A Comparison of Techniques to Measure Commercial Building Infiltration Rates Paul Crovella State University of New York, College of Environmental Science and Forestry, Department of Construction Management and Wood Products Engineering, Syracuse, NY 13210. *Corresponding email: PLCrovella@esf.edu ABSTRACT Determining building envelope air tightness is essential for understanding energy use and air quality in existing buildings. This study first reviewed the testing requirements for four methods of pressurization for determining envelope air tightness in commercial buildings: ASTM E 779-03, CAN 149.15-96, The British ATTA Standard 1, and ASHRAE RP-935. The required environmental conditions to allow testing were compared to weather data in Syracuse, NY. It was found that the available days for testing varied between 5 (ASTM E779-03) to 182 (CAN 149.15). Suggestions were made to improve these limitations. Next two of the methods (ASTM E779-03 using blower doors, CAN 149.15 using building air handling units) were applied to a 3,950 m2 university building. Although one test did not collect enough data to meet the threshold, the two methods showed close agreement (< 1.5% difference) in measured building leakage rates at 75Pa. Data analysis showed that the two methods easily allowed for the building to be classified for code or contract leakage conformance. Finally a discussion is included of using testing results to predict energy savings due to envelope sealing. KEYWORDS Building Air Tightness, Energy Use, Infiltration Rate, Blower Door Test INTRODUCTION Approximately 40% of the total energy used in the US is used by buildings (EIA, 2010). Efficiencies in this realm represent an enormous potential for reducing our dependence on non-renewable energy sources and our production of greenhouse gases. Additionally, the EPA estimates that we spend approximately 90% of our time inside these buildings (EPA 2010). The quality of comfort provided by these enclosures directly affects our well-being. In 2005 the US Dept of Energy (DOE 2006) estimated that 40% of the energy used to heat and cool buildings was lost due to uncontrolled flow through the envelope. The energy used to heat and cool commercial buildings represents 6-7% of the total energy used in the US (EIA, 2010). Envelope leakage in commercial buildings accounts for 2-3% of the total energy used in the US. This energy loss in commercial buildings has not been addressed as aggressively as in the residential sector, due in part to a lack of evidence on verifiable gains due to testing and retrofits (Woods 2007). The objective of this work was to investigate the ability of various air tightness testing methods to accurately predict the natural infiltration and potential energy savings in commercial buildings. In 1999, Persily (1999) found that although the data is limited, commercial buildings do have significant levels of air infiltration. Using multiple data sets he found that the leakage is not correlated to age, size, or construction type. In 2005 Emmerich, et al (2005) showed that

energy savings of between 3 and 36% could be attained by improving envelope performance of sample commercial buildings (one-story retail, two-story office, four story apartment) when modeled in five US cities (Miami, Phoenix, St. Louis, Bismark, Minneapolis). The greatest savings corresponded to the cities with the greatest need for heating. Brennan and Cummings (2002) have shown the potential health consequences of air leakage through the building envelope materials. Brennan and Clarkin (2007) cite four different standards for testing commercial buildings using fan pressurization techniques. Further research has shown at least two other non-fan pressurization techniques that have been developed in Europe (Roulet 2002, Persily 1997). European codes have developed air tightness requirements and testing standards for construction of commercial buildings. Some states (Massachusetts, Wisconsin, Michigan, Rhode Island, Georgia, Minnesota, Florida) in the US have adopted codes specifying air permeance of components and assemblies. However to date, no code-required air-tightness testing has been included in the IECC. Nor has the government promoted air sealing of commercial buildings with the same levels of support as weatherization of residential buildings. This study investigates a number of the factors limiting widespread testing of commercial buildings and accurate prediction of energy savings due to air sealing. METHODS Two approaches for testing envelope air tightness of commercial buildings have been developed independently by a number of groups. The first approach is to mechanically force air through the envelope, and measure the flow required to maintain a known pressure differential. The second approach is to release a tracer gas and allow natural infiltration to change the concentration over time. Due to the relative simplicity and repeatability of the mechanical pressure methods, these are currently used by the residential industry for detached single-family homes to determine air leakage (e.g. ASHRAE 119). Larger commercial buildings present a number of unique conditions that must be addressed differently than in single-family homes. Four pressurization methods to determine the air-tightness of commercial buildings were reviewed and their requirements compared: ASTM E779-03 Standard Test Method for Determining Air Leakage Rate by Fan Pressurization, CGSB 149.15-96 Determination of the Overall Envelope Airtightness of Buidings by the Fan Pressurization Method Using the Buildings Air Handling Systems, British Air Testing and Measurement Association Standard 1: Measuring Air Permeability of Building Envelopes, and an ASHRAE Research Report “Protocol for Field Testing of Tall Buildings to Determine Envelope Air Leakage Rate”(Banfleth et al, 1998). All of the methods requires that testing be done to determine the amount of air flow required to create a specified pressure differential across the building envelope. These data are fit to a power law function to model the airflow induced by any pressure differential:

Q = CΔPn (1)

where Q is airflow rate (L/s), ΔP is the pressure differential across building envelope (Pa), C is the flow coefficient (L/s Pan), and n is the flow exponent (dimensionless).

