Abstract
Part 1 of this paper examines the uncertainties (errors) inherent in the determination of the low-pressure leakage of a building envelope. Current procedures use high-pressure data (typically 50 Pa) as a measure of the infiltration potential of an envelope. In reality, infiltration occurs at much lower pressures (typically 4 Pa). As a consequence, large uncertainties are inherent in the current procedures. It is shown that a technique for direct measurement of Q4 could reduce the uncertainty by a factor of three or more. One of the keys to such a measurement is to consecutively measure Δp with and without an imposed flow in a short time. In Part 2 of this paper, a technique is described that enables such measurements to be made. Practical application: The paper describes how estimates can be made of the uncertainty in the low-pressure leakage of a building envelope obtained from conventional leakage measurements at high pressures.
| Original language | English |
|---|---|
| Pages (from-to) | 71-80 |
| Number of pages | 10 |
| Journal | Building Services Engineering Research and Technology |
| Volume | 28 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - 2007 |
| Externally published | Yes |
ASJC Scopus subject areas
- Building and Construction
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In: Building Services Engineering Research and Technology, Vol. 28, No. 1, 2007, p. 71-80.
Research output: Journal Publication › Article › peer-review
TY - JOUR
T1 - Determining the adventitious leakage of buildings at low pressure. Part 1
T2 - Uncertainties
AU - Cooper, E. W.
AU - Etheridge, David W.
N1 - Funding Information: Cooper E W MEng School of the Built Environment, Institute of Building Technology, University of Nottingham, UK Etheridge D W PhD, BSc, CEng, MCIBSE, AMRAeS School of the Built Environment, Institute of Building Technology, University of Nottingham, UK, david.etheridge@nottingham.ac.uk 02 2007 28 1 71 80 Part 1 of this paper examines the uncertainties (errors) inherent in the determination of the low-pressure leakage of a building envelope. Current procedures use high-pressure data (typically 50 Pa) as a measure of the infiltration potential of an envelope. In reality, infiltration occurs at much lower pressures (typically 4 Pa). As a consequence, large uncertainties are inherent in the current procedures. It is shown that a technique for direct measurement of Q 4 could reduce the uncertainty by a factor of three or more. One of the keys to such a measurement is to consecutively measure Dp with and without an imposed flow in a short time. In Part 2 of this paper, a technique is described that enables such measurements to be made. sagemeta-type Journal Article search-text Determining the adventitious leakage of buildings at low pressure. Part 1: uncertainties EW Cooper MEng and DW Etheridge PhD, BSc, CEng, MCIBSE, AMRAeS School of the Built Environment, Institute of Building Technology, University of Nottingham, UK Part 1 of this paper examines the uncertainties (errors) inherent in the determination of the low-pressure leakage of a building envelope. Current procedures use high-pressure data (typically 50 Pa) as a measure of the infiltration potential of an envelope. In reality, infiltration occurs at much lower pressures (typically 4 Pa). As a consequence, large uncertainties are inherent in the current procedures. It is shown that a technique for direct measurement of Q4 could reduce the uncertainty by a factor of three or more. One of the keys to such a measurement is to consecutively measure Dp with and without an imposed flow in a short time. In Part 2 of this paper, a technique is described that enables such measurements to be made. Practical application: The paper describes how estimates can be made of the uncertainty in the low-pressure leakage of a building envelope obtained from conventional leakage measurements at high pressures. List of symbols a,b coefficients in equation (3) cL coefficient in equation (19) Cp wind pressure coefficient ((/) defined by equation (17) K,n coefficients in equation (2) P pressure (absolute) (Pa) p pressure due to motion (Pa) q flow rate through opening (m3 /s) Q leakage flow rate (m3 /s) S sign of Dp ((/) U reference wind speed (m/s) z height (m) o instrument error (%) r density (kg/m3 ) Dp pressure difference (Pa) Subscripts E exterior ext external 1, 2 opening 1, opening 2 I interior int internal L leakage of envelope m measured value 50 at 50 Pa 4 at 4 Pa 0 z0/ 0 1 Introduction The importance of adventitious leakage has long been known, and standards exist in several countries. Its importance has recently been recognised in the UK by Part L of the Building Regulations and Associated Ap- proved Documents.1 These documents set requirements for the air leakage of new buildings in the form of a maximum value for the air permeability (eg, 10 m3 /(hm2 ) at a pressure of 50 Pa). Thus, for a given building, the requirement can be satisfied by demonstrating, by means of Author for correspondence: DW Etheridge, School of the Built Environment, Institute of Building Technology, University of Nottingham, UK. E-mail: david.etheridge@nottingham.ac.uk Building Serv. Eng. Res. Technol. 