Under Floor Air Distribution for Better Indoor Air Quality

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Volume-5, Issue-3, June-2015 International Journal of Engineering and Management Research Page Number: 744-755

Shaik Gulam Abul Hasan1, Shaik Mohd Amoodi2, Ganoju Sravan Kumar3 1,2Assistant Professor, Mehanical Department, Vidya Jyothi Institute of Technology, C.B. Post, Aziz Nagar, INDIA 3Assistant Professor, Mehanical Department, MGIT, C.B. Post, Aziz Nagar, INDIA

ABSTRACT the main cycles are; vapour-compression, absorption, UAD systems are shown to offer potential for initial steam-jet or steam-ejector, and air. capital savings, which may be achieved by lowering slab-to- 1.2 Applications of refrigeration: slab heights, reducing cooling capacity requirements due to In commerce and manufacturing, there are many stratification, thermal inertia improvements, minimizing uses for refrigeration. Refrigeration is used to liquify gases ducting, and reducing construction schedules.UAD systems - oxygen, nitrogen, propane and methane, for example. In are also shown to provide significant energy efficiency advantages due to fan energy savings, extended free cooling compressed air purification, it is used to condense water and improved chiller COP, thereby reducing life-cycle vapor from compressed air to reduce its moisture content. building costs. Additionally, improvements in occupant In oil refineries, chemical plants, and petrochemical plants, thermal comfort and Indoor Air Quality (IAQ) are achieved. refrigeration is used to maintain certain processes at their Unlike displacement systems, UAD systems extend these high needed low temperatures (for example, levels of IAQ to applications with significant movement in alkylation of butenes and butane to produce a and/or heating. high octane gasoline component). Metal workers use In typical office environments, UAD systems are refrigeration to temper steel and cutlery. In transporting also able to provide more than three-to-five times the temperature-sensitive foodstuffs and other materials by maximum sensible cooling capacity of comparable displacement systems without subjecting occupants to trucks, trains, airplanes and sea-going vessels, refrigeration draughts or to an excessive vertical temperature gradient. is a necessity. They also improve air flow in the occupancy microclimate 1.3 Air-Conditioning: and provide the opportunity for localized control of air flow Air-conditioning is a process that simultaneously and direction, further enhancing individual thermal comfort. conditions air; distributes it combined with the outdoor air These advantages raise worker productivity and lower to the conditioned space; and at the same time controls and absenteeism rates. The ease with which UAD systems can be maintains the required space’s temperature, humidity, air rearranged to satisfy new office layouts improves flexibility, reducing reconfiguration costs. movement, air cleanliness, sound level, and pressure differential within predetermined limits for the health and Keywords---- UAD systems, Indoor Air Quality (IAQ), air comfort of the occupants, for product processing, or both. flow The acronym HVAC&R stands for heating, ventilating, air-conditioning, and refrigerating. The combination of these processes is equivalent to the functions performed by air-conditioning. 1.4 Air-conditioning applications: I. INTRODUCTION Air conditioning makes deep plan buildings feasible, for otherwise they would have to be built 1.1 Refrigeration: narrower or with light wells so that inner spaces received The term refrigeration refers to cooling an area or sufficient outdoor air via natural ventilation. Air substance below the environmental temperature, the conditioning also allows buildings to be taller, since wind process of removing heat. Mechanical refrigeration uses speed increases significantly with altitude making natural the evaporation of a liquid refrigerant to absorb heat. The ventilation impractical for very tall buildings. Comfort refrigerant goes through a cycle so that it can be reused,

