Heat Pumps

Heat Pumps work by simply transferring heat from one location to another to provide space heating and, in some cases, to pre-heat domestic hot water.

There are three types of source heat pumps: ground air and water, all of which can be combined with Photovoltaic Cells (PV).  The benefit of heat pumps is that they do not require any external fuel, and are designed to heat a whole building.

The efficiency of a heat pump system is measured by its Coefficient of Performance (CoP); this is the ratio of units of heat output for each unit of electricity used to drive the compressor and pump for the ground loop.  The average CoP is 3-4, although some systems may produce a greater rate of efficiency.  This means that for every unit of electricity used to pump the heat, 3-4 units of heat are produced.

The most common type of heat pump is the ground source heat pump.  There are three important elements to a ground source heat pump; the first is the ground loop.  The ground loop is comprised of lengths of pipe buried beneath the ground either in a borehole or in a horizontal trench.  The pipe is usually in a closed circuit and filled with a mixture of water and anti-freeze; which is pumped around the pipe absorbing heat from the ground.  The second element is the heat pump; the way a heat pump works is similar to how a fridge uses refrigerant to remove heat from inside the fridge in order to keep the food cool.  A ground source heat pump works by extracting the heat from the ground and using it to heat your home.  The pump has three parts: the evaporator, which absorbs heat using the liquid in the ground loop; the compressor, moves the refrigerant round the heat pump and compresses the gaseous refrigerant to the temperature needed for the heat distribution circuit; the condenser, gives heat to a hot water tank which feeds the distribution system.  The final part is the heat distribution system; this consists of either under floor heating or radiators for space heating, and in some cases water storage for the hot water supply.

 

Ground source heat pumps are suitable for home installation; however, there are a number of factors that will need to be considered, such as:

  • It will need space outside for the ground loop
  • The ground will need to be suitable for digging a trench or borehole
  • The type of distribution system – ground source heart pumps can be combined with radiators but these tend to be larger with standard boiler systems.  Under floor heating is more effective as it works at lower temperatures.

Air and Water source heat pumps work in a different way to the ground source heat pump; they do not require a collection system, they simply extract heat directly from the source point of use.

Air source heat pumps can be fitted outside or in the house roof space.  They generally work better in slightly warmer temperatures: although they are used extensively used in Scandinavia.

Water source heat pumps can be used to provide heating to buildings near to rivers, streams and lochs.  They work in a similar fashion to Ground Source Heat Pumps; however, the loop is in the water source.

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