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Heating and ventilation systemsHealth Technical Memorandum03-01: Specialised ventilation for

healthcare premises

Part A: Design and validation


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Document Purpose Best practice guidance

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Health Technical Memorandum 2025

November 2007

PCT CEs, NHS Trust CEs, SHA CEs, Care Trust CEs, Foundation

Trust CEs , PCT PEC Chairs, NHS Trust Board Chairs, Special HA

CEs

Department of Health libraries, House of Commons library,

Strategic Health Authorities, UK Health Departments, Directors of

Estates and Facilities,

The document gives comprehensive advice and guidance to

healthcare management, design engineers, estates managers and

operations managers on the legal requirements, design implications

and maintenance of specialised ventilation in all types of healthcare

premises.

For Recipient's Use

Health Technical Memorandum 03-01: Specialised ventilation for

healthcare premises. Part A - Design and installation

LS2 7UE

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email:[email protected]

Ken HolmesDepartment of Health/Estates and Facilities Division

Quarry House, Quarry Hill

Leeds

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mailto:[email protected]:[email protected]:[email protected]


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Heating and ventilation systemsHealth Technical Memorandum 03-01:Specialised ventilation or healthcare premises

Part A: Design and validation

London: The Stationery Oice


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Heating and ventilation systems HTM 03-01: Specialised ventilation or healthcare premises Part A

ii

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iii

Preace

About Health Technical Memoranda

Engineering Health Technical Memranda (HTMs)give cmprehensive advice and guidance n the design,installatin and peratin f specialised building andengineering technlgy used in the delivery f healthcare.

The fcus f Health Technical Memrandum guidanceremains n healthcare-specific elements f standards,plicies and up-t-date established best practice. They areapplicable t new and existing sites, and are fr use atvarius stages during the whle building lifecycle.

Healthcare prviders have a duty f care t ensure thatapprpriate engineering gvernance arrangements are inplace and are managed effectively. The EngineeringHealth Technical Memrandum series prvides bestpractice engineering standards and plicy t enablemanagement f this duty f care.

It is nt the intentin within this suite f dcuments tunnecessarily repeat internatinal r Eurpean standards,industry standards r UK Gvernment legislatin. Whereapprpriate, these will be referenced.

Healthcare-specific technical engineering guidance is avital tl in the safe and efficient peratin f healthcarefacilities. Health Technical Memrandum guidance is the

main surce f specific healthcare-related guidance frestates and facilities prfessinals.

The cre suite f nine subject areas prvides access tguidance which:

ismorestreamlinedandaccessible;

encapsulatesthelateststandardsandbestpracticeinhealthcareengineering;

providesastructuredreferenceforhealthcareengineering.

Structure o the Health TechnicalMemorandum suite

The series f engineering-specific guidance cntains asuite f nine cre subjects:

Health Technical Memrandum 00Plicies and principles (applicable t all HealthTechnical Memranda in this series)

Health Technical Memrandum 01

DecntaminatinHealth Technical Memrandum 02

Medical gases

DESIGN & IDENTIFYOPERATIONAL

REQUIREMENTS

SPECIFICATIONSTECHNICAL & OUTPUT

PROCUREMENTCOMMISSIONING

MAINTENANCE

OPERATIONAL

MANAGEMENT

CONCEPTDISPOSAL

OngoingReview

CONSTRUCTIONINSTALLATION

RE-USE

Figure 1 Healthcare building life-cycle


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iv

HTM 07

Environment &Sustainability

HTM 08

SpecialistServices

HTM 01

Decontamination

HTM 02

MedicalGases

HTM 06

ElectricalServices

HTM 03

Heating &VentilationSystems

HTM 04

WaterSystems

HTM 05

FireSafety

Policies andPrinciples

INTERNATION

AL&EUROPEANSTA

NDARDS

I

NTERNATIO

NAL&EUROPEAN

STANDARD

S

INDU

STRY STANDARD

S

INDUSTRY STAND

ARD

S

HEA

LTH S

PEC IF IC DOCUMENTS

HE

A

L

TH

SPECIFIC

DO

CUM

ENTS HEALTH

SPECIF

IC

DOCUM

E

N

T

S

HTM 00

Health Technical Memrandum 03Heating and ventilatin systems

Health Technical Memrandum 04

Water systemsHealth Technical Memrandum 05

Fire safety

Health Technical Memrandum 06Electrical services

Health Technical Memrandum 07Envirnment and sustainability

Health Technical Memrandum 08Specialist services

Sme subject areas may be further develped int tpicsshwn as -01, -02 etc and further referenced int Parts A,B etc.

Example: Health Technical Memrandum 06-02 Part Awill represent:

Electrical Services Electrical safety guidance fr lwvltage systems

In a similar way Health Technical Memrandum 07-02

will simply represent:Envirnment and Sustainability EnCO2de.

All Health Technical Memranda are supprted by theinitial dcument Health Technical Memrandum 00

which embraces the management and peratinal pliciesfrm previus dcuments and explres risk managementissues.

Sme variatin in style and structure is reflected by thetpic and apprach f the different review wrkinggrups.

DH Estates and Facilities Divisin wishes t acknwledgethe cntributin made by prfessinal bdies,engineering cnsultants, healthcare specialists andNHS staff wh have cntributed t the review.

Figure 2 Engineering guidance


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v

Preamble

Health Technical Memrandum 03-01 Specialisedventilatin in healthcare premises is published in twparts: Part A deals with the design and installatin fventilationsystems;PartBcoversoperationalmanagement.

The dcument gives cmprehensive advice andguidance n the legal requirements, design implicatins,maintenance and peratin f specialised ventilatin inall types f healthcare premises.

The guidance cntained in this Health TechnicalMemrandum applies t new installatins and majrrefurbishments f existing installatins.

Health Technical Memrandum 03-01 supersedes allprevius versins f Health Technical Memrandum2025 Ventilatin in healthcare premises.

Who should use this guidance?

This dcument is aimed at healthcare management,design engineers, estates managers and peratinsmanagers.

Main changes rom Health TechnicalMemorandum 2025

This Health Technical Memrandum has been revised treflect the current guidance n theatre suite layut andrm sizes given in Health Building Nte 26, Vlume 1

Facilities fr surgical prcedures, including therecmmended air-change rates.

Other key issues

Itaddressestheissuesrelatingtopatientcomfortandthe preventin and cntrl f healthcare-assciatedinfectins. Specialised ventilatin systems play acentral rle in these imprtant areas.

Itlooksatthemethodsofcontrollingthecasualexpsure f staff t anaesthetic substances.

Itoutlinesthedesignandacceptancetestingofgeneraland ultra-clean ventilatin (UCV) systems.

Itsetsouttheminimumrequirementsforthedesignf air-handling units with regard t the cntrl fLegionella and safe access fr rutine inspectin andmaintenance.

Executive summary


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Heating and ventilation systems HTM 03-01: Specialised ventilation for healthcare premises Part A

vi

Malcolm Thomas Consulting Engineer Lead Author

Principal contributors

Craig Macintosh Principal Clinical Scientist WirralHospitals NHS Trust

Andy McGrath BSRIA Instrument SolutionsHelen & Philip Sturdy DSSR consultancy

Richard Gatley Apreco

Russell Pitman Henderson Green consultancy

Kevin Reynolds Deputy Head of Estates Sandwelland West Birmingham NHS Trust

Ian Fraser Department of Health

Main Steering Group and Working

Groups comprising representativesfrom:

Department of Health

Welsh Health Estates

NHS in Scotland

Health & Social Services, Northern Ireland

Health Protection Agency (HPA)

Building Research Establishment (BRE)

Building Services Research and Information Association(BSRIA)

University of Leeds

CIBSE Healthcare Group

IMechE/ASHRAE

IHEEM

HEFMABSI

Faber Maunsell consultancy

Couch Perry Wilkes consultancy

DSSR consultancy

Howorth Airtech

Medical Air Technology/Thermo Electric

BPG Medical

Admeco/Trumpf Medical Systems

Volkes SPX

Weiss Klimatechnik

Sound Research Laboratories

NHS Security Management Service

Pennine Acute NHS Trust

Hospital Infection Society (HIS)

Central Sterilising Club

HEVAC Air-handling Unit Manufactures Group

Acknowledgements


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vii

Contents

PrefaceExecutive summary

AcknwledgementsChapter 1 Intrductin 1

PreambleVentilatin in healthcare premises

Reasns fr ventilatinVentilatin applicatin examplesStatutry requirements

Health and Safety at Wrk etc Act 1974COSHHFire regulatinsPlants installed in units manufacturing medicinal prductsPlants installed in labratries

Cdes f practice and ther guidanceDesign and validatin prcessVentilatin terms in use

VentilatinAir-cnditiningSpecialised ventilatinLcal exhaust ventilatin

Chapter 2 Prvisin f ventilatin in healthcare buildings 8Natural ventilatinExtract ventilatin systemsSupply-nly ventilatinSupply and extract ventilatinCmfrt cling

Air-cnditiningSpecialised ventilatin

Lcal exhaust ventilatinVentilatin fr general areasAcceptable methds

Use f natural ventilatinMixed mde ventilatinMechanical extract ventilatinMechanical supply systemsBalanced ventilatinCascade ventilatinRecirculatin systemsChilled beams

Split cmfrt air-cnditinersDilutin ventilatin and clean air-flw pathsMechanical ventilatin systems

System selectin


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viii

Chice f central/lcal plantZning f the building

Chapter 3 Assessment f service requirement 13Selectin f design criteria

External design cnditinsInternal design cnditinsMinimum fresh-air requirementsLimiting supply air cnditins

