2 DBZTestWall ...... ,-...... 65 5.2.2.1 Construction ...... 66 5.2.2.2 Thermocouple Layout ...... 68 5-23 DBZCavityAir...... 70 5.2.3.1 Air Source ...... 70 5.2.3.2 DBZ Air Flow Control ...... 71 3 3 5 .2.3 -3 Temperature Control ...... 71 5.2.3 -4 Air Distribution through Cavity ...... 72 5.2.3 -5 Cavity Pressure Control ...... 75 5.2.4 Control of the Interior and Exterior Environment Temperatures .....-..-...... 76
6.0 Experimental Results and Discussion ...... 80 6.1 Convective Heat Transfer Mechanism within the DBZ Cavity ...... 80 6.2 No Warm side Insulation ...... 85 6.2.1 DBZAirCavityTemperatures ...... 88 6.2.1.I DBZ Air Inlet Temperatures Colder than the Average Static Cavity Temperature ...... 89 6.2.1.2DBZ Air Inlet Temperatures Warmer than the Average Static Cavity Temperature ...... 93 6.2.2 Warm Side Surface Temperatures ...... 102 6.2.3 45 mm DBZ Cavity ...... 105 6.3 RSI 0.79 Warrn Side tnsulation ...... 1 10 6.3.l DBZ Cavity Temperatures ...... 1 12 6.3.1.1 DBZ Air Inlet Temperatures Colder than the Average Static Cavity Temperature ...... 1 12 6.3.1.2 DBZ Air Inlet Temperatures Warmer than the Average Static Cavity Temperature ...... 1 14 6.3.2 Warm Side Surface Temperatures ...... 121 6.3.3 45 mm DBZ Cavity ...... 121
7.0 Conclusions and Further Research ...... t...t...... t...... 126
References ...... 131
Appendix A ...... 136 Appendix B ...... 140 Appendix C ...... 143 Appendix D ...... 159 Figure 3.1 Visible water vapour mils resulting fiom air leakage fiom the top of the building following the construction of a 'proper' air barrier...... 23
Figure 3-2 Typical DBZ cavity in a masonry wall retro fit...... 24
Figure 3.3 Differential air pressure scenarios- ...... 26
Figure 3 -4 Incorporation of fenestration with the DBZ cavity ...... 28
Figure 4.1 Heat transfer mechanisms responsible for the transport of heat through the DBZ wail ...... 38
Figure 4.2 Equivalent electrical circuit summarizing the heat flow system of the DBZ wall ...... 41
Figure 4.3 Fluid flow over a flat plate ...... 43
Figure 4.4 Development of the velocity boundary Iayer within a fluid flow over a flat plate ...... 45
Figure 4.5 DeveIopment of the thermal boundary layer within a fluid flow over a flat plat at constatn temperature ...... 45
Figure 4.6 Hydrodynarnic boundary layer development berween parallel plates (laminar flow) ...... 49
Figure 4.7 Thermal boundary layer development between parallei plates at constatn temperature...... 51
Figure 4.8 Cellular flow due to Natural Convection in a vertical cavity ...... 54
Figure 5.1 Schematic of test wall without warm side (intemal) insulation...... 61
Figure 5.2 Generic testing combinatins for a particular wall ...... 62
Figure 5.3 Laboratory layout ...... 64
Figure 5.4 Test wall components ...... ,...... 67
Figure 5.5 General dimensions of framing for the test wall ...... 68
Figure 5.6 Thermocouple layout in test wall with no intemal insulation ...... 70
vi Figure 5.7 DBZ air flow control. ...-...... +. .- - -. 72
Figure 5.8 DBZ hot-box, ...... 73
Figure 5.9 DBZ air manifold...... ,*-----.---.----..--- 75
Figure 5-10 Effects of a flow channel on exhaust DBZ air. ..-..-.-.----.---...------..---...... 76
Figure 5.1 1 Sharpedged orifice...... 77
Figure 5.1 2 Testing equipment controllers. ...-...---.-.--.-.. --..-.-.- .--...... -. .-. .. .-----.- .-.- .-...... 79
Figure 6.1 DBZ thermocouple readings not afEected by two-dimensionai heat flow. ,.. 8 1
Figure 6.2 Cross-section of the test wall without \varrn side insulation.....--. - .~..~~.~~~.~.~~. 85
Figure 6.3 Average DBZ air cavity temperatures for inlet temperatures colder than the static cavity temperature (no warm insulation); A) -1 O OC cold side ,B)
-20 cold side...... -.,.-...-. .-...... -.-.---.--.-..---.-.---.-..-----.----....--.. ...-...... 90
Figure 6.4 Average DBZ air cavity temperatures for inlet temperatures wanner than the static cavity temperature (no warm insulation); A) - 10 OC cold side ,B) -20 cold side ...... --.-...... - ----.---.-.----.-.------94
Figure 6.5 DBZ air temperature profiles for the 0.1 &min flow rate with inlet temperatures of 6.6 and 20.9 "C (no warm insulation)...... 95
Figure 6.6 Exponentid decay of DBZ air temperature as it travels through the cavity. 97
Figure 6.7 The relationship between the amount of cooling the DBZ air experiences and the temperature difference between the DBZ air inlet and the average cavity temperature (no warm side insulation)...... --.---.-..---..-.-...... 99
Figure 6.8 Average cavity Temperature Index: A) -lO°C cold side , B) -20 cold side (no warm side insulation) ...... --..-.a---.-.-..---...... -.-...-..-.. -- .-.. ---.-.. .. 101
Figure 6.9 Wmside surface temperatures for inlet temperatures colder than the static cavity temperature (no warm insulation); A) -10 OC cold side ,B) - 20 cold side...... 103
'igure 6.10 Wmside surface temperatures for inlet temperatures warmer than the static cavity temperature (no warm insulation); A) -1 O OC cold side ,B) - 20 cold side...... 105
Figure 6.1 1 DBZ air cavity temperature for al1 air flow rates tested. a) 45mm cavity, B) 89mm cavity (no warm side insulation)..- ...... -.-.--. - .-... 107
vii Figure 6.1 2 Warm side surface temperatures for al1 air flow rates tested- a) 45mm cavity, B) 89mm cavity (no warm side uisulation)-... ..--..---..--...-...... ----.-.-109
Figure 6.13 Cross-section of the test wail depicting the warm side insulation (RSI 0.79)...... - .-...... ~.~~.~..~~~..~....~...... 110
Figure 6.14 Average DBZ air cavity temperatures for inlet temperatures colder than the static cavity temperature @SI 0.79 warm insulation) ...... --.1 13
Figure 6.15 DBZ air temperature profiles for the 0.1 m/rnin flow rate with inlet temperatures of 4.8 and 15.2 OC (RSI 0.79 warm insulation. -1 O OC cold side temperature) ...... 1 15
Figure 6.16 Average DBZ air cavity temperatures for inlet temperatures warmer than the static cavity temperature @SI 0.79 warm insulation); A) -10 OCcold side , B) -20 cold side ...... 116
Figure 6.17 The relationship between the arnount of cooling the DBZ air experiences and the temperature difference between the DBZ air inlet and the average
cavi ty temperature (RSI 0.79 warm indation)--.... -..- turturturturturtur.-.tur. ---.-turtur.--. -.. 1 18
Figure 6.18 Average cavity Temperature Index: A) -10 OCcold side ,B) -20 cold side (RSI 0.79 warm insulation ...... -.--...... 120
Figure 6.19 Warm side wall surface temperatures for inlet temperatures colder than the static cavity temperature (RSI 0.79 warm insulation); A) - 1O OC cold side ,B) -20 cold side, ...... 122
Figure 6.20 Cornparision of the warm side wall surface temperatures for the static cavity with warm side insulation and without wam side insulation (-10 OC cold side)...... , ...... 123
Figure 6.2 1 Cavity Temperature for al1 air flow rates tested. A) 45mm Cavity B) 89mm Cavity (RSI 0.79 warm side insulation)...... -...... -.----- ....----..--. 124
Figure 6.22 Warm side surface temperatures for ail air flow rates tested. A) 45mm Cavity, B) 89mrn Cavity (RSI 0.79 warm side insulation) ...... - ..--125
Figure A. 1 Results of Air Leakage Measurements on Four Test Buildings. ..-...... 139
Figure B.1 Typical Floor Plan of the Building located at 321 Bloor Street East ...... 142
viii Table 6.1 Grashof and Reynolds Numbers for various wall configurations for DBZ air flow rates of 0-01, 0.04 and 0.1 &/min...... 83
Table 6.2 DBZ Inlet temperatures with the exterior temperature at -10 OC (no warm seinsaon) ...... 87
Table 6.5 DBZ inlet. temperatures . with the exterior temperature at -10 OC (RSI 0.79 wann side insulation)...... - .-.--...... 1 1 1
Table 6.7 Average cavity temperature changes for the 89 mm DBZ cavity with RSI 0.79 warm side insulation...... -....,-.--.-...-...--.--. -~~~----.-...... -- ...... 1 17 THE COMROL OF MOlSnrRE MO~IENTIN BUILDINGS USlNC THE DI'NAAIICBUFFER ZONE
1.O INTRODUCTION
Canada boasts a large number of 'old' buildings that have been designated as heritage
buildings. These heritage buildings typically consist of uninsulated masonry walls that have
endured the test of time. As a result of the lack of insulation and the low levels of moisture
in the interior air, the masonry walls have kept warm and dry. In an effort to upgrade these
buildings to meet current standards of efficiency and cornfort, changes to the interior
environment must be made. These changes include increasing the relative humidity of the
interior air and in some instances, the addition of thermal ùisulation in the exterior walls.
However? these changes will lead to walls that are colder than before and will increase the condensation potential of the wall. Given inevitable flaws in air barrier systems, warm moist air frorn the interior may lsak into the building envelope and darnage the masonry facade- As a result of the greatly increased condensation potentiai of the moisture-laden intenor air. the service life of the building is cornpromised,
The Dynamic Buffer Zone (DBZ) is an innovative system that will maintain the specified indoor conditions while preserving the exterior facade in a cost-effective manner.
This systern involves intentionally creating a controlled and pressurized space of air between the relatively constant intenor environment and the variable outdoor climate. To be effective. this air space should be maintained at a higher air pressure than the interior environment and the air used to pressurize the cavity must have a low moisture content.
Using outdoor air during cold weather wiil enswe that the moisture content of the air is low.
As the cavity air pressure is kept slightiy greater than the interior air pressure, this buffer zone prevents the deleterious effkcts of excessive moisture in the masonry wall by essentially eliminating the leakage of moist air fiom the interior to the exterior façade. This approach has been recently used in one of Toronto's valuable landmark buildings, the Canada
Life Building. Performance fmdings of a DBZ demonstration project undertaken on the East
Memorial building in Ottawa has also indicated that the system was effective in providing the
necessary condensation controi and moisture protection for the exterior masonry walls [I. 11.
The Dynamic Buffer Zone system has the potentiai to be more than just a 'perfect' air barrier. Conceptually, the DBZ system can be operated in two modes. The first mode is known as a 'balloon' system where air is pumped into the cavity on an as need basis ensuring that the cavity pressure remains greater than the intenor space pressure. The second mode is known as an 'exhaust' system. This system is based on providing a continuous flow of air through the DBZ cavity by intentionally exhausting air from the cavity while ensuring that the air pressure within the cavity is maintained above that of the interior space. It is the exhaust mode of operating the system which imparts a great deal of versatility to the DBZ system. By controthg the flow rate and the initiai temperature of the DBZ air, the DBZ system cm act as both an air barrier and as a dynamic insulation system that can provide greater thermal efficiencies when compared to the same envelope without airflow.
During the sumrner months. the DBZ system can be shut off- However, the system may have the potential to operate as an air conditioning system that can remove a portion of the soiar heat gain experienced by exterior walls and fenestration, The study of this aspect of the system is not within the focus of this thesis.
When building envelopes are altered, an important consideration of the upgrade is its effect on the intenor surface temperatures of the exterior wall. A decrease in surface temperatures would cause an increase in radiant heat losses experienced by people in close proximity of the walls. Furthemore, the surface condensation potential of the wall wodd
increase. Consequently, an important aspect of the DBZ system is how it affects wall surface
temperatures.
The objective of this study was to investigate the influence of an exhaust mode
Dynamic Buffer Zone system on wall surface ternperatures. This was achieved by constmcting an exhaust DBZ wail assembly within a laboratory and exposing it to controlled temperature conditions. After carefùl consideration of the possible factors af5ecting the performance of the system, a testing program was designed and executed to investigate the effects of the following variables on wall surface and DBZ cavity temperatures:
1. initial DBZ air temperature, 2. DBZ air flow rate, 3. DBZ cavity width, 4 addition of interior insulation on the warm side of the DBZ cavity, and 5. exterior ambient temperature.
This report also examines the difficulties encountered with humidiQing the interior space of buildings located in cold clirnatic regions. The DBZ principle is investigated and its advantages as a system to control both moisture and heat flow through the building envelope are discussed. To Merunderstand the experimental results observed and the heat transfer mechanisms within the DBZ cavity, a review of convective heat transfer was undertaken.
It is believed that this research will identiQ key factors that influence the thermodynamic performance of an exhaust Dynamic Buffer Zone systern. It is hoped that this study will not only advance the technical knowledge conceming the performance of the
Dynamic Buffer Zone system, but ais0 assist in establishing areas where more research is required. 2.0 INTERACTION OF MOISTURE WITH BULLDING ENVELOPES IN COLD REGIONS
The building envelope is designed and built to provide a space that can be maintained at different conditions than the outside environment. Hence the envelope must perform as a separator of two non-identical environments, which in cold weather regions can be substantially different [2.1]. Perhaps it is intuitive that the performance requirements of a wail are deterrnined essentially by the differences between the interior and the exterior environments. What is not intuitive is the fact that not only are the properties of the materials to be used for a wall important: but also their relative positioning within the \val1 has a great influence on the microclimate created within the wall. Hence, the components of the wall must be selected such that heat moisture and airflows are adequately controlled and iocated so that the position of any one element does not impede on the performance of the others.
Durability is not an intrinsic property of a material; it is the service conditions to which it is exposed which detemine the durability of a material [2.2]. Thus, durable walls can be built by selecting materials which can withstand the environment they are exposed to or by modification of the service conditions to suit the materials chosen or a combination thereof
C2.31.
A very important environmental factor that needs to be considered when evaluating the suitability of a building envelope design that is subjected to cold weather is the interior relative humidity. intentional humidification during the heating season is a common practice in many cotd regions. Buildings such as hospitals, schools, libraries, office buildings. and museums are humidified for reasons that may include human comfort, operation of
electronic equipment, and the control of dimensional changes of materials due to fluctuation
in relative humidities. Moisture escaping the interior building environment through the
building envelope can have serious detrimental effects on the durability of the envelope.
Although there are a variety of different materials that can be used for the
construction of building envelopes, the focus of this section is the susceptibility of masonry-
based building envelopes to damages related to moisture penetration.
There are a number of mechanisms which have the ability to wet masonry walls.
These include rain penetration, wicking of soi1 moisture, water pondinglflooding resulting
from faulty drains and flashings, and condensation resulting from moisture dihion and air leakage [2.4]. Building enclosure problems and deterioration resulting hmthe condensation mechanisrns can manifest itseif in the following rnanner:
1. apparent rain penetration dunng spring thaw.
2. spalling of the exterior masonry can result from the absorption of moisture by the cladding and subsequent fieeze-thaw action and sub-flourescence,
3. shifiing of the wall may result by the growth of ice tenses within weak porous mortar or at weak joints [2.5],
4. premature corrosion of metal compnents such as fasteners, cladding anchors, masonry ties and metal studs,
5. discolouration of the exterior facade due to emorescence,
6. bioiogical decay such as mould and mildew may occur on supporting surfaces such as drywall and wood;
7. damages of intenor finishes such as plaster and drywall. Another difficulty arising from winter humidification that needs tu !E briefly mentioned is condensation on interior surfaces of exterior walls. Ensuring that the intenor building envelope surfaces are kept above the dew point temperature of the inside air can avert this. However, this may prove chailenging when dealing with window surfaces because these surfaces are usually the coldest and at the same time the Lem flexible component with respect to modification in order to accommodate high relative humidities. The resulting condensation does not directly give rise CO durability issues, but can cause problems if the condensate leaks into adjacent building components. Furthemore. excessive condensation cm cause difficulty with maintaining the required interior relative humidity for buildings with a large arnount of fenestration or can just be unsightly.
Building envelope distress related to high indoor humidity levels duing cold weather cm be attributed to any or al1 of the following:
1. deficient building envelopes are designed due to the designers' limited understanding of: the forces acting on the envelope? the properties of the materials selected, the performance requirements of the envelope, and the construction process[2.6],
2. workmanship deficiencies in the air barrier of a building and the envelope in general;
3. occupancy changes after the design and construction of the building envelope that require higher indoor relative humidities because the envelope as designed was not able to manage the new higher humidity requirements.
The focus of this chapter and of the report is the accumulation of moisture within the building envetope as a result of condensation, specificaily that resulting from air leakage. 2.2 CONDENSATIONWITHIN THE BUILDINGENVELOPE
The amount of water vapour that a mass of air can contain depends on the temperature
of the air1. Air is saturated when it contains the maximum amount of water vapour at that
temperature. This state-point is also known as having a relative humidity of 100%. The
temperature at which this occurs is called the dew point temperature. Cùoling of air that is at
its dew point temperature will result in the release of water vapour. This ccmdensate wilt
attach itself to the first 'solid' surface it encounters at or below the dew point temperature.
Condensation of moisture within the exterior wail assembly cmbe the resdt of two
moisture movement mechanisms: vapour diffusion and air lealcage-
2.2.1 Vapour Diffusion
Vapour diffusion is a process that occurs when there is a difference in the moisture content of two adjacent air masses. This difference in moisture content also gives rise to a difference in vapour pressures The interior environment of buildings during the winter months are typically humidified and consequently will have a greater vapour pressure than the exterior environment. This resulting vapour pressure gradient \vil1 cause intenor water vapour molecules to migrate through the wall assembly to the outside in an effort to equilibrate the vapour pressures. At some point within the wall, the air's dew point temperature may be reached causing condensation to occur.
Molecular diffision in a gas results from the random molecular mixing in a stagnant fluid. The basic equation for molecular diffùsion is based on Fick's law C2.71:
'The humidity ratios for air at -20°C and +20°C are approximately 0.6 grams and 14.7 grarns of water vapour per kg of dry air respectively. where.
m~ - is the mass flux of component A (in a binary systern), A D, is the diffiision coefficient, and p, is the mass density of component A.
The mechanism of gas diffusion through the interstices and capillaries of a porous or granuiar solid is called structure sensitive dt-sion r2.81. Fick's Law in the following fom cm also describe this rnechanisrn :
where,
W is the mas of vapour transmitted, - P is the perrneability of the rnaterid, A is the cross-sectional area of the flow path. 0 is the time during which flow occurs, and
(PI -PI) e is the vapour pressure gradient across the material. Experimental measurement of the vapow permeability of many materials is essential because of the complex geometry of the flow passages and the strong dependence of permeability on relative humidity,
2.2.2 Air leakage
Air leakage cm be defined as the uncontrolled movement of air through a building envelope [S.9]. The air movement can be either into the building (infiltration) or out of the building (exfiltration). For air leakage to occur an air pressure difference mut exist between any two points, and there must be a continuous passage through the wall assembly at the
location of the pressure difference co~ectingthe t=vo snviionments. It is the exfiltration of
air from humidified buildings during the winter months which is of concem in cold weather
regions because of the threat of concealed condensation- As the air travels fiom the interior
of a building through the cracks and openings in the wall assembly, it may be cooled below
its dew point temperature. If this occurs, the air will release some of its water vapour in the
form of condensate.
The relationship describing airflow through an opening is based on Bernoulli's
equation for steady and incompressibIe flow. A common adaptation of the equation is [2.10]:
where.
0 is the flow rate, CI, is the discharge coefficient for the opening dimensionl les^)^ A is the cross sectional area of the orifice opening, AP is the pressure difference across the opening, and P is mass density of air.
The discharge coefficient CD' depends on the geornetry of the opening and the Reynolds
nurnber of the flow- Airflow through constant area ducts with fully developed flow is well
characterized by equation 2.3. However, the openings in a building envelope are not uniform
in geometry and the flow generally never becomes fully developed [2.11]. Generally, it is
not practical to individually identiQ, measure and calculate the flow through the many
possible openings through a building envelope. However, at a particular pressure and corresponding flow rate, an equivalent effective air leakage area, which represents the combined effects of al1 the openings in the building envelope, can be calculated using equation 2.3 in the foilowing forrn:
where,
A, is the total equivalent or effective air Ieakage area, Q, is the predicted flow rate at AP, (fiom pressure test data). AP, is the reference pressure difference across the opening, p is mass density of air, and Ci, is the discharge coefficient (dimensionless).
To make use of this relationship. a pressure difference and corresponding flow rate which is characteristic of the building envelope king exarnined must be determined. This cm be obtained by depressurization tests of the enclosure and measuring the corresponding flow rate. A value of 0.6 which is characteristic of a sharp-edged orifice, is ofien used for the discharge coeff~cient.
2.2.2.1 Pressure Sources
The pressure difference which is necessary to facilitate air Ieakage can result from at lest one if not al1 of these sources: stack effect, wind action and mechanical pressurization.
Stack effect results form the difference in air temperature of two air masses on opposite sides of a separating element The pressure difference arising from stack effect results from a difference in specific weights of the interior air and the exterior air, which are separated by the building envelope. Hence, the effect of stack pressure in heated buildings is greatest during the winter months [2.12]. The airflow pattern associated with stack effect is such that air infiltrates into the building through openings in the building envelope at lower
levels and exfiltrates at higher levels. A neutrai pressure plane exists somewhere between the upper and lower floors where the air pressure inside and the air pressure outside are equal.
The location of the neutral pressure plane is dependent on the vertical distribution of cracks and openings in the building envelope. It will be located such that the volume of air entering the building will equal the volume of air exithg the building. During the cooiing season the flow directions will reverse, but the air leakage rate will generally be lower because the difference between the indoor and outdoor air temperature is small. The relationship used to calculate the pressure difference due to stack effect is:
where,
qs is the pressure difference due to stack effect, Pa p is the air density, kg/m3 g is the gravitational constant, 9.8 1 m/s2 H is the height of observation, m H ,, is the height of the neutral pressure level, m, and T is the average absolute temperature, K
Wind action is another force, which can cause a pressure difference across a building envelope. Wind will increase the positive air pressure acting against the windward side and will also produce a negative pressure on both the leeward side and the walls parallel to the wind direction. The pressure exerted on roofs depends on their angle - suction on flat or low sloped roofs [2.13]. INTEIWCTION OF MOI~UREWlTH BUILDING ENVELOPESIN COLD REGIONS 12
Mechanical pressurization of the intenor envuonment resulting fiom the use of air
handling equiprnent is the third source of air pressurïzation- Depending on the purpose of the
equipment, the effect may be to increase or decrease the indoor air pressure by making the
supply of air into the building greater than the exhaust or alternatively, the exhaust larger
than the supply. In Canada many systems are designed and operated so that the building's
interior has a greater pressure than the outdoors Some reasons for this are to reduce
infiltration at doors and windciws to improve cornfort, and inhibit the entry of air pollutants
[2.14].
The pressure difference across a wail assembly and the pattern of air leakage depends
on the cornbined effects of stack action, wind action, and mechanical pressurization. These
different forces can act together or in opposition depending on the outdoor conditions.
characteristics of the building envelope and how the air handling system is operated. The net
pressure difference is approximately equai to the dgebraic sum of the individual mschanisms
[2.15]. Wind action acts interrnittently and its effects are generally a concem when examining the structural integrity of the air banier system. Stack action imposes. for the
most part, a continuous air leakage pattern during the heating season, that when aggregated over the entire season, can arnount to a formidable force. When mechanical pressurization is superimposed on stack effect, a common occurrence in Canada, pressure differences in upper floors are increased and reduced in lower floors such that the neutral pressure plane is lowered and exfiltration is increased in the upper floors [2.16]. ILNTER~CTIONOF MOISTUREWCTH BU~CDINCENVELOPES IN COLD REGIONS 13
2.3 QUANTITYOF CONDENSATIONDUE TO VAPOURDIFFUSION AND AIR LEAKAGE
To demonstrate the difference in condensation potential between water vapour di ffision and the air leakage mechanism? a 300 mm solid masonry wall will be examined.
A building located in the Toronto area will be considered during the month of
January. The building will be conditioned at 23 OC and 35% relative humidity. The Normals table provided by Environment Canada indicates that the average exterior temperature in
Toronto for the month of Januq is -8 OC- Furthetmore, it will be assumed that the outside relative humidity is 100%.
2.3.1 Vapour Diffusion
The amount of condensation that occurs due to vapour diffusion is dependent on the vapour pressure gradient, the penneance of the wall assembly and the dew point temperature.
The vapour pressure gradient can be closely approximated by the difference between the interior vapour pressure and the saturation vapour pressure of the outside air- The resistance to difhsion is provided by the 300 mm of brick bat has a permeance of 15.09 ng/(s m' Pa)
[2.17]. Hence, the arnount of condensation resulting fiom difision through a I 1 mL wall area during the month of January was estimated to be 254 g using steady-state conditions
(refer to Appendix A).
2.3.2 Air leakage
The arnount of condensation resuiting from air leakage is dependent on the rate and the duration of airflow, the moisture content of the intenor air, and the temperature to which the air is cooled- Large commercia1 buildings are often thought of as king fairly airtight [2.18]. The National Association of Architectural Metal Manufacturing specifies a maximum
leakage per unit of exterior wall area of 0.3 L/(s m') at a pressure difference of 75 Pa not
including the leakage through operable windows. There is limited idonnation on the leakage
characteristics of conventional building construction. However, the limited numkr of
investigations conducted indicate that office buildings are much leakier than anticipated. Air
leakage measurements in eight Canadian office buildings with sealed windows ranged fiom
0.61 to 2.4 L/(s ml) [2.19] and whole building pressurization tests in eight large American
office buildings found air leakage rates ranging from 1.OS to 5.22 L/(s m2) at 75 Pa [2.20].
