Boilers are pressure vessels designed to heat water or produce steam using controlled combustion of fuel such as natural gas, oil, or electricity. There are two primary types of boilers - firetube boilers where hot gases pass through tubes surrounded by water, and watertube boilers where water passes through tubes surrounded by hot gases. Boilers provide an effective method for heating buildings but require regular maintenance and fuel costs can be high. Safety is also an important consideration given the high pressures and temperatures involved.

1. BOILERS
Boilers are pressure vessels designed to heat water or produce steam, which can then be used
to provide space heating and/or service water heating to a building. In most commercial
building heating applications, the heating source in the boiler is a natural gas fired burner. Oil
fired burners and electric resistance heaters can be used as well. Steam is preferred over hot
water in some applications, including absorption cooling, kitchens, laundries, sterilizers, and
steam driven equipment.
Boilers have several strengths that have made them a common feature of buildings. They have
a long life, can achieve efficiencies up to 95% or greater, provide an effective method of heating
a building, and in the case of steam systems, require little or no pumping energy. However, fuel
costs can be considerable, regular maintenance is required, and if maintenance is delayed,
repair can be costly.
How Boilers Work
Both gas andoil firedboilersuse controlledcombustionof the fuel toheatwater.The keyboiler
componentsinvolvedinthisprocessare the burner,combustionchamber,heatexchanger,andcontrols.
The burnermixesthe fuel andoxygentogetherand,withthe assistance of anignitiondevice,providesa
platformforcombustion.Thiscombustiontakesplace in the combustionchamber,andthe heatthatit
generatesistransferredtothe waterthroughthe heatexchanger.Controlsregulate the ignition,burner
firingrate,fuel supply,airsupply,exhaustdraft,watertemperature,steampressure,andboiler
pressure.
Hot waterproducedbya boilerispumpedthroughpipesanddeliveredtoequipmentthroughoutthe
building,whichcaninclude hotwatercoilsinairhandlingunits,service hotwaterheatingequipment,
and terminal units.Steamboilersproduce steamthatflowsthroughpipesfromareasof highpressure to
areas of lowpressure,unaidedbyanexternal energysource suchasa pump.Steamutilizedforheating
can be directlyutilizedbysteamusingequipmentorcan provide heatthrougha heatexchangerthat
supplieshotwatertothe equipment.
The discussionof differenttypesof boilers,below,providesmore detail onthe designsof specificboiler
systems.
Types of Boilers

2. Boilersare classifiedintodifferenttypesbasedontheirworkingpressureandtemperature,fueltype,
draft method,size andcapacity,andwhethertheycondensethe watervaporinthe combustiongases.
Boilersare alsosometimesdescribedbytheirkeycomponents,suchasheatexchangermaterialsortube
design.These othercharacteristicsare discussedinthe followingsectiononKeyComponentsof Boilers.
Two primarytypesof boilersincludeFiretube andWatertube boilers.InaFiretube boiler,hotgasesof
combustionflowthroughaseriesof tubessurroundedbywater.Alternatively,inaWatertube boiler,
waterflowsinthe inside of the tubesandthe hot gasesfromcombustionflow aroundthe outside of the
tubes..
Firetube boilersare more commonlyavailableforlow pressure steamorhotwaterapplications,andare
available insizesrangingfrom500,000 to 75,000,000 BTU input(5).Watertube boilersare primarily
usedinhigherpressure steamapplicationsandare usedextensivelyforcomfortheatingapplications.
Theytypicallyrange insize from500,000 to more than 20,000,000 BTU input(5).
Cast ironsectional boilers(figure 3) are anothertype of boilercommonlyusedincommercial space
heatingapplications.These typesof boilersdon’tuse tubes.Instead,they’re builtupfromcast iron
sectionsthathave waterand combustiongaspassages.The ironcastingsare boltedtogether,similarto
an oldsteamradiator.The sectionsare sealedtogetherbygaskets.They’re available forproducing
steamor hot water,andare available insizesrangingfrom35,000 to 14,000,000 BTU input(2).
Cast ironsectional boilersare advantageousbecausetheycanbe assembledonsite,allowingthemtobe
transportedthroughdoorsand smalleropenings.Theirmaindisadvantageisthatbecause the sections
are sealedtogetherwithgaskets,theyare prone toleakage asthe gasketsage and are attackedby
boilertreatmentchemicals.
WorkingPressure andTemperature
Boilersare classifiedaseitherlowpressureorhighpressure andare constructedto meetASME Boiler
and Pressure Vessel Code requirements.Low-pressure boilersare limitedtoamaximumworking
pressure of 15 psig(pound-forcepersquare inchgauge) forsteamand160 psigfor hot water(2). Most
boilersusedinHVACapplicationsare low-pressure boilers.High-pressure boilersare constructedto
operate above the limitssetforlow-pressureboilers,andare typicallyusedforpowergeneration.
Operatingwatertemperaturesforhotwaterboilersare limitedto250o F
Fuel Type
In commercial buildings,natural gasisthe most commonboilerfuel,because itisusuallyreadily
available,burnscleanly,andistypicallylessexpensive thanoil orelectricity.Some boilersare designed
to burn more thanone fuel (typicallynatural gasandfuel oil).Dual fuelboilersprovide the operator
withfuel redundancyinthe eventof afuel supplyinterruption.Theyalsoallow the customertoutilize
the fuel oil during“peaktime”ratesfornatural gas. In timeswhenthe ratesfornatural gas are greater
than the alternate fuel,thiscanreduce fuel costsbyusingthe cheaperalternate fuel andlimitingnatural
gas use to occur onlyduring“off peak”times.
Electricboilersare usedinfacilitieswithrequirementsforasmall amountof steamor where natural gas
isnot available.Electricboilersare knownforbeingclean,quiet,andeasytoinstall,andcompact.The
lack of combustionresultsinreducedcomplexityindesignandoperationandlessmaintenance.Heating
elementsare easilyreplacedif theyfail.These typesof boilerscanbe usedtoproduce low or high
pressure steamorwater,and may be goodalternativesforcustomerswhoare restrictedbyemissions