The purpose of the pressurization test methods is to collect sufficient data to accurately determine the values of C and n. The resulting power law function can be used to predict infiltration under natural conditions (e.g. 4 Pa) and determine energy loss. Because the resistance to flow is affected by the shape of the airflow openings, the test methods all recognize the need to bound the value of n by the theoretical limits of 0.5 and 1.0. Tests with results outside these values are not considered valid. These limits represent the extreme cases of leakage occurring through fully turbulent flow (0.5) or fully laminar flow (1.0). In preparing to test a tall building envelope, there are two environmental factors that must be controlled to ensure the accuracy of the results: maximum outdoor wind speed, and the stack effect. The differential pressures created by a changing wind on the surfaces of an arbitrarily-shaped building are difficult to predict. However due to the relatively large pressure differentials created mechanically during building testing, the methods all suggest that the effect of wind be considered negligible if the wind speed is below a specified value. Table 1 lists some of the maximum allowable wind speeds using the different testing methods. Table 1.Comparison of Commercial Building Pressure Testing Standards Test Conditions. Testing Standard Max outdoor wind speed (m/s) Stack Effect ΔT height (m C) ASTM E779-03 CAN 149.15 British ATTMA Std 1 ASHRAE RP-935 (Protocol)

None (0-2 preferred) 5.56

6 4

≤ 200 <525 (10 story height)

<250 None (5-35 C outdoor temp)

Table 1 also includes information regarding the stack effect. Due to temperature stratification within the building envelope, the pressure differential across the building envelope is greater at the top of the building than at the base. This effect is accentuated by greater building height and greater indoor-outdoor temperature differential. The product of these two (height measured in meters and temperature difference measured in °C) is limited by each of the methods (RP-935 limits temperature difference alone). After reviewing the standards, the building was tested using the two principal techniques to create a pressure differential: a set of “blower doors”, and the building’s air handling system. ASTM E779-03 was used with the blower doors, and CAN 149.15 was used with the building’s air handling system. These tests were carried out on the F. Franklin Moon Library on the campus of the State University on New York College of Environmental Science and Forestry, located in Syracuse, NY (figure 1).

Figure 1 – Moon Library Figure 2 – Building sealed for testing The 1968 concrete/brick two-story structure has a 3950 m2 gross floor area. The floor plan is generally open with an elevator shaft and a large internal stairway. The building was depressurized for ASTM E779-03 by using a set of three blower doors in the main entrance and was pressurized for CAN 149.15 by using the building’s two supply air handlers (9650 l/s and 10679 l/s). Ventilation system inlets and outlets were sealed as necessary during the testing (Figure 2). Testing using the building air handler system was done by shutting off and sealing the exhaust system, and then using the supply air fans and varying the amount of recirculation air to pressurize the building. Airflow was determined by taking a hot-wire anemometer traverse of the supply duct. Testing using the blower doors was done by manually adjusting a set of three blower doors to create different pressure differentials and then summing the airflows through each to get a total air flow. The data acquisition and analysis requirements are shown in Table 2 Table 2. Acceptable Data Collection and Analysis Requirements. Testing method Number of data points Testing range (Pa) Fit test or quality ASTM E779-03 CAN 149.15 British ATTMA Std 1 ASHRAE RP-935

at least 5 5

7(10-15 for wind > 3 m/s) 6

10-60 0-75

10-50 or 20-60 12.5-75

Report 95% conf. limit r>0.990 r2>0.980

n/a RESULTS To perform a building envelope air tightness test, the weather conditions must match acceptable test conditions. To understand these limitations, the weather data for 2009 for the Syracuse, NY airport was compared to the environmental conditions required for testing a ten story building. The resulting number of days of acceptable test conditions is shown in Table 3. Table 3 Acceptable Days for Testing a Ten Story Building during 2009 in Syracuse, NY. Method Wind limit Stack effect limit Combined limits ASTM E779-03 83* 99 5

CAN 149.15 British ATTMA Std 1 ASHRAE RP-935

322 332 239

195 114 240

182 112 172

*(“preferred” wind speed) The number of days meeting the combined temperature and wind conditions varied from 5 (ASTM E779-03) to 182 (CAN 149.15). The wind speed cited by ASTM E779-03 is a “preferred” value, there is no “maximum” value mentioned in the standard. Although the wind and temperature values from 2009 are daily averages taken at the airport, building testing is often done at times and with exposures that correspond to these averages. The results of testing the building provided a full set of data for the ASTM E779-03 test. The CAN 149.15 test was stopped after only three data points were captured. After capturing the first two data points with one supply air fan, the second fan was started. As the recirculation dampers adjusted, the building pressure rose to over 112Pa, well outside the test range, and high enough to deform building components. At this point the damper was adjusted to a capture a reading at 75 pa and then the test was ended. The two power law curves fit to the data are shown in Figure 3. The results for the CAN 149.15 test are not valid due to a lack of data points. Further the curve fit to the data has an unacceptable flow exponent of < 0.5. This can be caused be testing a building with a surfaces that deform during the test, as possible occurred here.

