FORMULAS

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WATER SIDE HVAC FORMULAS. BTUH = GPM x 500 x T (water). TONS = GPM x ΔT. 24. (CH water) (CT Ton = 15,000 BTUH). FTHD = psi x 2.31. S.G.. NPSHA.
AUSTIN

SAN ANTONIO

WESLACO

formulas Fan, Pumps and Drives

Water Side HVAC Formulas



BTUH

=

TONS

=

FTHD

=

NPSHA ha

=

GPM x 500 x T (water) GPM x ΔT (CH water) (CT Ton = 15,000 BTUH) 24 psi x 2.31 S.G. ha – hvpa + hst – hfs

=

Absolute Pressure in feet of liquid on surface supply level.

h vpa

=

Head in feet corresponding to vapor pressure of liquid at the

( ) ( ) ( )

CFM 1 RPM 1 SP 1 3 BHP 1    =     =     =    2 Affinity Laws, Note: (CFM = GPM) BHP 2 CFM 2 RPM 2 SP 2 Hertz x 120 Synchronous Motor RPM =  Poles z (D – d ) Belt_Length = 2c + [ 1.57 x (D + d )] + 4c RPM Motor DIA Fan Sheave     = RPM Fan DAI MotorSheaves



2

2





BHPActual = 1.73 x Amps x Volts x motor x P.F. Amps Actual Volts Actual Rule of Thumb: BHPActual = HP (name_plate) x      x Volts Rated Amps Rated



 x in.   W.G. (For Fans) BHP =    CFM 6,350 x fan

GPM x FTHD BHP =       x S.G. (For Pumps) 6,350 x pump



 



temperature being pumped.

hst

Static height that the liquid level is above (+) or below (–)

=

hfs

=



the pump centerline All suction line losses including the entrance loss and friction losses through pipe, valves and fittings.

Electrical Equations Amps x Volts x Ph 1,000 KW = KVA x P.F. = P.F. x Amps x Volts x Ph 1,000 BHP x 0.746 KW motor input =  motor V = IR KVA = 

W = V x I = I² x R KWDC =

x Volts  Amps1,000

Refrigeration

Air Side HVAC Formulas BTUHTotal

=

BTUHSensible =

BTUHSensible + BTUHLatent (1.08) x (CFM) x ΔT

BTUHTotal =

ACH

Pvelocity PTotal

(4.5) x (CFM) x ΔH 60 x CFM = Floor Area x Ceiling Height

( ) ( ) ( )

V 2 V 2 P =     =     C = 136.8, g = 32.2 C 2g 4,005 = PVelocity + PStatic

KW / ton = 12 / EER COP = EER / 3.412 = 12 / (KW / ton) / 3.412



1 Cond. Tons = GPM x ΔT x (1 + COP ) 24

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