ASTM E741-23

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E741 − 23
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. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.9 This international standard was developed in accor-
dance with internationally recognized principles on standard-
1.1 This test method covers techniques using tracer gas
ization established in the Decision on Principles for the
dilution for determining a single zone’s air change with the
Development of International Standards, Guides and Recom-
outdoors, as induced by weather conditions and by mechanical
mendations issued by the World Trade Organization Technical
ventilation. These techniques are: (1) concentration decay, (2)
Barriers to Trade (TBT) Committee.
constant injection, and (3) constant concentration.
1.2 This test method is restricted to a single tracer gas. 2. Referenced Documents
1.3 The associated data analysis assumes that one can 2.1 ASTM Standards:
characterize the tracer gas concentration within the zone with D4480 Test Method for Measuring Surface Wind by Means
a single value. The zone shall be a building, vehicle, test cell, of Wind Vanes and Rotating Anemometers (Withdrawn
or any conforming enclosure. 1999)
E260 Practice for Packed Column Gas Chromatography
1.4 Use of this test method requires a knowledge of the
E631 Terminology of Building Constructions
principles of gas analysis and instrumentation. Correct use of
E779 Test Method for Determining Air Leakage Rate by Fan
the formulas presented here requires consistent use of units,
Pressurization
especially those of time.
E1186 Practices for Air Leakage Site Detection in Building
1.5 Determination of the contribution to air change by
Envelopes and Air Barrier Systems
individual components of the zone enclosure is beyond the
2.2 ASHRAE Documents:
scope of this test method.
ASHRAE Handbook of Fundamentals Chapter 23
1.6 The results from this test method pertain only to those ASHRAE Standard 62 Ventilation And Acceptable Indoor
conditions of weather and zonal operation that prevailed during Air Quality
the measurement. The use of the results from this test to predict
3. Terminology
air change under other conditions is beyond the scope of this
test method.
3.1 Definitions:
3.1.1 For definitions of general terms related to building
1.7 The text of this test method references notes and
construction used in this test method, refer to Terminology
footnotes which provide explanatory material. These notes and
E631.
footnotes (excluding those in tables and figures) shall not be
3.2 Definitions of Terms Specific to This Standard:
considered requirements of this test method.
3.2.1 air change flow, Q, n—the total volume of air passing
1.8 This standard does not purport to address all of the
through the zone to and from the outdoors per unit time (m /s,
safety concerns, if any, associated with its use. It is the
3 3
m /h, ft /h).
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
mine the applicability of regulatory limitations prior to use.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
This test method is under the jurisdiction of ASTM Committee E06 on the ASTM website.
Performance of Buildings and is the direct responsibility of Subcommittee E06.41 The last approved version of this historical standard is referenced on
on Air Leakage and Ventilation Performance. www.astm.org.
Current edition approved July 1, 2023. Published July 2023. Originally approved Available from American Society of Heating, Refrigerating, and Air-
in 1980. Last previous edition approved in 2017 as E741 – 11 (2017). DOI: Conditioning Engineers, Inc. (ASHRAE), 1791 Tullie Circle, NE, Atlanta, GA
10.1520/E0741-23. 30329, http://www.ashrae.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E741 − 23
3.2.2 air change rate, A, n—the ratio of the total volume of
A = pertaining to air change rate.
air passing through the zone to and from the outdoors per unit
avg = average.
of time to the volume of the zone (1/s, 1/h).
bias = pertaining to bias.
C = pertaining to concentration.
3.2.3 envelope, n—the system of barriers between a condi-
est = estimated.
tioned building zone and the outdoors.
GA = pertaining to the gas analyzer.
3.2.3.1 Discussion—This includes exterior doors, windows,
i = pertaining to time or location.
roofs, walls, floors and ductwork. It excludes interior
inj = pertaining to the injection period.
partitions, ducts, and so forth, that separate conditioned zones.
lower = lower limit.
3.2.4 single zone, n—a space or set of spaces wherein the
meas = pertaining to the measurement.
concentration of a tracer gas is maintained uniformly through- mix = pertaining to the mixing period.
precis = pertaining to precision.
out and that only exchanges air with the outside.
rep = pertaining to replicates.
3.2.4.1 Discussion—Multizone buildings are difficult to
sample = pertaining to a discrete tracer gas or air sample.
treat as single zones and meet the uniformity of tracer gas
target = pertaining to the desired level of tracer gas.
concentration required in this test method. Single zones within
test = pertaining to the test period.
multizone buildings are difficult to isolate such that they
tracer = pertaining to the tracer gas.
exchange air only with the outside and not to other zones
twt = weighted according to tracer gas flow.
within the building via ventilation ducts, electrical conduits,
upper = upper limit.
elevator shafts, stairs, and other pathways.
vol = pertaining to the volume of the zone.
3.2.5 tracer gas, n—a gas that is mixed with air and
zone = pertaining to the zone under study.
measured in very small concentrations in order to study air
1 = first occurrence under discussion.
