ASTM E741-00(2006)e1
(Test Method)Standard Test Method for Determining Air Change in a Single Zone by Means of a Tracer Gas Dilution
Standard Test Method for Determining Air Change in a Single Zone by Means of a Tracer Gas Dilution
SIGNIFICANCE AND USE
Effects of Air Change—Air change often accounts for a significant portion of the heating or air-conditioning load of a building. It also affects the moisture and contaminant balances in the building. Moisture-laden air passing through the building envelope can permit condensation and cause material degradation. An appropriate level of ventilation is required in all buildings; one should consult ASHRAE Standard 62 to determine the ventilation requirements of a building.
Prediction of Air Change—Air change depends on the size and distribution of air leakage sites, pressure differences induced by wind and temperature, mechanical system operation, and occupant behavior. Air change may be calculated from this information, however, many of the needed parameters are difficult to determine. Tracer gas testing permits direct measurement of air change.
Utility of Measurement—Measurements of air change provide useful information about ventilation and air leakage. Measurements in buildings with the ventilation system closed are used to determine whether natural air leakage rates are higher than specified. Measurements with the ventilation system in operation are used to determine whether the air change meets or exceeds requirements.
Known Conditions—Knowledge of the factors that affect air change makes measurement more meaningful. Relating building response to wind and temperature requires repetition of the test under varying meteorological conditions. Relating building response to the ventilation system or to occupant behavior requires controlled variation of these factors.
Applicability of Results—The values for air change obtained by the techniques used in this test method apply to the specific conditions prevailing at the time of the measurement. Air change values for the same building will differ if the prevailing wind and temperature conditions have changed, if the operation of the building is different, or if the envelope changes between measurements because of c...
SCOPE
1.1 This test method covers techniques using tracer gas dilution for determining a single zone's air change with the outdoors, as induced by weather conditions and by mechanical ventilation. 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 characterize the tracer gas concentration within the zone with a single value. The zone shall be a building, vehicle, test cell, or any conforming enclosure.
1.3 Use of this test method requires a knowledge of the principles of gas analysis and instrumentation. Correct use of the formulas presented here requires consistent use of units, especially those of time.
1.4 Determination of the contribution to air change by individual components of the zone enclosure is beyond the scope of this test method.
1.5 The results from this test method pertain only to those conditions of weather and zonal operation that prevailed during the measurement. The use of the results from this test to predict air change under other conditions is beyond the scope of this test method.
1.6 The text of this test method references notes and footnotes which provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered requirements of this test method.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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´1
Designation: E741 – 00 (Reapproved 2006)
Standard Test Method for
Determining Air Change in a Single Zone by Means of a
Tracer Gas Dilution
This standard is issued under the fixed designation E741; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
´ NOTE—X5.2.3 and X5.2.5 were editorially corrected in September 2009.
1. Scope 2. Referenced Documents
1.1 This test method covers techniques using tracer gas 2.1 ASTM Standards:
dilution for determining a single zone’s air change with the D4480 Test Method for Measuring SurfaceWind by Means
outdoors, as induced by weather conditions and by mechanical of Wind Vanes and Rotating Anemometers
ventilation. These techniques are: (1) concentration decay, (2) E260 Practice for Packed Column Gas Chromatography
constant injection, and (3) constant concentration. E779 Test Method for Determining Air Leakage Rate by
1.2 This test method is restricted to any single tracer gas. Fan Pressurization
The associated data analysis assumes that one can characterize E1186 Practices forAir Leakage Site Detection in Building
thetracergasconcentrationwithinthezonewithasinglevalue. Envelopes and Air Barrier Systems
The zone shall be a building, vehicle, test cell, or any 2.2 ASHRAE Documents:
conforming enclosure. ASHRAEHandbookofFundamentals Chapter 23
1.3 Use of this test method requires a knowledge of the ASHRAEStandard62
principles of gas analysis and instrumentation. Correct use of
3. Terminology
the formulas presented here requires consistent use of units,
3.1 Definitions of Terms Specific to This Standard:
especially those of time.
1.4 Determination of the contribution to air change by 3.1.1 air change flow, Q, n—the total volume of air passing
through the zone to and from the outdoors per unit time (m /s,
individual components of the zone enclosure is beyond the
3 3
scope of this test method. m /h, ft /h).
1.5 The results from this test method pertain only to those 3.1.2 air change rate, A, n—the ratio of the total volume of
air passing through the zone to and from the outdoors per unit
conditionsofweatherandzonaloperationthatprevailedduring
themeasurement.Theuseoftheresultsfromthistesttopredict of time to the volume of the zone (1/s, 1/h).