Air purityHumidity cntrl requirementsNise levels

Calculatin f building ladsAir infiltratinSummertime temperaturesPeak heating lad

Cndensatin riskPeak cling ladAnnual energy cnsumptin

Calculatin f plant requirementsAir-supply vlumesPlant sizingPlantrm size and lcatinPrvisin f primary servicesInlet and discharge sizing and lcatinHeat-rejectin devices

Chapter 4 Air-handling unit design and specificatin guidance 18General requirements

Lcatin and accessTechnical requirements

AHU drainage systemLayut f AHUPrvisin f dampersVibratinSequence f cmpnents

FansGeneral requirements

Acceptable typesSelectin

Lcatin and cnnectinSupply fan drive arrangementsExtract fan drive arrangementsCntrl

Heater-batteriesGeneral requirements

Acceptable typesLcatinCntrl

Cling cilsGeneral requirementsSelectinLcatinCntrl

Humidifiers


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Contents

ix

Design needGeneral requirementsAcceptable typesSelection

LocationControl

FiltrationGeneral requirementsDefinition of filter termsSelectionLocationControl

Energy recoveryGeneral requirementsLocation

ControlAttenuationGeneral requirementsAcceptable types and location

Chapter 5 Air distribution system 31Air distribution arrangements

Ductwork distribution systemsDuctwork materials and constructionFire aspects, damper types and locationsDuct sectionsStandard ductwork fittingsThermal insulation

Noise generation within the ductworkVolume control damper locationsCleaning and access door locationsFlexible ductingDiffuser and grille selection and sizingTransfer grille size and locationPressure stabilisers size and location

Chapter 6 Automatic controls 37General requirements

Objectives of the control systemLocation of controls

Fire aspectsTime switching

Start-up controlSet-back controlUse control

Environmental controlTemperature control methods and applicationHumidity control methods and applicationMulti-zone control methods and application.Alarms and indication

Chapter 7 Specialised ventilation systems 45General information

Air-movement controlTemperature and humidity controlRemoval and dilution of waste anaesthetic gases


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x

Fire aspectsDr prtectinSystems design

Operating department ventilatin systems

GeneralFire aspectsDr prtectinStandard air-mvement cntrl schemes

Air terminals and air distributin within rmsAutmatic cntrlVentilatin f perating department ancillary areasReceptinSterile pack bulk streRecvery

Ultra-clean ventilatin systems

General requirementsTypes f UCV systemFiltersNise levelLighting and perating lightsCntrls and instrumentatin

Extract systemsHd extract systemsBench extract systemsSafety cabinet and fume-cupbard extract systems

Plantrm ventilatinGeneral requirements

Assessment f ventilatin levelsChice f ventilatin system

Ventilatin f hydrtherapy suitesGeneral requirementsCntrl f hydrtherapy pl installatins

Chapter 8 Validatin f specialised ventilatin systems 66DefinitinsCmmissining

Lcatin f dampers and test hlesCmmissining persnnelCmmissining brief

Pre-cmmissining checksStandard f installatinCleanliness f installatinCertificatin f equipmentEquipment tests

Dynamic cmmissiningAir-handling and distributin systemRm-air distributin

Air-cnditining plantCntrl system

Specific perfrmance standardsAir mvementPlant capacity and cntrlNise levels generalFilter challenge


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Contents

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Bacteriological samplingVentilation system commissioning/validation report

Validation of UCV operating suitesGeneral

Basic requirementUCV unit validation procedureTest and measuring conditionsTest and measuring equipmentTest grid vertical unitsTest grid horizontal unitsUCV terminal challenge tests (vertical and horizontal systems)Vertical UCV terminal air velocity testsHorizontal UCV terminal air velocity testUCV entrainment test (vertical systems only)UCV visualisation

UCV noise levelUCV control system checksUCV theatre microbiological testsUCV validation report

GeneralAir intakeDamperDuctingFanAttenuator/silencerFilter

Appendix 1 Use and function of typical equipment used in ventilation systems 81

Heater coil/batteryHumidifierChiller battery/cooling coilEliminatorDrainage systemAccess doors and observation portsEnergy recoveryTypical plant

Appendix 2 Recommended air-change rates 83Appendix 3 Hierarchy of cleanliness 84Appendix 4 Leakage flows in m3/s through closed door gaps 85

Appendix 5 Recommended air-flow rates in m3/s through a doorway between rooms of different

cleanliness to control cross-contamination 86Appendix 6 Typical approximate pressures in an operating suite when a given door is open 87Appendix 7 Operating suites standard design solutions 88Appendix 8 Design of air-movement control schemes for operating theatres 97

GeneralPeripheral room type

Single flowParallel multi-flowParallel/series multi-flowSeries multi-flow (unbalanced)Series multi-flow (balanced)Bay

Air-movement control in peripheral roomsSingle flow rooms


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Parallel multi-flw rmsParallel-series multi-flw rmsSeries multi-flw (unbalanced)Series multi-flw (balanced)

BayOperating rmCrridrs

Dr peningTransfer grillesPressure-relief dampersPressure stabilisersDr leakage flwsRm temperature estimatinRelief f excess air frm perating rm when all drs are clsed

By transfer devices via the anaesthetic rm

By pressure stabilisers t the crridrReferences 118Acts and regulatinsBritish StandardsDepartment f Health publicatinsChartered Institutin f Building Services publicatinsHeating & Ventilating Cntractrs Assciatin (HVCA) publicatinsOther publicatins


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1

Preamble

1.1 Health Technical Memrandum 03-01 Specialised ventilatin in healthcare premises ispublished in tw parts: Part A deals with the designandinstallationofventilationsystems;PartBcvers peratinal management.

1.2 The dcument gives cmprehensive advice andguidance t healthcare management, designengineers, estates managers and peratinsmanagers n the legal requirements, designimplicatins, maintenance and peratin fspecialised ventilatin in all types f healthcarepremises.

1.3 The guidance cntained in this Health TechnicalMemrandum applies t new installatins andmajr refurbishments f existing installatins.

1.4 Health Technical Memrandum 03-01 supersedesall previus versins f Health TechnicalMemrandum 2025 Ventilatin in healthcarepremises.

Ventilation in healthcare premises

1.5 Ventilatin is used extensively in all typesf healthcare premises t prvide a safe andcmfrtable envirnment fr patients andstaff. Mre specialised ventilatin is prvided in

primary patient treatment areas such as peratingdepartments, critical care areas and islatin units.

1.6 It is als installed t ensure cmpliance with qualityassurance f prcessed items in pharmacy andsterile services departments, and t prtect stafffrm harmful rganisms and txic substances (frexample in labratries).

1.7 The sphisticatin f ventilatin in healthcarepremises is increasing. Patients and staff have aright t expect that it will be designed, installed,perated and maintained t standards that will

enable it t fulfil its desired functins reliably andsafely.

Reasons or ventilation

The Building Regulatins require that all enclsedwrkspaces be ventilated by either natural rmechanical means. The fllwing are sme f thefactrs that determine the ventilatin requirements f

a wrkspace: humanhabitation(minimumfresh-air

requirement);

theactivitiesofthedepartment,thatis,extractionf durs, aersls, gases, vapurs, fumes and dust sme f which may be txic, infectius, crrsive,flammable, r therwise hazardus (see the Cntrlf Substances Hazardus t Health (COSHH)Regulations);

dilutionandcontrolofairbornepathogenic

material; thermalcomfort;

theremovalofheatgeneratedbyequipment(fr example catering, wash-up, sterilizing areas,electricalswitchrooms,andsomelaboratoryareas);

thereductionoftheeffectsofsolarheatgains;

thereductionofexcessivemoisturelevelstopreventcondensation(forexamplehydrotherapypools);

combustionrequirementsforfuelburning

appliances; make-upsupplyairwherelocalexhaust

ventilatin (LEV) etc is installed.

Mechanical ventilatin systems are expensive in termsf capital and running csts, and planning slutinsshuld be sught which take advantage f naturalventilatin, prvided the abve criteria are met.

1 Introduction


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2

Statutory requirements

Increased health risks to patients will occur ifventilation systems do not achieve and maintain therequired standards. The link between surgical siteinfection and theatre air quality has been wellestablished. Plants serving a conventional operatingdepartment, for instance, will be required to ensure theseparation of areas within the suite by maintaining aspecific direction of air flow between rooms, evenwhen doors are opened. They will also maintain theselected operating departments environmentalconditions regardless of changes in outside air

conditions or activities within the space.

In addition, ultra-clean ventilation systems (which aredesigned to provide a zone around the patient that iseffectively free of bacteria-carrying airborne particleswhile the operation is in progress) have been shown tosignificantly reduce surgical site infection in patientsundergoing large joint replacement surgery. Their usefor other forms of surgery may well be indicated.

Health and Safety at Work etc Act 1974

1.8 The Health and Safety at Work etc Act 1974is the core legislation that applies to ventilationinstallations. As these installations are intended to

prevent contamination, closely control theenvironment, dilute contaminants or containhazards, their very presence indicates that potentialrisks to health have been identified.

COSHH

1.9 The Control of Substances Hazardous toHealth (COSHH) Regulations 2002 place uponmanagement an obligation to ensure that suitablemeasures are in place to protect their staff andothers affected by the work activity. These methodsmay include both safe systems of work and theprovision of a specialised ventilation system. Inlaboratories the requirements are often met by theprovision of fume cupboards and microbiologicalsafety cabinets.