2 = last occurrence under discussion.
movement.
3.2.6 tracer gas analyzer, n—a device used to measure the
3.3.4 Other Notations:
concentration of tracer gas in an air sample.
3.2.7 tracer gas concentration, C, n—the ratio of the quan-
∆t = time interval between periodic samples.
tity of tracer gas in air to the quantity of that air (moles/mole
(t) = function of time.
3 3
or m /m ).
(t, i) = function of time, t, and location, i.
t(n, 1−α) = t-distribution value for n degrees of freedom and
3.3 Symbols:
3.3.1 Variables: a two-sided probability of α.
4. Summary of Test Method
A = air change rate (1/s, 1/h).
4.1 This test method uses the measurement of tracer gas
C = concentration (dimensionless).
dilution to determine air change within a building or other
CONF = confidence limit value (units of the variable mea-
enclosure that is characterized as a single zone. The measure-
sured).
ment of the concentration, and sometimes the volume rate of
d = desired precision (dimensionless).
the tracer gas that is injected into the zone, allows calculation
ESE = estimated standard error.
of the volume rate of outgoing air from the zone. From this,
i = location number.
one can infer the volume rate of incoming air. Three techniques
k = constant.
are presented: (1) concentration decay, (2) constant injection,
n = number of data points.
and (3) constant concentration. Each technique employs spe-
N = number of sampling locations in the zone.
3 3 3
cific tracer gas injection and sampling strategies. Other tech-
Q = flow (m /s, m /h, ft /h).
niques exist but are beyond the scope of this test method. Table
s = sample standard deviation (units of the variable
1 summarizes the three techniques.
estimated).
t = a specific time (s, h).
4.2 Choice of Technique—In choosing a technique for
T = a period of time (s, h).
measuring air change, consider the quantity to be measured, the
3 3
V = volume (m , ft ).
comparative capabilities of the techniques, and the complexity
α = probability (dimensionless).
of the required equipment.
ε = error (units of the variable estimated).
4.2.1 Air Change Quantity to Be Measured—Choose be-
ν = coefficient of variation (dimensionless).
tween direct measurement of air change rate or air change flow.
3.3.2 Superscripts:
Conversions between rate and flow and vice versa are subject
to the precision and bias of the measurement of the zone
' = value at the end of the test.
volume. To obtain air change rate directly, use the tracer gas
− = mean value.
decay technique. To obtain air change flow, use the constant
3.3.3 Subscripts:
injection or constant concentration techniques.
5. Significance and Use
5.1 Effects of Air Change—Air change often accounts for a
A common way of expressing air change rate units is ACH = air changes per
hour = 1 ⁄h. significant portion of the heating or air-conditioning load of a
E741 − 23
TABLE 1 Summary of Air Change Measurement Techniques
the operation of the building is different, or if the envelope
changes between measurements because of construction or
NOTE 1—Speed of Measurement—A one-time measurement of air
deterioration. To determine air leakage sites, follow Practices
change is most quickly acquired with the concentration decay technique
and least quickly with the constant concentration technique.
E1186.
NOTE 2—Time-Varying Air Change—The constant concentration and
5.6 Fan Pressurization—A related technique (Test Method
constant injection techniques may be useful for measuring air change rates
E779) uses a fan to pressurize the building envelope. Measure-
that vary with time.
ments of corresponding air flows and pressure differences
NOTE 3—Complexity of Zone Geometry—Whereas all the techniques
across the envelope characterize envelope airtightness as either
require uniform tracer gas concentration, the constant concentration
the air leakage rate under specified induced pressure differ-
technique may be useful to achieve this in a zone with complex geometry.
ences or the equivalent leakage area of the envelope. These
NOTE 4—Equipment Complexity—The complexity of the required
factors permit modeling natural air change due to wind and
equipment is lowest for the tracer gas decay technique and highest for the
temperature differences. However, direct measurement of natu-
constant concentration technique.
ral air change is not possible with Test Method E779. Test
Type of Air Steady-State Concentration
Tech- Volume Control of Method E779 permits comparison of different buildings, iso-
Change Assumption Measurement
nique Tracer Gas
lation of leakage sites, and evaluation of retrofit measures.
Measurement Required? Relative To
Concentration Decay—Section 8
Average Rate No Approximate initial Other samples
6. Apparatus
target
Regres- Rate Yes Approximate initial Other samples
6.1 The apparatus includes means for distributing the tracer
sion target
gas, means for obtaining air samples, a gas analyzer to measure
Constant Injection—Section 9
Average Flow No Flow rate to Absolute stan-
tracer gas concentration in the air samples, and other measure-
within 2 % dard
ment devices.