744 Copyright © 2011-15. Vandana Publications. All Rights Reserved. www.ijemr.net ISSN (ONLINE): 2250-0758, ISSN (PRINT): 2394-6962 applications are quite different for various building types Cool conditioned air – typically between 63F and and may be categorized as 68F – is supplied at floor level through diffusers at very • Low-Rise Residential buildings, including single low velocity. The air is then heated by the internal loads of family houses, duplexes, and small apartment the space and rises to the ceiling where it returns back to buildings the central air handling unit. Potential advantages of an • High-Rise Residential buildings, such as tall under floor air distribution system compared to a dormitories and apartment blocks traditional ceiling-based system include improved thermal • Commercial buildings, which are built for comfort, improved air quality, and reduced energy commerce, including offices, malls, shopping consumption (CBE 2002). All of this sounds rather simple, centers, restaurants, etc.Institutional buildings, but many design issues can greatly influence system which includes government buildings, hospitals, performance and success of the application, for example: schools. the type of plenum used – pressurized or non-pressurized, 1.5 The Importance of Air Conditioning and open or partitioned; how interior and perimeter loads are to Refrigeration: be met; how humidity will be controlled; and diffuser The most common, and arguably most important, selection – passive or active. Once the design is complete, use for refrigeration is food preservation. It used to be that the entire system must be constructed, commissioned, and people had to go to a market every day and buy fresh then maintained to ensure that present and future system groceries before they perished. Early methods of food operation and occupant comfort are sustained.A preservation such as cold cellars and salting were Maintaining a high level of indoor air quality (IAQ) expensive, difficult to regulate, and didn’t maintain the become increasingly important to today’s business owners same quality as what we are used to today. After the and their employees, engineers are challenge to improve discovery of bacteria the importance of refrigeration HVAC Design. Design to provide comfort and better became clear. Low temperatures slow chemical and Indoor Air Quality with traditional air distribution system biological processes including bacterial growth which consumes high amounts of energy and there for, results in spoils food. Modern refrigeration provides an environment high operational cost the challenge HVAC engineers face too cold for harmful bacteria to flourish, keeping people is to provide comfort while reducing energy consumption healthy.With contemporary refrigeration units I can buy and the operating expenses that company it. In response to lunch meat on Sunday and have it last all week long. A new regulation and rising energy costs, the HVAC industry reliable method for keeping foods cold means I have to is changes at a rapid pace, providing today’s engineers shop less frequently. It also allows for foods to be frozen with new tools to meet this challenge. and eaten out of season. Even if I ran out of my frozen Under floor aid distribution (UAD) turns air fruits and vegetables, I could also buy out-of-season supply upside down, allowing a floor plenum to deliver edibles from a place where they are in-season. Foods can conditioned air to the space via floor grilles in the raised be refrigerated and transported across the country and floor system. The floor plenum typically consists of across the world. This means that I can now have a more pedestals and removable floor panels that can be rapidly diverse diet than what is grown in my area. Current reconfigured. Supply air is introduced through diffusers at refrigeration technology has changed our diets and floor level and is exhausted at the ceiling through return or lifestyles to be more diverse and healthy. relief grilles.Under floor air distribution systems introduce 2.Under Floor Air Distribution (UFAD): air at the floor level, with return grilles located near the ceiling. The space is divided into two zones, an occupied Under floor air distribution systems have been zone extending from the floor to head level, and an utilized since the 1950’s to serve spaces having high heat unoccupied zone extending from the top of the occupied loads, such as computer rooms and control centers, but zone to the ceiling. The systems are designed to condition they are still relatively uncommon in an office the lower occupied zone only temperature conditions in the environment. Most buildings are designed using a upper zone are allowed to float above normal comfort conventional overhead distribution system, which ranges. To avoid occupant discomfort, air is introduced generally supplies cold conditioned air (typically 550F) at into the space between 65°F and 68°F. In contrast, the ceiling and relies on complete mixing from floor to traditional overhead ventilation systems supply and return ceiling to maintain space temperature. In order to achieve air at the ceiling. The system produces a large single zone complete mixing, the conditioned air must be delivered of fully-mixed, room-temperature air. Using a liquid and through the diffusers at relatively high velocity. The beaker analogy, Figure 1 & Figure 2 is a simplified concept behind an under floor air distribution system is to illustration of the difference between an under floor system create a stratified condition from floor to ceiling, rather and a conventional fully-mixed system. than mixed, and rely on the natural buoyancy of the air to In the under floor system, cool liquid introduced remove heat and contaminants away from the occupants. from below flows through the occupied zone, picking up heat and contaminants and pushing them into the

