Residential Commissioning to Assess Envelope and HVAC System Performance

Craig P. Wray, P. Eng. Max H. Sherman, Ph.D. Member ASHRAE Fellow ASHRAE

ABSTRACT Residential commissioning is a new procedure to ensure that a house can perform optimally, or at least meet basic safety, health, comfort, and energy intents. Many procedural elements, such as visual inspection and functional performance diagnostics, already exist in a fragmented environment. Most can be integrated into new industry guidelines for testing and tuning system performance in new and existing houses. This paper describes a consolidated set of practical diagnostics that can be used now to commission envelope and HVAC system performance. Where possible, we discuss the accuracy and usability of available diagnostics based on recent laboratory work and field studies. We also describe areas in need of research and development, such as practical field diagnostics for enve- lope thermal conductance and combustion safety.

INTRODUCTION evaluations of houses using appropriate and agreed upon Houses do not perform optimally or even as many codes procedures. Many procedural elements already exist in a frag- and forecasts predict. For example, Walker et al. (1998a) mented environment; some are ready now to be integrated into found large variations in thermal distribution system effi- a new process called residential commissioning (Wray et al. ciency—as much as a factor of two even between side-by-side 2000). For example, California’s Title 24 energy code already houses with the same system design and installation crew. provides some commissioning elements for evaluating the This and other studies (e.g., Jump et al. 1996) indicate that energy performance of new houses. leakage testing and sealing can readily achieve a 25% to A house consists of components and systems that need to 30% reduction in installed cooling capacity and energy be commissioned, such as building envelopes, air distribution consumption. As another example, consider that the building systems, cooling equipment, heat pumps, combustion appli- industry has recognized for at least 20 years the substantial ances, controls, and other electrical appliances. For simplicity impact that envelope airtightness has on thermal loads, energy and practicality, these components and systems are usually use, comfort, and . However, Walker et al. evaluated individually, but we need to bear in mind that many (1998a) found 50% variances in airtightness for houses with of them interact. Therefore, commissioning must not only the same design and construction crews within the same subdi- identify the energy and non-energy benefits associated with vision. improving the performance of a component, it must also indi- A substantial reason for these problems is that few houses cate how individual components interact in the complete are now built or retrofitted using formal design procedures. building system. For this paper, we limit our discussion to Most are field assembled from a large number of components, diagnostics in areas of particular concern with significant and there is no consistent process to identify problems or to interactions—envelope and HVAC systems. These areas correct them. Solving the problems requires field performance include insulation quality, windows, airtightness, envelope

Craig Wray is a mechanical engineer and Max Sherman is a senior scientist in the Energy Performance of Buildings Group, Lawrence Berke- ley National Laboratory, Berkeley, Calif.

Buildings VIII/Mechanical Systems—Practices 1 moisture, and duct system airflows, duct leakage, cooling energy performance of the large number of existing houses, as equipment charge, and combustion appliance backdrafting well as the indoor environmental performance of all houses. with spillage. The remainder of this paper first describes what residen- Characteristic Elements tial commissioning is, its characteristic elements, and how one Residential commissioning, like every other commis- might structure its process. Subsequent sections describe a sioning process, includes the following three characteristic consolidated set of practical diagnostics that the building elements. industry can now use. Where possible, we also discuss the Metrics. For whole buildings, there are two broad perfor- accuracy and usability of these diagnostics based on recent mance objectives of interest—energy performance (e.g., laboratory work and field studies. We conclude by describing consumption, peak load) and indoor environmental perfor- areas in need of research and development, such as practical mance (e.g., IAQ, comfort). Various qualitative or quantitative field diagnostics for envelope thermal conductance and metrics can represent each objective. Each metric is simply a combustion safety. scale to rank the performance element of interest for the rele- There are several potential benefits for builders, consum- vant components or systems. Three examples of a metric are ers, code officials, utilities, and energy planners of commis- specific leakage area, which is a metric for the airtightness of sioning houses using a consistent set of validated methods. the ; duct leakage, which is a metric for the Builders and/or commissioning agents will be able to optimize air leakage from a duct system; and house depressurization, system performance and reduce consumer costs associated which is a metric for the backdrafting potential of combustion with building energy use. Consumers will be more likely to get appliances. what they paid for and builders can show they delivered what It is necessary to consider relationships between such was expected. Code officials will be better able to enforce metrics due to the energy and indoor environmental perfor- existing and future energy codes. As energy reduction mance interactions between components and systems (Koles measures are more effectively incorporated into the housing et al. 1996). For example, it is necessary to quantify specific stock, utilities and energy planners will benefit through leakage area, duct leakage, and house depressurization to greater confidence in predicting demand and greater assur- understand the impact that reducing duct leakage flows to save ance that demand reductions will actually occur. Performance energy can have on combustion safety in tight houses. improvements will also reduce emissions from electricity Diagnostics. Diagnostics are usually defined as relatively generating plants and residential combustion equipment. quick short-term field procedures. These procedures involve Research to characterize these benefits is underway. measurements and perhaps analyses to evaluate performance metrics for a system or component under functional test or WHAT IS RESIDENTIAL COMMISSIONING? actual building site conditions. An example of a diagnostic is a duct leakage test. Commissioning has its roots in shipbuilding, where the While it is also possible and sometimes preferable to eval- term describes the process that ensures a new vessel is seawor- uate metrics using data taken over an entire season, time limi- thy and ready for service. This process has many specific defi- tations make it impractical to collect and analyze such long- nitions. The variation relates to the scope of commissioning term information during residential commissioning. These and the activities related to it. Some commissioning projects limitations will be largely dependent on the value of the begin early in the design stage and continue through ongoing commissioning process to the involved parties. However, for operations and maintenance. Others include activities to opti- an existing house, commissioning can often use readily avail- mize performance beyond design intents (super-commission- able historical data either as part of diagnostics or to set norms. ing) or to adjust performance of existing facilities (retro- Norms. Norms are benchmarks against which compo- commissioning). nent or system performance is compared. Examples of norms In a narrow sense, one can simply think of residential are the various building standards that specify requirements commissioning as a process only for new houses. This process for minimum or maximum specific leakage area, for maxi- would assure the owner that all required equipment is installed mum duct leakage, and for maximum house depressurization correctly, the final product is assembled correctly, and the levels. A specific example is the California Title 24 norm that house can perform as intended. Such a process might be duct leakage be 6% or less of the nominal total airflow through carried out after installation and construction are complete and the . before the buyer occupies the new house. For the purposes of New and existing houses can use the same metrics and this paper, we broaden our definition of residential commis- diagnostics, although some diagnostics may not be appropri- sioning to include many other activities, such as rating, audit- ate at all stages of the construction process. However, the ing, super-commissioning, or retro-commissioning. As such, norms for existing houses will have to be adjusted to account it represents an expansion of processes currently carried out by for the stage of the house in its life-cycle and the economic people, such as home energy raters, home inspectors, auditors, viability of meeting stricter standards than those in place at the and weatherization contractors. This expansion includes the time of construction. For example, a house built in 1930 does