1.10 The requirements to provide ventilation, implicitunder the Health and Safety at Work etc Act 1974and COSHH, have been made explicit by theManagement of Health and Safety at WorkRegulations 1999, the Workplace (Health, Safetyand Welfare) Regulations 1992 and the Provisionand Use of Work Equipment Regulations 1998,all issued as a result of European Directives.

1.11 Where specialised ventilation plant is provided aspart of the protection measures, there is a statutoryrequirement that it be correctly designed, installed,

Ventilation application examples

Requirement Reason Application

Statutory Health and Safety at Work etc Act

COSHH Regulations

Local exhaust ventilation (LEV)

Operating departments

Laboratories

Pharmacies

Areas containing identified biological or chemical hazards

Areas containing oxygen-displacing gases

Enclosed workspaces

Workshops

Functional Comfort Situations where the quality of the environment for staff and patients is critical to their general performance andwell-being

Clinical Reduction of surgical site infection Ultra-clean operating suites, conventional operatingsuites and treatment rooms used for all types of surgicalprocedures

Obstetrics and maternity procedures

Source and protective isolation Isolation units for patients who present a biological,chemical or radiation hazard to others

Isolation units for patients with a reduced immune system


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1 Introduction

3

cmmissined, perated and maintained. The lcalexhaust ventilatin (LEV) sectin f COSHHrequires that the plant be inspected and tested atleast every 14 mnths by a cmpetent persn and

that management maintain cmprehensive recrdsf its perfrmance, repair and maintenance.

1.12 Certain substances have wrkplace expsure limits(WELs) set ut in the Health and Safety Executives(2005) Guidance Nte EH40 Wrkplaceexpsure limits: cntaining the list f wrkplaceexpsure limits fr use with the Cntrl fSubstances Hazardus t Health Regulatins 2002(as amended). If specialised ventilatin systems areprvided in rder t achieve these standards, they

will be subject t the COSHH Regulatins as

abve.

Fire regulations

1.13 The fire regulatins require that, if ventilatinductwrk penetrates the cmpartment rsubcmpartment f a building, it shuld bedesigned and installed s as t cntain the spread ffire (see Health Technical Memrandum 05-02 Guidance in supprt f functinal prvisins frhealthcare premises fr further guidance).

Plants installed in units manuacturing medicinalproducts

1.14 Plants installed in units manufacturing medicinalprducts t the standards set ut in the currentEurpean guide t gd manufacturing practice(http://ec.eurpa.eu/enterprise/pharmaceuticals/eudralex/hmev4.htm) may als be subject tparticular legislatin with regard t their peratinin additin t that mentined abve.

1.15 Recrds shuld be kept f equipment design andcmmissining infrmatin. The Health and SafetyExecutive, Medicines Inspectrate and therinterested bdies have a statutry right t inspectthem at any time. All recrds shuld be kept fr atleast five years.

Plants installed in laboratories

1.16 Specialised ventilatin plants installed inlabratries dealing with research, develpmentr testing, whether invlving drugs, animals rgenetically mdified rganisms, may be subject tparticular legislatin with regard t their peratinin additin t that mentined abve. Furtherinfrmatin is given by the Health & Safety

Cmmissins Health Services Advisry Cmmitteein:

Safe wrking and the preventin f infectin in

clinicallaboratoriesandsimilarfacilities;The management, design and peratin fmicrbilgical cntainment labratries.

Note

If the ventilatin plant has been installed t dilute rcntain harmful substances (the definitin f whichnw includes micrrganisms), its failure may expsepeple t unacceptable levels f hazard. Prven failurescan give rise t a civil suit against the designers andperatrs by the individuals wh have been affected.

This wuld be in additin t the actins brught as aresult f breaching the statutry requirements.

Codes o practice and other guidance

1.17 All ventilatin systems shuld cnfrm tthe principles set ut in the Health and SafetyCmmissins Apprved Cde f Practice andguidance dcument Leginnaires disease: thecntrl fLegionella bacteria in water systems(cmmnly knwn as L8), and Health Technical

Memrandum 04-01 The cntrl fLegionella,hygiene,safehotwater,coldwateranddrinkingwater systems.

1.18 The Department f Health publicatinThe Health Act 2006: cde f practice fr thepreventin and cntrl f healthcare assciatedinfectins is a cde f practice that has beenbrught ut t help NHS bdies t plan andimplement hw they can prevent and cntrlhealthcare-assciated infectins. It sets ut criteriaby which managers f NHS rganisatins are

t ensure that patients are cared fr in a cleanenvirnment and where the risk f healthcare-assciated infectins is kept as lw as pssible.Specialised ventilatin systems ften play a centralrle in achieving this bjective.

This dcument deals with the healthcare-specificaspects f ventilatin. Basic infrmatin n the design,installatin, cmmissining and testing f ventilatinsystems is cntained in dcuments prduced by thefllwing (see the References sectin):

theCharteredInstituteofBuildingServicesEngineers(CIBSE);
http://ec.europa.eu/enterprise/pharmaceuticals/eudralex/homev4.htmhttp://ec.europa.eu/enterprise/pharmaceuticals/eudralex/homev4.htmhttp://ec.europa.eu/enterprise/pharmaceuticals/eudralex/homev4.htmhttp://ec.europa.eu/enterprise/pharmaceuticals/eudralex/homev4.htmhttp://ec.europa.eu/enterprise/pharmaceuticals/eudralex/homev4.htm


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4

InternationalandBritishStandards(ISOandBSEN);

theBuildingServicesResearchandInformation

Association(BSRIA);

tradeassociationssuchastheHeatingandVentilating Cntractrs Assciatin (HVCA).

Design and validation process

1.19 It is essential, when undertaking the design f aspecialised ventilatin system, that the prject be

cnsidered as a whle. The prcess mdel set ut inTable 1 shuld ensure that all relevant factrs arecnsidered.

Table 1 Design and validation process model

Step Question Design statement and information required Comment

1 Why is the system required? Healthcare applicatinsStatutry elementsNn-healthcare applicatins

2 What is the required system perfrmance? Rm air-flw patternAir-change rateDifferential pressures

Air qualityRm air-cnditinNise limits

3 What are the cnstraints n the distributinsystem?

Ducts:Lcatin, size, materialsDampers, access, insulatin

Fire cnsideratinsRm terminals

4 What are the minimum requirements fr the

air-handling units (AHUs)?

Intake/discharge psitins

Leginella, health and safetyAccess, fire, electrical safetyLeaks, insulatin, cleanlinessFiltratin, drainage

5 What cntrl functins are required? User cntrl requirementsEstates cntrl functinsEnergy managementEnvirnmental cnditinsCntrl sequence lgicRun, set-back, Off philsphy

6 Hw will the system perfrmance bevalidated?

Validatin methdlgyInstruments used

Design infrmatin required:designair-flowratesdesignairvelocitiespressuredifferentialsnoiselevelsairqualityinstallationstandard

7 The system will nly be acceptable t the client if at the time f validatin it is cnsidered fit fr purpse and will nlyrequire rutine maintenance in rder t remain s fr its prjected life.

8 Handver t client1 Basic design infrmatinCmmissining resultsValidatin reprt

Nte: 1. When new ventilatin systems are accepted fr use, full infrmatin as t their designed mde f peratin tgetherwith recmmended maintenance prcedures shuld be prvided as part f the handver prcedure


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1 Introduction

5

Ventilation terms in use

1.20 Thetermsventilationandair-conditioningareften used interchangeably t describe the same

equipment. A general explanatin f the terms isgiven belw.

Ventilation

1.21 Ventilatin is a means f remving and replacingthe air in a space. In its simplest frm this may beachieved by pening windws and drs.

1.22 Mechanical ventilatin systems prvide a mrecntrllable methd. Basic systems cnsist f afanandcollectionordistributionductwork;morecmplex systems may include the ability t heat

and filter the air passing thrugh them.1.23 Ventilating equipment may be required in rder t

remve smells, dilute cntaminants and ensure thata supply f fresh air enters a space.

Air-conditioning

1.24 Air-cnditining is the ability t heat, cl,dehumidify and filter air. Fr full air-cnditining,humidificatin may als be prvided. This meansthat the climate within a space being supplied by

an air-cnditining plant can be maintained at aspecific level regardless f changes in utside aircnditins r the activities within the space. Air-cnditining equipment may be required in rdertoprovideclosecontrolofcomfortconditions

within a space.

Specialised ventilation

1.25 In healthcare premises, certain activities willnecessitate the prvisin f ventilatin equipment

with additinal special features in rder t achieve

and maintain specific cnditins. These may beneeded in rder t assist with the treatment fpatients r maintain the health and safety f staff.The precise reasn fr prviding specialisedventilatin will depend upn the intendedapplicatin. The list belw indicates sme f themre typical reasns:

a. t remve, cntain r dilute specificcontaminantsandfumes;

b. t ensure the islatin f ne space frmanother;

c. t preserve a desired air-flw path frm a cleantoalesscleanarea;

d. toprovidecontrolofthecleanlinessofaspace;

e. toprovideclosecontroloftemperature;

f. t prvide clse cntrl f humidity.

1.26 The fllwing departments will usually have

specialised ventilatin requirements, either fr asingle rm r thrughut a suite f rms:

a. operatingdepartment;

b. lasersurgeryunit;

c. operativeimagingunit;

d. intensivetreatmentunit;

e. infectiousdiseasesisolationunit;

f. wardshousingimmunocompromisedpatients;

g. manufacturingpharmacy;h. specialisedimaging,X-rayandscanningunit;

j. pathologycontainmentlaboratories;

k. mortuaryanddissectionsuite;

m.researchlaboratories;

n. sterileservicesdepartment;

p. emerging treatment technlgies, includinggene therapy and stem cell units.

