ISO 21773:2021

Methods of test and characterization of performance for energy recovery components

This document specifies methods for testing and characterizing the performance of air-to-air heat/energy exchangers when used as devices to transfer heat or heat and water vapor between two airstreams used in ventilation systems. It also specifies methods to characterize the performance of exchangers for use in calculation of the energy performance of buildings. This document is applicable to: — fixed-plate exchangers (also known as recuperators), — rotary exchangers, including heat wheels and total energy wheels (also known as regenerators), — heat pipe exchangers using a heat transfer medium, excluding those using mechanical pumping. This document does not provide a method for measuring the response of exchangers to the formation of frost.

Méthode d'essai et caractérisation des performances des composants récupérateurs d’énergie

General Information

• Status: Published
• Publication Date: 17-Jun-2021
• ICS: 23.120 - Ventilators. Fans. Air-conditioners
• ICS: 91.120.10 - Thermal insulation of buildings
• Technical Committee: ISO/TC 86/SC 6 - Testing and rating of air-conditioners and heat pumps
• Drafting Committee: ISO/TC 86/SC 6/WG 10 - Energy recovery ventilators
• Current Stage: 6060 - International Standard published
• Start Date: 18-Jun-2021
• Due Date: 06-Oct-2020
• Completion Date: 18-Jun-2021

Overview

ISO 21773:2021 - Methods of test and characterization of performance for energy recovery components - defines standardized laboratory methods to test and characterize air-to-air heat/energy exchangers used in ventilation systems. The standard applies to fixed-plate (recuperators), rotary exchangers (heat wheels / total energy wheels / regenerators) and heat pipe exchangers (excluding mechanically pumped heat-transfer media). ISO 21773:2021 supports reliable performance metrics for product rating and for calculating the energy performance of buildings. It does not cover measurement of exchanger response to frost formation.

Key topics and technical requirements

• Performance metrics: definitions and calculation methods for effectiveness (sensible, latent, total), recovery efficiency ratio (RER), outside air correction factor (OACF), exhaust air transfer ratio (EATR), and energy/ humidity transfer rates.
• Pressure drop: procedures for measured and standardized pressure-drop testing across exchangers.
• Leakage testing: methods to quantify air cross-transfer and leakage that affect indoor air quality and net recovery.
• Test rig and installation: requirements for test apparatus, station locations, static pressure management, and instrument calibration.
• Test procedures: stability limits, data sampling rates, data collection periods, inlet temperature and humidity conditions, and test temperature limits for effectiveness tests.
• Uncertainty and inequality limits: specified limits for uncertainty in effectiveness, pressure drop, RER and leakage tests to ensure repeatable results.
• Reporting: required test result formats and content. Informative annexes include example data collection/calculation, best practices, and expressions for system-level performance calculations.

Practical applications and users

ISO 21773:2021 is intended for:

• HVAC product manufacturers - to test, develop and benchmark energy recovery components.
• Testing and calibration laboratories - to perform accredited, repeatable performance tests (aligned with ISO/IEC 17025).
• Energy modelers and building performance engineers - to obtain reliable exchanger metrics for building energy simulations and compliance calculations.
• Consultants, specifiers and commissioning agents - to select equipment and verify in-situ performance accounting for EATR and OACF.
• Regulators and certification bodies - to define product rating and labeling criteria.

Using ISO 21773:2021 improves comparability of test data, supports accurate building energy calculations, and helps optimize HVAC system efficiency and indoor air quality.

Related standards

• ISO 3966 (flow measurement), ISO 5167-1 (differential pressure flow), ISO 5801 (fan testing), ISO 13253 (ducted air-conditioner testing) and ISO/IEC 17025 (laboratory competence) are normative references cited by ISO 21773:2021.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 21773
First edition
2021-06
Methods of test and characterization
of performance for energy recovery
components
Méthode d'essai et caractérisation des performances des composants
récupérateurs d’énergie
Reference number
©
ISO 2021
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved

Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 4
5 Metrics . 5
5.1 General . 5
5.2 Effectiveness . 6
5.3 Pressure drop . 6
5.3.1 Measured pressure drop . 6
5.3.2 Standardized pressure drop . 6
5.4 Recovery efficiency ratio . 7
5.5 Outside air correction factor . 8
5.6 Exhaust air transfer ratio . 8
5.7 Sensible energy transfer rate for the supply airstream . 8
5.8 Humidity transfer rate for the supply airstream . 8
5.9 Total energy transfer rate for the supply airstream . 8
6 General test requirements . 9
6.1 Test apparatus . 9
6.2 Installation . 9
6.3 Static pressures . 9
6.4 Instrument calibration . 9
7 Effectiveness tests .10
7.1 Test requirements .10
7.2 Stability limits when testing effectiveness .10
7.3 Data collection period .11
7.4 Data sampling rates .11
7.5 Temperature and humidity conditions: inlets to exchanger .12
7.6 Test temperature limits .12
8 Pressure drop tests .12
9 Leakage tests .13
9.1 General test requirements .13
9.2 Outside air correction factor .13
9.3 Exhaust air transfer ratio .13
10 Uncertainty limits.13
10.1 General .13
10.2 Uncertainty limits for effectiveness tests .14
10.3 Uncertainty limits for RER .14
10.4 Uncertainty limits for measured pressure drop tests .14
10.5 Uncertainty limits for leakage tests .14
11 Inequality limits .15
11.1 General .15
11.2 Inequality limits for thermal tests.15
11.3 Inequality limits for leakage tests .15
12 Reporting of test results .15
12.1 Pressure drop test results .16
12.2 Leakage test results .16
12.3 Thermal test results .16
12.4 Uncertainties .16
Annex A (informative) Example of test data collection and calculation of metrics .17
Annex B (informative) Best practices .21
Annex C (informative) Expression of performance metrics for use in calculation of system
performance . .32
Annex D (informative) Inequality limits for use when condensate flow rate can be measured .37
Annex E (informative) Expressions, used in other standards, related to effectiveness as
defined in this document .38
Bibliography .44
iv © ISO 2021 – All rights reserved

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 86, Refrigeration and air-conditioning,
Subcommittee SC 6, Testing and rating of air-conditioners and heat pumps.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
INTERNATIONAL STANDARD ISO 21773:2021(E)
Methods of test and characterization of performance for
energy recovery components
1 Scope
This document specifies methods for testing and characterizing the performance of air-to-air heat/
energy exchangers when used as devices to transfer heat or heat and water vapor between two
airstreams used in ventilation systems. It also specifies methods to characterize the performance of
exchangers for use in calculation of the energy performance of buildings. This document is applicable
to:
— fixed-plate exchangers (also known as recuperators),
— rotary exchangers, including heat wheels and total energy wheels (also known as regenerators),
— heat pipe exchangers using a heat transfer medium, excluding those using mechanical pumping.
This document does not provide a method for measuring the response of exchangers to the formation
of frost.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3966, Measurement of fluid flow in closed conduits — Velocity area method using Pitot static tubes
ISO 5167-1, Measurement of fluid flow by means of pressure differential devices inserted in circular cross-
section conduits running full — Part 1: General principles and requirements
ISO 5801, Fans — Performance testing using standardized airways
ISO 13253, Ducted air-conditioners and air-to-air heat pumps — Testing and rating for performance
ISO/IEC 17025:2017, General requirements for the competence of testing and calibration laboratories
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www. iso. org/obp
— IEC Electropedia: available at https:// www.electropedia . org/
3.1
effectiveness
actual energy transfer rate (sensible, latent, or total) divided by the maximum possible energy transfer
rate
Note 1 to entry: The formula for effectiveness is given in 5.2.
3.2
exhaust air transfer ratio
EATR
tracer gas concentration difference between the leaving supply air (3.12) and the entering supply air
(3.11), divided by the tracer gas concentration difference between the entering exhaust air (3.13) and
the entering supply air (3.11), which quantifies the air quantity transferred from the exhaust to the
supply
Note 1 to entry: The formula for EATR is given in 5.6.
Note 2 to entry: It can be expressed as a percentage for rating purposes, but is used as a ratio in the calculation
of RER (3.6).
3.3
fixed-plate exchanger
exchanger with multiple alternate airflow channels, separated by a heat or heat and water vapor
transfer plate(s) and connected to supply and exhaust airstreams
3.4
heat pipe exchanger
exchanger with an array of finned and sealed tubes that are placed in side-by-side supply and exhaust
airstreams, which may include an internal wick structure in each tube, and filled with a heat transfer
medium
Note 1 to entry: Thermosiphon exchangers are a subset (or type) of heat pipe exchanger in which the heat transfer
medium moves by gravitational forces only.
3.5
outside air correction factor
OACF
factor defined as the entering supply air (3.11) divided by the leaving supply air (3.12)
Note 1 to entry: The formula for OACF is given in 5.5.
3.6
recovery efficiency ratio
RER
ratio of the recovered energy rate divided by the sum of the calculated combined fan power and the
auxiliary power
Note 1 to entry: The formula for RER is given in 5.4.
Note 2 to entry: RER can be characterized as gross, or as net in which case EATR (3.2) is accounted for.
3.7
rotary exchanger
exchanger with porous discs, fabricated from materials with heat or heat and water vapor retention
capacity, that are regenerated by collocated supply and exhaust airstreams
3.8
standard air
3 -5
dry air with a density of 1,204 3 kg/m and a dynamic viscosity of 1,824 7 x 10 kg/(m∙s)
Note 1 to entry: These conditions approximate dry air at 20 °C and 101,325 kPa absolute.
3.9
station
location in the test apparatus at which conditions such a temperature, humidity, pressure or airflows
are measured
Note 1 to entry: indicated in Figure 1 as 1, 2, 3 and 4.
2 © ISO 2021 – All rights reserved