2 Buildings VIII/Mechanical Systems—Practices not come close to meeting current energy consumption limits. are performing to their norms, the improved performance of The retrofitting required to meet new insulation level require- new components or systems may make replacement worth- ments in this example would be prohibitively expensive. while.

The Commissioning Process BUILDING ENVELOPE DIAGNOSTICS When commissioning is discussed, many in the building The building envelope is important to house performance industry think of commercial buildings, although it is still because envelope loads dominate its mecha- uncommon to commission these buildings at any stage of their nisms. HVAC system thermal loads, equipment sizing, struc- life cycle. Most descriptions of commercial building commis- tural durability, and occupant comfort are based on having the sioning include the following three general steps: develop a envelope perform as intended. In new houses, installation fail- commissioning plan, carry out inspections and functional ures cause immediate problems. For example, Christian et al. performance tests, and review operations, maintenance, and (1998) indicate that insulation deficiencies can increase training procedures (Wray et al. 2000). whole-wall heat transfer by about 14%, which will increase Commissioning processes for houses are different. One energy consumption and reduce comfort. Having an appropri- reason is that commercial buildings tend to be more unique ate window type installed correctly can be even more impor- compared to one another, are large, have complex control tant. Carmody et al. (2000) indicate that for double-glazed systems, and have staff who manage operations and mainte- windows in a typical southern-climate house, a low-e film and nance (O&M). As a result, a common step in the commission- vinyl frame can reduce peak cooling loads by about 25% ing process for these buildings is developing unique compared to using clear glazing and an aluminum frame. documentation: a distinct commissioning plan and a building- Window emittance is the most important contributor to this specific O&M manual. This step is not warranted for most difference. Consequently, mislabeled windows that are houses because they tend to be more similar compared to one installed with an inappropriate emissivity or orientation can another, are small, have few control systems, and have no cause substantial energy and comfort problems. As the build- O&M staff. Another reason is that we anticipate residential ing ages, loss of durability caused by poor material selection commissioning can sometimes provide better performance and installation (e.g., insulation settling, damage than is called for in the design; most commercial commission- from pre-installation UV exposure, water intrusion) can result ing ignores this goal. in further performance reductions over time. The residential commissioning process that we envision has three main phases, which are generic guidelines geared to Insulation Quality specific commissioning issues or system and component types Visual Inspection. Several quantitative techniques for can probably encompass: evaluating the thermal performance of insulation systems are Audit and Diagnostic. In the first phase of commission- described in the literature (Wray et al. 2000). These include the ing, metrics for the house are surveyed. The results of this use of field diagnostic tools, such as heat flux transducer survey are then compared with the norms for the house. For arrays, hot boxes, and the Envelope Thermal Test Unit new construction, the norms will be those such as California (Modera et al. 1984), which is based on the guarded hot box Title 24 standards or the equivalent local building codes. For concept. Some field techniques involve whole-building ther- an existing house, the norms may be based on design intents mal conductance tests (Janssen and Rasmussen 1985; Sand- (if any were ever documented) or on what a particular compo- berg and Jahnsson 1995). However, due to measurement nent should be able to do compared to other similar houses. biases in some cases, lack of portability or commercial avail- Tuning and Tweaking. The performance of many ability in other cases, the need for expert users, excessive time components and systems may not meet the norms, but it may requirements, and high equipment costs, these diagnostics are be possible to improve their performance by making minor impractical in a residential commissioning environment. As a adjustments, repairs, or retrofits on the spot. An example is result, qualitative visual inspections (Consol 1999) will often sealing leaky ducts. Such tuning and tweaking can often play a key role instead. provide significant improvements in performance for very Visual inspection determines the presence or absence of little marginal cost. The purpose of this step is to improve the deficiencies, such as incorrect framing, incorrect insulation performance of the house to at least the design intent. Some- times, that intent will be unknown. In those cases, the optimi- type, incorrectly installed insulation, incorrect air and vapor zation will be to other norms, such as the best performance barrier placement, barrier damage, and blocked ventilation achievable within cost limits. pathways (e.g., between attic and soffitt vents). Such inspec- Opportunity Identification. After the tuning and tweak- tions are simpler and most useful when carried out, during ing, there still may be components that are not performing up construction. The inspection of building assemblies should to their potential. This commissioning step provides the client happen before the framing and insulation is sealed from view, with information about what potential repair or retrofit oppor- when it is easier to correct problems. Inspection of these tunities need further consideration. Even when components assemblies in existing houses often cannot be carried out and

