Refrigeration Formulas
Compression work, coefficient of performance and more
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Compression Work
Compressor work can expressed as
W = h q (1)
where
W = compression work (Btu min)
h = heat of compression (Btu/lb)
q = refrigerant circulated (lb/min)
Compression Horsepower
Compression horsepower can be expressed as
P = W / 42.4 (2)
where
P = compression power (hp)
W = compression work (Btu min)
Alternatively
P = c / (42.4 COP) (2b)
where
P = compression power (hp)
c = capacity (Btu/min)
COP = coefficient of performance
Compression horsepower per Ton
p = 4.715 / COP (2c)
where
p = compressor horsepower per Ton (hp/Ton)
COP = coefficient of performance
COP - Coefficient of Performance
COP = NRE / h (3)
where
COP = Coefficient of Performance
NRE = Net Refrigeration Effect (Btu/lb)
h = heat of compression (Btu/lb)
Net Refrigeration Effect
Net refrigeration effect can be expressed as
NRE = hl - he (4)
where
NRE = Net Refrigeration Effect (Btu/lb)
hl = enthalpy of vapor leaving evaporator (Btu/lb)
he = enthalpy of vapor entering evaporator (Btu/lb)
Capacity
c = q NRE (5)
where
c = capacity (Btu/min)
q = refrigerant circulated (lb/min)
NRE = Net Refrigeration Effect (Btu/lb)
Compressor Displacement
d = c v / NRE (6)
where
d = compressor displacement (ft3/min)
c = capacity (Btu/min)
v = volume of gas entering compressor (ft3/lb)
NRE = Net Refrigeration Effect (Btu/lb)
Heat of Compression
h = hlc - hec (7)
where
h = heat of compression (Btu/lb)
hlc = enthalpy of vapor leaving compressor (Btu/lb)
hec = enthalpy of vapor entering compressor (Btu/lb)
Volumetric Efficiency
μ = 100 wa / wt (8)
where
μ = volumetric efficiency
wa = actual weight of refrigerant
wt = theoretical weight of refrigerant
Compression Ratio
CR = ph / ps (9)
where
CR = compression rate
ph = head pressure absolute (psia)
ps = suction pressure, absolute (psia)
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