Constant Concentration—Section 10
Flow No Mean concentration Absolute
6.2 Tracer Gas—See Appendix X1 for information on tracer
within 2 % of target standard
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 con-
building. It also affects the moisture and contaminant balances
centration of tracer gas in air.
in the building. Moisture-laden air passing through the building
envelope can permit condensation and cause material degrada- 6.3 Tracer Gas Injection and Distribution Apparatus—
tion. An appropriate level of ventilation is required in all There are several means for releasing the appropriate volume
buildings; one should consult ASHRAE Standard 62 to deter- of tracer gas and distributing it in the zone.
mine the ventilation requirements of a building. 6.3.1 Tracer Gas Metering and Injection Devices—These
include (1) a graduated syringe or other container of known
5.2 Prediction of Air Change—Air change depends on the
volume with a means for controlled release of its contents and
size and distribution of air leakage sites, pressure differences
(2) a compressed tracer gas supply with a critical orifice, a
induced by wind and temperature, mechanical system
critical orifice metering valve, an electronic mass flow
operation, and occupant behavior. Air change may be calcu-
controller, or other tracer gas flow rate measurement and
lated from this information, however, many of the needed
control device.
parameters are difficult to determine. Tracer gas testing permits
6.3.2 Tracer Gas Distribution Devices—These include (1)
direct measurement of air change.
fans that permit good mixing of tracer gases injected manually
5.3 Utility of Measurement—Measurements of air change
within the zone (oscillating or hassock fans, or, ducted forced
provide useful information about ventilation and air leakage.
air systems can serve this purpose), (2) tubing networks that
Measurements in buildings with the ventilation system closed
dispense tracer gas via manifolds and automated valves and (3)
are used to determine whether natural air leakage rates are
pressure-operated valves that stop the flow from a tubing
higher than specified. Measurements with the ventilation sys-
network when the tubing is not pressurized. (Note that leaks in
tem in operation are used to determine whether the air change
tubing networks release tracer gas at unintended locations.)
meets or exceeds requirements.
6.4 Tracer Gas Sampling Apparatuses—Examples include
5.4 Known Conditions—Knowledge of the factors that af-
containers for manual sampling and automatic samplers that
fect air change makes measurement more meaningful. Relating
employ containers or networks.
building response to wind and temperature requires repetition
6.4.1 Materials for Sampling Apparatuses—Select and
of the test under varying meteorological conditions. Relating
check materials used in tracer gas sampling systems carefully
building response to the ventilation system or to occupant
for their reactivity and absorption of the tracer gas in use.
behavior requires controlled variation of these factors.
Depending on the tracer gas, desirable materials include glass,
5.5 Applicability of Results—The values for air change copper, and stainless steel. Metal foil is appropriate for flexible
obtained by the techniques used in this test method apply to the containers. Other acceptable materials include polypropylene,
specific conditions prevailing at the time of the measurement. polyethylene, and nylon. Materials that absorb tracer gas
Air change values for the same building will differ if the degrade the accuracy of the measurement. Other materials
prevailing wind and temperature conditions have changed, if release substances that interfere with tracer gas analyzer
E741 − 23
accuracy. Depending on the tracer gas, materials to avoid tion is required. A digital optimal adaptive proportional control
include soft plastics, like vinyl and TFE-fluorocarbon. algorithm has been used effectively for constant concentration
measurements (1).
6.4.2 Manual Samplers—These include syringes, flexible
bottles, or air sample bags with a capacity of at least three
7. Hazards
times the minimum sample size of the gas analyzer used. These
containers shall have an airtight seal to assure that the sample
7.1 Safety is the responsibility of the user of this test
is not diluted or contaminated. Each container shall have a
method. Tracer gases have safe maximum concentration limits
label that keys it to a record of the time and location that it was
due to health and, in some cases, explosiveness. Table X1.1
used. Do not reuse sample containers without first confirming
presents, as a guide, the maximum allowable concentration in
that they are not contaminated with tracer gas.
air for some tracer gases that have been used for air change
6.4.3 Automatic Samplers—These apparatuses comprise ei-
measurements. The tracer gas supplier’s material safety data
ther a sampling network or automated samplers.
sheet also provides information about health, fire, and explo-
6.4.3.1 Sampling Networks—These include (1) tubing, (2) a sion hazards.
manifold or selection switch (the manifold receives, combines,
7.2 Health Limitations—Use the current OSHA information
and averages equal flows from individual legs of the network;
on the permissible exposure limit (PEL) to determine the
the selection switch, often solenoid-driven, permits sampling
maximum safe concentration for the tracer gas chosen for the
of individual legs of the network), and (3) a pump that draws
test. Use a concentration that is at most one tenth of the
air samples through the network at a rate that minimizes delays
maximum safe concentration. Avoid using tracer gases for
between the time air samples leave the zone and the time they
which no OSHA PEL exists.
reach the gas analyzer.
NOTE 1—Special circumstances may cause one tenth of PEL to be too
6.4.3.2 Automated Samplers—These self-contained units,
high a concentration. For example, the heat of a lit cigarette decomposes
such as syringe samplers, are programmed to draw air samples
some tracer gases into potentially hazardous by-products when air is
at defined time intervals. Place such devices at different
inhaled through the cigarette. In such cases, lower tracer gas concentra-
locations throughout the zone to be evaluated when required. tions are required.