The air leakage results of an investigation of four buildings located in Ottawa were also
found to be fairly leaky. The test buildings varied in height from 1 1 to 22 stories and the air
leakage rates vax-ied from 1.27 to 2.44 L/(s m') at 75 Pa as the graph in appendix A
summarizes. The results of this investigation will be utitized in subsequent calculations.
As discussed earlier, the pressure difference driving air leakage results fiom the
combined effects of stack effect, wind action, and mechanical pressurization. ft will be consrrvatively assurned that the mechanical pressurization will be positive and équal to 10
Pa. The pressurization resuiting from stack action can be estimated using equation 3.5.
Assuming that a wall 15 m above the neutral pressure plane is being examined, the stack pressurization occumng for the January conditions outlined previously is estimated to be 20
Pa. Since wind effects are usually intermittent and variable, they will be neglected. Hence, the net pressurization is 30 Pa 15 m above the neutral pressure plane. The results of the air leakage study in Ottawa indicate that a conservative estirnate of the air leakage rate at 30 Pa is 0.73 Lis per m2of building envelope area. The hygrotherrnal mechanisrn of the heat and moisture exchange between the flowing air and the masonry is compiex [2.21]. However, for the purpose ofdernonstration, it wili be assurned that the exfiltrating air will leave the building envelope saturateci at the outdoor temperature. Hence, the total moisture condensed within the 11 m2 masonry wall area considered during the rnonth of January is estimated to be 1O8 kg (refer to Appendix A).
A cornparison of the potentiai for condensation resulting fonn diffusion and air leakage demonstrates that the exfiltration of interior air through the building envelope to the outside cm be much more detrimental to the performance of the wall. Not only is air exfiltration potentially more damaging than diffusion because of its greater capacity to transport moisture. but also because the resulting condensation will Iikely concentrate in crack locations (e.g. around window flrames) unlike that of difffusion which will be more uniforrnly distributed throughout the wall-
In addition to the transfer of water vapour. air leakage wiii also cause the heating load in winter and the cooling load in sumrner to increase, cold drafts, increased difficulty in maintaining a controlled relative humidity, and facilitate the transfer of smoke, odours and other pollutants [2.22].
2.4 L~MITINGCONDENSATION WTHIN THE BUILDINGENVELOPE
The two mechanisms identified as king responsible for transport of moisture into the building enclosure are vapour diffusion and air leakage. Consequently, to successlÜlly limit condensation within the enclosure a building envelope must include a vapour retarder and an air barrier. 2.4.1 Vapour Retarder: Control of Vapour Diffusion
Although the mechanisrn of air leakage has the potential to deposit a much greater amount of moisture, vapour dimision should not be overlooked because the cumulative effects of vapour diffusion during the heating season can also be significant. Vapour diffusion can adequately be controlled with the use of a vapour retarder instailed on the warm side of the building envelope. A vapour retarded is a material that has a high resistance to vapour difision. It is not necessary for the vapour retarder to be perfectly continuous because deficiencies such as perforations, holes and lapped joints in conventional construction practices are usually a small portion of the entire building envelope area.
2.4.2 Air Barrier: Control of Air Leakage
As stated previously, both an air pressure difference and openings through the wall assembly are necessq to facilitate air leakage. The pressure difference that can occur is not easily controlled. Thus, the function of an air barrier is to control or limit the area of leakage paths through the building envelope. Openings through the building envelope which air can leak are nurnerous in most normal constructions. For exampie. air can leak through cracks between window fiames and the structure, or through masonry walls because both the masonry units and the rnortar stuink leaving cracks and openings, or through cracks that form between the masonry wall and the steel he,again resulting from shrinkage or differential movements. Hence, an effective air barrier demands a great amount of attention dunng the design and construction stage. An air barrier may consist of one material or a system of rnaterials. If an air barrier is to be effective during the entüe senice Iife of the structure it must have the following attributes: air impermeability, continuity, structura! integrity, and durability D.231.
Air ImperrneabiIity: The fündamentai characteristic of an air barrier is that it, the
body material and the joints offer a high resistance to air flow. However, this does not
mean that it needs to be impermeable. Part 5 of the Ontario Building Code specifies
that the material which provides the principle resistance to air leakage within the air
barrier system is required to have an average leakage characteristic less than 0.02 Ys
m' at a 75 Pa pressure difference.
Continziiry: There are many intrusions that the wdl air barrier encounters -
windows. ceiling, columns and services. It is imperative that these intrusions are
comected to the air barrier so that there is no break in the air tightness of the building
envelope.
Strucfriral Infegriry: The air bamier must have sufficient strength or be supported
by a wall component that has sufficient strength? to resist the positive pressure or
suction pressures exerted on it. This means that the air banier must be able to resist
peak wind pressures and sustained loading without compromising its performance.
Durabiliry: It is expected that the air bamier is to perform effectively for the entire
service Life of the structure. The air barrier must be compatible with adjoining
rnaterials and resistant to deterioration under the imposed loads within the service
environment [2.24]. Thus, materials andor systems used should have a proven record
of performance- Another important critena which influences the effectiveness of an air barrier is its location within the building envelope. The discussion thus far has focused on through-the- wall air leakage. From the perspective of energy conservation and condensation resulting from through the wall air leakage, it does not rnatter wtiere the air barrier is located.
However, in dealing with total condensation potential, the location of the air barrier is important. Stack action between the heated interior buiIding space and colder vertical air spaces incorporated into the wall assembly can occur in the same way as that between the building and the outside air if the wall space is 'comected' to the interior space in at lest two different heights. During this air interchange, interior air will enter the air space at the higher cracks/openings become coo1ed and expel some of its moisture and flow back into the interior area €rom the cracks located Iower in the wall assembly C2.251. A fimher consequence of this convective Ioop is a reduction of the thermal resistance of the wall assembly. It may be concluded that the need for the plane of air tightness to be located on the intenor side of the building envelope. However, with the air banier located on the interior, cooling of the corners of the corners of a building due to wind action may occur. This cooling effect will increase the condensation potential of the affected areas.
In summary, the performance and durability of building envelopes is significantly affected by their ability to control moisture movement. This is especially true for intentionally humidified buildings found in cold climates. Both vapour diffusion and air leakage must be addressed when designing a building envelope. However, air leakage requires special attention because of its greater potential to transport moisture and the design and constructionci properly. 3.0 THE DYNAMIC BUFFER ZONE SYSTEM
it has been established that an effective air barrier is an essential component of any durable building envelope for humidified structures in cold regions This is not only tme for new construction. but also for retrofits of existing structures, especialiy for those masonry structures where the existing envelope was not designed to control the current standards for high interior hurnidities. Such cases arise when factories are converted into office space, schools are transformed into housing units, or old office buildings upgrade the air handling equipment to inciude humidification. These occupancy changes usually bring about changes in the requirements of the indoor environment such that higher relative humidities and better temperature control are both required-
The difficulties encountered with the design of 'new' building envelopes for existing structures arise because many of these buildings are constnicted with older materials and dated construction practices [3,1]. Furthemore, additional limitations will be placed on the design if the structure has ken designated as a heritage building that does not allow the exterior facade to be altered in any significant manner. Thusl the question which faces the building envelope designer is how to modiQ the existing envelope in a cost effective manner such that adequate control of kat, moisture and air flow is achieved without undermining the durability of the existing wall or without altering the exterior facade?
There exists little documented information on the appropriate measures that should be implemented to control heat, moisture and air flow when renovating the interior of a solid masonry structure C3.21. However, if a design approach based on fundamental building science principles is adopted, a technically based cost effective solution cm be attained. Many masonry built buildings such as commercial and industrial buildings have stood the test of tirne remaihg in excellent shape for many decades. This is amibuted not only to the use of appropriate materials and constniction practices, but also to the interior environment to which the building envelope was exposed. The interior spaces were not intentionally humidifïed and would rareiy have a relative humidity above 10% during the coldest months L3.31. Furthemore, the placement of steam heating systems within the building envelope, and the lack of insulation within the endope ensured that sufficient amounts of heat would penetrate the masonry wall to remove any moisture that may have entered the building envelope.
With today's concem for the environment and the conservation of energy, the addition of thermal insulation to these previously uninsulated walls is often thought of as a prudent first step in the rehabilitation process. It is generally accepted that the placement of additional insulation on the exterior face of an existing facade is the best approach because the building will not be exposed to large variations in temperature and moisture content, and its thermal mass can be utilized.
The addition of interna1 insulation is often coiitemplated for the control of heat flow when upgrading a masonry building envelope that cannot have its exterior facade altered. In addition to adding intemal insulation, an air barrier system and a vapour retarder are instailed to facilitate the control of air leakage and vapour diffusion respectively. The obvious advantages to this approach are significant energy conservation, warmer interior wall THEDYWAICIIC BUFFER ZONE SYSlFM 21 finishes, increased occupant comfort near exterior waiis and the elimination of wall surface condensation. However, there are some potential drawbacks:
Condensation within the wall components behuid the insulation is more likely because those components wiil be well beiow the dew point of the interior air during cold weather,
Since less heat will be reaching thermal bridged daces such as whdow fiames and floor slabs, there will be an increase in risk for condensation, mould growth and dust markings in those areas,
The masonry wall is now more susceptible to fkost damage because the insulation greatly reduces the heat flow into the wall which would have promoted drying of the wall if water found its way into the masonry,
Interna1 insulation will affect the stress distribution in the exterior wall. Exterior sdaces will hardly be aEected, but the interior masonry surfaces will become much colder. This generally results in a masonry wall that has a more uniform stress distribution. However, it is thought that thermal differential movement between the now colder exterior wail and any adjoining warmer interior cross-walls, floor slabs or window splays may Iead to cracking of the masonry located in these intersections C3.41. An investigation was conducted to examine the effects of adding intenor insulation to a four-storey masonry watehouse in Winnipeg [3.5]. The effect of thermal bndging at the floor level subsequent to adding interior insulation was shown to be fairly significant. The rnasonry wall at the Boor slab level was found to be 10°C above the temperature of the masonry found at the mid-height of the walI. This finding demonstrates that the fear of cracking of the masonry in these areas due to differential temperatures needs to be investigated;
Thermal bridges such as floor slabs, cross-walis and window splays can result in significant heat loss that will undermine the effectiveness of the interior insulation [3 -61,
Although these concems exist, little long-tenn research has been performed to substantiate the above noted nsks associated with intemally insulating masonry structures. Since little information is available, it may be possibte to assess the effects of adding interna1 insulation through detailed cornputer modeling on a project by project basis to determine the viabiliv of such an approach.
Assuming that the preservation of the exterior facade is of primary importance, and in view of the potential drawbacks associated with the addition of interna1 insulation, it wodd be prudent to design a retrofit building envelope without the addition of intemal insulation.
The new design should ensure that the rnasonry would be exposeci to the same environment which it has 'seenT since it was constructed. This entails not incorporating any thermal indation into the envelope in order to let heat escape into the masonry. A Merarpcct of the design involves controlling the flow of the added interior space moimire into the envelope. This is achieved by installiag a vapour retarder and an air bamer. It should be noted that the associated decrease in air leakage due to the retrofit would also contribute to a decrease in the heatïng and cooling loads for the building.
This approach of only controlIing moisture and airflow also has its limitations. As discussed earlier, a vapour retarder can easily be incorporated into an existing wall.
However, providing an air barrier that is continuous and provides air tightness at the numerous joints and interfaces associated with an existing wail can prove to be very challenging. A prime exarnple of this occurred when a Canadian office building that was built in the late 1950's was convened into an art gailery [3.7]. During the twenty-year Iife of the gallery, the enclosure suffered many failures due to air leakage of hurnid interior air through the wall assembiy. The repairs were designed to control air leakage, but as the vapour trails at the top of the building in Figure 3.1 show, the repairs were not successfbl after several attempts. Thus, it can be appreciated that condensation resulting fiom air leakage can accumulate withïn in the wall assembly even with focused attempts to install proper air barriers; however, the moisture quantities accumulated can potentiaily be smailer. hother potential dificulty of this approach that is wt detrimental to the building envelope is the possible occurrence of condensation on highly conductive interior surfaces, such as window fiames, that are thermally bridged with the exterior environment.
The above noted problems arise with conventional design and construction ptactices.
These problems can be overcome with the implementation of a non-conventional and versatile air barrier system called the Dynamic BufEer Zone system.
Figure 3.1 Visible water vapour trails resulting from air leakage from the top of the building following the constructioa of a 'proper' air barrier. Source: see 13 -71 THEDYNMIIC BU- ZONE S~M 24
3.2 DYNAMCBUFFER ZONE PRJNCIPLE
The developrnent of the Dynamic Buffer Zone @BZ) system is attributed to the late
Kirby Garden, a tesearcher at the National Research Council of Canada- The system is based on the concept of intentionaily controlling conditions in an air space between the indoor environment and the outdoors. Those conditions of the air inside the airspace that need to be controlled are temperature, moisture content and air pressure.
Exterior -. -
-
- - DBZ Cavity
Masonry Wall------New Interior Finish - (Gypsum Board) \
. - A - .-- --
Figure 3.2 Typical DBZ cavity in a masonry waU retrofil.
With respect to masonry wall retrofits, the necessary air space can be an existing interstitial space, if appropriate, or can be constnicted on the wann side of the building envelope. For example, a two or four inch' cavity can be constnicted such that the interior
' Conventional fi-aming member dimensions THEDYNA~IIC BUFFER ZONE SY~ 25 sîde of the masonry wall forms one side of the cavity and the interior finish provides the other boundary of the cavity as shown in Figure 32. To ensure that both the size of the fan delivering air to the cavity and the heater used to kat the air is optimlled2, the interior finish that fonns the inside boundary of the cavity must be sealed at al1 intersections with intrusions such as ceilings, window -es and columns. Furthemore, the rnasonry forming the exterior boundary of the cavity should be face sealed if it is excessively Ieakf.
To address the concern of cold weather air exfiltration of hurnid interior air through the building envelope, it is essential that:
1. the air pressure of the cavity remain slightiy greater than the indoor air pressure, and
2. the moisture content of the air supplied to the cavity be equal to or less than the moisture content of the outdoor air.
Theoretically, the cavity air pressure needs only to be 0.1 Pa greater than the intecior space air pressure to prevent air leakage kom the interior space. The actual amount of cavity pressurization that should be used is dependent of the specific project. Typicdly a 5-10 Pa pressure difference should suffice. Air taken fiom the outdoors is ideal for the DBZ supply air because it will have a very low moishue content at winter ternperatures. As Figure 3.3 demonstrates, the requirement for pressurization will ensure that interior humid air will not leak outwards into the building envelope because the pressurized cavity will act as a barrier.
If any leakage of air fiom the cavity occurs, the requirement for the DBZ air to have a low moisture content will ensure that the threat of condensation within the envelope is eliminated.
' To be determined by budget and/or construction limitations THE DWAMIC BUFF€R ZONESYSEht
Exterior
- DBZ Cavity
------if Leaka e through construction ?;) irnpe dections
Scenario # I Scenario #2
+ Air Pressure - Air Leakage
Figure 3.3 Differential air pressure scenarios.
There are two possible modes of operating the DBZ system. ïhe first option is known as a "balloon" system where air is pumped into the cavity on an as needed basis. That is, when the pressure inside the cavity drops below a specified lower limit, fans are activated to pressurize the cavity to the specified upper iimit The air inside the cavity will then leak out through the cracks of the exterior wall and through any imperfections in the intenor wall finish until the lower prescribed pressure limit is reached, afier which the process will repeat itself. The altemate mode, which holds more potential, is the exhaust system. This system entails supplying a continuous flow of air into the cavity and intentionally exhausting air from the cavity so that the pressure within the cavity is maintained at a predeterrnined pressure. How and where the air is exhausted is dependent on a number of factors that are specific to the structure involved.
In addition to walls and roofs, the DBZ system can also incorporate windows to provide additional thermal comfort and condensation control by increasiag the window surface temperatures and thus allow higher indoor humidzties. This system wiU also eliminate the need for convective uni& used to prevent cold drafts below windows. The DBZ air could be introduced into the window by drilling through the window heand penetrating the space between the panes of a double glazed unit to allow air from the adjoining DBZ wall cavity to flow between the panes. Attention must be given to ensure that the structural integrity of the window is not comprornised. A fiuther complication of this system is the possible difficulty in achieving the required flow between the panes of glas.
This is due to the fluid dynamics involved with small diameter holes in the window he used to distribute the air into a relatively large volume of air between the panes of glas. A more practical and effective method exists for pro tecting windows fiom surface condensation and controlling the solar heat gain of the interior space. This is achieved by consbucting an
'intenor' window comected to the intenor finish such that the DBZ air could travel fiom the wall DBZ cavity to between the extenor window and the new interior window as shown in
Figure 3.4. The new window would be operable to allow access to the extenor window [3.8,
3-91. Furthemore, this method of construction enables the installation of blinds between the interior and exterior window to limit the entry of solar radiation through the window. THEDYNMIIC BUFFER ZONE SVSTEM 28
I Exterior Interior
! Solar Shading Protection
Existing W ind.ow
New tnterior Finis A'-(~ypsum Board)
Figure 3.4 Incorporation of fenestration with the DBZ cavity,
Although the temperature of the cavity air supplied is not important when dealing
with the prevention of air exfiltration, it is important fiom the viewpoint of thermal cornfort and surface condensation. During winter conditions the temperature of the DBZ air as it travels between the point of enûy into the building and the point of entry into the DBZ cavity
should be at least the dew point temperature of the interior air. This will prevent condensation fiom occurring on the exterior surfaces of the distribution ductwork used to transport the DBZ air within the building. However, lower DBZ air temperatures can be tolerated if the ductwork was lightiy insulated and a vapour retarder was installed on top of the insulation. THEDIWAI~IIC BUFFER ZONES~ICI 29
The exhaust mode of operation imparts a great amount of versatility to the DBZ system so that it can be utilized as more than just a 'perfect' air bacriet. By controlling the flow rate and the initial temperature of the DBZ air, the DBZ system can act as both an air bmrier and as a dynamic insulation system that can provide greater thermal efficiencies when compared to the same envelope without airflow.
Additionai advantages of the exhaust DBZ system are:
its ability to promote dryhg of the masonry following the occurrence of rain penetration and to allow air borne contaminants to be contained in a space and controlled, and
its ability to increase the temperature of interior fuiishes of the exterior wall by supplying DBZ air that is above the indoor air temperature. This will elirninate 'd&' associated with wall that are not insulated and increase thermal comfort.
33 DYNAMICINSULATION
A dynamic Uisulation system consists of a heat-carrier fluid, such as air, king circulated by natural or mechanical means through an air cavity or through penneable thermal insulation in a building envelope. This system causes the once static building envelope to act as an air-to-air heat exchanger reducing the thermal Ioad or improving the comfort conditions of the indoor space [3.10 1. The moving air Stream through the air cavity or the insulation absorbs some of the heat that would be conducted through the static building envelope.
The objective of this section of the report is to provide a brief overview of dynamic insulation systems and to inform the reader of the potential for the Dynamic Buffer Zone to provide not only air leakage control, but also greater themal eficiency andor codon Dynamic insuiation systems have ken rigorously investigated in many European
countries since the 1970's. France is one country in which the building industry has been
active in developing technological solutions for dynamic insulation systems 13.1 11.
Dynamic insulation systems rnay be classified according to the following [3.12]:
1. Type of medium in the fluid fiows Cavity or duct Porous medium
2. Type of fluid circulation forced or natural
3. Type of fluid air or liquid
4- Wall-fluid interaction open systems: an 'extemal' fluid such as outdoor air flows through the building envelop closed systems: fluid flows in a controlled manner inside the component without fluid renovation
5. Fluid flow direction parallel to wall surface perpendicular to wall surfaces - in same direction of heat flow or in opposite direction of heat flow
It may seem that there are a nurnber of possible dynamic insulation configurations; however, many combinations are not feasible because of technological problems or because of issues related to physics [3.13]. Only a few systems have actuaily ken developed. 'Open' systems using airflow in envelope cavities and thmugh permable insulation have been the most popular configuration E3.141. The majority of the proposed technologies investigated in a research program sponsored by the French Government in the eariy 1980's belong to the
cavity-wall category [3.15,3.16].
The exhaust Dynarnic Buffer Zone system when viewed as a dynamic idation system is, according to the above criteria, classified as an open cavity system with forced airflow parallel to the wdl surfaces. Again it must be ernphasized that details regarding the design and construction of the system is projet specific and it is not within the scope of this report to discussed possible configurations. However, some general eficiency aspects of operating the DBZ as a dynamic insuiation system will be discussed.
33.2 DBZ - A Dynamic Insulation System
An iniportant aspect of the energy performance of dynarnic insulation is how it is integrated with a building's mechanical system. The exhaust DBZ system will be the focus of the following discussion.
In winter conditions, the outdoor air used for the DBZ wall cavity wilt be introduced into the cavity at a temperature Iower than the indoor temperature. Consequentiy, the air
Stream will capture heat that would otherwise be lost to the outdoors. The effectiveness of this dynarnic insulation system is dependent on what happens to this heated air once it hrts been exhausted from the wall cavity. The first option is to combine the exhaust DBZ air with the building's ventilation air if the DBZ cavity is fiee of contarninants that could cause odour or respiratory problems. Alternatively, if there is sufficient airflow, the exhaust DBZ air could constitute al1 of the ventilation requirements for the building, The second option is to exhaust the cavity air to an energy recovery unit such as a heat pump. The recovered heat can be used either as an auxiliary heat source for ventilation air or the hot water system. THE DYNAMICBU- ZONESYSCEM 32
Coupling the DBZ system with a heat recovery unit during the coolhg season cm
provide fûriher energy swings. This is achieved by directing exhaust building ventilation air
through the DBZ cavity. This air stream is able to cool the extenor wall, which is absorbing
kat fiom the exterior, especially solar heat. The heat recovery unit can then be utilized to
emact the energy that is absorbed by the air and used to supplement hot water heating. If a
heat recovery unit is not feasible, savhgs fiom reduced air conditioning costs are still achieved by simply exhausting the heated air fiom the building.
The thermal efficiency the DBZ dynamic insulation system would be sensitive to
factors related to construction:
1. The exterior side of the cavity should be as airtight as possible to maximize the recovery of heated air, especially because the cavity will be pressurized, and
2. Irregularities in the flow path of the air, such as stagnation areas or short circuits, will reduce the amount of heat recovered by the auflow.
Although the context for the application of the Dynamic Buffer Zone system thus far has focused on the retrofit of masonry buildings, there exists a wide-spread potential for its application in a variety of retrofits and in new construction. Specialty structures such as hospitals, museums, indoor swirnming pools and tropical exhibits in cold clirnates that need high indoor humidity and consequently are at high risk of moisnire damage are ideal candidates for the DBZ system. The DBZ system provides a flexible buiiding envelope system that can be altered to accommodate changes in the interior environment. THECONTROL OF MOISTUREMOVEMENT IN BUILDINGS USING THE D\'IYAMH=~UFFER ZONE 33
4.0 DBZ WALL - EEAT TRANSFER MECHSMS
The purpose of this chapter is to examine the relevant beat transfer modes that &eçt an exhaust type Dynarnic Buffet Zone wall. The various kat energy tramfer modes will be briefly examined. This will be followed by an exadnation of the interaction of the DBZ air and the wail fkom a heat energy perspective. Finally, convective heat transfer will be examined more closely since this is a very important heat tramfer mechanism Hècting the
DBZ air temperature.
4.1 THERMALENERGY TRANSFER
Thermal energy is transferred from one region to another by three possible modes: conduction, convection and radiation. The transit of energy is due to a temperature difference between the two regions.
4.1.1 Conduction
The tenn conduction refers to the heat transfer that occurs in a stationary medium that has a temperature difference across it. Conduction heat transfer transports energy fiom particles of a medium at high energy levels to those particles of lower energy by transfemng kinetic energy between the particles at the atomic level [4.1]. The transfer of kinetic energy through gases, liquids and solids occurs in the following manner:
1. gases: by the elastic collision of molecules,
2. liquids: similar to gases, but the molecules are more closely spaced and the molecule
interactions are stronger and more muent; the rate of conduction heat transfer is
greater in liquids than in gases, and DBZ WALL- HEATTIUNSFERMECHANISMS 34
3. solids: the transfer of kinetic energy may be attributed to atomic activity in the form
of lattice vibrations. In a non-conductor, the energy transfer is entirely by lanice
vibrations, but in a conductor, it is also due to the translational motion of fiee
tlectrons f4.33.
The conduction heat transfer rate can be quantified using Fourier's law. The rate
equation for one-dimensional steady-staîe heat flow through a medium is expresseci as:
where,
Q is the heat flux through the element (W/rn2)? k is the thermal conductivity property of the element (W/m K), and
-aT is the temperature gradient across the element.
The thermal conductivity property of a medium depends on temperature and its moisture content. However, it cm be taken as a constant through the medium if the temperahue and moisture content differences across the element are not great.
4.1.2 Convection
The term convection refers to heat transfer that will occur between a surface and a moving fluid that are at different temperatures. Thermal convection involves two mechanisms for the transfer of heat energy. These two mechanisms are conduction and the bulk motion of the fluid. Consider the convective heat transfer that occurs between a cool fluid moving over a warm surface. At the interface between the fluid and the surface the fluid velocity is zero and increases to the bulk flow velocity some distance fiom the surface. DBZ WALL - HEATTRANSFER MECHANSMS 35
The contribution to heat transfer due to conduction is -test near the surface where the
fluid velocity is low. The contribution due to the bulk fluid motion can be viewed as picking
up this conducted heat and transporting it downstream where the heat eventuaily gets
transferred to the buk fluid [4.3],
Convective heat transfer is classifieâ according to the nature of the fluid flow:
forced convection occurs when the flow of fluïd is caused by extemai forces such as fans, pumps and wïnd,
fiee or nufural convection can occur when fluid flow results fiom a body force, such as gravity, acts on a fluid in which there is a density gradient, and
mUred convection is a combination of forced and fiee convection. This occurs when the fluid velocities are small andor the buoyancy forces are large.
