The Illustrated Guide to Ventilation: BG 2/2009 Pt. 1

58 Pages·2009·2.601 MB·English

by  Kevin Pennycook

A BSRIA Guide
www.bsria.co.uk
The Illustrated Guide
to Ventilation
Compiled by Kevin Pennycook
BG 2/2009

ACKNOWLEDGEMENTS
The guide has been compiled byBSRIA’s Kevin Pennycook with
additions from Roderic Bunn, and designed and produced by
Ruth Radburn.
BSRIA would also like to thank the following organisations who
kindly provided photographs, diagrams and information:
Atelier Ten
BRE
Building Services Journal
Department for Children, Schools and Families
Easter Group
Max Fordham
Monodraught
Passivent
SolarWall
Termodeck
Usable Buildings Trust
William Bordass Asociates
This publication has been printed on Nine Lives Silk recycled paper, which is
manufactured from 100% recycled fibre.
All rights reserved. No part of this publication may be reproduced, stored in a
retrieval system, or transmitted in any form or by any means electronic or
mechanical including photocopying, recording or otherwise without prior written
permission of the publisher.
©BSRIA 2009 January 2009 ISBN 978 0 86022 673 4 Printed by ImageData Ltd.
ILLUSTRATED GUIDE TO VENTILATION 1
© BSRIA BG 2/2009
INTRODUCTION
Effective ventilation, whether provided by mechanical or natural
means, is crucial to provide a comfortable, healthy and ultimately
productive working environment. This new guide addresses the
design and performance issues of the three main types of
ventilation:(cid:2)
(cid:23)(cid:3)
Natural ventilation(cid:2)
(cid:23)(cid:3)
Mechanical ventilation(cid:2)
(cid:23)(cid:3)
Mixed-mode ventilation.
The effective ventilation of buildings has always been a primary
design requirement. But in recent times more stringent energy
conservation standards have sought to improve the thermal
performance of building fabric and reduce levels of uncontrolled
infiltration. Among other things this has put greater emphasis on
the correct design of windows and mechanical ventilation systems.
No longer can designers expect natural infiltration to help
maintain air quality. What you specify and what you procure will
almost wholly determine what you’ll get.
Correct specification, careful detailing, accurate installation,
thorough commissioning and diligent post-handover fine-tuning
are now of equal importance in order to achieve a satisfactory
ventilation system. They are all of equal ranking. Skimp on any
one, and a ventilation design can be fatally compromised.
This guide therefore not only describes the basics of ventilation,
with copious pictures and illustrations to show how things work
and the often subtle differences between components, but also
points out key design checks that are necessary to achieve a high
quality system. Inevitably, the guide is often more geared to the
skilled designer than the lay client, but such guidance is rarely read
in isolation from other members of the project team. BSRIA is
also available to help its Members understand the more complex
issues that the Guide sometimes raises. It’s BSRIA’s view that it’s
better to provide too much information than leave readers with
begged questions.
Note that while the information in this Guide relates primarily to
non-domestic buildings, the basic information is relevant to all
types of buildings, particularly in terms of the usability and
maintainability of ventilation systems.
It is not desirable for readers to consider the various forms of
ventilation in isolation from allied subjects, such as passive design,
use of thermal mass, and controls. Inevitably these subjects are co-
related and often co-dependent. The guide therefore touches
upon the minimising of cooling loads, the contribution from
thermal massing, the control of ventilation, the commissioning of
systems, and the maintenance and upkeep of ventilation systems.
2 ILLUSTRATED GUIDE TO VENTILATION
© BSRIA BG 2/2009
The best example one can give is the humble window handle. It is
not unusual for far more design attention to be paid to the glazed
element than to the window handle and the friction stays that are
needed to keep window open. Clients and designers therefore
need to keep a very watchful eye on the specification of ancillary
items. They may be small, but they are not trivial. A few pennies
shaved during the value engineering exercise can result in less than
robust handles and stays, premature failure of which will seriously
weaken the performance of a ventilation strategy.
Controls can also ultimately dictate the success or failure of a
ventilation system. Like the window handle, the issue of controls
(particularly override controls for occupants) is often lost in the
bigger picture.
For example, motorised windows are often a packaged subcontract
item, which includes the suppliers’ dedicated wall-mounted
override controls. These are often generic controls that are rarely
tailored to a specific context. Result: the controls are not discussed
by the architect or services engineer, and end up being put in by
the specialist sub-contractor as part of the package subcontract,
without anyone on the design side overseeing their usability.
