dw172 specification for kitchen ventilation systems

HVCA

Heating andVentilatingContractors'Association

DW/1 72 Sped! leation for Kitchen Ventilation Systems

Specification ACKNOWLEDGEMENTSThe HVCA records its appreciation and thanks to themany people and organisations who gave advice andinformation during the preparation of thisspecification, in particular to those members of the

fo r Kit C 11111 endrafting panel who contributed their time, experienceand knowledge.

VentilationDW/172 DRAFTING PANEL

S yst e rn s Keith Waidron (Chairman)

Phil Gibson

Barry Pollard

Peter Rogers

Nigel Atkinson

Trevor Carter

Steve Garnham

Graeme Craig (Secretary)

ISBN 0-903783-29-0

First Edition 1999

©2005 HVCA

Heating and VentilatingContractors' AssociationEsca House 34 Palace CourtLondon W2 4JG

Tel: 020 7313 4900

Fax: 020 7727 9268

DgJ/ I 7 2 e-mail: [email protected]: www hvca.org.uk

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DW/1 72 Specification for Kitchen Ventilation Systems

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FOREWORD

Barry PollardChairman, Ductwork GroupHeating and Ventilating Contractors' Association

Since its publication in 1999, the HVCA ' Standardfor Kitchen Ventilation

Systems (DW/171) has sold an impressive 2,300 copies. More importantly, ithas become widely acknowledged as the standard for kitchen ventilation design

throughout in the UK.Like any other standard, however, it must be revised and updated from time to time, inthe light of new thinking, new procedures and new developments.This review process has now been completed by the 1-IVCA Ductwork Group. Theresult is this new publication— designated DW/ 172 and re-badged as a specificationrather than simply a standard, in recognition of the authoritative status it has achievedwithin the kitchen ventilation sector.Among the many amendments and clarifications contained in the new document, threeare worthy of particular note.Firstly, the previous publication made reference to the feasibility of establishing a testprocedure for grease filters. Since then, the Loss Prevention Council has published —and the Association of British Insurers has endorsed — LPS 1263, which sets out the

procedures, including the testing and grading of grease filters, required to reduce therisk of fire in commercial kitchens.Secondly, the section on appliances and their coefficients has been significantlyexpanded, and now includes advice on the requirement for an interlock between the

ventilation system and the gas supply.And, finally, for the purpose of this specification, stainless steel is the only suitablematerial for the fabrication of canopies, and mesh filters can only be used as asecondary method of grease extraction. For ventilated ceilings, however, somemanufacturers incorporate anodized aluminium into the supporting frame. This form ofconstruction should be agreed with the client or specifier.All other sections have been revised and updated in the hope and expectation that theHVCA's Specfi cation for Kitchen Ventilation Systems (DW/172) will be widely usedby all sectors of the catering industry.

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CONTENTS Page

Acknowledgements 1

Drafting Panel 1Foreword 3Specifications and Contents 5

Section 1 Introduction. 7Section 2 Considerations prior to design 8Section 3 Design Criteria 9Section 4 Canopy Dimensions 11Section 5 Extract Flow Rates 12Section 6 Make-up Air 17Section 7 Types of Canopy 20Section 8 Ventilated Ceilings 22Section 9 Spigot Connections 26Section 10 Materials 27Section 11 Construction 28Section 12 Polishing 29Section 13 Grease Filtration 29Section 14 Canopy Lighting 34Section 15 Ductwork 35Section 16 Installation 38Section 17 Fans 39Section 18 Attenuation 42Section 19 Dampers 42Section 20 Fire Suppression 43Section 21 Service Distribution Units 46Section 22 Odour Control 47Section 23 Heat Recovery 49Section 24 Testing and Commissioning 50Section 25 Cleaning and Maintenance 51

Appendix A Filter Classifications 53Appendix B Conversion Factors 54Appendix C IP Ratings 55Appendix D Fire and Smoke Extract Ductwork 56Appendix E Air Conditioned Kitchens 58Appendix F Bibliography 60

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DW/1 72 Specijicatioii for Kitchen Ventilation Systems

OBJECTIVEThe satisfaction derived from a building by the usercomes significantly from the satisfactory performanceof the systems, which serve the building. The purposeof the kitchen ventilation systems is to removecontamination from the cooking processes, ventilatethe surrounding ancillary areas and provide safe andcomfortable conditions for the occupants.

This publication is therefore primarily intended to:- Provide information for customers who are

appointing (by competition or negotiation) acontractor.

- Provide a specification for kitchen ventilationsystem installation.

- Provide a level of workmanship that may be verifiedby independent assessment.

- Be a significant aid in producing installations thatwill, given correct operation and with propermaintenance, provide satisfactory service over manyyears.

QUALITY ASSURANCEThis specification can be used as one criterion that willassist customers and specifiers in performing theirimportant role of defining the standard of installationthey require.

The HVCA anticipates that this specification will becomplementary to quality assurance schemes andquality assessment schedules. Where forming the basisof an independent certification scheme, it defines goodpractice in standards of installation.

SCOPEThis specification covers the type of kitchen ventilationsystems usually found in commercial premises.

The specification is not intended for residentialpremises, although some of its provisions will apply.

This specification makes use of terms "should","shall" and "must" when prescribing procedures:- The term "must" identifies a requirement by law at

the time of publication.- The term "shall" prescribes a procedure which it is

intended to be complied with, in full and withoutdeviation.

- The term "should" prescribes a procedure which it isintended to be complied with unless, after priorconsideration, deviation is considered to beequivalent or better.

PUBLICATION AND REVIEWUser feedback on the wording or the requirements ofthe specification will be welcomed to assist incontinued updating.

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OTHER DUCTWORK GROUP PUBLICATIONSDW/100 Ductwork Publication PackDW/143 A Practical Guide to Ductwork Leakage

TestingDW/144 Specification for Sheet Metal Ductwork -

Low, Medium & High Pressure/Velocity AirSystems

DW/154 Specification for Plastics DuctworkDW/172 Specification for Kitchen Ventilation

SystemsDW/191 Guide to Good Practice - Glass Fibre

DuctworkTRI19 Guide to Good Practice - Cleanliness of

Ventilation Systems

DW/1 72 SpecifIcation for Kitchen Ventilation Systems

SECTION 1Introduction1.1 A cooker canopy is currently defined by the

CEN European Standards Committee as beinga device intended to collect contaminants fromabove a cooking appliance and remove themfrom the room. In practice kitchen canopieshave become much more than basic extractsystems.

The prime function of a kitchen canopy is toprotect the area surrounding the cookingprocess from soiled matter and flame to maketolerable and safe the immediate area forpeople to work in. An air flow shall be createdacross the cooking process to capture thefumes created, and the by-products of thisvapour shall be collected and contained bymeans of the filters within the canopy, allowingthe cleaner air to be discharged.

1.3 The Food Safety (General Food Hygiene)Regulations place an onus on the proprietor ofa 'food business' to ensure that all hazards areidentified and that steps are taken to ensurethat adequate safety features are in place. Partof that process requires that there must besuitable and sufficient means of either naturalor mechanical ventilation.

1 .4 The Workplace (Health, Safety and Welfare)Regulations also require that 'an effective andsuitable provision must be made to ensure thatevery enclosed workplace is ventilated by asufficient quantity of fresh air'.

1 .5 Ventilation is required in both the kitchen andthe adjoining areas because:

• Considerable convective and radiant heat isgiven off by the cooking equipment.

• The air becomes laden with odours, greasefumes and products of combustion.

• During meal preparation and washing up,humidity is increased over a wide area.

• Air is required to dilute and replaceproducts of combustion from gas firedappliances.

• Supply air is required to ensure completecombustion of the fuel and provide safeoperation of the gas equipment. Details ofthese requirements are contained in theBuilding Regulations, BS 6173 and theCIBSE Guide B2.

The British Standard BS 6173, Installation ofgas-fired catering appliances for use in alltypes of catering establishments (2nd and 3rdfamily gases), includes a requirement that gasfired catering appliances cannot be operatedwithout the kitchen ventilation system inoperation. Therefore an air proving deviceshall be installed in the kitchen ventilationsystem and interlocked with the gas supply forthe kitchen. The kitchen ventilation contractorshall be specifically responsible for providingthe air proving mechanism.

1 .7 The four main emissions that require removalare:

• Smoke

• Expanded air from the heat loadsurrounding the cooking device.

• Precipitation of moistures existing in thefood into a vaporous state, primarilyconsisting of steam, grease and cookingodours.

• Exhaust fumes from combustion appliancessuch as gas, charcoal or mesquite.

The removal of these cooking vapours and thesupply of make-up air together with details ofthose ancillary services that can be supplied bythe kitchen ventilation contractor, are thetopics to be covered by this publication.

1.9 Although this Specification has been writtenwith commercial kitchens in mind, many of theaspects covered and recommendations made,may also apply to domestic kitchen situations.

• Air replacement and consistency oftemperature are required in adjoining areas.

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1.2

1.6

1.8

DW/1 72 Speci/ication for Kitchen Ventilation Systems

SECTION 2Considerations prior todesign2.1 In order for the most economical and effective

design to be prepared, it is important that thefollowing information must be made availableto the designer:

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• The type, size and power source of theappliances being ventilated. If gas, therequirements of BS 6173 shall be met.

• The layout of the appliances and their powerconsumption where known.

• The dimensions, height and layout of theroom that contains the appliances to beventilated.

• Whether ventilation is to be provided bymeans of a canopy or ventilated ceiling.

• If a canopy, is it to be at high or low level,wall or island mounted.

• Where a ventilated ceiling is to be used,whether a plenum or modular cassette typeis required, at what height it should be setand the level of services running throughthe ceiling void (to include floor topreferred finished ceiling height and floorto slab height).

• Whether grease is being produced in thecooking process and if so, whether filtrationis to be provided by means of baffle filters,cartridges, water wash or cold water mist. Ifgrease is not produced, whether theextraction point can be fitted with a baffleplate or grille.

• Whether the ductwork is to be constructedto either DW/ 144 or a fire ratedlsmokeexhaust specification and whether the fanshave to be fire rated.

• Whether lighting is required within thecanopy or ceiling, and if so what type.

• Whether mechanically powered make-up airis required, and if so whether it is to besupplied through the canopy, through theHVAC system or a combination of both.

• Where air is supplied through the canopy, isit to be by means of front face grilles,perforated plate diffusers or internal slotdischarge.

• Details of access into the building so thatthe number of sections in which the canopyis to be fabricated can be determined. Theavailabl.e headroom and ceiling heightwhere appropriate are essential.

• The position of discharge to ensure thatnoise or odour does not create a nuisance.

• The amount of air to be handled by thecanopy or ceiling. This will determine thetype, size and number of filters and spigotsrequired.

• Whether approvals from theAuthority have been obtained.

Local

• It is now known that some cookingprocesses, where there is incompletedegradation of certain organic materials,generate fumes which are carcinogenic.This is possible irrespective of size ofkitchen, and it is therefore important toensure that there is an effective ventilationsystem for all cooking operations to ensurethe health and safety of the kitchenpersonnel. Care shall be taken to avoiddrawing extract air through the breathingzones of members of staff operating thecooking equipment. Care shall always betaken if discharging into a public area isnecessary.

• The method of internally cleaning the insidesurface of the ductwork extract system,which, in turn, will determine the size ofaccess panels and their frequency.


SECTION 3Design criteria3.1 Whilst differing design approaches exist to

providing a solution which satisfies theventilation requirements of a kitchen, thefollowing methodology has been found toprovide a satisfactory outcome and is proposedas a suitable procedure to adopt to achieve asatisfactory design.

• At the time of publication of thisSpecification, no legislation exists in theUK regarding maximum permissible roomtemperatures in the workplace. Even withthe most efficient ventilation systems, airtemperatures taken in the kitchen in theproximity of the cooking equipment couldbe well in excess of 28 degC due to radiantheat from the cooking equipment beingconverted to convective, sensible heat.

• Internal noise level should be from NR4O -NR5O.

• Average lighting levels of 500 lux at thework surface.

• Dedicated make up air systems to be 85%maximum, of the extract flow rate.

• Minimum air change rate of 40 per hour -not to be used as a basis of design of thecanopy or ventilated ceiling.

3.2 Variable speed regulation can also enhanceenergy efficient use of the system and plantwhen there is partial or low load cookingconditions. However, care shall be exercised inmaintaining correct velocities through thegrease filters when cooking is in process. Forrecommended face velocities see Table 13.

3.3 Whilst these criteria are ideal, it is unlikely toachieve a controlled environment within akitchen due to the natural but varying heatgains from the cooking equipment.

3.4 Staff comfort should be a prime considerationwhen designing a make-up air system. Thesupply air temperatures should therefore be

selected for either room distribution or spotcooling around the canopy or ventilatedceiling. The ideal discharge temperatures forthe various supply options are shown in Table

Table 1: Discharge Air Temperatures I

Inboard canopy supply air outside ambient

Outboard canopy supply air minimum lOdegC'Ventilated ceiling supply air minimum 16 degC

HVAC general make-up air minimum 16 degC

3.5 Humidity is also difficult and expensive tocontrol, but the ventilation system should bedesigned to provide a sufficient ventilation rateto maximise comfort. With particular referenceto dishwashing machines, unless provided withtheir own condensers, these machines shall beprovided with dedicated extract ventilation tocontrol the amount of vapour being dischargedinto the environment. Dishwashers shall alsobe ventilated to avoid the potential healthhazards.

3.6 Fresh air ventilation rates must be sufficient toensure that the CO exposure levels to whichthe kitchen staff are subjected do not exceedthe COSHH limits of 300 parts per million(ppm) for 10 minutes, or the World HealthOrganisation (WHO) guide-lines of 10 ppm asan average over 8 hours.

3.7 Whilst the ventilation of ancillary areas wouldnormally fall within the scope of the mainventilation system, the following notes areincluded for the guidance of the designer.

3.7.1 Cold Rooms - It is important to establishwhether the compressor/condenser sets are tobe located:a) On top of the Cold Room and above the

ceiling.b) Built into the Cold Room and discharging

into the area.c) Mounted externally and remote from the

Cold Room.

When cold room condensers discharge directlyinto ceilings or rooms, then they should haveindividual extract and possibly dedicatedsupply systems.

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3.7.2 Dry Stores - A ventilation rate of 10 airchanges per hour is recommended. If the roomdoor leads on to the kitchen area, mechanicallyintroduced supply air and a transfer grille atlow level in the door should be provided torelieve the air for capture by the kitchen

3.7.3 Servery - A ventilation rate of 12 air changesper hour is recommended but great care shouldbe taken with the position of grilles anddiffusers. The servery is usually locatedbetween the kitchen and the dining area. Thenumber of people, the heat from the food,display cabinets, and the fact that the ceilingmay well be lowered to provide an architecturalfeature will all affect the design. Too much airmovement may cause 'skinning' and cooling ofthe food. Too little will result in discomfort forboth kitchen staff and the customers.

3.7.4 Chef's Office - A ventilation rate of 6 airchanges per hour is recommended but comfortcooling may be considered desirable as the areais often used as a dining facility for visitors.Privacy should be maintained by avoiding theuse of transfer air grilles.

