Heat pumps use electricity to extract heat from the ground or the outside air which is heated by the sun. By exploiting this freely available energy they can reach efficiencies of up to and over 400%. More information on how heat pumps work is available on our renewable technologies page.
There are two main types of heat pumps.
Ground source heat pumps (GSHP) run water through horizontal or vertical below ground heat collectors to extract the heat. Because below ground temperatures are generally stable, ground source heat pumps can reach the highest efficiencies
Air source heat pumps (ASHP) draw in outside air to extract its heat. As the air temperature fluctuates a lot more they are less efficient than GSHPs with maximum efficiencies of around 300%. However, if space is an issue they can be an ideal solution. They also negate the costs of having to install ground collectors.
We can also install water source heat pumps. These draw in water directly from a reservoir (below ground or a lake/river).
Most heat pumps output to water based heating distribution although air heating systems are also available.
Although Heat pumps can output temperatures of up to 55°C they function best when outputting at lower temperatures of around 35°C. Traditional heating distribution systems use radiators which need to be run at temperatures around 85°C. This is because they rely on convection and radiation to heat rooms, causing uneven room temperatures.
Therefore, unless a supplementary heating system (a gas boiler for example) is installed in parallel with a heat pump to top up the temperature a different distribution system is required.
We highly recommend that either oversized radiators, fan assisted convectors, skirting board radiators or, ideally underfloor heating is installed along with heat pump. This allows the house to be heated with lower temperatures and the heat pump to run at maximum efficiency thus minimizing or removing the demand for supplementary heating.
In homes with insulation below better than current recommended standards we recommend a back-up heating solution tied into the heat pump system to boost temperature output for domestic hot water and as a support for the very coldest weather. This can come in one of several forms from simply tying in an existing or new boiler, to solar thermal collectors or a wood burning stove.
A buffer vessel is required for the heating system which is usually about 100Litres for a family home. The heat pump keeps this at the required temperature so that there is always hot water available when heating is required without having to wait for the heat pump to start up.
A heat pump suitable hot water cylinder needs to be installed if domestic hot water is required as well.
We recommend that these two functions are combined with a stratified storage cylinder which can accept all the heating inputs and output to high and low temperature heating systems and provide hot water through an in built hot water coil.
Heat pumps are floor mounted units about the size of a washing machine (size varies with the output required). With the cylinder and other equipment a space of about 1m x 2m is required for a heat pump installation. Components can be split up into nearby rooms or put into an out building. Alternately, there are air source heat pump models which can be installed externally.
The pumps, compressor, and fans (air source) in heat pumps do make low running noise and so should be located away from bedrooms or quiet areas of the house.
Ground collectors are required for ground source heat pumps and are sized to the peak load of the heat pump. These can come in the form of horizontal single pipe or slinky loops buried a meter underground or verical boreholes.
Horizontal collectors require a very large area to extract the required heat, typically a very large garden or small field. The ground works require 1m x 1m metre trenches to be dug at 2m spacing so having space available that can be excavated using machinery is essential for horizontal ground loops.
Alternatively, if space is limited vertical boreholes can be drilled for circulated ground loops. Boreholes drilled to around 100m are the most efficient heat source due to the stable temperatures at lower levels. They need to be spaced 6m apart and 3m away from buildings but as long as the drilling equipment can be accommodated they can be situated in small areas. Drilling costs are high so this is often the most expensive solution.
With all types of ground collector it is essential that they are properly sized. Too small, and they take more energy than the ground can recuperate over the summer months causing it to freeze after a few years damaging the local environment and stopping the heat pump from functioning properly.
With high installation costs it is uneconomical to significantly oversize the collectors. We will size the collectors based on general ground data from the area but will slightly over size the collectors to ensure ground cooling does not occur.
For large installations we recommend trail loop/boreholes are installed and tested before going ahead to ensure the correct number are installed
Based on a typical installation a ground source heat pump will supply about 60% of your home’s heating and hot water energy free of charge, with an air source heat pump providing about 50%.
The electrical running cost of the system is about equivalent to the running cost of a high efficiency gas system as electrical cost is currently much higher than that of Gas. However, the electrical cost can be directly offset with a solar Photovoltaic array. In sites without mains gas heat pumps are by far the most efficient option available.
The government is planning to bring in the Renewable Heating Incentive (RHI) for domestic heat pump systems in 2013. This will function much like the Feed in Tariff for electricity generation paying you for each kWh the solar system produces.
In the meantime the Renewable Heating Premium Payments scheme is providing a voucher of £850 for air source heat pumps and £1250 for ground source to be claimed against the cost of your installation. If you claim this you will still be able to claim RHI payments. Please see our grants and funding page for more information.
We have experience installing many different types of heat pumps but will typically specify one by a preferred manufacturer, such as Dimplex, Nibe or Stiebel Eltron. We prefer these heat pumps because of their high quality, durability, and product support.
Please take a look at some of our previous heat pump installations on our case studies page