Buildings VIII/Mechanical Systems—Practices 3 techniques that are more complex are generally required to Windows avoid destroying the exterior or interior surfaces of the assem- Until recently, there were no practical field diagnostics to bly. evaluate window radiative properties and behavior (e.g., glaz- These inspections do not quantify assembly thermal resis- ing gap thickness, emittance, solar heat gain coefficient, tance or conductance (R-value or U-factor). However, data daylight transmittance, and UV transmittance). A few inex- from these inspections, in conjunction with building plans or pensive quantitative tools are now commercially available and an assembly material audit, can subsequently be used to calcu- more tools are under development. An example is a prototype late assembly thermal performance. These calculations can be handheld spectrometer to determine window emittance class carried out using well-developed commercially available soft- (Griffith 1999). This surface-contact tool uses an infrared ware. Some of this software can also predict thermal param- emitter and detector to evaluate the aggregate normal reflec- eters, such as local and average surface temperatures as well tance of a multipane glazing assembly. Simple LEDs are used to indicate whether the glazing is clear, has high-solar-gain as heat loss or gain rates. Unfortunately, most of this software low-e coating, or has low-solar-gain low-e coating. The spec- is intended for research use rather than design or commission- trometer cannot distinguish which pane has the coating. ing. Current efforts sponsored by the ASHRAE Technical However, another tool that uses laser reflection to measure Committee on Energy Calculations to create simplified meth- glazing gap thickness is available for this purpose (EDTM ods of analysis may help alleviate this shortcoming. 2000). Visible differences in laser reflection intensity indicate Infrared Inspection. Infrared thermography systems which pane has the coating. and thermometers (radiometers) detect long-wave radiation Using noncontact infrared thermographic techniques in during a scan of a building assembly and convert the long- the field to assess window performance is generally imprac- wave radiation signal to a surface temperature using a fixed tical due to radiation transmission and reflection effects. The surface emissivity. Most thermographic systems and scanning magnitude of these effects can be highly variable depending radiometers produce false color images of the scan on a video on the physical properties of the glass, the presence of surface display for easier viewing of intensity differences. Thermo- coatings, and the surface finish. graphic scanning equipment is expensive—the cost of a new Airtightness system is in the range of $12,000 to $60,000. “Point source” radiometers are substantially less expensive (a few hundred Three diagnostic techniques can be used to quantitatively dollars). They simply display a spot-area-average temperature evaluate the airtightness of building envelope elements. They as a meter reading. The spot area increases as the distance from include using a , AC pressurization (Sherman and the surface of interest increases. This device can be used as a Modera 1986), or pulse pressurization (Modera et al. 1987). Only the first technique is well developed and commercially crude screening mechanism to rapidly locate envelope available. A blower door consists of a calibrated flow meter element deficiencies. combined with a fan mounted in a fabric or rigid panel, which The field use of any infrared inspection technique (ASTM is located in an open door or window. It is used to determine 1990) is limited and may not be repeatable for several reasons. airflow through the envelope as a function of pressure differ- These include equipment thermal instability at very high or ence imposed by the blower (ASTM 1999; CGSB 1986). very low outdoor temperatures, poor resolution at low indoor- A two-point blower door test with multiple pressure outdoor temperature differences, and distortion of surface difference and flow readings at each point provides a statisti- temperature patterns by solar radiation and wind effects, cally better envelope leakage estimate than multiple points differential heating or cooling rates of dry and wet areas, and with a single reading at each point (Sherman and Palmiter nonuniform or specular emissivities. Infrared inspection 1994). However, a two-point test cannot distinguish leakage generally cannot quantify assembly thermal conductance or differences due to envelope changes at different pressures even framing fractions (DEG 2000). (e.g., a vent opening as the pressure differential Within the limitations described above, infrared inspec- increases). Multiple points can more clearly show such compliance, as well as instrumentation failures. Single-point tion can qualitatively identify areas of anomalous heat transfer tests, although quick, are unreliable for quantifying leakage caused by design and/or construction deficiencies of the build- because there is no method to check the accuracy of the result. ing envelope. Examples include lack of insulation, displaced However, single-point tests are useful qualitatively during air- or improperly installed insulation, wet insulation, thermal sealing work to assess progress toward a planned airtightness bridging, air leakage, and air intrusion. Pressurizing or depres- goal. surizing the building using a blower door during a thermo- Blower door tests are susceptible to wind effects (Modera graphic scan can highlight air leakage paths that might and Wilson 1990) and stack effects. A practical wind speed otherwise be confused as insulation anomalies. Thermo- limit with a single outdoor pressure tap located in a sheltered graphic scanning can also be useful in identifying envelope region is approximately 8 mph (13 km/h) or less. This sections with internal convective loops. constraint limits the times when accurate testing can be carried

4 Buildings VIII/Mechanical Systems—Practices out. Manifolds connecting pressure taps on four faces of a Electrical Inspection. Two types of electrical devices are building can be used in some cases for linear pressure-differ- well developed and commercially available for field assess- ence averaging and fluctuation damping in an attempt to ments of the moisture content in building materials—surface reduce wind-effect-related precision errors and to extend scanning dielectric meters and penetrating conductance conditions under which the test may be carried out (CGSB meters. 1986). General guidelines suggest testing only when the Surface scanning devices emit low-frequency electro- outdoor temperatures are in the range of 41ºF to 95ºF (5ºC to magnetic waves and detect their disturbance to determine 35ºC). In cold climates, this constraint severely limits times average moisture content. These devices are believed to be when accurate testing can be carried out. good indicators of high relative moisture content near the surface of nonconductive porous building materials (wood, Envelope Moisture drywall, plaster, roofing, insulation, carpet, and concrete). As Diagnostics to assess moisture-damage susceptibility are a result, they are best used for comparative sampling over not well developed. In particular, most diagnostics can only different regions of a surface to indicate the range of moisture evaluate the presence of moisture rather than the susceptibility content (e.g., a suspected wet region compared to a known dry to moisture damage. These diagnostics typically involve region of similar material). Apparent high moisture content visual and electrical inspection techniques. In some cases, regions can then be checked with a subsurface resistance infrared thermography has been used (Knehans and Styer probe. An advantage of this device is that it does not damage 1983; Wild et al. 1998). However, that method requires envelope surfaces. A further advantage is that it can rapidly substantial further development before it is ready for use in test large regions and provide continuous readings. residential commissioning. There are no formal standards for Penetrating conductance devices determine the moisture assessing water damage or measuring the moisture content in content of nonconductive porous building materials near their building assemblies. Two diagnostic protocols have been exposed surfaces. This method is based on measuring the developed recently by inspection agencies in an attempt to fill resistance between the probes, which varies with moisture this void (NHCID 1998, GAHI 2000). These protocols are content. A disadvantage of this method is that it damages the meant to address water damage that has occurred in southeast- envelope surface during probe insertion. It is also time ern U.S. houses clad with exterior insulation and finish consuming to insert and remove probes at each test site. systems (EIFS). However, probe insertion has the advantage that it can also Visual Inspection. A visual surface inspection for excess provide a tactile indicator of subsurface structural decay. moisture within the building envelope can be carried out by All these electrical devices are sensitive to conductive determining the presence or absence of deficiencies, such as materials, such as metal fasteners, flashing, and joints, which wetness, microbiological growth (e.g., mold and mildew), can cause false positive readings. Scanning device readings discoloration, texture changes, and material dimensional also require correction to account for material type. Although changes, decay, or structural dislocation. Surface inspections several studies report accuracy when these devices are used are a useful screening technique, but the absence of visible with wood products (James 1988; Warren 1994; ASTM deficiencies does not exclude the presence of excess moisture 1998a), there appear to be no published data describing their within the envelope. As a result, invasive tests may be neces- accuracy for other materials, especially when combined as sary when occupants have associated allergic symptoms and/ building assemblies. or there is high relative indoors with no significant internal moisture sources and proper ventilation. Invasive AIR DISTRIBUTION SYSTEM DIAGNOSTICS tests can include tactile probing of envelope sections with a Residential air distribution systems include fans and sharp probe and dismantling of envelope sections for internal ducts for space conditioning and ventilation. Poor construc- inspection. Internal inspection involves looking for similar tion and operation of the air distribution systems can cause problems as those listed for surface inspections, as well as for comfort problems, poor indoor air quality, and structural mois- problems, such as leaks, from plumbing systems. ture problems, as well as wasted energy. In particular, ducts Visual inspection focuses on observing existing prob- that are part of the thermal distribution system may be the lems. It is not appropriate in general for use during construc- single worst performer in the energy performance of a house tion except for evaluating envelope detailing and plumbing (Jump et al. 1996). Much of the problem can be attributed to system integrity. To evaluate moisture-damage susceptibility installing ducts outside conditioned space, duct leakage, duct of new construction, checklists can be used in visible inspec- insulation compression, and other poor installation practices. tions of likely defects that may lead to future damage. As a Compared to the space conditioning system, the ventilation supplement to visual inspection, impermeable or absorbent system in most houses is simple. It consists of operable materials temporarily applied to surfaces can be used in qual- windows, , and a few (if any) intermittently oper- itative comparative tests (Lichtman et al. 1999). However, ated local exhaust fans. However, such systems are not always these supplemental tests tend to be impractical because they reliable for their intended purposes. To address this issue, are time consuming. more houses are beginning to also use whole-house ventila-

