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Commonly Used HVAC Formulae and Conversions: Air Side

This document provides commonly used HVAC formulae and conversions for air, water, fans, pumps, and air conditioning. It includes formulae to calculate total heat, sensible heat, latent heat, humidification rate, airflow in CFM, and air pressure drop. It also includes formulae for water flow rate, heat transfer, chiller capacity, fan horsepower, and pump horsepower. Miscellaneous conversions between units like BTUs, Watts, HP, and Therms are also included.

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Wisam Ankah
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183 views5 pages

Commonly Used HVAC Formulae and Conversions: Air Side

This document provides commonly used HVAC formulae and conversions for air, water, fans, pumps, and air conditioning. It includes formulae to calculate total heat, sensible heat, latent heat, humidification rate, airflow in CFM, and air pressure drop. It also includes formulae for water flow rate, heat transfer, chiller capacity, fan horsepower, and pump horsepower. Miscellaneous conversions between units like BTUs, Watts, HP, and Therms are also included.

Uploaded by

Wisam Ankah
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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CommonlyUsedHVACFormulaeandConversions

AirSide

QTotal=CFMx(hihf)x4.5Btuh

QSensible=CFMx(titf)x1.085Btuh

QLatent=CFMx(GriGrf)x.068Btuh

Humidification=CFMx(GrfGri)/1,555lbs/hr

CFM=l/sx2.12

AirPressureDrop(in.wg)=Pa/249

WaterSide

Q=USGPMx(titf)x500Btuh

Q=USGPMx(titf)x450Btuh(50%E.G.)

Q=USGPMx(titf)/24Tons

USGPM=l/sx15.85

WaterPressureDrop(ft.wg)=kPax0.335
1.0PSI=2.31wg

7,000Grains=1.0lb

Miscellaneous

1.0 Ton=12MBH=12,000Btuh
1.0 Therm=100,000Btuh=100MBH

COP=3.516/(kw/Ton)

EER=Tonsx12/(TotalkWinput)

Btuh=Wattx3.412

HP=kWx1.3405

1BoilerHP=33.48MBH

1USGallon=8.33lbs

Latentheatofvaporizationofsteaminair(average)=1,050Btuh/lb

TheAffinityLaws(Fan/PumpLaws)

rpm2Flow2
=
rpm1Flow1

P2 Flow22
=
P1 Flow1

mhp2 Flow23
=
mhp1 Flow1

PumpBHP=USGPMxHead(ft.wg)

3960xPumpEfficiency

FanBHP=CFMxS.P.(incheswg)

6356xStaticEfficiency

AirConditioningFormulas

1Btu=amountofheatrequiredtoraise(orlowertemperatureofone
poundofwater1oF

1tonrefrigeration=12,000Btu/h=200Btu/min

1watt=3.412Btu/h

1horsepower=2545Btu/h

1lb=7000grains

1ft(head)=0.433psi

1squarefootEDR(equivalentdirectradiation)=240Btu

1boilerhorsepower=33,479Btu/h

No.ofairchanges(N)=60cfm/ft3

Sensibleheat(Btu/h)=1.08Qt
Wheret=differencebetweenenteringandleavingdrybulb
temperatureandQ=airflowrateincubicfeetperminute

Latentheat(Btu/h)=0.68Qg
Whereg=differenceinmoisturecontentofenteringand
leavingair,grainsperpoundofdryair

Waterquantity(gpm)requiredforheatingandcooling=q/500twater
Whereq=loadinBtu/h

Chillercapacity(tons)=gpm(chilledwater)xt(water)/24
ForAir:
1lb/h=4.5Q
1ton=Qh/2670

cfmxstaticpressure(in.w.g.) Densityofair
Fanhp=

6356xEfficiency x
Densityofstandardair

Smallfans0.400.50efficiency
Largefan0.550.60efficiency

ForWater:
1lb/h=500gpm
1ton=(gpm)t/24
gpmxfthead
Pumphp= x SpecificGravity
3960xEfficiency

Smallpumps0.400.60efficiency

Largepumps0.700.85efficiency

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