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Feasibility of building envelope air leakage measurement using combination of air-handler and blower door
Energy and Buildings 62 (2013) 436–441
Contents lists available at SciVerse ScienceDirect
Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild
Feasibility of building envelope air leakage measurement using combination of air-handler and blower door Min-Hwi Kim a , Jae-Hun Jo b , Jae-Weon Jeong a,∗ a b
Division of Architectural Engineering, Hanyang University, Seoul 133-791, Republic of Korea Division of Architectural Engineering, Inha University, Incheon 402-751, Republic of Korea
a r t i c l e
i n f o
Article history: Received 6 December 2012 Received in revised form 25 January 2013 Accepted 15 March 2013 Keywords: Building air tightness Air handler fan pressurization test Blower door test Envelope leakage
a b s t r a c t An air-handler fan pressurization method can be used to estimate envelope leakage in large or tall buildings. However, because the size of a building’s air handling system is designed only to meet heating and cooling demands, there may be many unanticipated problems on the test site. For example, one may not be able to perform the envelope leakage test using the air-handler fan(s) with relatively high pressure differences across the building envelope (e.g. 50–75 Pa). In order to overcome the insufficient pressurization problem faced during the air handler fan pressurization test, a combination of an air-handler and a blower door is proposed and verified by performing a pressurization test in an office building. It was found that the proposed method is feasible for evaluating the overall envelope leakage in large or tall buildings. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Envelope leakage is caused by pressure differences across a building envelope, that are generated by wind and/or stack effects. Unbalanced air flow introduced by a centralized HVAC system or by mechanical ventilation equipment may also affect the amount of envelope leakage [1]. Air leakage or infiltration in buildings may cause an increase in heating and cooling demands, noise, condensation and mold growth problems on the exterior wall surface. The building air tightness has become an important factor affecting indoor air quality and energy consumption in a building [2–4]. Generally, there are two methods of measuring air leakage in a building: the tracer gas method [5] and the fan pressurization method [6]. The former has better accuracy than the fan pressurization method, but requires well-trained experts and has a higher measurement cost. Therefore, the latter, which is relatively inexpensive and simple, is more widely used. As for the fan pressurization approach, the blower door test method [7,8] is commonly used in residential or small buildings. Envelope leakage is measured by pressurizing (or depressurizing) the building using a fan installed on a door or an operable window. The pressure inside the building is increased to 70 Pa by the blower door fan(s) and reduced gradually at 5–10 Pa intervals by modulating the fan speed. By measuring the pressure difference and coincident blower door fan flow rate, the leakage coefficient (C)
∗ Corresponding author. Tel.: +82 2 2220 2370; fax: +82 2 2220 1945. E-mail address: [email protected] (J.-W. Jeong). 0378-7788/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.enbuild.2013.03.034
and exponent (n) of the power-law equation (Eq. (1)) is determined [6,9–11]. The values of C and n represent the leakage characteristics of the building envelope. Q = C · (P)
n
(1)
where Q is the air leakage rate, m3 /s, C the leakage coefficient, m3 /(s Pan ), P the pressure difference, Pa, n the leakage exponent, dimensionless. In general, the blower door test approach can also be applied to air leakage measurement in large and tall buildings. However, it may require high air flow to reach the initial target differential pressure (i.e. over 50 Pa), so one may need to use many blower door fans or a large fan [12]. On the other hand, the CGSB 149.1596 standard [12] and some literature [13–17] recommend the use of air-handlers that already exist in a test building for measuring air leakage, especially in a large and tall building. The air handler fan pressurization is a practical solution to measure the envelope leakage in tall or large buildings. However, since the capacity of the air-handler fan is commonly selected to meet the ventilation and air conditioning needs of the zone, the airflow may not be sufficient to make the pressure difference exceed 20 Pa. In order to solve the insufficient pressurization problem in the use of the air handler fan, the combination of both air-handler and blower door fans is suggested in this research. In terms of envelope leakage measurement in tall and large buildings using the air-handler fan, there are some existing measurement standards which can be applied. ASTM E779-10 [6] and CIBSE TM23 [10] refer to the measurement of air tightness using a large fan. ISO 9972 [9] and EN 13829 [11] indicate the typical fan
3 times or more Pressurize + depressurize Flow coefficient (C), flow exponent (n)
25–50 Pa maximum value: 50–60 Pa (larger buildings: 60 Pa) 5–10 times (10 Pa interval) Pressurize + depressurize m3 /(h m2 ) @50 Pa
3 m/s
Typical floor wind speed: 3 m/s or less The Meteorological Agency wind speed: 6 m/s or less Smaller buildings: minimum 50 Pa–100 Pa·larger building: 25–50 Pa 5 times Pressurize + depressurize ACH50 0–2 m/s
5–10 times Pressurize + depressurize ELA@4 Pa
10–60 Pa
◦
ASTM E779–03
In the literature [13,14], conventional fan pressurization methods using blower doors or air-handlers have not be able to pressurize a test zone up to the recommended target pressure (e.g. 50 Pa) in large and tall buildings. In order to solve this insufficient pressurization problem, a combination of both blower door and air handler fans is suggested. When a centralized air handler cannot pressurize the test zone sufficiently, the blower door may be used simultaneously with the air handler to pressurize the zone up to the target pressure (e.g. 50–60 Pa). By modulating the blower door fan flow, one may reduce the pressure differentials gradually in the conventional fan pressurization test (Fig. 1). The air handler fan flow is maintained at its full capacity during the test period as controlled by the blower door. The air handler fan flow begins to decrease when the blower
Table 1 Test conditions in existing fan pressurization test standards.