3.10
static pressure differential
static pressure at supply outlet minus the static pressure at exhaust inlet
Note 1 to entry: A positive pressure differential occurs when the static pressure at station (3.9) 2 is higher than
the static pressure at station 3. A negative pressure differential occurs when the static pressure at station 2 is
lower than the static pressure at station 3.
3.11
entering supply air
supply air inlet
outdoor airflow
OA
outside air entering the exchanger
Note 1 to entry: Indicated in Figure 1 as 1.
3.12
leaving supply air
supply air outlet
supply airflow
SA
outside air after passing through the exchanger
Note 1 to entry: Indicated in Figure 1 as 2.
3.13
entering exhaust air
exhaust air inlet
return airflow
RA
indoor air entering the exchanger
Note 1 to entry: Indicated in Figure 1 as 3.
3.14
leaving exhaust air
exhaust air outlet
exhaust airflow
EA
indoor air after passing through the exchanger
Note 1 to entry: Indicated in Figure 1 as 4.
Key
1 entering supply air 2 leaving supply air
3 entering exhaust air 4 leaving exhaust air
5 exchanger
Figure 1 — Schematic diagram of airflows for heat and energy recovery exchangers
4 Symbols and abbreviated terms
Symbol Term Units
-6
C Tracer gas concentration at station i (i = 1, 2, 3, 4) 10
i
c Specific heat of condensate at its measured temperature kJ/(kg⋅°C)
p
c Specific heat of dry air at station i (i = 1, 2, 3, 4) J/(kg⋅°C)
p,i
δT Maximum deviation of any temperature reading of T from T K
i i AVE,i
δW Maximum deviation of any humidity ratio reading of W in from W kg water / kg dry
i i AVE,i
air
ΔP Pressure drop through the exchanger, exhaust air stream, measured Pa
e
ΔP Pressure drop through the exchanger, exhaust air stream, at reference Pa
e,ref
conditions
ΔP Pressure drop through the exchanger, supply air stream, measured Pa
s
ΔP Pressure drop through the exchanger, supply air stream, at reference condi- Pa
s,ref
tions
∆ps Static pressure differential Pa
2,3
ΔT Temperature change in the supply airstream °C or K
1-2
ΔW Humidity change in the supply airstream kg water / kg dry
1-2
air
ε Effectiveness %
ε Sensible effectiveness %
sensible
ε Latent effectiveness %
latent
ε Total effectiveness %
total
a
F Outside air correction factor (OACF) 1
oac
h Enthalpy of air at station i (i = 1, 2, 3, 4) kJ/kg dry air
i
a
Some quantities of dimension 1 are defined as ratios of two quantities of the same kind. The coherent derived unit is
the number 1 (ISO 80000-1:2009, 3.8).
b
T and W are defined and discussed in Annex E.
e e
4 © ISO 2021 – All rights reserved

