A heat pump is a system which is able to extract low grade heat from the air, ground or water and concentrate it to provide useful heat for space and water heating. Energy is only required to concentrate this heat and so can provide a heat output up to four times the energy input. Heat pumps (in spite of their name) can also produce space cooling during the summer. In this process high grade heat is extracted from a building and converted into a lower grade of heat which can then be diffused back into the earth or atmosphere. Thus a single system can produce space heating, space cooling and hot water.
The advantages of heat pumps are:
- Electricity and low grade heat are available from a variety of source
- Systems are available in all sizes from heating one room to heating a single or multiple dwellings
- Some systems are reversible in that they can both heat and cool
- Electricity to operate the heat pump can come from renewable sources
- Natural refrigerants are starting to be used which have zero or very low environmental impact
- Electricity to operate the heat pump can come from renewable sources.
- Space if a ground source collector is used
- Efficiency drops with decreasing air temperature for air source systems
- Higher initial costs than conventional systems
- Refrigerant needs to be recovered at end of life of the system because of its greenhouse warming potential.