3.1.3 envelope, n—the system of barriers between a condi-
air change under other conditions is beyond the scope of this
test method. tioned building zone and the outdoors.
3.1.3.1 Discussion—This includes exterior doors, windows,
1.6 The text of this test method references notes and
footnoteswhichprovideexplanatorymaterial.Thesenotesand roofs, walls, floors and ductwork. It excludes interior parti-
tions, ducts, and so forth, that separate conditioned zones.
footnotes (excluding those in tables and figures) shall not be
considered requirements of this test method. 3.1.4 tracer gas, n—a gas that is mixed with air and
measured in very small concentrations in order to study air
1.7 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the movement.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
bility of regulatory limitations prior to use.
contactASTM Customer Service at service@astm.org. ForAnnual Book ofASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
1 3
This test method is under the jurisdiction of ASTM Committee E06 on Withdrawn.
Performance of Buildings and is the direct responsibility of Subcommittee E06.41 Available from American Society of Heating, Refrigerating, and Air-
on Air Leakage and Ventilation Performance. Conditioning Engineers, Inc. (ASHRAE), 1791 Tullie Circle, NE, Atlanta, GA
Current edition approved Oct. 1, 2006. Published October 2006. Originally 30329, http://www.ashrae.org.
approved in 1980. Last previous edition approved in 2000 as E741–00. DOI: A common way of expressing air change rate units is ACH=air changes per
10.1520/E0741-00R06E01. hour=1/h.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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E741 – 00 (2006)
3.1.5 tracer gas analyzer, n—a device used to measure the
target = pertaining to the desired level of tracer gas.
concentration of tracer gas in an air sample.
test = pertaining to the test period.
3.1.6 tracer gas concentration, C, n—the ratio of the twt = weighted according to tracer gas flow.
quantity of tracer gas in air to the quantity of that air tracer = pertaining to the tracer gas.
3 3
upper = upper limit.
(moles/mole or m /m ).
vol = pertaining to the volume of the zone.
3.1.7 single zone, n—a space or set of spaces wherein the
zone = pertaining to the zone under study.
concentration of a tracer gas is maintained uniformly through-
1 = first occurrence under discussion.
out and that only exchanges air with the outside.
2 = last occurrence under discussion.
3.1.7.1 Discussion—Multizone buildings are difficult to
3.2.4 Other Notations:
treat as single zones and meet the uniformity of tracer gas
concentration required in this test method. Single zones within
multizone buildings are difficult to isolate such that they
Dt = time interval between periodic samples.
exchange air only with the outside and not to other zones
(t) = function of time.
within the building via ventilation ducts, electrical conduits, (t, i) = function of time, t, and location, i.
t(n, = t-distribution value for n degrees of freedom
elevator shafts, stairs, and other pathways.
1−a) and a two-sided probability of a.
3.2 Symbols:
3.2.1 Variables:
4. Summary of Test Method
4.1 This test method uses the measurement of tracer gas
A = air change rate (1/s, 1/h).
dilution to determine air change within a building or other
C = concentration (dimensionless).
enclosure that is characterized as a single zone. The measure-
CONF = confidence limit value (units of the variable mea-
ment of the concentration, and sometimes the volume rate of
sured).
the tracer gas that is injected into the zone, allows calculation
d = desired precision (dimensionless).
of the volume rate of outgoing air from the zone. From this,
ESE = estimated standard error.
onecaninferthevolumerateofincomingair.Threetechniques
i = location number.
are presented: (1) concentration decay, (2) constant injection,
k = constant.
and (3) constant concentration. Each technique employs spe-
n = number of data points.
cific tracer gas injection and sampling strategies. Other tech-
N = number of sampling locations in the zone.
3 3 3
niquesexistbutarebeyondthescopeofthistestmethod.Table
Q = flow (m /s, m /h, ft /h).
1 summarizes the three techniques.
s = sample standard deviation (units of the variable
4.2 Choice of Technique—In choosing a technique for
estimated).
measuringairchange,considerthequantitytobemeasured,the
t = a specific time (s, h).
T = a period of time (s, h). comparative capabilities of the techniques, and the complexity
3 3
V = volume (m,ft ).
of the required equipment.
a = probability (dimensionless).
´ = error (units of the variable estimated).
TABLE 1 Summary of Air Change Measurement Techniques
n = coefficient of variation (dimensionless).