745 Copyright © 2011-15. Vandana Publications. All Rights Reserved. www.ijemr.net ISSN (ONLINE): 2250-0758, ISSN (PRINT): 2394-6962 unoccupied zone above. In the fully-mixed system, cooler The spacing and location of these ducts are dependent on liquid delivered from above mixes with all the liquid to the air supply requirement and the plenum depth, with maintain a constant temperature throughout the beaker. shallow plenums and / or high air quantities requiring more This dilutes contaminants but does not effectively purge air supply duct outlets under the floor. UFAD diffusers are them. The figure 1 shows a beaker filled and emptied from specially designed grilles with a user adjustable damper to the top, much like an overhead mixed ventilation system. regulate flow. Sealing the under floor plenum is critical to optimizing the operation of a UFAD system. Air leaking through the floor tiles into the occupied zone is of minimal concern because it is leaking into the occupied space. Air leaking into the space between the walls, however, is wasted energy. All knockouts and holes in the drywall below the raised floor must be sealed during construction. The advantages of pressurized plenums include low first cost and easily changed layouts. This is the most commonly used plenum design. The figure shows a beaker filled with cool water 4.1.2 Neutral Plenums: from the bottom, with warm water exiting from the top. With the neutral plenum design, the same layout as the pressurized plenum may be used, but the pressure difference between the plenum and the room is kept as close as possible to zero. Floor diffusers either contain integral fans, are ducted from a central source, or both. In many cases, these closely resemble conventional ceiling supply systems.Advantages include the possibility of multiple small zones (as with multiple tenants) and insensitivity to construction details. Disadvantages include higher first costs due to ducting and/or fan connections under the floor, lower flexibility as the grilles are individually ducted, and potentially higher noise levels.This design is rarely used, but may be effective in III. ROOM AIR DISTRIBUTION tenant buildings where the utilities will be paid by the tenant. Characterizing how air is introduced to, flows 4.2 Plenum Details: through, and is removed from spaces is called room air Plenum heights typically range from 14” to 18”, distribution. Air distribution systems fall into three general occasionally going as low as 12”. The plenum height is categories distinguishable from one another by the usually determined by the height requirements of other temperature and velocity profiles they create in the equipment that will be located under the floor. The number occupied space. of inlets required to supply the plenum with sufficient air 1. Mixing (or dilution) to run the diffusers is dependent upon the plenum size and 2. Displacement. the number of diffusers, which in turn is determined by the 3. Hybrid under floor system. load of the space. As a general rule, the longest distance from the supply air outlet in the plenum and the farthest diffuser IV. DESIGN AND CALCULATIONS OF should not exceed 50-65 feet. Distances longer then this UNDER FLOOR AIR DISTRIBUTION are subject to thermal losses and the discharge temperature of the diffuser may be too high. 4.1 Plenum Design: If zone control is desired from the under floor The raised floor office can be supplied with plenum, the plenum can be partitioned into separate zones. conditioned air from below the floor in two ways The zones in the under floor plenum should correspond to pressurized plenum or neutral plenum. building zones having similar load requirements. However, 4.1.1 Pressurized Plenums: it isnot necessary to partition the under floor plenum into The pressurized plenum (the area between the zones and doing so can make future office layout changes slab and the raised floor) is essentially a large duct more difficult. If an office layout must be changed, the maintained at a constant pressure differential to the room partitioned plenum will need to be changed to match the above; typically between 0.05 and 0.10 in. pressure (w.g.). new layout. Because of the special heating and cooling This pressure is maintained through the supply of requirements of the perimeter of the building, it may be conditioned air from a number of supply duct terminations. necessary to create a perimeter zone in the under floor