3.7.5 Refuse Store - The Local Authority should beconsulted for their particular requirements, buta dedicated extract system providing aminimum of 15 air changes per hour is

3.7.6 Preparation Areas - The treatment will dependupon the type of food being prepared andwhether these areas are 'open' to the kitchen orwhether a separate room is to be provided.Where open to the kitchen then the overall airchange rate should be sufficient, with supplyair introduced to the preparation area itself.When very low room ambient spacetemperatures are required then a separate areais required. Where low room temperatures arenot required, then a ventilation rate of 20 airchanges per hour is recommended.

3.7.7 Toilet Areas - Whether for food handlingpersonnel or customers, separate and dedicatedextract systems with duplicate fans shall beinstalled for toilet areas. A ventilation rate of10 air changes per hour is recommended.Negative pressure should be maintained in alltoilet areas at all times.

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3.7.8 Kitchen - For areas within larger kitchens thatare not affected by canopies or covered by theareas described in 3.7.1 - 3.7.7, then a generalventilation rate of 40 air changes should beused.

3.7.9 Dishwash and Potwash Areas - In addition todedicated machine extract, general roomextract should also be considered. Aventilation rate of 30 air changes per hour isrecommended.

Mechanically powered make-up air should notbe taken from 'dirty' areas such as wastestorage areas or pot wash rooms. Care shouldalso be taken that unwelcome draughts are notcreated around customers. Make-up air shallnot be drawn from an adjacent eating area ifsmoking is permitted.

3.9 Diversity factors shall not be applied to reducethe extract flow rate calculated from Table 2when partial or intermittent use of appliances isproposed.

exhaust system.

3.8

recommended.


SECTION 4Canopy dimensions4.1 The dimensions of a canopy are invariably

determined by the size of the cateringequipment that it is serving.

4.2 Unless restricted by walls, the plan dimensionsof the canopy shall always exceed the plandimensions of the catering equipment by aminimum of 250mm on each free side, and by250mm at the front and rear. It shall be notedthat the overhang dimensions are to the insideof the condensation or stiffening channel, orthe supply plenum, the appropriate dimensionshall be added when specifying the overallcanopy size.

4.5 Canopies less than 400mm high will be lessefficient than normal because of a reducedcollection volume and therefore, where there isa restricted soffit height, consideration shouldbe given to increasing the face velocity tocompensate irrespective of design dutycalculated. It is also recommended to increasethe size of the canopy to aid capture when theideal flow rate cannot be achieved.

With kitchens that have high ceilings, providedthat the canopy is installed at the correct heightto allow access to the filters and therequirements for minimum hood depth havebeen achieved, then consideration should begiven to providing an infill section to fill thegap between the top of the canopy and theunderside of the ceiling.

4.3 For combination steamers and certain types ofbaking ovens the overhang at the front shouldbe increased to a minimum of 600mm to copewith the steam or fumes released when thedoors of the appliance are opened.

4.4 The height of the canopy is often governedprimarily by the ceiling height. The undersideof the canopy should be located between 2000and 2 100mm above the finished floor level, thetop should project into the ceiling by aminimum of 25mm to allow the false ceilingtrim to be attached. (see illustration in fig. 1).

4.7 Where a canopy is installed at a level higherthan 2 100mm, then overhang dimensions shallbe increased at a minimum rate of 1:1, i.e.100mm vertical + 100mm horizontal.

The distance between the lowest edge of thegrease filter and the top of the cooking surfaceshould be 450mm minimum. This is to avoidthe risk of excessive temperatures or fire in thefilter which could cause the extracted grease tovaporise and pass through to the ductwork.This dimension will vary with the type ofcooking appliance and may be reduced wherea fire suppression system is fitted.

4.9 Where gas-fired salamander grills aremounted at high-level in close proximity to the

4.6

Fig 1 - Typical Canopy Dimensions

4.8

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grease filters/extract plenum of a canopy, themanufacturer of the grill should supply adeflector cowl for the flue opening on top ofthe grill. This will encourage products ofcombustion to be directed away from thecanopy and cool prior to being drawn throughthe filters. This will reduce the potential offire-flares, which are known to occur withsuch appliances, being drawn into the greasefilters to possibly ignite grease and oil depositsbeyond. It will also help to preventdiscolouration of the stainless steel surfacesimmediately above these grills andcarbonisation of deposits on the grease filters.

SECTION 5Extract flow ratesExtract and Supply Air Flow Rates

Whilst systems extracting from equipmentproducing contaminant such as dust dependupon air streams of sufficient velocity beingcreated to enable capture to take place, thisconcept cannot be applied to a heat producingprocess such as cooking. All cookingprocesses create approximately 35% radiantand 65% convected heat which, in the absenceof cross-draughts, rises vertically in a thermalupdraught called a 'plume'. This is shown infig 2. Most of the contaminant released fromthe food and heat source is entrained withadditional air which causes the plume toenlarge and the average temperature andvelocity to decrease. The rate of exhaust fromthe hood shall equal or slightly exceed the flowrate of the plume, additional extract air (seeTable 3; Canopy Factors) will be required toresist the cross-draughts that would otherwisecarry the plume away from the canopy.

1.i H k k iCANOPY

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Fig 2 -Air Flow Pattern

5.2 The calculation of the optimum extract flowrate is the most important element of canopydesign as too much air will cause as manyproblems as too little. Whilst the size of thecooking appliances determines the size of thecanopy to be supplied, it is the type ofappliance that determines the volume of air tobe extracted. Those that require ventilation areshown in Table 3.

5.1

/I/L

APPLIANCE

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DW/1 72 SpecifIcatiw for Kitchen Ventilation Systems

The 'Thermal Convection Method' ofcalculation should be the only method used.Other methods have been included in thisdocument for use only when insufficientinformation is available at the design stage(see sections 5.5 to 5.8).

5.3 Method I - Thermal ConvectionMethodThis method follows the procedure covered inthe CIBSE Guide B2 but has been expanded toinclude a wider range of equipment. Whendetails of the equipment to be ventilated areknown, then each cooking appliance shall beallocated a thermal convection coefficient,which is the recommended volume of air to beextracted in m3/s per m2 of surface area of theappliance. The area of each appliance ismultiplied by the factor for that appliance, thetotal value for each item of equipment underthe canopy/ventilated ceiling shall be addedtogether to determine the total volume to be

Coffee MakerMicrowave Oven/ToasterBains Marie, Hot CupboardServery Counter - Hot FoodWater Boiler/Still/Beverage Unit

Light Duty Boiling Pan, Tilting KettleRefrigeration Unit

extracted. The factor will vary depending onwhether the appliance is gas or electricity, andthese are scheduled in Table 2. Refer to 5.4 forworked example of flow rate calculation.

The theoretical extract air volume would onlybe achieved under draught-free laboratoryconditions. The type, location of thecanopy/ventilated ceiling and the likelihood ofcross-draughts will also have an affect uponthe amount of air required. The more enclosedthe cooking operation, the less the exhaust airneeded to ventilate it, whilst appliances openon all four sides will need a larger volume ofexhaust air than where only one side is open.The canopy factors given in Table 3 shalltherefore be multiplied by the calculatedvolume to determine the actual extract flowrate. Consideration shall also be given to the'active area' of ventilated ceilings when theheight increases. See Section 8.5.2.

0.20 0.150.24 0.240.25 0.200.30 0.25

see manufacturer's literature

continued overleaf

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Table 2: Appliance, Coefficient and Temperature Schedule

Appliance CoefficientGas Electric

SurfaceTemp

MISCELLANEOUS m3/sper m2 °C

Benches, Spreaders and Worktops 0.03 0.03 25Sink 0.15 0.15 25Pass Through Dishwasher* 0.30 0.30 61Pan/Utensil Wash Machine 0.40 0.40 42

Rack and Flight Dishwasher see manufacturer's literature 58*NB - thefigures quoted are for the machine only, the room in which they are located needs to be treated

separately.

HEATING/WATER- 0.03 25

0.03 2557737898

DW/1 72 Specifkatioii for Kitchen Ventilation Systems

GENERAL COOKINGInduction Rob, Ceramic Stove - 0.10 30Pastry and High Output Bakery Oven** 0.25 0.20 86Steamer/Pressure Cooker 0.30 0.20 125Pasta Cooker 0.30 0.20 120Bratt Pan, Tilt Skillet 0.32 0.26 190Boiling Table, Hob Top, Stock Pot Stove 0.35 0.25 190

Heavy Duty Boiling Pan 0.35 0.25 146

Open Top Range and Oven 0.35 0.25 190Steaming and Roasting Oven 0.35 0.30 98Combination Steaming Ovens** 0.35 0.30 92Tandoori Oven 0.35 0.30 90Fan Assisted Convection Oven** 0.38 0.30 86Pizza Oven** 0.38 0.30 92Low/Med Duty Deep Fat Fryer 0.45 0.35 190Low/Med Duty Grill 0.50 0.30 220**NB - multiply the coeffIcient factors by 2 f ovens are double stacked.

FLAME COOKING

Griddle (mild steel) 0.30 0.25 190Griddle (chrome) 0.45 0.40 290Conveyor Pizza Oven 0.45 0.40 90Heavy Duty Deep Fat Fryer 0.50 0.45 190

Heavy Duty Bratt Pan 0.55 0.45 240Solid Top Oven Range 0.60 0.51 420Upright or Chain Broiler 0.75 0.55 190Salamander or Steakhouse Grill 0.75 0.55 260Rotisserie 0.75 0.55 190

Chargrill/Charbroiler 0.95 0.52 350Chinese Wok Range 1.10 - 280

Chinese Wok Range (induction) - 0.40 50Mesquite Grill 1.20 420

Table 3: Canopy factors

Type Open Both Ends Open One End Closed Both EndsLow Level 1.15 1.10 1.05Passover 1.15 1.10 1.05Overhead Wall 1.25 1.20 1.15Overhead Wall, Island Mounted 1.50 1.40 1.30Island 1.35 1.25 1.15

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5.4 Example of flow rate calculation: Method 1

1. Determine the mode! type, plan size andpower source for each item of cookingequipment located under the canopy.

2. Calculate the plan area of the cookingequipment from Fig 3 and from Table 2,allocate a thermal coefficient for each itemof equipment.

3. Multiply the area by the coefficient toobtain a theoretical extract flow rate foreach item.

4. Add the individual rates to arrive at a totalextract flow rate for the canopy.

5. Select the appropriate canopy factor to suitthe type and location of canopy.

6. Multiply the total by the canopy factor toarrive at the total extract flow rate.

Table 4: Calculations for method I (based on the equipment illustrated in fig. 3J:

Specific extract flow rate required

The calculation of extract flow rates forventilated ceilings should be in accordancewith the procedures set out above.

Where concentrated high-heat cookingappliances create a possible 'hot spot' within acanopy or ventilated ceiling area, partitioningof the grease filter plenum shall be consideredto provide a higher dedicated extract duty

= 1.395 m3/s

above such equipment. In such circumstancescare shall be taken to ensure maximum airduties are not exceeded for the particular filterbank selected. Make up air and extract spigotsshall be sized and positioned accordingly.

Following the determination of the requiredextract flow rate, the number and type of filtersshall be selected.

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DW/1 72 Spec/f Icatioii for Kitchen Ventilation Systems

Fig 3 - Typical Cooking Equipment Line-Up

Item Plan Size Power Area Coefficient Flow RateGriddle 600 x 750 gas 0.4500 0.30 0.135

Open top range 900 x 750 gas 0.6750 0.35 0.236

Solid Top Range 750 x 750 gas 0.5625 0.60 0.338Bench 500 x 750 - 0.3750 0.03 0.011

Twin Fryers 650 x 750 Elec 0.4875 0.35 0.171Salamander Grill 750 x 400 gas 0.3000 0.75 0.225

Theoretical extract volume requiredCanopy Factor - overhead wall open both ends

= 1.116m3/sx 1.25


5.5 Method 2 - Face Velocity Method (This is aprovisional method when there is insufficientinformation available regarding the cookingequipment)

The volume of air to be extracted may bedetermined by selecting a velocity across theface area of the canopy that is appropriate forthe type of appliances expected to be used. Thecapture velocity is multiplied by the canopyarea to determine the volume of air to beextracted.

The capture velocity should be selected toensure an even distribution of air across thecanopy face, this velocity will vary accordingto the cooking application and whether thecanopy is either wall or island mounted.

• Light loading - 0.25 mIs. Applies tosteaming ovens, boiling pans, bains marieand stock-pot stoves.

• Medium loading - 0.35 mIs. Applies todeep fat fryers, bratt pans, solid and opentop ranges and griddles.

• Heavy Loading - 0.5 mIs. Applies tochargrills, mesquite and specialist broilerunits.

5.6 Method 3 - Appliance Power Input (This is aprovisional method when there is insufficientinformation available regarding the cookingequipment)

When details of the cooking equipment to beused is limited to the amount of power required

rather than the physical size of the appliance,then the power input method may be used.Each type of appliance is allocated arecommended flow rate in m3/s which is thenmultiplied by the power input in kW todetermine the flow rate required for eachappliance. The total air required is thendetermined by adding together therecommended extract rate for each item ofequipment.

5.7 Method 4 -Air Changes (This is a provisionalmethod when there is insufficient informationavailable regarding the cooking equipment)

These can vary widely depending on the sizeof kitchen, type of cooking, number of peoplepresent, and therefore not recommended as amethod of calculating air volumes. Whilst 40air changes per hour should be regarded as aminimum for comfort in the absence of anyother information, it is not unusual for rates ashigh as 60 - 120 to be created when high-output equipment is densely located in arelatively small space.

5.8 Method 5 - Linear Extract (This is aprovisional method when there is insufficientinformation available regarding the cookingequipment)

Favoured in the United States, this methoddepends upon selecting a flow rate to suit aparticular type of canopy. The figures, whichare listed in the Table 5, do not vary with thecanopy width and are given in m3/s per linearmetre of active filter length.

Table 5: Flow rates (m3/s per linear metre of canopy)

Type of CanopyWall_Mounted

Light Duty0.23 - 0.31

Medium Duty0.31 - 0.46

Heavy Duty0.31 - 0.62

Extra Heavy Duty0.54 +

Single Island 0.39 - 0.46 0.46 - 0.62 0.46 - 0.93 0.85 +Double Island 0.23 - 0.31 0.31 - 0.46 0.39 - 0.62 0.77 +Eyebrow 0.23 - 0.39 0.23 - 0.39 — —Passover/Backshelf 0.15 - 0.31 0.31 - 0.46 0.46 - 0.62 not recommended

NB - Extract rates for double island canopies are for active filter length, i.e. double the rate for an equivalentlength wall Canopy

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DW/172 S;7 f'/c. for Kitchen Ventilation Systems

SECTION 6Make-up Air6.1 In order for the kitchen extract system to

function correctly, it is essential that anallowance shall be made for the provision ofreplacement air. This should be achievedeither by introducing mechanical supply air, orby making provision for natural infiltration.

Where a natural ducted inlet for relief air isselected it should be as short as possible, athigh level and with filtration since theincoming air is likely to be contaminated.