Buildings VIII/Mechanical Systems—Practices 5 Figure 1 Repeatability of DeltaQ duct leakage test. tion, which is sometimes directly linked to the space condi- DeltaQ Test. This test is based on changing the airflows tioning system. Furthermore, the proposed ASHRAE through distribution system leaks by turning the air handler on Standard 62.2 is expected to require mechanical ventilation in and off while pressurizing and then depressurizing the build- all new houses. Such ventilation practices and requirements ing envelope to various pressure differentials using a blower mean that minimizing the impact of air-handler and ventila- door. The advantages of this test (compared to duct pressur- tion airflows on fan power is of increasing importance to util- ization) are that it determines envelope leakage at the same ities and energy planners (in terms of peak power) and time as duct leakage, and there are no requirements for residents (higher energy bills). At the same time, ensuring sealing or for separation of the supply and return systems at the good delivery effectiveness and room-by-room distribution air handler by a seal. This makes the test less time consuming efficiency of thermal and ventilation distribution systems and less susceptible to leakage caused by poor sealing or seal depends on maintaining proper airflow through these systems. failure during the test. Air leakage to outside through supply and return leaks is determined directly with the ducts at oper- ating pressures. Testing the system at operating pressure Duct Leakage significantly reduces the uncertainty that occurs when Several quantitative diagnostics are available to uniquely converting measured duct leakage at other than operating determine duct leakage (Walker et al. 1998a; Walker et al. pressures to measured operating pressures. The DeltaQ test 1999; Francisco and Palmiter 2000)—the DeltaQ test, the duct can only be used in finished houses because it requires an pressurization test, the house pressure test, and the nulling envelope that can be pressurized. pressure test. The pressure pan test (Siegel and Manclark Test precision and bias are susceptible to wind speed and 1998) is not included in this list because its pressure indication direction variation that result in envelope pressure fluctua- does not uniquely determine leakage. As a result, it is not tions. Resulting fractional errors in duct leakage can be large, recommended for commissioning except as a rapid screening although absolute flow errors will remain small. The practical supplement to more elaborate tests. The cost and accuracy of limit for wind speeds when accurate testing can be carried out duct leakage testing is in the process of being improved by is not currently known. Research is in progress to determine several researchers and the ASTM standard test method for the wind limitations for this test. As Figure 1 shows, prelimi- measuring duct leakage is being rewritten to include newer nary data for a single building indicate good repeatability— methods (E1554 – which will be completed in 2001). The stan- 0.5% to 1.0% of air-handler flow for a 95% confidence inter- dard (and our discussion) focuses on the DeltaQ and duct pres- val (Wempen 2000). These data are from 20 tests in mild surization tests because they are the simplest in terms of weather for wind speeds of 5 mph (8 km/h) or less with a tight equipment and procedure, are more robust, and, in some cases, duct system and envelope (about 7% return leakage, 2% are more flexible in terms of the types of houses or systems supply leakage, and a normalized envelope leakage of about that can be tested. 0.5).