2.3. Air-handler and blower door combination approach
ISO 9972:2006/EN13829
CGSB standard 149.15 [12] describes a detailed procedure for a building leakage test using air-handlers existing in a test building. Shaw et al. [16,17] measured envelope leakage in several multistory buildings using these air-handlers. Tamura and Shaw [24] obtained air leakage range of 610∼2440 cm3 /(s m2 ) by conducting air-handler fan pressurization tests for eight Canadian buildings. By normalizing the measured air leakage for the unit envelope area, an air tightness performance index was categorized into three classes: tight (500 cm3 /(s m2 )), average (1500 cm3 /(s m2 )), and leaky (3000 cm3 /(s m2 )) at 75 Pa. Bahnfleth and Yuill [13] performed the air handler fan pressurization test in two large buildings. They compared the test results with those acquired by the tracer gas and the orifice plate methods, and indicated that the air handler fan pressurization approach is applicable to assess envelope leakage. Jeong et al. [14] measured the envelope leakage in two university buildings using an air handler fan pressurization approach. In addition to the leakage characteristics, they studied the effect of the elevator shaft on the whole building air leakage rate.
Wind speed limit (or temperature limit) Pressure difference measurement range Number of measurement Pressurization/depressurization Derivation of the result
2.2. Pressurization test using air-handlers
Outdoor/indoor temperature difference: <10 ◦ C
CIBSE TM23:3000
The method of using multiple blower door fans in large building leakage tests is basically the same as using a single blower door fan for residential or small building leakage tests. However, when using multiple blower door fans, the interlock of every fan is important because they should work as one single fan during the test. As indicated in the literature [18,19], the blower door(s) should be located on each floor to avoid a pressure differential between floors. Existing blower door manufacturers [20,21] provide automatic control programs to control multiple fans from a single computer. On the other hand, CIBSE TM-23 prescribes air leakage measurement using a large fan. Sharples et al. [22] performed a fan pressurization test using a 90 kW, 2000-mm diameter fan in several large buildings which had over 5000 m2 floor area. England’s BRE [23] also conducted air leakage measurements using a large fan in a complex building.
Outdoor/indoor temperature difference times building height <250 mK
2.1. Blower door test method
Ambient temperature: 5–35 C outdoor and indoor temperature difference times building height: <200 m◦ C
CAN/CGSB 149.15-96
2. Leakage measurement in tall and large buildings
Stack effect driving force
pressurization method, but it can also be applicable to tall and large building envelope leakage tests. Meanwhile, CAN/CGSB 149.15 [12] is the standard that describes the air-handler fan pressurization approach. Table 1 is a summary of test conditions recommended by existing measurement standards.
437
Temperature limit for each floor Ambient temperature, ◦ C Building stories ∼10 5 5 11–20 21–30 10 31∼ 15 20 km/h (5.56 m/s) (8–10 h then prognostic wind speed) 0–75 Pa
M.-H. Kim et al. / Energy and Buildings 62 (2013) 436–441
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M.-H. Kim et al. / Energy and Buildings 62 (2013) 436–441
Fan HVAC system
[13] suggested a tracer gas or orifice plate method. Jeong et al. [14] used fan inlet sensors installed at the inlet of the supply air fan. One may also use existing air flow sensors installed for a building’s mechanical system control if sensor accuracy can be secured. Otherwise, conventional duct insertion type portable flow measuring devices (e.g. pitot tubes) can be used [25,26], which would reduce the accuracy of the measurement. 2.4.2. Preparation of air-handler for the fan pressurization test When an air-handler fan is used for the pressurization test, the air handling unit should operate in 100% outdoor air mode (i.e. economizer mode). The exhaust air outlet (or damper) and return air damper of the air-handler should be closed and sealed (Fig. 2). If the exhaust air outlet and return air damper cannot be sealed since they are not accessible, all the exhaust air grills inside the test zone should be sealed.
Blower Door Fan
Fig. 1. Air leakage test configuration using air-handler fan and blower door.
door cannot reduce the zone pressure below a certain level. The proposed approach has not been suggested before. 2.4. Combination test process In the preparation stage of the test, one should consult mechanical drawings and visit the test site to identify the location, accessibility, and service zone of each air-handler. The outdoor air inlet and exhaust air outlet locations, and the controllability of dampers and fans in each air handler should also be checked. After sealing leakage components which should not be considered as envelope leakage, one may activate the air handler at 100% of the outdoor air mode (e.g. economizer mode) and check the maximum pressure differential built in the test zone. If the zone pressure reaches the target pressure, the test can be performed by the air handler only. Otherwise, one should determine whether to use the blower door in parallel with the air handler. Once the test is started, the rest of the procedure is identical to the conventional fan pressurization test approach. 2.4.1. Supply air flow measurement in the air-handler fan pressurization test In order to measure the outdoor air (or supply air) flow rate in the air-handler fan pressurization test, Bahnfleth and Yuill
2.4.3. Test site preparation prior to air leakage testing Elevator shaft vents and toilet vents on the roof should be sealed if they are accessible. Otherwise, all elevator doors and toilet exhaust grilles on each floor should be sealed. All the interior doors should remain open to make the entire test zone reach a uniform pressure differential during the test. CGSB-149.15 [12] recommends that the outside pressure should be measured in at least three different locations (i.e. the first, the middle, and the top floors), and then averaged to get an instantaneous averaged outside pressure. As for the inside pressure, the CGSB standard recommends that it should be measured at the center of the middle floor. Bahnfleth and Yuill [13] and the ASTM standard [6] suggest measuring the outside pressure by averaging pressures measured in four different directions of the building envelope so as to minimize the effect of wind. 2.4.4. Testing procedure In the fan pressurization test, the indoor-to-outdoor pressure difference should be reduced gradually from the maximum (e.g. 50–60 Pa) to low pressure in 5–10 Pa intervals. Both the air-handler and the blower door are operated until the pressure difference reaches the maximum target pressure, and then the zone pressure decreases by adjusting the blower door fan flow. It is relatively easier to adjust the flow rate of the blower door fan than the air-handler fan in the field test. When the blower door fan flow reaches zero and the zone pressure is further reduced, the air-handler fan flow begins to adjust. The air flow rate of the air-handler can be adjusted by modulating the inlet vane of the fan, the fan speed, or the supply air damper. The indoor-to-outdoor pressure differences before and after the test should be measured to perform the zero-pressure correction.