Aithough there are three possible types of convective heat transfer modes, there is onIy one expression that describes heat flow due to convection. This expression is known as
Newton's iaw of cooling:
where, .. 9 is the convective heat flux (w/mZ), Ts is the surface temperature, T, is the bulk fluid temperature, and h is the convective heat transfer coeficient (w/m2 K).
The value of the convection heat transfer coefficient is what distinguishes the different types of convection heat transfer modes. Determinhg the heat transfer coefficient for a particular situation can be dificult This coefficient is a fluid mechanic property of the system that is dependent on the conditions in the boundary layer that exists dong the sudace of interest. DBZ WALL- HEATTRANSFER MECHANISMS 36
The boundary layer characteristics depend on the nvface geometry, the nature of the fluid
motion and a nurnber of fiuid thermodynamic and transport properties 14-41. This will be
Merdiscussed in the next section.
4 Radiation
All matter emits thermal radiation. The emission of radiative energy may be
attributed to changes in the electron contiguration of the constituent atoms or molecules
[4.5]. Unlike conduction or convection, radiant heat energy transfer involves a change in
energy form, fiom internai energy at the source to eiectromagnetic energy for transmission
and then back to interna1 energy at the receiver (4.61. This transfer of energy occurs between
two or more bodies at different temperatures that are separated by a space (air or vacuum) or
a medium that is transparent to the electromagnetic waves.
Radiation energy that is emitted by a surface is derived fiom the thermal energy
stored within the material that is bound by the radiating surface. The heat flux emitted by a surface is expressed as:
where,
E is the heat flux emitted by the surface, is the Stefan Boltzmann constant (5.67 XIO-' w/m2 K) E is the emissivity - radiative property of the surface, O< 6 <1 T is the temperature of the surface, K.
The surface emissivity depends strongly on the surface material, its temperature, and its finish as it is a measure of how efficientty a surface emits energy relative to a blackbody. A blackbody is an idea1 radiator and its surface emissivity is taken as one. DBZ WALL- WTTRANSFER MECHANlSMS 37
Surfaces can also absorb radiation occurring fiom its surroundings (irradiation). The radiation that is absorbed by the surface will increase the thermal energy of the material. The amount of energy absorbed is dependent of the wavelength of radiation behg received and the absorptivity property of the surface. For a given temperature, the absorptance of a noa- blackbody is equd to its emissivty (Kirchhoff s Law).
4.2 DBZ WALL- HEATTRANSFER MECHANISMS
The DBZ wall as describeci in Chapter Three presents a heat transfer scenario that involves convective heat flow within the cavity. This section will focus on the modes of heat transfer through that same wall except it will be assurned that there will be no air leakage into or out of the DBZ air cavity.
The heat transfer mechanisms involved in the flow of thermal energy through the wall are summarized in Figure 4.1. It is evident that al1 three heat transfer mechanisms
(conduction, convection and radiation) are actively transporting energy through the wall.
With reference to Figure 4.1, thermal energy is king transported through the identified zones in the following manner:
1. Heat is transported between the interior space and the interior wall finish by radiation natural convection and conduction.
2. Heat is conducted through the interior finish,
3. The air element in the cavity lmses or gains heat fiom the interior wall finish and the exterior wall primarily by convection and conduction. The type of convection transfer is dependent on the fluid and thermodynarnic conditions of the air within the cavity. The same air element will also loose or gain heat axially to adjacent air elements (on top and below) by conduction. There will also be a radiation exchange of energy between the wall surfaces lining the cavity, DBZ WALL- HUT TRANSFERMECHA~YISRIS 38
4. Heat is conducted through the exterior wall;
5. Heat is transported between the exterior wall daceand the outside air by radiation and natural convection and conduction.
Heat Transfer Zones
A \ lnterior Wall Exterior Wall Finish - - DBZ Caviîy
m - Mass Flow Rate C - Conduction R - Radiation IR - Irradiation h - Convection
Figure 4.1 Heat transfer mechanisms responsible for the transport of heat through the DBZ wall. DBZ WALL- HEATTRANSFER MECHANISRIS 39
To better understand how the temperature of the DBZ air changes with distance traveled within the cavity consider a element of air withui the air flow as it travels hou@ the cavity depicted in Figure 4.1. As the air travels down through the cavity, it will lwse or gain heat energy in an effort to achieve thermal equilibrium with its surrounàings. The rate of heat flow into the air etement will be dependent on two factors: i) the difference between the interior space temperature and the DBZ air temperature (assuming the DBZ air temperature is cwler than the interior space temperature) and ii) the thermal resistance between the interior and the DBZ air (Ri). The rate of heat flow out fiom the air element will also be a fimction of two factors: i) the difference in temperature between the DBZ air and the exterior environment, and ii) the thermaI resistance between the DBZ air and the exterior (&).
It is important to note that the thermal resistances, Ri and & , include die convective coefficient of the air cavity. Since the flow of air is completety enclosed within the cavity, an energy balance may be applied to determine how the mean temperature of the air eiement changes. For this wall, it can be assumed that kinetic and potential energy changes of the air as well as energy transfer through the air element by conduction in the axial direction are negligible [4.7]. Consequently, the change in temperature this element of air undergoes will be dependent on the net difference between the two heat flow rates discussed above and the heat capacityl of the air element. The equivalent electrical circuit summariting the heat flow system involving the air element is depicted in Figure 4.2. The heat capacity of the air
I At constant pressure DBZ WALL- HEATTRANSFERMECHANISMS 40
element is detennined by the mass of the air molecules and the specific heat of air? The
specific heat of air for the expected temperature range of the DBZ air is approximately 1007
JkglK. Hence, the change in temperature that the air element will experiences is expressed as:
where,
AT is the change in temperature the DBZ air experiences, 4 is the heat flow into or out from the air element, c, is the specific heat of air at constant pressure, and m is the mass of the air element.
As expected, for a given size of air element, the net rate of heat flow fiom the air element will dictate the change in temperature the element undergoes. Consequently, in addition to the temperature gradients noted previously, the relative magnitudes of the interior
(R;) and the extenor (%) thermal resistances will have a significant impact on heat flow into and out of the air element and hence its change in temperature. The air element will continue to change temperature until thermal equilibrium is reached - the rate of heat flow into it equals the rate of heat flow out of it.
"lhe specific heat of a substance is the amount of heat required CO raise the temperature of one gram of the substance by one degree Kelvin. The heat capacity of a substance is the amount of heat required to raise the temperature of a given quantity of the substance by one degree Kelvin [4.8]. DBZ WALL- HEATTRANSFER MECHANIS~IS 41
-- -\,,- . - -7-/- -- A Ti is the interior ambient air temperatura, /' t /' Te,, is the exterior ambient air temperature, Toez is the average DBZ air temperature, /i T, is the warm surface temperature of the cavity, /8 ,' 1 Tc is the cold surface temperature of the cavity, an /' m is the mass flow rate of the DBZ air. L - [fl - --
Ci ,, is the total thermal conductance between the intenor air and surface w, C, ,, is the total thermal conductance between the exterior air and surface c, c,, is the radiative thermal conductance between surfaces w and c, C\V DBZ is the convective thermal conductance between surface w and the DBZ air, is the convective thermal conductance between surface c and the DBZ air, DBZ is the equivalent conductance which accounts for the abili of DBz air to accept Coez or release heat energy; a fundon of the rnass flow rate ana the specific heat capacit
Figure 4.2 Equivalent electrical circuit summarizing the heat flow system of the DBZ walt.
An important question that needs to be addressed is how the equilibrium temperature of the cavity during flow conditions differs from that of the static condition. The answer lies with how the convection coeficient of the cavity changes because this coefficient is the only DBZ WALL- HEATTRANSFER MECHANISMS 42
thermal characteristic of the wall that will change when air is forced thtough the cavity,
Based on the preceding discussion, the following can be said about the DBZ air,
1. The temperature of the DBZ air at a particular location within the cavity of a
finite height of wall is dependent on the Ri/% ratio, the interior and exterior
environment temperatmes, the DBZ inlet temperature and the DBZ mass flow
rate;
2. The equilibrium temperature of the DBZ air in an infinite height of wall will be
dependent on the Ri/% ratio, the interior and exterior environment temperatures,
and the velocity of the DBZ air within the cavity because it will influence the
convection coefficient of the DBZ air within the cavity;
3. The arnount of time required to reach equilibrium is determineci by the absolute
values of Ri and &, the mass flow rate, and the magnitude of the temperature
difference between the interior and the exterior environments.
It is apparent that the temperature change the DBZ air experiences as it travels through the cavity is influenced by many factors. The most important of these would appear to be the interior and exterior thermal resistances, The DBZ air within the cavity contributes to these thermal resistances. The characteristics of the thermal resistance of the DBZ air is dependent upon the type of convective heat transfer occurring within the cavity.
Consequentiy, an important first step to understanding how the DBZ air temperature changes with distance traveled within the cavity is to determine what kind of convective heat transfer is occurring within the cavity. - DBZ WALL- HEATTRANSFER MECHANISMS 43
4*3*1 Forced Convection Basics
The purpose of the following discussion is to highlight the principles of forced convection heat transfer. To do so, consider the unconfined flow of a fluid at a temperature of T, over a horizontal plate with a uniform temperature Ts as shown in Figure 4.3.
Convective heat transfer between the fluid and the piate will occur if the fluid temperature and the plate temperature are aot equal. As stated previously, the local heat flux is expressed by equation 4.2 as h(T,-Tm)-
Figure 4.3 Fluid flow over a flat plate. Source: adapted fiom [4.2] p. 289.
Determination of the convection coefficient, h, is the key to solving convection heat tramfer problems. This task is not a simple one because the coefficient is dependent on the boundary layer found dong the surface over which the fluid flows.
The characteristics of the various boundary layers that can be found on a surface subjected to fluid flow are dependent on the fluid properties such as, density, viscosity thermal conductivity and the specific heat of the £luid. In addition, boundary layers are dependent on the surface geometry and the fiow conditions. This section will briefly discuss DBZ WALL- HEATTRANSFERMECHANISMS 44
the concept of a velocity boundary layer and a thermal boundary layer and their importance
to determining the convection coefficient.
43.1.1 Velocity Bouadary Layer
The velocity boundary layer is the region of the fluid next to the surface of an object where the fluids velocity has diminished because of the shearing resistance created by the surface boundary. Outside the boundary layer, the velocity of the fluid is equal to the bulk fluid velocity.
To better understand the development of the velocity boundary layer, consider the flat plate in Figure 4.4. A fluid approaching the plate has a UIUform velocity u,,. However, as the fluid cornes into contact with the plate (the Ieading edge), the fluid touching the pIate has zero velocity because of the no-slip condition charactenzing continuum flows [4.9]. These fluid particles will slow the fluid particle above them, which inturn will slow those particles above them. This retardation effect results because of the shear stresses caused by the plate.
Eventualty, some distance 6 above the plate the shear stresses become negligible. That distance 6 is called the boundary layer thickness. As the fiuid proceeds downstream, the fluid particles adjacent to the plate continue to be subjected to the shear stresses imposed by the plate and thus continue to decelerate. Hence, these particles fürther slow the particles above them and as a result the thickness of the boundary layer continues to grow downstream from the leading edge of the plate. DBZ WALL- H~TTRANSFER MC:CHA~YISBIS 45
Figure 4.4 Development of the velocity boundary hyet within a fluid aow over a flat plate, Source: adapted fkom [4.2] p. 289.
43.1.2 Thermal Boundary Layer
Consider the fluid flow scenario depicted in Figure 4.5 where the plate has a uniform temperature Ts . and the bulk fluid temperature is Tm, A thermal boundary layer will only develop if the surface and the free strearn temperatures are different, Assuming this is the case, the fluid particles that are in contact with the plate's surface will reach thermal equilibrium with the plate temperature and then they will transfer thermal energy to the fluid particles in the adjoining fluid Stream- This exchange of thermal energy between particles will continue upward away from the plate into the fluid strearn until the thermal effects of the plate are not sensed by the fluid.
Figure 4.5 Development of the thermal boundary Iayer withii a fluid flow over a flat plate at constant temperature. Source: adapted fiom [4.2] p. 290 DBZ WALL- HEATTRANSFERMECHANISMS 46
This distance defines the thickness of the boundary layer and is denoted by 4. Since at the
interface between the fluid and the plate the velocity of the nuid particle is zero, it follows
that Fourier's law for thermal conduction can be applied and that [4.1 O] :
Furthermore, the ktflux through this layer (Le, y+) must equal the total heat flux into the
fiuid such that:
It follows that the conditions in the thermal boundary layer determine the rate of heat
transfer across the boundary layer because those conditions strong 1y influence the wall temperature gradient [4.11].
1.3.1.3 Bouodary Layer: Laminar or Turbulent Flow . Convection transfer rates are dependent on the flow regirne of the boundary layer. A larninar boundary layer is characterized by a highly ordered nuid motion which has velocity components parallel and perpendicular to the surface dong which the flow is occurring over.
It is the perpendicular component that can contribute to the transfer of energy through the boundary Iayer. DBZ WALL- HUT TRANsmt MECHANISIUS 47
On the other hand, a turbulent boundary layer is characterized by a highly irregular particle fiow which causes mixing and consequentiy enhances the transfer of energy through the boundary layer. Determination of the Qow regime is exarnined in Section 4.32.1.
The objective of the preceding discussion was to bnefly introduce the general process of convective heat transfer. It has been established that calculating the convection coefficient associated with a particular problem is the key to soIMng convective heat transfer problems.
This heat transfer coefficient can be difficult to calculate because of its sensitivity to themial and fluid dynamics.
4.3.1.4 Convection Coeffkients
Using the definition of the convection coefficient, equation 4.6, and employing various dimensionless variables, a dimensionless parameter that is dependent on the convection coefficient can be defined [4.12]. This parameter is called the Nusselt numkr and is expressed as:
where,
O Y = y&, where L is some chatacteristic length, T* = (T-TJ(Ta0 -T& kf is the thermal conductivity of the fiuid, and h is the convection coefficient,
Hence, the Nusselt number provides a measure of the convective heat transfer occurring at the surface. For a given geometry and fluid type the Nusselt number is a function of the
Reynolds number, ReL, and the nondimensionalized distance traveled, x' (= fi).If ihis DBZ WALL - HEAT TRANSFER MECHAN~S~CLS 48 fùnction were known, the Nusselt nurnber for various veiocities and element iengths (eg. length of a plate over which the fluid traveled) can be calculated- This would then enable the calculation of the local convection coefficient, h- The local convection coefficient is the coefficient that corresponds to a particular location dong the flow path. If the average convection coefficient is of interest, it cm be obtained by integratuig the over the surface of the body such that
There are two approaches that can be taken to obtain the relationship between the
Nusselt number and the flow conditions for a particular geometry and fluid type. One approach is based on experimental work. This entails performing heat tram fer measurements under controlled conditions and correlating the data in te- of the appropriate dirnensionless parameters. The other approach is based on theoreticai calculations for solving the momenturn and energy equations associated with the boundary layer for a particular geometry- However, usefiil results are only arrived at for simple flow situations I4.131.
Calculating convection coefficients is not within the scope of this study; however there has been much work in this area [4.14,4- 15,4.16,4.17].
4.3.2 Interna1 Forced Convection Flow
External forced convection has been used to discuss the mechanism of heat transfer involving fluids and boundaries. However, the air flow within the DBZ cavity represents the case of intemal flow. Hence, the following sections will focus on interna1 flow between parailel plates since parallel plates most closely represent a typical wall. 4.3.2.1 Velocity Boundary Layer
The flat plate example in the previous section was wed to qualitatively describe the formation of the thermal and velocity boundary layer for extemal flow forced convection conditions. When dealing with flow of a fluid between two surfaces (interna1 flow) the formation of the boundary layer is slightiy modified. Consider the parallel plates in Figure
4.6. The fluid is now in contact with two surfaces and thus two velocity boundary Layers form. The key difference between internal flow through parallel plates and extemal flow over a simple plate is that with internal flow, the upper and lower boundary layers will eventually merge at the centre line between the two plates and will not continue to grow in thickness. Thus, following the merger of the two velocity boundary layers, viscous effects extend over the entire cross-section.
Figure 4.6 Hydrodynamic boundary Iayer development between parallel plates (laminar flow). Source: adapted fiom [4.2] p. 420. -
The distance fiom the point of entry of the fluid and the point to where the two velocity boundary layers merge is termed the hydrodynamic entry length. The area downstream of this area is called the f'ülly developed region- The velocity profile no longer changes with distance in the fûlly developed region. DBZ WALL- HEATTRANSFERMECXANISBE 50
Determining whether the flow is laminar or turbulent is an important consideration for calculating the size of the hydrodynam-c enûy length. The omet of turbulent flow is typically thought to occur when the Reynolds nurnber (ReD) is approximately 2300 [4.18].
For fülly developed flow between paraifel plates the Reynolds number is expressed as:
Re, =- %Ph V
where,
u, is the mean fluid velocity, Dh is the hydraulic diameter, 2 x distance between the plates, and v is is the kinematic viscosity of the fluid,
With interna1 flows, the velocity profile varies over the cross-section which makes it necessary to work with a mean velocity u,. This mean velocity is defined by considering the rate of mass flow between the plates such that:
rit= u,,A,p [4. 1O] where p is the density of the fluid and is the cross-sectional area. For steady and incompressible flow, and a constant cross-sectional area, the mass flow rate and the rnean velocity are constants. Another expression for the mean velocity, u, ,between parallel plates is given by (-. 191:
where,
a is the distance between the plates, p is the viscosity, and -dp is the change in pressure in the axial direction. ctr DBZ WALL- HEAT TRANSFER MECHANLSMS 51
43.2.2 Thermal Boundary Layer
Consider the same parallel plates as before, but now the plates have the uniforrn temperature, Ts , and the fluid enters between the plates at the uniform temperature T,, ,as shown in Figure 4.7. The fluid is in contact with two surfaces, as with the case of the velocity boundary layer, two thermal boundary layers will fom and will eventually merge.
In the instance where both plates are kept at the same temperature, the two thermal boundary
Iayers will merge at the centre of the plates.
As with the velocity profiles, the fluid temperature varies through the cross-section.
Consequently, a mean temperature of the fluid must be defined so as to provide a convenient reference temperature so that the local heat flux for interna1 forced convection problems can be expressed as:
where h is the local convection heat transfer coeficient.
Figure 4.7 Thermal boundary Iayer development between parallel plates at constant temperature (Iaminar flow). Source: adapted from [4.2] p. DBZ WALL- HWTTRANSFER MECHANISMS 52
Unlike the mean flow velocity, the mean temperature of the flow will change with distance traveled as long as Ts+. Tm. As such, the cross-section temperature profile is constantly changing with distance traveled. Thus, it would seem that a hlly developed thermal region could never be achieved. However, it has been shown that although the temperature profile changes with distance, the relative shape of the profile no longer changes in the fUy developed region, It is at this point that the fluid flow is considered to be thermaIly fùily developed-
It can also be shown that in the thenndly fdly developed region of a Buid with constant properties, the local convection is not a fûnction of distance mveled within the plates and thus is a constant [4-201. However, this is not the case in the entrance region where the convection coefficient will be dependent on the distance traveled. For example, right at the entrance, the boundary layer thickness is zero and thus the convection coefficient is very large. As the thermal boundary layer increases in thickness, the convection coeficient will rapidly decrease until the boundary layer becomes Mly deveioped
The conditions considered thus far pertain to a system where the parallel plates have the same uniform temperature. If this was not the case, and the individual plates were kept at different temperatures, there would exist a convection coefficient for the warm plate and a second for the cool plate 14-21]. This becomes evident when one examines the earlier expression given for the convection coefficient (equation 4.5).
4 Naturat Convection
Heat transfer involving motion of a fluid resulting fiom buoyancy forces king exerted on the fluid is called natural convection heat transfer. In the DBZ cavity, the buoyancy force would be due to the presence of a density gradient in the air and the action of DBZ WALL- HEAT TRANSFERMECHANISMS 53 gravity. The density gradient is a result of a temperature gradient within the air because the
DBZ cavity walls will usuaily be at two different temperatures.
The processes for heat transfer in natural convection are very similar to those that dominate in forced convection [4.22]. As such, inertia and viscous forces are fimdamental to the heat transfer process. The essential difference between forced and nahirai convection is that buoyancy forces drive the flow in naniral convection and an extemal force &ives fiow in forced convection heat transfer.
Heat transfer coefficients for natural convection are generally much lower than those for forced convection because the flow velocities associated with natural convection are usualIy much smaller [4.23].
43.3.1 Natural Convection - Enclosures
During no-flow conditions in the DBZ cavity, a cellular air flow pattern resulting fiom nadconvection may facilitate heat transfer through the wall Figure 4.8. Cellular flow occurs when air in the cavity will becomes heated on the warm side of the cavity and ascends along it as it becomes less dense and along the cold sufface, the air will become cooled and descend as it becomes more dense,
The onset of cellular flow is dependent on the relative magnitudes of the buoyancy forces to the viscous forces. As with forced convection, nondimensiondizing the goveming momenturn and energy equations of the boundary layer will yield important dimensionless parameters. One such parameter is called the Rayleigh number. This non-dirnensiodess parameter expresses the ratio of the buoyancy forces to the viscous forces as: DBZ WALL - HWTTRANSFERMECHAIYISMS 54
where,
% is the Rayleigh number, g is the gravitational constant, p is the volumetric thermal expansion coefficient, for an ideal gas, =lm L is the width of the enclosure, v is the kinematic viscosity of the fluid, a is the thermal difhsivity of the fluid, and ( - T) is the difference between the wall ternperatures.
TI 'Tt
Figure 4.8 Cellular flow due to Nahiral Convection in a vertical cavity.
For Rayleigh numbers less than approximately 1000, effective cellular flow does not occur because the buoyancy forces cannot overcome the resistance imposed by the viscous forces. DBZ WALL- HEATTRANSFERMECHANISMS 55
Hence, heat transfer primarily occurs by conduction. With larger Rayleigh numbea,
buoyancy driven flow becomes intensified such that the flow becomes concentrated in thin
boundary layers adjacent to the side-wails and the core becomes nearly stagnant f4.241.
nie formation of a verticai temperature gradient withîn the air space is a consequence
of cellular flow. The temperature gradient is orientated such that the upper portions of the
wall would be warmer than the lower portions of the waiL
This variation in temperature is a result of a heat flux gradient caused by the cellular
flow. Thus, when examining the interior side of the wall, there would be less heat flow into
the top regions of the wall as compared to the bottom regions. Similarly, when examining
the wall cavity, there would be greater heat flow to the outside fiom the top of the wall as
cornpared to the bottom of the wall. Hence, the convection heat flow action causes a vertical
upward movement on heat in the air space [4.25].
Heat transfer coefficients for natural convection are generalLy not very large.
Consequently, heat Ioss or gain associateci with radiation shoutd not be ignored when
determining air space convection coefficients 14.261.
4.33.2 Combined effets of Natural Convection and Radiation
Radiation transfer across air spaces between parailel plates at two different temperatures is expressed as:
where,
FA is a configuration factor, taken here as one, FE is the emissivity factor accounting for the departure fiom blackbody emissivities, DBZ WALL- HEATTRANSFER MECHANISMS 56
CT is the Stefan Boltzmann constant.
The kat flux associated with the radiation exchange as describeci above, can then be used to calculate a fictitious radiation coefficient, h, for use in simple heat flow theory as follows f4.273:
Hence, the net thermal conductance for the air space would be the sum of the appropriate convection coefficient and the radiation coefficient, h,.
43.4 Mixed Convection
Thus far, forced and fiee convection has been discussed independently. However, there are instances where both types of convective heat transfer mechanism are occurring simultaneously. For example, the air beïng forced into a channel may cause a temperature gradient and thus if the forced air velocity is not suficiently large, buoyancy effects cm be significant. On the other hand, buoyancy effects can be significant simply because each of the parallel plates are at different temperatures and the forced air velocity is smail. Mixed convection is said to take place when both natural convection and forced convection have a relatively equal role in the heat transfer.
The effects of buoyancy on heat flow in a forced flow situation are dependent on the direction of the buoyancy force relative to that of the forced flow. The two possibilities that exist in a DBZ cavity are assisting flow and opposing flow. In assisting Bow, the buoyancy DBZ WALL - HEAT'CRANSFER MECHANISMS 57
induced flow is in the same direction of the forced flow and thus acts to increase the rate of
heat hansfer associated with pure forced convection. In opposing flow, the buoyancy flow is
in the opposite direction of the forced flow and thus acts to decrease the rate of heat transfer
associated with pure forced convection [4-281-
The magnitude of the natural convection contribution depends on many factors
especially the wall to bulk fluid temperature difference, the distance between the plates and
orientation, coefficient of volumetric expansion, and the flow velocity [4.29]. Mked
convection probiems typicaily have a lateral velocity component in the flow resulting from
the buoyancy flow [4.30]. Hence, the major effect of buoyancy is to alter the velocity and
temperature fields in the forced convection flow and thus altering the Nusselt numbers
[4.3 11. Much experimentai work has ken undertaken in the area of mixed convection, but
the results do not correlate well with theoretical calculations because of the nurnber of
complexities involved [4.32]. A suggested expression used to relate natural and forced
convection coefficients for opposing flow rnixed convection involving laminar flow between plates that have a uniform temperature is [4.33]:
113 N, =IN: - ~i.1 [4.16]
For assisting flow it was suggested to replace the subtraction sign with an addition sign.
However, equation 4.16 is considered to be a first approximation.
An important dimensionless parameter used to determine the type of convective heat transfer mechanism is the Grashof number. It is a measure of the relative importance of the buoyancy force to the viscous force acting on the fluid and is expressed as: DBZ WALL- HEATTRANSFER MECHANISMS 58 where Pr is the Prandtl number of the fluid and is equal to 0-71 for air at normal intenor ambient conditions. Recall that the Reynolds number is a measure of the ratio of the inertial to viscous forces acting on a fluid element. Consequently, dendetermining the influence of natural convection on forced convection heat transfeer, the following criteria can be used to determine the relative importance of each of the mechanisrns [4.34] :
the natwal convection effect may be neglected,
Gr. the forced convection effects may be neglected, and
Gr, the combined effects of forced and naturai convection must be (~e,)' accounted for.