6 Buildings VIII/Mechanical Systems—Practices This test is also susceptible to stack effects, which may is prone to errors of more than 20% in many cases and near a affect the apparent leakage area of the envelope and duct factor of two in worst cases due to flow nonuniformities and system. This bias is not expected to be large. Outdoor temper- radiant effects (Palmiter and Francisco 2000). While using a ature limits to reduce stack-effect-induced pressure variation tracer gas can be very accurate, it requires expensive, delicate are unknown, but we expect that the suggested outdoor equipment and a well-trained technician. It is also subject to temperature limitations for envelope airtightness tests are errors induced by flow nonuniformity, which are difficult to probably also applicable. assess in the field. Measuring individual duct branch flows Duct Pressurization Test. This test can be used in unfin- and summing them can lead to substantial errors because of ished or finished houses. It uses a small fan-assisted flow the addition and subtraction of many uncertain numbers. As meter (and in some cases a blower door as well) to determine described later in this paper, much of the uncertainty is due to duct leakage by pressurizing the duct system to 25 Pa with the inaccuracy when commercially available flow hoods are used supply-and-return sealed. Sealing grilles can be diffi- or when duct leakage is not properly taken into account. Fan cult (e.g., hard to reach on high vaulted ceilings) and time curve interpolation cannot be relied upon because manufac- consuming (e.g., taping each grille, often while standing on a turer’s fan curve data are not easily or generally available for ladder). Sometimes it is also difficult or impossible to install residential systems. When it is available, it may not accurately the air-handler seal due to the equipment configuration. All of represent the installed performance of the fan due to system these seals are susceptible to failure during the test. If separate effects. These effects can vary significantly and are difficult to supply-and-return leakage data are required, then the supply- estimate. In addition, it is not possible to measure the static and-return sections at the air handler must be separated by a pressure drop in the duct system at the same locations as those seal. Duct leakage to outside is determined by pressurizing the used to produce the manufacturer’s fan curve. house with a blower door to the same pressure as the duct Fan-Assisted Flow Meter. This device uses a calibrated system (25 Pa), so there is no pressure difference to drive flow meter combined with a fan to determine air-handler flows across duct leaks to inside. airflow. It can be attached to the air-handler cabinet at its The duct pressurization test requires that the operating access door or at a return grille if the return ducting is well static pressure in the supply and return duct systems be sealed. With the air handler running, air is blown into the air measured. Measured operating pressures at plenums are then handler or return (with the return sealed if connecting to the air used to convert leakage measured at the imposed pressure (25 handler). The goal of this test is to reproduce the pressure Pa) to operating conditions. An advantage of measuring these difference between the supply plenum and conditioned space pressures is that they are also a useful indicator of ducts that under normal system operating conditions. If this operating are undersized or that are restrictive due to their topology and pressure cannot be achieved due to capacity limits of the fan fittings. However, these operating pressures may be a poor on the flow meter, then multiple measurements of flow and indicator of the pressure at duct leaks, whose location is supply plenum static pressure are used to extrapolate to the unknown. As a result, the duct pressurization test is less appro- operating pressure. priate in houses with leaky ducts. The precision is primarily It is time consuming to attach the flow measurement affected by conversion from imposed to operating pressure— device to the air handler or return. Additional time is required conversion increases uncertainty. The absolute precision error to seal off the return upstream of the air handler if the device in flow increases with increasing duct leakage flow, but the is connected to the air-handler cabinet. Based on field tracer fractional uncertainty remains approximately constant. gas tests (Walker et al. 1998b), we expect the accuracy of this The duct pressurization test is also susceptible to wind test method is approximately ±10%. However, the actual and stack effects, but less so than for the DeltaQ test because accuracy is unknown at this time and cannot be easily esti- it does not use envelope pressure in its calculations to deter- mated due to the possibility of flow pattern changes within the mine duct leakage. air handler or static pressure measurement errors. Further research is needed to establish the accuracy of this method. Air-Handler Airflow Flow Plate and Grid. This new device uses a calibrated Several diagnostic tools and techniques can be used to multiple-orifice plate with attached upstream and downstream determine airflow through the air-moving equipment of cool- pressure manifolds to determine air-handler airflow. The ing and heating systems. However, there is currently no refer- device is inserted into an body in place of the filter. ence method for field use. Two of the most promising practical The pressure drop of the device is intended to be similar to that and commercially available tools include a fan-assisted flow of an air filter. In general, the “measured” airflow needs to be meter (Walker et al. 1999) or a flow plate and grid (Palmiter corrected to account for the difference in supply plenum static and Francisco 2000). pressure with the device installed instead of the filter. Also, Other techniques include using the air temperature differ- when the flow plate is mounted at a filter grille, the return duct ence across the air-handler (Downey and Proctor 1999), a leakage needs to be added to the measured flow. tracer gas (Walker et al. 1998b), the sum of duct branch flows, Using fan-assisted flow meter measurements as a refer- or fan curve interpolation. Of these other techniques, the first ence, preliminary comparisons of airflows obtained using the

Buildings VIII/Mechanical Systems—Practices 7 flow plate and grid in 74 houses indicate its measurements are flow grid. Of these, only the first is accurate and reliable. The within 17% of the “reference” method (Palmiter and Francisco other methods are error prone due to the effects of flow 2000). In 54% of the house, differences are less than 5%. nonuniformities, difficulties in estimating effective flow areas Reasons for differences are not reported, but they might be (anemometry), uncertainty in determining insertion depth related to plenum static pressure measurement errors. Fran- (pitot tube), low velocities, misaligned sampling of the cisco (2000) has indicated that upstream flow disturbances, airstream, fouling (flow grid), and duct leakage. such as 90º bends in the return duct as close as 3 in. (75 mm) to the plate, do not adversely affect measurement accuracy. Of particular note, conventional nonpowered flow hoods are sometimes an order of magnitude less accurate than what Distribution System Airflows many in the HVAC industry believe. Laboratory test data Several diagnostics are available to determine airflow shown in Figure 2 demonstrate the large unacceptable impre- rates through air distribution systems. They include a fan- cision of several commercially available flow hoods. We assisted flow hood (Walker et al. 1999), a conventional flow obtained these data using a single-branch duct with and with- hood (no fan assist), anemometry, a pitot tube traverse, or a out various grilles, with an inline flow nozzle as a reference.

Figure 2a Accuracy of conventional nonpowered flow hood 1.

Figure 2b Accuracy of conventional nonpowered flow hood 2.

8 Buildings VIII/Mechanical Systems—Practices Figure 2c Accuracy of conventional nonpowered flow hood 3.

Figure 2d Accuracy of conventional nonpowered flow hood 4.

In some cases, measurement errors are as large as 50%, but grille type. Grilles with more side discharge than direct they are typically about 15% to 25%. Field data that we have discharge are more likely to cause recirculation regions. gathered using a fan-assisted flow hood for comparison ASHRAE (1988) recommends using a pitot tube traverse of support these findings. The measurement errors are likely due the duct section upstream of a grille, with and without the hood to recirculation regions that occur within the hood and nonuni- in place, to determine a flow correction factor that will account formity of flow at the flow hood sampling points. Manufac- for measurement errors. Such a practice is impractical for turers recommend using a hood size close to the grille size to most residential systems. First, traverses can be difficult or reduce this problem. However, this is often not possible impossible in many cases. Second, the correction can be very because most of these hoods are intended for use in commer- specific to a given grille. Obtaining this correction factor for cial buildings and are much larger than most residential grilles. each grille makes the use of the flow hood redundant. The extent of this problem also depends on flow rate, duct Fan-Assisted Flow Hood. A fan-assisted flow hood is topology upstream of the grille (e.g., nearby elbows), and similar to a conventional hood but also has a fan-assisted flow

