1、Designation: E741 11Standard Test Method forDetermining Air Change in a Single Zone by Means of aTracer Gas Dilution1This standard is issued under the fixed designation E741; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、 of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers techniques using tracer gasdilution for determining a single zones air change with theoutd
3、oors, as induced by weather conditions and by mechanicalventilation. These techniques are: (1) concentration decay, (2)constant injection, and (3) constant concentration.1.2 This test method is restricted to any single tracer gas.The associated data analysis assumes that one can characterizethe trac
4、er gas concentration within the zone with a single value.The zone shall be a building, vehicle, test cell, or anyconforming enclosure.1.3 Use of this test method requires a knowledge of theprinciples of gas analysis and instrumentation. Correct use ofthe formulas presented here requires consistent u
5、se of units,especially those of time.1.4 Determination of the contribution to air change byindividual components of the zone enclosure is beyond thescope of this test method.1.5 The results from this test method pertain only to thoseconditions of weather and zonal operation that prevailed duringthe
6、measurement. The use of the results from this test to predictair change under other conditions is beyond the scope of thistest method.1.6 The text of this test method references notes andfootnotes which provide explanatory material. These notes andfootnotes (excluding those in tables and figures) sh
7、all not beconsidered requirements of this test method.1.7 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility
8、of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D4480 Test Method for Measuring Surface Wind by Meansof Wind Vanes and Rotating Anemometers3E260 Practice for Packed Column Gas ChromatographyE631 Terminology of Building ConstructionsE779 Test Method for Determining A
9、ir Leakage Rate byFan PressurizationE1186 Practices for Air Leakage Site Detection in BuildingEnvelopes and Air Barrier Systems2.2 ASHRAE Documents:4ASHRAE Handbook of Fundamentals Chapter 23ASHRAE Standard 623. Terminology3.1 Definitions:3.1.1 For definitions of general terms related to buildingcon
10、struction used in this test method, refer to TerminologyE631.3.2 Definitions of Terms Specific to This Standard:3.2.1 air change flow, Q, nthe total volume of air passingthrough the zone to and from the outdoors per unit time (m3/s,m3/h, ft3/h).3.2.2 air change rate, A, nthe ratio of the total volum
11、e ofair passing through the zone to and from the outdoors per unitof time to the volume of the zone (1/s, 1/h).53.2.3 envelope, nthe system of barriers between a condi-tioned building zone and the outdoors.1This test method is under the jurisdiction of ASTM Committee E06 onPerformance of Buildings a
12、nd is the direct responsibility of Subcommittee E06.41on Air Leakage and Ventilation Performance.Current edition approved Sept. 1, 2011. Published October 2011. Originallyapproved in 1980. Last previous edition approved in 2006 as E741 00 (2006)1.DOI: 10.1520/E0741-11.2For referenced ASTM standards,
13、 visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn. The last approved version of this historical standard is referencedon www.astm.o
14、rg.4Available from American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. (ASHRAE), 1791 Tullie Circle, NE, Atlanta, GA30329, http:/www.ashrae.org.5A common way of expressing air change rate units is ACH = air changes perhour = 1/h.1Copyright ASTM International, 100 Barr Ha
15、rbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.3.1 DiscussionThis includes exterior doors, windows,roofs, walls, floors and ductwork. It excludes interior parti-tions, ducts, and so forth, that separate conditioned zones.3.2.4 tracer gas, na gas that is mixed with air a
16、ndmeasured in very small concentrations in order to study airmovement.3.2.5 tracer gas analyzer, na device used to measure theconcentration of tracer gas in an air sample.3.2.6 tracer gas concentration, C, nthe ratio of thequantity of tracer gas in air to the quantity of that air(moles/mole or m3/m3
17、).3.2.7 single zone, na space or set of spaces wherein theconcentration of a tracer gas is maintained uniformly through-out and that only exchanges air with the outside.3.2.7.1 DiscussionMultizone buildings are difficult totreat as single zones and meet the uniformity of tracer gasconcentration requ
18、ired in this test method. Single zones withinmultizone buildings are difficult to isolate such that theyexchange air only with the outside and not to other zoneswithin the building via ventilation ducts, electrical conduits,elevator shafts, stairs, and other pathways.3.3 Symbols:3.3.1 Variables:A =
