Heat Pumps


Heat pumps are magic. For every unit of electrical energy you put in to the system, you get between 3 and 4 units of heat out. They could be seen to stretch the definition of renewable energy but the extra energy they extract from the ground or air leads to a system efficiency well over 100%!


You may not think it, but there is free heat energy underneath your garden and in the air surrounding your home. This is low-grade heat energy is different from the electrical energy in the socket, but it’s a free, continually replenishing resource which a heat pump can concentrate and draw into your home.


They work because the grounds temperature is pretty constant throughout the year, therefore in cold winter months, the ground remains warmer, and in hot summer months, the ground is cooler than air temperature. The amazing thing is that in hot summer months, some systems can work in reverse and acts to remove excess heat from the house, keeping your cool!


How do they work?


Ground Sourced Heat Pump


A ground source heat pump circulates a mixture of water and antifreeze around a loop of pipe - which can be installed either vertically (deep into a borehole), horizontally (under your garden). Heat from the ground is absorbed into this fluid and is pumped through a heat exchanger in the heat pump. Low grade heat passes through the heat pump compressor and is concentrated into a higher temperature useful heat capable of heating water for a conventional central heating system or under floor heating. The now cool fluid passes back into the ground-loop where it absorbs further energy from the ground in a continuous process while heating is required.


Water Sourced Heat Pump


If you are lucky enough to live next to a pond or lake it is sometimes appropriate to use the water as a source of heat or as a sink for cooling. Depending on the temperature of the water source, either an open or closed loop system can be setup, using a similar heat exchange method to the ground source heat pump.


Air Sourced Heat Pump


An air source heat pump works along the same principles – just now the loop of pipe is instead called a heat exchanger, in contact with the outside air only. This system is usually cheap and easier to install but will not offer the same efficiency or capacity of heat delivery.



Of course both ground and air source heat pumps have some impact on the environment as they need electricity to run, but this is far less the using electric heaters alone or a gas-powered boiler to heat ones home.


What are the benefits of Heat Pumps?


  • Lower carbon emissions – with an average ground source heat pump saving around 1.8 tonnes of carbon emissions every year, when replacing an oil boiler.
  • Lower fuel bills – more cost effective than traditional electric, gas, oil heating.
  • A sustainable investment – as the grid decarbonises and renewable energy becomes the primary electricity source; heat pumps become completely renewable, saving energy along the way.


How much do they cost and how much can I save?


A typical 8 to 12kW system costs £6,000 to £12,000 plus the price of connection to the distribution system. This can vary with property and location. Running costs will depend on a number of factors - including the size of your home and how well insulated it is. The Department for Energy and Climate Change (DECC) have announced that the Renewable Heat Incentive (RHI) is expected to be launched in April 2011. It is designed to provide financial support to encourage the uptake of renewable and low carbon heat technologies like heat pumps. It is currently in a planning stage and no final decisions have yet been made by DECC but it is hoped that it will provide a financial benefits, similar to those of the Feed-in Tariff. For more information and updates on the RHI visit the Energy Saving Trust's Heat Pump webpage