Uniformly distributed floor sources of buoyancy can give rise to significant spatial inhomogeneities within rooms
Author(s)
Type
Journal Article
Abstract
Displacement ventilation, where cool external air enters a room through low-level vents and warmer air
leaves through high-level vents, is characterised by vertical gradients in pressure arising from the warmer
indoor temperatures. Models usually assume that horizontal variations of temperature difference are small
in comparison and are, therefore, unimportant. Small-scale laboratory experiments and computational fluid
dynamics were used to examine these flows, driven by a uniformly heated floor. These experiments and
simulations show that the horizontal variations of temperature difference can be neglected for predictions of the bulk ventilation rate; however, they also evidence that these horizontal variations can be significant and
play a critical role in establishing the pattern of flow within the room — this renders the horizontal position of
the low- and high-level vents (relative to one another) important. We consider two cases: single-ended (where
inlet and outlet are at the same end of the room) and opposite-ended. In both cases the ventilation flow rate
is the same. However, in the opposite-ended case a dead zone is established in the upper part of the room
which results in significant horizontal variations. We consider the formation of this dead zone by examining
the streamline patterns and the age of air within the room. We discuss the implications for occupant exposure
to pollutants and airborne disease.
Impact Statement:
Exposure to indoor air pollution and airborne diseases are major factors in human health and well being.
Guidance on appropriate ventilation rates is typically based on bulk ventilation rates, either in terms of the
amount supplied per individual or as air exchange rates for a space. Such bulk measures assume homogeneous
conditions within a space while, in practice, there are often significant spatial variations in properties. This
paper shows that in displacement ventilation, where it is commonly assumed that horizontal variations are
negligible, in fact simply altering the horizontal position of an outlet vent can lead to large variations in
indoor air quality. Consequently, exposures based on average values can be misleading. This finding also
has important implications for the location of sensors to measure the conditions of indoor environments,
something which is becoming increasingly commonplace
leaves through high-level vents, is characterised by vertical gradients in pressure arising from the warmer
indoor temperatures. Models usually assume that horizontal variations of temperature difference are small
in comparison and are, therefore, unimportant. Small-scale laboratory experiments and computational fluid
dynamics were used to examine these flows, driven by a uniformly heated floor. These experiments and
simulations show that the horizontal variations of temperature difference can be neglected for predictions of the bulk ventilation rate; however, they also evidence that these horizontal variations can be significant and
play a critical role in establishing the pattern of flow within the room — this renders the horizontal position of
the low- and high-level vents (relative to one another) important. We consider two cases: single-ended (where
inlet and outlet are at the same end of the room) and opposite-ended. In both cases the ventilation flow rate
is the same. However, in the opposite-ended case a dead zone is established in the upper part of the room
which results in significant horizontal variations. We consider the formation of this dead zone by examining
the streamline patterns and the age of air within the room. We discuss the implications for occupant exposure
to pollutants and airborne disease.
Impact Statement:
Exposure to indoor air pollution and airborne diseases are major factors in human health and well being.
Guidance on appropriate ventilation rates is typically based on bulk ventilation rates, either in terms of the
amount supplied per individual or as air exchange rates for a space. Such bulk measures assume homogeneous
conditions within a space while, in practice, there are often significant spatial variations in properties. This
paper shows that in displacement ventilation, where it is commonly assumed that horizontal variations are
negligible, in fact simply altering the horizontal position of an outlet vent can lead to large variations in
indoor air quality. Consequently, exposures based on average values can be misleading. This finding also
has important implications for the location of sensors to measure the conditions of indoor environments,
something which is becoming increasingly commonplace
Date Issued
2023-06-20
Date Acceptance
2023-05-08
Citation
Flow: Applications of Fluid Mechanics, 2023, 3, pp.1-18
ISSN
2633-4259
Publisher
Cambridge University Press
Start Page
1
End Page
18
Journal / Book Title
Flow: Applications of Fluid Mechanics
Volume
3
Copyright Statement
© The Author(s), 2023. Published by Cambridge University Press. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.
License URL
Identifier
https://www.cambridge.org/core/journals/flow/article/uniformly-distributed-floor-sources-of-buoyancy-can-give-rise-to-significant-spatial-inhomogeneities-within-rooms/BF3ADBE776163E0E722ABC4141FA9136
Publication Status
Published
Date Publish Online
2023-06-22