Symbol Term Units
h Heat of vaporization of water J/kg
fg
ṁ Measured condensate flow rate kg/s
condensate
ṁ Mass flow rate of dry air at station i (i = 1, 2, 3, 4) kg/s
i
a
m /m Ratio of supply air outlet mass flow rate to exhaust air inlet mass flow rate 1
s e
a
η Combined efficiencies of the supply and exhaust air fan and drive 1
fs,fe
ps Static pressure at station i (i = 1, 2, 3, 4) Pa
i
Auxiliary power input to the exchanger (e.g. to rotate a wheel) kW
q
aux
Q Humidity transfer rate kg water/(kg dry
latent
air ∙ s)
Q Sensible energy transfer rate W
sensible
Q Total energy transfer rate W
total
Q Leaving supply volume flow rates m /s
Q Entering exhaust volume flow rates m /s
ρ Dry air density at station i (i = 1, 2, 3, 4) kg/m
i
a
R Exhaust air transfer ratio (EATR) 1
eat
R Gross recovery efficiency ratio (gross RER) W/W
rer,gross
R Net recovery efficiency ratio (net RER) W/W
rer,net
Θ Purge angle °
T Average value of temperature readings taken at station i (i = 1, 2, 3, 4) dur- °C
AVE,i
ing a measurement period
T Measured temperature of the condensate °C
condensate
b
T Temperature efficiency %
e
T Dry-bulb temperature at station i (i = 1, 2, 3, 4) °C
i
T Wet-bulb temperature at station i (i = 1, 2, 3, 4) °C
WB,i
a
U Expanded relative uncertainty 1
W Average value of humidity readings taken at station i (i = 1, 2, 3, 4) during a kg water/kg dry
AVE,i
measurement period air
b
W Humidity efficiency %
e
W Humidity at station i (i = 1, 2, 3, 4) kg water/kg dry
i
air
μ Dynamic viscosity at station i (i = 1, 2 3 or 4) kg/(m∙s)
i
-5
μ Dynamic viscosity of standard air = 1,824 7 x 10 kg/(m∙s)
s
a
Some quantities of dimension 1 are defined as ratios of two quantities of the same kind. The coherent derived unit is
the number 1 (ISO 80000-1:2009, 3.8).
b
T and W are defined and discussed in Annex E.
e e
5 Metrics
5.1 General
The performance of an air-to-air heat/energy exchanger is primarily characterized by its sensible,
latent, and total effectiveness [see Formulae (1), (2) and (3)] its pressure drops [see Formulae (4), (5),
(6) and (7)], its recovery efficiency ratio [see Formulae (8) and (9)], the outside air correction factor [see
Formula (10)], and its exhaust air transfer ratio [see Formula (11)]. Formulae (1) to (3) reproduced with
permission from ANSI/ASHRAE 84:2020. Formulae (4) through (11) are based on formulae in ANSI/
ASHRAE 84-2020 with permission from ANSI/ASHRAE. Annex E provides guidance on equivalence
between the metrics provided in this document and related metrics in use in certain other standards.
Derived metrics that are needed for use in calculating the performance of complete systems include
sensible energy transfer rate (see Formula (12)), humidity transfer rate (see Formula (13) and enthalpy
transfer rate (see Formula (14)).
See Clause 4 for the units of different quantities.
5.2 Effectiveness
The sensible, latent, and total effectiveness (ε , ε and ε ) are defined by Formulae (1), (2)
sensible latent total
and (3):

mc Tc− T
()
21pp,,12 2
ε = (1)
sensible

mc Tc− T
()
min pp,,11 33

mh Wh− W
()
21fg,,12fg 2
ε = (2)
latent

mh Wh− W
()
minfgf,,11 g 33

mh −h
()
21 2
ε = (3)
total

mh −h
()
min 13
where
ṁ is the mass flow rate at station i (i = 1, 2 or 3)
i
ṁ is the lesser of ṁ and ṁ
min 2 3
c is the specific heat of dry air at station i (i = 1, 2 or 3)
p,i
h is the heat of vaporization of water at station i (i = 1, 2 or 3)
fg,i
T is the dry-bulb temperature at station i (i = 1, 2 or 3)
i
W is the humidity at station i (i = 1, 2 or 3)
i
h is the enthalpy at station i (i = 1, 2 or 3)
i
5.3 Pressure drop
5.3.1 Measured pressure drop
The air friction pressure drops (ΔP and ΔP ) at specific conditions and air mass flow rate through the
s e
exchanger are defined by Formulae (4) and (5):
ΔPp=−sps (4)
s 12
ΔPp=−sps (5)
e 34
where ps is the static pressure at station i (i = 1, 2, 3 or 4).
i
5.3.2 Standardized pressure drop
6 © ISO 2021 – All rights reserved

Air friction pressure drops at reference conditions (ΔP and ΔP )can be determined by Formulae (6
s,ref e,ref
and (7):
 ρ  μ   ρ  μ 
1 s 2 s
ΔPp= sp  − s    (6)
sr, ef 1 2
     