3. regulations.Sizesrange from30,000 to 11,000,000 BTU inputwithoverall efficiencygenerallyinthe
range of 92% to 96% (2). Sizeand Capacity
Modular Boilersare small insize andcapacityand are oftenintendedtoreplace alarge single boilerwith
several small boilers.Thesemodularboilerscaneasilyfitthroughastandarddoorway,and be
transportedinelevatorsandstairways.The unitscanbe arrangedina varietyof configurationstoutilize
limitedspace orto accommodate newequipment.Modularboilerscanbe stagedto efficiently meetthe
demandof the heatingload.
Key Components of Boilers
The keyelementsof aboilerinclude the burner,combustionchamber,heatexchanger,exhauststack,
and controls.Boileraccessoriesincludingthe flue gaseconomizerare alsocommonlyusedasan
effectivemethodtorecoverheatfromaboilerandwill be discussedbrieflyinthe sectionBestPractices
for EfficientOperation.
Natural gas boilers employ one of two types of burners, atmospheric burners, also called
natural draft burners and forced draft burners, also called power burners. Due to more
stringent federal and state air quality regulations, low NOx burners and pre-mix burners are
becoming more commonly used and even required in some areas. By ensuring efficient mixing
of air and fuel as it enters the burner, these types of burners can ensure that NOx emissions are
reduced. Safety Issues
All combustionequipmentmustbe operatedproperlytopreventdangerousconditionsordisastersfrom
occurring,causingpersonal injuryandpropertyloss.The basiccause of boilerexplosionsisignitionof a
combustible gasthathasaccumulatedwithinthe boiler.Thissituationcouldarise inanumberof ways,
for example fuel,air,orignitionisinterruptedforsome reason,the flame extinguishes,andcombustible
gas accumulatesandisreignited.Anotherexample iswhenanumberof unsuccessful attemptsat
ignitionoccurwithoutthe appropriate purgingof accumulatedcombustiblegas.
There isa tremendousamountof storedenergywithinaboiler.The state change of superheatedwater
froma hotliquidtoa vapor (steam) releasesanenormousamountof energy.Forexample,1ft3 of water
will expandto1600 ft3 whenitturnsto steam.Therefore,“if youcouldcapture all the energyreleased
whena 30 gallonhome hotwatertank flashesintoexplosivefailure at332oF, you wouldhave enough
force to sendthe average car (weighing2,500 lbs) toa heightof nearly125 feet.Thisisequivalentto
more than the heightof a 14 story apartmentbuilding,startingwithaliftoff velocityof 85milesper
hour!” (5).
Boilersafetyisakeyobjective of the National Boardof BoilerandPressure VesselInspectors.This
organizationreportsandtracksboilersafetyandthe numberof incidentsrelatedtoboilersandpressure
vesselseachyear.Theirworkhasfoundthatthe number one incidentcategoryresultingininjurywas
poor maintenance andoperatorerror(5).Thisstressesthe importance of propermaintenance and
operatortraining.
Boilersmustbe inspectedregularlybasedonmanufacturer’srecommendations.Pressure vessel
integrity,checkingof safetyrelief valves,watercutoff devicesandproperfloatoperation,gaugesand
waterlevel indicatorsshouldall be inspected.The boiler’sfuelandburnersystemrequiresproper
inspectionandmaintenance toensure efficientoperation,heattransferandcorrectflame detection.