The Grashof number, GrL, and the Reynolds number, ReL, are evaluated for the characteristic length, L, being the distance between the two parallel plates.
In surnmary, it is evident that the heat transfer process in the DBZ cavity can be rather complicated and dependent on a number of factors. Perhaps the most important factors are the fluid and thennodynatnic conditions of the air within the cavity. 5.0 LABORATORY RESEARCH
The objective of this portion of the study was to investigate the influence of specific
DBZ airfiow characteristics, boundary conditions and cavÎy configuration on the temperature profile of a test wall incorporating a exhaust DBZ system. Air was introduced into an interior wall cavity at various initial temperatutes and flow rates. The effects of the exterior temperature and the addition of wami sîde (interior) insulation was also investigated.
Wall temperatures were measured once a dynamic steady-state equilibrium was reached. A description of the test method and apparatus follows.
An exhaust DBZ wall assembly was constructed and a testing program was designed to investigate the effects of the following on wall temperatures:
1. initial DBZ air temperature, 2. DBZ cavity width, 3. DBZ flow rate, 4. addition of wann side (interior) insulation, and 5. outdoor temperature.
A typical test consisted of a DBZ wall panel that was 1.69 m in height and 0.72m in width being subjected to constant intenor and extenor temperatures within a climate simulator. The DBZ air was introduced at the top of the cavity fiom the cold guardroom side and exhausted from the bottom of the cavity into the warm guardroom as is shown in Figure A manifold located at the top of the cavity was used to uniformly distribute the air through the cross-section of the cavity. The DBZ air flow rate was set using a flow meter and the size of the exhaust holes were chosen so as to produce a cavity preswkation of 10 Pa relative to the warm guardroom. The flow rate and the initial temperature of the DBZ air through the cavity were varied for a particular set of interior and exterior conditions, and wall construction. A generic flow chart representing the possible combinations of test variables is depicted in Figure 5.2; for the number of variables illustrated, eighteen tests would have been performed for the one wail configuration. Temperatures through the wall at three different heights (345, 800, and 1255 mm) frorn the DBZ inlet were monitored and recorded once a dynamic steady-state equilibrium was achieved. Equilibrium typically occurred six to twelve hours foilowing the start of the test. Table 5.1 sumrnarizes the various temperatures and flow rates tested for four wall configurations. Cold Guardroom Wam Guardroo
Exterior Insulat ion- \:
DBZ Cavity
F Iow Channel 1 ,/. Buffer Area - '. , 4TZ Air Exhaut
Figure 5.1 Schematic of test wall without warm side (intemal) insulation. 1-1 1-1 Configuration
i \ f 3 r 7 DBZ inlet DBZ Inlet DBZ Met Temperature Temperature Temperature #1 ?Y2 #3 \ J i J \ J I 1
I I 1
Extenor Temperature 1
Figure 5.2 Generic testing combinations for a particular waII. Table 5.1 Various test wall configurations'
CONFIGURATION 89mm wide DBZ cavity, no interior insuiation, +WC #l interior tern~ekatore C - initial DBZ Temperature CC) DBZ Fiow Rate (m3/min) Exterior Temperature 5 0*01,0.04,0.1 -10 ;-20 15 0,01,0.04, O- 1 -10 ;-20 20 0.0 1,0.04, O. I . -10 ;-20 CON~GURATION 89mm wide DBZ cavity, RH0.79 interior insulation, #2 +1ûT interi& temperature Initial DBZ Temperature CC) DBZ Flow Rate (m'/min) Exterior Temperature 5 0.0 1,0.04,0.1 -10 ;-20 15 0.0 1, 0.04,O. 1 -10 ;-20 CONFIGURATION 45mm wide DBZ cavity, no interior insulation, +WC #3 inteaior temnerature Initial DBZ ~empeitureCC) 1 DBZ Flow Rate (m'/min) 1 Exterior Temperature 5 0.0 1,0.04, O. I -20 15 0.0 1, 0.04, O. 1 -20 20 0.0 1,O-04, O. 1 -20 CONFIGURATION 45mm wide DBZ cavity, RSI 0.79 interior insulatioa, #4 +WC interior temperature Initial DBZ Temperature CC) 1 DBZ Flow Rate (m'/min) 1 Exterior Temperature
'The flow rates chosen were based on air flows used for a DBZ system implemented for the renovation of the building located at 32 1 Bloor Street Refet to Appendix B for caIculations. 5.2.1 Testing Facility Layout
The laboratory investigation was conducted in the Building Science laboratory located at the University of Toronto. A schematic of the laboratory and a general layout of the essential testing components and equipment is shown in Figure 5.3. The laboratory consists of a work area, a climate simulator, and a cornputer facility. The climate simulator is partitioned into two adjoining rooms that are separated by removable wal1 panels.
WORK AREA
Wann Room Cold Room
Figure 53 Laboratory layout. 5.2.2 DBZ Test Wall
The test wall was designed to simulate a masonry wail. Masonry walls have been constnicted in many different configurations and widths; fiom load bearing to infill for a steel hestructure and fiom one brick in width to as many as nine wythes. The solid masonry wall cross-section that was simulated by the test wall was 700 mm thick The following differences between the test wall and the masonry wall are rationaiid as foiiows:
1. the influence of the thermal mass of the mammy was neglected because steady- state conditions were investigated. However, the thermal resistance of the masonry was approxirnated with the addition of 25 mm extnided polystyrene insulation and 9.5 mm of plywood, and
2. 9.5mm plywood was used to simulate the interior gypsum board finish. This material was chosen because it has a thennal resistance simila.to 15-9 mm (5/8") gypsurn board and it is a relatively easy matenal to work with-
Other effects that are not accounted for in the experimental wall panel that are present in actual building envelopes are Iisted below:
1. masonry walls are typically not air tight, the test panel was constmcted airtight otherwise the theoretical anaiysis of the wall would be too complicated, and
2. thermal bridging effects of the DBZ cavity constniction are ignored.
Although the purpose of the extenor insulation used for the test wall was to simulate the thermal resistance of the chosen masonry wall, the conclusions drawn fiom the experimental and theoretical work can be universally applied to any fairly airùght wall incorporating a exhaust DBZ system. 5.2.2-1 Construction
The basic test wail consisted of a DBZ cavity, buffer area, 25 mm of uisulating board,
leakage valves, a manifold, a flow channe1 and 25 mm of insulating board. The general
arrangement of these components within the climate simuiator's partition wall is depicted in
Figure 5.4. The components that are the focus of this section are the construction of the DBZ
cavity, buffer area, and the leakage valves.
The purpose of the baer area was to prevent two-dimensional heat flow fiom the
perimeter of the DBZ cavity. The original intent was to distribute DBZ air into both the DBZ
cavity of the test wall and the b&er area around its perirneter. Temperature readings would
only be taken within the DBZ cavity area Unfortunately, control of the bder air
temperature proved difficult and the idea was abandoned. Consequently, the buffer area
remained as a stagnant air cavity that was completely separate fiom the DBZ cavity.
Leakage vaives were incorporated into the test wall to provide controlled air Ieakage
from the DBZ cavity (Figure 5.4). As testing progressed it was decided not to use the valves because airtight testing configurations were more amenable to theoretical analysis and would more likely represent actual field conditions.
Conventional 2 by 4 inch lumber was used to constact the fÎame for both the DBZ
cavity and the buffer area The dimensions of the entire wafl (buffer and DBZ cavity) were
12 19 mm wide by 2057 mm long. The gross dimensions of the DBZ cavity were 71 8 mm
wide by 1829 mm high. The clear distance between the bottom of the manifold and the
centre of the exhaust holes was 1690 mm- The configuration of these two areas is shown in
Figure 5-5-
Elevation (Fram in g)
Figure 5.5 Genenil dimensions of framing for the test WPII.
The frame was enclosed to form the DBZ cavity and the buffer area cavity by fastening 9.5
mm plywood on both sides of the frame. The plywood used to fom the DBZ cavity was kept
separate fiom the buffer area plywood to facilitate access into the cavity for testing modifications to thermocouple locations, the width of both the manifold and the DBZ cavity. The buffer area plywood and framing was sealeci to the frame such that exchange of air between the baer area and the DBZ cavity could not occur. The DBZ cavity plywood was sealed to the framing with tape. Smoke pencils together with cavity pressufization were used to confkn the air tightness of the both the DBZ cavity and the buffer area.
The width of the DBZ cavity was 89 mm for wall configuration's #1 and #2, This size of cavity was examined because it is a common construction Çaming material dimension. Alterations to the wi& of the cavity and the manifold were made such that the new construction was 45mm wide, which is another common dimension in construction fkming.
5.2.2.2 Thermocouple Layout
The thennocouple placement for the test wall without any interior insulation is shown in Figure 5-6, The thennocouple configuration used for the test wall with interior uisulation was the same as that depicted in Figure 5.6 except that the warm surface thermocouples were mounted on the surface of the insulation. Elevrttion ( Warm Guardroorn) Vertical Cross-Section
Cold Guardroom Warm Guardroom
.,Il LI Manifold X DDZ inid Thcrmoeouple . IZ82 Met w bl W- i>( (no1 visible in ihis view) Themocoiiplc PSm 178mm SSmm ' lm'17~nim' y\,/a DBZ Cavity n-n m ara .'\ Ride-Section Thermocouple Warm Surfacc Th~rtnocouplc ,' 5, mm- -\DBZ Cavity :&y -!hrfoceDBZ Caviiy Thcrmocouple 2( , Surlàce Therniocouplc DBZ Cnviiy \*' Ta pcd (Drilled and Taped) \ \ (noi visible in ihis vicw) Surface Thermocouplé ' ' A Drillel (no, visMe in this vhv) ; 3 Cold and Warm Surface 2, 1 1 , ~~mocouplc
Figure 5.6 Thermocouple layout in test wall with no interna1 insulation. Figure 5.6 depicts al1 themiocouples placeci, but the DBZ Cuvity Surfiace
Thermocouples (DRILLED) were not utilized in the analysis of the results. The reason for
this is that these thermocouples were placed by inserthg the thermocouples through hoies
drilled through the 9.5 mm plywood hmthe wamifold guardroom so that the thermocouple
lay flush with the cavity side of the plywood. This me- of installation was chosen
becaw it wouid Iimit the disruption to airflow in the cavity since no thermocouple wire
other than the wire for the mid-section themocouples were placed in the cavity . However,
initial testing demonstrated that these themocouples were very sensitive to depth of placement. Consequently, €me gauged thermocouples were raped to the surface of the plywood on the cavity side as is depicted in Figure 5.6.
5.2.3 DBZ Cavity Air
There were many aspects to the control of the DBZ air for the cavity that needed to be addressed for the experimental work. These are discussed below.
5.23.1 Air Source
The supply air for the DBZ air cavity was provided by a compressed air tap provided in the Building Science laboratory. A relative hwnidity probe was used to determine the rnoisture content of the air fiom the compressed air tap. The air was found to contain very little moisture. The calculated water content of the air was approximately 0.00 18 kg of water per kg of dry air. This corresponds to the water content of air at -8 OC and 100% relative humidity. 5.23.2 DBZ Air Flow Control
The air £iom the pressure tap was directed into the cold room through a rubber hose.
The hose was then split to supply two airflow control valves - one used for the air flow meter and the other for a relief valve (Figure 5.7). The valves would be adjusted such that the desired air flow rate through the DBZ cavity would be achieved. A gas flow meter rnanufactured for measu~glow flow rates was used to measure the DBZ airflow.
Air from TAP
Figure 5.7 DBZ air flow control.
5.2.3.3 Temperature Control
Subsequent to king discharged fiom the air flow meter, the DBZ air was directed through a copper coi1 tube contained within an insulated hot-box (Figure 5.8). Since the
DBZ air was introduced into the cavity fiom the cold side of the test wall, the hot-box was used to provide a reservoir of heat in order to raise the temperature of the DBZ air to the desired Ievel. The copper coi1 enabled a faster transfer of heat fiom the hot-box to the DBZ
air. Once the DBZ air traveled through the coil, the air was then evenly distributed through
DBZ cavity by way of a manifold. Three equally spaced fuie gauged thermocouples were
located at three of the exit holes at the base of the manifold. The average of these three thermocouples constituted the measured DBZ inlet temperature. A heater located in the hot- box would be activated by the HP computer using the cornputer program DBZ (refer to
Appendix D) depending on the difference between the required and the rneasured DBZ air inlet temperature.
Air to
Insu
Figure 5.8 DBZ hot-box.
5.2.3.4 Air Distribution through Cavity
Manifold
The primary fùnction of the manifold, which was located at the top of the DBZ cavity, was to evenly distnbute the DBZ inlet air through the full cross-section of the cavity and to ensure that laminar air flow was introduced into the cavity. The manifold design is depicted in Figure 5.9. Air directeci bmthe hot-box was divided in order to supply two half inch PVC conduits leading into the manifold These two conduits served to minirnize the formation of a temperature gradient within the manifold that could occur at slow flow rates.
Preliminary testing indicated that thm wouid be difaculty achieving 5 OC and 15 OC
DBZ air inlet temperatures at the 0.01 m'/min flow rate. Thus, in order to atmin better temperature control at low fiow rates, the sudace area of the air in the manifold had to be kept to a ininunm. Furthemore, kat gain or Ioss hmthe DBZ air within the manifoId had to be reduced Hence, the fiaal configuration of the manifold and the use of 25 mm extnided polystyrene insulaiion and expandable foam. In addition to controiiing heat fiow, the extruded polystyrene insdation served to produce vertical streamlines within the cavity. LAOORATOHSRESEARCH 75
Elevation Section A-A
Valve t
\ 12 mm PVC Pipe Expandable Foam 25 mm Extruded Polystyr Sealant
\ ' Hole \ 6rnrnPlywood
/ ' Thermocou le Locatioi 6.3 mm hole (typ. P Plan - Bottom
Figure 5.9 DBZ air manifold, Flow Channel
A flow channel was used at the bottom of the DBZ cavity to provide a more uniforrn exhaust of DBZ air. The idealïzed effects of the channel are illustrated in Figure 5.10 below.
- -- Cold Guardroom Warm Guardrwm
.-. . -Flow Stream lines 1- . -.- -, I-1" / - Flow Channel Exterior ' Insulation--: - & 4 I_) + DBZ Exhaust Air : ------
Figure 5.10 Effects of a flow channel on exhaust DBZ air.
5.2.3.5 Cavity Pressure Control
A nominal pressure of 10 Pa relative to the warm guardroom was maintained within the cavity by instailing sharp edged orifice plates at the bottom of the cavity on the warm side of the wall (Figure 5.4 and 5.1 1). The holes of individual plates were uniform in diameter and equally spaced. The plate that was installed for a test was the one which developed a 10
Pa air pressure within the cavity for the flow king tested. The air pressure was measured with a micro manometer at the mid-height of the wall panel. - Square-Edge Orifice \ Uniform D~ameter
- --50 u;\ Hole for Fasteninp- ,
Figure 5. l 1 S haFp-edge onf;.ce.
Since the flow rate was controlled and the test wall was very airtight, the DBZ air
cavity pressure was not a influencing factor on wall temperatures. That is, the exhaust holes
were chosen to match the flow rate required.
5.2.4 Control of the Interior and Exterior Environment Temperatures
The IBM system located in the computer room monitored the temperature in the
wann and cold rooms of the climate simulator with thermal tramducers (Figure 5.12). The measured room temperature reading was compared with the pre-set desired temperature
input. A computer program adjusted the warm and cold room temperatures to within + 1.0 K via relays that controlied the air conditioning system inside each of the rwrns. The temperatures maintained by this system served as the coarse air temperature control for the interior and exterior environment temperatures that the test wall was exposed to.
Refined temperature control was achieved with construction of a guardroom on each side of the test wall and with the use of the HP computer system (Figure 5-12). The guardroorns were constmcted to dampen the fluctuations associated wi th the coarse temperature control of the warm and cold room and to provide a microclimate within the warm and cold rooms. The HP system recovered temperature information fiom the guardrooms via a thennocouple scanner and compared them with pre-set temperature inputs into the cornputer pro-- DBZ (refer to appendix D). The program DBZ then sent the appropriate voltage signal to relay switches controlling the heating elements located in each of the guardrooms. The mesured guardroom temperatures utilized by the prograrn DBZ for temperature control were taken from the average of three thermocoupies located at the top, middle and bottom of each of the two guardrooms- AIso, fans were used in each guardroom to lirnit the formation of temperature gradients fiom the ceiling to the floor. Furthemore, for this system to work, the coarse temperature in the wann room and the cold room \vas set below the required test ternperatures.
6.0 EXPERIMENTAL RESULTS AND DISCUSSION
This chapter will present and discuss the experimental results obtained during the testing program outlined in Chapter Five. The fust section will discuss what type of convective heat transfer is occurring within the DBZ cavity when air is forced through the caviv This information will provide the foundation for the discussion of the test results-
Following this, the experimentai results wili be presented and discussed. The results are separated into two main categories: DBZ wall without interior insutation and DBZ wall with interior insulation. Wall surface temperatures and DBZ cavity temperatures were monitored over a 1.2 m height to determine the influence of:
1) DBZ air flow rate. 2) Initial DBZ air temperature (inlet temperature), 3) Cold side temperature. 4) Insulation on the wann side of the DBZ cavity (interior insulation); 5) DBZ cavity width (89 mm and 45 mm).
For each category of the results, the effécts of the DBZ flow rate. the DBZ inlet temperature. the exterior temperature and the reduction of the DBZ cavity width on the average cavity and surface temperatures will be exarnined.
6.1 CONVECTIVE HEAT TRANSFER MECHANISM WITHIN THE DBZ CAVITY
Pior to surnmarizing and discussing the experimental results. it is helpfui to establish what type of convective heat transfer is occurring within the DBZ cavity. During static conditions, natural convection is responsible for the heat transfer occumng within the DBZ cavity. To determine the type of convective heat transfer occurring when air ESPERI~IENTALRESULTS AND DISCUSSION 81
is forced through the cavity. the following dimensionless parameters must be used: Gr, Re,;
Re,. In order to mode1 and anaiyze the wall, it will be assumed that the wall behaves like two parallel plates'. It is believed that this is an appropriate assurnption because the wall temperature readings were taken approximateiy from the middle-third of the wall as descnbed in Chapter Five. Consequently, it is believed that two-dimensional heat flow conditions associated with the sides of the wdl framing do not influence the temperature readings (Figure 6.1). This hypothesis was confirmed by data that showed little variation between the thermocouple measurernents at a given height within the wall.
DBZ Test Area
Two-Dimensional Heat Flow
Thennocouple
Figure 6.1 DBZ thermocouple readings not affected by hvo-àimensional heat flow.
With a parallei plate configuration, there are no horizontal temperature gradients. EXPERIMENTALRESULTS AND D~SCUSSION 82
As previously outlined, the Grashof nurnber is a ratio of buoyancy to viscous forces.
The ratio is dependent on three characteristics of the wall: cavity temperature, the difference in temperature between the opposite sides of the cavity, and the cavity width. Since the cavity temperature varies with height, the Grashof number will also Vary with height because it is dependent on temperature. Consequently, the Grashof numbers and the required physical properties of air were evaiuated at the average temperature of the cavity. Average cavity temperatures were calculated by averaging the measured cavity temperatures both vertically through the height of the cavity, and horizontally through the cross-section of the cavity (Appendix C)- Further. the Grashof nurnbers were evaluated for static wall conditions.
This was also considered to be appropriate since the temperatures within the cavities during forced flow conditions did not Vary considerably from static wall temperatures
The Reynolds nurnber is the ratio of the inertia and viscous forces. Re, is used to determine whether the flow condition is laminar or turbulent. Re, is used to determine the influence of buoyancy forces in the ratio, ~r/'eL.The Reynolds number is a huiction of the cavity width and the air velocity. The average cavity velocities were estimated by dividing the measured flow rate by the cross-sectional area of the cavity. The average DBZ air velocity in the 89 mm cavity for the flow rates, 0.01. 0.04. 0.1 m3/min were 2.6, 10.4 and
26.1 mm/s respectively. For the 45 mm cavity, these velocities were doubled.
The Grashof and Reynolds numbers were calculated for the various wall configurations and exterior temperatures tested. This information is summarïzed in Table
6.1. Table 6.1 Grashof and Reynolds Numbers for various wall configurations for DBZ air flow rates of 0.01,0.04 and 0.1 m3/min.
Section 43.4 summarized the criteria for the relative influence of forced convection air flow and natural buoyancy forces on convective heat transfer. As previously stated, for values of Gr.Rel>> 1, heat transfer within the cavity would primarily be a result of natural convection. Based on this criteria, the heat transfer mechanism within the DBZ cavity during forced air flow conditions for the three flow rates tested was found to be dominated by natural convection,
As Table 6.1 demonstrates. decreasing the cavity width by one-half had a significant impact on the effectiveness of buoyancy forces. However, the Gr/~elratio is still greater than one which indicates that inertial forces associated with the flows tested are not sufficient to significantly change the heat transfer characteristics of the 45 mm cavity.
In general, the Grashof number increased considerably when the exterior temperature was decreased fiom - 10 to -20 OC. This is a result of the Grashof nwnber being proportional to the thermal expansion coeficient (lm which increases with decreasing cavity temperatures.
The Grashof number is proportionai to the thermal expansion coefficient and the temperature difference between the opposite sides of the cavity. The addition of warm side insulation caused the average cavity temperatures to decrease and thus, the thermal expansion coe ficient tu increase. However, the temperature di fference across the cavity decreased by an even greater amount. Consequently, the Grashof numbers decreased when the warm side insulation was installed. EXPERIME~ALRESULTS AND DISCUSS~ON 85
6.2 NO WARM SIDE CNSULATION
This section examines the results of tests carried out on a mode1 wall (Figure 6.2)
consisting of an 89 mm DBZ cavity which has no insulation added to the warm side of the
cavity. The target DBZ inlet temperatures were 5, 15 and 20 OC, and the DBZ air flow rates
tested were 0.01. 0.04 and 0.1 m'/min. The cold side guardroom temperatures inve~igated
were - 10 and -20 OC and the warm side guardroom temperature was set at +18 OC-
Cold Guardroom y Y". ..' ._r Wam Guardroo Cold Side .v .y .. Warm Side + r--= DBZ Air Inla DEL Ca\in
kterior Insulatïon RSI 0.79 ' (Simulate Masonry Wall) +- ..l 'f
Figure 6.2 Cross-section of the test wall without warm side insulation.
The measured DBZ air inlet temperatures are sumrnarized in Tables 6.2 and 6.3.
Although the mget DBZ inlet temperatures were used as inputs into the DBZ computer program controlling the experiment, the measured inlet temperatures varied fiom the target input temperatures. This is as a result of the computer program allowing the actual inlet ESPERIME~ALRESULTS AND D~SCUSSION 86 temperatures to fluctuate i1.0 K fiom the desired inlet temperature. This temperature variation was used to maximize the life of the solid state relays by minhizing the nurnber of rimes they were king activated during the experiments. The same approach for temperature control of the warm and cold guardrooms was used. îhe results. as summarized in Appendix
C,show that the temperatures rarely deviated M.3 K fiom the input temperatures of -10, -20
OC for the cold guardroom and +18 OC for the warm guardroom,
For the slow DBZ air flow rate of 0.01 m'/min, none of the target inlet temperatures were attained. This is most likely due to the low mass flow rate of the air entenng the wall.
When a DBZ inlet temperature of 5 OC was desired. the heater within the DBZ hot-box kvas never activated which meant that the air being delivered into the manifold was approximately at the cold guardroom temperatures. However, once in the manifold. heat from the warm guardroom and the DBZ cavity below the manifold was suficient to raise the air temperature above the target temperature of 5 OC- Insulation was added to the wann side of the test watl over the area occupied by the manifold to decrease the heat flow, but this only resulted in a slight decrease in the inlet temperature. This indicates tha: a large portion of the heat warrning the manifold came fiom the cavity itself-
When the DBZ air inlet temperature of 15 OC was desired, the temperature in the DBZ hot-box was consistently between 60 and 65 OC. Nonetheless, this was not sufficient to mise
the temperature of the DBZ air to the desired 15 OC because of the heat loss that occurred as the air traveled from the hot box to the manifold. Attempts to insil!ate and decrease the distance between the manifold and the hot box were helpfiil, but not effective enough as the inlet temperature achieved was only approximately 1 1.5 OC. ESPERIMENTALRESULTS AND DISCUSSION 87
Table 6.2 DBZ Inlet temperatures with the exterior temperature at -10 OC (no warm . side insulation). -10 OC Extenor Flow Rate DBZ Inlet ("C) 0.0 1 (m3/min) 0.04 (m'/min) O. 1 (m3/min) I Measured 8.4 11.5 n.a, 6.6 16.3 21-1 6.6 1 16.2 20.9 Taraet 5 I5 20 5 15 20 5 1 15 20
Table 6.3 DBZ inlet temperatures with the exterior temperature at 30OC (no warm side insulation). - -20 OC Exterior Flow Rate DBZ Met ("c) 0.01 (m'/min) 0.04 (m3/min) 0.1 (m3/min) Measured 6.9 11.6 ma. 6.6 16.2 20.7 5-8 16 20.3 Target 5 15 20 5 15 20 5 15 20
In order to overcome this temperature control dificulty, the introduction and control of the DBZ air (flow and temperature) into the wall was relocated to the warm side of the climate simulator- This resulted in DBZ inlet temperatures that remained above 12 OC. Thus, this set-up was not used and the system described in Chapter Five was implemented. It was conceded that the required inlet temperatures for the 0.01 m3/min flow rate would not be attained with this apparatus.
Analysis of the results associated with this wall configuration will begin first by exarnining the average cavity temperatures measured. The surface temperatures of the wall exposed to the warm guardroom will then be discussed. This will then be followed by looking at the effects of decreasing the width of the DBZ cavity frorn 89 mm to 45 mm. ESPER~MEKTALRESULTS AND D~SCUSSION 88
6.2.1 DBZAirCavity Temperatures
The average cavity temperature at each distance fiom the inlet (345, 800, 1257 mm)
was calculated throughout the experiments using the trapemidal rule as expressed below:
mg = CTW+ 2TM+ TC) l4 16- II where,
T,, is the temperature reading of the exterior surface of the warm side plywood, TM is the temperature reading in the middle of the cavity, and Tc is the temperature reading of the intenor surface of the coId side plywood.