7.3 Explosive Limits—If the tracer gas is explosive, the
6.5 Gas Analyzer—This device shall be suited for the tracer
tracer gas concentration shall never exceed one tenth the lower
gas used and the concentrations within the zone studied. It shall
explosive limit.
be properly calibrated and have a precision of better than
65 % at concentrations employed in the tracer gas study. See
7.4 Compressed Gas Equipment—Observe the supplier’s
Appendix X2 for calibration information.
safety information and CGA (2) information on the
transportation, use, and storage of compressed gas cylinders,
6.6 Ancillary Measurement Devices:
regulators, and related equipment.
6.6.1 Portable Meteorological Station—This records wind
speed and direction and outdoor temperature. Meteorological
8. Procedure for the Concentration Decay Test Method
data collected at a local weather station are acceptable.
8.1 Summary—To determine average air change rate, one
6.6.2 Temperature Measurement—Use a thermometer or
introduces a small volume of tracer gas uniformly into the
record the output of thermocouples, thermistors, resistance
zone, ensures a uniform concentration, and then measures
thermal devices (RTDs), and so forth.
tracer gas concentration at known times. One calculates the
6.6.3 Timing Device—This provides a common standard for
average air change rate for that period as the difference
all events relating to the measurement procedure, including gas
between the logarithms of the initial and final tracer gas
injection times, sampling times, and meteorological driving
concentrations divided by the time period. When required, one
forces. The timing device shall determine time differences
shall obtain additional air samples to test the hypothesis that
between events within a 1 % uncertainty.
the air change rate was constant during the test with an optional
6.7 Data Acquisition and Control System—This equipment
regression analysis of the logarithms of additional tracer gas
is optional for all but the constant concentration technique.
concentration measurements. Fig. 1 gives a simplified over-
6.7.1 Data Acquisition—Appropriate interfaces provide view of this test method.
temperature, wind speed, wind direction, and tracer gas con-
8.2 Preparation:
centration data to a computer or other machine-readable data
8.2.1 Ancillary Measurements—Refer to 11.1.
storage unit.
8.2.2 Zonal Operation—Prepare the zone according to 11.2.
6.7.2 Control of Processes—A computer uses current tracer
8.2.3 Tracer Gas Injection Volume—Determine the volume
gas concentration information to control metering and switch-
of the tracer gas to be injected V according to the
tracer
ing equipment to deliver tracer gas to the appropriate parts of
following steps:
the network. When a feedback process controls gas
8.2.3.1 Estimate the volume of the zone V in the same
zone
concentrations, based on gas concentration measurements, an
units as V will be measured (15.3),
tracer
algorithm that minimizes deviation from the target concentra-
The boldface numbers in parentheses refer to the list of references at the end of
Precision refers to the standard error of the measurement. this standard.
E741 − 23
8.4 Sampling—First, perform spatial sampling to confirm
uniformity of concentration, using 13.3. When the uniformity
of concentration criterion 12.4.1 is confirmed, then sample as
follows:
8.4.1 All Conditions—At a minimum, take a second set of
spatial samplings (13.3) at the end of the sampling period, for
the period T . Check for tracer gas sources in adjacent spaces,
test
according to 13.4.3.
8.4.2 Time Series for the Optional Regression Method—
Take representative samples at intervals, as determined in
8.2.4.2. A minimum of five such samples is required for the
regression method (8.5.3.2).
8.5 Analysis:
8.5.1 Analyze Tracer Gas Concentrations—Analysis of
tracer gas concentration takes place either on site concurrently
FIG. 1 Simplified Summary of the Apparatus and Procedure for
with the sampling process, or off site, if the samples are stored
the Concentration Decay Method
in sealed, labeled containers. Analyze and record the tracer gas
concentration of each sample, together with the sampling time
and location, according to the procedures in Section 14.
8.2.3.2 Determine the target tracer gas concentration C
target
Eliminate any concentration data that are outside the 5 %
at the high end of the detection limits of the gas analyzer, and
precision range of the analyzer.
8.2.3.3 Compute the following:
8.5.2 Confirm Uniformity of Concentration—Assess the
V 5 C × V (1)
tracer target zone
concentrations of the spatial samplings for uniformity of
8.2.4 Sampling—Emplace the desired apparatus for concentration, according to 12.4.1. Confirm uniformity of
sampling, according to one of the methods described in Section
tracer gas concentrations at the beginning and end of the
13. Note that manual sampling, 13.1, or direct automated sampling period (8.4.1). Estimate the measurement precision
sampling, 13.2.2, are the most likely choices.
using 14.1.3.