4. LIFTS:-
Terminology
• Lifts [UK] = Elevators [US]
• Escalators (= moving staircases)
• Conveyors (or moving walkways
lifts:-
Circulation/Movement of people in buildings
• Mode (horizontal or vertical)
• Movement type (natural or mechanically assisted)
• Human behaviour (complex, unpredictable)
• Design objectives
• Free flow of people & goods
• Safe operation, comfort & service
• Occupy minimum space & require less costs
• Aesthetics, disabled access, etc
Circulation elements in buildings include:
• Corridors
Physical • Portals (e.g. entrance, door, gate)
• Stairways
or
architectural
elements
• Ramps
• Human factors
• Physical dimensions
• Occupancy ellipse 600 mm by 450 mm (0.21 m2)
• Personal space (buffer zone)
• Female: 0.5 m2 (0.8 m diameter circle)
• Male: 0.8 m2 (1.0 m diameter circle)
• Density of occupation
• Desirable: 0.4 person/m2
• Comfortable: 1.0 person/m2
• Dense: 2.0 person/m2
• ‘Crowding’: 3.0 person/m2
• Crowded: 4.0 person/m2
• Human factors
• Interpersonal distances
• Public distance: > 7.5 m (far); 3.6-7.5 m (near)
• Social distance: 2.1-3.6 m (far); 1.2-2.1 m (near)

5. • Personal distance: 0.75-1.2 m (far); 0.45-0.75 m (near)
• Intimate distance: < 0.45 m
• Major design concerns
• Circulation efficiency
• Location & arrangement (prevent bottlenecks)
• Coordination with lobby, stairway & corridor
• Fire & safety regulations
• Handling capacity (quantity of service)
• Interval or waiting time (quality of service)
• Consideration by lift functions
• Passenger, goods, firemen, shuttle, observation
• Escalator – typical design
• Speed: 0.5 and 0.65 m/s, up to 0.9-1.0 m/s on deep
systems like subway
• Step widths: 600, 800 & 1000 mm; min. step or
tread length = 400 mm
• Inclination: usually at angle 30o
• 35o if rise < 6 m & speed < 0.5 m/s
• Boarding and alighting areas
• Safe boarding, 1.33 – 2.33 flat steps
• Escalator – typical applications
• Low- to medium-rise buildings
• Large no. of people e.g. airports, subway stations,
department stores, shopping malls
• Escalator arrangements
• Parallel
• Multiple parallel
• Cross-over or criss-cross
• Walkaround
• Escalator: handling capacity
• N = (3600 x P x V x cos θ) / L
• N = no. of persons moved per hour
• P = no. of persons per step
• V = escalator speed (m/s)
• L = length of step (m)
• θ = angle of incline
• Ce = 60 V k s (persons/minutes)
• V = speed along the incline (m/s)
• k = average density of people (people/step)
• s = number of escalator steps per metre
• Passenger lifts
• Different requirements in various building types

6. • Like commercial, hotels, hospitals, residential
• Grouping of passenger lifts
• Position & layout
• Machine room/space
• Hydraulic lifts: ideally at the lowest level
• Electric traction lifts: directly above the lift well
• Machine room-less lifts
• Observation lifts
• Glazed or partially glazed lift car within a glazed
or open-sided lift well
• Also called wallclimber, scenic, glass, panoramic
or bubble lifts
• Within an atrium or external to the building
• Design considerations
• Visual impact (attracting sightseers)
• Lift speed & handling capacity
• Space requirements & maintenance
• Lifts for the aged & disabled
• Provision for wheelchair
• Good lifts & service lifts
• Car sizes, payloads, well dimensions
• Dumbwaiter (e.g. in restaurants)
• Stair lifts
• Inclined lifts
• Scissor lifts