6.2 Where mechanical input is selected, the systemshall provide a maximum 85% of the totalextracted volume, with the remaining 15%infiltrating naturally into the kitchen fromsurrounding areas. The mechanical or 'fanassisted' method should ensure that the kitchenremains under negative pressure thuspreventing the potential transfer of kitchenodours to areas outside the kitchen.

6.3 Make-up air may be introduced into thekitchen by means of the canopy or ventilatedceiling, or through the ventilation system or bya combination of all three. Where air isintroduced through the canopy, the variousoptions are shown in Figs 4 and 5.

6.4 The fan powered system provides positivecontrol and therefore should be the preferredmethod used. With natural infiltration thefollowing problems may occur:

• unfiltered air will enter the kitchen.

• air may otherwise be drawn from dirtyareas.

• draughts and discomfort may be caused incold weather.

• uncontrolled air movement may affect thecooking process.

• 'cooling' cannot be provided to personsadjacent to the canopy.

Fig 4 - Outboard Supply Systems

'7

75%TO

85%

PERFORATED FRONT FACEOR GRILLE

UPTO85%

FRONT FACE WITHOPTIONAL SPOT COOLING

APPROX 20%

DOWNFLOW DISCHARGE GRILLECOMBINATION SUPPLY

TOTAL85%


100% + ENTRAINMENT

UP TO

I

COMBINED OUTBOARD/INDUCTION

100% + ENTR INMENT

I

UP TO- 70 /

/MAXth%\\jCOMBINED OUTBOARD/CAPTURE

Fig 5 - Inboard Combined Supply Systems

6.5 Make- Air Temperatures

6.5.1 A minimum air entry temperature of10°C shall be selected for canopiesand 16°C for ventilated ceilings.

6.5.2 For general make-up air, standardtemperatures as specified in Section 3should be used.

6.6 When selecting plant for kitchen make-up air,the following shall form part of the ventilationsystem:

18

• Filters made of synthetic materials andhaving a minimum efficiency of F6 (seeAppendix A). Glass fibre products shall notbe used.

• Means of varying the fan duty shall beprovided to give the flexibility toaccommodate future changes in roomusage, occupancy and types of cookingundertaken. An electrical interlink with theextract plant shall be installed.

• Where located within the kitchen, plantshall be accessible for cleaning. A packagedair handling unit is preferable as individualplant items will present hygiene problems.

• A natural ducted airway allowing outsideair into the kitchen shall be provided. Thisagain should be positioned at high level, beas short as possible and shall be filtered.Care shall be taken with the location of thedischarge grille because with low externaltemperatures, discomfort may beexperienced by the kitchen users. Thisoption should not be selected when large airvolumes are involved.

• Whilst door transfer grilles may be used inconjunction with other input systems, thereis usually inadequate space toaccommodate sufficient grilles to handlethe large volumes of air required withkitchen extract systems. Transfer grilles indoors however, help to minimise airpressure influences on opening and closure.

100% + ENTRAINMENT

MAX 50%

SLOT LENGTH = FILTER LENGTH

INDUCTION OR ENTRAINMENT

I

100%+:NTR7NMENT--1

MAX15%

CAPTURE AIR STREAM

NB: When the air is inboard then that duty shall be added to the calculated extract flow rate to determine thevolume handled by the fan.


• Visible or audible means of proving theexistence and indicating the supply air filtercondition shall be installed, as dirty filterswill adversely affect the air balance.

6.7 Where a natural make-up air system isselected, the resistance shall be included in theoverall system resistance against which theextract fan will have to operate.

6.8 Care shall be taken with re-circulated air toensure that it is not taken from 'dirty' areas.

6.9 Whilst air conditioned kitchens are theexception in the United Kingdom, where it isdecided to cool the make-up air, further detailsare given in Appendix E. Fig 7- Low Level Wall

6.10 Details of the various types of natural airtransfer systems are shown in Figs. 6-8 below:

NB. Fire dampers should only be required in fire compartment walls.

FD,.,Il

FILTER

Fig 8 - InternalAir Transfer

Fig 6 - Outside Air

FILTER

cDI. FD


SECTION 7Types of Canopy7.1 The only material to be used in the fabrication

of canopies in accordance with thisspecification shall be type 304, ultra-finegrained stainless steel.

7.2 There are a number of types and style ofextract canopy that have been developed; thesecan be broadly classified as follows:

• Overhead wall type canopy - wall or islandmounted

• Overhead island type canopy

• Low level wall type canopy

• Passover type canopy

Fig 9 - Typical Extract Only Filter Canopies.

20

• Counter type canopy

• Eyebrow canopy

• Condensation canopy

Most styles of canopy can be provided with anintegral make-up air facility; these can take theform of:

• Front face perforated diffuser

• Front face grille

• Internal slot - Induction, entrainment,capture, compensating or short circuit.

• Grille or louvres for spot cooling

Examples of the various types andcombinations available are shown in Figs.9-11:

?T

OVERHEAD WALL MOUNTED.

-..--..-

OVERHEAD SINGLE ISLAND.

LOW LEVEL WALL MOUNTED.

r'4?'TE

L1LJOVERHEAD DOUBLE ISLAND.

-..---..-

COUNTER OR PASSOVER.

ij.iE______EYEBROW.

DW/1 72 Specificarioiz for Kitchen Ventilation Systems

L1GRILLE

L'.1BAFFLE PLATE

Fig JO - Non-Filter Canopies

[/cDRAIN

CONDENSE DRAIN

DRAIN

MOISTURE ELIMINATOR

Fig 11 - Condensation Canopies

2]


Section 8Ventilated Ceilings8.1 Whilst the use of canopies is ideal for handling

contaminants produced in concentrated areas,where the cooking equipment generates greaseand water vapour over a wider area, the use ofventilated ceilings should be considered as aviable option.

Ventilated ceilings should also be considered:-

• Where due to structural limitations, lowfloor to finished ceiling levels make the useof canopies impractical.

• Where false ceiling aesthetics are importantand visibility cannot be impaired bycanopies.

• Where cooking equipment generates lowlevels of discharge over large areas, such asfood production and food preparationkitchens.

8.2 The calculation of minimum extract flow ratesfor ventilated ceilings shall be in accordancewith the procedures set out in Section 5 of thisdocument. The supply system shall bedesigned to provide the conditions set out insection 3 and 6.

8.3 There are two types of ventilated ceilingsystem available:-

• Modular Cassette Ceiling

8.4.1 The Modular Cassette type ceiling is atotally integrated systemincorporating dedicated extract,partitioned or dedicated supply, andflush mounted luminaires. Theceiling comprises a grid system whichsupports extract and supply cassettes,and luminaires. The extract filters, ofproprietary design, filter and separatethe contaminant from the air beforepassing into the ceiling void forcentral collection and discharge toatmosphere. The grease is collectedboth inside the extract cassette and ina non-drip integral or perimetertrough for removal and cleaning.

8.4.2 The extract cassettes should bedesigned for easy removal and sizedfor cleaning in conventionalcommercial dishwashers. Extractcassettes shall be located over thecooking appliances with blank, supplyfilters, or luminaires being fitted inthe non-active areas of the kitchen.

8.4.3 Supply cassettes may be integratedinto the ceiling design to providemake up air, comfort ventilation orspot cooling.

8.4.4 For secure installations, panels should

8.5 Calculating Size of "Active" Exhaust Zones

8.5.1 The dimensions of exhaust zones shallbe determined by the size of thecatering equipment that it is serving.

8.4 Modular Cassette System

be lockable.

• Plenum Ceiling

Fig 12 - Cassette Type Ceiling.

22


8.5.2 The plan dimensions of the exhaustzones should exceed the plandimensions of the catering equipment.As the finished ventilated ceilingheight increases, consideration shouldbe given to either increasing the'active' area of the ceiling to avoidmigration of vapour, or increasing thevolume flow. The increase in theextract rate should also reduce the

TABLE 6- Extract Cassette Overhang

possibility of 'thermal cooling' of therising particles back to solid matter,thus stopping the grease returning towork surfaces.

8.5.3 Modular Cassette and PlenumSystems shall have the followingextract cassette overhang as aminimum.

CENTRAL COOKING ISLANI) & WALL MOUNTED COOKING EQUIPMENT

Grease Producing Equipment At Least 500mm Overhang of Equipment

Steam Producing Equipment At Least 750mm Overhang of Equipment

TABLE 7- Ventilated Ceiling Factors

FINISHED CEILING HEIGHT IFACTOR EXTRACT FLOW RATE

AFFL (m FACTOR2.2 1.10

2.5 1.00

2.7 1.082.9 1.16

3.1 1.243.3 1.323.5 1.40

As the finished ventilated ceiling height increases, the extract flow rate shall also be increased.

NB The optimum ceiling height for ventilated ceilings should be 2.5m. This ceiling height therefore has a multiplefactor of 1.00. As with ceilings above this height, those below require an increase in extract volume because ofproblems created with potential cross draughts (i.e. 2.2m height = 1.1factor).

8.6 Plenum System 8.6.1 With no proprietary components, theplenum system comprises a series offilter plenum modules which allow

23

Fig 13 - Plenum Type Ceiling.


the extract air to pass through a singleor double bank grease filter forcontaminant separation before passinginto a plenum box and duct systemand discharge to atmosphere.

8.6.2 Supply grilles are integrated into theceiling design to provide make up aircomfort ventilation or spot cooling.

8.6.3 Secure installations are not achievablewith plenum systems.

8.6.4 Grease filters shall be located inaccordance with procedures set out inSection 13.

8.7 Supply and Extract Ductwork

24

8.7.1 The alternatives for removing extractair and supplying intake air should be:

• via partitioned voids

• totally ducted system.

8.7.2 Where partitioned voids are selectedthere should be no direct duct/spigotconnection to the extract filters.Extract should be by means ofbellmouths in a sealed plenumconnected to a ductwork system.Supply air should be introduced via aduct system through bellmouths intothe supply void.

8.7.3 For most efficient operationbellmouths should be not more than3m apart in each plenum zone.Velocities at the face of a bellmouthshall not exceed 3rnls.

8.7.4 Where a ducted system is selected itcomprises separate dedicatedductwork with coimections to bothsupply and extract cassettes, viaplenum boxes.

8.7.5 Where a plenum design is selectedopen voids above the ceiling shall besealed. Void depths shall be 200mmminimum to 1250mm maximum. For

8.8

voids exceeding 1250mm a top cover(galvanised steel) shall be fitted atmaximum 1250mm above finishedceiling height.

8.7.6 Open builders work plenurns shall notbe used as any part of an extractsystem where grease laden air is beingextracted. In these areas, the exhaustzone shall be top capped. Openbuilders work plenums may be usedfor supply air plenums and extract airplenums for steam laden air only.Where open builder work plenums areselected for extract of steam laden air,services passing through this voidshould be contained within agalvanised duct/trunking.

Construction

8.8.1 The material to be used in themanufacture of ventilated ceilingsshould typically be 304 gradestainless steel. Some manufacturersincorporate anodized aluminium intothe supporting frame; this form ofconstruction should be agreed withthe client or specifier.

8.8.2 The structure that supports theventilated ceiling shall be adequatefor the total weight imposed. As aguide the average installed weight ofboth types of ventilated ceiling,ranges between 18kg/rn2 - 25kg/rn2.

8.8.3 Services, other than ductwork, shallnot pass through the extract voidwhere grease laden air is being carried.

8.8.4 Where other services are routedthrough voids that carry supply orsteam laden air, access arrangementsshall be provided so that adequate andregular cleaning can be achieved.Steam extract and supply air voids,builders-work partitions, etc. shall bepainted with an anti-fungicidal,dispersion coating to avoid thecollection of airborne dust and dirtparticles.


8.8.5 The ceiling void shall be sealed to thebuilding structure to ensure that anairtight plenum is created in order toavoid any short-circuiting of the airsystems.

8.8.6 Where gas services are run throughthe ventilated ceiling void, theinstallation must comply withBuilding Regulations or run within aventilated sleeve to atmosphere.

8.8.7 All mechanical and electricalservices, other than ductwork, shall berun outside the extract zone, exceptfor electrical services to lights whichshall be fitted with heat resistantcabling. The services columns shallextend through the zone and terminateoutside the extract zone.

8.8.8 Installed height of ventilated ceilingscan vary from 2200mm to 3500mmabove finished floor level dependingupon structural limitations and thetype of appliances being ventilated.

8.8.9 To minimise potential fire risks, it isrecommended that:

• The ventilated ceiling should becleaned and maintained regularly.

• All partitions in the ceiling voidshould be constructed from'smooth' cleanable surfacematerials that are easy to clean andwill not harbour growth of bacteria.Material thickness of partitioningshould be at least 0.80mm.

• Where there is grease producingequipment, the ceiling zone shallbe completely segregated from anyadjacent zone by non-combustibleimperforate downstands extendingfrom the structural soffit to theceiling. This partition shall bemanufactured from galvanisedsteel. The perimeter of each zoneshall be segregated by cavitybarriers from any otherconventional ceiling void with the

barrier being fire rated to astandard determined by thebuilding owners risk assessment,but with a minimum integrity of 30minutes and fire stopped.

8.8.10 With both ventilated ceiling options,care should be taken if futuremodifications to the kitchen layout areconsidered. It is important to ensurethat the provision of extract zoningwithin the ceiling void is revised tocomply with the modifiedrequirements and also that sufficientextract and supply air is available toaccommodate changes. The guidanceof the ventilated ceiling supplier shallbe sought prior to modificationstaking place to ensure the integrity ofthe system is not compromised.

8.9 Lighting

8.9.1 Integral lighting may be incorporatedinto either ventilated ceiling system.Illumination levels shall follow therecommendations of Section 14.Minimum requirement shall be 1P55-rated luminaire, achieving an averageof 500 lux at working heightthroughout the area to be served bythe ventilated ceiling. For areas otherthan the kitchen refer to CIBSELighting Codes.

8.9.2 Care should be taken with theselection of lighting components asgeneral lighting as well as tasklighting should be considered. Theintroduction of supply air through thelight fitting should be considered toextend the life of the capacitors,improve illumination efficiency andassist in maintaining the cleanliness ofthe tubes reflectors and diffusers.Emergency lighting shall be to BS5266-I.

8.9.3 The ventilated ceiling supplier shouldsupply photometric data on eachproject to ensure the optimumluminance levels will be achieved.

25


8.10 Cleaning and Maintenance SECTION 9For the cleaning and maintenance of ventilatedceilings see the relevant notes under Section Spigot Connections

9.1 The size of the spigots serving both the supplyand extract plenums, should be determined byselecting a size appropriate for the air velocity.

9.2 The extract spigot area should be determinedby dividing the total extract flow rate by adesign velocity of 5-7 mIs. and the supply airvolume a velocity of 3-5 mIs.

9.3 The width of the spigots should depend on thesize and shape of the filter housing, the angleof the filters and whether a wall or island stylecanopy is used.

9.4 The number of spigots shall be determined bythe length and width of the canopy and anyrestrictions in the ductwork layout but, as ageneral rule, there should be at least one spigotfor every 3m of canopy to ensure an even airflow.

26


SECTION 10Materials10.1 Stainless Steel

10.1.1 Unless indicated to the contrary in anyparticular project specification, allvisible surfaces of the canopy andventilated ceilings shall have the finegrained finish on view, with allunpolished surfaces concealed.