The average cavity temperatures measured for the three flow rates tested, 0.01, 0.04 and 0.1 m'/min. will be discwed in two categories. These results are detaded in Appendix
C. The first category will deal with DBZ air inlet temperatures that are less than the average static cavity temperature and the second category will deal with the DBZ air inlet temperatures that are warrner chan the average static cavity temperature.
Temperature gradients within the cavity made it necessary to calculate the average static cavity temperatures. These temperatures were calculated by averaging the measured cavity temperatures both vertically, through the height of the cavity, and horizontally, through the cross-section of the cavity, during no flow conditions (Appendix C). Al1 results for forced flow conditions will be evaluated with reference to the average static cavity temperature associated with the same cold side temperature tested. it is believed that the average static cavity provides an appropriate reference for judging the performance of the
DBZ system. ESPERIMENTALRESULTS AND DISCUSS~OK 89
6.2.1.1 DBZ Air Inlet Temperatures Colder than the Average Static Ca* Temperature
Enteresting results were attained for DBZ air inlet temperatures that were cooier than the average static cavity temperature. Parùcular attention should be given to the results for the coldest DBZ air inlet temperature for the 0.04 and the 0.1 m3/min flow rates. These resuits are compared to static conditions in Figure 6.3.
For an exterior temperature of -1 0 OC. the DBZ air inlet temperature for each fiow was 6.6 OC. However, as shown in the Figure, the average cavity temperature for the first set of therrnocouples. 345 mm from the inlet, had readings of 1 1.8 OC for the 0.04 m3/min flow and 1 1 .O°C for the 0.1 m3/min flow. Furtherm~re~the temperature readings at the 800 and
1275 mm levels only varied slightly fiom the readings at the 345 mm level. In Section 6.1, it was established that buoyancy forces have a significant effect on the heat transfer mechanism within the cavity when the air vetocities within the cavity are relatively slow (Table 6.1).
Consequently, it is possible that the above results are consistent with the occurrence of induced buoyancy within the cavity. This effect cm be explained as follows. The DBZ air leaves the manifold at a temperature of 6.6 OC which is well below the average static cavity temperature of 12.4 OC. Thus, the air at the top of the cavity is more dense compared to the air found in the lower regions of the cavity. Since there is a density gradient within the cavity and the heavier air is on top, mixing of the air within the cavity would then be induced, The warmer air within the lower regions of the cavity wouid rise and mix with the falling colder air near the manifold. DBZAir Temperature ('C)
- - - - - (Flow rate, DBZAir hkt Temp.) ( 0.1 mA3hin,6.6.C) (0-04 mA3/min.6.6%) (0.01 mA3/min.8.4.C)
tStatic Condition
Test Conditions: 1) Cold side Guardroom Temperature -10% 2) No Wann side hsuhtion 3) Average static cavity Temperature of 12A°C 4) Warm side Guardroom Temperature + 1 8 'C
OB2Air lempenture (OC)
(Flow rate. OB2 Air Inlel lemp.) ( 0.1 mA3/min. 6.6-C) (0.04 mA31min. 6.6% ) (0.01 mA31min.8.4-C) (0.01 ma3/min. 1 1 S'C)
StaticCondition
1est Conditions: 1 ) Cold side Guardroom Temperature -20 'C 2) No Wann side hsuiation 3) Average static cawty Temperature of 11.t'C 4) Warm stde Guardroom Temperature +18 'C
Figure 63 Average DBZ Air uvity temperatures for inlet tempeartures colder than the average static cavity temperature (no warm side insulation); A) -10 "C cold side, B) -20 OCcold side. EXPERIMENTAL RESULTSAND DISCUSSION 91
An additional laboratory test was conducted to ver@ the above hypothesis for
different temperature conditions. The parameters of the test were as follows: 45 mm \vide
DBZ cavity. DBZ inlet temperature of 15. l°C, DBZ flow rate of 0.04 m3/min and warm and
cold guardroom temperatures of +25 "C and - 10°C respectively. The cavity temperatures
measured once themai equilibriurn was reached were 18.3, 18.0, and 18.0 "C at the 345, 800
and 1257 mm ievels respectively. The average static cavity temperature was estimated to be
20 "C using steady-state calculations (Appendix C). The DBZ air was therefore introduced
into the cavity approximately 5.0 K below the average static cavity temperature, The DBZ
cavity temperatures measured indicate that an induced mixing of the air within the cavity occurred. The fact that a 45 mm DBZ cavity was used shouid not influence the results significantly because buoyancy forces still dominate, although to a lesser extent as shown in
Table 6-1.
It is important to note that the above phenornenon is believed to have occurred because of the small inertia forces associated with the flow rates tested. Consequently, it follows that if larger cavity velocities were tested such that the Gr/ReL2ratio becomes equal to or smaller than one. the temperature profile of the DBZ air would demonstrate a warming trend from the manifold down through the cavity to the exhaust holes.
When the exterior temperature was decreased fiom - 10 to -20 OC, the average cavity temperature decreased by 1.1 K from 12.4 OC to 1 1-3 OC. Most of the change in temperature occurs across the cotd side insulation (RSI 0.79) since it composes approximately 70% of the wall's thermal resistance. Kt is not surprising then that, as Figure 6.3 demonstrates, the results ESPERIMENTALRESULTS AND DISCUSSION 92
for the -20 OC cold side temperature were similar to those obtained for the cold side testing at
-10 OC.
Figure 6.3 also shows that there is a change in the temperature gradient through the
height of the cavity when DBZ air is introduced at temperatures below the static equilibrium
temperature of the cavity. For the 0.04 and 0.1 m3/min flow rates, the temperature profile
remains fairly constant between 345 and 1257 mm fiorn the iniet- However, under static
conditions the cavity air temperature decreased 2.0 K between 345 and 1257 mm fiom the
inlet. This change in the temperature profile is betieved to be due to the induced buoyancy
effect. Furthemore, the cooler cavity temperatures associated with the induced buoyancy
action indicate that the convective heat transfer that occurred within the cavity decreased.
Hence. it is possible that the induced buoyancy action increased the thermal resistance of the
DBZ cavity. It was also obsewed that the cavity temperature gradient was influenced by the
rate of airîlow within the cavity. For the same inlet temperature, the 0.1 m'/min 9ow has a greater cooling effect. This dependency on cavity velocity is lùrther revealed at the slower
flow rate of 0.01 m3/min. At this flow rate, there is a temperature difference at the upper portions of the wall which declines to almost no temperature difference at the 1257 mm level.
At this level the 0.0 1 m3/min flow cavity temperature equals the static cavity temperature. 6.2.1.2 DBZ Air Inlet Temperatures Warmer than the Average Static Cavity Temperature
Tests were also camed out using DBZ inlet air that had initial temperatures that were wrarrner than the average static cavity temperature. The results of these tests are swnmarized in Figure 6.4. The effects of the DBZ idet temperature and flow rates on cavity temperatures are significantly different compared to when the det temperatures were cooler. This is illustrated by Figure 6.5, which compares the cavity temperatures when the DBZ air initial temperature of 6.6 and 20.9 OC for the 0.1 m3/min flow rate were tested with cold side guardroom temperature set at -10 OC. Unfortunately, data conceming the 0.01 m'/min flow rate for DBZ inlet temperatures greater than the average static cavity temperature of approximately 12 OC was not possible to attain for reasons discussed previously.
Consequently, the following discussion wiIl focus on the remaining flow rates of 0.04 and 0-1 m'/min.
Figure 6.4 shows that both the DBZ inlet temperature and the DBZ flow rate have an impact on the cavity temperature through the height of the watl. This becomes apparent if the combination of air flow and the inlet temperahxe of the DBZ air is viewed as being a rate of heat energy being supplied to the wall. Because of this added energy, the cavity is no longer in thermal equilibrium. Consequently, the air must lose this energy as it travels down the cavity in an effort to regain thermal equilibrium with the warm and cold guardroorn temperatures. Thus, the ternperature gradient measured through the height of the cavity reveals this energy dissipation. - (Flow rat.. DBZ ~irtnl& lemp.) ( 0.1 mA31min.20.9-C) (0.04 me31rnin. 21 .toc) ( 0.1 mA31min. t6.2-C) (0.04 mA31rnin. 16.3.C)
Test Conditions: 1) Cold ride Guardroorn Temperature -fO'C 2) No Wmn ride Insuhtion 3) Average static cavdy ioao Temperature of 12.4% O) Warm side Guardroom Temperature +18'C
1ZOO
DBZ Air Temperature (OC)
- (Flow rate, D BZ Air lnlet Temp.) ( 0.1 mA31rnin.20.3.C) (0.04 mA31min. 20.7.C) ( 0.1 mA3/min. 16.0aC) (0.04 mA31min.16.2'C) '-1
Test Condiîiins: 1 ) Cold side Guardroom Temperature -ZOgC 2) No Wam side hsubtion 3) Average static cavity Temperature of 11 .J°C 4) Warm side Guardroorn Temperature +18'C
Figure 6.4 Average DBZ Air cavity temperatures for inlet tempeartures warmer than the average static cavity temperature (no warm side insulation); A) -10 "Ccold side, B) -20 OCcold side. OB2 Air 1empemture ('Cl CO 6 O 8 0 10 O 12 0 14 O 16 O 18 O 20 O O. ------. -- (Flow rate. Dût Air Inlet lemp.) ( 0.1 mA3/min, 20.9.C)
est Conditions: 1 ) Cold side Guardroom Temperature -10% '2) No Wann side Insulalion 3) Average stalic cavity Temperature of 1ZA'C 4) Warrn side Guardroom Temperature + 1B.C
Figure 6.5 DBZ air temperature profiles for the 0.1 m3/min tlow rate with inlet temperatures of 6.6 and 20.9"C (no warm side insulation).
The test resuIts summarized in Figure 6.4 clearly demonstrate that for the same DBZ inlet temperature, the greater flow rate will produce warmer cavity temperatures At the faster flow rate, the DBZ air has a smaller detention time within the cavity and hence, has less time to lose energy to reach thermal equilibriurn. Furthemore, it seems that the effect of the flow rate becomes more pronounced as the DBZ inlet temperature increases. There is a much greater difference between the temperature profiles of the 0.04 and 0.1 m3/min flows at a DBZ inlet temperature of 21°C as compared to a DBZ inlet of 16.2 OC (Figure 6-4). This result cm be explained by examining the heat flow potential fiom a control volume of air within the cavity. As the DBZ air inlet temperature increases so does the heat loss potential from that control volume to the warm and cold guardrwms. However, as the flow rate increases there is a greater supply of heat to the control volume. This allows the control volume to have a greater temperature as compared to a slower flow rate. Hence, what becomes important is the ratio of the rate at which heat is king lost from the control volume to the rate of heat king supplied to the control volume. For example, uicreasing the flow rate fiom 0.04 to O. 1 m'/min and the DBZ inlet temperature from 16 to 20 OC represents a large increase in the rate of heat supptied to the wall- However, the increase in the rate of heat loss associated with increasing the DBZ air inlet temperature from 16 to 20 OC is definitely not as great. Eventually, for an infinite wall. the cavity temperature reached will be equal for various flow rates as long as there is no change in the convection coefficients of the cavity associated with the change in the flow rate-
Another interesting finding is that the DBZ air temperature seems to decay exponentially with distance from the inlet. That ist the change in temperature the DBZ air experiences; for a given distance, decreases with distance traveled with in the cavity. This is ciearly evident for testing conducted with the exterior temperature set at -20 OC for the DBZ air inlet temperatures greater than 20 OC as shown in Figure 6.6. This finding is consistent with a theoretical analysis of the convective heat transfer in a circuiar tube subjected to uniforrn exterior temperature [6-11- OB2 Air Temperature ('C) 8 0 10 0 12.0 14.0 16.0 18.0 20.0 22.0
( 0.04mA3/min. 20.7"C)
------Static Condition ( 0.1 mA3/min, 20.3"C)
"Test Conditions: 1) Cold side Guardroom Temperature -20% 2) No Wann side Insulation 3) Average static cavity Temperature of 11.3'C 4) Warm side Guardroom Temperature + 18'C
7
Figure 6.6 Exponential decay of DBZ air ternperature as it travels through the caviîy.
Table 6.4 summarizes the change in cavity ternperature with distance traveied Ekom the manifold and the total heat transfer rate, q, that occurs between the inlet and the 1257 mm distance. The total heat transfer rate is expressed as:
q=QpcPAT where.
9 is the total heat transfer rate, Q is the DBZ air flow rate, P is the air density, C~ is the specific heat capacity of air at constant pressure (1007 J/kg/K), and AT is the change in temperature the DBZ air experiences Corn the inlet to the 1257 mm level. ESPERIMENTAL RESULTS AND DISCUSSION 98
Tabte 6.4 Average cavity temperature changes for the 89 mm DBZ cavity without interior insulation.
- C Flow Rate 0.04 m'/min 0-1 m3/min Exterior Temperature -10°C -20°C - 10°C -20°C ' DBZ inlet Ternoerature°C 16.3 1 21.1-- - 162 1 20.7 16.2- - 1 20-9-- - 16. . 1 203 Distance Interval -e in Air0 Temarature ("0
This Table shows that for both flow rates and exterior temperatures tested, there is a
significant increase in the total heat transfer when the DBZ inlet temperatures are increased
from approximately 16 to 21 OC. For the slower flow rate of 0.04 m'/min, a majority of the
heat transfer occurs within the first 345 mm. However. as the flow rate is increased to 0-1
m'/min the heat transfer is distributed more to the lower sections of the cavity. Furthemore,
the flow of 0.1 m3/min, which is 2.5 times greater than the 0.04 m3/min flow rate, has a heat
transfer rate that is approximately two times greater than that of the 0.04 m3/min flow.
Figure 6.7 presents some of the test results show in Table 6.4. The relationship
between the arnount of cooling the DBZ air expenences between the inlet and the 1257 mm
level (DBZ Air: Tinrcl- Tiu,,,) is shown as a tùnction of the difference between the DBZ air
inlet temperature and the average static cavity temperature (TDBz - Tg,,* ,,,). Since the
static cavity temperature used is an average and is specific to the warm and cold side
temperatures maintained for that particular test, this graph is only intended to provide an
approximation of the relationship. The temperatures varied only slightly between tests
(Appendix C). Thus general conclusions can still be drawn from this graph. rest Conditions: h 1) Cold side Guardroom Temperature -1 O'Cand -20°C - 2) No Wam side Insulation 0.04
Temperature +18'C
Figure 6.7 The relationship between the amount of cooling the DBZ air experiences and the temperature difference between the DBZ air inlet and the average cavity temperature (no warm side insulation).
Figure 6.7 demonstrates that, for the flow rates tested, there is no apparent advantage
to heating the DBZ air significantly above the average static cavity temperature since most of
the added heat energy of the air will be lost in approximately the first 1.2 m. The inability of
the DBZ air to maintain its temperature is due to the small specific heat capacity of air and
also the small mass of the air. Furthemore, the amount oîcooling seems to be only slightly
dependent on the flow rate. A 2.5 times increase in the velocity of the air does not have a
significant impact on the cavity temperature at the 1.2 m level nor through the height of the
cavity as is depicted in Figure 6.4. To merinvestigate the influence of decreasing the cold side temperature fiom -10 to -20 OC on cavity temperatures through the height of the wall, the use of a temperature index may be helpfùl. The temperature index is expressed as:
rT = (T-To)/(Ti - TJ
Ti denotes the warm guardroorn temperature, T, denotes the cold guardroom temperature, and T is the temperature of the location of interest,
The temperature index is a function of the wall's thermal conductance. If the conductance rernains constant, the temperature index for a given location within the wall also remains the sarne regardless of what the interior and exterior temperatures are. This is because the temperature index represents the ratio of the thermal resistance between the exterior and the particular point of interest in the wall to the total thermal resistance of the wall. Hence, differences behveen warm and cold guardroorn temperatures for the various tests involving the same wall construction are not a concern when the temperature index is utilized. Under static conditions, the value of the index varies between O and 1; the greater the value of the index, the higher the temperature.
Figure 6.8 presents the cavity temperature index for testing involving the cold side
temperatures of -10 and -20 OC respectively. It is evident that there are no significant differences between the temperature index graphs for the two exterior temperatures tested.
This indicates that there was no change in the heat transfer mechanisms within the cavity when the exterior temperature was decreased to -20 OC. 062 Cavity temperature Index O 4 O 6 0.8
Ilest Conditions: 1) Cold ride Guardmom Temperature -1O.C 2) No Wam ride hsufntion 3) Average static canty Temperrture of l2.4.C 4) Wam side Guardroorn - Temperature +18*C 1 ZOO
(DBZ Air Inlet T ernp.. Flow rate)
DBZ Cavity Temperature Index 0.4 0.6 0.8
. -. 'Test Conditions: 1) Cold side Guardroom Temperature -20'C 2) No Warm side lnsulation 3) Average static cavity Temperature of 11.3'C 4) Warm side Guardroorn Temperature +18*C
- - StaticConditions -(6.9.0.01) .6,(11.6.O 01) -(6.6. O 04) -(16.2. O 04) - - 0 - -(20.7.0.04) -(5.8.0.1) -(16.0. 0.1) - - -(20.3.0.1) ------(062 Air lnlet Temp.. Flow rate)
Figure 6.8 Average Cavity Temperature Index: A) -10 'C cold side, B) -20 OCcold side (no warm side insulation). 6.2.2 Warm Side Sudace Temperatures
When changes are made to a building envelope, an important aspect of the change is its effect on interior wall surface ternperatures- Exposing people to a decrease in wail temperature may cause them to feel uncornfortable because of increased radiant heat losses-
Con~equently~an important aspect of the DBZ system is how it affects the warm side wail surface temperatures as compared to static conditions.
In general, the relatively large variation in average cavity temperatures depicted in
Figures 6.3 and 6.4 did not significantly affect warm side surface ternperatures of the wall.
The general trends in the surface temperature profiles were similar for both of the cold side guardroorn temperatures tested. For the slowest flow rate of 0.0 1 m'/min, the wall surface temperatures observed remained essentially unchanged from the static surface temperatures.
For the 0.04 and 0.1 m3/min flow rates with DBZ inlet temperatures greater than the average static cavity temperature, wall surface temperatures were warmer than static conditions as shown in Figure 6.9. Further. the wanning effect increased with an increasing flow rate.
However, the effect of flow rate and DBZ inlet temperature on surface temperatures were relativeIy small. The warming effect decreased from a maximum of 2.0 K at the 345 mm level to Iess than 1 .O K at the 1257 mm level. EXPERIAIENTALRESULTS AND DISCUSS~ON 103
Wann Side Wall Surface Temperature (OC)
(Flow rate. DBZ Air lnlet Temp.) ( 0.1 rnA3/min.20.9"C) (0.04 mA3/min. 21 -1°C) ( 0-1 mA31rnin. 16.2'C) (0.04 mA31min. 16.3'C)
Static Condition .-*
Test Conditions: 1) Cold skie Guardroom Temperature -1O'C 2) No Warm side Insulafion 3) Average static cavity Temperature of 12.4-C 4) Warm side Guardroom Temperature +18"C
Warrn Side Wall Surface Temperature (OC)
(FI& rate, 062 ~ir-lriletTernp.) ( 0.1 mA3/min. 20.7'C) (0.04 mA3/min.21.1 "C) ( 0.1 mA3/min. 16.0°C) (0.04 mA3/min.
Static Condition .-+
Test Conditions: 1) Cold side Guardroom Temperature -20°C 2) No Warm side Insulalion 3) Average static cavity Temperature of 11.3'C 4) Wann side Guardroom 1200 Temperature + 18'C
1400
Figure 6.9 Warm side wall surface temperatures for DBZ air inlet temperatures colder than the average static cavity temperature. A) -10 OC cold side, B) -20 "Ccold side (no warm side insulation). Figure 6.10 depicts the warm side wdl surface temperatures rneasured when DBZ air
inlet temperatures were coider than the average static cavity temperatures. No noticeable change in surface temperatures was measured when the cold side guardroom temperature was
-10 OC. However, a slight decrease in surface temperatures occurred when the cold side guardroom temperature was -20 OC. Temperatures were colder ar the 345 mm distance by
0.75 K and at the 1257 mm level they were only slightly colder (less than 0-1 K).
There is some discrepancy between the results for the two cold side temperatures tested, It is believed that some of the deviation is a result of slight variations in the warm side temperatures and the positioning of a fan that was used to ensure more uniform warm side conditions. ESPERIME~TALRESULTS AND DISCUSSION 105
Warm Side Wall Surface Temperature (OC)
(Flow rate, 082 Air Inlet Tom p.) tao - ( 0.1 mA3/min. 6.6-C) (0.04 mA3/min.6.6-C) Static Condition
1j Cold side Guardroom Temperature -1 0% '2) No Warm side lnsulation 3) Average static cavity Temperature of 12A°C 4) Wann side Guardroom Temperature +lB°C
Warm Side Wall Surface Temperature (OC) 10 12 14 16
(Flow rate, DBZ Air lnlet Temp.) ( 0.04 mA.3/min. (O. 1 mA31min.
Condition
Test Conditions: 1) Coid side Guardroom Temperature -2O'C 2) No Warm side insulation 3) Average static cavity Temperature of 11-3°C 4) Warm side Guardroom Temperature + 18'C
Figure 6.10 Warm side surface temperatures for DBZ air inkt temperatures
warmer than the average static cavity temperature. A) -10 OCcold side, B) -20°C cold side (no warm side insulation). 6.2.3 45 mm DBZ Cavity
Minimizing the width of the DBZ cavity couid greatly increase the usable flwr area
of a building. Consequently, testing was conducted to determine what effect decreasing the
DBZ cavity width by one-half, from 89 mm to 45 mm, would have on cavity and surface
temperatures. The tests were conducted for a cotd side temperature of -20 OC using the same
flow rates of 0.01, 0.04 and 0.1 m3/min. The DBZ air iniet temperatures measured were
similar to those achieved for the 89 mm cavity tests-
The average cavity temperature results for the 45 mm and the 89 mm cavity are
surnmarized in Figure 6.1 1. The results for the static condition were not significantly
different than those obtained for the 89 mm cavity. The thermal conductance of the cavity
essentially remains equal to that of the 89 mm cavity because the effectiveness of natural
convection heat transfer within the cavity ody becomes impaired for cavity widths smaller
than 20 mm. Hence, the fairly good agreement between the static condition results for these
two cavity widths, There are slight discrepancies that are believed to be a result of
di fferences between the guardroom temperatures for the two tests (Appendix C) and possibly
due to the accuracy of the thermocouples.
The cavity temperature results for the various flows tested were also similar to those
obtained for the 89 mm cavity results. Two reasons can be given to explain this finding-
Fiar, although the Grashof number for the 45 mm cavity decreased considerably because of
its dependency on cavity width, the ~r/~e~'ratio is still considered to be well greater than one (Table 6.1). This indicates that the buoyancy forces still dominate the convection heat transfer mechanism within the cavity. EsPERI~IEKTALRESULTS AND DISCUSSION 107
OB2 Air Tempemture (OC) 10 12 14 -- - -.
Test Conditions: 1) 45 mm Cavity 2) Cold ride Guardroom Temperature -20% 3) No W8m side lnsuktion 4) Average static cavity Tempemture of 10.8.C 5) Warm side Guardroom Temperature +18'C
(DBZAir Inlet Temp.. Flow rate)
DBZ Alr Tom penture (OC) 4 O 6 O a O 10 O 12 O 14 O 16 O
Test Conditions: 1) 89 mm Cavity 2) Cold ride Guardroom Temperature dO0C 3) No W arm side Insulation 4) Average static cavtty Temperature of 11 -3-C 5) W amside Guardroom Temperature +18T
(082 Air 8nl.t Temp.. Flow rate)
Figu rc 6.1 1 DBZ air cavity temperature for al1 air flow rates tested. A) 4Smm Cavity, B) 89mm Cavity (no warm side insulation). ESPERI~IENTALRESULTS AND DISCUSSION 108
Consequently, the increase in the convection coefficient that could occur by increasing the air velocities, which occurs by decreasing the cavity by one-haif, does not manifest itself. The second reason responsible for the similarity between the results is the fact that the same mass flow rates were king forced through each of the cavities. mat is, although the velocity of the air in the 45 mm cavity is double of that in the 89 mm cavity, the cavity is only as half as wide and thus, there is only one-haif as much air in the cross-section of the cavity.
Combining these two affects results in the sarne mass of air king forced through the 89 mm and the 45 mm cavity for a given flow rate.