Fig. 2. Preparation of air handler for the fan pressurization test.
M.-H. Kim et al. / Energy and Buildings 62 (2013) 436–441
439
Table 2 TEST-1 results. Test no.
Test 1–1 Test 1–2 Test 1–3 Test 1–4 Test 1–5
Building pressure (Pa)
11.37 10.11 7.70 4.58 4.62
OA flow rate (m3 /s)
Envelope leakage (m3 /s)
AHU-1
AHU-2
AHU-3
8.10 7.19 6.28 5.36 4.45
6.80 6.05 5.30 4.55 3.80
0.83 0.83 0.83 0.83 0.83
14.46 12.75 11.04 9.34 7.63
4.1. TEST-1: air-handler fan pressurization test
Fig. 3. Test building.
After the test is completed, all sealing locations must be checked and sealing materials should be removed. All the dampers and fans of air handlers should return to normal operation mode. Recording the sealing locations and system operation modes during the test is very helpful for the final check process.
3. Field measurement 3.1. Test building overview The test building (Fig. 3) is a 5-story office building located in Daejeon, Korea. It is a steel-structured building with 616,400 m2 total floor area, served by four air handlers. One air handler (i.e. AHU-4) is installed in the mechanical room on the basement floor, serving the first and the second floors. The air handler in the first floor mechanical room (i.e. AHU-1) serves the atrium. Two air handlers (i.e. AHU-2 and AHU-3) are located in the mechanical room on the fifth floor and serve the rest of the building. The proposed fan pressurization test was performed for two consecutive days. 3.2. Measuring equipment
TEST-1 was performed on April 21, 2012 using existing airhandler fans. Outdoor air temperature and wind speed were 12.52 ± 0.23 ◦ C and 1.26 ± 0.72 m/s, respectively, which satisfies the existing measurement standards. All the interior doors which did not have a security problem were opened during the test. The elevator shaft vent and restroom vents were all sealed on the rooftop. Differential pressure gauges were installed on each floor to measure the indoor-to-outdoor pressure differences. The air flow rates of air-handlers were adjusted by modulating the fan speed. During the test, return air dampers and exhaust air dampers were completely closed, and the exhaust air outlets located on the roof and ground floor were completely sealed with plastic sheeting. In this field test, AHU-4 was out of order, unfortunately, so the test was performed only with the remaining three air handlers. Table 2 shows the TEST-1 results. The outdoor air flow rates at each air hander were measured for each of the five different building pressures (i.e. Test 1–1 to Test 1–5). The maximum pressure difference realized in TEST-1 was 11.37 Pa. Although this pressure difference was much lower than the conventional target value, the fan pressurization test was performed by decreasing the building pressure gradually from the maximum pressure acquired in Test 1–1. The base pressure measured before and after the test was −1.2 Pa. Air flow rates of the air-handlers were corrected for the outdoor and indoor temperature difference based on ASTM standards. Q [m3 /s] = 3.557(P [Pa])
0.563
Fig. 4 shows the log–log plot of the TEST-1 results. The resulting power-law equation is expressed as Eq. (2). The R2 value of the power-law equation is 0.91.
The blower door equipment used in the test was the Retrotect OMG model with three fans at a maximum of 12.74 m3 /s of air flow rate. The measurement accuracy is ±5% for air flow rate and ±0.2 Pa for pressure. Three fans constituted the blower door module. Two modules, that is, six blower door fans, were used in the test. The indoor-tooutdoor pressure difference was measured with Testo 521-3, which has a measuring range of 0–2.5 hPa and an accuracy of ±0.1%. The outdoor air temperature, humidity, and wind speed were measured with a Vantage Pro-2 weather station.
4. Measurement results Fan pressurization tests were performed by using the airhandlers (TEST-1), and both air handler and blower door fans (TEST-2). The test results acquired from TEST-1 and TEST-2 were compared with each other for verifying the reliability of the proposed measurement approach (i.e. combination of air handlers and blower doors).
(2)
Fig. 4. Pressurization test using the air-handler fan.
440
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Table 3 TEST-2 results. Test no.
Building pressure (Pa)
Blower door fan flow rate (m3 /s)
Test 2–1 Test 2–2 Test 2–3 Test 2–4 Test 2–5
48.92 39.89 35.66 32.59 28.08
15.80 13.25 11.87 11.14 9.83
OA flow rate (m3 /s)
Envelope leakage (m3 /s)
AHU-1
AHU-2
AHU-3
6.35 6.35 6.35 6.35 6.35
5.21 5.21 5.21 5.21 5.21
0.83 0.83 0.83 0.83 0.83
28.99 26.38 24.96 24.20 22.86
Table 4 Comparison of predicted air leakages at 4 Pa and 50 Pa.
Leakage rate, m3 /s @ 4 Pa Leakage rate, m3 /s @ 50 Pa
Eq. (2) (TEST-1)
Eq. (3) (TEST-2)
7.85 30.97
9.82 29.12
50 Pa which could not be reached in TEST-1. The log–log plot of TEST-2 results and the power-law equation (Eq. (3)) derived from it are shown in Fig. 5. The R2 -value of the power-law equation was 0.99. Q [m3 /s] = 5.415 (P [Pa])
Fig. 5. Pressurization test using the air-handler fan and blower door fan.