8.2.4.1 Sampling Duration—Table 2 illustrates minimum
8.5.3 Calculate Air Change Rate—Calculate air change rate
sampling durations based on a 10 % uncertainty at the 95 %
by the averaged method or the regression method as follows:
confidence level in the determination of air change rate, a
8.5.3.1 Averaged Method—Calculate C , the average of the
tracer gas concentration measurement precision error (14.1.3),
concentrations at the time t that confirmed the uniformity of
ν , of 5 % of reading, and various air change rates. Refer to
meas
concentration criterion (8.4). Calculate C , the average of the
Eq A1.1 for the general case. Note that when using the
concentrations at the time t that confirmed the uniformity of
regression method the minimum test duration is often less than
concentration criterion at the end of the test (8.4.1). Calculate
the test duration values shown in Table 2. This decrease in test
¯
mean air change rate A by Eq 2:
duration is primarily due to the inclusion of more than two data
¯
points in the determination of the best fit line as described in
A 5 @lnC~t ! 2 lnC~t !#/~t 2 t ! (2)
2 1 2 1
8.5.3.2.
8.5.3.2 Optional Regression Method—Calculate C , the av-
8.2.4.2 Sampling Frequency—For the optional regression t
erage of the concentrations for the time period (t) after
method (8.5.3.2), there shall be a minimum of five points,
satisfying the uniformity of concentration criterion (8.4). Plot
approximately evenly distributed over the measurement period.
the data on axes of ln C(t) against t, as illustrated in Fig. 2.
8.3 Tracer Gas Injection—Note that manual injection, 12.2,
With the assumption of constant air change, the following
is the simplest acceptable technique of those available in
relationship holds:
Section 12. Record the time and volume of the injection.
lnC~t! 5 2At1lnC~0! (3)
Distribute the tracer gas uniformly in the zone according to
12.4.3 in order to meet the uniformity of concentration
Perform a regression of ln C(t) against t. In a typical
criterion of 12.4.1.
regression program on a hand-held calculator or spreadsheet
program, one performs a regression on Y against X to find the
constants a and b in the relationship:
TABLE 2 Examples of Minimum Durations Between the Initial and
Y 5 aX1b (4)
Final Samples for the Above Assumptions
Air Change Rate (1/h) Minimum Duration of Test (h)
In this case A corresponds to a, ln C(0) corresponds to b, ln
0.25 4
C(t) corresponds to Y, and t corresponds to X. Establish
0.5 2
1 1
confidence intervals for A, according to Appendix X3.1.
2 0.5
8.5.4 Reporting of Ancillary Measurements—Refer to 15.4
4 0.25
for reporting of ancillary measurements.
E741 − 23
FIG. 2 Concentrations and Estimate of Concentrations Plotted
Logarithmically
9. Procedure for the Constant Injection Test Method
9.1 Summary—To determine the average air change flow,
FIG. 3 Schematic Diagram of the Apparatus for the Constant In-
jection Method
inject tracer gas uniformly into the zone at a known, constant
rate, ensure a uniform concentration, and then measure tracer
gas concentration at known times. Calculate the average air
change flow for the measurement period as the product of the
9.2.3.4 Compute the following:
tracer gas flow rate times the average of the inverses of
measured concentration less a correction for the beginning and Q 5 C × V × A (8)
tracer target zone est
ending concentrations:
Eq 1 presents one method used to calculate an initial dose of
1 V C2
zone tracer gas C(0) ≈ C in order to obtain a more rapid tracer
target
Q avg 2 ln
S F G F GD
tracer
C t2 2 t1 C1
gas concentration equilibrium.
A 5 (5)
V
zone 9.2.4 Sampling—Emplace the desired apparatus for
It is not necessary to know the volume of the zone if the
sampling, according to one of the methods described in Section
beginning and ending concentrations used in the calculation
13. Automated sampling (13.2) offers a convenient means to
are approximately equal and the equation above reduces to:
obtain a time series. Place the intake of each sampling unit
away from tracer gas injection points.
Q avg
S F G D
tracer
C
A 5 (6) 9.3 Tracer Gas Injection—Inject tracer gas at a constant,
V
zone
known rate; metered injection (12.3) is one method. Record the
Or for flow:
starting time, duration, and rate Q of the injection. Also
tracer
note any initial measured dose of tracer gas used to achieve an
Q 5 Q avg (7)
F G
tracer
C
equilibrium. Distribute the tracer gas in the zone according to
Test the assumption of constant air change for the time pe-
12.4.3 in order to meet the uniformity of concentration
riod with an optional analysis of confidence intervals of the
criterion of 12.4.1. If the equilibrium concentration falls
tracer gas concentrations after equilibrium has occurred. Fig.
outside of the range for accurate measurement, adjust the flow
3 gives a simplified overview of this test method.
rate appropriately. Do not use concentration data that are
9.2 Preparation:
outside the 5 % precision range of the analyzer.
9.2.1 Ancillary Measurements—Refer to 11.1. The constant
9.3.1 Tracer Gas Injection Uncertainty and Bias—The un-
injection technique requires determination of zone volume
certainty of the tracer gas injection rate shall be less than 2 %.