ρ μ ρ μ
     
s 1 s 2
 ρ  μ   ρ  μ 
3 s s
ΔPp= sp  − s    (7)
er, ef 3 4
     
ρ μ ρ μ
 s  3   s  4 
where
ρ is the density at station i (i = 1, 2, 3 or 4) kg/m
i
ρ is the standard density of air = 1,2043 kg/m
s
μ is the dynamic viscosity at station i (i = 1, 2 3 or 4) kg/(m∙s)
i
-5
μ is the dynamic viscosity of standard air = 1,8247 x 10 kg/(m∙s)
s
5.4 Recovery efficiency ratio
a) The gross recovery efficiency ratio (R ) of a heat/energy exchanger is defined by Formula (8):
rer,gross

mh −h
21 2
R = (8)
rerg, ross
ΔΔPQ PQ
s 23e
+ +q
aux
1000⋅ηη1000⋅
fans,,fane
b) The net recovery efficiency ratio (R ) of a heat/energy exchanger is defined by Formula (9):
rer,net
hR− h
()
23eat

mh −
1−R
()
eat
R = (9)
rern, et
ΔΔPQ PQ
s 23e
+ +q
aux
1000⋅η 11000⋅η
fans fane,
,
where
ΔP and ΔP are the measured pressure drops across the supply and exhaust sides of the exchanger,
s e
respectively
Q and Q are the leaving supply and entering exhaust volume flow rates
2 3
η and η is the supply and exhaust air fan and drive combined efficiencies
fs fe
q is the total auxiliary power input to the exchanger (e.g. to rotate a regenerative wheel,
aux.
a pump, and to operate controls)
R is the exhaust air transfer ratio (EATR) expressed as a ratio
eat
In laboratory testing of heat/energy exchangers it is not usually possible to measure the power required
to move air through the exchanger directly, as the blowers in the test system also are required to
overcome friction pressure of the conditioning equipment, flow measurement equipment, etc. Therefore,
the power required to move air through the exchanger shall be calculated, based on a reference fan and
drive total efficiency which is selected for the purposes of comparison of one exchanger to another. For
example, a performance rating agency could elect to use a reference fan and drive total efficiency of
0,50 in the calculation of RER for all the exchangers for which it provides ratings.
5.5 Outside air correction factor
The outside air correction factor (F ) of a heat/energy exchanger at a specific operating condition is
oac
defined by Formula (10):

m
F = (10)
oac

m
where ṁ are the mass flow rates at stations 1 and 2
1,2
5.6 Exhaust air transfer ratio
The exhaust air transfer ratio (R ) of a heat/energy exchanger at a specific operating condition is
eat
defined by Formula (11):
CC−
R = (11)
eat
CC−
where C are the concentration of tracer gas at stations i (i = 1, 2, 3 or 4) during the test described in 9.3.
i
NOTE To express exhaust air transfer ratio as a percentage, multiply by 100.
5.7 Sensible energy transfer rate for the supply airstream
Sensible energy transfer rate (Q ) into or out of the supply airstream for an exchanger at a specific
sensible
operating condition is defined by Formula (12):

Qm=⋅ Tc −Tc (12)
()
sensible 21 pp,,12 2
where
T are the temperatures at stations 1 and 2
1-2
c are the specific heats of dry air at stations 1 and 2
p1,2
5.8 Humidity transfer rate for the supply airstream
Humidity transfer rate (Q ) into or out of the supply airstream for an exchanger at a specific
latent
operating condition is defined by Formula (13):

Qm=⋅ΔW (13)
latent 21−2
where ΔW is the humidity change for the supply airstream.
1-2
5.9 Total energy transfer rate for the supply airstream
Total energy transfer rate (Q ) into or out of the supply airstream for an exchanger at a specific
total
operating condition is defined by Formula (14):

Qm=⋅Δh (14)
total 21−2
where Δh is the enthalpy change for the supply airstream.
1-2
8 © ISO 2021 – All rights reserved