4.2. TEST-2: air-handler and blower door combination TEST-2 was performed by pressurizing the test building using both the air-handler and blower door simultaneously. The blower door module was installed at the main entrance located on the first floor. TEST-2 started with measuring the base pressure, and AHU-1 through AHU-3 operated at their maximum air flow to pressurize the building. The blower door was activated to increase the building pressure up to the target pressure (i.e. 50 Pa) which could not be reached by the air handlers only. By reducing the blower door fan flow, a series of pressurization tests were performed at 5 Pa intervals until the building pressure reached 30 Pa. In TEST-2, air handlers kept working at their initial operation mode during the test. Table 3 shows the TEST-2 results. The base pressures measured before and after the test were 5.81 Pa. In TEST-2, one can observe that the maximum pressure difference between the air handler and blower door fans was close to
0.430
(3)
There could be significant intervention in air-handler fan flows due to operation of the blower door. However, the static pressure of the air-handler fans was monitored throughout the whole test (Fig. 6) and did not affect the blower door operation. Consequently, the combination of air handler and blower door fans is applicable to the building pressurization test when the test zone cannot be pressurized sufficiently by air-handlers only. The envelope leakages of the test building at 4 Pa and 50 Pa, predicted by two different power-law equations (i.e. Eqs. (2) and (3)), are summarized in Table 4. It shows that Eq. (3) derived from TEST2 provides 23% higher envelope leakage at 4 Pa compared with Eq. (1) from TEST-1. However, one can also see that there are insignificant discrepancies between the leakage rates at 50 Pa predicted by the two power-law equations. In general, the air leakage rate measured or predicted at 50 Pa is commonly used to rate the air tightness of a building. Consequently, one may conclude that the envelope leakage measurement approaches used in both TEST-1 and TEST-2 can be used for predicting the value at the 50 Pa pressure difference. On the other hand, the Effective Leakage Area (AL , m2 ) at the 4 Pa pressure difference was determined for each measurement approach using ASTM E779-03. The ELA range for the 95% confidence interval in each test method was also calculated (Table 5). It shows that the ELA values match well in the given confidence range, so one can conclude that the combination of air handler and
Fig. 6. Air handler fan static pressure during the measurement.
M.-H. Kim et al. / Energy and Buildings 62 (2013) 436–441 Table 5 Assessment of the entire building air leakage area. Test method 2
ELA, (@ 4 Pa, AL , m ) 95% confidence interval
441
References
TEST-1
TEST-2
2.95 (1.38–6.30)
3.67 (1.96–6.88)
blower door fans can also predict the envelope leakage at the low rated pressure differential (i.e. 4 Pa). 4.3. Man-hour information In the air handler fan pressurization test (i.e. TEST-1), ten people sealed the selected locations in the test building for four hours. By normalizing it for the envelope area of the building (i.e. 3654.7 m2 ), one may conclude that 0.01 man-hours was taken per unit envelope area (i.e. 0.01 man-hour/m2 ) in the sealing activity. A similar result can be found in the literature [13]. As for the differential pressure gauge installation, two people worked for one hour to locate five pressure gauges with pressure tabs (i.e. 0.4 man-hour/pressure gauge). In TEST-2, the man-hours for installing the blower door module were required in addition to comparing with TEST-1. In the test building, two persons spent a half hour to locate and adjust the blower door (i.e. 1.0 man-hour/blower door). 5. Conclusion In this research, it was found that the air-handler fan pressurization approach (i.e. TEST-1) may not generate an adequate indoor-to-outdoor pressure difference recommended by existing test standards, because of the insufficient capacity of air handler fans and/or unfavorable site conditions. However, it was also found that the power-law equation derived from the air-handler fan pressurization test can provide reliable envelope leakage not only for low pressure (i.e. 4 Pa) but also for high pressure (i.e. 50 Pa). The suggested method of combining both air-handler and blower door fans (i.e. TEST-2) shows that one can build up the building pressure close to the recommended target pressure, so the test can be performed with more favorable conditions. The reliability of test results acquired from the suggested method was not much enhanced compared with the air-handler fan pressurization approach. However, higher target pressure, which can be acquired by the suggested approach, would be appropriate for the tall building cases in order to minimize the measurement uncertainty caused by harsh outdoor conditions. Acknowledgement This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MEST) (No. 2012001927).
[1] J. Jokisalo, J. Kurnitski, M. Korpi, T. Kalamees, J. Vinha, Building leakage, infiltration, and energy performance analyses for Finnish detached houses, Building and Environment 44 (2009) 377–387. [2] I. Hers, R. Zapf-Gilje, L. Li, J. Atwater, The use of indoor air measurements to evaluate intrusion of subsurface VOC vapors into buildings, Journal of the Air & Waste Management Association 51 (9) (2001) 1318–1331. [3] M.H. Sherman, J.M. Logue, B.C. Singer, Infiltration effects on residential pollutant concentrations for continuous and intermittent mechanical ventilation approaches, HVAC&R Research 17 (2) (2011) 159–173. [4] S. Chen, M.D. Levine, H. Li, P. Yowargana, L. Xie, Measured air tightness performance of residential buildings in North China and its influence on district space heating energy use, Energy and Buildings 51 (2012) 157–164. [5] American Society for Testing and Materials, ASTM E741-00 Test method for determining air change in a single zone by tracer gas dilution. [6] American Society for Testing and Materials, ASTM E779-10 Standard test method for determining air leakage rate by fan pressurization. [7] A. Sfakianaki, K. Pavlou, M. Santamouris, I. Livada, M.N. Assimakopoulos, P. Mantas, Air-tightness measurements of residential houses in Athens, Greece, Building and Environment 43 (2008) 398–405. [8] F.R.A. Alfano, M. Dell’Isola, G. Ficco, F. Tassini, Experimental analysis of air tightness in Mediterranean buildings using the fan pressurization method, Building and Environment 53 (2012) 16–25. [9] International Organization for Standardization, ISO Standard 9972 Thermal performance of buildings – determination of air permeability of buildings – fan pressurization method. [10] Charted Institution of Building Services Engineers, CIBSE Technical Memorandum TM23 Testing Buildings for Air Leakage. [11] European Committee for Standardization, EN 13829 Thermal performance of buildings – determination of air permeability of buildings – fan pressurization method. [12] Canadian General Standards Board, CAN/CGSB-149. 