| For those interested it operates in a similar way to a refrigerator working in reverse, it works on the principle of the vapour compression cycle within the pump. There is a volatile fluid known as a refrigerant. The refrigerant in the evaporator is heated by the heat source this causes it to turn into a gas. The gas then passes through the compressor; the compressor increases its pressure and causes its temperature to rise. The hot gas then moves to the condenser where it is condensed back into a liquid and in doing so it releases heat into the house via a distribution system. The refrigerant is then allowed to expand back to a low pressure through the expansion valve and pass back to the evaporator where it repeats the cycle in a closed loop. |
What are they?
There are three main types, these are:-
- Ground Source Heat Pump (GSHP),
- Water Source Heat Pump (WSHP), and
- Air Source Heat Pump (ASHP)
They function by extracting heat from the ground the water or the air respectively and releasing that heat energy at a higher temperature within a building. All heat pumps consume energy usually in the form of electricity to operate the pump that is required to transfer the heat. They can supply all the heating you would require, and ground source systems are the most effective. To compare the performance of heat pump the term coefficient of performance is used (COP) and it described the ratio of heat movement to energy input. In the table below the Best Average COP is used. This a seasonal average, since air source and water source vary in performance with the temperature of the environment. For ground source the underground temperature is however remarkably constant all year.
It should also be noted that you will need a reasonable amount of land for an effective GSHP, unless you drill down, and for a water source heat pump a body of water is essential!
Energetically are they worth it?
According to manufacturer information heat pumps provide between 2.5 and 5 times (or they have a COP of between 2.5 to 5) the energy they consume and by energy consumption they usually mean energy in the form of electricity. Electrical power generation and distribution is covered in another article, however when trying to compare like for like and come to conclusions regarding total energy consumption, the inefficiency of power generation must be factored in, and it never is! So here are the main points:-
- 1kWh of electrical energy consumed by the pump should deliver 4kWh of heat energy, and it would have a COP of 4.
- For a gas fired power station for example 1kWh in your house requires about 2.2kWh of gas energy to generate it, so in reality 2.2kWh is required to deliver 4kWh of heat energy, so should the COP value really be 1.8?
You decide!
Financially are they worth it?
The answer to this question is depends. It simply depends on the form of heating you have currently, if you are mains gas heated this technology make no sense on financial grounds, since one unit of gas energy is four times cheaper than one unit of electrical energy; the system will be cash neutral and will never pay for itself. If your only source of alternative heating is electrically powered at the standard rate, then it could be well worth the investment and pay back in about 8 years.
Data table
| Heat Pump | Best Average COP |
Very Rough Equipment and Installation Cost Grant are available to reduce this cost |
Annual Electrical Energy Requirement (16,000kWh/COP) |
Cost of Electrical Energy |
Cost of "Replaced" Energy |
Payback Time | ||||
| Gas | LPG | Electrical | Gas | LPG | Electrical | |||||
| Ground Source | 4 | £ 12000 | 4000 kWh | £ 536 | £ 608 | £ 864 | £ 2144 | 167 Years | 37 Years | 7 Years |
| Water Source | 2.8 | £ 8000 | 5700 kWh | £ 764 | £ 608 | £ 864 | £ 2144 | Never | 80 Years | 6 Years |
| Air Source | 2.8 | £ 6000 | 5700 kWh | £ 764 | £ 608 | £ 864 | £ 2144 | Never | 60 Years | 4 Years |
| This table gives the potential payback times for a various heat source pumps assuming that the total household heat requirement is satisfied. The requirement is assumed at slightly above the average at 16,000kWh each year. | ||||||||||