6 General test requirements
6.1 Test apparatus
The test apparatus shall consist of four measurement stations. Measurements shall be taken at each
station of temperature, humidity, dry air mass flow rate, tracer gas concentration, and static pressure.
6.2 Installation
The equipment to be tested shall be installed in accordance with the manufacturer’s instructions. See
Figures 2 and 3.
NOTE See Annex B for best practices of connecting an exchanger to test system.
6.3 Static pressures
Static pressures shall be measured according to ISO 3966, ISO 5167-1, ISO 5801 or ISO 13253.
6.4 Instrument calibration
All measurement instruments shall be calibrated using sensors, transfer standards, and primary
instruments that are traceable. Calibration shall be consistent with ISO/IEC 17025:2017, 6.4 and 7.4, in
order to minimize the bias of the instrument. The calibration curves associated with each instrument
shall be available as a permanent record.
Key
1 entering supply air 8 airflow measuring apparatus
2 leaving supply air 9 temperature, humidity and tracer gas measuring
3 entering exhaust air instruments
4 leaving exhaust air 10 air mixer
5 exchanger 11 air conditioning apparatus
6 static pressure control apparatus 12 relief inlet/outlet
7 static pressure measuring apparatus 13 optional recycling duct
NOTE Refer to ISO 13253:2017, Annex C.
Figure 2 — Basic schematic for ducted measurement setup
Key
1 entering supply air 8 airflow measuring apparatus
2 leaving supply air 9 temperature, humidity and tracer gas measuring
3 entering exhaust air instruments
4 leaving exhaust air 10 air mixer
5 exchanger 11 air conditioning apparatus
6 static pressure control apparatus 12 pressure relief
7 static pressure measuring apparatus
NOTE Refer to ISO 13253:2017, Annex C.
Figure 3 — Basic schematic for 2-room measurement setup
7 Effectiveness tests
7.1 Test requirements
The test duct, measuring equipment, and the equipment under test shall be operated until steady-state
equilibrium conditions are attained but for not less than 30 min. The equipment under test shall be
operated until steady-state conditions are attained before applicable test data are recorded.
For rotary wheel exchangers, the wheel speed shall be checked before and after each series of test runs.
The air volume flow rates for the test shall be specified by the test requestor for the leaving supply air
(station 2) and entering exhaust air (station 3).
Thermal effectiveness tests shall be performed with manufactured-specified static pressure differential
between the leaving supply air (station 2) and entering exhaust air (station 3).
7.2 Stability limits when testing effectiveness
When testing effectiveness, the following requirements shall be observed.
10 © ISO 2021 – All rights reserved

During effectiveness tests the inlet dry-bulb temperatures shall remain within limits such that δT and
δT shall not exceed the larger of 0,5 K or the value defined in Formulae (15) and (16).
δTT<× 00, 4 − T (15)
11AVEA,,VE 3
δTT<× 00, 4 − T (16)
31AVEA,,VE 3
where
δT is the maximum deviation of any temperature reading of T in K from T
1 1 AVE,1
δT is the maximum deviation of any temperature reading of T in K from T
3 3 AVE,3
T is the time-averaged mean value of all temperature readings T in K taken at station 1 during
AVE,1 1
the measurement period
T is the time-averaged mean value of all temperature readings T in K taken at station 3 during
AVE,3 3
the measurement period
During effectiveness tests the inlet humidity ratios shall remain within limits such that δW and δW
1 3
shall not exceed the larger of 0,000 4 kg /kg or the value defined in Formulae (17) and (18).
W DA
δWW<× 01, 0 − W (17)
11AVEA,,VE 3
δWW<× 00, 4 − W (18)
31AVEA,,VE 3
where
δW is the maximum deviation of any humidity ratio reading of W in kg /kg from W
1 1 W DA AVE,1
δW is the maximum deviation of any humidity ratio reading of W in kg /kg from W
3 3 W DA AVE,3
W is the time-averaged mean value of all humidity ratio readings W in kg /kg taken at
AVE,1 1 W DA
station 1 during the measurement period
W is the time-averaged mean value of all humidity ratio readings W in kg /kg taken at
AVE,3 3 W DA
station 3 during the measurement period
7.3 Data collection period
For all measurements of thermal performance or leakage, data shall be collected for a period of not less
than 30 min, during which the steady-state requirements in 7.2 shall be met.
For measurements of pressure drop through the exchanger, data shall be collected for a period of not
less than 5 minutes.
7.4 Data sampling rates
For all tests, sets of data shall be recorded at equal intervals of 1 min or less.
For all tests, at least 30 sets of data shall be collected.
For all measurements of thermal performance or pressure drop, each complete set of data shall be
obtained during a period of 10 s or less.
NOTE When testing leakage with tracer gases, it may not be possible to collect a complete set of data within
10 s or less. However, the requirement to collect at least 30 sets of data and to collect data over a period of 30 min
still applies.
7.5 Temperature and humidity conditions: inlets to exchanger
Tests at cooling conditions shall be carried out under the conditions given in one or more of the
columns T1 through T4 in Table 1. Tests at heating conditions shall be carried out under the conditions
given in one or more of the columns T5 through T8 in Table 2.
Table 1 — Conditions of test for thermal tests (cooling)
Standard test conditions
Parameter
T1 T2 T3 T4
dry-bulb 35,0
Temperature of entering
supply air (°C)
wet-bulb 23,0 24,0 31,0 24,0
dry-bulb 21,0 24,0 27,0 27,0
Temperature of entering
exhaust air (°C)
wet-bulb 15,0 17,0 20,0 19,0
Table 2 — Conditions of test for thermal tests (heating)
Standard test conditions
Parameter
T5 T6 T7 T8
dry-bulb 2,0 5,0 7,0 5,0
Temperature of entering
supply air (°C)
wet-bulb 1,0 3,0 6,0 3,0
dry-bulb 21,0 20,0 20,0 25,0
Temperature of entering
exhaust air (°C)
wet-bulb 14,0 15,0 12,0 18,0
7.6 Test temperature limits
For all tests, the arithmetic mean of the temperatures and mass flows at each of the inlets shall not be
different from the specified temperatures and mass flows for each test by more than the allowances in
Table 3.
Table 3 — Variation allowed during test
Readings Variation of arithmetical mean
values from specified test con-
ditions
Temperature of air entering
dry-bulb ± 0,3 K
wet-bulb ± 0,2 K
Mass flow ± 2,5 %
8 Pressure drop tests
Measured pressure drop across the heat/energy exchanger from stations 1 to 2 and stations 3 to 4 shall
be determined for every thermal test.
12 © ISO 2021 – All rights reserved