(15.3) in the presence of non-steady-state air change flow.
The bias of the assumed injection rate shall be no more than
9.2.2 Zonal Operation—Prepare the zone according to 11.2.
2 % of the true rate.
9.2.3 Tracer Gas Injection Flow Rate and Initial Volume—
Determine the volume flow rate of the tracer gas to be injected 9.4 Sampling—First, perform spatial sampling to confirm
Q according to the following steps: adequate uniformity of concentration using 13.3. When the
tracer
9.2.3.1 Estimate the volume of the zone being measured uniformity of concentration criterion 12.4.1 is confirmed, then
V in the same volume units as Q , sample as follows:
zone tracer
9.2.3.2 Estimate the air change rate A in the zone and 9.4.1 Spatial Sampling—At a minimum, take a second set of
convert it into A in the time units of Q , spatial samplings (13.3) at the end of the sampling period, for
est tracer
9.2.3.3 Determine the target tracer gas concentration C the period T . Check for tracer gas sources in adjacent spaces
target test
that is mid-range in the detection limits of the gas analyzer, and according to 13.4.3.
E741 − 23
9.4.2 Time Series Sampling—Take a representative sample a confidence interval calculation (X3.2) to these Q values tests
or set of spatial samples over a consistent timeframe for the how far the air change flow is from constant.
period T . A minimum of five such samples or five sets of 9.5.4 Correlation with Ancillary Measurements—Refer to
test
spatial samples is required during the measurement period. 15.4 for reporting of ancillary measurements.
Compute the average air flow rate with these data using Eq 7.
10. Procedure for the Constant Concentration Test
9.4.3 Concentration Equilibrium—If one chooses to test the
Method
assumption of constant air change for the time period, then one
shall continue to sample (9.4.2) after equilibrium has occurred. 10.1 Summary—To monitor changing air change flow, mea-
The criterion for equilibrium shall have been met if: sure and control tracer gas at a constant concentration with
automated equipment. The equipment measures tracer gas
Q
C 2 C
tracer
final initial
,0.05 (9) concentration and then injects enough tracer gas into the zone
U U
T V
test zone
to maintain a desired uniform concentration. Calculate the air
If one starts with a zero tracer gas concentration in the zone change flow for each measurement interval from the ratio of
and injects at a constant rate, the tracer gas reaches 95 % of the the required additional tracer gas to the desired concentration.
equilibrium concentration within the zone after a period of Fig. 4 gives a simplified overview of this test method. With this
time, T = 3 ⁄A. So, for A = 1, 2, and 3 per hour, T = 3, technique one is able to achieve a uniform tracer gas concen-
crit crit
1.5, and 1 hours, respectively. tration in many single zones with complex geometries.
10.2 Preparation:
9.5 Analysis:
10.2.1 Ancillary Measurements—Refer to 11.1.
9.5.1 Analyze Tracer Gas Concentrations—Analysis of
10.2.2 Zonal Operation—Prepare the zone according to
tracer gas concentration shall occur either on site concurrently
11.2.
with the sampling process, using network sampling (13.2.1)
10.2.3 Tracer Gas Injection Flow Rate and Initial Volume—
connected to a gas analyzer, or off site, if the samples are stored
This technique requires automated, switched, network injection
in sealed, labeled containers. Note that if off-site analysis
(12.3.2.2). Connect the injection apparatus to the gas metering
reveals that the mixing or equilibrium criterion has been
device and to the computer controlling the process of
violated, it is too late to remedy the problem with the
switching, sampling, and gas injection. Determine the target
measurement. Analyze and record the tracer gas concentration
tracer gas concentration C that is mid-range in the detec-
of each sample, together with the sampling time and location,
target
tion limits of the gas analyzer. Wait for the apparatus to achieve
according to the procedures in Section 14.
the target concentration. Eq 1 is another method to calculate an
9.5.2 Confirm Uniformity of Concentration—Assess the
initial dose of tracer gas C(0) ≈ C in order to reach the
concentrations of the spatial samplings for uniformity of target
target concentration more rapidly.
concentration, according to 12.4.1. Confirm uniformity of
10.2.4 Sampling—This technique requires automated,
concentration prior to the time of any grouping of points that is
switched, network sampling (13.2.1 and 13.2.1.2). Connect the
used to calculate air change flows. Estimate measurement
sampling apparatus to the gas analyzer and to the computer
precision using 14.1.3.
controlling the process of switching, sampling and gas injec-
9.5.3 Calculate Air Change Flow—Calculate the average air
tion. An important limitation on the accuracy of this technique
change flow for the measurement period using time series
tracer gas concentration data (9.5.3.1). One may test the
assumption of constant air change for the measurement period
(9.5.3.2) after an equilibrium tracer gas concentration has
occurred.
9.5.3.1 Average Air Change Flow—Compute average air
change flow with Eq 10.