746 Copyright © 2011-15. Vandana Publications. All Rights Reserved. www.ijemr.net ISSN (ONLINE): 2250-0758, ISSN (PRINT): 2394-6962 plenum to run a separate perimeter system. Typically only at the perimeter contradicts the concept of stratification in the perimeter is zoned from the core. a UFAD system. Not only does the long throw from the 4.3 Perimeter Systems: grille mix the air above the stratified layer into the The perimeter is typically the most difficult area occupied zone, wasting energy, but it also may roll up the of an under floor system to design. The perimeter is often glass and across the ceiling, where it drop into the handling much larger loads and require the most occupied zone causing discomfort for the occupants. equipment. In the past, the best way to handle the Although the concept of UFAD systems is to be modular, perimeter was to use fan powered terminals with reheat the function of handling perimeter loads is not modular. ducted to linear bar grilles. There are a couple challenges Those loads come with the building envelope, which is with this design concept. The throw of a linear bar grille always a line of some sort. The TAF-L Perimeter System ducted to the discharge of a fan powered terminal is very was designed to address all of these considerations. long, possible as long as 15-20 feet. Designing long throws

Fig no: 4.1 Typical under floor Plenum Configuration

4.4 Conference Rooms & Other Areas of Varying the heat from ceiling lights to be returned before it is able Load: to mix with the conditioned air in the occupied zone. There Much like the perimeter, conference rooms must will also be a small amount of “free cooling” due to the be handled separately to adjust for the varying load natural buoyancy of hot air. If the system must use 55oF conditions. The LHK fan powered terminal was designed supply air for humidity reasons, some of the return air can for this application. Like the PFC, the LHK fits within the be recirculated from the ceiling to the under floor plenum modular pedestal systems of the raised floor and is to raise the temperature of the air to 63oF to 68oF. available in various heights to fit under 12” through 18” Another option is to take the return air back to the raised floors. With the exception of its unique dimensions, air handling unit where it can be filtered and dehumidified the LHK is like any other series fan powered terminal. The before re-entering the under floor plenum. With this LHK has a supply inlet with a damper modulated by a option, you can more accurately control the air temperature controller and actuator. The LHK has an induced air inlet at the diffuser and you gain the cost benefits of the warmer which pulls air from the under floor plenum or from the supply air temperature. room depending on how the LHK is applied. 4.6 Humidity Issues: The LHK supply inlet would be open to the A potential problem with the higher supply plenum with the induced air inlet ducted to the room as the temperatures used in under floor supply systems is the return. The discharge would then be flex ducted to TAF- higher potential moisture content of the warmer supply air R’s in the room. used in these systems. The supply system must reduce 4.5 Return Air: relative humidifies to less than 60% to meet IAQ concerns, Due to the upward air flow, returns should be and this requires dew points less than 65oF. This implies located at the ceiling or on a high side wall. This allows either reheat or blending of air to achieve a 65oF supply,

55oF dew point condition.System designs utilizing testing shows that there is 100% mixing in the occupied condenser water reheat, run-around coils, face & bypass, zone under these conditions. and other strategies can be employed to solve these The stratification in this installation results in a potential design problems. Other possible solutions include supply - exhaust ΔT similar to the typical 18oF to 20oF ΔT the use of a separate system to dry outside air or the use of common in most conventional systems. desiccant dehumidification. Climate and building For example, with 64oF supply air in a 74oF room, operation are important considerations when designing a the room exhaust, at the ceiling, will probably be about UFAD system. In humid climates, it may be necessary to 82oF, for an 18oF ΔT. operate the HVAC system 24 hours a day to maintain This means that one diffuser can handle: acceptable humidity levels in the building. 18oF ΔT x 100 CFM x 1.08 = 1944 BTUH or 1944 BTUH 4.7 Sizing Jobs: ÷ 3.41 = 570 watts of internal load. The optimum design point for the TAF-R is 80 - Lights are typically 0.75 W/sq.ft, but with ceiling 100 CFM when a 10oF room / supply differential is used. stratification are probably not a part of the room load (but At this point, the noise is negligible and the pressure are seen by the air handler). If computers and printers required is less than 0.10”. Throw will be less than 6 ft., supply about 1W/sq.ft load and occupants add about 1.2 preserving the desired ceiling stratification layer. Our W/sq.ft, this translates to:

4.8 Design Guide To Under Floor Air Distribution:  Do not include excess safety factors; it will lead 4.8.1 Design Decisions: to over airing the zone spaces, resulting in many When beginning the design of a UFAD system occupant comfort complaints and loss of the certain key differences and concepts need to be stratification layer. remembered to avoid incorporating elements of traditional 4.8.2 Zoning Decisions: overhead mixing systems: Because of the under floor air supply plenum  Under floor systems work best when a aspects of a UFAD system, zoning decisions have a few stratification layer is established at 6 feet above complexities: the access floor. This creates a partial  Thermal decay, the increase in cooling supply air displacement ventilation effect within the room temperature due to heat transfer to the floor slab and improves ventilation effectiveness, and access flooring, limits the zone maximum contaminant control, heat capture, and reduces travel distance from the terminal discharge into loads within the space, transferring them directly the plenum to the furthest diffuser to 50-60 feet. to the return air. So for a typical side-fed core location the  Airflows need to be closely matched to the loads maximum zone size would be 120 ft by 60 ft, or within the occupied zone so as not to over air the 7200 ft2 or less. space, losing the partial displacement ventilation  Open office interior zones, those that have fairly effect. uniform loading, lend themselves to pressurized  Mixing only occurs within the occupied zone and plenums using passive swirl diffusers. happens so efficiently that it is normal for a 3 to  Zones with high heating loads need to consider 5º F temperature gradient to occur, right at the the use of ducted linear bar diffusers that deliver ASHRAE 55 comfort standard limit. the conditioned air to the load point (usually exterior walls with glazing) without significant

thermal decay. Insulate ductwork to prevent loss overhead system, with the following similarities and of cooling capacity. differences:  Perimeter zone size may be restricted by  Central cooling and heating equipment, as well as ASHRAE 90.1, requirements for exposure ductwork mains and branches to zone mixing zoning, which limits linear wall per exposure to terminals, can be nearly identical to traditional 50 feet. overhead systems. s. Systems that do not employ  Locating zone-mixing terminals in vertical the use of zone mixing terminals require special equipment closets does take up more useable consideration based on the volume and floor space compared to locating the units within temperature from the air-handling source. the underfloor plenum, but is a good choice for  When using zone fan powered mixing boxes reasons of ease of maintenance and minimizing (FPMB) above the access floor the chases must obstructions within the plenum. provide adequate room to locate the terminal as  When high cooling or dehumidification loads are well as provide required service clearances. present, such as conference rooms and rooms  UFAD systems use diffusers in the access floor, with plants, process or large equipment or solar much closer to the occupants, so special care loads, consider conditioning these spaces with needs to be exercised in their layout. Since it is a traditional VAV terminals using lower non-ducted system, simply swapping floor panels temperature (50 to 55ºF) primary air. This hybrid can make relocations easy. system design will result in smaller central  UFAD systems work best with uniformly loaded equipment, as well as ductwork mains and thermal areas. In high-load and variable-loaded branches zones, UFAD can be used in conjunction with 4.9 General Layout: traditional overhead systems. This creates an When beginning the layout of a UFAD system it overall hybrid system that utilizes the best is best to think of it as an upside down conventional features of both types of systems (figure 10b).

Fig no. 4.2 UFAD with Zone Mixing System

4.15.1 About This Document: Data", "Non Dimensional Temp" and "Diffuser Type" These user notes describe how to use the worksheets should not be modified; they cannot be hidden spreadsheet-based (Excel 2007) version of the UFAD due to VBA limitations. Only IP (Inch-Pound) units can be design tool for calculating the design cooling load and used. zone design cooling airflow required for an Under floor In the "Model" worksheet, user inputs are entered Air Distribution (UFAD) system. only in cells with a light blue background and the outputs 4.15.2 Overview of the UFAD Cooling Load Design Tool (calculated values) are displayed in cells with a gray Spreadsheet: background (see Figure 1). The data input and output are The design tool is composed of eight worksheets organized into three sections, named “Common Inputs”, but just the "Model" and "Comparison" should be used. “Zone Inputs”, and “Results”. In the “Common Inputs” The other worksheets are for calculation purposes and section there is only, in this version, one input that should be accessed only by expert users. The specifies the under floor plenum configuration. “Calculation2”, “Calculation4”, “Calculation6”, "Working