19、air change rate (1/s, 1/h).C = concentration (dimensionless).CONF = confidence limit value (units of the variable mea-sured).d = desired precision (dimensionless).ESE = estimated standard error.i = location number.k = constant.n = number of data points.N = number of sampling locations in the zone.Q
20、= flow (m3/s, m3/h, ft3/h).s = sample standard deviation (units of the variableestimated).t = a specific time (s, h).T = a period of time (s, h).V = volume (m3,ft3).a = probability (dimensionless). = error (units of the variable estimated).n = coefficient of variation (dimensionless).3.3.2 Superscri
21、pts:8 = value at the end of the test. = mean value.3.3.3 Subscripts:A = pertaining to air change rate.avg = average.bias = pertaining to bias.C = pertaining to concentration.est = estimated.GA = pertaining to the gas analyzer.i = pertaining to time or location.inj = pertaining to the injection perio
22、d.lower = lower limit.meas = pertaining to the measurement.mix = pertaining to the mixing period.precis = pertaining to precision.rep = pertaining to replicates.sample = pertaining to a discrete tracer gas or air sample.target = pertaining to the desired level of tracer gas.test = pertaining to the
23、test period.twt = weighted according to tracer gas flow.tracer = pertaining to the tracer gas.upper = upper limit.vol = pertaining to the volume of the zone.zone = pertaining to the zone under study.1 = first occurrence under discussion.2 = last occurrence under discussion.3.3.4 Other Notations:Dt =
24、 time interval between periodic samples.(t) = function of time.(t, i) = function of time, t, and location, i.t(n,1a)= t-distribution value for n degrees of freedomand a two-sided probability of a.4. Summary of Test Method4.1 This test method uses the measurement of tracer gasdilution to determine ai
25、r change within a building or otherenclosure that is characterized as a single zone. The measure-ment of the concentration, and sometimes the volume rate ofthe tracer gas that is injected into the zone, allows calculationof the volume rate of outgoing air from the zone. From this,one can infer the v
26、olume rate of incoming air. Three techniquesare presented: (1) concentration decay, (2) constant injection,and (3) constant concentration. Each technique employs spe-cific tracer gas injection and sampling strategies. Other tech-niques exist but are beyond the scope of this test method. Table1 summa
27、rizes the three techniques.4.2 Choice of TechniqueIn choosing a technique formeasuring air change, consider the quantity to be measured, thecomparative capabilities of the techniques, and the complexityof the required equipment.4.2.1 Air Change Quantity to Be MeasuredChoose be-tween direct measureme
28、nt of air change rate or air change flow.Conversions between rate and flow and vice versa are subjectto the precision and bias of the measurement of the zonevolume. To obtain air change rate directly, use the tracer gasdecay technique. To obtain air change flow, use the constantinjection or constant
29、 concentration techniques.5. Significance and Use5.1 Effects of Air ChangeAir change often accounts for asignificant portion of the heating or air-conditioning load of abuilding. It also affects the moisture and contaminant balancesin the building. Moisture-laden air passing through the buildingenve
30、lope can permit condensation and cause material degrada-tion. An appropriate level of ventilation is required in allbuildings; one should consult ASHRAE Standard 62 to deter-mine the ventilation requirements of a building.5.2 Prediction of Air ChangeAir change depends on thesize and distribution of
31、air leakage sites, pressure differencesE741 112induced by wind and temperature, mechanical system opera-tion, and occupant behavior. Air change may be calculatedfrom this information, however, many of the needed param-eters are difficult to determine. Tracer gas testing permits directmeasurement of
32、air change.5.3 Utility of MeasurementMeasurements of air changeprovide useful information about ventilation and air leakage.Measurements in buildings with the ventilation system closedare used to determine whether natural air leakage rates arehigher than specified. Measurements with the ventilation
33、sys-tem in operation are used to determine whether the air changemeets or exceeds requirements.5.4 Known ConditionsKnowledge of the factors that af-fect air change makes measurement more meaningful. Relatingbuilding response to wind and temperature requires repetitionof the test under varying meteor
34、ological conditions. Relatingbuilding response to the ventilation system or to occupantbehavior requires controlled variation of these factors.5.5 Applicability of ResultsThe values for air changeobtained by the techniques used in this test method apply to thespecific conditions prevailing at the ti