1.27 Ventilatin may be prvided in a wide variety fways. These will include:

extensive purpse-built air-handling unitshousedintheirownplantrooms;

proprietarypackagedsystemsoftensitedoutsideonaroof;or

wall-munted electric fans lcated at the pintf use.

1.28 A fixed vlume f air may be supplied, ftenexpressed in terms f the resulting number f air

changes per hur (ac/h), within the space beingventilated. Alternatively the vlume f air suppliedmay be varied in rder t maintain a specificpressure relatinship between the area suppliedand ther surrunding areas. In sme situatinsa cmbinatin f bth methds may be adpted.

1.29 Mdern plants shuld be fitted with the means trecver energy frm the extract air withut causingcntaminatin f the incming supply air.

1.30 Ultra-clean systems use the same basic plant and

equipment as standard air-cnditining systems,but are in additin fitted with a terminal devicethat supplies the air in a unidirectinal manner tthe wrking area. Their standard f filtratin will


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be capable f delivering air with a very lw particlecunt t the space that they serve.

Local exhaust ventilation

1.31 Lcal exhaust ventilatin (LEV) is a term used tdescribe systems installed t prevent hazardussubstances frm entering the general atmspheref the rm in which they are being used. Theirprimary functin is t prtect staff frm the effectsf their wrk activity.

1.32 Simple LEV systems cmprise a receptr r capturehd, extract ductwrk and a fan. These are used tcntain industrial types f hazard such as fumesfrm welding prcesses, gas discharges frm

standby battery banks and dust frm wdwrkingmachinery.

1.33 The vapur given ff when large quantities fchemicals are decanted int ready-use cntainersand fumes frm X-ray film prcessing units areexamples f chemical hazards ften cntrlled byLEV systems.

1.34 In labratries, pharmaceutical manufacturingfacilities and perating suites, LEV systems usuallytake the frm f semi-pen-frnted cabinets within

which the hazardus substance is manipulated.

These cabinets either have their wn filtered airsupply r are fed with air frm the rm. Theair extracted frm the cabinet is passed thrugha high-efficiency filter befre being dischargedeither t the atmsphere r back int the rm.Micrbilgical safety cabinets, labratry fumecupbards, cyttxic drug cabinets and fixed rmbile disinfectin enclsures are all examples fthis type f facility.

1.35 Mrtuaries and dissectin suites may have LEVsystems incrprated within the dissectin table,

specimen bench and bne saw.1.36 The layut f a typical plant that cnfrms t the

regulatins fr healthcare applicatins is shwn inFigure 1. Fr an explanatin f the equipment usedin the diagram, seeAppendix 1.


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Figure 1 Example o a typical operating theatre ventilation system

M D VC DIntake

Attenuator AttFogcoil

Supply fan &blast plate

Primaryfilter

Chiller &eliminator

Heaterbattery

Trimmerbattery

Lay upprep room

Operating room Anaesthetic r

Secondaryfilter

Drainagesystem

Energyrecoverydevice

Extract Extra


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8

2.1 Planning cnstraints caused by a buildings shapeand/r the functinal relatinships f specific areas

will invariably result in sme measure f deepplanning, thus reducing the pprtunity fr naturalventilatin.

2.2 Hwever, ventilatin csts can be minimised byensuring that, where practicable, cre areas arereserved fr thse rms that need t havemechanical ventilatin. Examples are:

sanitary facilities, dirty utilities and thse rmswhere clinical r functinal requirements havespecificenvironmentalneeds;and

thse rms where fr reasns f privacy,absence f slar gain etc windwlessaccmmdatin is acceptable.

2.3 Other spaces apprpriate t cre areas are thse

which have nly transient ccupatin and therefrerequire little r n mechanical ventilatin (frexample circulatin and strage areas).

Natural ventilation

2.4 Natural ventilatin is usually created by the effectsf wind pressure. It will als ccur if there is atemperature difference between the inside and theoutsideofabuilding.Thethermo-convectiveeffect frequently predminates when the windspeed is lw, and will be enhanced if there is adifference in height between inlet and utletpenings.

2.5 Ventilatin induced by wind pressures can inducehigh air-change rates thrugh a building, prvidedair is allwed t mve freely within the space frmthe windward t the leeward side. Hwever, inmst healthcare applicatins, internal subdivisins

will restrict r prevent this effect.

2.6 It is almst impssible t maintain cnsistent flwrates and ensure that minimum ventilatin rates

will be achieved at all times. Hwever, thisvariability is nrmally acceptable in such areas asffice accmmdatin, staff areas, library/seminarrms and dining rms, where pening windws

(f a design that facilitates natural ventilatin)shuld be prvided.

Note

Ifnaturalventilationissingle-sided,itwillusuallynly be effective fr a three-metre depth within thespace. Beynd that it will need t be supplemented bymixed-mde r frced ventilatin.

2.7 Current guidance restricts the pening f windwsforsafetyreasons;also,asmanydesignsaretop-hung, their ability t permit natural ventilatin islimited. It may therefre be necessary t prvidededicated ventilatin penings in the fabric f thebuilding t allw a sufficient natural flw f airint and ut f the space.

2.8 In all cases, excessive heat gain, indr air-qualityrequirements r external nise may limit rpreclude the use f natural ventilatin.

2.9 Detailed guidance n natural ventilatin can befund in CIBSEs (2005) Applicatins Manual

AM10 Natural ventilatin in nn-dmesticbuildings.

Extract ventilation systems

2.10 Extract ventilatin is required in sanitary facilities,dirty utilities and rms where drus butnon-toxicfumesarelikely;thisistoensureairmvement int the space. A single fan/mtr unitshuld be prvided t meet this need. There is nhealthcare requirement t prvide a separate ful/dirty extract system.

2.11 WCs shuld have an extract rate as set utin Apprved Dcument F f the BuildingRegulatins. Where WCs are lcated in shwer andbathrm spaces, the ventilatin required fr the

WC will nrmally be adequate fr the whle space.

Supply-only ventilation2.12 Mechanical supply ventilatin is required in areas

where it is imprtant t maintain a psitive

2 Provision o ventilation in healthcarebuildings


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pressure in rder t prevent the ingress f lessclean air (fr example in units caring fr immun-cmprmised patients, aseptic suites in pharmacies,packing rms in sterile services departments,operatingtheatresandtheatrepreparationrooms;air-change rates are given inAppendix 2).

Supply and extract ventilation

2.13 Mechanical supply and extract ventilatin shuldbe prvided in rms where there is a need tcntrl rm pressure in relatin t adjacentspaces. Critical care areas, islatin suites andtreatment areas are typical applicatins.

Comort cooling

2.14 Cling is very expensive in terms f energy cstsand shuld be prvided nly where necessary tmaintain a cmfrtable envirnment fr staffand patient, r t ensure satisfactry peratin fequipment. The imaging department in particularmay require cling t ffset the equipment lad.

2.15 Calculatins and thermal mdelling shuld beundertaken t ensure that, during the summertime,internal temperatures in patient areas d nt exceed28oC (dry bulb) fr mre than 50 hurs per year.

2.16 Certain nn-patient areas may als require cling(fr example labratries and ther areas that aresubject t high heat gains frm equipment).

2.17 Where deep planning f ther cntinuuslyccupied spaces (fr example ffices) isunavidable, there will als be ccasins whenacceptable levels f cmfrt can nly be maintainedby cling.

2.18 Refrigeratin plant shuld be f sufficient capacityt ffset heat gains and maintain areas at a

temperature that des nt exceed the externaldesign shade temperatures by mre than abut 3 K,taking int accunt the level f design risk fr theapplicatin.

Air-conditioning

2.19 Owing t capital and running csts, full air-cnditining shuld be used nly in essential areas.These include perating departments, critical careareas, manufacturing pharmacies and areas withparticularly sensitive equipment.

Specialised ventilation

2.20 Owing t the nature and extent f activities carriedut in healthcare buildings, there will be a need

fr a wide range f specialised ventilatin systems.Infrmatin n systems fr individual departmentsis given inChapter 7.

Local exhaust ventilation

2.21 Wherever the escape f chemicals, txic fumes,bilgical materials r quantities f dust int thegeneral area wuld present a hazard t theccupants, LEV must be prvided. This is astatutry requirement under COSHH.

Ventilation or general areas2.22 Appendix 2prvides recmmended air-change

rates, temperatures and pressures fr general areasrequiring mechanical ventilatin in healthcarebuildings.

Acceptable methods

Use o natural ventilation

2.23 The airtightness f new buildings has imprved t

the pint that infiltratin thrugh building leakagecan n lnger be relied upn t prvide sufficientair flw. Attentin must therefre be given t theprvisin f purpse-made ventilatin penings tachieve the necessary flw rates. The air enteringthe penings may need t be cntrlled bymtrised dampers linked t temperature and/rccupancy sensrs in the ventilated space.

2.24 Internal partitins, fire cmpartment walls andcloseddoorwayscanoftenimpedetheflowpath;

when this happens, the prcess will be mre

dependent n single-sided ventilatin.Nevertheless, even with this degree fcmpartmentatin, acceptable ventilatin may stillbe achieved withut windw penings, which

wuld prejudice safety, security r cmfrt.

2.25 Sme types f windw (fr example vertical sliding)can enhance single-sided air change by temperaturedifference, and these will imprve the verall rate fnatural ventilatin in prtected r sheltered areas

where the effect f wind pressure is likely t beminimal.