28,1 (2007) pp. 71Á80 # The Chartered Institution of Building Services Engineers 2007 10.1177/0143624406072330 a pressurisation test, that the leakage at 50 Pa (Q50), falls below a certain level. The adoption of 50 Pa is a compromise. Natural ventilation pressures are typically an order of magnitude B/50 Pa and Q50 is not an ideal indicator of the infiltration potential of an envelope. A pressure difference of 4 Pa is commonly taken to be typical of natural ventilation, and ideally, the leakage Q4 at this pressure would be determined. However, leakage measure- ments at such low pressures are perceived to be subject to large errors arising from pres- sures generated by wind and buoyancy during the test. In Part 2 of this paper, a new technique capable of relatively accurate mea- surement of the low-pressure leakage is de- scribed. In this Part of the paper, the uncertainties in the low-pressure leakage are estimated, and it is demonstrated that a direct measurement of Q4 offers considerable reduc- tions in uncertainty compared to the conven- tional high-pressure technique. 1.1 Terminology In much of this paper, the term 'uncer- tainty' is used as a measure of the accuracy of a technique. The 'error' in a measure- ment is the difference between the true value and the measured value. In a practical measurement, the error cannot be known, and it is only possible to speak of the 'uncertainty'. The uncertainty is the range in which the error is expected to lie (with a specified probability). This is the terminol- ogy adopted by Etheridge and Sandberg,2 where a fuller discussion of accuracy can be found. Here, a simpler approach is adopted. For example, the total uncertainty is ob- tained by adding the constituent uncertain- ties, and the distinction between random and systematic errors is ignored. This ap- proach is justified here, because the interest lies in the comparison of uncertainties for different techniques. By making some as- sumptions, the error can be calculated theoretically, and when this is done, the term 'error' is adopted. 2 Current procedure Current procedures are exemplified in the UK by CIBSE TM23,3 and the ATTMA Technical Standard 1.4 There are differences in detail between these and other procedures, but the basic aim is the same, ie, to determine Q50, the leakage of the envelope when a uniform pressure difference of 50 Pa is applied across it. A steady flow fan test is used for this purpose, as illustrated in Figure 1. Combina- tions of fans may be used in practice,4 but for current purposes, the simple arrangement shown in Figure 1 is sufficient. A flow meter is used to measure the fan flow rate Q, and a differential pressure transducer is used to measure the resulting pressure difference across the envelope. The pressure difference Dp is defined by: Dp0Pext (Pint (1) where Pint is the internal pressure, and Pext is the external pressure. Typically, measurements are made at about 10 pressures over the range 20Á60 Pa. The actual range and the number of measurements may depend on conditions at the time of the test,4 but ideally the maximum pressure should exceed 50 Pa, so that the leakage at 50 Pa can be obtained by inter- polation. Pint Q U fan p flow meterPext Figure 1 Conventional steady leakage test 72 Determining the adventitious leakage of buildings at low pressure If a pressure difference of 50 Pa cannot be achieved with the available fan, measurements of Q and Dp over a range of lower pressures (with a minimum of 10,4 or 20 Pa,3 ) may be acceptable. The measurements are used to determine the coefficients K and n in the so- called power law Dp0KQn (2) where K and n are obtained by fitting (2) to the measured data. A value for Q50 can then be found by extrapolation, ie, by putting Dp0/ 50 in equation (2). The reason why Q50 is chosen as a measure of the envelope leakage is that the effect of wind and buoyancy pressures should be rela- tively small at this value of Dp. 2.1 Proposed procedure In Part 2 of this paper, a technique capable of measuring the leakage of an envelope at low pressure is described. In this part of the paper, the uncertainty associated with a direct measurement of the low-pressure leakage (at 4 Pa) is examined and compared with the uncertainty when the conventional (high-pressure) procedure is used to determine Q4. 