Buildings VIII/Mechanical Systems—Practices 9 meter attached by a flex duct. Unlike a conventional hood, this equipment cooling capacity by 8% to 22% and the energy effi- device does not require an elaborate seal at the gap between the ciency ratio (EER) by 4% to 16%, depending on outdoor hood and the adjacent building surface because the integrated conditions. fan maintains a relatively neutral pressure difference between the interior and exterior of the hood. At the same time, the fan Charge Level assist also eliminates the backpressure problems that are created by conventional flow hoods. The location of the Several diagnostic techniques are available to assess the measurement device at the end of 6 ft (2 m) or more of flex refrigerant charge level in residential cooling equipment. duct attached to the flow hood virtually eliminates errors due These techniques include superheat or subcooling tests, a to flow nonuniformities. gravimetric test, a sight glass, thermostatic expansion valve Figure 3 shows data from laboratory tests of a fan-assisted (TXV) frosting, “feeling the lines,” or motor signature analy- sis. Of these, only the superheat and subcooling tests are quan- flow hood that were obtained in a manner similar to those titative, practical, well developed, and reliable. Those tests are described above for the conventional flow hoods. It appears not standardized but are commonly specified by equipment this device can achieve significantly better accuracy—its manufacturers. average relative error is approximately 2%, and no error is The other techniques are qualitative in some cases, unre- worse than 5%. Unfortunately, such devices are not yet liable, time consuming, or not well developed. Although the commercially available but can be easily constructed of gravimetric test can accurately determine the amount of refrig- readily available components. Such a device is under devel- erant and noncondensable fluids in a cooling system, it is prob- opment now to address this need, but it will require field test- lematic because the amount of refrigerant required for optimal ing to assess its accuracy and usability. system performance is often unknown. This problem occurs due to the use of refrigerant line lengths and coils that do not COOLING EQUIPMENT DIAGNOSTICS conform to manufacturer’s specifications. In particular, it is Even in new houses, cooling systems rarely perform as difficult to quickly estimate the internal volume of coils, espe- intended (Sherman et al. 1987). Aside from inadequate airflow cially when tubing wall thickness is unknown. Furthermore, across coils, low refrigerant charge levels are a volumetric calculations are insufficient to account for evapo- significant cause of this problem. Refrigerant charge has a rator heat transfer characteristics that differ from those of the particularly important impact on the capacity and efficiency of manufacturer-specified coil. Only a functional performance cooling equipment without a thermostatic expansion valve test, such as the superheat and subcooling tests, can account (TXV). For example, laboratory test data from Farzad and for this difference. O’Neal (1988) for capillary-tube-controlled equipment indi- Superheat/Subcooling Tests. These tests (Downey and cate that a common charge deficiency of 15% can reduce Proctor 1999) assess charge level by determining the refriger-

Figure 3 Accuracy of fan-assisted flow hood.

10 Buildings VIII/Mechanical Systems—Practices Figure 4 Refrigerant superheat charging chart. ant thermodynamic state at a specific point in the system. For facilitate equipment charge evaluation when it is operating at the superheat test, which is used for cooling equipment with a other than design conditions. fixed metering device (capillary-tube or short-tube orifice), At this time, there are no standards specifying tempera- the location is the inlet at the condensing unit. The ture and pressure measurement accuracy or specific measure- concept here is to make sure that the refrigerant is fully evap- ment locations for a superheat test. As a result, there can be orated upon leaving the evaporator. For the subcooling test, significant variability in “measured” superheats. Example which is used for TXV-equipped cooling equipment, the loca- problems include measuring the indoor wet-bulb within the tion is the condenser exit at the condensing unit. In this case, house rather than within the return plenum downstream of the concept is to make sure that the refrigerant is fully return duct leaks, measuring outdoor air temperature remotely condensed upon leaving the condenser. from the condensing unit in direct sunlight with an unshielded sensor, and measuring refrigerant line temperature down- Consider the superheat method. Refrigerant suction line stream of a line restriction or with an uninsulated sensor that temperature and pressure, condenser inlet air dry-bulb temper- has poor surface contact. Uncertainties in these measurements ature, and evaporator inlet air wet-bulb temperature are can easily lead to “measured” superheat errors of 10ºF (6ºC) measured after the cooling equipment runs for about 15 or more. Laboratory test data from Farzad and O’Neal (1988) minutes to achieve equilibrium (steady-state operation). for capillary-tube-controlled equipment indicate a 10ºF (6ºC) “Measured” superheat is based on the difference between the superheat error can result in a charge assessment difference of measured suction line temperature and the refrigerant satura- about 5% to 9%, depending on outdoor temperature. tion temperature corresponding to the measured refrigerant The superheat method cannot be used in cool weather pressure. Proper charge is typically indicated by a “measured” (outdoor air temperature less than 50ºF or 10ºC). This limita- superheat not lower than 5ºF (3ºC) and within 5ºF (3ºC) of a tion is primarily to protect the compressor from failure due to target superheat at test conditions. Refrigerant charge is low if insufficient lubricant circulation under these conditions. The the “measured” superheat is more than 5ºF (3ºC) above the method also cannot be used in hot, dry climates (e.g., summer target superheat at test conditions. Charge is high if the in Fresno, California) when there is a low return air wet-bulb “measured” superheat is more than 5ºF (3ºC) below the target temperature coincident with a high outdoor air dry-bulb superheat at test conditions. temperature. Testing in the spring when outdoor air dry-bulb The target superheat is determined using the equipment temperatures are not too hot can circumvent this problem. “superheat chart.” Figure 4 (Downey and Proctor 1999) shows Alternatively, the indoor wet-bulb can be elevated artificially such a chart, which typically relates superheat (5ºF to 40ºF, by overheating and humidifying the house. This latter tech- 3ºC to 22ºC) as a function of outdoor air dry-bulb and return nique requires further development to determine appropriate air wet-bulb temperatures. The intent of these targets is to strategies.