10.1.2 All polished sheet surfaces shall beprotected with a removable, laminatedfilm.

10.1.3 For special canopy applications forthe offshore and food processindustries type 316 acid resistantstainless steel should be required(manufacture reference: EN 10088).Where such specialised stainless steelis necessary, the client shall indicatethis requirement from the outset.

10.1.4 Abbreviations

= Dull polished both sides.= Dull polished one side.= Bright Annealed= Descaled or unpolished

10.2.2 For the fabrication of front face dis-charge grilles, 1 .0mm perforatedstainless steel sheet shall be used, thefree area selected to suit the designconditions. This arrangement will notprovide directional control of the airdischarge

10.3.1 To avoid condensation, canopies thatare provided with a supply plenumshall have all internal surfaces of thatplenum thermally insulated. Theinsulant shall be a rigid foil faced nonfibrous slab, with a class 1 spread offlame.

10.3.2 Insulating boards are available invarious thicknesses and should befixed to the plenum with acombination of adhesive, tape andstick pins.

10.3.3 Fibre based insulating materials mustnot be used in a food environment.

10.2 Perforated Sheet

10.2.1 For the diffusion or equalisation of airwithin the supply plenum of a canopy,0.8mm perforated sheet should beused.

27

10.3 Insulation

DP2DPi2A2B

TABLE 8- Material Weights(in kg/rn2)_______

2.0mm or 14g1.6mm or 16g1.2mm or 18g1.0mm or 20g0.8mm or 22g

Stainless Steel16.04 kg/rn212.87 kg/rn210.30 kg/rn27.77 kg/rn26.40 kg/rn2


SECTION 11Construction11.1 General

11.1.1 The canopy should be easy to clean,be constructed of non-combustiblematerials and be located so as not tointerfere with the cooking process.

11.1.2 Canopy sections shall bemanufactured in an all-formed, foldedand welded construction with jointsmade such that there are noobstructions or obtrusions likely tocause injury or encourage growth ofbacteria.

1 1.1.3 All external canopy surfaces shouldbe vertical to facilitate cleaning,match the ceiling line and maximisethe internal collection volume.

11.1.4 A minimum 50mm x 25mm channelshould be formed as an integral partof the valance to provide rigidity tothe exposed edge for the fullperimeter of the canopy. Provided thatthe air flow rate has been correctlyselected, condensation should notform and with the exception of'condensation' canopies, there will beno requirement for drain plugs.

For ventilated ceiling construction,refer to Section 8.

1 1 .2 Canopies and ventilated ceilings should befabricated using the material thicknessesshown in Table 9. The material thickness shall

TABLE 9- Sheet Thicknesses

Stainless SteelValance up to 600mm high 0.9mmValances over 600mm high 0.9mm - 1.2mmFilter Housing 0.9mm - 1.2mmFlat Panel Ventilated Ceilings 0.9mm - 1.2mmCoffered Ventilated Ceilings 0.55mm - 1.1mm

Supply plenums 0.9mm - 1.2mm

Spigots

28

0.7mm

be selected to ensure that no distortion occursthrough either welding or the weight of thepanel itself

1 1.3 Fabrication

11.3.1 Cut blanks should be notched andfolded into sub sections. These foldedjoints shall be contained 'inboard' ofthe canopy construction to ensureconcealment on completion of thefinal assembly.

11.3.2 Consideration should be given tominimise the number of componentsin which a canopy is delivered to site.This will depend upon both the size ofcanopy, site access and conditions.

11.3.3 Canopies which in length exceed thatwhich can be made from a standardsheet, shall be made in sections whichare joined by means of a 20-25mmwide full height internal flange orstanding seam. After erection,standing seams shall be covered by afull height cover trim to provide asmooth surface to facilitate cleaning.

11.3.4 Canopies that are made usingextruded section must not be used asthe joint between the sheet and sectionprovides a natural harbour for thegrowth of bacteria.

1 1 .4 Sealant

11.4.1 The use of sealant shall be limited tojoints or those areas where a hygienicseal is required. The sealant must beof silicon type foodservice quality.

1 1.4.2 For site use, a clear, white or greysealant should be used for making aseal between the canopy and a tiledwall or ceiling.

11.4.3 Conventional sealant should be usedfor spigot and ductwork joints.

11.4.4 All products shall be installed inaccordance with the manufacturers'recommendations.

DW/1 72 S; ik'atio;: for Kitchen Ventilation Systems

SECTION 12 SECTION 13Polishing Grease Filtration12.1 All visible welds shall be ground to a smooth 13.1 A UK standard for the testing of grease filters

surface and reinstated to the finish of the base has been set by the publication of the Lossmaterial by polishing. Prevention Certification Board's document

LPS 1263 - REQUIREMENTS FOR THE12.2 The type of disc used for the grinding and LPCB APPROVAL AND LISTING OF THE

polishing processes may vary according to the FIRE PERFORMANCE OF KITCHENgrade of material and joint being polished. EXTRACT SYSTEMS. All grease filters used

in commercial kitchen ventilation systems12.3 The polished areas should be covered with a should comply with LPS 1263.

low tack vinyl tape to replace the originallaminated pvc protection destroyed by the Filters are used primarily in commercialwelding. kitchen extract systems for the removal of

flammable grease deposits.1 2.4 Abrasive discs that have been used on other

materials shall not be used with stainless steel. The grease extracted by the filters shall becollected and removed so that it will notaccumulate in either the canopy plenum or theductwork system, or fall back onto the cookingsurface. In the event of fire the filter shall alsolimit the penetration of flame downstream intothe canopy plenum.

The filter shall be constructed so that there areno sharp edges or projections and shall beeasily removable for regular cleaning.

Primary filters that retain grease within thefiltration matrix until cleaned, shall not be used(not to be confused with those designed withpurpose made integral collection reservoirs).The mesh type filter shall not be suitableexcept for secondary filtration.

LPS 1263 describes tests to determine both thegrease removal efficiency and the flameresistance of grease filters. The tests are basedon procedures that are already in place and arebased on the American UL 1046 (F Class) forflame arrestance, and the German VDI 2052(G Class) for the grease extraction efficiency.

The main requirements of the UL1046 test arethat;

• There shall be no flame extension of morethan 450mm beyond the filter. (MFL)

29


Where the 'G' represents the grease removal efficiency, and 'F'; represents the capacity of the filter to restrict thelength of flame.

The designer shall specif' the class of filter required based on the building and cooking risk factors, and it shallbe the responsibility of the canopy contractor to provide a filter of the appropriate GF rating.

Details of test procedures do not fall within the scope of this document, and further information should be obtainedfrom the Loss Prevention Council.

30

• The filter remains intact throughout the test

• There is no ignition of collected grease onthe downstream side of the filter

• No grease falls back onto the cookingsurface

• No flame exists downstream beyond a timeof 120 seconds (DFP)

The results of the VDI test for grease removalefficiency will be:

50% of the smallest particle size will beremoved from the air stream.

This removal will be achieved at plus or minus20% of the specified airflow.

The required performance of the filter will bebased on the results of both tests and to the riskfactor of the cooking and building type.

Table 10- Cooking Risks

Risk Level Examples of type of cooking equipmentLight Boiling with no risks of vapourMedium Conventional frying or processes emitting steady vapour flowHeavy Open flame grilling, flame cooking and sudden emissions of hot vapour

Table 11 - Building Risk

Risk Level Example of type of building in which kitchen is locatedKi Small commercial building of single occupancy typeK2 Small commercial building of multi-occupancy type1(3 Medium size commercial building of single occupancy typeK4 Medium size building of multi-storeyK5 Large size commercial building of single occupancy typeK6 Large size commercial building of multi-occupancy typeK7 Special risks including large shopping complexes and airport terminals

Table 12- Recommended Performance of Filters to comply with LPS 1263

Risk Assessment (GF Class Required)Cooking Risk

Light Medium Heavy

—

K! GF2O GFS2 GF8OK2 GF28 GF58 GF85

—K3 GF36 GF64 GF9OK4 GF44 GF7O GF94K5 GF52 GF8O GF98K6 GF6O GF85 GF1O1K7 GF68 GF9O GF1O4

DW/1 72 SpecijIcatio;i for Kitchen Ventilation Systems

13.2.1 Grease filters fall into two maincategories; primary and secondary.Typically, most canopies incorporateonly primary grease filters and theseshall be specified in accordance withLPS 1263. Primary grease filters shouldbe flame retardant and capable of re-moving as much airborne particulate(i.e. grease, oil etc) from the air streamas possible, to maximise the filtrationprocess within the canopy. Secondarymesh type impingement filters can beincorporated to the rear of the primaryfilters providing they do not affect thefire arrestance criteria as required byLPS 1263. Inclusion of secondarymesh type impingement filters shallnot reduce the LPS 1263 requirementfor the primary grease filter.

13.2.2 The use of secondary filters,sometimes referred to as coalescers,serves to encourage airborne gases tocondense on the surfaces and therebysubstantially reduce the moisturecontent of the air being extracted.

13.2.3 Disposable panel type filters shall notbe used for grease extraction. Wherehigh levels of contaminant areproduced, then higher degrees ofgrease separation can be achieved bythe use of cartridge, water wash orwater mist systems.

13.3 Examples of type of grease filter currentlyavailable and their main properties are shownin Table 13.

13.4 Mesh Impingement Filters

13.4.1 There is no barrier to flame withinthese filters; therefore mesh filtersshall not be used as a primary greasefilter.

13.5 Baffle Filters

13.5.1 Baffle filters comprise a number ofinterlocking vanes which whenassembled form a two-pass greaseremoval device. The pressure dropremains constant and the bladesprovide a barrier in the event of aflash fire. Baffle filters should befabricated entirely from stainlesssteel.

13.5.2 The grease laden air passes throughthe filter and by a series of forcedchanges in direction and velocity, thegrease becomes separated in the airstream and is deposited on the verticalvanes. The deposited grease is thendrained off through a number of weepholes spaced at adequate intervalsinto a collection drawer which shallbe regularly cleaned.

13.5.3 The capacity of the collection drawershall be sufficient to suit the type ofcooking and frequency of cleaningand because the grease is retained,care shall be taken to ensure that thegrease collection drawer is isolatedfrom the extract air stream asillustrated in figure 14 to prevent re-entrainment.

Fig 14— TypicalAirfiow Through Filter Housing

'3.1. CONTAMINATED AIR

2. GREASE SEPARATION

3. CLEANED AIR

4. GREASE COLLECTION DRAWER AT END OF FILTER BANK.

5. GREASE COLLECTION ISOLATED FROM AIR MOVEMENT

6. SLOPING GREASE COLLECTION CHANNEL WITH LOW POINT

-6

AT DRAWER


13.5.4 For plenums that contain more thanone filter, supports may be required toensure that the housing remainsstable. Filters shall be easilyremovable and installed so as tominimise air leakage around theperimeter.

13.5.5 Where installations are beingrefurbished, baffle filters shall not beinstalled in a plenum previously usedwith mesh filters unless a collectiondrawer and grease run is added andthe plenum is revised to avoid re-entrainment. Any increase inresistance shall be taken into accountwhen selecting a new fan orconsidering the adequacy of theexisting one.

13.6 Baffle filters shall be installed at an angle ofnot less than 45 deg from the horizontal.

1 3.7 Cartridge Filters

13.7.1 Cartridges filters comprise a highvelocity slot opening onto a series ofbaffles which cause multiple directionchanges to the air flow.

13.7.2 Available in a combination of size andlength to suit the air flow, cartridgefilters shall be installed over the fulllength of the extract plenum, with anintegrally designed slope to allow thetrapped grease to fall through a drainto a grease drawer.

13.7.3 Should be for used with moderate toheavy grease load applications.

13.8 Water Wash

32

13.8.1 The water-wash system comprises anextract plenum similar to the one usedwith cartridge filters, but alsoincorporates an inbuilt self cleaningsystem that has the dual function ofcatering for routine maintenance aswell as providing fire protection to theplenum and duct.

13.8.2 Water-wash canopies are operated bya control panel. The basic panel is amanual system where the operatorpushes a start and stop button at thebeginning and end of the cookingprocess each day. Automatic systemsare also available which allow thecontrol of a set number of systemswith pre-set sequencing of watercycles, and automatic starting andstopping.

13.8.3 Cleaning is achieved by spraying theinterior of the canopy extract chamberwith pressurised hot water via anintegral pipe work system,automatically injecting the plenumwith a predetermined amount ofdetergent. The waste water flows fromthe system through a plumbed drain.

13.8.4 The wash cycle is generally activatedfor between 2 and 3 minutes at the endof the day after the cooking equipmentand fans have been turned off.

13.9 Continuous Cold Water Mist

13.9.1 Tn addition to the water wash system acold water mist can be incorporated toenhance grease extraction. The watermist system runs continuously duringthe cooking operation. The vapourentering the canopy passes throughthe mist which causes the greaseparticles in suspension to drop intemperature, solidify, increase in sizeand drop to a drainage trough fromwhich it is flushed to a drain.

13.9.2 The mist system has an additionaladvantage in that the continuous flowof cold water cools both the canopyand the exhaust air, is particularlysuitable for solid fuel applianceswhere the mist will also extinguish hotembers that may be drawn up into thecanopy.

13.10 The bacterium legionella occurs naturally inwater sources and, when in sufficient numbers,can cause 'legionnaires disease' by theinhalation of water laden air in an aerosol form

DW/1 72 'iiti for Kitchen Ventilation Systems

by susceptible individuals. This is unlikely tooccur with water wash and water mist systemsdue to the fact that the water supply to thesystem is constantly changing and theconfined nature of the spray. If it is thoughtthat there is cause for concern, then furtherguidance must be obtained from either:

• HSC document - "The prevention andcontrol of legionellosis - Approved Code ofPractice L8"

• CIBSE Technical Memorandum:Minimising the risk of legionnaires disease(TM13: 1991)

• The Institute of Plumbing publication -"Legionnaires' Disease - Good PracticeGuide for Plumbers"

13.1 1 Typical wash plenums are illustrated in fig15.

Table 13- Types of Canopy Grease Filter and Their Main Properties

Type

Baffle

RecommendedFace Velocity

4.5 - 5.5 mIs(at slot)

Advantages

InexpensiveNon - over

Loading_pressure drop

Disadvantages

Higher pressure dropthan mesh filters

Cartridge 4.0 - 5.5 mIs(at entry)

Higher efficiencyNon overloadingpressure drop

Higher pressure drop thanbaffle filtersSpecial plenum fabricationrequired

Water Wash 4.0 - 5.5 mIs(at entry)

Higher efficiencyNon overloadingLow maintenance

Expensive. Very highpressure drop.Hot water supply anddrains required.

Cold Water 4.0 - 5.5 m/s(at entry)

Very efficient.Low maintenance.Non overloading

Expensive.Very high pressure dropHot and cold watersupplies and drainsrequired

For types and properties of ventilated ceiling filters, refer to Section 8

33

Fig 15 - lvpical Water Wash Plenums.