15-96 Determination of the overall envelope airtightness of buildings by the fan pressurization method using the building’s air handing systems. [13] W.P. Bahnfleth, G.K. Yuill, B.W. Lee, Protocol for field testing of tall buildings to determine envelope air leakage rate, Final report, ASHRAE RP-935, Atlanta, American Society of Heating, Refrigeration and Air-Conditioning Engineers Inc., 1998. [14] J.W. Jeong, J. Firrantello, J. Freihaut, W. Bahnfleth, A. Musser, Case studies of building envelope leakage measurement using an air-handler fan pressurization approach, Building Services Engineering Research and Technology 29 (2008) 137–155. [15] C.Y. Shaw, L. Jones, Airtightness and air infiltration of school buildings, ASHRAE Transactions 85 (1979) 85–95. [16] C.Y. Shaw, D.M. Sander, G.T. Tamura, Air leakage measurements of the exterior walls of tall buildings, ASHRAE Transactions 79 (1973) 40–48. [17] C.Y. Shaw, J.T. Reardon, M.S. Cheung, Changes in air leakage levels of six Canadian office buildings, ASHRAE Journal (1993). [18] A. Zhivov, D. Bailey, D. Herron, Air Leakage Test Protocol for Measuring Air Leakage in Buildings, US Army Engineer Research and Development Center, Champaign, IL/Washington, DC, 2009. [19] C. Genge, Controlling air leakage in tall buildings, ASHRAE Journal (2009) 50–60. [20] Retrotect, http://retrotec.com/ (accessed 12.11.12). [21] BlowerDoor GmbH, http://www.blowerdoor.de/en.html (accessed 12.11.12). [22] S. Sharples, S. Closs, N. Chilengwe, Airtightness testing of very large buildings: a case study, Building Services Engineering Research and Technology 26 (2005) 167–172. [23] BRE, Building Research Establishment, http://www.bre.co.uk/ (accessed 12.11.12). [24] T.G. Tamura, C.Y. Shaw, Studies on exterior wall air tightness and air infiltration of tall buildings, ASHRAE Transactions 82 (1976) 179–190. [25] The Energy conservatory, http://www.energyconservatory.com/products/ products6-.htm (accessed 12.11.12). [26] Paragon controls incorporated, http://www.paragoncontrols.com/ (accessed 12.11.12).
Contents lists available at SciVerse ScienceDirect
Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild
Feasibility of building envelope air leakage measurement using combination of air-handler and blower door Min-Hwi Kim a , Jae-Hun Jo b , Jae-Weon Jeong a,∗ a b
Division of Architectural Engineering, Hanyang University, Seoul 133-791, Republic of Korea Division of Architectural Engineering, Inha University, Incheon 402-751, Republic of Korea
a r t i c l e
i n f o
Article history: Received 6 December 2012 Received in revised form 25 January 2013 Accepted 15 March 2013 Keywords: Building air tightness Air handler fan pressurization test Blower door test Envelope leakage
a b s t r a c t An air-handler fan pressurization method can be used to estimate envelope leakage in large or tall buildings. However, because the size of a building’s air handling system is designed only to meet heating and cooling demands, there may be many unanticipated problems on the test site. For example, one may not be able to perform the envelope leakage test using the air-handler fan(s) with relatively high pressure differences across the building envelope (e.g. 50–75 Pa). In order to overcome the insufficient pressurization problem faced during the air handler fan pressurization test, a combination of an air-handler and a blower door is proposed and verified by performing a pressurization test in an office building. It was found that the proposed method is feasible for evaluating the overall envelope leakage in large or tall buildings. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Envelope leakage is caused by pressure differences across a building envelope, that are generated by wind and/or stack effects. Unbalanced air flow introduced by a centralized HVAC system or by mechanical ventilation equipment may also affect the amount of envelope leakage [1]. Air leakage or infiltration in buildings may cause an increase in heating and cooling demands, noise, condensation and mold growth problems on the exterior wall surface. The building air tightness has become an important factor affecting indoor air quality and energy consumption in a building [2–4]. Generally, there are two methods of measuring air leakage in a building: the tracer gas method [5] and the fan pressurization method [6]. The former has better accuracy than the fan pressurization method, but requires well-trained experts and has a higher measurement cost. Therefore, the latter, which is relatively inexpensive and simple, is more widely used. As for the fan pressurization approach, the blower door test method [7,8] is commonly used in residential or small buildings. Envelope leakage is measured by pressurizing (or depressurizing) the building using a fan installed on a door or an operable window. The pressure inside the building is increased to 70 Pa by the blower door fan(s) and reduced gradually at 5–10 Pa intervals by modulating the fan speed. By measuring the pressure difference and coincident blower door fan flow rate, the leakage coefficient (C)
∗ Corresponding author. Tel.: +82 2 2220 2370; fax: +82 2 2220 1945. E-mail address: [email protected] (J.-W. Jeong). 0378-7788/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.enbuild.2013.03.034
and exponent (n) of the power-law equation (Eq. (1)) is determined [6,9–11]. The values of C and n represent the leakage characteristics of the building envelope. Q = C · (P)
n
(1)
