ISO 7615-1:2024

International
Standard
ISO 7615-1
First edition
Energy performance of building
2024-09
systems — Underfloor air
distribution systems —
Part 1:
General overview
Reference number
© ISO 2024
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ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3  Terms and definitions . 1
4 Symbols and subscripts . 3
5  Technical specifications and considerations . 4
5.1 Technical specifications .4
5.1.1 Major approaches to designing underfloor plenums .4
5.1.2 Major types of diffusers .4
5.1.3 Major types of underfloor terminal units .5
5.2 Technical performance consideration .6
5.2.1 Space air stratification .6
5.2.2 Thermal decay .6
5.2.3 Air leakage of underfloor plenum .6
5.2.4 Acoustic performance .7
5.3 Comfort consideration .7
5.4 Maintenance of conformity .7
Annex A (informative)  Descriptions of different approaches in underfloor plenum designs . 8
Annex B (informative)  Descriptions of different types of underfloor diffusers .12
Annex C (informative)  Descriptions of different types of perimeter terminal units in underfloor
air distribution (UFAD) systems . 17
Annex D (informative)  Examples of underfloor air distribution (UFAD) system design .23
Bibliography .28

iii
Foreword
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This document was prepared by Technical Committee ISO/TC 163, Thermal performance and energy use in
the built environment, Subcommittee SC 1, Test and measurement methods.
A list of all parts in the ISO 7615 series can be found on the ISO website.
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.

iv
International Standard ISO 7615-1:2024(en)
Energy performance of building systems — Underfloor air
distribution systems —
Part 1:
General overview
1 Scope
This document provides a general overview, including terms and definitions and technical specifications
for an underfloor air distribution (UFAD) system. A UFAD system includes a raised floor, a zone air handling
unit (AHU), an underfloor plenum and underfloor air diffusers. This document is applicable to all types of
systems which utilize underfloor plenum to supply conditioned air into the occupied space.
This document is not applicable to AHUs, ceiling-based air diffusers or displacement ventilation systems.
2 Normative references
This document referred to in the text in such a way that some or all of their content constitutes requirements
of the following document. For dated references, only the edition cited applies. For undated references, the
latest edition of the referenced document (including any amendments) applies.
ISO 7730, Ergonomics of the thermal environment — Analytical determination and interpretation of thermal
comfort using calculation of the PMV and PPD indices and local thermal comfort criteria
ISO 13731, Ergonomics of the thermal environment — Vocabulary and symbols
ISO 16818, Building environment design — List of test procedures for heating, ventilating, air-conditioning and
domestic hot water equipment related to energy efficiency
3  Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 7730, ISO 13731 and ISO 16818
and the following apply.
ISO and IEC maintain terminology 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
underfloor air distribution system
UFAD system
forced air delivery system which takes advantage of the underfloor plenum to supply the conditioned air
produced from the air handling unit into the occupied space through underfloor air diffusers mounted on
the raised floor
3.2
raised floor
elevated interior floor composed of modular panels above the structural slab to form the underfloor plenum
for the passage of conditioned air supplied from the air handling unit

3.3
underfloor plenum
void space between raised floor and the slab, where technical services are placed, and the conditioned air is
supplied from the air handling unit before being supplied into the occupied space
3.4
underfloor air diffuser
air supply outlet mounted on the raised floor through which the conditioned air produced from the air
handling unit is supplied into the occupied space
3.5
thermal plume
movement of the occupied space air in the upward direction caused by the buoyancy effect above the internal
heat gain components
Note 1 to entry: Internal heat gain usually includes occupants, lighting and electric equipment.
3.6
space air stratification
formation of a stratified environment in the air in the occupied space, having an elevated temperature with
height caused by the thermal buoyancy
3.7
personal thermal comfort system
device, under the control of the occupant, to either heat or cool, or both, the immediate thermal environment
of an individual occupant, without affecting the thermal environment of the other occupants
3.8
thermal decay
increase or decrease in temperature of the conditioned air supplied from the air handling unit as it travels
through the underfloor plenum, mainly caused by the convective heat transfer from/into the upper surface
of the slab and lower surface of the raised floor
3.9
pressurized plenum
underfloor plenum configuration where the conditioned air is blown from the air handling unit into the
underfloor plenum to maintain positive pressure in the underfloor plenum relative to the occupied space
3.10
neutral plenum
underfloor plenum configuration where the conditioned air is blown from the air handling unit into the
underfloor plenum to maintain almost the same pressure as the occupied space
3.11
ducted plenum
underfloor plenum configuration where the conditioned air is blown from the air handling unit into air
ducts in the underfloor plenum
Note 1 to entry: Underfloor air diffusers are connected to ductwork, similar to conventional ceiling based air
distribution systems.
3.12
stratification height
height of the virtual horizontal surface separating two zones with different air temperature profiles
3.13
occupied space
volume of the conditioned space vertically between the floor and the ceiling, which can be divided into the
lower occupied zone and the upper mixed zone

3.14
lower occupied zone
volume of the occupied space below the stratification height
3.15
upper mixed zone
volume of the occupied space above the stratification height
3.16
interior zone
volume of the occupied space usually farther than 5 m from the exterior envelope, whose thermal loads are
not typically affected by the exterior conditions, such as outdoor air temperature and solar radiation
3.17
perimeter zone
volume of the occupied space adjacent to the exterior envelope, usually within 5 m, whose thermal loads are
highly affected by the exterior conditions (e.g. outdoor air temperature and solar radiation)
3.18
underfloor terminal unit
unit installed under the raised floor at the end of an air distribution system intended to control air flow rate,
pressure or temperature, or to mix air flows
4 Symbols and subscripts
Symbol Quantity Unit
A area m
4 3
B buoyancy flux m /s
H height m
m number of plumes –
n number of diffusers –
Q airflow m /s
T temperature °C
W room convective heat extraction (also known as cooling load) W
θ discharge angle from vertical °
dimensionless number representing the stratification in the occupied
Φ –
[3]
space
dimensionless number representing the ratio of momentum to buoy-
Γ –
[3]
ancy forces
Subscripts Significance
DA diffuser discharge air
diff diffuser
eff effective
os occupied space
oz lower occupied zone
RA return air
5  Technical specifications and considerations
5.1  Technical specifications
5.1.1  Major approaches to designing underfloor plenums
UFAD systems can take advantage of the underfloor plenum by blowing conditioned air into the occupied
space through the underfloor plenum, which allows UFAD systems to operate as the personal thermal
comfort system. Typical plenum heights integrated with UFAD systems are 0,15 m to 0,45 m from the
structure slab. According to
...