Figure 3 – Air Leakage Graph for Moon Library Tests

Determination of the leakage at 75 Pa allowed for a number of comparisons to be made: The determination of average air tightness value (above ground envelope) of 1.79 l/s/m2 places the building well below the 6.6 l/s/m2 value of 29 low-rise buildings from northern climates compiled by Emmrich (Emmrich 2005). Including the below ground envelope, it can be shown to meet the US Army Corps of Engineers Standard (Zhivov, 2010) (1.08 l/sec/m2 <

1.268 l/sec/m2). Using units defined by the British Code, the volume leakage of 6.45 m3/m2/hr places this building below the code maximum for new buildings (13 m3/m2/hr at 75Pa) and near the average for new office construction in Britain (6.5 m3/m2/hr at 75 Pa). Using this single 75 Pa measurement the building can be shown to be “better than average” in envelope performance. However the determination of the flow coefficient and the flow exponent allow an extrapolation to be made. To predict energy use due to infiltration a leakage area (ASTM E779-03) of 0.464 m2 was calculated. This opening size helps determine the predicted leakage under natural conditions (4 Pa). The flow rate by extrapolation at 4 Pa is 1195 l/sec.

DISCUSSIONS The purpose of setting a value for maximum wind and stack effect is to reduce the noise in relation to the signal (mechanically induced pressures). Applying these requirements to a sample year eliminated from 50-98% of the days available for testing. In order to allow for testing during more varied conditions, a better approach may be to set a performance level for this ratio. Currently E779-03 requires that at least one pressure tap be placed on each side of the building, and more if the building is over three stories. CAN 149.15 requires that pressure taps be placed on the leeward side of the building and on the roof. Both of these are designed to average the wind pressure differentials on different building faces. The British ATTMA Std 1 requires that pressure differential before testing be measured for 30 seconds, and that during that time the pressure vary no more than +/- 5 Pa. This latter method allows for a performance based approach which may allow testing under more varied conditions. The US Army Corps of Engineers (Zhivov, 2010) suggest taking a set of 12 bias pressure readings over 20 seconds and requiring that no reading exceed 30% of the minimum test pressure. This approach more clearly associates the noise and signal levels. Redefining how the test conditions are determined might also allow the reporting requirements to be adapted. Currently the variety of number of data points required, testing range, and confidence limits or regression values (Table 2) do not align with the performance criteria suggested above. If the goal is to test a building for a code or contract requirement (e.g. leakage at 50 or 75 Pa) the data collection could be handled differently than if the goal is to predict natural leakage (at 2.5 or 4 Pa). Although the CAN 149.15 test failed to meet acceptable testing conditions to fit a curve, the measured leakage value at 75 Pa compared very well to the value from the ASTM E779 test (within 1.5%). Currently ASHRAE 119 allows the leakage rates determined for single-family homes to be used to predict energy loss, and industry methods have been standardized to determine the return on investment for air-sealing and weatherization. This has allowed for individual and government investment to flow into this industry. To advance the development of a similar system for the commercial building sector, the testing parameters need to be adjusted in light of the unique considerations of commercial buildings. The results from these tests need to be combined with a methodology (e.g. Emmrich 2005) to predict energy savings, and these results have to be validated. CONCLUSIONS

Determining appropriate cost-efficient energy conservation measures in existing commercial buildings will require widespread, consistent air tightness testing. A study of the current methods showed that there are differences in testing requirements and data presentation among the methods that could limit their wide spread use. The sample building showed that tests using different methods to determine leakage at 75 Pa provided nearly identical results. This information could be very useful for code or contract compliance. However to predict energy savings due to air sealing, the quality of the test data must be defined by how well it correlates to actual infiltration values. Further testing of buildings will be required to develop and validate these metrics. ACKNOWLEDGEMENT This work would not have been possible without the invaluable assistance of Bruce Marcham from the SUNY-ESF Physical Plant. Thanks as well goes to the NYS Weatherization Directors Association and Dale Sherman for use of the blower doors. Weather data on campus was provided by the SUNY-ESF mapping lab. REFERENCES ASTM 1995 Standard E741-95 Test method for determining air change in a single zone by

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