where Q is the air leakage rate, m3 /s, C the leakage coefficient, m3 /(s Pan ), P the pressure difference, Pa, n the leakage exponent, dimensionless. In general, the blower door test approach can also be applied to air leakage measurement in large and tall buildings. However, it may require high air flow to reach the initial target differential pressure (i.e. over 50 Pa), so one may need to use many blower door fans or a large fan [12]. On the other hand, the CGSB 149.1596 standard [12] and some literature [13–17] recommend the use of air-handlers that already exist in a test building for measuring air leakage, especially in a large and tall building. The air handler fan pressurization is a practical solution to measure the envelope leakage in tall or large buildings. However, since the capacity of the air-handler fan is commonly selected to meet the ventilation and air conditioning needs of the zone, the airflow may not be sufficient to make the pressure difference exceed 20 Pa. In order to solve the insufficient pressurization problem in the use of the air handler fan, the combination of both air-handler and blower door fans is suggested in this research. In terms of envelope leakage measurement in tall and large buildings using the air-handler fan, there are some existing measurement standards which can be applied. ASTM E779-10 [6] and CIBSE TM23 [10] refer to the measurement of air tightness using a large fan. ISO 9972 [9] and EN 13829 [11] indicate the typical fan
3 times or more Pressurize + depressurize Flow coefficient (C), flow exponent (n)
25–50 Pa maximum value: 50–60 Pa (larger buildings: 60 Pa) 5–10 times (10 Pa interval) Pressurize + depressurize m3 /(h m2 ) @50 Pa
3 m/s
Typical floor wind speed: 3 m/s or less The Meteorological Agency wind speed: 6 m/s or less Smaller buildings: minimum 50 Pa–100 Pa·larger building: 25–50 Pa 5 times Pressurize + depressurize ACH50 0–2 m/s
5–10 times Pressurize + depressurize ELA@4 Pa
10–60 Pa
◦
ASTM E779–03
In the literature [13,14], conventional fan pressurization methods using blower doors or air-handlers have not be able to pressurize a test zone up to the recommended target pressure (e.g. 50 Pa) in large and tall buildings. In order to solve this insufficient pressurization problem, a combination of both blower door and air handler fans is suggested. When a centralized air handler cannot pressurize the test zone sufficiently, the blower door may be used simultaneously with the air handler to pressurize the zone up to the target pressure (e.g. 50–60 Pa). By modulating the blower door fan flow, one may reduce the pressure differentials gradually in the conventional fan pressurization test (Fig. 1). The air handler fan flow is maintained at its full capacity during the test period as controlled by the blower door. The air handler fan flow begins to decrease when the blower
Table 1 Test conditions in existing fan pressurization test standards.
2.3. Air-handler and blower door combination approach
ISO 9972:2006/EN13829
CGSB standard 149.15 [12] describes a detailed procedure for a building leakage test using air-handlers existing in a test building. Shaw et al. [16,17] measured envelope leakage in several multistory buildings using these air-handlers. Tamura and Shaw [24] obtained air leakage range of 610∼2440 cm3 /(s m2 ) by conducting air-handler fan pressurization tests for eight Canadian buildings. By normalizing the measured air leakage for the unit envelope area, an air tightness performance index was categorized into three classes: tight (500 cm3 /(s m2 )), average (1500 cm3 /(s m2 )), and leaky (3000 cm3 /(s m2 )) at 75 Pa. Bahnfleth and Yuill [13] performed the air handler fan pressurization test in two large buildings. They compared the test results with those acquired by the tracer gas and the orifice plate methods, and indicated that the air handler fan pressurization approach is applicable to assess envelope leakage. Jeong et al. [14] measured the envelope leakage in two university buildings using an air handler fan pressurization approach. In addition to the leakage characteristics, they studied the effect of the elevator shaft on the whole building air leakage rate.
Wind speed limit (or temperature limit) Pressure difference measurement range Number of measurement Pressurization/depressurization Derivation of the result
2.2. Pressurization test using air-handlers
Outdoor/indoor temperature difference: <10 ◦ C
CIBSE TM23:3000
The method of using multiple blower door fans in large building leakage tests is basically the same as using a single blower door fan for residential or small building leakage tests. However, when using multiple blower door fans, the interlock of every fan is important because they should work as one single fan during the test. As indicated in the literature [18,19], the blower door(s) should be located on each floor to avoid a pressure differential between floors. Existing blower door manufacturers [20,21] provide automatic control programs to control multiple fans from a single computer. On the other hand, CIBSE TM-23 prescribes air leakage measurement using a large fan. Sharples et al. [22] performed a fan pressurization test using a 90 kW, 2000-mm diameter fan in several large buildings which had over 5000 m2 floor area. England’s BRE [23] also conducted air leakage measurements using a large fan in a complex building.
Outdoor/indoor temperature difference times building height <250 mK
2.1. Blower door test method
Ambient temperature: 5–35 C outdoor and indoor temperature difference times building height: <200 m◦ C
CAN/CGSB 149.15-96
2. Leakage measurement in tall and large buildings
Stack effect driving force
pressurization method, but it can also be applicable to tall and large building envelope leakage tests. Meanwhile, CAN/CGSB 149.15 [12] is the standard that describes the air-handler fan pressurization approach. Table 1 is a summary of test conditions recommended by existing measurement standards.
437
Temperature limit for each floor Ambient temperature, ◦ C Building stories ∼10 5 5 11–20 21–30 10 31∼ 15 20 km/h (5.56 m/s) (8–10 h then prognostic wind speed) 0–75 Pa
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Fan HVAC system
[13] suggested a tracer gas or orifice plate method. Jeong et al. [14] used fan inlet sensors installed at the inlet of the supply air fan. One may also use existing air flow sensors installed for a building’s mechanical system control if sensor accuracy can be secured. Otherwise, conventional duct insertion type portable flow measuring devices (e.g. pitot tubes) can be used [25,26], which would reduce the accuracy of the measurement. 2.4.2. Preparation of air-handler for the fan pressurization test When an air-handler fan is used for the pressurization test, the air handling unit should operate in 100% outdoor air mode (i.e. economizer mode). The exhaust air outlet (or damper) and return air damper of the air-handler should be closed and sealed (Fig. 2). If the exhaust air outlet and return air damper cannot be sealed since they are not accessible, all the exhaust air grills inside the test zone should be sealed.