DW/1 72 Speciflcatioii for Kitchen Ventilation Systems

SECTION 14Canopy Lighting14.1 Lighting in a kitchen canopy should provide an

average illumination level of approximately500 lux at the working surface and standardfluorescent type fittings, installed at a height of1200mm above the cooking surface shouldfulfil this requirement. In comparison withother systems of lighting, the fluorescentfitting is generally the most efficient andeconomical option with the best lifeexpectancy. They should be incorporated intoa suitable housing to isolate them from thecooking process. See CIBSE Code forLighting, Lighting at Work, BS ISO 8995 andBS EN 12464- 1.

14.2 The lighting housing should be recessed intothe canopy to provide an easily cleanablesurface devoid of unnecessary, inaccessiblejoints and seams. Where surface mountedcanopy lights are unavoidable, then smoothsurfaces and good 'clean-down' propertiesshould be provided.

14.3 The light enclosure shall be sealed against theingress of grease and moisture. Surfaces facingthe cooking area shall be designed to achieve arating of 1P55 - see appendix C for details of IPratings.

14.4 All sealing gaskets between the removablereflector and the light housing shall be of foodquality neoprene and be able to withstandtemperatures up to 100 deg C.

14.5 The lighting lens shall be made from atemperature resistant material such aspolycarbonate sheet or safety glass. In bothcases, the outer surface should be of a smoothand easy to clean finish. Care shall be taken toensure that where polycarbonate sheet is used itshall be capable of withstanding thetemperatures generated by the cookingprocesses.

14.6 The light housing shall have an easilyremovable cover for easy access and

34

replacement of the fluorescent tubes.

14.7 The light housing should be designed withadequate ventilation, especially at either end.

14.8 Wiring from the light fittings to any junctionpoint on the canopy must be heat resistant andinstalled in a low smoke and fume (LSF)material. The power supply should be part ofthe electrical services contract.

14.9 The light housing shall be manufactured froma material or colour which will ensuremaximum light reflection downwards towardsthe working surface.

14.10 The following formulae should be used todetermine the level of illumination achievedwhen details of the lighting components areknown.

14.10.1 The level of illumination in lux shouldbe calculated as follows

No. of tubes x average tube life x ufx mfcanopy area

14.1O.2The number of fittings requiredshould be calculated as follows

Canopy area x required level of illuminationaverage tube life x ufx mf

The inclusion of double tube fittings does notnecessarily double the level of illumination. Afactor of 1.5 times higher should be used togive the correct level of illumination whenusing double tube fittings.

14.10.3Where mf= maintenance factor = 0.70uf= utilisation factor = 0.38and average tube life is given inTable 14.

TABLE 14- Average Tube Life I

Tube Length Output Average Life600mm 18 Watt 1100 hours

1200mm 36 Watt 2800 hours1500mm 58 Watt 4550 hours1800mm 70 Watt 5600 hours


14.10.4These figures are based oninformation supplied bymanufacturers of 'warm white' tubes.Should alternative products beselected, then different factors may

14.10.5 Where standard light tubes are used,these shall be encapsulated within aprotective sheath to render themshatterproof.

14.10.6 Natural deterioration in illuminationoccurs to all fluorescent tubes.Annual replacement should ensure theoriginal lighting level is maintained.

14.10.7 The CIBSE Code for Lighting shall becomplied with (see Appendix F).

14.1 1 Where surface mounted lighting is to be usedall electrical wiring shall be concealed abovethe canopy.

14.1 2 Alternative positions for the location of lightfittings are shown in fig 16.

SECTION 15Ductwork1 5.1 The correct standard of ductwork selected to

complete the installation is as important as theselection of the canopies themselves.

15.2 For the distribution of supply air to the canopy,the ductwork has no special requirements otherthan the application of thermal insulationwhere the supply air is tempered and theinstallation at a minimum F6 filtration level forthe incoming air. Bird mesh screens to the rearof any inlet louvre shall be incorporated.Insect mesh shall not be used as it can becomeeasily blocked.

15.3 Under normal circumstances and providing itruns within the fire compartment of thekitchen itself, extract ductwork shall also haveno special requirements.

15.4 All ductwork as described in 15.2 and 15.3shall be low pressure Class A and be inaccordance with HVCA Specification numberDW/144 with a minimum thickness of 0.8mm.

15.5 Where it is not possible to immediatelydischarge the captured air within the confinesof the kitchen fire zone, fire rated ductworkmust be used to comply with BS 3476 part24/B S 5588 part 9. For further information seeAppendix D.

1 5.6 Where total 'grease tightness' is requiredwithin the kitchen fire zone, all ductworkwithin the kitchen compartment and notdischarging directly to atmosphere shall beconstructed from either 1.2mm stainless steelor 1.6mm zintec, be of fully weldedconstruction with welded angle iron flangesand use full faced gaskets. Gaskets shall benon porous, impervious to grease and cookingoils and capable of withstanding the highertemperatures experienced in kitchen extractsystems. Mild steel ductwork should also bepainted externally with 2 coats of protectivepaint before leaving the manufacturers works.

15.7 Where a waterwash or watermist type filtrationsystem is used, horizontal ductwork shall slopeback to the canopy with a fall of 1:50.

—35

apply.

FLUORESCENT IN ROOF

FLUORESCENT IN SUPPLY PLENUM

BULKHEAD LIGHT

Fig 16 - Location of Lighting.


15.8 Grease filters do not remove all of the airbornegrease produced therefore care should be takenagainst staining the fabric of the building at thedischarge point.

15.9 Particular attention shall be paid to the designof ductwork to extract steam from dishwasherand pot washing machines due to the very highlevel of humidity present. With the risk ofcondensation, the following precautions shallbe considered to prevent leakage through theduct joints.

15.11 When designing kitchen supply and extractsystems the duct velocities shown in Table 15shall be followed.

Table 15- Duct Velocities

Main RunsSupply Extract6-8 mIs 6-9 rn/s

Branch Runs 4-6 mIs 5-7 rn/s

• Use of stainless steel ductwork with slipjoints in the direction of the flow ofcondensation.

• Ductwork installed with a fall back to themachine.

• Apply external thermal insulation tominimise the condensation.

• Ensure that longitudinal joints are not onthe bottom of the ductwork.

• Site-weld cross joints on stainless steelductwork, particularly across the bottomand for 50mm up each side.

• Ensure that cleaning doors are not on theunderside of the ductwork.

• Consider the use of all-welded plasticductwork.

15.10 No system shall be connected into the kitchenextract system where the route selected doesnot minimise the number of changes indirection and possible grease traps. Whereducts from more than one canopy are joinedtogether, then branch cormections should beflush on the underside.

36

Internal thermal or acoustic lining should notbe used, and turning vanes should be avoidedwherever possible.

Where it is not possible to immediatelydischarge the captured air within the kitchenfire compartment, fire rated ductwork shall berequired. For further information see AppendixD.

15.12 All interior surfaces of the ductwork shall beaccessible for cleaning and inspectionpurposes. In the absence of a detailed cleaningspecification/method, access doors shall beinstalled at 3m centres. The panels shall be ofat least the same thickness material as theductwork, be grease tight using a heat-proofgasket and contain minimum projections intothe duct. For recommended cleaningprocedures refer to section 25 and the HVCApublication TR/1 9 - "Guide to Good Practice -Cleanliness of Ventilation Systems" (seeAppendix F).

15.13 On horizontal duct runs, access doors shouldbe installed on the side of the duct, with theunderside of the door at least 40mm above theunderside of the duct. On vertical ducts,cleaning doors shall be provided at each floorlevel.

15.14 Discharge points shall be positioned such thatthe extracted air cannot be entrained into asupply system. The ductwork shall dischargeat least I .Om above any openable window.

15.15 The discharge terminal shall be open withoutmesh and designed to achieve an exhaust orefflux velocity of 12-15 mIs or as required bythe Local Authority from whom approval shallbe sought. However, consideration should begiven to situations where the lack of amesh/guard might allow hand access tooperating fan blades.

15.16 All exterior ductwork should be supportedwith fixings that do not penetrate the duct wall.Where this is not possible, the duct wall shallbe made good with sealant and steel washers.

Spigots 3-5 mIs 5-7 rn/s

DW/1 72 Specificat;ii for Kitchen Ventilation Systems

15.17 The use of a 'chinaman's hat' type of cowl 15.18 Drains shall be installed at the base of all risersshould not be used due to the potential (see Fig 17).downdraught caused and the risk of re-entry ofthe extract air back into the building.Alternative types of discharge terminal areshown in fig 17 and 18.

O.6D

D

300 MAX

RED

15 rn/s

UCING CONE SOLID TOP CONE

Fig 18- Alternative Terminals without internal drains

D+

OPEN TOP CONE & DRAIN INDUCTION TYPE SLEEVE TYPE

Fig 19- Alternative Terminals with internal drains

37

Fig 17- Drain


SECTION 16Installation16.1 To ensure the smooth running of an

installation, the following items shall beestablished at an early stage of the contract.

16.2 Canopies and ventilated ceilings are usually asecond fix item. The installation should beprogrammed to follow completion of themechanical services first fix, but before eitherthe cooking equipment or false ceilings areinstalled.

16.3 Because of the many canopy sizes, accessroutes should be established to ensure thatcomponents can be easily manoeuvred into thebuilding at the appropriate stage ofconstruction. Consideration shall be given byall parties to special access or lifting provisionsthat may be required.

16.4 The canopy clearance from the finished floorlevel to its underside is usually set at 2000 -2100mm. If alternative levels are required, theyshall be stipulated prior to the production ofthe manufacturing drawings.

16.5 Canopies and ventilated ceilings are usuallyinstalled before the catering equipment whichcan make setting out points difficult toestablish. Pre-determined datum points agreedformally with the catering equipmentinstallation contractor should ensure that thecanopy or ventilated ceiling can be suspendedprecisely over the intended equipment positionand in line with service distribution units.

16.6 The canopy and ventilated ceilingmanufacturer should be advised at an earlystage on the type of fixings to be used andwhether any secondary support provisions arerequired. Various suspension methods may beused, but the number of fixing points shall beselected to carry the weight, maintain both theshape, integrity of the finished installation andinclude provision to overcome any sitediscrepancies.

16.7 The canopy and ventilated ceilingmanufacturer shall be advised of any wall

38

finishes to be applied such as tiles or plasticfacings. It shall also be established whetherthe canopy is to be installed prior to thesefinishes. If the canopy is to be installed firstthen dimensional tolerances shall be agreedwith the main contractor. Where a canopy isrecessed between two walls then a finisheddimension needs to be established beforemanufacture is started. Ventilated ceilings areusually installed after the wall finishes arecomplete. As such the finish should extend toat least 50mm above the installed height of theventilated ceiling. The provision of ceilingtrims will then be undertaken by the ventilatedceiling contractor, with care exercised to avoidbreaching the air-tight integrity of theventilated ceiling system.

16.8 Canopies are fabricated to specific geometricshapes and dimensions. During theinstallation, inaccuracies in the buildingstructure may be highlighted. For complexinstallations the canopy supplier shouldprovide templates prior to the delivery of thecanopy.

16.9 Protective finishes such as vinyl film, impact-type wrapping, protective boarding and tapeshall be left in place until the final cleaningprogramme. The canopy and ventilated ceilingcontractor would not normally be expected toreturn at later date to undertake this workunless specifically instructed to do so at tenderstage.

16.10 For canopies, the provision of ceiling trimswill normally be undertaken by the falseceiling contractor. Care should exercised whenfastening trims to a canopy to avoid fixingspenetrating the canopy skin. Even greater careshall be taken on waterwash canopies to avoidbreaching the watertight integrity. Ventilatedceiling installers should fit wall trims and sitemeasure infill pieces to tie in to their system.

16.1 1 Prior to leaving site the canopy and ventilatedceiling installer shall arrange for the canopy /ventilated ceiling to be inspected by the clientto ensure that the installation has beencompleted to his satisfaction.

16.12 The supplier shall ensure that thecanopy/ventilated ceiling performance ratingplate has been fitted.


SECTION 17Fans17.1 Care shall always be taken with the location of

the supply and extract fans to ensure that thereis sufficient space for regular cleaning andmaintenance. Limited space shall not restrictselection of the correct fan.

1 7.2 Kitchen ventilation systems have relativelyhigh resistances against which a fan has tooperate. The fan should be selected to handlethe design resistance with up to an additional10% pressure margin allowed to suit possibleextensions to the original kitchen plan.Regulation of the air flow should be achievedby either variable speed control if the selectedfan is suitable, or by the use of balancingdampers.

17.3 Backward curved centrifugal, mixed flow oraxial flow impellers are preferred as they areless prone to unbalance and are more easilymaintained and cleaned due to their openconstruction. Fixed or adjustable metalimpellers with a robust and open constructionshall be used, as lightweight multi-vane orplastic-type impellers can warp and are proneto collecting concentrations of grease. Plasticbladed fans can however be used where thecanopy extracts non-grease producing, lowtemperature fumes.

17.4 Conditions within the kitchen in which the fanhas to operate are normally between 40 and 60degC at 95% relative humidity. Most motorsare rated to 1P55 and are capable of operatingwithin these conditions without the necessityto mount the motor out of the airstream.

1 7.5 For fans that have the motor within theairstream and are ventilating from cookingequipment that produces higher levels oftemperature and humidity indicated in 17.4,then the specification for the motor shall beupgraded to withstand more onerousconditions.

17.6 An audible andlor visual indicator should beincluded to warn of fan failure. This should tooperate on pressure difference rather than air

movement because of the possibility of greasebuild-up on the vanes.

17.7 The provision of drain holes at the lowest pointof the motor to allow condensation to drainfreely is recommended, these shall be of theporous type to avoid downgrading the Index ofProtection (IP) of the motor.

1 7.8 Both variable and two speed regulation arenow common features, but it is essential thatwhen grease is being produced, the systemshall operate at its design duty. A minimumextract level shall be set within the regulator toensure that, even when set at low speeds, anacceptable ventilation rate is maintained asreduced speeds may cause the carry-over ofgrease through the filter. This facility is astandard feature of the controller withproprietary speed regulators.

1 7.9 Where a make-up air system is selected, thespeed regulators for both the supply andextract fans shall be electrically interlocked toensure that the desired balance is maintained.

17.10 BS 6173 states that an interlock of theventilation system to the gas supply serving thecooking equipment shall be installed so that, inthe event of air flow failure, the gas supply isswitched off. The supply fan shall also beisolated when a fire suppression system isactivated in fire mode. This will involve thefitting of an automatic solenoid valve in thegas supply pipe work and an airflow-sensingdevice such as a pressure switch, vane switchor torque switch. The inclusion of thisinterlock is a requirement for all new poweredextract systems. For existing installationswhere cooking equipment replacement is likefor like, no action is required. However, thecontractor shall quote for the inclusion at alltimes; failure to do so could lead to legalissues. If an existing kitchen has any form ofupgrade, then the contractor shall quote for theinclusion. The Client's insurance company mayhave a requirement that this work is done; thismay reduce the premium paid.

17.1 1 Fans selected for use with dishwasher systemsshall be fitted with 'tropicalised' motors thatare capable of operating in the saturatedatmosphere, or a fan with a motor out of the

39


airstream. The fan should be electrically linkedto start with the washer and include anautomatic run-on timer to disperse residualmoisture as the system cools down. Anotheroption is to specify anti-condensation heatersfor larger motors, or for smaller motors toconnect a single phase 24 volt supply to awinding when the motor is idle to provide alittle heat and thus prevent condensation build-up.