NOTE 1—Speed of Measurement—A one-time measurement of air
3.2.2 Superscripts:
change is most quickly acquired with the concentration decay technique
and least quickly with the constant concentration technique.
NOTE 2—Time-Varying Air Change—The constant concentration and
8 = value at the end of the test.
constantinjectiontechniquesmaybeusefulformeasuringairchangerates
− = mean value.
that vary with time.
NOTE 3—Complexity of Zone Geometry—Whereas all the techniques
3.2.3 Subscripts:
require uniform tracer gas concentration, the constant concentration
techniquemaybeusefultoachievethisinazonewithcomplexgeometry.
NOTE 4—Equipment Complexity—The complexity of the required
A = pertaining to air change rate.
equipment is lowest for the tracer gas decay technique and highest for the
avg = average.
constant concentration technique.
bias = pertaining to bias.
Type of Air Steady-State Concentration
Tech- Volume Control of
C = pertaining to concentration.
Change Mea- Assumption Measurement
nique Tracer Gas
surement Required? Relative To
est = estimated.
Concentration Decay—Section 8
GA = pertaining to the gas analyzer.
Average Rate No Approximate initial- Other samples
i = pertaining to time or location.
target
inj = pertaining to the injection period.
Regres- Rate Yes Approximate initial Other samples
sion target
lower = lower limit.
Constant Injection—Section 9
meas = pertaining to the measurement.
Average Flow No Flow rate to within Absolute stan-
mix = pertaining to the mixing period.
2% dard
precis = pertaining to precision. Constant Concentration—Section 10
Flow No Mean concentration Absolute stan-
rep = pertaining to replicates.
within2%oftarget dard
sample = pertaining to a discrete tracer gas or air sample.
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E741 – 00 (2006)
4.2.1 Air Change Quantity to Be Measured—Choose be- 6. Apparatus
tweendirectmeasurementofairchangerateorairchangeflow.
6.1 The apparatus includes means for distributing the tracer
Conversions between rate and flow and vice versa are subject
gas,meansforobtainingairsamples,agasanalyzertomeasure
to the precision and bias of the measurement of the zone
tracer gas concentration in the air samples, and other measure-
volume. To obtain air change rate directly, use the tracer gas
ment devices.
decay technique. To obtain air change flow, use the constant
6.2 Tracer Gas—See Appendix X1 for information on
injection or constant concentration techniques.
tracer gases and equipment used to measure their concentra-
tions. Appendix X1 also contains tracer gas target concentra-
5. Significance and Use
tion levels and safety information.
6.2.1 Tracer Gas Concentration Standard—A known con-
5.1 Effects of Air Change—Air change often accounts for a
centration of tracer gas in air.
significant portion of the heating or air-conditioning load of a
6.3 Tracer Gas Injection and Distribution Apparatus—
building. It also affects the moisture and contaminant balances
There are several means for releasing the appropriate volume
inthebuilding.Moisture-ladenairpassingthroughthebuilding
of tracer gas and distributing it in the zone.
envelope can permit condensation and cause material degrada-
6.3.1 Tracer Gas Metering and Injection Devices—These
tion. An appropriate level of ventilation is required in all
include (1) a graduated syringe or other container of known
buildings; one should consult ASHRAEStandard62 to deter-
volume with a means for controlled release of its contents and
mine the ventilation requirements of a building.
(2) a compressed tracer gas supply with a critical orifice, a
5.2 Prediction of Air Change—Air change depends on the
criticalorificemeteringvalve,anelectronicmassflowcontrol-
size and distribution of air leakage sites, pressure differences
ler, or other tracer gas flow rate measurement and control
induced by wind and temperature, mechanical system opera-
device.
tion, and occupant behavior. Air change may be calculated
6.3.2 Tracer Gas Distribution Devices—These include (1)
from this information, however, many of the needed param-
fans that permit good mixing of tracer gases injected manually
etersaredifficulttodetermine.Tracergastestingpermitsdirect
within the zone (oscillating or hassock fans, or, ducted forced
measurement of air change.
air systems can serve this purpose), (2) tubing networks that
5.3 Utility of Measurement—Measurements of air change
dispensetracergasviamanifoldsandautomatedvalvesand(3)
provide useful information about ventilation and air leakage.
pressure-operated valves that stop the flow from a tubing
Measurements in buildings with the ventilation system closed
network when the tubing is not pressurized. (Note that leaks in
are used to determine whether natural air leakage rates are
tubing networks release tracer gas at unintended locations.)
higher than specified. Measurements with the ventilation sys-
6.4 Tracer Gas Sampling Apparatuses—Examples include
tem in operation are used to determine whether the air change
containers for manual sampling and automatic samplers that
meets or exceeds requirements.
employ containers or networks.