9 Leakage tests
9.1 General test requirements
For rotary regenerative wheels, the leakage tests shall be performed with the wheel rotating at the
same speed as for the effectiveness test.
Tracer gas, sampling equipment, and gas concentration levels shall be selected so as to be capable of
accurately measuring the exchanger internal leakages. The injection concentration of the tracer gas
shall be sufficient that an exhaust air transfer ratio of 0,002 5 can be measured by the device being
used.
The tracer gas generation equipment shall be designed to provide a stable concentration of tracer
gas that is uniform in the duct to which the tracer gas is introduced. The tracer gas shall be nontoxic,
identifiable, measurable and inert.
Measurement equipment such as a gas chromatograph analyser, photoacoustic infrared spectroscopy
analyser, or an alternative instrument with uncertainty no greater than 5 % shall be provided. If the
analyser will be sequentially measuring the tracer gas concentration in samples from more than one of
the stations, then either the data or the sample from the beginning of each sample measurement period
shall be purged until the concentration readings have stabilized.
Ducts and other components of the test equipment shall not be permeable to or absorbent of the tracer
gas and shall not allow air leakage.
9.2 Outside air correction factor
Outside air correction factor (OACF) shall be determined by measurement of mass air flows.
OACF shall be determined at positive, negative, and zero values for static pressure differential between
the station 2 supply outlet and the station 3 exhaust inlet, at a specified airflow. The static pressure
differential values and airflows shall be chosen to represent the range of conditions for intended use
of the exchanger. OACF may be determined during thermal test or at lab ambient conditions. If OACF
is determined at lab ambient conditions, the air mass flow rates and pressure differential shall be
identical to the thermal tests from which RER is determined.
9.3 Exhaust air transfer ratio
Exhaust air transfer ratio (EATR) shall be determined by measurement of tracer gases.
EATR shall be determined at positive, negative, and zero values for static pressure differential between
the leaving supply (station 2) and the entering exhaust (station 3). The static pressure differential
values and airflows shall be identical to those in 9.2.
10 Uncertainty limits
10.1 General
A testing laboratory meeting the requirements of ISO/IEC 17025 can achieve the uncertainty limits of
this clause. If necessary, a laboratory and its customer can agree on different uncertainty limits to meet
their needs.
Formulae (19) through (25) are based on ANSI/ASHRAE 84:2020 with permission from ANSI/ASHRAE.
10.2 Uncertainty limits for effectiveness tests
For testing of effectiveness, the expanded relative uncertainties U(ε ) and U(ε ) shall satisfy
s l
Formulae (19) and (20):
U ε
()
s
<00, 5 (19)
ε
s
U ε
()
l
<00, 7 (20)
ε
l
10.3 Uncertainty limits for RER
For RER testing, the expanded relative uncertainties U(R ) for the gross RER and U(R ) for
rer,gross rer,net
the net RER shall satisfy Formula (21):
UR
()
rer
<01, 0 (21)
R
rer
where R is the recovery efficiency ratio, either gross or net.
rer
10.4 Uncertainty limits for measured pressure drop tests
For measured pressure drop testing, the expanded relative uncertainties U(ΔP ) and U(ΔP ) shall satisfy
s e
Formulae (22) and (23):
UPΔ
()
s
<01, 0 (22)
ΔP
s
and
UPΔ
()
e
<01, 0 (23)
ΔP
e
10.5 Uncertainty limits for leakage tests
For OACF testing, the expanded relative uncertainty U(F ) shall satisfy Formula (24):
oac
UF
()
oac
<00, 2 (24)
F
oac
where F is the outside air correction factor.
oac
For EATR testing, the expanded relative uncertainty U(R ) shall satisfy Formula (25):
eat
UR
()
eat
<00, 3 (25)
R
eat
where R is the exhaust air transfer ratio.
eat
14 © ISO 2021 – All rights reserved