17.12 Flexible connections shall be suitable for usewith a grease laden atmosphere, positivelyfixed by clamps or bonding to prevent airleakage. Under fire conditions the materialmust have a minimum integrity of at least 15minutes and be selected to suit the temperature

Table 16: Flexible Connections -Temperature Ratings

of the flumes being exhausted. Table 16 listsmaterials with the maximum temperatures atwhich they are suitable for continuousoperation:

Fire retardant PVC coated nylon 40°CLoaded PVC coated glass fibre (acoustic) 40°CNeoprene coated glass cloth 120°CAluminised glass cloth 150°CSilicon coated glass cloth 2O0°

17.13 The following table compares the advantagesand disadvantages of the various types of fan.

Table 17: Types of Fan

FAN TYPES ADVANTAGES DISADVANTAGES

1. Centrifugal 1) Large range of pressure and volumeFan Sets characteristics

2) No temperature limitations

3) Robust and easily maintained

4) Adaptable changes in systemrequirements with pulley/motorchanges

5) Standby motors can be morereadily fitted

1) An expensive option

2) Requires more space than is usuallyavailable in the kitchen

3) Requires regular maintenance tocheck drive belt wear unless directdriven fans are used

4) Forward curved fans should only beused for supply systems

2. BifurcatedFans

1) Robust with no temperaturelimitations

1) Less expensive than the centrifugalfan but not a cheap option

40

2) With motor out of air stream thisfan is still considered one of thesafest options with high temperatures

3) Easily installed into a ductworksystem

4) Robust and easily maintained

2) Heavy in construction and thereforenot always easy to support

3) This fan is best situated within aplantroom since on large duties, thefan can be bulky in size and too noisyfor siting within a working environment

4) In-duct noise - will probably requireattenuation

5) Restricted range of resistance capability

6) Standard unit not readily available withspeed regulation.


Table 17: Types of Fan

FAN TYPES ADVANTAGES DISADVANTAGES

3. Belt Driven 1) Compact with an extensive duty 1) This fan needs regular maintenance - inAxial Fans range especially when operating in hot environments the drive belts are likely

contra-rotation. to fail more regularly (visual or audiblealarm for fan failure is an option)

2) Few temp limitations2) Not as robust as the above fans but

3) Easily installed into a ductwork suitable for most kitchen applicationssystem

4) A less expensive option

4. Axial Fans(Metal Impellers)

1) Compact with an extensive dutyrange especially when operating inseries

1) High temperature limitations but willserve for most general kitchen ventsystems

2) Easily removed for maintenanceand cleaning

2) Not as robust as items 1 and 2 but stillsuitable for most kitchen applications

3) A cheaper option than the aboveunless dual fans are necessary

5. 'In-Line'Centrifugaland Mixed FlowImpellers

1) Compact with a good duty rangewhich can serve many kitchen ventsystems

2) Generally less expensivethan the above options.

1) High temperature limitations but willgenerally serve the majority of kitchensystems

2) Not as robust as items 1 and 2 but stillsuitable for most kitchen applications

3) Easily removed for maintenanceand cleaning

3) Forward curved fans shouldonly be used for supply systems

6. Roof Extract 1) Compact and, where the motor is 1) High temperature limitations butFans (Vertical encased outside the air stream, will generally serve the majority of kitchenJet Discharge has a good temperature range vent systemswith CentrifugalImpellers) 2) Easily removed for maintenance 2) With poor roof access this

and cleaning type of fan can be a problem tomaintain

3) No space restrictions3) More expensive than in-line/axial fans

4) Good external appearance but dispenses with necessity of dischargeductwork

41

DW/1 72 Speciflcation for Kitchen Ventilation Systems

SECTION 18Attenuation18.1 Kitchen extract systems usually operate at

sensitive times such as early in the morningand late at night, so the amount of noisegenerated shall be kept to a minimum. Thelevel of noise and vibration from the plant shallnot be transmitted through either the structureof the building or the ductwork so as to be anuisance for those either working in theconditioned space, or in adjoining premises.

18.2 The average human cannot distinguishbetween two sound pressure levels up to 2dBapart. Above this level there a perceptibleincrease in the overall level of noise. Acousticequipment shall therefore be selected to limitthe increase in level to 2dB above ambient.

18.3 Tolerance of noise levels is subjective, butwithin the conditioned space a level betweenNR4O and NR5O would normally beacceptable. The atmospheric side of anysystem requires individual examination butLocal Authorities will usually advise on theirspecific noise requirements. Local Authoritiesusually refer to BS 4142 - "Rating of IndustrialNoise Affecting Mixed Residential andIndustrial Areas" as the basis of their criteria.Generally, the maximum acceptable noise levelat the discharge point of the system is thatwhich should not increase the overall level bymore than 2dB(A). This is difficult to achievein residential areas and wherever possible,vertical discharge of ducts, slower running fansand lower duct discharge velocities should beselected. Where this is not possible, then in-line attenuators shall be installed.

18.4 Where in-line attenuators are used, they shallbe constructed so that there is no greaseimpregnation into the acoustic media. Aprotective membrane shall be specified for thispurpose, this will reduce the designperformance of the attenuator. This should betaken into account when selection is made.

18.5 Isolation of vibration using correctly specifiedresilient mountings or pads, together with heat resistant flexible connections to the ductwork shouldensure minimum transmission to the structure.

42

SECTION 19Dampers19.1 Volume control dampers are often necessary

but should be kept to a minimum andincorporate the following features:

• For extract systems, the damper blades shallbe fabricated from stainless steel.

• The operating mechanism shall be outsidethe airstream and be capable ofwithstanding the higher air temperaturesassociated with kitchen extract systems.

19.2 If a fire suppression system is incorporatedwithin the system and a volume controldamper is used in an extract spigot, then theduct protection nozzle shall be downstream ofthe damper.

19.3 In accordance with BS 5588, fire dampersshall not be used in the extract system from akitchen as the fire authorities may use theextract fan to clear smoke from the kitchen.

19.4 When fire dampers are required on the supplyside, the following points should beconsidered:

• The damper shall be of a robustconstruction suitable for its application andbe complete with an installation framewhere appropriate.

• A visual or audible alarm to signal damperclosure should be considered if the firedamper is in a remote location.

19.5 Back-draught dampers should not be used asthey are difficult to clean and prevent a natural'stack' effect from the kitchen which wouldotherwise release overnight lingering smells.

19.6 For Ventilated Ceilings volume controldampers shall be installed either in thededicated ductwork or on the plenum boxes.


SECTION 20Fire Suppression

The significant presence of flammable greaseand related particles contained within kitchenextract systems, combined with the possibilityof fire ignition caused by the cookingequipment, creates a hazard level above thatwhich is normally encountered in otherventilation systems.

20.2 Where ventilation systems exhaust greaseladen air and vapour mixtures from a kitchen,the design must provide a level of protection toensure the well being of occupants and firefighting personnel, and limit the damage to theproperty and cooking equipment.

20.3 Whilst the correct maintenance and use ofcooking appliances and ventilation systemswill help prevent potential fires, it is equallyimportant that in the event of a fire it isimmediately detected and extinguished andprevented from spreading to other areas of thebuilding.

20.4 Where a surface fire suppression system isspecified, manufacturers instructions shall befollowed. See Fig 20 for a typical systemlayout.

20.5 Suppression may be achieved by using carbondioxide, chemicals or water. Carbon dioxide isnot generally used due to the high initial costand the lack of cooling capability.

20.6 Chemical Systems

20.6.1 Almost all fire suppression orextinguishing systems use specialchemical agents which provideprotection to the kitchen canopy.Chemically based systems can be in aliquid or dry agent form, but the liquidtype is preferable as a greater level ofcooling to the seat of the fire isprovided and post activation clean-uptime is much quicker.

206.2 These systems are activated eithermanually or automatically in the eventof a fire. Thermal fusible links, whichcan be calibrated for varyingtemperatures, are strategically locatedin the extract air path above thecooking equipment to be protected.

20.6.3 When the fire suppression system isactivated, mains energy supplies suchas gas or electricity serving theappliances, must immediately beautomatically shut off and isolated.

20.6.4 The chemical agent stored within the

20.1

.FUSIBLE LINK DETECTION_Iè4

1. DUCT PROTECTION2. PLENUM PROTECTION3. APPLIANCE PROTECTION4. MANUAL PULL STATION

Fig 20 - Fire Suppression Schematic

43


system is released along thedistribution pipework and dischargedat high velocity through spray nozzlestoward the appliances that requireprotection. When the extinguishingagent comes into contact with hotgreasy surfaces foam is formed whichsuppresses the combustible vapoursand prevents the fire restarting. Thisprocess is called saponification.

20.6.5 Some systems can also be activatedmanually by remote located pullstations normally positioned adjacentto exit doors along escape routes. Thismay be the requirement of the localfire officer or design engineer.

20.7 Water Systems

equipment requiring protection andwhether extraction is by means of acanopy or ventilated ceiling. In allcases, the relevant manufacturer'srecommendations shall be strictlyfollowed as they will advise on nozzlerequirements and if single or multiplesystems are needed.

20.8.2 The following are typical greaseproducing appliances requiringprotection, but it is good practice toseek the advice of the fire suppressionsystem manufacturer or installer.

• Fat fryer, fat cooker

• Griddle

• Salamander and chargrill20.7.1 The principle of this system is almost

identical to the chemical type with thesame design philosophy, installationcharacteristics, mains shut off actionand alarm status. However, the systemcan only be used where there is asprinkler main available.

20.7.2 Special 'sprinkler' style nozzles withsuitable temperature ratings suppliedwith water directly from the mainsprinkler storage system are used tospray a fine water mist discharge ontothe cooking appliances. This systemhas the advantage of a plentiful supplyof water and less 'down-time' after afire as only the area where the fireoccurs is sprayed, whereas with achemical system, the whole canopy isflooded.

20.7.3 The water spray performs a dualfunction when fighting a fire. Thesprayed mist first absorbs the heatgenerated and becomes steam. This inturn displaces the air locally andhence starves the fire of the oxygennecessary for combustion.

20.8 System Design

44

20.8.1 The size and extent of a firesuppression system will depend on thetype of kitchen in question, the type of

• Oven ranges

• Bratt pans

• Pizza ovens

• Char broiler

• Chinese Wok Ranges

• Mesquite Grill

• Rotisserie

• Open Tandoori

20.9 Installation Considerations

20.9.1 A layout drawing of the proposedsystem shall be provided for co-ordination purposes and used duringthe installation works.

20.9.2 An approved fire suppressioncontractor, who is also capable ofpreparing the design and obtaining hisequipment from a single source shallbe appointed. All work shall becarried out in accordance with thetechnical manuals of the equipmentmanufacturer/supplier to ensure thatwarranties are not invalidated.

DW/172 Se'i,'tr:r: for Kitchen Ventilation Systems

20.9.3 For successful and correct operation,the internal temperature shall not fallbelow 0 degC or rise above 54 deg C.

20.9.4 Chemical fire suppressant is analkaline compound, all due care andattention must be taken whenhandling such a substance. Contactwith eyes and skin must be avoidedand COSHH Regulations compliedwith.

20.11.2 Good housekeeping shall be practisedand the following check list issuggested as a general guide:

• Keep the hazard area clean

• Flammable and corrosive cleanersmust be avoided.

• The kitchen exhaust ventilationsystem should always be runningwhen the kitchen is in use.

20.10 Testing and Commissioning

20.10.1 Once the system has been completelyinstalled it shall be commissioned andtested in accordance with themanufacturer's recommendations.

20.1O.2There is normally a requirement totest the release assembly mechanismbefore the gas cartridges are installed.Also individual components like pullstations, mechanically or electricallyactivated valves, electrical switches,pressure switches and the detectionsystem shall be fault tested in-situ.

20.10.3Once the system testing andcommissioning process is complete,acceptance certificates for theinstallation shall be completed forapproval and signature. The customeror end user is then in a position toarrange financial cover with arecognised insurance companyagainst loss or serious damage to thekitchen or the building as a whole.

• Grease Filters should always be inplace when the ventilation systemsare running to minimise greasebuild up in the ductwork andrestrict the spread of flame into theductwork.

• System efficiencybe maintainedmonitoring.

• System tampering should beavoided

• Regular visual checks on thewhole system undertaken by theowner/kitchen head

• For further information refer to theABI/BSRJA document, "Fire RiskAssessment for Catering Extract".

20.11.1 Following handover of the system, itis recommended that a 12 monthmaintenance contract with the firesuppression installation contractor isentered into. The agreement shouldnormally include 12 month guaranteefor provision of spare parts requiredand labour against any installation ormanufacturing fault. Subsequentmaintenance should be required atregular six-monthly intervals withmajor system overhaul every 3 yearsmaximum.

45

should alwaysby regular

20.1 1 Maintenance


SECTION 21Service Distribution Units21.1 Service distribution units are purpose made

self-supporting stainless steel enclosuresdesigned to house the various piped andelectrical services between the point at whichthey enter the kitchen and the cookingappliance. (see Fig 21) They are increasinglyspecified as part of the 'canopy ventilation'package to ensure that interface problems arekept to a minimum, especially where thevertical columns connect to the underside ofthe grease tight extract housing. Ventilatedceilings shall be co-ordinated with verticalcolumns in order to minimise the loss of activeextract filters.

21 .2 Each element shall be sized to suit theparticular services being used in the kitchen, toensure compatibility and be totally integratedwith the installed canopy.

21.3 Each unit normally comprises two columns,one to house the electrical works and one toprovide the piped services such as hot and coldwater, drinking water, steam, condense, waste,gas and compressed air. The vertical columnshould have adjustable plinths to accommodateuneven or sloping floor finishes.

46

21 .4 For columns containing gas services aventilation grille is required at high and lowlevel.

21 .5 Controls for the fire suppression system arenormally housed within the electrical columnand if a water-wash system is fitted, then thecontrol panel should be housed within thepipework riser.

21.6 The horizontal raceway or spine runningbetween the columns is the section of thedistribution unit from which the connections tothe cooking equipment are made. To preventdamage from mobile catering equipment a'bumper' rail should be considered, whichshould be either be fabricated in stainless steelor preferably supplied in rubber.

21.7 The units, which can be either wall-mounted orisland type, provide for single pointconnections for all site services. Space can beallocated to allow for future expansion andaccess is provided to the interior of thedistribution unit by either hinged or removablepanels with quick release fixings.

21 .8 All pipework connections between the spineand the cooking equipment should be made byusing quick-release or proprietary connections.It is essential that integral services are carriedout by competent tradesmen and in accordancewith the relevant codes of practice.

Fig 21 - Typical Services Distribution Unit


21 .9 Mains isolators, circuit breakers, sockets,plugs and internal wiring can all be fitted atmanufacturer's works to minimisecoordination problems at site. Combined gasand electricity 'knock-off' buttons shall beprovided on the end of each vertical column.

21 .10 When the integral services are factory fitted,then the supplier shall be responsible fortesting and certification and for the provisionof earth bonding.

21 .1 1 Service distribution units can be supplied as asimple stainless steel housing for theinstallation of plumbing, electrical, and fireprotection services by others or as a fully fittedpre-fabricated system complete with allmechanical and electrical services.