3 Uncertainties in current steady test The value of Q50 obtained from the conven- tional steady test can be used to estimate Q4, but the estimate will be subject to uncertainty. In the following, the uncertainty is esti- mated for the simple case illustrated in Figure 1. There are two identical adventitious open- ings, each with the following flow character- istic: Dp0aq2 'bq (3) which can be written as q0 b 2a ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1'4 a b2 Dp s (1 (4) where a and b are the flow coefficients of each opening. A quadratic equation is used in preference to equation (2) because it is be- lieved to more closely represent the flow characteristics of adventitious openings. The reasons for this can be found in work of Chiu and Etheridge,5 and in earlier references cited therein. For the case in Figure 1, the leakage characteristic of the envelope (the combina- tion of the two openings) is given by Q0 b a ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1'4 a b2 Dp s (1 (5) It follows from equation (5) that the value of Q4 can be found from the measured values, Qm and Dpm, using Q4 0Qm ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 ' 16 a b2 s ( 1 ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 ' 4 a b2 s Dpm ( 1 (6) It is first assumed that the measured values of Q and Dp have no instrument errors, and that the wind and buoyancy pressures are equal to zero. This means that the uncertainty in Q4 is due purely to uncertainty in a/b2 (the shape parameter of the leakage characteristic). The range of a/b2 encountered for buildings is approximately 0.04Á2.0.2 Equation (6) can thus be used to calculate the corresponding range of Q4 for a given Dpm. Figure 2 shows the consequential errors for different values of Dpm, assuming that the actual value of a/b2 is 0.2. Thus, when Q4 is obtained from a single measurement at 50 Pa, the uncertainty is EW Cooper and DW Etheridge 73 9/28%. This decreases to9/23% when Dpm is 25 Pa. At 4 Pa, the uncertainty is of course equal to zero. The uncertainties at other pressures are shown for interest. If it is assumed that the instrumentation uncertainty for each of Q and Dp is9/5%, the corresponding uncertainty in Q4 is9/10%. It is doubled, because an error in Dpm will itself lead to an error in Qm. On this basis, the uncertainties (in still-air conditions) are9/38% with Dpm 0/50 Pa and 9/10% for a direct measurement of Q4. Thus, a direct measurement of Q4 would reduce the uncertainty by a factor of four compared to the current procedure. The problem with such a low value of Dp, of course, is the effect of pressures due to wind and buoyancy. 4 Uncertainty due to wind and buoyancy Uncertainties due to wind arise from two sources: a) changes in the external wind pressure, Pext; b) changes in flow rates induced through the openings by the fan. Both of these sources are included in the following analysis, although it will be seen below that it is possible to eliminate source (a). In the following analysis, buoyancy is included for generality, and a uniform internal temperature is assumed for simplicity. Figure 3 identifies the parameters involved. The measured pressure difference, Dpm, is obtained as the difference between Pint and Pext Dpm 0Pext (Pint (7) where flow is considered to be positive into the space. 30.0 20.0 10.0 0.0 10.0 20.0 30.0 0.01 0.1 1 10 log10 (a/b2) errorinQ4% DelP=50 Pa DelP=25 Pa DelP=10 Pa DelP=5 Pa DelP=2 Pa Figure 2 Uncertainty in Q4 due to uncertainty in a/b2 for different Dpm Cp1 Cp2 Cpext Pext PE0 Q U q2 z2 q1 z1 fan p flow meterPint PI0 z E I Figure 3 Parameters involved in analysis 74 Determining the adventitious leakage of buildings at low pressure In the case of two openings, ignoring the difference between densities, the relation be- tween q1, q2 and Qm is Qm 'q1 'q2 00 (8) Using equation (3), equation (8) can be written as Qm 0( b 2a  ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1'4 a b2 jDp1j s (1 S1 ' ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1'4 a b2 jDp2j s (1 S2 (9) where S1 and S2 denote the signs of Dp1 and Dp2 ('/ for inward flow). The pressure at ground level in the exterior when there is no air motion (U0/0) is denoted by PE0, and the internal pressure at the same level is denoted by PI0. Since the density is uniform in the exterior, in the presence of wind the external pressure is the sum of the hydrostatic pressure and the wind pressure. Thus, at z0/0 Pext 0PE0 'pext (10) Air movement inside the envelope is assumed to be