Most of the inputs that characterize the building These charts show the loads for the UFAD system are inserted in the “Zone Inputs” section. The results are being analyzed and for an equivalent overhead system displayed in a tabular form in the "Results" section and subject to the same heat gains (and from which the UFAD some of the most important results are displayed in the five loads have been derived). For the UFAD system the figure graphs reported next to the table. On the right-hand side of shows how the cooling load is divided between the cooling the page, there are three groups of figures. In the first are load in the supply plenum, the zone (room) and the return shown the temperature stratification profiles and the plenum. On the far right side, there is a histogram of the plenum temperatures of the interior and perimeter zones. design cooling airflow rates for both the interior and Below this first group are cooling load charts, for interior perimeter zones. A detailed description of the inputs and and perimeter zones. outputs are listed below under "Input and Output Descriptions."

Fig no.4.5 UFAD cooling load design tool spread sheet.

Fig no. 4.6 UFAD cooling load design tool spread sheets.

4.15.3 Input And Output Descriptions: Table 1 lists and describes the user input data in the order of appearance in the worksheet. The output data are listed and described in Table 2.

Table 1. Description of User Inputs for UFAD Cooling Load Design Tool Common Inputs Plenum Using the drop-down menu, the user may choose among the following four plenum Configuration configurations: “Series” – The conditioned air is first supplied to the plenum of the interior zone from which it flows to the perimeter zone. “Reverse Series” – The conditioned air is supplied first to the plenum of the perimeter zone (directly from a shaft, duct, or air highway) and then flows to the interior zone. “Design Interior and Perimeter as Independent Zones” – The conditioned air is supplied Independently (different airflow rates and (optionally) different supply temperatures) to the interior and perimeter zones. "Common" - The conditioned air is supplied to the plenum that is considered well-mixed. The Average diffuser discharge temperature is the same in both the interior and perimeter zones.

Parameter Zone Unit Sym Description Room Height I-P ft H ft Height between the raised floor and the suspended ceiling. 2 Floor Area I-P ft A f Floor area of the zone analyzed. Floor Level I-P - - Using the drop-down menu, the user may choose among the following three floor levels: “Ground Fl.” – The floor slab is in contact with the ground. “Middle Fl.” – The floor is between other floors. “Top Floor” – The floor under the roof. Diffuser Type I - - Using the drop-down menu, the user may choose among the following two diffuser types for interior zones: “Swirl” – ‘Standard’ swirl diffusers “VAV Directional I.” – Diffusers that automatically vary the air flow rate and keep the throw height constant Diffuser Type P - - Using the drop-down menu, the user may choose among the following two diffuser types for perimeter zones: “Linear Bar Grille” – Linear bar grille diffusers are used. When this option is chosen the software will ask the user to enter the length of the bar grille. The default value is 18 in. “VAV Directional P.” – Diffusers that automatically vary the air flow rate and keep the throw height constant Number of diffusers I-P - n Using the drop-down menu, the user may choose among the following Two diffuser types for perimeter zones: “Linear Bar Grille” – Linear bar grille diffusers are used. When this option is chosen the software will ask the user to enter the length of the bar grille. The default value is 18 in. “VAV Directional P.” – Diffusers that automatically vary the air flow rate and keep the throw height constant Design Cooling I-P kBtu/hr WOH Design cooling load calculated using traditional cooling Load or load software (e.g. ASHRAE RTS method, etc.). This Calculated for an Btu/(hr cooling load is the sum of the zone and the return Overhead (mixing) ft2) plenum cooling load. The design cooling load for the System analyzed zone should be calculated using the assumption of well mixed air. The overhead cooling load should be calculated for the same set point temperature used for the UFAD system ("Design Average Temperature in the Occupied Zone - Toz,avg,d).The user has the option to input the cooling load in kBtu/hr or Btu/(hr ft2) by using the drop-down menu in the "Units" column. 0 Design Average I-P F Toz,avg,d Room (or zone) design air temperature set point. In an Temperature in the overhead system this is the thermostat temperature set Occupied Zone point. For a stratified environment, it is the average occupied zone temperature. 2 Estimated Category I-P cfm/ ft qleak,2 Category 2 leakage is defined as uncontrolled air leakage 2 from the pressurized under floor plenum (through gaps Leakage between panels, electrical floor outlets, etc.) that enters the room and can still contribute to the removal of the heat load. For well sealed raised floors (carpet, tape, 752 Copyright © 2011-15. Vandana Publications. All Rights Reserved. www.ijemr.net ISSN (ONLINE): 2250-0758, ISSN (PRINT): 2394-6962