Blower Door Fan
Fig. 1. Air leakage test configuration using air-handler fan and blower door.
door cannot reduce the zone pressure below a certain level. The proposed approach has not been suggested before. 2.4. Combination test process In the preparation stage of the test, one should consult mechanical drawings and visit the test site to identify the location, accessibility, and service zone of each air-handler. The outdoor air inlet and exhaust air outlet locations, and the controllability of dampers and fans in each air handler should also be checked. After sealing leakage components which should not be considered as envelope leakage, one may activate the air handler at 100% of the outdoor air mode (e.g. economizer mode) and check the maximum pressure differential built in the test zone. If the zone pressure reaches the target pressure, the test can be performed by the air handler only. Otherwise, one should determine whether to use the blower door in parallel with the air handler. Once the test is started, the rest of the procedure is identical to the conventional fan pressurization test approach. 2.4.1. Supply air flow measurement in the air-handler fan pressurization test In order to measure the outdoor air (or supply air) flow rate in the air-handler fan pressurization test, Bahnfleth and Yuill
2.4.3. Test site preparation prior to air leakage testing Elevator shaft vents and toilet vents on the roof should be sealed if they are accessible. Otherwise, all elevator doors and toilet exhaust grilles on each floor should be sealed. All the interior doors should remain open to make the entire test zone reach a uniform pressure differential during the test. CGSB-149.15 [12] recommends that the outside pressure should be measured in at least three different locations (i.e. the first, the middle, and the top floors), and then averaged to get an instantaneous averaged outside pressure. As for the inside pressure, the CGSB standard recommends that it should be measured at the center of the middle floor. Bahnfleth and Yuill [13] and the ASTM standard [6] suggest measuring the outside pressure by averaging pressures measured in four different directions of the building envelope so as to minimize the effect of wind. 2.4.4. Testing procedure In the fan pressurization test, the indoor-to-outdoor pressure difference should be reduced gradually from the maximum (e.g. 50–60 Pa) to low pressure in 5–10 Pa intervals. Both the air-handler and the blower door are operated until the pressure difference reaches the maximum target pressure, and then the zone pressure decreases by adjusting the blower door fan flow. It is relatively easier to adjust the flow rate of the blower door fan than the air-handler fan in the field test. When the blower door fan flow reaches zero and the zone pressure is further reduced, the air-handler fan flow begins to adjust. The air flow rate of the air-handler can be adjusted by modulating the inlet vane of the fan, the fan speed, or the supply air damper. The indoor-to-outdoor pressure differences before and after the test should be measured to perform the zero-pressure correction.
Fig. 2. Preparation of air handler for the fan pressurization test.
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Table 2 TEST-1 results. Test no.
Test 1–1 Test 1–2 Test 1–3 Test 1–4 Test 1–5
Building pressure (Pa)
11.37 10.11 7.70 4.58 4.62
OA flow rate (m3 /s)
Envelope leakage (m3 /s)
AHU-1
AHU-2
AHU-3
8.10 7.19 6.28 5.36 4.45
6.80 6.05 5.30 4.55 3.80
0.83 0.83 0.83 0.83 0.83
14.46 12.75 11.04 9.34 7.63
4.1. TEST-1: air-handler fan pressurization test
Fig. 3. Test building.
After the test is completed, all sealing locations must be checked and sealing materials should be removed. All the dampers and fans of air handlers should return to normal operation mode. Recording the sealing locations and system operation modes during the test is very helpful for the final check process.
3. Field measurement 3.1. Test building overview The test building (Fig. 3) is a 5-story office building located in Daejeon, Korea. It is a steel-structured building with 616,400 m2 total floor area, served by four air handlers. One air handler (i.e. AHU-4) is installed in the mechanical room on the basement floor, serving the first and the second floors. The air handler in the first floor mechanical room (i.e. AHU-1) serves the atrium. Two air handlers (i.e. AHU-2 and AHU-3) are located in the mechanical room on the fifth floor and serve the rest of the building. The proposed fan pressurization test was performed for two consecutive days. 3.2. Measuring equipment
TEST-1 was performed on April 21, 2012 using existing airhandler fans. Outdoor air temperature and wind speed were 12.52 ± 0.23 ◦ C and 1.26 ± 0.72 m/s, respectively, which satisfies the existing measurement standards. All the interior doors which did not have a security problem were opened during the test. The elevator shaft vent and restroom vents were all sealed on the rooftop. Differential pressure gauges were installed on each floor to measure the indoor-to-outdoor pressure differences. The air flow rates of air-handlers were adjusted by modulating the fan speed. During the test, return air dampers and exhaust air dampers were completely closed, and the exhaust air outlets located on the roof and ground floor were completely sealed with plastic sheeting. In this field test, AHU-4 was out of order, unfortunately, so the test was performed only with the remaining three air handlers. Table 2 shows the TEST-1 results. The outdoor air flow rates at each air hander were measured for each of the five different building pressures (i.e. Test 1–1 to Test 1–5). The maximum pressure difference realized in TEST-1 was 11.37 Pa. Although this pressure difference was much lower than the conventional target value, the fan pressurization test was performed by decreasing the building pressure gradually from the maximum pressure acquired in Test 1–1. The base pressure measured before and after the test was −1.2 Pa. Air flow rates of the air-handlers were corrected for the outdoor and indoor temperature difference based on ASTM standards. Q [m3 /s] = 3.557(P [Pa])
0.563
Fig. 4 shows the log–log plot of the TEST-1 results. The resulting power-law equation is expressed as Eq. (2). The R2 value of the power-law equation is 0.91.
The blower door equipment used in the test was the Retrotect OMG model with three fans at a maximum of 12.74 m3 /s of air flow rate. The measurement accuracy is ±5% for air flow rate and ±0.2 Pa for pressure. Three fans constituted the blower door module. Two modules, that is, six blower door fans, were used in the test. The indoor-tooutdoor pressure difference was measured with Testo 521-3, which has a measuring range of 0–2.5 hPa and an accuracy of ±0.1%. The outdoor air temperature, humidity, and wind speed were measured with a Vantage Pro-2 weather station.