5.4 Known Conditions—Knowledge of the factors that af-
6.4.1 Materials for Sampling Apparatuses—Select and
fectairchangemakesmeasurementmoremeaningful.Relating
check materials used in tracer gas sampling systems carefully
building response to wind and temperature requires repetition
for their reactivity and absorption of the tracer gas in use.
of the test under varying meteorological conditions. Relating
Depending on the tracer gas, desirable materials include glass,
building response to the ventilation system or to occupant
copper,andstainlesssteel.Metalfoilisappropriateforflexible
behavior requires controlled variation of these factors.
containers. Other acceptable materials include polypropylene,
5.5 Applicability of Results—The values for air change
polyethylene, and nylon. Materials that absorb tracer gas
obtainedbythetechniquesusedinthistestmethodapplytothe
degrade the accuracy of the measurement. Other materials
specific conditions prevailing at the time of the measurement.
release substances that interfere with tracer gas analyzer
Air change values for the same building will differ if the
accuracy. Depending on the tracer gas, materials to avoid
prevailing wind and temperature conditions have changed, if
include soft plastics, like vinyl and TFE-fluorocarbon.
the operation of the building is different, or if the envelope
6.4.2 Manual Samplers—These include syringes, flexible
changes between measurements because of construction or
bottles, or air sample bags with a capacity of at least three
deterioration. To determine air leakage sites, follow Practice
timestheminimumsamplesizeofthegasanalyzerused.These
E1186.
containers shall have an airtight seal to assure that the sample
5.6 Fan Pressurization—A related technique (Test Method is not diluted or contaminated. Each container shall have a
labelthatkeysittoarecordofthetimeandlocationthatitwas
E779)usesafantopressurizethebuildingenvelope.Measure-
ments of corresponding air flows and pressure differences used. Do not reuse sample containers without first confirming
that they are not contaminated with tracer gas.
acrosstheenvelopecharacterizeenvelopeairtightnessaseither
6.4.
...
This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately,ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
An American National Standard Designation: E 741 – 00 (Reapproved 2006)
Designation:E741–95
Standard Test Method for
Determining Air Change in a Single Zone by Means of a
Tracer Gas Dilution
This standard is issued under the fixed designation E741; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
´ NOTE—X5.2.3 and X5.2.5 were editorially corrected in September 2009.
1. Scope
1.1 This test method describescovers techniques using tracer gas dilution for determining a single zone’s air change with the
outdoors, as induced by weather conditions and by mechanical ventilation. 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 characterize the
tracer gas concentration within the zone with a single value. The zone shall be a building, vehicle, test cell, or any conforming
enclosure.
1.3 Use of this test method requires a knowledge of the principles of gas analysis and instrumentation. Correct use of the
formulas presented here requires consistent use of units, especially those of time.
1.4 Determination of the contribution to air change by individual components of the zone enclosure is beyond the scope of this
test method.
1.5 The results from this test method pertain only to those conditions of weather and zonal operation that prevailed during the
measurement. The use of the results from this test to predict air change under other conditions is beyond the scope of this test
method.
1.6 The text of this test method references notes and footnotes which provide explanatory material. These notes and footnotes
(excluding those in tables and figures) shall not be considered requirements of this test method.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D4480 Test Method for Measuring Surface Wind by Means of Wind Vanes and Rotating Anemometers
E260 Practice for Packed Column Gas Chromatography
E779 Test Method for Determining Air Leakage Rate by Fan Pressurization
E1186 Practice for Air Leakage Site Detection in Building Envelopes Practices for Air Leakage Site Detection in Building
Envelopes and Air Barrier Systems
2.2 Other Documents:
ASHRAE Handbook of Fundamentals, Chapter 23
5 4
ASHRAE Standard62 ASHRAE Documents:
ASHRAEHandbookofFundamentals Chapter 23
This test method is under the jurisdiction of ASTM Committee E-6E06 on Performance of Buildings and is the direct responsibility of Subcommittee E06.41 on Air
Leakage and Ventilation.
Current edition approved Sept. 10, 1995. Published November 1995. Originally published as E741–80. Last previous edition E741–93.on Air Leakage and Ventilation
Performance.
Current edition approved Oct. 1, 2006. Published October 2006. Originally approved in 1980. Last previous edition approved in 2000 as E741–00.