etc.), a typical range is 0.05-0.1 cfm/ft2; for not well sealed raised floors, a typical value is ~ 0.25 cfm/ft2 or greater. 0 Setpoint F Tplenum Temperature of the air entering the supply plenum. Temperature of Air Entering Supply Plenum Number of I - m Design number of occupants in the interior zone; should Occupants be consistent with original overhead load calculations. Zone Orientation P - - Using the drop-down menu, the user may choose among the following Four zone orientations for perimeter zones: “North”, “East", "South" and "West". Length of the Extn P ft LP Length of the outside wall of the selected perimeter Wall of the zone. Perimeter Area

Zone. I-P = the description is applicable to both interior and perimeter zones; I = the description is applicable only to interior zone; P = the description is applicable only to perimeter zones.

Table 2. Description of Output Data for UFAD Cooling Load Design Tool Results Parameter Zone Unit Sym Description Airflow (through I -P cfm Q Total room airflow rate delivered by the diffusers only in diffusers) the studied zone Design airflow (through I -P cfm QRoom Total (combined) room airflow rate; sum of airflow rate diffusers & leakage) through the diffusers (Q) and Category 2 leakage. Temperature of Air I –P °F TRlenu Temperature of the air entering the supply plenum Entering Supply Plenum m Diffuser Discharg I –P °F Ts Temperature of the air entering the room from the diffusers. Temperature This temperature is equal to the average temperature of the plenum. Air Temperature at 4 I –P °F T4 Air temperature at 4 in. (ankle height). in.Height Set point Air Temperature I –P °F Tset Thermostat setpoint temperature. This temperature is (at 48 in.) different from the average temperature in the occupied zone. This is the temperature that has to be set at the thermostat to obtain Toz,avg in a thermally stratifiedenvironment. Air Temperature at 67 I –P °F T67 Air temperature at 67 in. (head height for a standing person) in.Height Return Air Temperature I –P °F TR Temperature exiting the room at ceiling height and entering the return plenum. Return Plenum Air I –P °F TRP Temp. exiting the zone return plenum. This is not the air Temperature temperature going to the AHU. The return plenum air temperatures for the different zones on a given floor have to be properly weighted to calculate the average air temperature returning to the AHU from that floor. This calculation is not performed in the design tool. Average Temperature in I –P °F Toz,avg Average temperature in the occupied zone. The design tool the Occupied Zone determines the airflow rate that, for the given boundary conditions, makes Toz,avg =Toz,avg,d. We believe that this temperature is closer to the one perceived by people in a thermally stratified environment, as opposed to the set point

temperature at the thermostat height of 48 in. (1.2 m). Temperature difference I –P °F ΔToz Air temperature difference between head (67 in.) and ankle between the head and the (4 in.) heights of a standing occupant. According to ankle (from 67 in. to 4in.) ASHRAE 55-2004, the maximum allowable temperature difference between head and ankle is 5.4°F (3°C).If the temperature difference is higher that 5.4°F a red circle appears next to the number, if it is lower than 5.4°F a green circle appears, and if it is equal a yellow circle appears. Airflow (through diffusers I –P cfm/ ft2 Q Airflow rate through the diffusers expressed in cfm/ft2 Airflow per diffuser I –P cfm/ Q Airflow rate per diffuser. In the design condition this value diff should be equal to or less than the value recommended by the diffuser vendor. 2 Design airflow (through I –P cfm/ ft QRoom Total (combined) room airflow rate (Qroom) expressed in diffusers & leakage) cfm/ft2.