Given the fairly good agreement between the cavity temperatures for the 89 mm cavity and the 45 mm cavity, it would be expected that the surface temperatures would dso agree. Figure 6.12 sumrnarizes the warm side surface temperatures for both the 45 mm and the 89 mm cavity. Although the general relationship between the static temperature profile and the various DBZ air flows and inlet temperatures are similar to those of the 89 mm cavity, the temperature profile for the static condition of the 45 mm cavity is approximately
1.O K cooler. The explmation of why this may have occurred is not certain. However. the data presented in Appendix C indicate that it may possibly be due to variations between the guardroom temperatures. As with the 89 mm cavity, a DBZ inlet temperature of approximately 6 OC doesn't have any significant cooling effect on the wall surface temperatures. However, the warmer DBZ inlet temperatures seem to exhibit a greater wanning effect on the surface of the wall. The increase is, however, less than 1.0 K and perhaps can be attributed to differences in the warm guardmom temperature charactenstics. EXPERIBIENTAL RESULTSAND DISCUSSION 109
Warm Side Sudace Tempwature (*C)
vest Conditions: 1) 45 mm Cavity 2) Cold side Guardroom Temperature -20% 3) No Wam side Insulalion 4) Average stalic cavity Temperature of 10.8.C 5) Warm side Gurfdmam Temperaiure *18'C
Stalic ,-(5.8. 0.01) -(f&9.0.01) -(6.5. 0.04) -O- (16.3,0.04) - - O - - (20.8.0.04) -(6. 0.1) -(15.8. 0.1) - - a - - (20.5.0.1) - (OB2Air Met remp.. Flow rate)
Warm Side Surface Temperature (OC) 0 1 O 12 14 16
Ttsf Conditions: 1) 89 mm Civity 2) Cold side Guardroom Temperaiure -20% 3) No Warm r~dmInsulauon 4) Average srauc eavtty Temperature of 11 3'C 5) Warm side Guardroom Temperature 18'C
Static -(6.9. 0.01) ~(11.6.0.01) -(6.6.0.04) ~-(16 2. 0.04) --O-- (20.7. 0-04) 8. 0-1) +(16.0. O 1) --*--(20.3. 0.1) - .-- -. -
(OB2 Air klrt Tmmp.. Flow rate]
Figure 6.12 Warm side surface temperatures for al1 air flow rates tested. A) 4Smm Cavity, B) 89mm Cavity (no warm side insulation). . 6.3 RSI 0.79 WARM SIDE INSULATION
This section examines the effects of adding insulation to the warm side of the DBZ
cavity. A 25 mm Insulating board with an RSI value of 0-79 was used. A schematic of the
test wall is shown in Figure 6.1 3. ïhe insuiating board used was the same as that used on the
cold side of the cavity to simulate the masonry wall. Consequently, for this portion of the
experiment, the DBZ cavity had the same thennai resistance on either side of it (excluding
variations in the air film resistance). The same DBZ flow rates of 0.0 1. 0.04 and 0.1 m3/min
were tested. The DBZ inlet temperatures tested were 5 and 15 OC. A DBZ inlet ternperature
of 20 OC was not investigated because it was felt that 15 OC was sufficiently wanner than the
average static cavity temperature. The cold guardroorn temperatures tested were -10 and
-20 OC. The warm guardroom was set at +18 OC.
Cold Guardroom . ,i :<% :<% ,.. Warm Guardroom . . Cold Side L'- . Warm Side
DBZ Air lnla
€.terior lnsulation RS10.79 . WmSide lnsulatio (Simulate Masonry Wall) r
Figure 6.13 Cross-section of the test wall depicting the warm insulation (RSI 0.79). ESPERIIIENTAL RESULTSAND DISCUSSION 111
The measured DBZ air inlet temperatures are surnmarized in Tables 6.5 and 6.6.
Although DBZ inlet temperatures of 5 and 15 OC were desired, as descnbed earlier,
temperature control techniques caused some variation. As a result of the interior insulation
significantly reducing the temperature of the cavity and thus reducing the heat flow to the
manifold, the 5 OC DBZ inlet temperatures for the 0.01 m'/min flow rate was more easily
attained during these set of tests. However, this reduction in heat flow resulted in more
difficulty with achieving a DBZ inlet temperature of 15 OC. Consequently, this target
temperature was not tested for the 0.01 m3/min flow rate. As stated previously, this is
believed to be a result of the combined effects of an extremely slow mass flow rate and the
reduction in temperature of the cavity.
As previously discussed in Section 6-2-1. ail results for forced flow conditions will be
discussed with reference to the average static cavity temperature-
Table 6.5 DBZ ialet temperatures with the exterior temperature at -10 OC (RSI 0.79 warm side insulation). 0 1 - 1 OC Exterior 1 Flow-- Rate-- f DBZ Inlet (OC) 0.01 (m3/min) 0.04 (m3/min) O. 1 (m'/min) Measured 5 -4 n.a 5.7 15 4.8 15.2 Target 5 15 5 15 5 15
Table 6.6 DBZ inlet temperatures with the exterior temperature at -20 OC(RSI 0.79 warm side insulation). 1 -20 OC Exterior 1 Flow Rate 1 4 i DBZ Inlet ("Cl 0.01 (m3/min) 0-04 (m3/min) O. 1 (m'/min) I Measured 4.5 n.a 7.5 16.7 6.5 16.1 Target 5 15 5 15 5 15 6.3.1 DBZ Cavity Temperatures
The DBZ air cavity temperatures measured for the three flow rates tested will be averaged using equation [6.1]. These results are detailed in Appendix C. The fim category of results that will be discussed deal with DBZ air inlet temperatures that are less than the average static cavity temperature. The second category wiII deal with the DBZ air inlet temperatures that are warmer than the average static cavity temperature.
6.3.1.1 DBZ Air Inlet Temperatures Colder than the Average Static Cavity Temperature
When the cold side temperature was -10 OC. the average static cavity temperature increased from 2.6 to 6.6 OC at the 345 mm level and from 0-9 to 5.4 OC at the 1257 mm level,
The coolest DBZ air inlet temperatures measured were 5.4, 5.7 and 4.8 OC for the 0.01, 0.04 and 0.1 m'/min flow rates respectively. Thus, it would seem possible that some induced buoyancy action may occur even though these temperatures are only slightly cooler than the static cavity temperature at the top of the cavity.
As Figure 6.14 indicates, there is some cooling of the DBZ air cavity temperatures relative to static conditions for the 0.04 and 0.01 m3/min flow rates. Again it is believed that this is a result of an induced buoyancy action. The degree of cooling resulting from this apparent buoyancy action seems to have little dependence on the rate of flow. This may be due to the small difference between the inlet temperature and the average cavity temperatures tested. As discussed earlier, it is believed that the 0.01 m3/min flow lacks sufficient inertia forces to influence cavity temperature as indicated in Figure 6.14. DBZ Air Temperaturm (OC)
(Flow rate. DBZ Air lnlet
I- I- ( 0.1 mA31min.4.8-C) 4 +- (0.04 mA31min.5.7-C) 1 (0.01 mA3/rnin. 5.4'C)
Static Condition
vert Conditions: 1 ) Cold side Guardroom Temperature -10% 2) RSI 0.79 Warm Side lnsulation 3) Average static cavity Temperature of 5.9'C 4) Wam side Guardroom Temperature +18 'C
Figure 6.11 Average DBZ air cavity temperatures for inlet tempeartures colder than the average static cavity temperature (RSI 0.79 warm side insulation, -10°C cold side temperature).
A subsequent test was conducted to determine the effects of introducing DBZ air that is well below the average static cavity temperature. The test was carried out using a 45 mm wide DBZ cavity. The flow rate tested was 0.04 m3/min and the rneasured DBZ air inlet temperature was 2.8 OC. This was significantiy cooler than the average static cavity temperature estimated to be approximately 7.5 OC using theoretical steady-state calculations
(Appendix C). The warm and cold side guardroom temperatures were 24.9 and -9.9 OC respectively. Once equilibrium was established, the average cavity temperatures rneasured were 6.5, 6.5, and 6.4 OC at the 345, 800 and 1257 mm levels respectively. Hence, two key ESPERIMEKTALRESULTS AND DWSSION 114
indications of induced buoyancy action were observed. First, the DBZ cavity temperatures
did not cool a great deal even though a DBZ inlet temperature of 2.8 OC was used. Secondy,
the fairly vertical temperature profile through the monitored distance of approximately 1.2 m
is consistent with previous results that indicated an induced buoyancy action,
The average cavity temperatures for testhg with the cold side temperature at -20 OC did not demonstrate any induced buoyancy action because al1 the DBZ inlet temperatures were warmer than the average static cavity temperature of 1-7OC (Figure 6.15 b).
6.3.1.2 DBZ Air Inlet Temperatures Warmer than the Average Static Cavity Temperature
The foIlowing discussion will deal with the DBZ inlet air temperatures that are warmer than the average static cavity temperature. The effect of the DBZ air inlet temperature and flow rates on cavity temperatures are significantly different compared to when the DBZ air inlet temperatures were cooler. This is illustrated by Figure 6.15 which compares cavity temperatures measured with the cold side guardroom temperature set at -10
OC and the DBZ air inlet temperature and DBZ air inlet temperatures of 4.8 and 15.2 "C for the 0.1 m'/min flow rate.
As Figure 6.16 demonstrates, with the cold side temperature at -20 OC, the slowest flow rate of 0.0 1 m'/min had an inlet temperature of 4.5 OC. This was approximately 2.0 K warmer than the 2.5 OC static temperature at the 345 mm level. However, this flow essentially had no impact on the average cavity temperatures. This is attributed to the very small inertia forces and mass flow rate associated with such a slow flow rate. ESPERI~IWALRESULTS AND DlSClrss10~ 115
DBZ Air Temperature (OC) 6 8 10 12 14 - .- (Flow rate, DBZ Air lnlet Temp.) ( 0.1 mA31min. l5.2'C) \
'Test Conditrons: 1) Cold side Guardroom Temperature -10'C 2) RSI 0.79 Wam Side lnsulation 3) Average static cavity Temperature of 5.S0C 4) Warm side Guardroom Temperature +18 'C
Figure 6.15 DBZ air temperature profiles for the 0.1 m'/min flow rate with inlet temperatures of 4.8 and 15.t°C (RSI 0.79 warm side insulation, -10°C cold side temperature).
However. the remaining flow rates of 0.04 and 0.1 m'/min had significant impacts on the DBZ cavity temperatures observed. For the sarne DBZ inlet temperature, the greater flow rate wiil produce warmer cavity temperatures. As previously explained, this is as a result of the DBZ air having less tirne to cool down at a faster flow rate. FutthennoreT the characteristic exponential decay of the DBZ air temperature is evident in Figure 6.16. 082 Air Temperature ('C) 6.0 8.0 10.0 120 (4.0 16.0 18.0 20.0
E -2 g 800 est Conditions: Cold side Guardroom lmC Cm Temperature -1 0% 6 rooo 2) RSI 0.79 Wann Side Insulation 3) Average static cavity Temperature of 5.9'C 4) Warm skie Guardroorn Temperature 41 8 'C
062 Air Temperature ('C)
(Flow rate. DBZA~~lnlct lemp.)
Test Conditions: t 1) Cold side Guardroom Temperature -20'C 2) RSI 0.79 Warm Side lnsulation 3) Average static cavity Temperature of 1.7.C 4) Wam side Guardroom Temperature +18 'C 'ï
Figure 6.16 Average DBZ air cavity temperatures for inlet temperatures warmer than the average static cavity temperature (RSI 0.79 warm side insulation); A) -10°C cold side, B) -20 "C cold side. - - -
Table 6.7 surnmarizes the change in DBZ air temperature with distance fiom the DBZ
inlet for the 0.04 and 0.1 m'/min flow rates and for the DBZ inlet temperatures that were
warmer than the average çavity temperature. The total heat transfer that occurs between the
inlet and the 1257 mm level is aiso calculated-
Table 6.7 Average cavity temperature changes for the 89 mm DBZ cavity with RSI 0.79 warm side insulation.
Flow Rate 0.04 m'/min 0.1 m'/min Exterior Temperature - I 0°C 1 -20°C - 10°C -20°C DBZ Inlet Temperature 15Oc 1 16.7 Oc 153OC 16.1 Oc Distance Interval Change in Air Temperature CC) Change in Air Temperature ("C) Intet to 345 mm 3 -8 6.8 2.0 3 .O 345 mm to 800 mm 3 -4 5.2 2.1 2.9 800 mm to 1257 mm 1 -6 2.0 1.7 2.4 Total Change in Temp (K) 1 8-8 1 14 1 5.8 1 8.3 - - - - m Total Heat Transfer Rate(W/m2) 7.2 1 11.4 1 11.8 1 16.8
From this table, it is evident that for a particular DBZ inlet temperature, the larger the flow rate, the greater the heat transfer and the warmer the cavity temperatures Furthemore, as expected, an increase in heat transfer occurs when the cold guardroom temperature is decreased from -1 0 to -20 OC and when the rate of air flow increases. It is important to note that the increase in total heat transfer that occurs when the flow rate increases is primarily due to the increase in the rate of air flow and not because of an increase in the convection heat transfer coefficient. This is because the inertia forces associated with the velocity of the air are retatively smatl in cornparison to the buoyancy forces, even at the larger flow rate of
0.1 m3/rnin. Figure 6.17 presents some of the test resuits shown in Table 6.7, It shows the relationship between the arnount of cooling the DBZ air experiences between the inlet and the 1 2S7rnm level (DBZ Air: Ti,,,a- T,,,,,) as a function of the difference behueen the DBZ air inlet temperature and the average static cavity temperature (TDBz - T- aGw). This graph is intended to ody provide an approximation of the relationship because the static cavity temperature used is an average, and is specific to the wami and cold side temperatures maintained for that particular test. These temperatures only varied slightly between tests
(Appendix C)?thus the general conclusions drawn from this graph are not considered to be compromised.
1) Cold side Guardroom Temperature -10% and -20% 2) RSI 0.79 Wam Side Insula!ion 3) Wam side Guardroom Temperature +18 'C
2 4 6 8 1O 12 14 16 1WC (082 Air) - T.utic ,vit, (OC)
Figure6.17 The relationship between the amount of cooling the DBZ air experiences and the temperature difference between the DBZ air inlet and the average cavity temperature (RSI 0.79 warm side insulation). ESPERIICIENTAL RESULTSAND DISCUSSION 119
Figure 6.17 demonstrates that for the flow rates tested, there is no signiticant
advantage to heat the DBZ air significantly above the average static cavity temperature
because most of the added heat energy of the air is lost within the first 1.2 m. Further, it
seems that the cooling experîenced by the DBZ air is a funçtion of the flow rate.
In general, the results obtained for testing of the DBZ wall with warm side insulation
were similar to the redts obtained for the DBZ wall without wann side insulation- The
major difference in behaviour of these two wdl configurations is that the DBZ air cooled down much more quickly in the wdl which had wami side insulation installeci- This result is expected because the addition of the insulation significantly reduced the heat flow from the wam guardroom to the air moving within the cavity. Consequently, the net rate of heat fiow from the air within the cavity was much greater when insulation was added to the warm side of the cavity.
To furthet- investigate the effects of decreasing the exterior temperature from -10 to
-20 OC on average cavity temperatures, the temperature index will be utilized once again.
Figure 6.18 represents the average cavity temperature index for testing with the cold guardroom temperature set at -10 and -20 "C respectively- There is adequate agreement between the graphs for DBZ idet temperatures greater than the static wall temperature.
However, for the remaining DBZ idet temperatures, the correlation is not as good. This is believed to be the result of the induced buoyancy action that was present for the - 10 OC testing and not for the -20 OC testing. This induced buoyancy action will alter the heat transfer characteristics of the cavity and thus change the temperature index values. ESPERILIEMAL RESULTSAND DISCUSSIOI~~ 120
062 Cavity iemperrture Index 0.1 0.2 0.3 0.4 0.5 0.6 O.? 0.8 0.9
test Conditions: 1) Cold side Guardroom Temperature -lO°C 2) RS10.79 Warm Side lnsulation 3) Average static cavity Temperature of 5.9% 4) Warm side Guardroorn Temperature +18 'C
StaticCondition
+(15.0.0.04)
(DBZ Air Inlet Temp.. Flow nt.)
DBZ Cavity Temperature lndex 0.4 0.5 0.6 0.7 0.8 0.9
test Conditions: 1 ) Cold side Guardroom Temperature -20aC 2) RS10.79 Warm Side lnsulation 3) Average static cavity Temperature of 1.7'C a) Warm side Guardroorn Temperature +18 'C
"tatic Condition +(4.S. 0.01) +(7.5.0.04) -(16.7.0.04) -(65 0.1) -.0 - -(16.1.0.1) - -- (DE2Air Inlet Temp.. Flow me)
Figure 6.18 Average Cavity Temperature Index: A) -10°C cold side, B) -20°C cold side (RSI 0.79 warm side iosulation). 6.3.2 Warm Side Surface Temperatures
Figure 6.19 surnmarizes the swface temperatures measured for the testing of the 89
mm cavity with warm side insulation installed. The thermocouples taking the temperature
readings were placed on the surface of the insulation exposed to the warm guardroom.
Figure 6.19 shows that decreasing the exterior temperature to -20 OC had little
influence on surface temperatures Slightly warmer surface temperatures were only measured for the larger flow rate of 0.1 m3/min. It reasonable to expect that much of the temperature variations that may occur within the DBZ cavity would be dampened by the intenor insulation so that the wmside surface temperatures would be approximately equal to the warm side guardroom temperature- Generally. this is what is depicted in Figure 6.19.
Furthemore. the surface temperatures measured when interior insulation ws added were generally \vanner than those for the wall without insulation. This is a reasonable result because the addition of the insulation reduces the temperature decrease that occurs across the wam side air film, thus making the warm side surface temperature warmer compared to the situation where no insulation is added. The effect of adding wann side insdation on warm side surface temperatures for static wall conditions is shown in Figure 6.20-
6.3.3 35 mm DBZ Cavity
Tests were also conducted to determine the effects of decreasing the DBZ cavity width by one-half, from 89 mm to 45 mm, when wiarm side insulation was installed, The
tests conducted were for a warm and cold side guardroom temperatures of +18 OC and -20 OC respectively. The sarne DBZ air flow rates of 0.01,0.04, and 0.1 m3/min were used. Wann Side WaII Surfacm Temperature ('C)
8 10 12 14 16 18 20
(Flow rate, DBZ Air lnlet Temp.) ( 0.1 mA3/min. 15.2-C) ( 0.1 rnA3/min.4.BmC) (0.04 mY/min. 15%) (0.04 mA3/min. 5-7'C) (0.01 mA3/min.5.4%) Static Condition
Test Conditions: 1) Cofd side Guardroorn Temperature -1OœC 2) RSI 0.79 Warm Side Insulation 3) Average static cavity Temperature of 5.S0C 4) 'Nam side Guardroom Temperature +18 'C
Warm Side WaII Surface Temperature (OC)
(Flow rate, DBZ Air lnlet Temp.) ( 0.1 mA3/min, 16.1.C) ( 0.1 mA3/min.6.5-C) (0.04 mA3/min. 16.7-C) (0.04 mA3/min. 7.S°C) (0.01 rnA3/min.4-5-C)
Test Conditions: 1) Cold side Guardroorn Temperature -20°C 2) RSI 0.79 Warm Side lnsulation 3) Average static cavity Temperature of l.I°C 4) Warm side Guardroom Temperature +18 'C
Figure 6.19 Warm side wall surface temperatures for DBZ air inlet temperatures colder than the average static cavity temperature. A) -10°C cold side, B) - 20 OCcold side (RSI 0.79 warm side insubtion). Warm Siâe Surface Temperature (*C)
RSI 0.19 Wam Side lnsulation
No Warm Side Insubtion
1) 89 mm Cavity 2) Cold side Guardroom Ternpemwe -10% 3) Warm side Guardroom Tempemtuie +18'C
e
Figure 6.20 Cornparison of the warm side surface temperatures for the static cavity with warm side insulation and without warm side insulation (eold side temperature -1o0c).
As Figure 6.21 shows the results of the testing for the DBZ air cavity temperatures were not significantly different than those obtained for the 89 mm cavity. As explained in
Section 6.2.3, the sirnilarïty between these results is attributed to the sarne air mas flow rate being used for both of the cavity sizes. It should be noted that the average temperatures for the 45 mm cavity were slightly cooier. This may be attributed to the cooler DBZ inlet temperatures achieved for the 45 mm cavity. Figure 6.22 shows the fairly good agreement between the warm side surface temperatures for the 89 mm and the 45 mm cavity. DBZ Air Temperature ('C)
1) 4Smm Civity 2) Cold side Guardroom Temperature -20% 2) RSI 0.79 Warm Side lnsulation 3) Average statîc cavity Temperature of 1.3-C 4) Warm side Guardroom Temperature +18 'C
StaticCondition .+ (4.9. 0.01) -(6.5. 0.04) -c- (16.2. 0.04) .+. (6-0. 0-1) --a--(15.6. 0.1)
(062Air Inlet Temp.. Flow rate)
DBZ Air Temperature (OC) 6 8 10 12 14
-0
mest Conditions: 1) 89mm Cavity 2) Coid side Guardroom Temperature -20% 2) RSI 0.79 Wam Side lnsulation 3) Average static cavity Temperature of 1.TOC 4) Warm side Guardroom Temperature +18 'C
StaticCondition -(4.5. 0.01) .-, (7.5.0.04)
(082 Air lnlet Temp.. Flow rate)
Figure 6.21 Cavity Temperature for al1 air flow rates tested. A) 45mm Cavity B) 89mm Cavity (RS10.79 warm side insulation). Warm Side Wall Surface Temporature (OC) 4 6 8 10 12 14 16 II 20 O -.
Test Conditions: 1) 4Smm Cavity 2) Cold side Guardroom Ternperature -2O'C 2) RSI 0.79 Warm Side Insulation 3) Average static cavity Temperature of 1.3.C 4) Warm side Guardroom Temperature +18 'C
Static -(5.8.601) -(6.5. 0.04) -(16.3. 0.04) -(6. 0.1) -(15.8. 0.1)
Warm Side Wall Surface Temperature (OC) 1 O 12 14 16 18
- *
Test Conditions: 1) 89mm Cavity 2) Cold side Guardroom Temperature -ZO°C 2) RS10.79 Warm Side lnsulation 3) Average static cavity Temperature of r .toc 4) Warm side Guardroom Temperature +18 'C
Static -(6-9. 0.01) -(6.6. 0.04) +(16.2. 0.04) -(5.8, 0.1) -(16-0. 0-1) (062 Air Inlet Temp., Flow nt.)
Figure 6.22 Warm side surface temperatures for a11 air flow rates tested. A) 45mm Cavity, B) 89mm Cavity (RSI 0.79 warm side insulation). 7.0 CONCLUSIONS AND FURTHER RESEARCH
The objective of this study was to investigate the influence of an exhaust type
Dynamic Buffer Zone system on wali sudiace temperatures because surface temperatures of a wall in contact with a DBZ cavity codd be afTected by the DBZ airflow.
A comprehensive test program was developed and executed to determine how certain conditions of the DBZ air and wall construction affect the temperature of the forced air within a simulated wall cavity. The characteristics investigated were: the initiai DBZ air temperature, DBZ air flow rate, DBZ cavity width, insulating the warm-side of the DBZ cavity and the exterior temperature.
The DBZ flow rates investigated were determined by estimating what the flow rate through an equivalent size wall for a particular project that specified a maximum flow rate for an entire floor (Appendix 9). The DBZ cavity widths of 89 mm and 45 mm were chosen because these dimensions are conventional framing sizes and would be representative of typical cavity widths used in actual construction.
For the DBZ flow rates and the cavity widths chosen. fluid and therrnodynamic parameters indicated that the convection heat transfer mechanism within the DBZ cavity would be dominated by buoyancy forces. This is because the inertia forces associated with the DBZ air velocity within the cavities were relatively small. NumericaI calculations seem to be confinned by an observed induced buoyancy action that occwred when initial DBZ air temperatures cooler than the average static temperature were introduced at the top of the cavity . ~o;uc~usro~sAND FURTHER RESWRCH 127
nebuoyancy action slightly cooled the cavity temperatures cornpared to static
conditions. Consequently, it seems possible that the induced buoyancy action may have the
potential to increase the thermal resistance of the cavity with respect to static conditions.
This needs to be investigated Mer. The degree and charactenstics of the cavity cooling
seem to be a function of the DBZ airflow rate such that the larger the flow rate the greater the
cooling. Also, for the two flow rates of 0.04 and 0.1 m'/min, the buoyancy action caused the
temperature profile to be nearly vertical through the 1.2 m monitored. For the larger flow
rate of 0.1 m'/min (26.1 mm/s cavity velocity), 1.0 K was the largest degree of cooling
observed. It would also seem reasonable that the affect of the induced buoyancy action
would also be a function of the wall height and the difference in temperature between the
inlet DBZ air and the average static cavity temperatures.
Completely different results were observed when the DBZ air inlet temperature \vas greater than the average static cavity temperature, The average DBZ air temperature decreased exponentially as it traveled from the inlet down through the cavity. The degree of the temperature decay increased as the difference between the DBZ air temperature and the static cavity temperature becarne greater. Furthemore, as the flow rate increased, the amount of cooling the DBZ air experienced decreased.
Decreasing the DBZ cavity width from 89 mm to 45 mm essentially had no effect on
DBZ cavity temperatures. As explained earlier, this is attributed to two reasons. First, buoyancy forces still dorninate the inertia forces. Second, the same mass flow rates were being forced through each of the cavities. Co~ctusro~sAND FURTHERRESEARCH 128
The addition of insulation to the wann side of the DBZ cavity and changing the cold
room temperature had the same influence. En general, the effect of these two variables was to
change the equilibrium temperature of the cavity and thus affiect the amount of cooling the
DBZ air experienced. The interior insulation also caused the wall surface temperatures to be
slightly warrner than those of the wall without interior insulation- Furthemore, the
insulation seemed to dampen the temperature variation within the DBZ cavity.
When utilizing the DBZ cavity as an air barrier system or as a dynamic insulation
system, it is desirable to minimize the amount of heat that is initially added to the outdoor air
that is used for the DBZ air. This will reduce the costs associated with initial heating of the
DBZ air and it will also allow the DBZ air to capture heat that would otherwïse have ken
lost to the exterior environment.
It is important to stress that the experimental results obtained are specific to the fluid
and thermodynamic conditions of the DBZ cavity. If greater velocities were tested, such that
the inertia forces were greater than buoyancy forces (Gr/ReJ, the results would have ken
much different. The degree of change in cavity temperatures would be dependent upon how
the flow conditions within the cavity influence the convection coefficient.
For the flow rates investigated and with the DBZ inlet source located at the top of the
cavity, an initial DBZ air temperature of approximately 5.0 K below the average static cavity
temperature seems to be a viable temperature that will not have any significant impact on
interior wall surface temperatures. However, the DBZ air temperature should never be colder than the dew point temperature of the interior air space. This restriction will prevent condensation frorn occumng on the surface of the distribution system used to transport the CONCLUSIONS AND FURTHERRESURCH 129
DBZ air from the exterior to the DBZ cavity. Furthemore, decreasing the DBZ cavity width from 89 mm to 45 mm is an alternative that does not significantly alter the performance of the DBZ system. in addition to reducing construction costs, a 45 mm DBZ cavity will increase the usable floor area of a building.
Upon completion of this study it becarne apparent that further research is necessary in a number of areas. In the author's opinion, this research should be fôcused in the followîng areas :
1. It has ken stated that the ideal initial temperature of the DBZ air shouid be below that of
the static cavity temperature. Thus. DBZ inlet temperatures below the average static
cavity temperature should be investigated hrther together with the effect on wali surface
temperatures of greater air velocities. These velocities should be large enough so that
buoyancy effects are not a factor and forced convection is the dominant convective heat
transfer mechanism since the influence of buoyancy forces has been investigated herein.
