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Chiller Efficiency (kW per Ton)

Also known as kW/ton · chiller efficiency

kW/ton=W˙ [kW]Q˙ [tons]\mathrm{kW/ton} = \frac{\dot{W}\ [\text{kW}]}{\dot{Q}\ [\text{tons}]}

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Constant used — built into this formula, no need to enter
TR=3516.8528420667 W\mathrm{TR} = 3516.8528420667\ \text{W}Ton of refrigeration · exact

Learning zone

Chiller plants are bought and argued over in kW per ton, the inverse-efficiency metric: how much electricity it costs to make a ton of cooling. Because it is inverted, lower wins. A 1970s reciprocating machine ran 1.0–1.2 kW/ton; a modern centrifugal at full load hits 0.50–0.60, and with cold condenser water on an autumn night can dip under 0.40. Relate it to the other scales with kW/ton = 12/EER = 3.5169/COP.

The number every plant engineer actually chases is plant kW/ton, which includes chilled-water pumps, condenser pumps and the cooling-tower fans — typically 0.15–0.30 kW/ton of parasitic load on top of the chiller. A "0.55 kW/ton chiller" inside a 0.85 kW/ton plant is a familiar disappointment, and it is usually the constant-speed pumps that did it. Worked example: a 500-ton machine drawing 300 kW runs 300/500 = 0.60 kW/ton, which is EER 20 and COP 5.86 — respectable, and worth about $95 an hour at $0.32/kWh when it runs flat out.

Chiller Efficiency (kW per Ton)
kW/ton=W˙ [kW]Q˙ [tons]\mathrm{kW/ton} = \frac{\dot{W}\ [\text{kW}]}{\dot{Q}\ [\text{tons}]}
Where
  • kW/ton\mathrm{kW/ton}= Specific power
  • W˙\dot{W}= Compressor power input
  • Q˙\dot{Q}= Cooling capacity
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Part of this formula set

Refrigeration capacity and efficiency

6 formulasTons, COP, EER and kW per ton — the four ways the trade states the same chiller performance, and how to convert between them.