Refrigeration Formulas
Calculate compression work, coefficients of performance and more.
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 = h l - h e (4)
where
NRE = Net Refrigeration Effect (Btu/lb)
h l = enthalpy of vapor leaving evaporator (Btu/lb)
h e = 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 (ft 3 /min)
c = capacity (Btu/min)
v = volume of gas entering compressor (ft 3 /lb)
NRE = Net Refrigeration Effect (Btu/lb)
Heat of Compression
h = h lc - h ec (7)
where
h = heat of compression (Btu/lb)
h lc = enthalpy of vapor leaving compressor (Btu/lb)
h ec = enthalpy of vapor entering compressor (Btu/lb)
Volumetric Efficiency
μ = 100 w a / w t (8)
where
μ = volumetric efficiency
w a = actual weight of refrigerant
w t = theoretical weight of refrigerant
Compression Ratio
CR = p h / p s (9)
where
CR = compression rate
p h = head pressure absolute (psia)
p s = suction pressure, absolute (psia)
Related Topics
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Air Conditioning
Air Conditioning systems - heating, cooling and dehumidification of indoor air for thermal comfort.
Related Documents
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Calculating Cooling Loads
Calculating chiller and cooling tower refrigeration loads - in tons. -
Cooling Load - Convert between kW/ton to COP or EER
Convert between cooling load units like kW/ton, COP and EER. -
Cooling Power vs. Airflow and Duct Sizes
Typical relations between cooling power (tons cooling), air flow and duct size -
Net Refrigeration Effect
The quantity of heat absorbed from a refrigerated space. -
Refrigerants - Environmental Properties
Physical and environmental properties of some common refrigerants. -
Refrigeration Machinery - Required Ventilation
Ventilation required for refrigeration machinery and compressors in hot areas.
