Efficiency, Cost & Carbon Comparison

Page last updated 28th February, 2010 by Corny


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The efficiency of a heat pump is dependent upon the temperature to which the building hot water is heated, and with air source heat pumps, the performance falls with falling external temperatures. As the efficiency or co-efficient of performance (COP) decreases the economic advantage of running a heat pump diminishes. Furthermore with a reducing COP the carbon emissions increase to achieve the same energy output.

In considering different fuels it is important to be aware of the carbon emission differences. For example gas has 0.194kg of CO2 related to every kWh used, whereas electricity has 0.422kg per kWh, this is 218% more.


Running Cost

The break even cost point can be determined by the following formula. It indicates that heat pump plant should have a COP greater than 3.01 for the operating cost to be more favorable than gas.


  Electrical cost p/kWh / Gas cost p/kWh x boiler efficiency = COP for energy equality
  11.41p / 3.52p x 0.93 = 3.01 (COP)
    Typical energy figures August 2009.


Carbon Comparison

To determine the break even point for carbon emissions use the following formula. It indicates that heat pump plant should have a COP greater than 2.02 for the carbon emissions to be more favorable than gas.


  CO2/kWh of electricity / CO2/kWh of gas x boiler efficiency = COP for carbon equality
  0.422kg CO2/kwh / 0.194kg CO2/kwh x 0.93 = 2.02 (COP)
    CO2 figures from part L 2006.



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