2.26 Natural crss-flw ventilatin is able t givereasnable air distributin fr a distance f up t6 metres inwards frm the external facade, prvided


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that reasnably clear air paths are maintained.Beynd this distance in areas where clear air pathscannt be maintained and in areas where highminimum air-change rates are specified

mechanical ventilatin shuld be prvided.2.27 Further infrmatin can be fund in Health

Technical Memrandum 55 Windws, BS 5925and CIBSEs (2005) Applicatins Manual AM10 Natural ventilatin in nn-dmestic buildings.

Mixed mode ventilation

2.28 Mixed mde ventilatin is an assisted frm fnatural ventilatin. Fans are fitted in purpse-made damper-cntrlled ventilatin penings.

Alternatively, a separate draw- r blw-thrughventilatin unit may be installed. In bth cases thedampers and fans are cntrlled by temperatureand ccupancy sensrs t ensure a minimumair-flw rate while taking advantage f naturalventilatin effects when present.

2.29 Where natural r mixed mde ventilatin isadpted with cmplex air paths, the designershuld prduce an air-flw diagram in rder tensure crrect prvisin f air-transfer devices.CIBSEs (2000) Applicatins Manual AM13

Mixed mde ventilatin gives guidance.Mechanical extract ventilation

2.30 General extract systems can vary in cmplexityfrm a single wall-munted fan t a ducted airsystem with dual extract fans.

2.31 Replacement air either is prvided by a centralsupply system r enters the building thrugh gapsin the structure r purpse-made penings. Unlessspecial precautins are taken, the latter may resultin an unacceptable level f draughts ccurring in

winter, and pssible risk f unacceptable levels fnise transmissin.

2.32 If individual systems are used, the ventilatin canbe perated intermittently, prvided it cntinues trun fr at least 15 minutes after the rm is vacated(as with light-switch-perated fans in individualtilets).

2.33 If general exhaust systems are used, filtered andtempered replacement air shuld be prvided viaa central supply plant t adjining lbbies rcrridrs, t prevent the risk f discmfrt causedby the ingress f cld air. Fire cmpartmentatinrequirements must be maintained.

2.34 Infrmatin n specialised extract systems is giveninChapter 7.

Mechanical supply systems

2.35 Where mechanical supply systems are required,the fresh air shuld be tempered and filtered befrebeing delivered t the space in rder t aviddiscmfrt.

2.36 The air shuld be heated using a cnstant rvariable temperature surce, but generally nly tthe space air temperature. In mst instances, thelw pressure ht water (LPHW) heating systemshuld ffset any fabric lss s that set-back rmtemperatures can be maintained during unccupied

perids withut the need fr the ventilatin systemt perate.

Balanced ventilation

2.37 A balanced ventilatin system is a cmbinatinf bth a supply and an extract system f equalvolume;eitherasinglespaceorawholebuildingmay be cnsidered t be balanced.

2.38 A balanced system is necessary in instances whereit is essential t maintain cnsistent air mvement

within an area (fr example treatment rms).

Cascade ventilation

2.39 In perating departments, it is nrmal practice tsupply air t the perating rm and allw it tflw thrugh less clean areas crridrs, utilityrms etc (frm where it is eventually extracted).

Recirculation systems

2.40 Air recirculatin systems are nrmally used inHEPA-filtered clean rms where the extract air issignificantly cleaner than the utside supply and

where dur levels are nt significant.2.41 Recirculatin is als rutinely used in the canpy

sectin f ultra-clean perating theatre ventilatinsystems.

2.42 Where the designer is cnsidering the installatinf an air recirculatin system, due accunt must betaken f:

a. minimum fresh-air-supply vlume requiredby the Building Regulatins Part F Nn-domesticBuildings;

b. preventin f cntaminatin f supply air frmvitiatedairinextractsystems;


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c. preventin f stratificatin ccurring withinplenum chambers and mixing bxes, whichmayresultinfreezingofdownstreamcoils;

d. ensuring sufficient velcities thrugh cntrldampers (ideally 56 m/s) t prvide suitableauthorityandgoodshut-off;

e. mdulating cntrl f mixing t prvideoptimumon-plantconditions;

f. useoffreecoolingbycyclingthedamperstominimum fresh air when the enthalpy f theutside air is greater than that f the extract airunder cnditins when cling is required.

Chilled beams

2.43 The use f chilled beams fr the prvisin fheating, cling and ventilatin is increasinglycmmn in healthcare premises.

2.44 Active chilled beams prviding tempered, filteredair t the rm can prvide effective lcal cntrlf envirnmental cnditins.

2.45 Care shuld be taken in psitining chilledbeams t ensure that cld draughts are avided,particularly when used in the cling mde. Thecntrl settings shuld ensure that the external

elements f the beam are always abve dew-pint.Manufacturers f these devices are able t prvidespecific advice n the siting and design limits ftheir equipment.

2.46 Chilled beam units shuld be easily accessible frcleaning and maintenance.

Split comort air-conditioners

2.47 Split cmfrt air-cnditiners, rm cnditinersr cassette units are used increasingly wherethere is a small lcal requirement fr cling frperatinal purpses. They can prvide an effectiveecnmic slutin t cling needs where a centralrefrigeratin system is nt practicable.

2.48 A fresh-air make-up system t the standardrequired by the Building Regulatins Part F Nn-dmestic Buildings must be prvided.

2.49 Split units may be used fr single applicatins ras multiple linked units that can independentlyprvide either heating r cling all served by asingle utdr unit. These systems help t maintain

a mre precise temperature cntrl acrss multiplerms, with maximum energy efficiency.

2.50 Whether single r multiple systems are used, it isessential that the designer give due cnsideratin tthe surce f electrical supply, lcatin f the heatrejectin unit, envirnmental effects t the

refrigerant used and drainage prvisin fr thecling-cil cndensate.

2.51 Recirculated rm air affects indr air qualityand may increase the risk f healthcare-assciatedinfectin (HCAI). Split units shuld therefre ntbe used in critical care areas.

2.52 The units shuld be easily accessible fr cleaningand maintenance.

Dilution ventilation and clean air-low paths

2.53 Dilutin ventilatin has been used t cntrl levelsf hazardus substances in a space. This apprachin itself is n lnger cnsidered acceptable.COSHH requires that knwn hazardus substancesshuld be substituted fr safe alternatives. If this isnt pssible, they shuld be cntrlled at surce byusing a clsed system (such as an anaesthetic gasscavenging unit) r a prtective enclsure (suchas a fume cupbard). A gd level f backgrundventilatin will assist in diluting any casual releasef the substance.

2.54 The expsure f staff t casual spillages fsubstances such as medical gases in anaestheticrms shuld in the first instance be dealt with byestablishing a clean air-flw path. Air shuld besupplied at high level and extracted at lw leveldirectly behind the anaesthetic equipment psitin.The philsphy f establishing a clean air-flw path frm the air-supply pint, t the staff, n t thepatient, and ut via a lw-level extract wuld alsapply in recvery rms and birthing rms. Asuitable air-change rate will prvide backgrund

dilutin ventilatin as an additinal safeguard. Thisapproachensuresthatallreasonablestepsaretakent prevent r cntrl expsure (f staff) t thehazardoussubstanceasrequiredbyCOSHH.

2.55 In perating theatres, patients will be n a clsedbreathing circuit in a rm with a high air-changerate. Under these circumstances, the dilutin effect

wuld be cnsidered sufficient t cntrl any casualexpsure t anaesthetic gases.


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Mechanical ventilation systems

System selection

2.56 Natural ventilatin is always the preferred slutinfr a space, prvided that the quantity and qualityf air required, and cnsistency f cntrl t suitthe requirements f the space, are achievable. If thisis nt the case, a mechanical ventilatin system willbe required.

Choice o central/local plant

2.57 Mechanical ventilatin is expensive t perate itshuld therefre be used nly when the space beingserved requires ventilatin. In additin, lads n

air-cnditining plant are rarely cnstant wing tchanges in slar gain, ccupancy, the use f heat-generating equipment and lights. Therefre cntrlf the supply-air temperature is critical.

2.58 If the ventilatin lads thrughut a departmentr building are in phase, r are nt significant,a central plant with single zne cntrl can beadpted. Hwever, this is rarely the case, s thecnditin r quantity f supply air t differentareas r znes f the building must be variedaccrdingly. This can be achieved by either

prviding individual plants t each zne rprviding separate cntrls fr each zne such asprvided by a variable air vlume (VAV) system.

Where there is a high density f rms with similarventilatin requirements in an area f a building rdepartment, it is usually ecnmical t cmbinethem int a central system.

2.59 In large buildings, a chice between a singledistributin system and multiple smaller systemsmay arise. Large distributin systems and theirplant can have the advantage f lwer perating

csts, but require mre space fr vertical shafts.In general, very lng runs f ducting shuld beavided t prevent undue heat lsses r gains,excessive leakage, and difficulties in balancingduring cmmissining. As the pressure lsses in thelng runs will be greater and a higher initial staticpressure will be required, this will lead t a mreexpensive class f ductwrk.

2.60 Multiple smaller distributin systems may be mreexpensive in capital and perating csts but theyavid lng runs, large ducts and vertical shafts, and

this may reduce verall building csts. They alsprvide a mre rbust service, as the failure f anindividual system des nt prevent the use f therest f the building.

Zoning o the building

2.61 The efficiency and effectiveness f any ventilatinr air-cnditining installatin depends largely

n the zning and cntrl f the installatin. Thefactrs t cnsider when determining the zning fa ventilatin system fr a building r departmentare:

a. periodsofoccupancy;

b. fresh-air/ventilationrequirements;

c. smke cntrl.