11 Inequality limits
11.1 General
Formulae (26) through (31) are reproduced with permission from ANSI/ASHRAE 84:2020.
11.2 Inequality limits for thermal tests
For all tests, the measured dry airflow mass flow rates shall satisfy Formula (26):
 
mm−+mm−
12 34
<00, 5 (26)

m
minimum 13,
()
For all thermal performance tests, the water vapor mass measured flow rates shall satisfy Formula (27):
 
mW −+mW mW −mW
11 22 33 44
<02, 0 (27)

mW −W
minimum 13, 13
()
NOTE For thermal performance tests in which condensation occurs and the steady-state condensate flow
rate is measured, the Formula (D.1), found in Annex D, may optionally be substituted for Formula (27).
For all thermal performance tests, the measured energy flow rates shall satisfy Formula (28):
 
mh −+mh mh −mh
1122 33 44
<02, 0 (28)

mh −h
minimum 13, 13
()
For all thermal performance tests, the measured sensible energy flow rates shall satisfy Formula (29):
 
mc tm−+ct mc tm− ct
11,pp12,22 33pp,34 ,44
<02, 0 (29)

mc tt−
()
p 13
minimum 113,
()
  
where mc is the lesser of mc and mc
pm,,inimum 13 11,p 33,p
()
NOTE For thermal performance tests in which condensation occurs and the steady-state condensate flow
rate is measured, the Formula (D.2), found in Annex D, can optionally be substituted for Formulae (28) and (29).
11.3 Inequality limits for leakage tests
During testing to determine OACF, the measured airflow mass flow rates shall satisfy Formula (30):
 
mm−+mm−
12 34
<00, 5 (30)

m
minimum 13,
()
During testing to determine EATR, the measured tracer gas flow rates shall satisfy Formula (31):
 
mC −+mC mC −mC
1122 33 44
<01, 5 (31)

mC −C
minimum 13, 13
()
12 Reporting of test results
Reporting of test results shall include all of the items in this Clause.
Measurements made in accordance with this document need to be reported in context in order to
accurately characterize exchanger performance.
Annex A provides an example of acceptable reporting format (see Tables A.1 to A.7).
12.1 Pressure drop test results
Any report of pressure drop shall include the leaving supply and entering exhaust mass airflows or
airflow volumes at standard air conditions and the static pressure differential.
12.2 Leakage test results
EATR and OACF measurements shall be reported together and at the same test conditions, and shall
include:
the leaving supply and entering exhaust mass airflow or airflow volumes at standard air conditions;
the static pressure differential;
the barometric pressure.
12.3 Thermal test results
Any report of:
— effectiveness,
— temperature, humidity or enthalpy change ratio in the supply airstream, or
— sensible, humidity or total energy transfer rate
shall include:
— the leaving supply and entering exhaust mass airflow or airflow volumes at standard air conditions;
— the barometric pressure, dry-bulb temperature, a humidity metric for the leaving supply and
entering exhaust airstreams, and static pressure differential.
12.4 Uncertainties
Each reported test result shall include its expanded uncertainty with its coverage factor and level of
confidence.
16 © ISO 2021 – All rights reserved

Annex A
(informative)
Example of test data collection and calculation of metrics
Table A.1 — Information supplied by manufacturer
Manufacturer information
Manufacturer:
Address:
Model information
Mode
...