SECTION 22Odour Control22.1 Odour pollution problems are particularly

difficult to solve, as the level of odourproduced can vary dependant upon thecooking process involved, such as the cookingcycle, the position of the discharge and thewind speed and direction. All systems shouldbe offered therefore on the basis of odourreduction rather than elimination.

22.2 Whilst conventional systems should normallydischarge at least im above roof eaves level,with an effective odour control systeminstalled, it should be possible for thedischarge to be made at a low level.

22.3 When low level discharge is considered, thefollowing shall be taken into consideration:

• Whether the discharge is into confinedareas such as courtyards.

• Whether it is positioned too close to airintake systems.

• The discharge velocity.

• The height above external ground level.

• Approval has been obtained from the LocalAuthority to comply with BuildingRegultaions.

22.4 Molecules of cooking odours are generated bythe combustion of animal and vegetable matterwhich results in a particulate and gaseousmixture. The particulate phase comprises smallfood deposits and hydrocarbons or smoke, theconcentration level of which will vary with thetype of cooking. Whilst smoke can be reducedby removing the particulate, it is the gaseous orvapour phase which contains the odour andtherefore needs to be treated.

22.5 These molecules are too small to be removedby filtration alone, the solution is found byselecting a combination of equipment from thefollowing options, the extent of which willvary according to the problem.

47


48

• A basic filtration unit for use with lowodour problems may be supplied containingthree stages of progressively more efficientfilters. Disposable pleated filters precede a95% efficient bag filter, followed by a 99%efficient absolute filter. This system willnot deal with the gaseous phase but isintended to reduce the visible particulate,i.e.smoke, to a maximum level of 0.3microns and all components should to bemonitored closely and replaced whenrequired. This system should only be usedwhere a high efficiency canopy filtrationhas been installed such as water wash ormist system.

• An alternative to the 3-stage disposablefiltration, as described above, is theElectrostatic Precipitator and, like thedisposable filters, is only intended toremove visible smoke particles from theexhaust airstream rather than the gaseousphase that tends, to account for most of thecooking odours. Therefore, this should notbe considered as a prime source of odourcontrol. Where installed, panel filtersshould be fitted both upstream anddownstream of the electrostatic filter toprovide some protection from largercontaminant that may have passed throughthe grease filters. It should be noted thatelectrostatic filters become ineffective attemperatures over 60°C and are not suitablefor relative humidity levels above 75%.

• Activated carbon provides an effectivemedium for eliminating odour but can beeasily rendered disfunctional through theimpregnation of contaminants within itsporous granule composition. Grease is theworst such contaminant; it is thereforeessential to protect the carbon cells withmulti-stage pre-filters upstream of thesystem. The maximum operating efficiencyof carbon filters is very much dependantupon them working within definedconditions - an air temperature notexceeding 40 deg C and a maximumrelative humidity of 60%. To maximise bestuse of carbon cells a strict maintenanceregime for changing all filters shall beadopted. Local Authority approval shall be

sought before carbon filters are used in anykitchen extract system.

• As an alternative to using activated carbon,odour absorbing granular chemicals such aspotassium permanganate or metal iron saltsmay be used. The chemical oxidises theodorous gases into a solid form and retainsthem. However, compliance with LocalAuthority regulations shall be ensuredbefore the use of these systems, as they areprone to the same limitations that exist withactivated carbon.

• Providing staged pre-filters are installed,odour neutralising liquid spray systems canbe injected upstream of the extract fan. Thecooking odours are neutralised by starvingthe odour molecules of oxygen. This makesa recirculation system possible for electriccooking equipment whereby, after passingthrough the neutralising section the air iscooled to remove excess heat, 20% isdischarged at low level as clean air toatmosphere and the remaining 80% can bereintroduced into the kitchen as make-upair.

• Special ultra violet lights can be installed,either within the filter housing, ventilatedceiling plenum or as a remote unit, whichgenerate trace quantities of ozone. In thepresence of ultra violet light, the ozonereacts with the organic compounds in thefat, odour by photolysis and ozonolysis toleave an end product of primarily onlycarbon dioxide and water.

22.6 Whatever type of pollution control isimplemented, the increase in system resistanceshall be included when selecting the fan.

DW/1 72 Sveiz for Kitchen Ventilation Systems

SECTION 23Heat Recovery23.1 Whilst the initial capital cost may be high, the

use of heat recovery for its energy efficiencyand conservation value is becoming anincreasingly important design feature. If aspecific payback period has to be achieved.then calculations should be made to evaluatean economic timescale.

23.2 There are two main methods of recovering heatin a kitchen environment:

Air to Air - The removal of heat from theexhaust air which is transferred to theincoming supply air.

Air to Water - The removal of heat from theexhaust air which is transferred to a domesticwater supply.

23.3 The selection of waste heat recovery plantshould be from the following types:

• Heat Recuperator - Plate heat exchangers ofthe 'cross flow' type having adjacent platesforming narrow ducts for alternate supplyand exhaust air to pass. Heat is transferredthrough the plates with no cross-contamination between the air passages (60- 80% efficient). A face and by-pass dampershall always be included to allow fresh air toby-pass the recuperator when furtherheating to the room being served is nolonger required.

• Run Around Coils - Coils can be fittedacross the extract and supply ducts wherebythe higher temperature of the extract airtransfer heat to a water/ethylene glycol mixin the interconnecting pipework (50 - 60%

efficient). A circulating pump andpressurisation provisions are required forthe pipework system.

• Rotary Recuperator - (Heat Wheel) -Consists of a revolving cylinder dividedinto segments packed with coarsely-knittedmetal mesh. As the cylinder rotates, the

mesh absorbs heat from the exhaust andalternately transfers it to the supply air.(Approx 80% efficient)

• Heat Pipes - These are self contained unitsoperating on a vaporising / condensingcycle. Hot exhaust air causes fluid in thelower part of the pipes to evaporate andtransfer heat to the supply air passing overthe upper section. The vapour cools andcondenses for the cycle to start again(approx 55 to 70% efficient).

It should be noted that, with the exception ofthe run around coils, these arrangementsrequire the supply and extract ductwork to berun in close proximity.

23.4 It is important that whichever heat recoveryoption is incorporated. it shall be protectedfrom grease build-up by the installation of airfilters upstream of the equipment.

—49


SECTION 24Testing andCommissioning24.1 This section covers the requirements for

testing the completed installation. Theresponsibility for this will depend upon theparticular contract provisions.

24.2 The following information shall be recordedduring the testing and commissioning process.The supply and extract systems shall beoperating simultaneously when commissioningis carried out.

• The velocity through the grease filters andgrilles.

• The velocity in the ductwork and at the bellmouths.

• The supply and extract flow rates.

• Ambient and air temperatures in theductwork.

• The total pressure drop for the system.

• Starting and running currents used by thefan(s).

• Illumination levels.

• Sound levels in the kitchen and at the pointof discharge.

24.3 The manufacturer's data shall be consulted toestablish the technical information on thefilters and the three most important items are:

50

• Flow rate for each filter size used.

• Recommended velocity passing through thefilter.

• The pressure drop across the filter.

• Whilst the grease extraction rate may bestated, this is not relevant to testing.

24.4 The air velocity passing through the filter orgrille shall be first determined by using ananemometer. This figure is then multiplied bythe face area of the filter or grille to arrive atthe extract flow rate. The flow rate througheach filter is then added to give the totalquantity of air being extracted through eachcanopy. This is then checked to ensure that thedesign conditions are being achieved.

24.5 Manometers and pitot tubes should be used todetermine the air volume flow rates throughthe ductwork, but care shall be taken to ensurethat readings are taken in areas where there islittle turbulence such as in straight runs ofductwork so that the results do not becomedistorted.

24.6 Noise levels shall be checked to ensure that amaximum internal noise level of NR4O-50 isnot exceeded and the maximum level at thepoint of discharge of the extract should notincrease the overall ambient noise level bymore than 2db(A) on completion of theinstallation. The use of vertical discharge, slowrunning fans and low duct velocities shouldhelp to achieve these levels.

24.7 Each installed canopy or ventilated ceilingshall be fitted with a 'rating plate'. Forcanopies this shall be on the inside left end ofeach canopy on which the followinginformation shall be recorded.

• Name, address and telephone number of thecanopy supplier.

• Date of installation and canopy serialnumber.

• Design extract and supply flow rates.

• Design pressure drop across the canopywhen measured at the extract spigot.

• Similar information for any supply systemfitted to the canopy.

This information will be invaluable at a futuredate when upgrades to either the cookingequipment, canopy or ventilated ceiling arebeing considered.


24.8 Further advice on commissioning may be SECTION 25obtained from the CIBSE and BSRIAapplication manuals (see Appendix F).

Cleaning andMaintenance25.1 For the efficient operation of a kitchen

ventilation system the following maintenanceprocedures shall be implemented. For detailedrequirements refer to the HVCA publicationTRII9 Guide to Good Practice - Cleanliness ofVentilation Systems.

25.2 The interval between visual inspections ofelements of the system incorporated in thekitchen should be determined by the particularcooking process, but shall never be more thanonce a week. All metal surfaces shall bechecked to ensure that there is no accumulationof grease or dirt and that there is no surfacedamage.

25.3 Checks shall be made to ensure that thestiffening channel is free from debris and thatinstalled lights are working. Filters shall beeasily removable and the inside of all housingsand grease collection drawers, where fitted,should be cleaned regularly.

25.4 Typically the minimum cleaning period forbaffle type self draining filters and collectiondrawers is once each week, for secondary meshfilters at least twice each week. By the natureof their construction, secondary mesh typefilters have a limited life and shall be replacedwhen necessary. However, specificmanufacturers' information should becomplied with.

25.5 It should be considered that the areaimmediately above any cooking appliances,including extract plenums, pose the greatestrisk of the ignition of any accumulated grease.Extract plenums for both canopies andventilated ceilings are considered as a specificsection of the grease extract system; in thecourse of a scheduled specialist duct clean,extract plenums should be included by them aspart of the clean. Frequency of cleaning isdefined in TRI19 Guide to Good Practice —Cleanliness of Ventilation Systems.

51


25.6 All metal surfaces shall be cleaned with asuitable metal cleaner. Caustic or abrasivematerials shall not be used as they will scratchthe surface which will encourage the growth ofharmful bacteria. Compliance with theappropriate COSHH Regulations must beensured with all cleaning materials.

25.7 Where the canopy/ventilated ceiling containsremovable filters or cartridges the filtermanufacturers cleaning instructions shall befollowed. They shall only be removed forcleaning after the system has been shut-downto avoid grease contaminated air depositing onthe internal surfaces of the ductwork andtherefore causing a future potential fire hazard.Extreme caution shall be exercised if removingfilters from above hot appliances. In generalmost filters are designed to fit inside, and beput through the cleaning cycle of mostcommercial dishwashers. In heavy dutyapplications decarbonising and/or soak tanksmay prove to be a more effective cleaningmethod, whilst in lighter applications handwashing in hot water using a standard dilutionof a proprietary dc-greasing agent or washing-up liquid may be adequate.

25.8 When excessive residue remains followingroutine cleaning, then a heavy duty detergentor proprietary stainless steel cleaner may berequired.

25.9 Where a cartridge system has been installed,then the plenum forms an integral part of thedesign, it shall be cleaned at the same time asthe cartridge. The efficiency of these systemswill depend upon the extracted grease that iscollected in the plenum being removed byregular cleaning at least twice a week.

25.10 Where canopies/ventilated ceilings areprovided with an integral make-up air system,the airways and supply filters should be keptclean to maintain airflow. Dirt accumulationand blockages will increase resistance andaffect the system performance.

25.1 1 In addition to daily cleaning and a weeklymaintenance programme, periodic 'deephygiene cleaning' shall be undertaken by aspecialist contractor to ensure that the foodenvironment maintains a safe and clean

52

standard. Due to the fact that standardtechniques and chemicals used for dailycleaning do not remove the accumulations ofcarbon fat grease deposits and limescale inmany normally inaccessible areas, allaccessible main ductwork runs and branches,including fitted equipment shall be inspectedand cleaned. To assist in the inspection ofductwork, cleaning doors shall be installed atregular intervals (see section 15.13).

25.12 Manufacturers shall be consulted formaintenance procedures for proprietary plantand fire suppression systems where fitted.

25.13 Where grilles are fitted, they shall have easilyremovable cores to facilitate cleaning.

25.14 Failure to implement these maintenanceprocedures, will cause an accumulation ofgrease and dirt in the ventilation system whichwill promote the growth of harmful bacteria,increase the risk of fire, reduce airflow throughthe kitchen and impair the overall systemperformance and efficiency (see section15.12).

DW/l 72 Specification for Kitchen Ventilation Systems

Appendix AFilter ClassificationsAl Table 18 is included to show the filter

classifications based on the EuropeanNormalisation standard (EN 779) and theirrelation to the old EU rating (Eurovent 4/5).

A2 The EN standard is more stringent than the oldEurovent classification, and was adoptedthroughout Europe from January 1994. Thenew British Standard reference becomes BSEN 779 and the main changes are:

• Filters with an initial dust spot efficiencybelow 20% are classified as 'arrestancefilters' (formerly 'coarse G filters') andhave a 'G' rating of from Gi - G4 with a testpressure of 250 pascals.

• Filters with an initial dust spot efficiencyabove 20% and an average dust spotefficiency above 40%, are classified as'efficiency filters' (formerly 'fine F filters')and have an 'F' rating of F5 - F9.

HighEfficiencyParticulateAir Filter

EN1O (EU)EN11 (EU)EN12 (EU)EN13 (EU)

H10Hi!H12H13

85%95%

99.5%99.95%

Table 18- Filter Types and Classifications

Type EN 779 New Class Efficiency Test Standard

CoarseDustFilter

FineDustFilter

EN1(EU)EN 2 (EU)EN 3 (EU)EN 4 (EU)

EN5 (EU)EN6 (EU)EN7 (EU)EN8 (EU)EN9 (EU)

GiG2G3G4

F5F6F7F8F9

65%65% - 80%80%-90%

90%

40% - 60%60% - 80%80% - 90%90% - 95%

95%

GravametricArrestance

Dust SpotEfficiency

D.O.P.Efficiency

53

DW/1 72 Specitwation for Kitchen Ventilation Systems

APPENDIX BConversion FactorsLENGTHFROM TO MULTIPLY BYFeet Metres 0.3048Metres Feet 3.28 1Inches Millimetres 25.4Millimetres Inches 0.0394

FLOW RATEFROM TO MULTIPLY BYcfm m3/s 0.0004719m3/s cfm 2119cfm litres/sec 0.4719litres/sec cfm 2.119cfmlft m3/s per m 0.00 1548m3/s per m cfm / ft 646fm mIs 0.00508mis fpm 196.85

PRESSUREFROM TO MULTIPLY BYInches wg Pascals 249Pascals Inches wg 0.00402

WEIGHTFROM TO MULTIPLY BYPounds Kilograms 0.4536Kilograms Pounds 2.2046

POWERFROM TO MULTIPLY BY

Horsepower Kilowatts 0.746Kilowatts Horsepower 1.34

CAPACITYFROM TO MULTIPLY BYGallons Litres 4.546Litres Gallons 0.22US Gallons Litres 3.785Litres US Gallons 0.264

HEATFROM TO MULTIPLY BYBtu/Hr Watts 0.2931Watts Btu/Hr 3.412

TEMPERATURETo Convert Deg C to Deg F: x 1.8 + 32To Convert Deg F to Deg C: -32 x 0.556

54

An index of protection known as an IPrating, is anindication of the degree of protection that is providedby the enclosure to a piece of electrical equipment.There are two numbers in an IP rating, the first of whichindicates the protection against the ingress of solids andthe second its protection against the ingress of liquids.