Annual Book of ASTM Standards, Vol 11.03.
ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatservice@astm.org.ForAnnualBookofASTMStandards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Annual Book of ASTM Standards, Vol 14.02.
Withdrawn.
Annual Book of ASTM Standards, Vol 04.11.
Available from American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. (ASHRAE), 1791 Tullie Circle, NE, Atlanta, GA 30329,
http://www.ashrae.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
´1
E 741 – 00 (2006)
ASHRAEStandard62
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3 3
3.1.1 airchangeflow,Q,n—thetotalvolumeofairpassingthroughthezonetoandfromtheoutdoorsperunittime(m /s,m /h,
ft /h).
3.1.2 air change rate, A, n—the ratio of the total volume of air passing through the zone to and from the outdoors per unit of
time to the volume of the zone (1/s, 1/h).
3.1.3 envelope, n—the system of barriers between a conditioned building zone and the outdoors.
3.1.3.1 Discussion—This includes exterior doors, windows, roofs, walls, floors and ductwork. It excludes interior partitions,
ducts, etc.,and so forth, that separate conditioned zones.
3.1.4 tracer gas, n—a gas that is mixed with air and measured in very small concentrations in order to study air movement.
3.1.5 tracer gas analyzer, n—a device used to measure the concentration of tracer gas in an air sample.
3.1.6 tracer gas concentration, C, n—the ratio of the quantity of tracer gas in air to the quantity of that air (moles/mole or
3 3
m /m ).
3.1.7 single zone, n—a space or set of spaces wherein the concentration of a tracer gas is maintained uniformly throughout and
that only exchanges air with the outside.
3.1.7.1 Discussion—Multizonebuildingsaredifficulttotreatassinglezonesandmeettheuniformityoftracergasconcentration
required in this test method. Single zones within multizone buildings are difficult to isolate such that they exchange air only with
the outside and not to other zones within the building via ventilation ducts, electrical conduits, elevator shafts, stairs, and other
pathways.
3.2 Symbols:
3.2.1 Variables:
A = air change rate (1/s, 1/h).
C = concentration (dimensionless).
CONF = confidence limit value (units of the variable measured).
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.
3 3 3
Q = flow (m /s, m /h, ft /h).
s = sample standard deviation (units of the variable estimated).
t = a specific time (s, h).
T = a period of time (s, h).
3 3
V = volume (m,ft ).
a = probability (dimensionless).
´ = error (units of the variable estimated).
n = coefficient of variation (dimensionless).
3.2.2 Superscripts:
8 = value at the end of the test.
− = mean value.
3.2.3 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.
Available from American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc., 1791 Tullie Circle, N.E., Atlanta, GA 30329.
A common way of expressing air change rate units is ACH=air changes per hour=1/h.
´1
E 741 – 00 (2006)
i = pertaining to time or location i. pertaining to time or location.
inj = pertaining to the injection period.
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 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.
3.2.4 Other Notations:
Dt = time interval between periodic samples.
(t) = function of time t. function of time.
(t, i) = function of time function of time, tand location , and location, i.
t(n, = t-distribution value for n degrees of freedom and a two-sided probability of a.
1−a)
4. Summary of Test Method
4.1 This test method uses the measurement of tracer gas dilution to determine air change within a building or other enclosure
that is characterized as a single zone.The measurement of the concentration, and sometimes the volume rate of the tracer gas that
is injected into the zone, allows calculation of the volume rate of outgoing air from the zone. From this, one can infer the volume
rateofincomingair.Threetechniquesarepresented:(1)concentrationdecay,(2)constantinjection,and(3)constantconcentration.
Each technique employs specific tracer gas injection and sampling strategies. Other techniques exist but are beyond the scope of
this test method. Table 1 summarizes the three techniques.
4.2 Choice of Technique—In choosing a technique for measuring air change, consider the quantity to be measured, the
comparative capabilities of the techniques, and the complexity of the required equipment.
4.2.1 Air Change Quantity to Be Measured—Choose between direct measurement of air change rate or air change flow.
TABLE 1 Summary of Air Change Measurement Techniques
NOTE 1—Speed of Measurement—A one-time measurement of air
change is most quickly acquired with the concentration decay technique
and least quickly with the constant concentration technique.
NOTE 2—Time-Varying Air Change—The constant concentration and
constantinjectiontechniquesmaybeusefulformeasuringairchangerates
that vary with time.
NOTE 3—Complexity of Zone Geometry—Whereas all the techniques
require uniform tracer gas concentration, the constant concentration
techniquemaybeusefultoachievethisinazonewithcomplexgeometry.
