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Cooling Load - Convert kW/ton to COP or EER

Convert cooling load units kW/ton, COP and EER

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Chiller efficiency depends on heat removed and energy consumed.

Absorption chillers are rated in fuel consumption per ton cooling. Electric motor driven chillers are rated in kilowatts per ton cooling.

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

If the efficiency of a chiller is rated to 1 KW/ton, then

  • COP = 3.5
  • EER = 12

Cooling Load in - kW/ton

The term kW/ton is commonly used for larger commercial and industrial air-conditioning, heat pump and refrigeration systems.

The term is defined as the ratio of energy consumption in kW to the rate of heat removal in tons at the rated condition. The lower the kW/ton - the more efficient the system.

kW/ton = Pc / Er                                                                  (1)

where

Pc = energy consumption (kW)

Er = heat removed (ton)

Coefficient of Performance - COP

The Coefficient of Performance - COP - is the basic parameter used to report efficiency of refrigerant based systems.

The Coefficient of Performance - COP - is the ratio between useful energy acquired and energy applied and can be expressed as

COP = Eu / Ea                                                     (2)

where

COP = coefficient of performance

Eu = useful energy acquired (btu in imperial units)

Ea = energy applied (btu in imperial units)

COP can be used to define the cooling efficiency for a cooling system - or the heating efficiency for a heat pump system.

  • CoolingCOP is defined as the ratio of of the heat removal to the energy input to the compressor
  • Heating - COP is defined as the ratio of the heat delivered to the energy input to the compressor

COP can be used to define the efficiency at single standard or non-standard rated conditions, or as a weighted average of seasonal conditions. The term may or may not include the energy consumption of auxiliary systems such as indoor or outdoor fans, chilled water pumps, or cooling tower systems.

  • higher COP - more efficient system

COP can be treated as an efficiency where COP of 2.0 = 200% efficiency. For unitary heat pumps, ratings at two standard outdoor temperatures of 47oF and 17oF (8.3oC and -8.3oC) are typically used.

Energy Efficiency Ratio - EER

The Energy Efficiency Ratio - EER - is a term generally used to define cooling efficiency of unitary air-conditioning and heat pump system.

The efficiency is determined at a single rated condition specified by an appropriate equipment standard and is defined as the ratio of net cooling capacity - or heat removed in Btu/h - to the total input rate of electric power applied - in Watts. The units of EER are Btu/Wh.

EER = Ec / Pa                                                          (3)

where

EER = energy efficient ratio (Btu/Wh)

Ec = net cooling capacity (Btu/h)

Pa = applied electrical power (Watts)

This efficiency term typically includes the energy requirement of auxiliary systems such as the indoor and outdoor fans.

  • higher EER -  more efficient system
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