4. Measurement results Fan pressurization tests were performed by using the airhandlers (TEST-1), and both air handler and blower door fans (TEST-2). The test results acquired from TEST-1 and TEST-2 were compared with each other for verifying the reliability of the proposed measurement approach (i.e. combination of air handlers and blower doors).
(2)
Fig. 4. Pressurization test using the air-handler fan.
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Table 3 TEST-2 results. Test no.
Building pressure (Pa)
Blower door fan flow rate (m3 /s)
Test 2–1 Test 2–2 Test 2–3 Test 2–4 Test 2–5
48.92 39.89 35.66 32.59 28.08
15.80 13.25 11.87 11.14 9.83
OA flow rate (m3 /s)
Envelope leakage (m3 /s)
AHU-1
AHU-2
AHU-3
6.35 6.35 6.35 6.35 6.35
5.21 5.21 5.21 5.21 5.21
0.83 0.83 0.83 0.83 0.83
28.99 26.38 24.96 24.20 22.86
Table 4 Comparison of predicted air leakages at 4 Pa and 50 Pa.
Leakage rate, m3 /s @ 4 Pa Leakage rate, m3 /s @ 50 Pa
Eq. (2) (TEST-1)
Eq. (3) (TEST-2)
7.85 30.97
9.82 29.12
50 Pa which could not be reached in TEST-1. The log–log plot of TEST-2 results and the power-law equation (Eq. (3)) derived from it are shown in Fig. 5. The R2 -value of the power-law equation was 0.99. Q [m3 /s] = 5.415 (P [Pa])
Fig. 5. Pressurization test using the air-handler fan and blower door fan.
4.2. TEST-2: air-handler and blower door combination TEST-2 was performed by pressurizing the test building using both the air-handler and blower door simultaneously. The blower door module was installed at the main entrance located on the first floor. TEST-2 started with measuring the base pressure, and AHU-1 through AHU-3 operated at their maximum air flow to pressurize the building. The blower door was activated to increase the building pressure up to the target pressure (i.e. 50 Pa) which could not be reached by the air handlers only. By reducing the blower door fan flow, a series of pressurization tests were performed at 5 Pa intervals until the building pressure reached 30 Pa. In TEST-2, air handlers kept working at their initial operation mode during the test. Table 3 shows the TEST-2 results. The base pressures measured before and after the test were 5.81 Pa. In TEST-2, one can observe that the maximum pressure difference between the air handler and blower door fans was close to
0.430
(3)
There could be significant intervention in air-handler fan flows due to operation of the blower door. However, the static pressure of the air-handler fans was monitored throughout the whole test (Fig. 6) and did not affect the blower door operation. Consequently, the combination of air handler and blower door fans is applicable to the building pressurization test when the test zone cannot be pressurized sufficiently by air-handlers only. The envelope leakages of the test building at 4 Pa and 50 Pa, predicted by two different power-law equations (i.e. Eqs. (2) and (3)), are summarized in Table 4. It shows that Eq. (3) derived from TEST2 provides 23% higher envelope leakage at 4 Pa compared with Eq. (1) from TEST-1. However, one can also see that there are insignificant discrepancies between the leakage rates at 50 Pa predicted by the two power-law equations. In general, the air leakage rate measured or predicted at 50 Pa is commonly used to rate the air tightness of a building. Consequently, one may conclude that the envelope leakage measurement approaches used in both TEST-1 and TEST-2 can be used for predicting the value at the 50 Pa pressure difference. On the other hand, the Effective Leakage Area (AL , m2 ) at the 4 Pa pressure difference was determined for each measurement approach using ASTM E779-03. The ELA range for the 95% confidence interval in each test method was also calculated (Table 5). It shows that the ELA values match well in the given confidence range, so one can conclude that the combination of air handler and
Fig. 6. Air handler fan static pressure during the measurement.
M.-H. Kim et al. / Energy and Buildings 62 (2013) 436–441 Table 5 Assessment of the entire building air leakage area. Test method 2
ELA, (@ 4 Pa, AL , m ) 95% confidence interval
441
References
TEST-1
TEST-2
2.95 (1.38–6.30)
3.67 (1.96–6.88)
blower door fans can also predict the envelope leakage at the low rated pressure differential (i.e. 4 Pa). 4.3. Man-hour information In the air handler fan pressurization test (i.e. TEST-1), ten people sealed the selected locations in the test building for four hours. By normalizing it for the envelope area of the building (i.e. 3654.7 m2 ), one may conclude that 0.01 man-hours was taken per unit envelope area (i.e. 0.01 man-hour/m2 ) in the sealing activity. A similar result can be found in the literature [13]. As for the differential pressure gauge installation, two people worked for one hour to locate five pressure gauges with pressure tabs (i.e. 0.4 man-hour/pressure gauge). In TEST-2, the man-hours for installing the blower door module were required in addition to comparing with TEST-1. In the test building, two persons spent a half hour to locate and adjust the blower door (i.e. 1.0 man-hour/blower door). 5. Conclusion In this research, it was found that the air-handler fan pressurization approach (i.e. TEST-1) may not generate an adequate indoor-to-outdoor pressure difference recommended by existing test standards, because of the insufficient capacity of air handler fans and/or unfavorable site conditions. However, it was also found that the power-law equation derived from the air-handler fan pressurization test can provide reliable envelope leakage not only for low pressure (i.e. 4 Pa) but also for high pressure (i.e. 50 Pa). The suggested method of combining both air-handler and blower door fans (i.e. TEST-2) shows that one can build up the building pressure close to the recommended target pressure, so the test can be performed with more favorable conditions. The reliability of test results acquired from the suggested method was not much enhanced compared with the air-handler fan pressurization approach. However, higher target pressure, which can be acquired by the suggested approach, would be appropriate for the tall building cases in order to minimize the measurement uncertainty caused by harsh outdoor conditions. Acknowledgement This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MEST) (No. 2012001927).
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