negligible, so the internal pressure at z0/0 is equal to PI0 Pint 0PI0 Thus, the measured pressure difference at ground level, Dpm, is given by Dpm 0PE0 'pext (PI0 (11) The pressure difference at height z1 is given by Dp1 PE1 (PI1 0PE0 (rEgz1 'p1 ((PI0 (rI gz1) (12) Thus Dp1 0PE0 (PI0 (Dr:gz1 'p1 (13) and using equation (11), equation (13) becomes Dp1 0p1 (pext 'Dpm (Dr:gz1 (14) Similarly, Dp2 can be written Dp2 0p2 (pext 'Dpm (Dr:gz2 (15) Substitution from equations (14) and (15) into equation (9) gives Qm 0( b 2a ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1'4 a b2 jp1 (pext 'Dpm (Dr:gz1j s (1 S1 ' ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1'4 a b2 jp2 (pext 'Dpm (Dr:gz2j s (1 S2 For given values of p1, p2, Pext, Dr and Qm, the value of Dpm can be obtained. Since wind speed is of interest, use is made of the surface wind pressure coefficients defined by Cp1 p1 ( pref 0:5rU2 ×Cp2 p2 ( pref 0:5rU2 ×Cpext pext ( pref 0:5rU2 (17) where pref is an arbitrary reference pressure and U denotes the wind speed. (16) EW Cooper and DW Etheridge 75 In the absence of wind and buoyancy pressures, the true value of Q4 is given by equation (5), with Dp0/4 Pa. In the presence of wind pressures, the measured value of Q4 is given by putting Dpm 0/4 in equation (16). In this way, the error in Q4 can be calculated for given values of U, Dr, Cp1, Cp2 and Cpext. Figure 4 shows the error as a function of wind speed (Dr0/0), with Cp1 0/0.25 and Cp20/ (/0.25. This corresponds to a building that is moderately exposed to the wind. The values of a and b used here are, respectively, 472.9 [Pa.s2 m(6 ] and 48.6 [Pa.s m(3], correspond- ing to true values of Q50 and a/b2 of 0.556 m3 / s and 0.2 Pa(1 . Two values of Cpext have been used, namely 0.1 and (/0.1. The former gives positive errors, and the latter gives negative errors. It is important to note that in a real measurement Cpext will not be known, so it is basically assumed that the uncertainty in Cpext is9/0.1 when the surface pressure coeffi- cients are 0.25 and (/0.25. Clearly, the errors can be large. As expected the uncertainty increases with wind speed and it can be much larger for Q4 than for Q50, because the wind pressures are larger in relation to the fan pressure. At first sight Figure 4 may be considered to rule out the use of a direct measurement of Q4. However, this is not the case. As noted in Etheridge and Sandberg,2 it is theoretically possible to adopt a measurement procedure that reduces the errors. 5 Uncertainty due to wind using procedure in Etheridge and Sandberg2 In the study by Etheridge and Sandberg,2 it is noted that when an envelope with a leakage characteristic given by Dp0aLQ2 'bLQ (18) is tested in the presence of moderate wind and buoyancypressures,themeasuredleakagechar- acteristic is given to a close approximation by Dpm 0aLQ2 m 'bLQm 'cL (19) In principle, this offers a means of redu- cing errors due to wind and buoyancy. The 40 30 20 10 0 10 20 30 40 0 1 2 3 4 5 wind speed U m/s errorinQ4% 4 Pa 10 Pa 25 Pa 50 Pa Figure 4 Error in Q4 due to wind pressures (errors in Q50, Q25 and Q10 also shown) 76 Determining the adventitious leakage of buildings at low pressure coefficientcL istheshiftinDp arisingfromwind and buoyancy when there is no applied fan flow. In principle it can be measured, by zeroing the pressure transducer before connecting it to the pressure tappings. Knowing cL, the coefficients aL and bL can be found by fitting equation (19) to the measured values of Q and Dp. Although this can be expected to work for buoyancy alone, as noted in Etheridge and Sandberg,2 it is less likely to work when wind is present. The reason for this is the unsteady nature of the wind pressures arising from fluctuations in both wind speed and direction. In general, it is not justifiable to assume that cL is constant during the course of the measurement. This can be seen by noting that wind speed fluctuations cover a range of frequencies that are low, requiring long aver- aging times to obtain constant means. A single pressure measurement may take 1 min, whereas the value of cL may change signifi- cantly from 1 min to the next. Thus, the problem of adopting this proce- dure with the conventional measurement tech- nique is that cL will vary with time by an unknown amount. However, in the proposed technique, the measurements with and without an applied flow are made consecutively in a matter of seconds. This allows any change in cL to be accounted for relatively precisely. Experimental evidence for this is presented in Part 2. On this basis, the uncertainty is estimated by assuming that the procedure by Etheridge and Sandberg is valid.2 Using equation (16) with