Design Cooling Load I -P W WOH Design cooling load calculated for an overhead (mixing) Calculated for an system expressed in W. Overhead (mixing) System UFAD Cooling Load I –P UCL The UFAD Cooling Load Ratio (UCLR) is the ratio of the Ratio (UCLR) R cooling load calculated for UFAD to the cooling load calculated for a well mixed system (e.g. Overhead or mixing ventilation). Supply Plenum Fraction I –P - SPF The Supply Plenum Fraction (SPF) is the ratio of the (SPF) cooling load removed in the supply plenum to the total UFAD cooling load. Zone Fraction (ZF) I –P - ZF The Zone Fraction (ZF) is the ratio of the cooling load removed in the zone (room) to the total UFAD cooling load. Return Plenum Fraction I –P - RPF The Return Plenum Fraction (RPF) is the ratio of the (RPF) cooling load removed in the return plenum to the total UFAD cooling load. UFAD Cooling Load I –P W W Design cooling load that the UFAD system has to remove

UFAD Cooling Load I –P W/ft2 W Same as above, but expressed in W/ft2

Supply Plenum Cooling I –P W - Cooling load in the supply plenum. Load Supply Plenum Cooling I –P W/ft2 - Same as above, but expressed in W/ft2. Load Zone Cooling Load I –P W - Cooling load in the zone (room).

Zone Cooling Load I –P W/ft2 - Same as above, but expressed in W/ft2.

Return Plenum Cooling I –P W - Cooling load in the return plenum. Load Return Plenum Cooling I –P W/ft2 - Same as above, but expressed in W/ft2. Load Length of the Linear Bar P In. - Length of the Linear Bar Grille in inches. The value is input Grill in a pop-up box when in the “Linear Bar Grille” option is selected in "Diffuser Type" input field for the perimeter zone. The default value is 18 in.

Zone. I-P = the description is applicable to both interior and perimeter zones; I = the description is applicable only tointerior zone; P = the description is applicable only to perimeter zones.

V. CONCLUSION [4] Webster, T., and F. Bauman. 2006. “Design guidelines for stratification in under floor air distribution (UFAD) Under floor air-distribution systems offer the systems.” HPAC Engineering (6). potential for improved indoor air quality and thermal [5] Bauman, Fred S., 2003. “Under floor Air Distribution comfort, reduced energy use, and easier reconfiguration (UFAD) Design Guide. American Society of Heating, compared with conventional overhead ventilation systems. Refrigerating and Air-Conditioning Engineers, Inc. However, achieving these benefits depends on the [6] ASHRAE. 1990. ANSI/ASHRAE Standard 113-1990, participation of architects, interior designers, contractors, Method of testing for room air distribution. Atlanta: facility managers, system operators, and occupants, as well American Society of Heating, Refrigerating and Air- as those working on the mechanical design.The concept is Conditioning Engineers, Inc. simple enough – put air in the plenum between 63°F and [7] http://escholarship.org/uc/item/7hh1t2z4 68°F, deliver it at floor level, let it heat up and natural [8] http://cbe.berkeley.edu/underfloorair/faqs_pr.htm buoyancy will move the air from the floor to the ceiling, [9] and then just bring it back to the central HVAC unit. But http://en.wikipedia.org/wiki/Underfloor_air_distribution once you get beyond the concept, there are numerous [10] http://www.cbe.berkeley.edu/ufad- design, construction, and operation issues that must be designtool/online.htm address in order to get the system to function as intended [11] over the life of the paper. www.ashrae.org/.../Journal%20Documents/.../20090625_0 30041_cu... [12] REFERENCES http://www.airzoneinc.com/less_money_underfloor_air_sy stem.html [1] ASHRAE. 1993. Handbook of Fundamentals, [13] www.escholarship.org/uc/item/5w53c7kr American Society of Heating, Refrigerating, and Air Conditioning Engineers, Inc., Atlanta. [2] ASHRAE. 2001. ASHRAE Handbook of Fundamentals, American Society of Heating, Refrigerating, and Air Conditioning Engineers, Inc., Atlanta. [3] Bauman, Fred. and Tom Webster. 2001. “Outlook for Under floor Air Distribution.” ASHRAE Journal. June 2001.