No protection

Protection against solidbodies larger than 50mm

Protection against solidbodies larger than 12mm.

Protection against solidbodies larger than 2.5mm.

Protection against solidbodies larger than 1mm.

Protection against dust(no harmful deposits).

Complete protection againstdust.

7

No protection

Protection against verticallyfalling drops of water

Protection against drops of rainwater at 1 Sdeg from the vertical.

Protection against drops of rainwater at 6Odeg from the vertical.

Protection against projections ofwater from all directions.

Protection against jets of waterfrom all directions.

Protection against jets of watersimilar to heavy seas.

Protection against the effects ofimmersion.

8

These indices are provided in accordance with 1EC529, BS5490 and D1N400 50.

Protection against prolongedeffects of immersion underpressure.

55

Appendix CIndices of Protection


First Figure

IP No

Second Figure

Protection IP No Protection

0

1

2

3

4

5

6

1

2

3

4

5

6


Appendix DFire Rated and SmokeExtract DuctworkDl When new kitchens are planned, it is important

that the Local Authority Building ControlOfficer is consulted to ensure compliance withthe Building Regulations and the FirePrecautions Act. The interpretation of thesestatutes may vary according to the LocalAuthority and early consultation will clarifyany special requirements with regard to firerated and smoke extract ductwork. A writtenrecord of all advice given should be recordedand retained.

D2 The main fire hazard arises from theoverheating of oils and fats in fryingequipment and the failure of temperaturemonitoring devices. Safe cooking in fats andoils generally takes place below 200 degC.Flammable vapours are given off at 200 - 230degC and spontaneous ignition occurs at 310 -360 degC. The timescale in moving from a safeto dangerous condition is quite short and theflash point of oil is reduced by repeatedoxidation caused through repeated use. Furtheradvice is available from the Fire ProtectionAssociation's guides to safe practice.

D3 Careless procedures while cooking, poorplanning of the kitchen layout, failure tomaintain equipment and poor waste disposalprocedures all lead to an increased risk of fire.

D4 The mechanical ventilation to a kitchen,although essential, can exacerbate theconsequences of a fire and it must be purposedesigned to contain damage or injury that mayoccur from smoke and toxicity. The systemmust be separate from and independent of allother systems in the building.

D5 Fire involving a deep fat fryer and itsextraction system will develop rapidly,produce considerable quantities of heat andsmoke, it may reach a stage of such violencethat it cannot be contained within the kitchenarea. Due to the fact that equipment damagemay be significant and disruption to normal

service may last for days, automaticallyoperated fire suppression systems arerecommended for cooking equipmentinvolving the use of oils and fats where thecapacity exceeds 10 litres, whether as a singleappliance or a combination of adjacentappliances.

The extract from equipment using oils or fatsshould be as short as possible and discharge toatmosphere directly above the equipment itserves. Where this is not possible, the designshall comply with the requirements of BS 5588where compartmentation is breached. Thiscurrently requires that in all non-domestickitchens:

• Ductwork carrying polluted air must haveseparate and independent extraction with norecirculation.

• No fire dampers are to be installed in theextract ductwork.

• If immediate discharge to atmosphere is notpossible and the ductwork needs to passthrough an adjacent fire compartment, thenthe ductwork system must be satisfactorilyconstructed and supported in order tomaintain the required level of fireseparation between compartments.

• It is essential that the installed systemcomplies with BS 476. Fire inside (Type B)is rated for stability, integrity and insulationfor the same period of time as thecompartment through which the ductpasses. In addition the duct shall also betested for fire outside (Type A) with theadditional requirement that the internalsurface of the ductwork within thecompartment shall also meet the insulationcriteria.

• Where canopies are installed on separatefloors, then they shall be served by separateextraction systems

There are three ways of protecting ductworkrecommended in BS 5588 wherecompartmentation is breached. These aredefined in DW/144 Appendix D andsummarised as follows:

D6

D7

56


Method I covers the provision of fire damperslocated where the duct penetrates fire resistingcompartments such as walls or floors. Theductwork itself is not fire resistant but the fireis not transferred through the system. Due tothe fact that fire dampers are not permitted inkitchen extract systems, this method shall notbe used.

Method 2 is where the duct runs within a firerated service duct from the kitchen directly tothe outside of the building. The service ductforms a compartment known as a protectedshaft which must not contain any other servicesor have fire dampers fitted. This method maybe used.

Method 3 is where the duct is in itself fireresistant and this is achieved by either theductwork being constructed from fire ratedmaterials, or where a protective material isapplied to suitably constructed and supportedconventional ductwork. Care shall be takenwhen providing extract ductwork which isfabricated from fire rated boards, as theboarding itself may absorb grease and beincapable of being cleaned.

D8 In all cases where fire rated ductwork issupplied, particular care shall be taken with thedesign of both fixings and supports to ensurethat they are suitable for the specified durationof fire protection . If a fire originates in or istransferred to the ductwork system, then it mayspread beyond its original location due to heatradiation or direct contact between theductwork material and an adjacent combustiblematerial. The ductwork route shall thereforetake account of this risk, have a minimumseparation of 500mm between uninsulatedductwork and any combustible material.

D9 For both fire rated and smoke extractductwork, the periods of stability, integrity andinsulation to which the ductwork isconstructed, must be the same as the rating ofthe compartment that is being breached. Theconstruction of fire rated ductwork, whichshall comply with BS 476, can either beprovided by specialist companies producingproprietary systems, or by the addition of fireinsulating materials to suitably constructed andsupported ductwork. General purposeductwork cannot be converted into a fire rated

system unless the materials and construction ofthe whole system is in accordance with therequirements of BS 3476.

D1O The fire rating of kitchen extract ductworkshall also include insulation, to ensure that afire outside the duct does not cause any greasethat has built up on the inside of the duct toignite. The insulation shall ensure thattemperatures on the outside of the duct shallnot exceed 140 degC average above ambient atany one point.

The requirements for smoke extract ductworkwill vary from Authority to Authority and willgenerally depend upon the size of the building,the area of openable windows, the number ofoccupants and whether the area to be ventilatedis located in the basement. With the use ofmotorised volume control dampers, it may bepossible to use either the supply or extractductwork as smoke extract ductwork providedthat it is constructed to the same standards asfire rated ductwork with additional care takenover the selection of the plant. Where thesupply ductwork is used as smoke extract, thenany filters installed will need to be by-passed.Smoke extract ductwork must also beconstructed so that in the event of a fire, it willretain at least 75% of its design cross sectionalarea.

Dl 2 A natural make-up air system shall be installedto provide the equivalent amount of air as thedesign volume for the smoke extract systemand the discharge shall be located to avoid anyrisk of recirculation of smoke back into thebuilding.

Dl 3 Smoke extract fans need to be located within Ihour fire rated compartments and motors mustbe rated to a minimum of 300degC for 1 hour(varies with Local Authority). Wiring shall beinstalled within protected circuits with powersupplied by a back-up generator in the event offailure of the main source of power.

D14 Further information on fire rated and smokeextract ductwork can be found in theAssociation of Specialist Fire Protection'spublication "Fire Rated and Smoke OutletDuctwork - An Industry Guide to Design andInstallation" (aka the Blue Book).

DII

57

DWII 72 Specification for Kitchen Ventilation Systems

Appendix EAir Conditioned KitchensEl Section 5 showed that the two main sources of

heat into a kitchen space comprised:Radiant - 35% (Qrad)

and Convective - 65% (Qconv)

E2 For estimating the air conditioning loadhowever, it is also necessary to consider otherheat gains such as those caused by lighting,solar, and people - (Qgen).

E3 The amount of Qrad and Qconv will vary withthe type of cooking equipment and the extractflow rate through the hood shall be equal to orhigher than the convection flow from theappliances to ensure that the Qconv and theassociated impurities are captured by thecanopy (see fig 22).

E4 Depending on the efficiency of the extractionsystem, there may also be an amount ofconvective heat that is not captured by thecanopy (Qesc), together with the radiant heat(Qrad) and general gains (Qgen), can betreated by means of an air conditioning system(see fig 23).

E5 An inefficient canopy with a low captureefficiency (Heff) will therefore have asignificant effect on the air conditioning load,and the relationship between canopy efficiencyand the amount of convective heat not beingcaptured can therefore be expressed as:

E6 Once these variables are established, the totalheat load (Qtot) can be calculated by using thefollowing energy balance equation:

Qtot = Sensible Heat (Qsens)+Latent Heat (Qlat)

It should be noted that the latent heat elementis normally insignificant in relation to the totalheat gain in a kitchen environment and if airconditioning is provided, then it is usually inthe form of comfort cooling as opposed to totalcontrol of both temperature and humidity, asthe capacity and cost of the plant required maynot be in proportion to the benefit derived.

E7 However, when the total load is required for airconditioning assessment, then each elementcan be calculated using the energy balanceequation shown in Fig. 24.

Fig 23 - Pattern of Heat Gain in Kitchen

Qesc = (1-Hem x Qconv.

QRAD35%

Fig 22 - Proportion ofAppliance Heat Emission

QRAD35%

58

E8 Where the amount of supply air requiredexceeds that which may be supplied throughthe canopy, then additional grilles and diffusersshould be provided as part of the main HVACsystem and positioned to provide optimumcomfort cooling for the staff.

E9 To summarise, both the extract flow rate andthe supply air volume shall be calculated toensure that both the convective and radiantheat generated is removed to maintain anacceptable level of comfort for the occupantsof the kitchen.(NB - air conditioning of the kitchen will notremove the direct discomfort caused by radiantheat emanating from the cooking equipment)

Fig 24 - Heat gain calculation

DWII 72 Specification for Kitchen Ventilation Systems

59

Sensible Heat Qsens=P x cpm x At x qs (kW)Latent Heat Qlat = P x Hfg x Ag x qs (kW)(specific latent heat of evaporating heating fromtables for properties of water and steam)

where:Qsens = Qrad + Qesc + Qgen. (kW)

(where Qesc = (1-Heft) x Qconv)

Qiat = latent heat given off by occupants etc.(kW)P = density of air. (kg/m3)Cp = specific heat capacity of air. (kj/kg degC)A = temperature difference between supply

airTs) and room condition (Tr) (deg C)(normally 8 - 10 degC)(Printers note A = Delta)

Ag = moisture content difference betweensupplyair (Gs) and room condition (Gr) (kg/kg)(Printers note -A = Delta)

qs = supply air flow rate (m3/s)Hfg = latent heat energy of moisture at room

conditions (kjlkg)(latent heat of vaporisation from steamtables)

DW/1 72 Spccijication for Kitchen Ventilation Systems

Appendix F Chartered Institution of Building ServicesEngineers (CIBSE) Tel: 0208 675 5211CIBSE Guide B: Installation and equipment data

Bibliography (1986)

Association for Specialist Fire Protection (ASFP) ISBN 0 900953 30 6. Section B2.B3: Ventilation and airTel: 01252 739142 conditioning (requirements and systems, equipmentFire Rated and Smoke Outlet Ductwork: An Industry and control).

Guide to Design and Installation (Blue Book)CIBSE Code for Lighting (2002)

Building Services Research and Information ISBN 07506563 79

Association (BSRIA) Tel: 01344 426511Application Guide LB65/94: Ventilation of Kitchens CIBSE Commissioning Code A (1996) Air Distribution

Systems ISBN 0900953 73 X

Commissioning of Fire Systems in Buildings (1994)ISBN 086022 2314 Technical Memorandum 13 (2002) Minimising the risk

of Legionnaires Disease ISBN 1 903287 23 5

Fire Risk Assessment - Catering Extract VentilationISBN 056022 588 7 CIBSE Guide B2 (2001): Ventilation and air

conditioning ISBN 1903287 16 2 (requirements and

British Standards Institution (BSI) Tel: 0208 996 systems equipment and control)9000BS 476: Fire Tests on Building Materials HMSO Tel: 020 7276 5203

Fire Precautions (Workplace) Regulations 1997 NoPart 24: 1987 Fire Resistance of Ventilations Ducts 1840

BS 4142: 1997 Rating of Industrial Noise Affecting Food Safety (General Food Hygiene) Regulations 1995Mixed Residential and Industrial ISBN 0110 532279Areas

The Gas (Installation and Use) Regulations 1998 (S.I.BS 5440: Part 1 Specification for Installation of flues 1998 No 2451)

BS 5440: Part 2 Specification for installation of gas HSC HSE Books Tel: 01787 881165appliances

Legionnaires Disease - Approved Code of Practice andguidance L8

BS 5588: Fire Precautions in the Design and ISBN 0717617726Part 9 1999 Construction of Buildings

Workplace (Health, Safety and Welfare) RegulationsB5 5720: 1979 Code of Practice for Mechanical 1992. Approved Code of Practice and Guidance L24.

Ventilating and Air Conditioning in ISBN 0717604136

BuildingsHSE Information Sheet: Ventilation of kitchens in

BS 6173 Installation of gas-fired catering catering establishments. Catering Sheet No 10

appliances for use in all types ofcatering establishments (2nd and 3rdfamily gases)

NOTE: The European/British Standards and other documents listed above are those available at the date ofpublication. Users should ensure that they consult the latest version.

60

Heating and Ventilating Contractors' AssociationTel: 020 7313 4900

1998 - Specification for Sheet MetalDuctwork iSBN 0-903788-27-4

DW/1 72 SpecifIcc!tioi! for Kitchen Ventilation Systems

2005 - Guide to Good Practice -Cleanliness of Ventilation SystemsISBN 0-903783-26-6

2000 - Practical Guide to AVLeakageTrainingISBN 0-903783-30-4

JS2 1/CD-Rom - COSHH Manual 1 Advice oncompliance with the Regulations

Joint Hospitality Industry Congress (JHIC) Tel: 01582424200

Catering Industry Guide to Food Safety (General FoodHygiene) Regulations 1995 ISBN 0-900-103-00-0

Loss Prevention Council (LPC) Tel: 0208 207 2345

1996 16A-

16B -

LPS 1263 -

Fish and chip FryingRangesCooking Equipment (other than fishand chip frying ranges)

REQUIREMENTS FOR THE LPCBAPPROVAL AND LISTING OFTHE FIRE PERFORMANCE OFKITCHEN EXTRACT SYSTEMS

Office of the Deputy Prime Minister

The Building Regulator 2000Approved Document B ISBN 0-1 1-75391 1-2

DW/144 -

TR/19/1 -

DQ/143 -

61

DW/1 72 Speckation for Kitchen Ventilation Systems

NOTES

62


NOTES

63

DW/1 72 Speckationfor Kitchen Ventilation Systems

NOTES

64

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