2.62 Where the ventilatin system is nt merelytempering the air, but als prviding the heatingand/r cling requirements, the fllwing

additinal factrs will need t be cnsidered:a. internalorperipherallocation;

b. orientationofwindows;

c. variationininternalloads;

d. level f cntrl required.

2.63 Fr single-zne plant in staff areas, lcal cntrl(with a run-n-timer if required) is recmmended,as the system can be turned ff when the space isnt in use, thus saving bth thermal and electrical

energy. Mst supply and extract systems,cnversely, are required t perate cntinuuslywhilethedepartmentisoccupied;thussomeformf time r use cntrl is necessary.

2.64 The cntrl f individual plant items is cveredinChapter 4, with examples f typical cntrlstrategies in Chapter 5. Fr cntrl f particularspecialised ventilatin and air-cnditiningsystems, seeChapter 7.

2.65 On rare ccasins a duplicate standby air-handlingplant may be justified. If installed, it must beprvided with a gas-tight damper at its junctin

with the supply distributin duct s that n back-flw can ccur. Standby plants can becme surcesf cntaminatin if warm mist air is allwed tdwell within them. Their design and cntrl systemmust ensure that this cannt happen.


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Selection o design criteria

External design conditions

3.1 The mst accurate data that is available fr thesummer and winter cnditins at the site shuld beused. The Met Office can supply data fr theUnited Kingdm (www.metffice.gv.uk).

3.2 Healthcare ventilatin systems will nrmally befullfreshair.

3.3 Lcal adjustments, such as fr height abve sealevel, expsure factr r ther climate peculiarities,shuld be made as apprpriate.

Internal design conditions

3.4 The design cnditins selected within patientareas must strike a balance between the cmfrtrequirements f staff and patients, wh ften havevery different levels f clthing and activity.

3.5 Recmmendatins fr the dry resultanttemperature and humidity f individual spaces areshwn n Activity DataBase A-sheets.Appendix 2gives a summary.

Minimum resh-air requirements

3.6 The dilutin f bdy durs is the critical factrin determining ventilatin requirements. Where

natural ventilatin r full fresh-air systems are used,all ventilatin air will be fresh.

3.7 Where dur dilutin is the verriding factr, it isrecmmended that 10 litres per secnd per persnshuld be taken as the minimum ventilatin rate.

3.8 In nn-standard applicatins such as labratries,aseptic suites, perating departments etc, theparticular requirements fr each area shuld becnsidered independently in rder t determine theverriding minimum requirement fr ventilatin.

Limiting supply air conditions

3.9 Fr mst applicatins in healthcare buildings, it isthe temperature differential between the supply and

rm air, rather than the actual temperature f thesupply air, which is the critical factr. Themaximum recmmended supply-t-rm-airtemperature differential is:

summer cling: 7 K

winter heating: +10 K.3.10 In areas that have high heat gains frm equipment

(fr example critical care areas), the summercling temperature differential limit givenabve may result in excessive air-change rates.

A differential f up t 10 K is acceptable in thesecircumstances, prviding the supply-air diffusersare f a type that prvide gd mixing.

3.11 If a humidifier is fitted, it is necessary t keepsupply-airhumiditybelow70%duringwinterinrder t minimise the risk f cndensatin n cld

surfaces.

Air purity

3.12 In healthcare premises, the standard f filtratinwill depend n the activities within the ccupiedspaces. With the exceptin f specialist areas (frexample manufacturing pharmacies), aerbilgicalrequirements are nt stringent, and filtratin isnly required t:

a. maintain hygienic cnditins fr the health and

welfare f ccupants, r fr prcesses such asfoodpreparation;

b. prtect finishes, fabrics and furnishings in rdertoreduceredecorationcosts;

c. prtect equipment either within the supply airsystem (that is, t prevent blcking f cils), rin the space itself t prevent dust build-up.

3.13 Given that almst all viable particles riginatefrm the ccupants f a space and nt frm theincming air, dilutin is the mre imprtant factr

aerbilgically. Therefre, fr general areas a G4filter is suitable. Mre critical areas will require anF7 filter. High-efficiency particulate air (HEPA)

3 Assessment o service requirement
http://www.metoffice.gov.uk/http://www.metoffice.gov.uk/http://www.metoffice.gov.uk/


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filters are required nly in ultra-clean systems(infrmatin n filter grades is given inChapter 4).

Humidity control requirements

3.14 Prviding humidificatin is expensive in termsf plant, running csts and maintenance, andtherefre its use shuld be restricted t where it isnecessary fr physilgical r peratinal reasns.

3.15 Humidificatin was riginally required fr smehealthcare applicatins (fr example peratingtheatres) in rder t cntrl the risk assciated withthe use f flammable anaesthetic gases. The usef such gases has nw ceased. Humidificatin istherefre n lnger required unless there is a very

specific applicatin requirement.Noise levels

3.16 Nise will be generated by fans, ductwrk fittings,dampers and grilles. The specified maximum niselevel will depend n the activities within theccupied spaces.

3.17 Attentin must be given t the reductin f tnalcmpnents. High tnal cmpnents frm airdiffusers etc can seriusly disturb cncentratinver lnger perids even when the verall nise

level is lw. Bradband nise causes less annyance.3.18 Attenuatin shuld be incrprated int the

ductwrk system r plant arrangement as necessaryt reduce nise frm fans and plant items in rdert achieve acceptable limits within rms at thedesign air flws.

3.19 The designer must als cnsider nise escaping tthe external envirnment, and this must nt beunacceptable t ccupants f adjacent areas rbuildings.

3.20 The verall nise levels shuld nt exceed thevalues given in Health Technical Memrandum08-01 Acustics.

3.21 Plant nise is subject t the Cntrl f Nise atWrk Regulatins 2005 and shuld nt exceed80 dB(A) within a plantrm. It shuld be reducedt lwer levels where the plant is near tdepartments sensitive t nise.

Calculation o building loads

Air iniltration

3.22 CIBSEs (2006) Guide A Envirnmental designprvides infrmatin and frmulae fr the

calculatin f air infiltratin. Pressure testingenables the true infiltratin rate t be established.In all cases the requirements f the apprpriatesectin f the Building Regulatins Part L2 must

be met.

Summertime temperatures

3.23 The calculatin methd fr determining thesummertime temperature is described in CIBSEsGuide A. It is very imprtant t select the timef day and time f year f peak ladings fr thecalculatins. These will be dependent n thebuilding rientatin and prprtin f slar tttal heat gain. In establishing design values, thedesign risk having regard t the functin and

ccupancy f the building shuld be cnsidered.3.24 Calculatins and thermal mdelling shuld

be undertaken t see whether, during thesummertime, internal temperatures in patient areas

will exceed 28oC dry bulb fr mre than 50 hursper year. It can generally be assumed that fr anaturally ventilated building, the internaltemperature will be apprximately 3 K abvethe external shade temperature. Fr a building

with simple mechanical ventilatin, the internaltemperature can never be less than the external

shade temperature and will invariably be higher.The relatinship between preferred indrtemperatures and mean utside temperature isdiscussed in CIBSEs Guide A.

3.25 Where calculatins indicate that internaltemperatures will exceed the selected design fra perid that exceeds the building design risk,methds f reducing temperature rise shuld beimplemented. Optins include:

reducingsolarandcasualgains;

theuseofchilledbeamsorceilings;

increasingventilationrates;or

prviding mechanical cling.

3.26 In sme situatins it may be pssible t alter thethermalmassofthestructuretomovethepeaktemperature event time s that it ccurs utside fthe ccupancy perid.

Peak heating load

3.27 Peak heating lcal calculatins are necessary n allmechanical supply systems t establish the size fheater-batteries and subsequently the central plant.


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3.28 Where ventilatin systems prvide tempered air tspaces that have supplementary LPHW t ffsetthe building fabric lsses, the plants heating ladshuld be based n the design values f the external

winter temperature and internal air temperature,and the calculated ttal air vlume (including asuitable allwance fr leakage).

3.29 Where the ventilatin system is the nly means fheating a space, an increase in lad equivalent tthe calculated fabric heat lsses frm the spaceshuld be added t the ventilatin lad. A check fsupply temperature difference shuld be made. If itexceeds 10 K, the ventilatin supply vlume shuldbe increased t suit.

Condensation risk

3.30 A check shuld be made t ensure that the selectedair cnditin will nt lead t surface cndensatinn lw-temperature elements f the ventilatedspace.

3.31 Where there are lcal surces f misture thatwuld require excessive levels f ventilatin tavid cndensatin, the designer shuld cnsiderthe capture and remval f misture at the surcef the evapratin via an exhaust hd r similar

device.3.32 In intermittently heated buildings, it is necessary t

cnsider the cndensatin risk at night set-backcnditins as well as during nrmal peratin.Calculatin methds fr this assessment are givenin CIBSEs Guide A.

Peak cooling load

3.33 In additin t the base data f air-flw rates andtemperatures, when calculating cling lads, thedesigner must take int accunt:

a. solarcoolingloads;

b. surfaceconductioncoolingloads;

c. internalgaincoolingloads;

d. cling lads due t high-level humiditycontrol;

e. methodofcontrolofinternalconditions;

f. fluctuatins in internal temperatures.

3.34 When the peak internal lads have been assessed

and a suitable allwance made fr nn-cincidence,the supply temperature can be calculated.