Buildings VIII/Mechanical Systems—Practices 11 COMBUSTION APPLIANCE DIAGNOSTICS 2. Formal standards are needed for assessing water damage and measuring the moisture content in building assemblies. While poor design or installation of the building enve- lope, combustion equipment, or air-moving equipment can 3. The impact of wind effects, as well as envelope and duct leakage, on the accuracy and repeatability of the new reduce efficiency, it can also lead to downdrafting and possi- DeltaQ duct leakage test needs further research. bly backdrafting with combustion gas spillage. Downdrafting is inward airflow from outdoors through a or chimney 4. Formal standards are needed for the calibration and use of when no connected combustion appliance is operating. Appli- airflow diagnostic tools, such as flow hoods with and with- ance backdrafting is the failure of an operating combustion out fan assist, and the flow plate and grid that temporarily appliance to reverse a downdraft and to establish a proper flow replaces an air filter. of combustion gas products toward outdoors through the 5. Formal standards are needed for superheat and subcooling attached flue or chimney. Spillage is the entry of combustion tests of cooling equipment. gas products into the indoor air. Any of these phenomena can 6. Research is needed to develop a method of assessing refrig- be caused by excessive depressurization of a house when erant charge in cool weather. exhaust equipment are operating. Such events, along with 7. The utility of temporarily elevating indoor needs insufficient ventilation for unvented combustion appliances, to be examined to extend the periods when the superheat can directly affect the indoor environment by causing health, method can be used to test cooling equipment in hot, dry comfort, or indoor air quality problems. climates. Substantial work has been carried out in Canada and the 8. The accuracy and repeatability of methods that determine United States over the past 20 years in an attempt to under- the potential for backdrafting and combustion gas spillage stand backdrafting and spillage events related to combustion needs further research. equipment venting and the operation of exhaust devices in houses, how long such events last, and how frequently they ACKNOWLEDGMENTS occur. Several “snapshot” style test protocols have been devel- This paper describes work supported by the Assistant oped (CGSB 1995; ASTM 1998b) to indicate the potential for Secretary for Energy Efficiency and Renewable Energy, problems. Specifically, four tests available to assess the back- Office of Building Technology of the U.S. Department of drafting and spillage potential are the house depressurization Energy under contract no. DE-AC03-76SF00098, and by the test, the downdrafting test, the appliance backdrafting test, and California Energy Commission through the Public Interest the cold-vent establishment pressure (CVEP) test. Energy Research program. Due to the short time span of these tests, it may be desir- The authors wish to acknowledge the contributions of able to sample multiple times over the life cycle of the build- LBNL staff who were involved in carrying out field and labo- ing, particularly when the envelope airtightness, air-moving ratory measurements that are described in this paper: Bass equipment, or combustion appliances change. However, long- Abushakra, Darryl Dickerhoff, Jennifer McWilliams, Iain term monitoring is probably impractical as a commissioning Walker, Duo Wang, and Jacob Wempen. tool to achieve this end. All these tests are problematic, because they are susceptible to wind effects, which can easily REFERENCES result in false positive or negative test results (Nagda and ASHRAE. 1988. ANSI/ASHRAE Standard 111-1988, Prac- Koontz 2000). Further research is needed to assess their accu- tices for measurement, testing, adjusting, and balancing racy and repeatability. However, given that life safety and of building heating, ventilation, air-conditioning and chronic health problems have been associated with combus- systems. Atlanta: American Society of tion gas spillage, it is still better to use these imperfect methods Heating, Refrigerating and Air-Conditioning Engineers, than not. Inc. ASTM. 1990. ASTM Standard C1060-90. Standard practice RESEARCH AND DEVELOPMENT NEEDS for thermographic inspection of insulation installations in envelope cavities of frame buildings. Philadelphia, For every building element discussed above, practical Pa.: American Society for Testing and Materials. diagnostics are available now to commission envelope and ASTM. 1998a. ASTM Standard D 4444-92. Standard test HVAC system performance. However, some of these diagnos- methods for use and calibration of handheld moisture tics require further research and development to assess or meters. West Conshohocken, Pa.: American Society for improve their usefulness and accuracy, so that they can be used Testing and Materials. more extensively and reliably. In particular, the following ASTM. 1998b. Guide for assessing depressurization- eight areas need further work: induced backdrafting and spillage from vented combus- 1. A practical diagnostic is needed to evaluate the in situ ther- tion appliances. Philadelphia, Pa.: American Society for mal conductance of envelope assemblies. Testing and Materials.