Subsequently, the building’s users may not know what the
controls do, and when to use them. Even the building’s architects
and designers can be flummoxed, which will be embarrassing. By
that time it’s too late to do anything about it.
It follows that ease of commissioning and maintenance become
vital to the performance of any ventilation system, whether natural
or mechanical or a mix of the two. In the end it comes down to
designing for managability and maintainability. There are a host of
BSRIA guides that give advice on these issues, and the relevant
ones are given in the bibliography. BSRIA Members can
download these guides in PDF from the BSRIA Bookshop, while
non-members can purchase printed versions on-line.
In conclusion it is worth quoting the old adage: build tight,
ventilate right. Do that – and provide well-designed and fully-
commissioned controls – and you won’t go far wrong.
Roderic Bunn
BSRIA January 2009
ILLUSTRATED GUIDE TO VENTILATION 3
© BSRIA BG 2/2009
4 ILLUSTRATED GUIDE TO VENTILATION
© BSRIA BG 2/2009
CONTENTS Page
ALPHABETICAL LIST OF SYSTEMS AND EQUIPMENT 6
NATURAL VENTILATION
Types of natural ventilation 7
Design and application issues 13
MECHANICAL VENTILATION
Types of mechanical ventilation 19
Design and application issues 21
Supply air terminal devices 26
Use with low carbon technologies 30
Control of mechanical ventilation 32
Key design and application checks 34
MIXED-MODE VENTILATION 38
MINIMISING COOLING LOADS 41
THERMAL MASS 42
Night cooling 43
CONTROL STRATEGIES 45
COMMISSIONING 47
MAINTENANCE AND UPKEEP 50
VENTILATION STANDARDS AND REQUIREMENTS 52
STANDARDS 53
REFERENCES/BIBLIOGRAPHY 54
ILLUSTRATED GUIDE TO VENTILATION 5
© BSRIA BG 2/2009
ALPHABETICAL LIST OF SYSTEMS AND EQUIPMENT
Activated carbon filters 25 Mixed-mode ventilation 38
Actuators 16 Natural ventilation 7, 48
Air distribution system 21 Natural ventilation components 13
Air filtration 23 Nozzles and drum-louvres 26
anemometer) 46 Perforated face diffusers 26
Carbon dioxide control 45 Photocatalytic filters 25
Carbon dioxide sensor 46 Pre-cooling control 45
Ceiling-mounted systems 28 Primary filters 23
Charged-media non-ionising filters 24 Rain sensors 46
Circular, square and rectangular diffusers 26 Re-usable filters 24
Commercial kitchens 19 Roll filters 24
Constant supply air temperature 32 Roof-mounted ventilation 11
Control strategies 45 Room air cleaners 25
Controls 39 Secondary filters 23
Cooling loads 41 Side-wall mounted grilles 29
Cross ventilation 9 Sill-mounted grilles 29
Dampers 15 Single-sided ventilation 8
Demand-controlled ventilation 22 Slab temperature sensors 46
Design solutions 39 Solar gain sensor 46
Displacement ventilation 28 Space temperature sensors 45
Ducted systems 49 Stack ventilation 10
Earth ducts 30 Summer ventilation: 14
Electrostatic filters 24 Supply and extract systems 20
External air temperature sensor 46 Supply ventilation 19
Extract ventilation 19 Swirl diffusers 26
Fabric energy Storage 42 System configuration 28
Fabric socks 27 Thermal capacity 42
Factories or industrial buildings 19 Thermolabyrinths 30
Fan motors 21 Toilets and bathrooms 19
Fans 21 Trickle ventilation 15
Floor mounted units 27 Ultraviolet irradiation systems 25
Floor-mounted systems 29 Underground car parks 19
Free-standing units 27 Variable air flow rate 32
Grilles 26 Variable supply air temperature 33
Ground-coupled air systems 30 Ventilated ceilings 29
Heat recovery 22 Ventilation and ground water cooling 31
High efficiency filters 23 Ventilators and louvres 15
Linear and slot diffusers 26 Wall mounted units 27
Local supply systems 29 Wind direction sensor 46
Localised industrial extraction 19 Wind speed sensor 46
Mechanical ventilation 19, 47 Windows 13
Mixed ventilation 28 Winter ventilation 14
6 ILLUSTRATED GUIDE TO VENTILATION
© BSRIA BG 2/2009
TYPES OF NATURAL VENTILATION
Natural ventilation makes use of the forces of wind and differences in air
to move air through a building. There are a number of different natural
ventilation air flow paths in buildings, the three main ones being:
(cid:23)(cid:3)
Cross ventilation
(cid:23)(cid:3)
Single-sided ventilation
(cid:23)(cid:3)
Passive stack ventilation.