2. The apparent induced buoyancy effect should be fiirther investigated. Based on the
proposed expianation for this phenornenon. it is likely that completely different
experïmental results would have been attained if the DBZ air was introduced at the
bottom of the cavity and exhausted at the top of the wall. If this were the case, DBZ air
inlet temperatures greater than the average cavity temperature would cause the induced
buoyancy action. DBZ inIet temperatures colder than the average static temperature
could also cause cooling of the cavity. The effects of cavity height and the difference in
temperature between the inlet DBZ air and the average static cavity temperature on the
induced buo yancy action should also be investigated, 3. The experimental wall tested was airtight. However, in practice it likely that air leakage
could occur from the DBZ cavity, especially when dealing with masonry structures.
Consequently. the effects of air leakage from the cavity on wall surface and cavity
temperatures should also be investigated.
4- There is no information available on typical DBZ air cavity velocities used in actuai
buildings. Since the heat transfer mechanism within the cavity is very dependent on the
fluid dynamic conditions of the cavity, a field study should be undertaken to determine
the range of DBZ air velocities used in practice. This will provide valuable information
to be used in the laboratory investigations suggested above,
5. It has been stated that the DBZ has the potential to function as a dynarnic insulation
system. This aspect of the DBZ should be further investigated by exarnining the heat
flow and mass balances associated with possible DBZ air flow conditions:
6. Finally. full-scale field tests should be conducted to monitor the performance of the DBZ
system. The tests should ensure controlled conditions in order to compare the
performance of the system in the laboratory and in the field. Quirouette, R;"The Dynamic BufFer Zone", The Construction Specifier, August 1997.
Garden, G.K.; The Building Envelope to 200 1 ': 1Oh Congress of the International Federation of Hospital Engineering, Edmonton, Alberta, July 1988, p.1.
Ibid.
Hutcheon, N.B.;"CDB 48. Requirements for Exterior Walls", Canadian Building Digest, National Research Council Canada 1963, p.5.
Richie, T.; "Moisture Degradation of Masonry Walls", National Research Council Canada. 1976, p. 1.
Hutcheon, N.B.; "Humidified Buildings", Canadian Building Digest, National Research Council Canada, 1963, p-5.
Quirouetee, R.L.; "The Air Barrïer Defined", Building Science Insight/National Research Council Canada, 1986, p- 1.
ASHRAE. 1997; "ASHRAE Handbook - 1997 Fundamentals", American Society of Heating, Refngerating and Air-Conditioning Engineers Inc., p. 5 -5. ibid.
Garden, G.K.; "CBD-72.Control of Air Leakage is Important", Canadian Building Digest, National Research Council Canada, 1965, p. 1. see C2.71, p. 25.1 1. ibid. p. 25.12.
Wilson, A.G- and Garden, G.K.; "Moistwe Accumulation in Walls Due to Air Leakage", DBR, National Research Council Canada, p.2. see [2.6].p.3. see C2.121. p.3.
Wilson, AG.; "CBD-23. Air Leakage in Buildings", Canadian Building Digest, National Research Council Canada. 1961.v.5- [2.16] see [2.14].
[2.17] see f2.71,p. 24.16.
[2.18] see [2.7], p. 25-19.
[2.19] Tamura, G.T. and Shaw, C.Y. "Studies on extenor wall air tigbess and air infiltration of ta11 buildings", ASHRAE transactions 82(1): 122, 1976,
[2.20] Penily, A.K. and Grot, R.A., "Pressurization of federal buildings", ASTM STP904, p. 184.1986.
f2.211 see [2,12]. p.4.
[2.22] see [2.9]. p. 1.
12-23] see [2.6].
[2.24] National Research Councii of Canada, "Air Barrier Systems for Walls of Low-rise Buildings: Performance Assessrnent", lnstitute for Research in Construction, 1997.
[2.25] see [2.15]. p.6.
13-11 Rousseau, M.Z. and Maurenbrecher. A.H.P.; "Rehabilitation of Solid Masonry Walls", Constmction Canada, Volume 32(5), 1WO, p. 1.
[32] ibid.
13-31 Hutcheon, N.B.; "Humidified Buildings", Canadian Building Digest, National Research Council Canada, l963? p. 1.
13 -41 Andersson, Ann-Charlotte; "Additional Thermal Insulation of Existing Buildings. Technical Consequences", Proceedings of the Fifth International Brick Masonry Conference, Washington DC, 1985. p. 642.
[3S] Rousseau, M.Z., Maurenbrecher, A.H.P., Said, M.N.A- and Shirtliffe, C.J.; "Monitoring the Hygrothermal Performance of a Masonry Wall with and wit hout Thermal Insulation", Proceedings of the 8Ih Canadaian Masonry Symposium, Jasper, Alberta 1998, p. 7. [3.7] Brand R, G.; "High Humidity Buildings in Cold Climates - A Case History", Durability of Building Components. ASTM STP 69 1, P. J. Sereda and G.G. Litvan, Eds., Ametkm Society for Testing Materials, 1980, p. 232.
[l8] Frarn, M.: "Murderous Moisture in Historic Buildings", The Canadian Architect p. 3 7-49.
[3.9] Warson, A.; "A watertight Solction", Engineering News Record, June 5 1995, p1 7.
[3.1 O] Bai 11y, N.R.; "Dynarnic Isulation Systems and Energy Conservation in Buildings", ASHRAE Transactions, Part One, 1987.
[3.12] Masoero M.: Aghemo C.; "Performance of an Innovative Ventilated Curtain-Wall Component", Thermal Performance of the Exterior Envelops of Buildings III, Dec 2- 5 1985, Clearwater Beach, Florida, p. 1005.
[3.13] ibid. p1004.
[3.14] see [3.10].
E3.151 Centre Scientifique et Technique du Batiment, Plan Constructiont and Ecole Nationale des Ponts et Chaussees. Proceedings of the International Conference on I~ovatingTechnologies in Building, 1983, Paris.
[3.16] Ministere de L'Urbansime et du Logement, "Programme Habitat Econome en Energie H2E85 - L'Habitat Hyperisole", Plan Construction, Paris.
[4.1] ASHRAE. 1977; "ASHRAE Handbook - 1977 Fundarnentals", American Society of Heating, Refiigerating and Air-Conditioning Engineers Inc., p 2.1.
[4.2] Incorpera F.P., Dewitt D.P.;"Fundamentals of Heat and Mass Transfer9', 41h Edition. John U7iley and Sons, 1996. p 4.
[4.3] ibid. p6.
[4.4] ibid. p8. l4.51 ibid.
C4.61 see [4.1]. p. 2.6.
[4.7] see [4.2]. p.43 1. 14-81 Chang R.; "Chemistry", 4h Edition,McGraw-Hill, 1991. p 227.
[4.9] Ro berson LA., Crowe C.T.; "Engineering Fluid Mechanics". 4m Edition, Houghton Mimin Company* 1990. p 336.
E4.1 O] see 14-21. p.29 1.
[4.11] ibid.
E4.121 see C4.21. p.3 14.
[4.13] see [4.2]. p.346.
[4.14] see [4..2].
[4.15] Grigull U.. Hahne E., Stephan K., Straub, J.; "Heat Transfer 1982", Proçeedings of the Seventh International Heat Transfer Conference, Munchen. Fed. Rep. of Germany .
14.1 61 Rohsennow, W., Hamet, J., Cho, Y.; "Handbook of Heat Tram fer97 ,>-rd Edition-McGraw-Hill, 1998.
[4.17] Rohsennow, W.. Harnet,; "Handbook of Heat Transfer", McGraw-Hill, 1973.
(4.1 81 see 14.21- p.449.
14.191 see [4.17]. p.5.59.
[4.20] see C4.21. p.428.
14.2 11 Wei-Mon Yan, Tsing-Fa Lin; "Buoyancy Effects on Low Reynolds Number Turbulent Forced Convection in Vertical Plate Channels with Symmetric of Assymetric Wall Temperatures", Journal of the Chineese Society of Mechanical Engineers, 1987, Vol, 8 No. 5. f4.221 see [4.2], p.485.
[4.23] see [4- 11. p.2.11.
[4.24] see 14.21. p.510. c4.251 Hutcheon N.B..Handegord G.; "Building Science for a Cold Climate", Construction Technology Centre Atlantic tnc., 1989. p 185.
C4.261 see C4.231. see t4.251. p.4.27.
see [42]. p.5 15.
Churchill S.W.; "Combined Free and Forced Convection in Charnels", in Heat Exchanger Design Handbook, E.U. Schlunder, editor-in-chiet p 25-14.
Tjeflan P.O.,Ytrehus T.; "Combined Free and Forced Laminar Convection in a Vertical Channel", in Numerical Methods in Thermal Problems,Proceedings of the Znd International Conference held in Venice Italy July 198 1, Pinendge Press. Swanse- U.K.
Kays W.M.. Crawford M.E.; "Convective Heat and Mass Transfer" 2" Edition. McGraw-Hill. 1980. p 329.
see (4.291. p.2.5.10-1.
14.331 see 14.291. p.2.5.10-6.
14-34] see 14-21. p.487.
[6.1] Incorpera F.P.. Dewitt D.P.; "Fundamentals of Heat and Mass Transfer". 4'h Edition. John Wiley and Sons. 1996. p 436. APPENDIXA
Condensation Potential Condensation Potentiai
The wdl being considered is a 11.15 m2 plain brick wall. Plain brick may present the
worst case scenario for both air leakage and vapour diffusion. The boundary conditions wd
for the month of January are as follows:
1. intenor - 23°C and 35% relative humidity, and
2. Extenor - -8OC and 100% relative humidity (-8°C is average daily temperature in
Toronto taken fiom NormaIs Tables; 1972)
Diffusion
The permeance of an average plain brick 3OOmm thick is 15.09 ng/(s.rn2.Pa). An average temperature profile through the wall utiIized to cdculate the saturation vapour pressure profile demonstrated that condensation would occur l3mm in from the exterior face at a vapour pressure of 420 Pa.
Steady state water îransmission through the wall by vapour difision occurs according to:
where.
W is the mass of vapour transmitted, gram (iI i? ) is the penneance of the matenal, ng/(s.m2.pa), A cross-sectional area of the flow path, m' 0 time during which flow occurs, seconds, and (pl- p,) is the vapour pressure digerence across the material, Pa.
Hence, W = 15.09* 1 l.l5*26789ûû*(O.3S*2809 - 420)* 1x109 = 254 grams of water. 138
Air Leakage
A plain brick wall located 15m above the neutral pressure plane is king considered
(approximately 5 floon). Stack effect and mechanical pressurization are only king considered, and the effects of wind action have ken ignored. The air leakage characteristic of the wall wiIl be that taken from the testing of four Ottawa buildings, Figure A. 1
The pressurization due to stack action can be calculated with equation [2.5].
Substituting h= 15 m and inside and outside temperatures of 23°C and -8°C respectively, the pressure due to stack is 20 Pa- Furthexmore, it will be assurned that mechanical pressurization wiIl produce 10 Pa pressure. Hence, the total e'diltrating pressure is 30 Pa.
Using the data of Figure A.1, the air leakage rate per square rneter of wall area is 0.73 m3/s.
For the month of January, this results in 21 800 m' of air exfiltration for a 1 1.15m2 wali area.
The water content of the interior air is 0.0061 kg of moisturekg of dry air and
0.00 19 1 kg of moisturekg of dry air for the exterior conditions. There is approximately 1.1 8 kg dry airim' at 23OC and 35% relative humidity. Assuming that the exfiltraring air leaves the outside surface of the brick wall at the outdoor temperature and saturated, the amount of rnoisture condensing is (0.006 1-0.00 19 1)* 2 1800* 1.18 = 108 kg of fiost. Figure A.l Results of Air Leakage Measurentents on Four Test Buildings. Source: Tamura, G. T.; "Predicting Air Leakage For Building Design1',6th CIB Congres, "the Impact of Research on the Built Environment", Budapest. vol l/lTOtt.? 1974. DBZ Air Flow Selectioo DBZ Air Flow Seiection
An extremely important aspect of the testing program that needed to be established
was what DBZ airftow rates should be examined. As a benchmark for experimental test flow
rates: the flow rates used for the DBZ system used in a renovation of the rnasonry building
located at 321 Bloor Street East. A 89mm wide DBZ cavity was used for this project A
typical floor plan is shown in Figure B. 1. The maximum fiow rate for the DBZ system was
600 CFM/floor. The total wall area (excluding fenestration) incorporating the DBZ system
was estimated to be 6000 square feet per floor. The ratio of the flow rate to the wall area is
0.0305 m/min. The experimental wall area is 1 .O94 m'. Thus, to achieve the sarne air flow to wall surface area ratio as for the above noted DBZ system, a flow rate of 0.033 m'/ min must be used in the test wall. It should be noted that the actual flow within parts of the DBZ cavity used in the noted project may be less than what was caiculated because the of air leakage through the masonx-y walls, especially around fenestration. Furthemore, areas within the cavity adjacent to stagnation zones would expenence larger flow rates.
Using 0.033 m3/min as a bench mark, it was decided that DBZ air flow rates of 0.01.
0.04 and 0.1 m'/min would be investigated in the labotatory for the test wall constnicted . Figure B.l Typical Floor Plan of the Building located at 321 Bloor Street East. APPENDIXC
Experimental Results This Appendix summarizes the test experimental results in two main sections: No warm side insulation and RSI 0.79 warm side insulation. The results are presented in a tabular format. To understand the tables, an explanation of the various column headings
the location of the thermocouples with reference to the DBZ air inlet location,
the thermocoupies taped to the exterior side of the warm side plywood used to fonn the warm side wall of the DBZ cavity,
3. Mid the thermocouples located in the rniddle of the cavity,
4. Cold the thermocouples taped to the interior side of the cold side piywood used to form the cold side wall of the DBZ cavity-
5. Average the average of the thermocouples noted above calculated using the trapezoidal rule,
6. Warm side Wall Surface the thennocouple located on the surface of the walI (interior surface of the warm side plywood) exposed to the warm side guardroom,
7. Guardroom the average of three thermocouples located through the height of the guardroom-
As outlined in Chapter Five, the temperature readings presented in the following tables for the Warm. Mid and Cold locations represents the average of two thermocouple readings located in the middle third of the wall for each of the above noted locations- No Warm Side Insulation
Test Conditions:
a) Cold Side Guardroom Temperature -lO°C b) 89mm DBZcavity c) No warm side insulation
1 Test: Static Condition 1 Distance Temperatures CC) 1 (mm) Warm Mid Cold Average Warm Side Wall Surface Guardroom 345 14-8 13.2 11.7 13.2 16-5 800 14.3 12.1 11.0 t 2.4 16.6 17.9 1257 13.8 11-1 10.3 11.6 16.5 -10.1 Average Cavi ty Temperature: 13.9"C
Test: 0.01 m'/min flow; DBZ inlet 8.4Oc Distance Temperatures (OC) (mm) Warm Mid Cold Average Warm Side Wall Surface Guardroom 345 14.3 12.1 11.0 12.4 16-6 800 14.2 11.7 10-7 12.1 16.5 17.8 1257 13.8 11.0 10-2 11.5 16.5 -9.9 Test: 0.0 1m'/min flow; DBZ inlet 11.5"C Distance . Temperatures ("C) (mm) Wm Mid Cold Average Warm Side Wall Surface 345 14.7 12-9 11.5 13.0 16.8 800 14.3 12-0 10.9 12.3 16.6 1 7.9 1257 13.8 11.1 10.3 11.5 16.5 - 10.0 Test: 0.04m5/min flow; DBZ inlet 66°C Temperatures CC) Guardroom - Warm j Mid 1 Cold 1 Average-, 1 Wam Side Wall Surface 14.1 11.3 10.6 11.8 i 6-6 14.5 11.4 10.8 12.0 16.7 18.1 14.3 11.2 10.7 11.9 16.7 -9.9 Im3/min flow; DBZ inlet 163°C
Distance Temperatures CC)- - Warm Mid Coid 1 Average Warm Side Wall Surface Guardroom 15.8 14-9 13-1 1 14.7 17-4 800 1257 Test: O.( 4m5/min flow: DBZ inlet 21 .l°C Distance Temperatures ("C) Warm Mid Cold Average Wann Side Wall Surface Guardroom 16.5 16.3 14.1 15.8 17.8 a 1 15.6 14.1 12-3 14.0 17.3 17.9 14.8 12.8 11.5 13.0 17.1 -9.9
Test: 0.1 m'/min flow; DBZ inlet 6.6"C Distance Temperatures (OC) (mm) ' Warm Mid - Cold Average Warm Side Wall Surface Guardroom 345 13.6 10-3 9.9 11.0 16.5 800 13.7 10.4 10.0 11.1 16.7 18.2 1257 13.5 10.2 9.8 10.9 16.6 -9.8 Test: O. 1m'/min flow; DBZ inlet 16.2"C Distance Temperatures CC) (mm) ' Warm Mid Cold Average Wam Side Wall Surface Guardroom 345 16.0 15.5 13.4 16.1 17.4 800 15.6 14.4 12.5 14.2 17.3 1 7-9 1257 15.0 13.4 11.9 1 13.4 16.7 -9.8 Test: O. 1m'/min flow; DBZ inlet 20.9"C Distance Temperatures CC) (mm) Warm Mid Cold - Average Warm Side Wall Surface Guardroom 345 17.6 18.7 15-6 17.7 18.1 800 16.3 16.0 13.6 15.5 17.5 17-8 1257 15.3 14.4 12.5 14.2 16.8 -9.7 No Warm Side Insulation
Test Conditions:
a) Cold Side Guardroom Temperature -20°C b) 89mm DBZ cavity c) No wann side insulation
1 Test: Static Condition Distance Temperatures ("C) (mm) Warm Mid Cold Average Warm Side Wall Surface Guardroorn 345 14.3 12.1 10.2 12.2 16.8 800 14.2 10.9 9 -6 11.4 17.0 18.2 1257 13.4 9-6 8.6 10.3 16-9 -19.6 Average Cavity Temperature: llJ°C
Test: 0.01 m'/min flow; DBZ inlet 6.9"C Distance Temperatures (OC) (mm) Warm Mid Cold Average Warm Side Wall Surface Guardroom 345 13.7 11.0 9.5 11.3 16.8 800 13.9 10.5 9.3 11.1 1 7-0 18.2 1257 13.2 9.5 9 -4 10.2 16.9 -19.6 Test: 0.0 1 m5/min flow; DBZ inlet 1lh°C Distance Temperatures CC)
(mm) Warm Mid Cold Average ' ' Wann Side Wall Surface Guardroom 345 14.3 12.2 10.2 12.2 16.7 800 14.2 11.0 9.6 11.5 16.9 18.1 1257 13.3 9.8 8 -6 10.4 16.7 -18.9 Test: O.Olm"/min flow; DBZ inlet 6.6T 1 / Distance Temperatures CC) 1 (mm) ' Warm Mid Cold Average Warm Side Wall Surface Guardroom I 345 13.5 10.4 9.2 10.9 16.5 1 800 13.8 10.3 9.2 10.9 16.9 18.2 1257 13.4 9.8 8-7 10.4 16-9 -1 8.8 I Test: 0.04rn3/min flow: DBZ inlet 16.2"c Distance Temperatures CC) (mm) Warm Mid Cold Average Warm Side Wall Surface Guardroom 345 15.2 14.0 11.5 13.7 17-2 800 14.6 12-3 10.2 1 12.4 17.1 18.1 L 1 1 L . 1257 1 13.7 1 10.8 1 9.3 1 11.2 1 16.9 1 -19.0 m Test: 0.04mJ/rninflow; DBZ inlet 20.'i°C Temperatures (OC) , Wann Mid Cotd Average Warm Side Wall Surface Guardrwm 15.7 15-0 12.4 14.5 17.5 I 14.8 12.8 10.5 12.7 17.1 18.0
1 Test: O. 1m'/min flow; DBZ inlet 5.S0C 1 Distance Temperatures (OC) (mm) Warm Mid Cold Average Warm Side Wall Surface Guardroom 345 13.1 9.5 8 -5 10.2 16.2 800 13.3 9-4 8.5 10.2 16.7 18.1 1257 13.1 9.1 8-3 9.9 16.8 -1 9-6 Test: O. 1m''/min flow; DBZ inlet 16.0°C Distance Temperatures (OC) (mm) Warm Mid Cold Average Warm Side Wall Surface Guardroom 345 15.7 15.0 12.1 14.5 1 7.4 800 15.2 13.5 11.0 13.3 !7.4 18.2 1257 14.5 12.2 10.2 123 17.3 -1 9.6 Test: O. 1 m'/min flow; DBZ inlet 203°C
Distance Temperatures (OC) (mm) Warm Mid Cold Average Warm Side Wall Surface Guardroom 345 17.1 18.0 14.2 16.8 18-1 800 15.9 15.2 12.2 14.6 17.5 18.1 1257 14.9 13-3 11.0 13.1 17.3 -19.1 No Warm Side Insulation
Test Conditions:
a) Cold Side Guardroom Temperature -20°C b) 45mm DBZ cavity c) No warrn side insulation
1 Test: Static Condition 1 Distance Temperatures CC) (mm) Warm Mid Cold Average Wann Side Wall Surface Guardroom 345 13.7 11.4 9.7 11.6 16.4 800 13.1 10.4 8.8 10.7 16.0 18.0 1257 12.8 9.5 8.4 10.1 16.0 - 19-8 Average Cavity Temperature: 10.8"C