Qm 0/0 gives the value of cL for the given wind conditions. The value of Dpm with a given value of Qm can then found using equation (16). The change in Dp due to the applied flow is then given by Dpm ÁcL. Figure 5 shows the resulting errors in Q4 for the same conditions as used in Figure 4. Comparison of Figures 4 and 5 shows that for U0/4 m/s, the uncertainty reduces by a large factor, from '/26 to (/ 13% to 5%. In fact, the error becomes independent of Cpext (source (a)) and is due purely to the change in flow rates through the openings (source (b)). The error will always be of the same sign, with its magnitude depen- dent on Cp1 and Cp2. It is worth noting here that at a wind speed of 4 m/s, the pressure difference across the openings is three times that imposed by the applied fan flow, yet the error in Q4 is still only 40.00 30.00 20.00 10.00 0.00 10.00 20.00 30.00 40.00 0 1 2 3 4 5 wind speed U m/s errorinQ4% Figure 5 Error in measured value of Q4 due to wind, using the procedure of Etheridge and Sandberg2 EW Cooper and DW Etheridge 77 5%. It will be seen in Part 2 that the experimental results with the pulse technique are consistent with this. 6 Extrapolation of high-pressure data to determine Q4 When measurements are made over a range of Dp with the conventional technique, equation (18) or equation (19) can be fitted to the data and used to determine Q4. Basically, the measured data is extrapolated to Dp0/4 Pa (although the use of equation (18) means that the curve is forced to pass through the origin). The problem with this approach is that errors in individual mea- surements tend to be magnified by the extrapolation, leading to relatively large errors in Q4. This can be seen simply by considering the effect of instrument errors, o, where oQ and oDp are the percentage errors in the measurement of Q and Dp, respectively. Figure 6 shows the actual leakage characteristic (solid line). One of the hatched lines shows the measured char- acteristic when oQ 0/2.5% and oDp 0/ (/2.5%. The other line corresponds to oQ 0/ (/2.5% and oDp 0/2.5%. The curve from which Q4 is determined will depend on the individual measurement points and they will tend to be randomly distributed within the boundary of the hatched lines. Thus, in principle, it is possible for the points to lie on the actual curve, and the error in Q4 will then be zero. Equally, the points could lie on curves that give the maximum (most positive) and minimum (most negative) errors. For the range shown in Figure 6, the maximum and minimum errors are about 38 and (/28%. The prob- ability that any of these combinations of points will arise is, of course, very small. Nevertheless, it can be seen that the uncer- tainty in Q4, arising purely from instrument uncertainties, is much larger than the instru- ment uncertainty in the measured data. Bearing in mind that the instrument uncer- tainty has been taken as half that used for the earlier estimates, and that no account has been taken of uncertainties arising from wind and buoyancy pressures, it seems clear that the uncertainty associated with curve-fitting is subject to large uncertainty. The uncer- tainty is similar in magnitude (and probably greater) than that associated with obtaining Q4 from a measurement of Q50. It is im- portant to note that the uncertainty arising U = 0 T = 0 60 50 40 30 20 10 0 0 0.1 0.2 0.3 0.4 0.5 0.6 Qm pm actual leakage Figure 6 Uncertainty in leakage curve (hatched lines) due to instrument error 78 Determining the adventitious leakage of buildings at low pressure from instrument error applies when the measurement conditions are otherwise ideal (U0/0, no buoyancy). 7 Comparison of uncertainties Table 1 shows a comparison of the uncertain- ties in Q4 associated with the three procedures, namely: a) where Q4 is estimated from a conventional measurement of Q50; b) the proposed technique, where Q4 is measured directly; c) where Q4 is estimated by extrapolation from high-pressure data. The values shown are for U0/0 and U0/4 m/s, with Cp1 0/0.25, Cp20/ (/0.25 and Cpext 0/ 9/0.1. With the conventional technique, the uncertainties arise from (i) uncertainty in a/b2 (Figure 2), (ii) effect of wind on Q50 (Figure 4), and (iii) instrument errors. With the proposed technique, errors arise from (i) wind effects (Figure 4) and (ii) instrument errors. Instrument uncertainty for proce- dures (a) and (b) is assumed be9/5%, whereas 9/2.5% is used for (c). The differ- ent uncertainties are simply added to obtain the total uncertainty. This is questionable, but for the purpose of comparison it is acceptable. It can be seen that the proposed technique leads to a reduction of the total uncertainty by a factor of at least three. 