3.35 Once the lwest required supply temperature f theair-handling unit (AHU) has been established, andan allwance made fr temperature rise thrugh thefan and ductwrk (usually 1 K fr lw-pressure

systems), the ff-plant enthalpy can be establishedfrm a psychrmetric chart r table.

3.36 The cling lads fr all plants n the chilledwater system shuld be calculated at each fthe individual peak times in rder t accuratelyestablish the required (diversified) capacity f thechiller.

Annual energy consumption

3.37 Annual energy cnsumptins f heating-nly

ventilatin systems are simple t calculate, basedn supply-t-external air temperature rise, andfrequency f ccurrence f external temperaturedata (see CIBSEs Guide A).

3.38 Minimum air vlumes are usually fixed by theroomloadsorfresh-airrequirements;however,thedesigner may increase air flw t sme rms rznes in rder t balance lads (as detailed inparagraphs 3.423.71).

3.39 The methd f zning and cntrl can significantlyinfluence energy cnsumptin.

3.40 The cncept f lad and plant peratin chartsis utlined in CIBSEs Guide A. The methdrequires the designer t establish the minimum andmaximum lads n all znes acrss the range fexternal temperatures between winter and summerdesign cnditins. Once the lad chart is cmplete,the plant chart cnverts the lads t supplytemperatures, which are then superimpsed nexternal air temperatures.

3.41 When all temperatures fr all znes are plttedn the plant peratin chart, set-pints andresetting schedules can be established. Frm thisinfrmatin, the utputs f individual heaters,clers and humidifiers can be established at anygiven external temperature. When thse lads arecmputed against annual frequency f ccurrencef external temperatures (as given in CIBSEsGuide A), the annual energy cnsumptin findividual elements, and thus the air-cnditiningsystem, can be established.


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Calculation o plant requirements

Air-supply volumes

3.42 The minimum air supply vlume fr a rm isdetermined by the greater f the fllwing threecriteria:

a. theminimumfresh-airrequirement;

b. the minimum supply vlume fr the rm ladas determined by the maximum heating rcoolingsupplytemperaturedifferential;

c. the desired air-change rate.

Plant sizing

3.43 Once the design air flw has been established, thecrss-sectinal area f the AHU can be calculatedbased n a maximum cil face velcity f 2.0 m/s.

3.44 In rder t establish the length f the AHU,it will be necessary t refer t manufacturersliterature, ensuring all necessary access panels andcmpnents are included as detailed inChapter 4.

3.45 The fan duty shuld be calculated by adding theresistances f all elements that cntribute t thepressure drp f the index circuit.

3.46 The main elements that must be cnsidered are:a. inletordischargelouvres;

b. plantentryanddischarge;

c. attenuators;

d. componentswithintheAHU;

e. duct-munted heaters and filters (including adustallowance);

f. ductworkdistribution;

g. ductwrk fittings including: fire dampers,vlume cntrl dampers, bends and sets, tees,changesofsection;

h. airterminaldevice;

j. discharge velcity.

3.47 Where packaged AHUs are installed, the fanpressure drp is usually quted as external plantresistance, and thus the designer des nt need tcalculate the resistances f individual plant items.The designer shuld, hwever, ensure that an

allowancehasbeenmadefordirtyfiltercnditins, and cnfirm whether the fan pressurequted is fan ttal r static pressure.

3.48 Resistances f ductwrk and fittings may beobtainedfromCIBSEsGuideA;however,thedesigner shuld exercise sme care when usingtabulated pressure lss infrmatin fr fittings that

are relatively clse tgether.3.49 Upn cmpletin f the resistance calculatin

exercise, the designer shuld make allwances frcalculatin and cnstructin tlerances as indicatedin Table 2.

Table 2 Typical an volume and pressure margins

CriteriaLow-

pressuresystems

Medium/high-

pressuresystems

Vlume flw rate margin frleaking and balancing requirements

+5% +5%

Ttal pressure lss margin:a. fr increase in vlume flw rate

(abve)

b. fr uncertainties in calculatin

Cmbined ttal pressure lssmargin

+5%

+5%

+5%

+10%

+10% +15%

Plantroom size and location

3.50 The ventilatin plant and assciated equipmentshuld be psitined t give maximum reductinf nise and vibratin transmitted t sensitivedepartments;andatthesametime,achieveanecnmic slutin fr the distributin f services.

3.51 It is nt recmmended that nise and vibratingenerating plant be hused either directly abver belw sensitive areas (fr example perating ranaesthetic rms) unless there is n alternative, in

which case additinal care and attentin must begiven t the cntrl measures.

3.52 The plant must als be lcated s that it is remtefrm pssible surces f cntaminatin, heat gainsand adverse weather cnditins. The design shuldensure that wind speed and directin have aminimal effect n plant thrughput.

3.53 Safe access t and arund plant is essential tfacilitate inspectin, rutine maintenance, repairand plant replacement.

Provision o primary services

3.54 Where mre than ne air-handling plant requirescling, remte central cling plants with pipedchilled water are preferred. In the case f a single


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plant, a multi-stage direct expansin clingcil with refrigerant piped frm an adjacentcmpressr/cndensing plant culd be cnsidered.If this ptin is selected, a refrigerant gas detectr

munted in the base f the duct and an alarmsystem audible t the end-user will als need t beprvided (as dictated by the COSHH Regulatins).

3.55 Clean, dry steam is preferred fr humidificatin,prvided that the biler water treatment desnt render the steam unusable fr directhumidificatin.

3.56 If a suitable supply f steam cannt be btainedfrm the steam main, a steam generatr shuldbe prvided lcally, r a self-generating humidifier

installed. The lcatin f a lcal steam generatr iscritical if cndensate is t drain back int it.

Inlet and discharge sizing and location

3.57 Air intakes and discharge pints shuld preferablybe lcated at high level, t minimise the risks fnise nuisance t surrunding buildings,cntaminatin and vandalism.

3.58 Intakes and discharges shuld be designed andlcated s that wind speed and directin have aminimal effect n the plant thrughput.

3.59 Helicpter landing pads in the vicinity fventilatin intakes and discharges can result inlarge shrt-term pressure changes. This can causepressure surges in supply systems and reverse airflws in extracts. Exhaust fumes frm the helicptermay als be drawn int intakes.

3.60 Intake pints shuld be situated away frm clingtwers, biler flues, vents frm il strage tanks,fume cupbards and ther discharges fcntaminated air, vapurs and gases, and places

where vehicle exhaust gases may be drawn in.

3.61 Where intakes have necessarily t be sited at rnear grund level, the area arund them shuld bepaved r cncreted t prevent sil r vegetatinbeing drawn in. They shuld als be caged rlcated within a cmpund t prevent rubbishbeing left in the vicinity. The likely prximity fvehicle exhausts shuld be taken int accunt whendetermining the prtected area arund the intake.

3.62 The discharge frm a general extract system mustbe lcated s that vitiated air cannt be drawn back

int the supply-air intake r any ther fresh-airinlet. Ideally, the extract discharge will be lcatedn a different face f the building frm the supplyintake(s). In any event, there must be a minimum

separatin f 4 m between them, with the dischargemunted at a higher level than the intake.

3.63 Discharges frm LEV systems shuld preferably be

vertical and usually nt less than 3 m abve rflevel. They shuld nt be fitted with a cwl thatculd cause the discharge t be deflecteddwnwards.

3.64 Each intake and discharge pint shuld be fittedwith crrsin-resistant weatherprf luvres rcwls t prtect the system frm driving rain(BS EN 13030, Class B).

3.65 It is recmmended that luvres be sized based n amaximum face velcity f 2 m/s in rder t preventexcessive nise generatin and pressure lss.

3.66 The inside f the luvres shuld be fitted with amesh f nt less than 6 mm and nt mre than12 mm t prevent leaves being drawn in andinfestatin by vermin.

3.67 The duct behind a luvre shuld be self-draining.If this is nt practicable, it shuld be tanked andprvided with a drainage system.

3.68 Cleaning access must be prvided either frm theutside via hinged luvres r by access drs inthe plenum behind the luvre. Where a cmmn

plenum is prvided, cleaning access shuld be via awalk-in dr.

Heat-rejection devices

3.69 The design cnditins given inChapter 2make nallwance fr the elevated temperatures that canccur n the rf f buildings. Refrigeratincndensers and cling twers shuld, ifpracticable, be shaded frm direct slar radiatin,r the design shuld be adjusted t take accunt fthe gain.

3.70 Air-cled cndensers shuld be the first chice frheat rejectin frm any refrigeratin plant.

3.71 Evaprative cling systems shuld nt be usedin healthcare premises unless limitatins f spacemean that they are the nly way that the clinglad can be met. If they are used, guidance npreventing and cntrlling leginellae must beclsely fllwed (see Health TechnicalMemrandum 04-01 The cntrl fLegionella,hygiene,safehotwater,coldwateranddrinking

watersystems;andtheHealthandSafetyCmmissins Apprved Cde f Practice andguidance dcument Leginnaires disease: thecntrl fLegionella bacteria in water systems(cmmnly knwn as L8)).


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General requirements

Location and access

4.1 AHUs shuld be lcated in an accessible areasecured frm unauthrised entry. Siting unitsin ceiling vids abve ccupied spaces is ntapprpriate.

4.2 Units lcated n rfs shuld have a safe means faccess tgether with suitable precautins t preventpersnnel r equipment falling r being blwn ffduring maintenance activities.

4.3 Units lcated at grund level shuld be securedwithin a cmpund t prevent unauthrised access.Measures shuld be taken t exclude vehicles frmthe vicinity t ensure that exhaust fumes will nt bedrawn int intakes.