1 V C
zone 2
Q 5 Q avg 2 ln (10)
F G F G
tracer
C t 2 t C
~ !
2 1 1
The uncertainty in the zone volume shall be less than 15 %
and the concentration shall never go outside 620 % of the
average concentration. However, if the zone volume is known
to 5 %, then the concentration shall vary by up to 640 %. If
these conditions are violated, then the user shall do an error
analysis (X6.2). Appendix X5 contains one method to measure
zone volume. One minimizes the need to know the volume of
the zone if the beginning and ending concentrations used in the
calculation are close to equal, and Eq 9 is satisfied.
9.5.3.2 Test for Constant Air Change Flow—If one has
achieved an equilibrium tracer gas concentration (9.4.3), then
one may test the assumption of constant air change flow by
FIG. 4 Schematic Diagram of the Apparatus Used for the Con-
calculating Q in Eq 10, using individual C data. Application of stant Concentration Technique
E741 − 23
is how frequently a portion of the zone may be measured in tracer gas equilibrium has been achieved (10.5.2) and the
order to assure good control of concentration. Given a uniform uniformity of concentration criterion (12.4.1) has been met.
tracer gas concentration, analysis and injection shall be at a Use the results of spatial sampling to estimate measurement
level five times more frequent than the dominant changes in A precision (14.1.3).
or every 5 min, whichever is more frequent. A choice of control
10.5.4 Measure Tracer Gas Injections—Determine and re-
strategies is available in the literature (1).
cord the amount of tracer gas injected Q (t, i) for each time
tracer
t and place i of injection.
10.3 Tracer Gas Injection—Metered injection (12.3) is re-
10.5.5 Calculate Average Air Change Flow—When the data
quired. After the tracer gas concentration level has reached
acquisition and control system is working properly, the sample
nominal equilibrium, the rate of tracer gas injection Q (t)
tracer
standard deviation of C(t) shall be less than 10 % of C and
shall be modulated to achieve C without overshooting by target
target
then one calculates:
more than 5 % within one sample cycle. A good control
t N
algorithm will minimize excessive deviation of C from C . 2
target
Q t, i
~ !
The record of time and Q (t) shall be automated and ( ( tracer
tracer
t5t i51
Q 5 (13)
ave t
entered in machine-readable form. Accurate determination of
C t
~ !
Q (t) is critical to this technique. Distribute the tracer gas in
(
tracer
t5t
the zone according to 12.4.3 in order to meet the uniformity of
where N is the number of branches serving the zone.
concentration criterion of 12.4.1.
10.5.5.1 Calculate Instantaneous Air Change Flow—If the
10.4 Sampling—Allow the tracer gas concentration to reach
tracer gas concentration is maintained within 2 % of the target
an approximate equilibrium throughout the zone before deter-
tracer gas concentration, then calculate the air change flow
mination of Q may begin (10.5.2).
over a time interval as:
10.4.1 Minimum Frequency—As a rule of thumb, take one
N
sample at each sampling location at least every 5 min. When
Q ~t, i!
( tracer
the concentration cannot be maintained within 5 % of C ,
i51
target
Q~t! 5 (14)
then reevaluate the injection control algorithm. Sample a C
target
minimum of five times during the test.
Use the built-in indicators of precision and bias of this
10.4.2 Minimum Duration—The minimum duration for
calculation to determine confidence intervals, as discussed in
sampling T and the resulting analysis depends on the air
test
X3.3.
change rate and the precision of the gas analyzer:
10.5.6 Correlation with Ancillary Measurements—Refer to
15.4 for reporting of ancillary measurements.
T . ν (11)
test GA
A
est
11. Procedures for Preparing the Zone
where ν is calculated in A1.4. The minimum duration for
GA
sampling also depends on how much the concentration changes
11.1 Ancillary Measurements—One shall determine the sta-
between samples as follows:
tus of building systems and envelope features, indoor and
outdoor temperatures, and wind speed and direction. When
C 2 C
final initial
T .U U (12)
test
required, one shall determine the volume of the zone or
0.02 A C
est target
changes in the status of building systems and envelope
Choose the larger T from Eq 11 and 12.
test
features. See Section 15 for details.
10.5 Analysis:
11.2 Preparation of the Zone—Determine how the zone is to
10.5.1 Analyze Tracer Gas Concentrations—Analyze and
be ventilated during the test, depending on what aspects of
record the tracer gas concentration C(t) of each sample as it is
operation are of interest. Appendix X4 gives some examples
collected together with the time and place it represents,
for two cases: (1) when all ventilation systems are in operation
according to the procedures in Section 14. An accurate mea-
and (2) when envelope leakage alone causes air change. Report
surement of C(t) is critical to this technique. Therefore, assess
clearly the status of all mechanical ventilation systems, all
calibration drift with periodic checks or by before-and-after
passive ventilation systems (windows and other openings), as
calibrations and subsequent adjustment of the concentration
well as any other envelope features that incorporate leakage
data, or by some other suitable method. Report the method
sites. When required, report changes in the status of these
used.
systems and features.