35、me of the measurement.Air change values for the same building will differ if theprevailing wind and temperature conditions have changed, ifthe operation of the building is different, or if the envelopechanges between measurements because of construction ordeterioration. To determine air leakage site
36、s, follow PracticeE1186.5.6 Fan PressurizationA related technique (Test MethodE779) uses a fan to pressurize the building envelope. Measure-ments of corresponding air flows and pressure differencesacross the envelope characterize envelope airtightness as eitherthe air leakage rate under specified in
37、duced pressure differ-ences or the equivalent leakage area of the envelope. Thesefactors permit modeling natural air change due to wind andtemperature differences. However, direct measurement of natu-ral air change is not possible with Test Method E779. TestMethod E779 permits comparison of differen
38、t buildings, iso-lation of leakage sites, and evaluation of retrofit measures.6. Apparatus6.1 The apparatus includes means for distributing the tracergas, means for obtaining air samples, a gas analyzer to measuretracer gas concentration in the air samples, and other measure-ment devices.6.2 Tracer
39、GasSee Appendix X1 for information ontracer gases and equipment used to measure their concentra-tions. Appendix X1 also contains tracer gas target concentra-tion levels and safety information.6.2.1 Tracer Gas Concentration StandardA known con-centration of tracer gas in air.6.3 Tracer Gas Injection
40、and Distribution ApparatusThere are several means for releasing the appropriate volumeof tracer gas and distributing it in the zone.6.3.1 Tracer Gas Metering and Injection DevicesTheseinclude (1) a graduated syringe or other container of knownvolume with a means for controlled release of its content
41、s and(2) a compressed tracer gas supply with a critical orifice, acritical orifice metering valve, an electronic mass flow control-ler, or other tracer gas flow rate measurement and controldevice.6.3.2 Tracer Gas Distribution DevicesThese include (1)fans that permit good mixing of tracer gases injec
42、ted manuallywithin the zone (oscillating or hassock fans, or, ducted forcedair systems can serve this purpose), (2) tubing networks thatdispense tracer gas via manifolds and automated valves and (3)pressure-operated valves that stop the flow from a tubingnetwork when the tubing is not pressurized. (
43、Note that leaks intubing networks release tracer gas at unintended locations.)6.4 Tracer Gas Sampling ApparatusesExamples includecontainers for manual sampling and automatic samplers thatemploy containers or networks.6.4.1 Materials for Sampling ApparatusesSelect andcheck materials used in tracer ga
44、s sampling systems carefullyfor their reactivity and absorption of the tracer gas in use.Depending on the tracer gas, desirable materials include glass,copper, and stainless steel. Metal foil is appropriate for flexiblecontainers. Other acceptable materials include polypropylene,polyethylene, and ny
45、lon. Materials that absorb tracer gasdegrade the accuracy of the measurement. Other materialsrelease substances that interfere with tracer gas analyzeraccuracy. Depending on the tracer gas, materials to avoidinclude soft plastics, like vinyl and TFE-fluorocarbon.6.4.2 Manual SamplersThese include sy
46、ringes, flexiblebottles, or air sample bags with a capacity of at least threetimes the minimum sample size of the gas analyzer used. Thesecontainers shall have an airtight seal to assure that the sampleis not diluted or contaminated. Each container shall have alabel that keys it to a record of the t
47、ime and location that it wasused. Do not reuse sample containers without first confirmingthat they are not contaminated with tracer gas.6.4.3 Automatic SamplersThese apparatuses comprise ei-ther a sampling network or automated samplers.TABLE 1 Summary of Air Change Measurement TechniquesNOTE 1Speed
48、of MeasurementA one-time measurement of airchange is most quickly acquired with the concentration decay techniqueand least quickly with the constant concentration technique.NOTE 2Time-Varying Air ChangeThe constant concentration andconstant injection techniques may be useful for measuring air change
49、 ratesthat vary with time.NOTE 3Complexity of Zone GeometryWhereas all the techniquesrequire uniform tracer gas concentration, the constant concentrationtechnique may be useful to achieve this in a zone with complex geometry.NOTE 4Equipment ComplexityThe complexity of the requiredequipment is lowest for the tracer gas decay technique and highest for theconstant concentration technique.Tech-niqueType of AirChange Mea-surementSteady-StateAssumptionRequired?Volume Control ofTracer GasConcentrationMeasurementRelative ToConcentration DecaySection