NOTE 4—Equipment Complexity—The complexity of the required
equipment is lowest for the tracer gas decay technique and highest for the
constant concentration technique.
Type of Air Steady-State Concentration
Tech- Volume Control of
Change Mea- Assumption Measurement
nique Tracer Gas
surement Required? Relative To
Concentration Decay—Section 8
Average Rate No Approximate initial- Other samples
target
Regres- Rate Yes Approximate initial Other samples
sion target
Constant Injection—Section 9
Average Flow No Flow rate to within Absolute stan-
2% dard
Constant Concentration—Section 10
Flow No Mean concentration Absolute stan-
within2%oftarget dard
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E 741 – 00 (2006)
Conversions between rate and flow and vice versa are subject to the precision and bias of the measurement of the zone volume.
To obtain air change rate directly, use the tracer gas decay technique. To obtain air change flow, use the constant injection or
constant concentration techniques.
5. Significance and Use
5.1 Effects of Air Change—Air change often accounts for a significant portion of the heating or air-conditioning load of a
building. It also affects the moisture and contaminant balances in the building. Moisture-laden air passing through the building
envelope can permit condensation and cause material degradation.An appropriate level of ventilation is required in all buildings;
one should consult ASHRAE Standard62ASHRAEStandard62 to determine the ventilation requirements of a building.
5.2 PredictionofAirChange—Airchangedependsonthesizeanddistributionofairleakagesites,pressuredifferencesinduced
by wind and temperature, mechanical system operation, and occupant behavior. Air change may be calculated from this
information, however, many of the needed parameters are difficult to determine.Tracer gas testing permits direct measurement of
air change.
5.3 Utility of Measurement—Measurements of air change provide useful information about ventilation and air leakage.
Measurements in buildings with the ventilation system closed are used to determine whether natural air leakage rates are higher
than specified. Measurements with the ventilation system in operation are used to determine whether the air change meets or
exceeds requirements.
5.4 Known Conditions—Knowledge of the factors that affect air change makes measurement more meaningful. Relating
building response to wind and temperature requires repetition of the test under varying meteorological conditions. Relating
building response to the ventilation system or to occupant behavior requires controlled variation of these factors.
5.5 Applicability of Results—Thevaluesforairchangeobtainedbythetechniquesusedinthistestmethodapplytothespecific
conditions prevailing at the time of the measurement. Air change values for the same building will differ if the prevailing wind
and temperature conditions have changed, if the operation of the building is different, or if the envelope changes between
measurements because of construction or deterioration. To determine air leakage sites, follow Practice E1186.
5.6 FanPressurization—Arelatedtechnique(TestMethodE779)usesafantopressurizethebuildingenvelope.Measurements
ofcorrespondingairflowsandpressuredifferencesacrosstheenvelopecharacterizeenvelopeairtightnessaseithertheairleakage
rate under specified induced pressure differences or the equivalent leakage area of the envelope. These factors permit modeling
naturalairchangeduetowindandtemperaturedifferences.However,directmeasurementofnaturalairchangeisnotpossiblewith
Test Method E779. Test Method E779 permits comparison of different buildings, isolation of leakage sites, and evaluation of
retrofit measures.
6. Apparatus
6.1 The apparatus includes means for distributing the tracer gas, means for obtaining air samples, a gas analyzer to measure
tracer gas concentration in the air samples, and other measurement devices.
6.2 Tracer Gas—See Appendix X1 for information on tracer gases and equipment used to measure their concentrations.
Appendix X1 also contains tracer gas target concentration levels and safety information.
6.2.1 Tracer Gas Concentration Standard—A known concentration of tracer gas in air.
6.3 Tracer Gas Injection and Distribution Apparatus—There are several means for releasing the appropriate volume of tracer
gas and distributing it in the zone.
6.3.1 Tracer Gas Metering and Injection Devices—These include (1) a graduated syringe or other container of known volume
with a means for controlled release of its contents and (2) a compressed tracer gas supply with a critical orifice, a critical orifice
metering valve, an electronic mass flow controller, or other tracer gas flow rate measurement and control device.
6.3.2 TracerGasDistributionDevices—Theseinclude(1)fansthatpermitgoodmixingoftracergasesinjectedmanuallywithin
thezone(oscillatingorhassockfans,or,ductedforcedairsystemscanservethispurpose),(2)tubingnetworksthatdispensetracer
gasviamanifoldsandautomatedvalvesand(3)pressure-operatedvalvesthatst
...
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