The latter relies on the temperature difference between the outside and
inside of a building to drive air movement.
Natural ventilation enables occupants to make their own decisions on
trade-offs between ventilation rate, external noise, draught and views
out. It is often better and more energy efficient to provide people with
tolerable conditions, and the means to change them, than with better
conditions with no means of control.
A schematic showing the various natural ventilation strategies described in the chapter on natural ventilation systems.
ILLUSTRATED GUIDE TO VENTILATION 7
© BSRIA BG 2/2009
Single-sided ventilation
Benefits
(cid:23)(cid:3)The simplest form of natural ventilation
Single-sided ventilation
(cid:23)(cid:3)Good occupant control for cellular spaces
with workgroups of between 6-10 people
(cid:23)(cid:3)Windows should be tall, ideally with top and
bottom openings
(cid:23)(cid:3)A space which can be daylit by perimeter
windows on one side is generally suitable for
single-sided ventilation up to a depth or
around six to seven metres
(cid:23)(cid:3)Low cost
Limitations
(cid:23)(cid:3)Dependent on the presence of wind for
good ventilation
(cid:23)(cid:3)Inappropriate window design or positioning
Schematic showing the principle of single-sided ventilation. and poor control of opposite elements can
lead to occupier discomfort
Cross-ventilation of some spaces may not be possible due to fixed or
structural partitioning. Where this is the case, single-sided ventilation (cid:23)(cid:3)Inadequate control over ventilation, either
due to poor automation or unusable manual
may be appropriate. If windows are designed with this in mind, a room
controls, can lead to windows being opened
depth of up to 6 – 7 m can be satisfactorily ventilated in this way.
while heating is on, wasting energy
Control issues
(cid:23)(cid:3)Not suitable for deep-plan spaces
The success of a natural ventilation strategy will not be determined purely
by technical specifications. Reality may not match the modelled (cid:23)(cid:3)May not be appropriate for noisy, polluted
assumptions about the extent and timing of window or vent opening and environments
closing, as the variables that determine occupants’ response to their
(cid:23)(cid:3)Motorised windows can be noisy and
conditions are many and varied. Workgroup size is also a factor. distracting, and prone to illogical operation
Ventilation effectiveness may be less determined by floor depth and free (cid:23)(cid:3)Activators and motors for automated
window area, and more by seemingly minor but critical things such as the windows are not fit-and-forget items, and
can require regular maintenance
robustness and usability of window handles, stays, and controls. Windows
that fail to stay open in breezy conditions may either remain closed or be left
propped open. Motorised windows that are noisy when they operate will be
regarded as nuisance technology that disrupts concentration. Facilities
managers may intervene to reduce complaints, but in so doing compromise
ventilation effectiveness. A night cooling strategy may fall into disuse.
Openable windows and vents therefore need as much care and detailing as
any mechanical ventilation or air-conditioning system. This means that a
high level of attention should be paid to the specification of windows,
motors and actuators. The same goes for glare control devices, which must
operate effectively throughout their range without adversely affecting
ventilation rates.
It is a false economy to buy the cheapest components. In general, where
motorised elements are concerned, it is always best to procure an integrated
system from a single source, rather than assemble the components – A typical outward opening fanlight (sometimes
called a clerestorey window, depending on the
window/vent, actuator, motor and linkage – from many suppliers, as they
location in the building).
may not match up properly. A weak link in the chain can fatally
compromise the ventilation strategy, leading to overheating, stuffiness and
occupant discomfort.
All ventilation devices, particularly those operated by occupants, need to be
robust and intuitive to use, and enable trade-offs to be managed between
ventilation rate, glare, noise, draughts, and views out. However, even the
most intuitive user control will benefit from clear explanation. This can be
achieved through good design, careful specification and proper labelling. It
is also important to locate the control devices near to the elements they are
supposed to control. User familiarisation and training during the initial
period of occupation is also desirable. These issues also apply to cross-
ventilation and stack ventilation.
A typical high-quality bottom-hung inward opening
window. These types of window are better with mid-
8 ILLUSTRATED GUIDE TO VENTILATION pane blinds. Also see page 41.
© BSRIA BG 2/2009