12 Buildings VIII/Mechanical Systems—Practices ASTM. 1999. ASTM Standard E779-99. Standard test tory, Environmental Energy Technologies Division, method for determining air leakage rate by fan pressur- Building Technologies Department, Windows & Day- ization. Philadelphia, Pa.: American Society for Testing lighting Group website http://windows.lbl.gov/ and Materials. win_prop/component_verification. Carmody, J., S. Selkowitz, D. Arasteh, and L. Heschong. James, W.L. 1988. Electric moisture meters for wood. Gen- 2000. Residential windows: A guide to new technologies eral Technical Report FPL-GTR-6. Madison, Wis.: U.S. and energy performance, 2d Edition. New York: W.W. Department of Agriculture, Forest Service, Forest Prod- Norton & Company. ucts Laboratory. Christian, J.E., J. Kosny, A.O. Desjarlais, and P.W. Childs. Janssen, J.E., and R.W. Rasmussen. 1985. An instrument for 1998. The whole wall thermal performance calculator— measuring building-envelope thermal resistance. Ther- On the net. Thermal Performance of the Exterior Enve- mal Performance of the Exterior Envelopes of Buildings lopes of Buildings VII. Atlanta: American Society of III. Atlanta: American Society of Heating, Refrigerating Heating, Refrigerating and Air-Conditioning Engineers, and Air-Conditioning Engineers, Inc., pp. 723-738. Inc., pp.287-299. Jump, D.A., I.S. Walker, and M.P. Modera. 1996. Field mea- CGSB. 1986. CAN/CGSB-149.10-M86. Determination of the surements of energy efficiency and duct retrofit effec- airtightness of building envelopes by the fan depressur- tiveness in residential forced air distribution systems. ization method. Ottawa, Calif.: Canadian General Stan- Proceedings of 1996 ACEEE Summer Study on Energy dards Board. Efficient Buildings. Washington, D.C.: American Coun- CGSB. 1995. CAN/CGSB-51.71-95. Method to determine cil for an Energy-Efficient Economy. the potential for pressure-induced spillage from vented, Knehans, A.H., and P.E. Styer. 1983. Thermography—A fuel-fired, space heating appliances, water heaters and diagnostic tool to locating wet insulation in built-up . Ottawa, Calif.: Canadian General Standards roofing systems. ASHRAE Transactions 89 (2B): 112- Board. 117. ConSol. 1999. CIEE final project report: Protocols for Koles, G., R. Hitchcock, and M.H. Sherman. 1996. Metrics energy efficient residential building envelopes. Stock- for building performance assurance. Lawrence Berke- ton, Calif.: Consol. ley Laboratory LBL-39203. DEG. 2000. Residential construction quality assessment Lichtman, G., R. Johnson, and D. Steussy. 1999. Construc- project: Phase I final report. Davis Energy Group Report tion defects underfoot: Concrete slab foundations to the California Energy Commission, CEC Report affected by moisture intrusion, deterioration. Claims P400-00-022. Magazine. Seattle, Wash. Downey, T., and J. Proctor. 1999. Residential central air con- ditioner service program final report. Report of Proctor Modera, M.P., M.H. Sherman, and S.G. de Vinuesa. 1984. Engineering Group to Pacific Gas & Electric Company. In-situ measurement of wall thermal performance: Data interpretation and apparatus design recommendations. EDTM. 2000. Manual IG thickness gauge, #MG1500. Elec- Lawrence Berkeley Laboratory LBL-17773. tronic design to market, Inc. website http:// www.edtm.com/mg1500.htm. Modera, M., M. Sherman, and P. Vacheron. 1987. Pulse pres- Farzad, M., and D.L. O’Neal. 1988. An evaluation of surization: A technique for measuring building air leak- improper refrigerant charge on the performance of a age. Lawrence Berkeley Laboratory LBID-1321. split system air conditioner with capillary tube expan- Modera, M.P., and D.J. Wilson. 1990. The effects of wind on sion. Texas A&M University, Energy Systems Labora- residential building leakage measurements. ASTM STP tory Report ESL-TR-88/07-01. 1067. Air change rate and air tightness in buildings. Francisco, P.W. 2000. Personal communication. August. Philadelphia, Pa.: American Society for Testing and Francisco, P.W., and L. Palmiter. 2000. Performance of duct Materials, pp. 132-145. LBL-24195. leakage measurement techniques in estimating duct effi- Nagda, N.L., and M. Koontz. 2000. Rationale for proposed ciency: comparison to measured results. Proceedings of method for assessing backdrafting and spillage. Presen- the 2000 ACEEE Summer Study on Energy Efficient tation at ASTM E6.41—Mechanical Systems Meeting, Buildings. Washington, D.C.: American Council for an Toronto, Ontario. Energy-Efficient Economy. NHCID. 1998. Moisture testing guide for wood frame con- GAHI. 2000. The GAHI protocol for exterior insulation fin- struction clad with exterior insulation and finish systems ishing systems (EIFS) moisture intrusion inspections— (EIFS), Version 3.01. Prepared for EIFS Review Com- One & two family homes. Atlanta: Georgia Association mittee. Wilmington, N.C.: New Hanover County of Home Inspectors. http://www.gahi.com/eifsprot.html. Inspection Department. Griffith, B.T. 1999. Field verification of components: Hand- Palmiter, L., and P.W. Francisco. 2000. Development of a held detector for low-e and spectrally selective coatings. simple device for field air flow measurement of residen- Berkeley, Calif.: Lawrence Berkeley National Labora- tial air handling equipment: Phase II. Final Report of

Buildings VIII/Mechanical Systems—Practices 13 Ecotope, Inc. to the U.S. Department of Energy, STTR nology transfer in residential thermal distribution sys- Grant #DE-FG03-97ER86060. tems. Lawrence Berkeley National Laboratory LBNL- Sandberg, P.I., and S. Jahnsson. 1995. Development of a 41118. method for the measurement of specific heat loss in Walker, I., M. Sherman, M. Modera, and J. Siegel. 1998b. occupied detached houses. Thermal Performance of the Leakage diagnostics, sealant longevity, sizing and tech- Exterior Envelopes of Buildings VI. Atlanta: American nology transfer in residential thermal distribution sys- Society of Heating, Refrigerating, and Air-Conditioning tems: Part II. Lawrence Berkeley National Laboratory Engineers, Inc., pp. 425-430. LBNL-42691. Sherman, M., and M. Modera. 1986. Low-frequency mea- Walker, I., M. Sherman, and J. Siegel. 1999. Distribution surement of leakage in enclosures. Lawrence Berkeley effectiveness and impacts on equipment sizing. Laboratory LBL-20121. Lawrence Berkeley National Laboratory LBNL 43724. Sherman, M.H., R.F. Szydlowski, P.G. Cleary, M.P. Mod- Warren, S.R. (editor). 1994. ASTM hand-held moisture era, and M.D. Levine. 1987. Development and imple- meter workshop. Madison, Wis.: Forest Products Soci- mentation of survey techniques for assessing in-situ ety. appliance efficiencies. Lawrence Berkeley Laboratory LBL-23455. Wempen, J. 2000. Repeatability of the DeltaQ duct leakage Sherman, M.H., and L. Palmiter. 1994. Uncertainties in fan test method. Final Report for the Office of Science, pressurization measurements. In Airflow Performance DOE Energy Research Undergraduate Laboratory Fel- of Envelopes, Components and Systems. Philadelphia, lowship Program. Pa.: American Society for Testing and Materials (STP Wild, W., K.A. Buscher, and H. Wiggenhauser. 1998. 1255), Modera and Persily, eds., pp. 262-283. LBL- Amplitude sensitive modulation-thermography to mea- 32115. sure moisture in building materials. Proceedings of Siegel, J., and B. Manclark. 1998. Pressure pans: New uses SPIE, Vol. 3361, Thermosense XX, pp. 156-163. and old fundamentals. Home Energy Magazine 15 (1): Wray, C.P., M.A. Piette, M.H. Sherman, R.M. Levinson, 37-42. Berkeley, Calif.: Energy Auditor & Retrofitter, N.E. Matson, D.A. Driscoll, J.A. McWilliams, T.T. Xu, Inc. and W.W. Delp. 2000. Residential commissioning: A Walker, I., M. Sherman, M. Modera, and J. Siegel. 1998a. review of related literature. Lawrence Berkeley National Leakage diagnostics, sealant longevity, sizing and tech- Laboratory LBNL-44535.

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