10.5.2 Concentration Equilibrium—Upon start-up of the
injection and sampling system, the injection system is in the
12. Procedures for Distributing Tracer Gas
full open position and C(t) asymptotically approaches the
12.1 Avoid Contamination—Contamination of the zone oc-
equilibrium target concentration C . After C(t) reaches
target
10 % of C , perform the uniformity of concentration test curs from improper handling of the tracer gas, leaks in the
target
tracer gas injection system, tracer gas re-entrainment, or the
(10.5.3).
prior presence of the tracer gas in the zone.
10.5.3 Uniformity of Concentration Test—If the sampling
network does not provide adequate spatial sampling to confirm 12.1.1 Handling Tracer Gases—Tracer gases are often dis-
uniformity of concentration, using 13.3, then perform manual pensed from pressurized gas bottles. Leakage during gas
spatial sampling. Begin the determination of Q after nominal dispensation changes desired concentrations. Locate the bottle
E741 − 23
outside the zone or test for leakage (13.4.2). For metered Each leg shall be fully charged with tracer gas so that there are
injection, test for tracer gas leaks as follows: no delays or uncertainties about the amount that reaches the
end of the leg.
12.1.1.1 Run the network from the room it is in through a
12.3.3 Record of Injection—Record the flow rate of tracer
sealed exit to the outdoors after it is attached to the metering
gas and its schedule for injection into each portion of the zone.
apparatus and gas supply but before it is distributed in the zone.
Record the location of each network port for dispensing tracer
12.1.1.2 Sample the air in the vicinity of joints in the
gas.
distribution network to confirm that it does not leak.
12.1.2 Conservation of Tracer Gas in the Zone—If the
12.4 Uniformity of Concentration—The data analysis in this
sample size is sufficient to affect the tracer gas concentration in test method assumes that the space being tested is idealized as
that zone, vent the gas analyzer to the zone where each sample
a single zone containing uniformly distributed tracer gas.
originates. Therefore, confirmation of uniformity of concentration is
12.1.3 Pre-Existing Tracer Gas—To sample for pre-existing required.
12.4.1 Uniformity of Concentration Criterion—When a pre-
tracer gas or any air constituent that may interfere with the
tracer gas analysis, obtain an air sample in the zone prior to cision and bias of 10 % is required, then gas concentrations at
representative locations throughout the zone shall differ by less
injecting the tracer gas. The sample may be drawn from
representative areas throughout the zone. than 10 % of the average concentration for the zone. Perform
spatial sampling (13.3) at least at the start and end of the
12.2 Manual Injection—Fill the injection container (6.2.1a)
measurement period from which data is to be used to perform
with the desired volume of tracer gas. Walk rapidly throughout
air change calculations.
the zone dispensing the tracer gas. Where the zone comprises
12.4.2 Calculate the Uniformity of Concentration—
interconnected rooms, plan how much gas must be dispensed
Calculate s , the sample standard deviation of C of the spatial
C
in each room in proportion to the total zonal volume. In such
samples obtained when the uniformity of concentration crite-
cases and in large single-volume zones, use multiple containers
rion was met and again for the second set of spatial samplings
for simultaneous injection as an alternative to single contain-
(8.4.1), and calculate their coefficients of variation (ν = s ⁄C).
C
ers. Another method is to inject tracer gas into the main air
12.4.3 Aids to Mixing—When the required uniformity of
supply duct while the fan is running. For techniques that
concentration does not occur, use additional mixing devices
account for the volume of tracer gas, ensure that the duct
and/or wait a longer period of time, and then resample and
system has no leaks outside the zone and that the measured
recalculate s and ν . Mixing devices include, but are not
C C
amount of tracer gas has been dispensed.
limited to, portable fans blowing from room to room or air
12.2.1 Record of Injection—Record the volume of tracer gas
supply fans serving the zone. When required, use a distribution
and the time and manner of injection.
network (13.4.2) to representative locations in the zone in
12.3 Metered Injection—Use a critical orifice, critical orifice concert with convection or fans.
metering valve, or an electronic mass controller to meter tracer
gas from a pressurized bottle. The flow shall be either (1) 13. Procedures for Sampling Tracer Gas
maintained at a constant level, (2) switched on and off at a NOTE 2—Sections 8 – 10 require the spatial average concentration in
the zone. This section describes appropriate sampling options.
constant level for controlled periods of time, or (3) the rate of
flow varied, depending on the requirements of the test. A
13.1 Manual Sampling—Draw air samples using a manual
computer is one means to control flow rates. sampler. See 6.3.2 for a description of manual samplers. Move
12.3.1 Direct Injection—The injection system is placed in throughout the region to obtain a representative sample. If a
uniform concentration has been verified, then the sample shall
the zone or in the air supply system to the zone while the fan
be
...