1 Test: O.Olm"/min flow; DBZ inlet 5.S0c Distance Temperatures (OC) (mm) ' Warm Mid Cold Average Warm Side Wall Surface Guardroom 345 13.3 10-5 9-2 10.9 16.2 800 12.9 10.1 8 -6 10.4 15.8 L 7.9 1257 12-5 10.3 8 -3 10.4 15-9 -20- 1 l Test: 0.01m3/min flow; DBZ inlet 10.9"c Distance Temperatures CC) (mm) Warrn Mid Cold Average WmSide Wall Surface Guardroom 345 13.8 11-4 9.8 11.6 16.4 800 13.2 10.5 8 -9 10.8 15.9 17.9 1257 12.6 9.5 8 -5 10.0 16-0 -19.8 Test: 0.04m3/min flow; DBZ inlet 63°C Distance Temperatures (OC) (mm) Warm Mid Cold Average Warm Side Wall Surface Guardroom 345 13.2 10.4 9-2 10.8 16.2 800 12.9 i O. 1 8.6 10.4 13.9 18-0 1257 12.8 9-7 8.6 10.2 15-9 - 19-4 Test: 0.04m?min flow; DBZ inlet 16.3OC Distance Temperatures CC) (mm) ' Wann Mid Cold Average Warm Side Wall Surface Guardroom 345 14.8 13-7 11.3 13.4 17-0 800 13.7 11-6 9.4 11.6 16.2 e 17.8 1257 13.1 10.4 9.1 10.8 16-0 - 19.6 Test: 0.04m3/min flow; DBZ inlet 20.S°C Distance Temperatures (OC) (mm) ' Warm Mid Cold Average Warm Side Wall Surface Guardroorn 345 15.6 15.4 12-5 14.7 17.5 800 14.0 12-3 9-9 12.1 16.4 17.9 1257 13.3 10-6 9.3 11.0 16.2 - 19-3 l Test: 0.1m3/min flow; DBZ inlet 6.0°C Distance Temperatures (OC) (mm) ' Warm Mid Cold Average Watm Side Wall Surface Guardroom 345 12.7 9-8 8.6 10.2 16-1 800 12.8 9-6 8.2 10.1 16.0 18.0 1257 12-7 9-3 8 -3 9.9 16.0 -19.8 Test: O. l m'/min flow; DE2 inlet 15.S°C Distance Temperatures (OC) (mm) Wm Mid Cold Average Warm Side Wall Surface Guardroorn 345 15.5 14.8 12.4 14.4 17.3 800 14.6 13.3 10-6 13.0 16.7 . 18.0 1257 14.0 12.0 10-2 12.1 16-4 - 19.5 Test: O. l m'/min flow; DBZ inlet 20S°C - - Distance Temperatures (OC) (mm) ' Warm Mid Cold Average WmSide Wall Surface Guardroom 345 17.2 17.8 14.8 16.9 18.2 800 15.5 15.3 12.4 14.6 17.1 18.0 1257 14.6 13.1 10.8 12.9 1 16.6 -20.0 RSI 0.79 Warm Side Insulation
Test Conditions:
a) Cold Side Guardroom Temperature -lO°C 6) 89mm DBZ cavity C) RSI 0.79 warm side insulation
Test: Static Condition Distance Temperatures (OC) I (mm) Warm Mid Cold Average WmSide Wall Surface Guardroom 345 7 -4 6.7 5.4 6.6 17-1 800 6.8 5.7 4.7 5.7 17.3 17-8 1257 6.6 5.3 4.5 5.4 17.2 -9-8 Average Cavity Temperature: 5.9OC
h Test: 0.01 m'/min flow; DBZ inlet 54°C Distance Temperatures (OC) (mm) Warm Mid Cold Average Wam Side Wall Surface Guardroom ' 345 7.2 6.5 5 -2 5.9 17.0 4 800 6.8 5.7 4-7 5.2 17.2 17.8 1257 6.5 5 -2 4-3 4.8 17-4 -9.9 Test: 0.04ms/min flow; DBZ inlet 57°C Distance Temperatures CC) (mm) Warm Mid Cold Average Warrn Side Wall Surface Guardroom 345 6.9 6-1 4-9 6.0 17.1 800 6.4 5 -4 4-3 5.4 17.3 17.9 1257 6.0 4-8 3 -9 4.9 1 17-4 -9-8 Test: 0.04rn'hnin flow; DBZ inlet 15.0°C Distance Temperatures CC) 1 (mm) Warm Mid Cold Average Warm Side Wall Surface Guardroorn 345 11.6 11.7 9.7 11.2 17.4 800 8 -5 8.0 6.5 7.8 17-3 17.8 1257 7.2 6.3 5.1 6.2 173 - 10.0
Test: 0.1 mJ/min flow; DBZ inlet 43°C Distance Temperatures eC) (mm) ' Warm 1 Mid Cold Average Warm Side Wall Surface Guardroom 345 6.3 5.3 4.3 5.3 17.1 800 6.2 5.1 4.1 5. 1 17.5 18.0 1257 6.1 4-8 3 -9 4.9 17-5 -9-9 Test: O. 1 m'/min flow; DBZ inlet 152°C Distance Temperatures (OC) (mm) Warm Mid Cold Average Warm Side Wall Surface Guardroom 345 13.3 13.9 11.5 13.2 17.5 800 11.4 11.8 9.5 11.1 17.6 17.9 1257 9.9 9.8 8.0 9.4 17.6 -10.0 RSI 0.79 Warm Side InsuIation
Test Conditions:
a) Cold Side Guardroom Temperature -20°C b) 89mm DBZ cavity C) RSI 0.79 warm side insulation
Test: Static Condition r I Distance Temperatures (OC) I ------(mm) Warm Mid Cold Average Warm Side Wall Surface Guardroom 345 3 -8 2-8 1 .O 2.6 16-9 1 800 2.8 1.5 0.0 1.S 17.1 18.0 1257 2.4 0.8 -0.4 0.9 16-8 -19.8 J 9 Average Cavity Temperature: 1.7OC
Test: 0.01m3/min flow; DBZ inlet 45°C Distance Temperatures CC) (mm) Warm Mid Cold Average Wami Side Wall Surface Guardroom 345 -8 2.9 1.1 2.7 3 16.9 - 800 2.7 1 -5 -0.2 1.4 17.1 18-0 1257 2.1 0-5 -0.7 0.6 16.7 - 19.8 1 Test: 0.04mJ/min flow: DBZ inlet 7S°C Distance Temperatures ("C) (mm) Warm Mid Cold Average Warm Side Wall Surface Guardroom 345 5 -6 5.2 3.1 4.8 17.1 800 3 -7 2.8 1.O 2.6 16.9 18.0 1257 2-9 1-6 O. 1 1.6 16.8 - 19.7 Test: 0.04m'lmin flow; DBZ inlet 16.7"C - Distance Temperatures (OC) (mm) ' Warm Mid Cold Average Warm Side Wall Surface Guardroom 345 10.4 10.6 8 .O 9.9 17.4 800 5.6 5.0 3 .O 4.7 17-1 18.0 1257 3 -9 2.8 1.1 2.7 16.8 - 19.3
b Test: 0.1 m'/min flow; DBZ inlet 6S°C Distance Temperatures CC) (mm) Warm Mid Cold 1 Average Warm Side Wall Surface Guardroom 345 6.6 6 -2 4.1 5.8 17.3 800 5.5 4.9 2.8 4.5 17.6 1 18.2 1257 4.8 3 -8 2.0 3.6 17-6 -19.6 Test: O. I m5/min flow; DBZ inlet 16.1°C Distance Temperatures (OC) (mm) ' Warm Mid - Cold Average Warm Side Wall Surface - Guardroom 345 13.1 14.2 10.7 13.1 17.7 RSI 0-79 Warm Side Insutation
Test Conditions:
a) Cold Side Guardroom Temperature -20°C b) 45mm DBZ cavity c) RSI 0.79 warm side insulation
Test: Static Condition Distance Temperatures (OC) (mm) Warm Mid Cold Average Warm Side Wall Surface Guardroorn 345 3.5 2.5 0.8 2.3 17.1 800 2.3 1 .O -0.5 1.0 16-5 17.8 1257 1.9 0.5 -0.7 0.6 1 16.1 -19.8 7 Average Cavity Temperature: 1.Soc
( Test: 0.01 rn3/rnin flow; DBZ inlet 4.9"C 1 Distance Temperatures CC) . (mm) Warm Mid Cold Average Warm Side Wall Surface - Guardroom 345 3.7 2-8 1 .O 2.6 17.8 800 2.2 1.O -0.6 0.9 16.8 17.9 1257 1.7 6.2 -0 -9 0.3 16.5 19.1 1 Test: 0.04mJ/min flow: DBZ inlet 6.S°C 1 Distance 1 Temperatures (OC). . (mm) Warm Mid Cold Average Wami Side Wall Surface Guardroom 345 5-7 5.1 3 .O 4.7 17-8 800 3-7 2-9 0.8 2.6 17-0 17.9 1257 2.6 1 -3 0-0 1.3 16.7 -19.7 Test: 0.04m'/rnin flow; DBZ inlet 16.t°C Distance -1-emperatures("C) (mm) Wm Mid Cold Average Warm Side Wall Surface Guardroom 345 1 OS 11.1 8.3 10.3 17.7
Test: 0.1 m'/min flow; DBZ inlet 6.0°C Distance Temperatures CC) (mm) Warm Mid Cold Average Warm Side Wall Surface Guardroom 345 6.1 5.7 3 -8 5.3 17.6 800 5.1 4.6 2-4 4.2 17.2 17.9 1257 4.4 3.4 2.7 3.2 17-1 -1 9-4 Test: 0.1 m'/min flow; DBZ inlet 15.6"C Distance Temperatures (OC) (mm) Warm - Mid Cold Average Warm Side Wall Surface Guardroom 345 12.8 13-6 10.8 12.7 17.8 800 10.2 10.9 7.6 9.9 17.5 17.9 1257 8 -2 8.1 5.7 7.5 17.3 - 19.4 Induced Buoyaacy Action Test #1
Test Conditions:
a) Cold Side Guardroom Temperature -lO°C b) Warm Side Guard Room Temperature c) 45mm DBZ cavity d) RSI 0.79 warrn side insulation e) Warm side guardroom +25OC
Test: 0.04mJ/min flow; DBZ inlet 2.S0c I 1 Distance Temperatures (OC) (mm) ' Wam Mid Cold Average Warm Side Wall Surface Guardroorn 345 8.1 6.5 5 -7 6.6 23 -5 800 7.9 6.3 5.4 6.5 23 -7 24.9 1257 8.0 6.2 1 5.5 6.4 23 -6 -10.1
Theoretical Steady-State Static Cavity Temperature
Thermal Resistance of Wall Components:
PIywood 9.5mm 0.083 .x2 (mA2K)/W Static Air Cavity 0.18 (mA2 K)/W Insulating Board 0.79 x2 (mA2 K)/W Air Films (ignore)
Total Thermal Resistance of Wall : 1-926(mA2 K)/W
Average Static Cavity Temperature : 24.9- (0.79+0.083+0.18/2)/1.926 * (24.9+10.1) = 7.4 OC lnduced Buoyancy Action Test #2
Test Conditions: a) Cold S ide Guardroom Temperature -lO°C b) Warm Side Guard Room Temperature c) 45mm DBZ cavity d) No warm side insulation e) Wmside guardroom +2S°C
Test: 0.04m3/min flow; DBZ inlet 15.1°c Distance Temperatures CC) (mm) Warm Mid Cold Average Warm Side Wall Surface Guardroom 345 20.4 18.0 16.8 183 24.0 - 800 20.2 17.6 16.4 18.0 24.1 24.9 1257 20.1 17-5 16.4 18.0 1 24.2 -9.9
Theoretical Steady-State Static Cavity Temperature
Thermal Resistance of Wail Components:
Ply~v~od9.5mm 0.083 x2 (mA2 K)/W S tat ic Air Cavity 0-1 8 (mA2 K)/W Insulating Board 0-79(mA2 K)/W Air Films (ignore)
Total Thermal Resistance of Wall : 1.136 (mA2 K)/W
Average Static Cavity Temperature : 24.9- (O.O83+O. l8/2)/l. 136 * (24.9+9.9) = 19.6 OC Code for HP Basic Program 'DBZ" Computer Code for HP Basic Program "DBZ*
10 ! Program 'DBZ'. USED TO READ TC'S AND CONTROL THE TEMP. 20 ! OF TWO CUARDROOMS AND THE DBZ AIR TEMPERATURE CONTROL BOX 30 ! READINGS ARE SENT DIRECTLY TO THE CBM 40 ! 50 ! ARRAY USED TO STORE TEMPERATURES FOR TEMPERATURE CONTROL 60 DIMContr(l:13) 70 ! 80 ! ARRAY USSED TO STORE 3 iNLET TEMPERTURES TO CALCULATE THE AVERAGE 90 ! 100 DIM Avg(l:4) 110 ! 120 ! ARRAY USED TO STORE 15 MIN DATA FOR RECORDMG PURPOSES 130 ! ONE DAY WlTH READiNGS EVERY 15 MINUTES 140 ! 150 DIM T(l:60,1:96) 160 ! 170 ! ARRAY USED TO STORE 15 MIN READINGS OF THE INLET. OUTLET AND 1 80 ! MIDHEIGHT X-SECTION THERMOCOUPLES 190 ! 200 DIM Ciplot( 1 :34.1:96) 210 ! 220 REAL XminZ,Ymin2,Xma'cZ,Yma3,Xinc2,Yinc2 230 lNTEGER Vxmin2.Vymin2,Vxrnax2TVymax2 240 ! 250 ! THE FOLLOWING DATA IS 1NFORMATION REQUIRED FOR PLOTTING 260 DATA 0.96.-2520,8,5.50.133,5,100 270 READ Xmin2,Xm~~2,Ymin2,Ymax2,Xinc2.Yinc2,Vxmin2,Vxmau2.Vymin2.Vymau2 250 ! 290 ! Set up serial interface 300 ! 3 10 CONTROL 9.0: 1 ! Reset serial interface 320 CONTROL 9,3;4800 ! Transmir speed 330 CONTROL 9,4;3 ! 8 bits, no parity, 1 stop bit (SN I ) 340 ASSIGN @Serial T09 350 ! 360 MASS STORAGE IS ":HP8290X,700,0" 370 ! 380 ! CLEAR GRAPHICS FROM SCREEN 390 ! 400 GCLEAR 410 ! 420 ! THE FOLLOWING INFORMATION MUST BE SUPPLIED BY USER 430 ! 440 INPUT "DESIRED DBZ AIR TEMPERATURE:",Dbzair 450 OUTPUT @Serial;CHRS(34);"DBZ air temperature = ";Dbzair,CHR$(34) 460 INPUT "DESIRED WARM GUARD ROOM TEMPERATURE:".Warmt 470 OUTPUT @Serial;CHR$(34);"Warm guard room temperature = ";Warmt;CHE'6(34) 480 INPUT "DESIRED COLD GUARD ROOM TEMP.",Coldt 490 OUTPUT @Serial;CHR$(34);'*Coid guard room temperature = ";Coldt;CHRS(34) 500 INPUT "DESIRED PAUSE BETWEEN TEMP. CONTROL IN SECU,N 5 10 OUTPUT @Serial;CHR$(34);"Pause in seconds = ";N;CHRS(34) INPUT "WHAT IS THE FLOW RATE OF THlS TRIAL:",Qf OUTPUT @Serial;CHR.S(34);"Fiow rate (mA3/min) = ";Qf;CHRS(34) OUTFUT @Serial;"" ! OUTPUT @Seriat;CH=(34);"J";CHRS(34);","; OUTPUT @Serial:CHR$(34);"Inlet";CHR$(34);"."; OUTPUT @Serial;CHRâ(34);"DBZBOXw;CHR$(33);",'q; ! FOR I=l TO 52 OUTPUT @Serial:CHRS(34); l;CHR%(34):","; NEXT 1 ! ! SURFACE TEMPERATURES ! OUTPUT @SeriaI;CHRS(34);" WS 1 ";CHFS(34);","; OUTPUT @Serial;CHRIS(34);qqWS2'*;CHU(34);","; OUTPUT @Serial;CH~(34);'*WS3'';CHRS(34);","; OUTPUT @Serial;CHR$(34);"CS 1 ":CHRS(34);","; OUTPUT @Serial;CHRS(34);"CSS";CHRS(34);"."; OUTPUT @Serial;CHRS(34);"CS3'q:CHRS(34);","; OUTPUT @Serial;CHRS(34);"WGRD'*:CHR$(34);","; OUTPUT @Serial;CHR$(34):"CGRD";CU U(34) OUTPUT @Serial;"" ! ! SUBROUTINE USED TO DRAW AXES OF GRAPH CALL Dra~vborder(Xmin2.Xmax2,Ymin2,Ymax2,Xinc2.YincZ,Vxmin2,Vxma,u2,Vymin.V,I ) 1 ! RESET ABSOLUTE TtME OF COMPUTER - JULIAN TlME ! SET TIMEDATE 2.086629 12E+ Il Ntirne=TIMEDATE ! !******* SET UP INITIAL READING ******* ! CLEAR 709 J=l ! J IS USED AS A COUNTER FOR THE WALL TC READINGS OUTPUT @Seriai:J;",": PRINT ! ! INLET DBZ AIR TEMPERATURE ! FOR Ii=l TO 3 OUTPUT 709:"AFI 4OAL 142" OUTPUT 709;"AS" ENTER 709:V LET Ternp=MCon(V) Contr(Ii)=Ternp NEXT Ii 1 000 Contr(4)=(Contr( 1 )+Contr(L)+Contr(3))/3 10 10 T( 1. l )=Contr(4) 1020 OUTPUT @Serial USING "3D.D,AT#";T(I,1 ),"," IO30 ! 1040 ! OUTLET DBZBOX AIR TEMPERATURE CONTROL BOX IO50 ! 1 O60 OUTPUT 709;"AF 18 1AL 18 1 " 1070 OUTPUT 709;"AS" IO80 ENTER 709;V 1090 LET Temp=FNCon(V) 1 100 T(2.1 )=Temp I 1 10 OUTPUT @Serial USING "3D.D&Y;T(2,1),"." 1120 ! 1 130 ! MEASURE INITIAL TEMP OF 52 TC'S IN WALL,SURFACE TEMPERATURES 1 140 ! NOTE: TC'S 199 & 209 ON PANEL IN WARM ROOM DO NOT WORK, 1 150 ! SO THEY HAD TO BE BY-PASSED. 1160 ! 1 170 ! UPPER MDDLE T.C. IN WALL 1180 FOR Ii=3 TO 18 1 190 OUTPUT 709;"AF 1 O3AL 1 18" 1200 OUTPUT 709;"AS" 12 1 0 ENTER 709;V 1220 LET Tcmp=FNCon(V) 1230 T(ii,I)=Temp t XO OUTPUT @Serial USING "3D.D,A,#";T(Ii,~."." 1250 NEXT Ii 1260 ! 1270 ! ORIGINAL 34 T.C. 1280 ! 1290 FOR Ii=19 TO 35 1300 OUTPUT 709:"AFl82AL 198" 13 10 OUTPUT 709;"AS" 1320 ENTER 709;V 1330 LETTemp=FNCon(V) 1340 T!Ii. I )=Temp 1350 OUTPUT @Serial USING "3 D.D.A,#":T(I i..f),"." 1360 NEXT Ii 1370 ! 1380 FOR Ii=36 TO 44 1390 OUTPUT 709;"AF200AL208" 1400 OUTPUT 709;"AS" 14 10 ENTER 709;V 1430 LET Temp=MCon(V) 3430 T(Ii. 1 )=Temp 1440 OUTPUT @Serial USlNG "3 D.D,A,#";T(Ii,J),"," 1450 NEXT li 1460 ! 1470 FOR li-45 TO 54 1480 OUTPUT 709;"AQ IOAL219" 1490 OUTPUT 709;"ASW 1500 ENTER 709;V 15 10 LET Temp=FNCon(V) 1 520 T(Ii, I )=Temp 1 530 OUTPUT @Serial USING "3 D.D,A,#";T(l i,J),"." 1540 NEXT li 1550 ! 1560 ! SURFACE TEMPERATURES 1570 ! 1 580 FOR I i=55 TO 60 1 590 OUTPUT 709;"AF 1 Z6AL 13 1 " 1 600 OUTPUT 709;"ASW 16 10 ENTER 709:V 1620 LET Ternp=FNCon(V) 1630 T(1i. 1 )=Ternp 1640 IF Ii<60 THEN 1650 OUTPUT @Serial USMG "3D.DTA,#";T(Ii.J),"," 1660 ELSE 1670 OUTPUT @Serial USMG "3D.D";T(IiJ) 1680 END IF 1690 NEXT Ii 1700 ! 1 7 10 ! SET UP INITIAL PLOTTiNG POINTS 1720 ! PLOT INLET, EXHAUST, MEIDHEIGHT MID-CROSS SECTION 1730 ! INLET AND EXHAUST AIR TEMP 1740 ! 1750 FORP=t T02 f 760 Gplor(P, 1)=T(P, 1; 1 770 NEXT P 1780 ! 1790 ! MIDHEIGHT MIDDLE OF CROSS SECTION TEMP 1800 FOR P=I!?TO22 1 8 10 Gplot(P, 1 )=T(P, 1) 1820 NEXT P 1830 ! 1840 ! TEMPERATURE CONTROL OF TWO GUARD ROOMS AND DBZ AIR TEMP CONTROL BOX 1850 ! WALL THERMOCOUPLE READINGS EVERY 15 MWUTES 1860 ! 1870 FORZ=I TO I.E+IO 1880 ! 1890 ! TEMPERATURE CONTROL 1900 ! I9 10 IF TIMEDATE-=2.086629984E+11THEN !(24 HRS) 1920 ! 1930 ! DBZ AIR TEMP CONTROL BOX 1940 ! 1950 FOR Ii= I TO 3 1 960 OUTPUT ïO9;"AF I4OAL 143" 1970 OUTPUT 709;"ASW 1980 ENTER 709;V 1 990 LET Temp=FNCon(V) 2000 Contr(1 i)=Temp 20 1 O PRlNT "Dbz INLET air temperature is:",Contr(Ii) 2020 NEXT Ii 2030 X I =(Contr( 1 )+Contr(2)+Conu(3))/3 2040 ! 2050 ! TURN HEATER ON OR OFF 2060 IF X l ~(Dbzair--5)THEN 2070 OUTPUT 709;"DC 1,3" 2080 END IF 2090 IF X I >(Dbzair+ 3)THEN 2 100 OUTPUT 709;"D01.3" 2110 ENDIF 2120 PRINT 2130 !*********PRlNTDBZCONTROLBOXTEMPTOSCREEN 3140 OUTPUT 709;"AF181AL18t" 2 150 OUTPUT 709;"AS" 2 160 ENTER 709;V LET Temp=MCon(V) PRINT "DbzBOX air temperature isn,Temp PRINT ! ! WARM GUARD ROOM TEMPERATURE CONTROL ! FOR li=5 TO 7 OUTPUT 709;"AFI 20AL 122" OUTPUT 709;"ASN ENTER 709;V LET Temp=FNCon(V) Contr(1 i)=Tem p PRlNT "WARM GUARD room temperature is:",Contr(Ii) NEXT li Conu(8)=(Contr(S)+Contr(6)+Contr(7))/3 XZ=Contr(S) ! TURN HEATER ON OR OFF IF X2<(Warmt-S) THEN OUTPUT 709;"DC 1.1 " END IF IF XZ>(Warmt+.S) THEN OUTPUT 709;"DO 1.1 " END IF PRINT ! ! COLD GUARD ROOM TEMPERATURE CONTROL ! FOR Ii=9TO 11 OUTPUT 709;"AF l23AL 125" OUTPUT 709;"ASn ENTER 709;V LET Temp=FNCon(V) Contr(1 i)=Temp PRINT "COLDGUARD room temperature is ",Contr(Ii) NEXT Ii PRINT PRINT Contr( 12)=(Contr(9)+Contr( 1 O)tContr( 1 1 ))/3 X3 =Con tr( 12) ! TURN HEATER ON OR OFF 1F X3<(Coldt--5) THEN OUTPUT 709;"DC 1.2" END IF IF X3>(Coldt+.S) THEN OUTPUT 70Ç;"DO 1 .Y END IF ELSE OUTPUT 709;"ûOI -3" OUTPUT 709;"DO 1, 1 " OUTPUT 709;"DO 1,2" PRMT "TIMEDATE IS :",TIMEDATE ASStGN @Serial TO STOP ! END PROGRAM END IF I ! SECOND MAIN LOOP ! WALL THERMOCOUPLE READINGS ! Diff=TIMEDATE-Ntime IF Diff>=900 THEN !15 MINUTE READINGS J=J+ 1 OUTPUT @SeriaI$;","; Ntime=TIMEDATE ! INLET TEMPERATURE FOR Pi= I TO 3 OUTPUT 709;"AF l4OAL 142" OUTPUT 709;"AS" ENTER 709;V LET Ternp=FNCon(V) Avg( Pi)=Tem p NEXT Pi Avg(4)=(Avg( 1 )+Avg(2)+Avg(3))/3 T( I ,J)=Avg(4) OUTPUT @Serial USING "3D.D,A,nt":T(IJ),"." ! ! DBZ AIR TEMPERTURE CONTROL BOX ! OUTPUT 709rWAF18 1 AL 18 1 " OUTPUT 709;"AS" ENTER 709;V LET Temp=FNCon(V) T(Z,J)=Ternp OUTPUT @Serial USiNG "3D.D.A.#";T(2.i),"." ! !UPPER MIDDLE TC ! FOR Ii=3 TO 18 OUTPUT 709:"AF103ALI 18" OUTPUT 709:"AS" ENTER 709;V LET Temp=FNCon(V) T(t iJ)=Temp OUTPUT @Serial USMG "3 D.D,A,#";T(Ii,J),"." NEXT li ! ! ORIGINAL 36 WALL T.C. ! FOR Ii=19 TO 35 OUTPUT 709;"AF 18SAL 198" OUTPUT 709:"ASm ENTER 709;V LET Temp=FNCon(V) T(1 i,J)=Temp OUTPUT @Serial USiNG "3D.D,A,#";T(li,J),"," NEXT li ! FOR Ii=36 TO 44 OUTPUT 709;"AFZOOAL208" OUTPUT 709;"AS" 3260 ENTER 709;V LET Tem p=FNCon(V) T( 1i,J)=Tern p OUTPUT @Serial USING "3 D.D,A.#";T(I iJ),"," NEXT Ii ! FOR Ii45 TO 54 OUTPUT iO9;"AF2 10AL2 19" OUTPUT 709:"ASW ENTER 709;V LET Temp=FNCon(V) T(1i,J)=Tem p OUTPUT @Serial USING "3 D.D,AIRr";T(Ii,J),n,n NEXT Ii ! ! SURFACE TEMPERATURES ! FOR 1i=55 TO 60 OUTPUT ?O9;"AF 1 26AL 13 I " OUTPUT 709;"AS" ENTER 709;V LET Tem p=FNCon(V) T(Ii,J)=Ternp OUTPUT @Serial USING "3 D,D.A.RrW:T(IiJ)."." NEXT Ii ! ! GUARD ROOM TEMPERATURES ! OUTPUT @Serial USlNG "3D.D.A,#":XS."." OUTPUT @Serial USING "3D.D";X3 ! ! PLOT (@ I 5 MIN) INLET, EXHAUST AND MIDHEIGHT MID X-SECTION TC'S ! VIEWPORT Vxmin2.Vxmax2,Vym in2,Vymax2 WINDO W XminZ.Xmax2.Ymin2,Ymax2 ! ! INLET AND DBZ AIR TEMP CONTROL BOX PLOT ! FOR P=l TO 2 Gplot(P,J)=T(P,J) PLOT J- 1 ,Gplot(P,J- l),-2 PLOT J.Gplot(P,J),- l NEXT P ! ! **** PLOT WARM AND COLD GUARD ROOMS ALSO ******* ! GpIot(j.J)=X3 PLOT J- 1 ,Gplot(j,J- l ),-2 PLOT J,Gplot(j,J),- 1 Gplot(4,J)=X2 PLOT J- I .Gplot(4,J- l ),-2 PLOT JVGplot(4,J),-1 ! ! MIDHEIGHT MID X-SECTION ! 3810 FOR P=l9 T0 22 3820 Gplot(P.J)=T(P$) 3830 PLOT J- i ,Gplot(PJ- l ),-2 3840 PLOT J,Gplot(PJ),- 1 3850 NEXTP 3860 ! 3870 WAITN 3880 ELSE 3890 WAITN 3900 END IF 3910 NEXTZ 3920 END 3930 ! 3940 ! 3950 !***************VOLTAGE CONVERSION TO TEMPERATURE******* ****** 3960 DEF MCon(V) 3970 ! 3980 IF V
Xx=Xmin+Xinc 1=2 END IF 4890 FOR I=J TO Xdiv+I STEP Xskip LINE TYPE 4,10 MOVE Xx,Ymax PLOT Ax,Ymin,- 1 SELECT 1 CASE 1 LORG 3 CASE Xdiv+l LORG 9 CASE ELSE LORG 6 END SELECT LMETYPE 1 LABEL TFUMS(VALS(MT(Xx*Xround+.99999)/Xround)) Xx=X.u+Xincf Xskip NEXT I ! LDIR 90 Yskip= 1 IF NPAR> 1 O AND Ydiv>7 THEN Yskip=2 IF Ydiv>6 AND ABS(Yinc)>=lO THEN Yskip=2 [F Ydiv>S AND ABS(Yinc)>=lOO THEN Yskip=2 IF Ydiv>4 AND ABS(Yinc)>=1000 THEN Yskip=2 Yy=Ymin J= t IF Yskip=l THEN 5210 IF (Ymin=O) OR (Ymax=O) THEN 5210 IF (Ymax/Ymin>O) THEN 52 t O IF (Ydiv MOD 2=1) OR (ABS(Yrnau)=ABS(Ymin) AND ((YdivQ) MOD 2=1) AND Ydivo2) THEN Yy=Ymin+Yinc J=2 END IF FOR I=j TO Ydiv+l STEP Yskip LINE TYPE 4,l O MOVE Xmax.Yy PLOT Xm in.Yy.- 1 SELECT 1 CASE 1 LORG 1 CASE Ydiv+ I LORG 7 CASE ELSE LORG 4 END SELECT LINE TYPE 1 LABEL TRIM$(VAL$(~T(Yy*Yround+.99999)/Yround)) Yy=Yy+Y inc* Yskip NEXT 1 ! LDIR O LORG 5 CSIZE 3 LINE TYPE 1 5420 SUBEND