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Heat Pumps

A great component for converting a low-cost electricity supply into a multiplied supply of heat.

Heat pumps convert electricity into heat using a refrigeration cycle.

They are most suited for lower temperature heating where the yield is best; often quoted as COP (Coefficient of Performance), this expresses the power output as heat as a multiple of the power input as units of electricity. Rarely better than 3-4.

If heat pumps are used in a low-temperature heating environment, they can be a great component where underfloor heating (for example) is circulating at 35-40 degC in a building with high insulation and low heat loss. At these output temperatures the heat pump operates efficiently.

If, however, a heat pump is retro-fitted to an older building with low insulation, high heat losses and a high-temperature wet heat distribution system this will be not only very disappointing in performance but also in cost. There have been quite a few very unsatisfactory installations which have given heat pumps a bad reputation. Most wet radiator-based systems are designed to run with water at 65-70degC and are sized to the room based on the heat that will be shed at these temperatures, so a radiator running at 35-40degC will fail to heat the room and to make matters worse all the options increase the cost. Increasing the output temperature (with current technology) will reduce the COP, making it more expensive or running the system for longer to try to reach optimum room temperatures will cost more.

Heat pumps can be used if there is on-site electricity generation but there must be a realistic plan for incorporating low temperature heat into the overall solution, most likely as a baseload.

Human ingenuity being what it is, there are a lot of clever people working hard to solve this problem and the current focus is on new refrigerants which condense and evaporate at higher temperatures, this then allows the heat pump to deliver higher temperature liquid heating temperatures whilst maintaining high COPs. If this is cracked then heat pumps become a viable retrofit for older buildings where old radiators need to operate at 65-70 C. …….Watch this space.