8 Conclusions The leakage at 4 Pa is a more realistic indicator of the infiltration potential of a building envelope than the leakage at 50 Pa. Current leakage measurement procedures are subject to a considerable uncertainty in the determination of infiltration potential, be- cause they rely on high-pressure leakage data. It has been shown that a technique for direct measurement of Q4 could reduce the uncertainty by a factor of three or more. The key to such a measurement is to consecutively measure Dp with and without an imposed flow in a short time. In Part 2 of this paper, a technique is described that enables such mea- surements to be made. Acknowledgements The initial development work was funded internally by the University of Nottingham. Subsequent funding was provided by the Engineering and Physical Science Research Council (EPSRC) and AirFlow Developments Ltd. Their support is gratefully acknowledged. References 1 Building Regulations: Part L 2006 (Conservation of fuel and power). Approved Documents Part L1A (new dwellings), L2A (new buildings other than dwellings). London, UK: NBS for the Office of the Deputy Prime Minister, 2006. Table 1 Comparison of total uncertainty for three methods Technique Total uncertainty in Q4 (U0/0 m/s) (%) Total uncertainty in Q4 (U0/4 m/s) (%) (a) Conventional steady, Dp0/50 Pa (/38 to '/38 (/40 to '/40 (b) Proposed technique (/10 to '/10 (/15 to '/10 (c) Extrapolation of high-pressure data (/38 to '/28 /U0/0 EW Cooper and DW Etheridge 79 2 Etheridge DW, Sandberg M. Building ventilation: theory and measurement. Chichester, UK: John Wiley & Sons, 1996. 3 Testing buildings for air leakage, CIBSE TM23. London: CIBSE, 2000. 4 ATTMA Testing Standard 1. Measuring air permeability of building envelopes, Issue 1. March 2006, http://www.attma.org/index.htm 5 Chiu Y-H, Etheridge DW. Calculations and notes on the quadratic and power law equations for modelling infiltration. Int J Ventilation 2002; 1: 65Á77. 80 Determining the adventitious leakage of buildings at low pressure Building Regulations: Part L 2006 (Conservation of fuel and power) . Approved Documents Part L1A (new dwellings), L2A (new buildings other than dwellings). London, UK : NBS for the Office of the Deputy Prime Minister , 2006 . Etheridge DW , Sandberg M. Building ventilation: theory and measurement . Chichester, UK : John Wiley & Sons , 1996 . Testing buildings for air leakage , CIBSE TM23. London : CIBSE , 2000 . ATTMA Testing Standard 1 . Measuring air permeability of building envelopes , Issue 1. March 2006 , http://www.attma.org/index.htm Chiu Y-H , Etheridge DW.
PY - 2007
Y1 - 2007
N2 - Part 1 of this paper examines the uncertainties (errors) inherent in the determination of the low-pressure leakage of a building envelope. Current procedures use high-pressure data (typically 50 Pa) as a measure of the infiltration potential of an envelope. In reality, infiltration occurs at much lower pressures (typically 4 Pa). As a consequence, large uncertainties are inherent in the current procedures. It is shown that a technique for direct measurement of Q4 could reduce the uncertainty by a factor of three or more. One of the keys to such a measurement is to consecutively measure Δp with and without an imposed flow in a short time. In Part 2 of this paper, a technique is described that enables such measurements to be made. Practical application: The paper describes how estimates can be made of the uncertainty in the low-pressure leakage of a building envelope obtained from conventional leakage measurements at high pressures.
AB - Part 1 of this paper examines the uncertainties (errors) inherent in the determination of the low-pressure leakage of a building envelope. Current procedures use high-pressure data (typically 50 Pa) as a measure of the infiltration potential of an envelope. In reality, infiltration occurs at much lower pressures (typically 4 Pa). As a consequence, large uncertainties are inherent in the current procedures. It is shown that a technique for direct measurement of Q4 could reduce the uncertainty by a factor of three or more. One of the keys to such a measurement is to consecutively measure Δp with and without an imposed flow in a short time. In Part 2 of this paper, a technique is described that enables such measurements to be made. Practical application: The paper describes how estimates can be made of the uncertainty in the low-pressure leakage of a building envelope obtained from conventional leakage measurements at high pressures.
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DO - 10.1177/0143624406072330
M3 - Article
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