4.4 Units may have a wrking life f 25 t 30 years.It can be anticipated that ver this perid there willbe a need t access every element within the unitfr deep cleaning. It is als quite pssible that themain fan and individual heater and chiller batteries

will need replacement. Suitably psitined servicecnnectin jints and adequate spacing shuldpermit these items t be withdrawn withutthe need t dismantle ther installed plant requipment. Batteries that are significantly widerthan 1 m shuld be split t permit withdrawal frm

bth sides.4.5 It is essential that AHUs are psitined s that

all parts are easily and safely accessible fr rutineinspectin and service. If a unit is lcated against a

wall r backs nt anther unit, access t all partsmust be available frm the frnt. Units greater than1 m wide shuld preferably have access frm bthsides r have access drs large enugh t permitthe full and safe entry f maintenance persnnel.

4.6 The area arund the unit shuld be tanked tprevent water penetratin t adjacent areas, andshuld be adequately drained.

4.7 Fire precautins shuld be incrprated inaccrdance with Firecde (the Health TechnicalMemrandum 05 series). See alsChapter 3.

4.8 Cmbustin equipment must nt be lcatedin a fire cmpartment that huses air-handlingequipment.

Technical requirements

4.9 The basic technical requirements f the whle fthe ventilatin system shuld meet the relevantclauses f Mdel Engineering Specificatin C04 Mechanical ventilatin and air-cnditiningsystems. This dcument cntains a menu f clausesthat cver a wide range f applicatins, s it isimprtant t select nly thse that are relevant tthe specific applicatin.

NoteAt the time f writing, Mdel EngineeringSpecificatin C04 was due fr revisin in rder tbring it int line with the revised standards set utin this Health Technical Memrandum. Wherecnflicts in specificatin arise, the Health TechnicalMemrandum takes precedence.

4.10 It is essential that the main plant/ductwrk islcated far enugh frm the flr t permit thecrrect installatin f drainage systems fr clingcils, humidifiers and heat-recvery systems. Easyaccess fr maintenance f drainage systems andtheir assciated pipewrk must be prvided.

4.11 Organic materials r substances that can supprtthe grwth f micrrganisms must nt be usedin the cnstructin f the plant r its distributinsystem. The Water Regulatins Advisry Schemes(WRAS) (2005) Water Fittings and MaterialsDirectry lists suitable materials fr sealants andgaskets.

4.12 The plant and its distributin system must ntcntain any material r substance that culd causer supprt cmbustin.

4 Air-handling unit design and speciicationguidance


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4 Air-handling unit design and specifcation guidance

19

4.13 Plants should have a high standard of airtightness.The double-skin method of construction withinsulation sandwiched between two metal faces isrecommended. The panels may be available in a

variety of colours at no additional cost. This canaid identification by colour-coding of units ina plantroom (for example green for generalventilation; blue for theatres; red for laboratoriesand isolation facilities; grey for extract etc).

4.14 The inside of the plant should be as smooth aspossible. Channels, rolled angles or formed sectionsthat could trap or hold moisture should be kept toa minimum. If stiffeners are required, they shouldbe fitted externally. If internal bracing has to befitted, it must be of a design that will not trap or

hold moisture.

4.15 Air flow across air treatment components suchas filters, heat exchangers and humidifiers will beinfluenced by the pattern of the approaching airstream. If unsatisfactory conditions are created, theperformance of the component will be reduced.

4.16 Access to items that require routine service such asfilters, fog coils and chiller batteries should be viahinged doors. The doors should be large enough(for example 500 mm minimum) to allow easy

access. Items requiring infrequent access, such asattenuators, may be via bolted-on, lift-off panels.All doors and panels should be close-fitting andwithout leaks.

4.17 Care should be taken during installation to ensurethat electrical and mechanical services are notinstalled in positions that will reduce or impedeaccess.

4.18 It can be difficult to turn off AHUs in order toinspect filters and drainage trays. Viewing ports andinternal illumination will therefore facilitate routine

patrol inspection of such items. Viewing portsshould be at a convenient height. In double-stackedunits, placing the viewing ports at the bottom ofthe access doors of the upper unit will remove theneed to use temporary ladders or steps whencarrying out patrol inspections.

4.19 Internal illumination should be provided byfittings to at least IP55 rating. Fittings should bepositioned so that they provide both illuminationfor inspection and task lighting. All lights in a unitshould be operated by a single switch.

4.20 Access to AHUs and items in the distributionsystem such as filters or heater/chiller batteriesshould be via fixed ladders and platforms or pulpit-

style movable steps. The installation of distributionductwork and other electrical or mechanicalservices should provide sufficient clearance to allowthe pulpit steps to be easily wheeled into position.

AHU drainage system

4.21 All items of plant that could produce moisturemust be provided with a drainage system. Thesystem will comprise a drainage tray, glass trap,air break and associated drainage pipework.

4.22 The drainage tray should be constructed of acorrosion-resistant material stainless steel ispreferred and be so arranged that it willcompletely drain. To prevent pooling, it is

essential that the drain connection should not havean up-stand and that a slope of approximately 1 in20 in all directions should be incorporated to thedrain outlet position. The tray must be completelyaccessible or, for smaller units, easily removable forinspection and cleaning.

4.23 Each drainage tray should be provided with its owndrain trap. The drain trap should be of the clear(borosilicate) glass type. This permits the colour ofthe water seal to be observed, thus giving an earlyindication of corrosion, biological activity orcontamination within the duct. The trap should

have a means for filling and incorporate couplingsto facilitate removal for cleaning. It should belocated in an easily visible position where it willnot be subject to casual knocks. The pipework

Removable drainage tray


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cnnecting it t the drainage tray shuld have acntinuus fall f nt less than 1 in 20.

4.24 Traps fitted t plant lcated utside r in unheated

plantrms may need t be trace-heated in winter.The trace-heating must nt raise the temperature fwater in the trap abve 5oC.

4.25 Water frm each trap must discharge via a clear airgap f at least 15 mm abve the unrestricted spill-ver level f either an pen tundish cnnected t aful drainage stack by way f a secnd trap, r aflr gully (r channel). A supprt shuld beprvided t ensure that the air gap cannt bereduced. Mre than ne drain trap may dischargeint the tundish prviding each has its wn air

break.4.26 Drainage pipewrk may be thermplastic, cpper

r stainless steel. Glass shuld nt be used. Thepipewrk shuld be a minimum diameter f22 mm and have a fall f at least 1 in 60 in thedirectin f flw. It shuld be well supprted andlcated s as nt t inhibit access t the AHU.

Layout o AHU

4.27 The AHU shuld be arranged s that mst itemsare under psitive pressure. Any item f plant

requiring a drain shuld be n the psitive pressureside f the fan. A recmmended layut is given inFigure 1.

4.28 A separate extract unit will generally be required frthe area served by each supply unit.

4.29 An energy recvery system will nrmally be fittedbetween the supply and extract units.

Provision o dampers

4.30 Fire- r smke-actuated dampers shuld be

prvided at the lcatins required by HealthTechnical Memrandum 05-02 Guidance insupprt f functinal prvisins fr healthcarepremises (see alsparagraph 5(c) in Appendix 1andparagraph 6.21).

4.31 Mtrised lw-leakage shut-ff dampers shuldbe lcated immediately behind the intake anddischarge f each supply and extract systemrespectively. They shuld be f the ppsed-bladetype, pening thrugh a full 90 degrees, and mustclse autmatically in the event f pwer failure r

plant shut-dwn t prevent any reversal f thesystem air flw.

4.32 The quality f mtrised dampers is critical. Theyshuld:

berigid;

have square cnnectins fitted with end andedgesealsofaflexiblematerial;and

have minimal play in linkages.

Theleakageonshut-offshouldbelessthan2%.

4.33 A manually perated islating damper shuldbe installed between the main AHU and itsdistributin system t enable the unit t be islated

when cleaning is in prgress.

4.34 Sme systems will require the fitting f a mainvlume cntrl damper s that the design air-flwrate can be set at cmmissining. The dampershuld be lckable in any psitin. If it will alsbe used fr plant islatin, it shuld be capable fbeing reset t give the design air flw withut theneed fr remeasurement.

4.35 Internal plant-islating dampers are nt required.Neither is the prvisin f fittings fr shut-ffplates between items within a unit.

Vibration

4.36 Vibratin frm a remte plantrm can betransmitted by the structure f the building, maybe regenerated and may smetimes be magnifiedmany times. Units shuld be selected t have theminimum vibratin generatin and t be installedn suitable anti-vibratin munts. Pipe andductwrk shuld incrprate anti-vibratincuplings, preferably in tw planes at rightangles, as clse t the vibratin surce as pssible.Cnsideratin shuld be given t the use f anti-vibratin pipe hangers and supprts.

Sequence o components

4.37 The fllwing arrangement f plant cmpnents istypical, althugh in many instances nt all elements

will be required:

a. fresh-airintake;

b. motorisedisolation/smokedamper;

c. frost/fogcoil;

d. prefilter;

e. energy-recoverydevice;


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f. attenuatr (these may be lcated in the intakeand discharge duct if they are f a suitable typeseealsoparagraph4.166);

g. fan;h. blastplate;

j. attenuator(see(f));

k. chillerbattery;

m.eliminator;

n. heater-battery;

p. humidifier;

q. finalfilter;

r. manual islatin/vlume cntrl damper.4.38 There may be instances where this arrangement is

nt apprpriate, and the plant arrangement shuldbe planned accrdingly.

Fans

General requirement

htm 0301 ventilation

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