How Heat Pumps Work

“What is a heat pump?” “How does a heat pump work?”
A ground source heat pump is an ultra-efficient way to extract heat from the ground or water sources to heat a home. Discover how a ground source heat pump works in this section.

Nature's underfloor heating

A ground source heat pump (GSHP) extracts solar energy stored in the ground or water sources and converts this to a higher temperature for use in a building’s heating distribution system.

Ground source heat pumps are extremely energy efficient, with every unit of electricity used (to drive the pump and compressor), producing between three and four units of heat.

1kW of electricity = 4kW of heat

This means heating costs are effectively quartered. This is known and the coefficient of performance (COP).

Due to their high efficiencies, CO2 emissions are significantly lower than traditional fossil fuelled systems (up to 43% lower than gas).

Video

This three minute video by Kensa Heat Pumps explains how a ground source heat pump works.

For a more detailed technical explanation an extended version is available here, with commentary from Kensa’s Technical Director, and co-founder, Guy Cashmore.

Heat pump diagram

kensa-ground-source-heat-pumps246

Heat pump process

  • A cold water anti-freeze mix is pumped through the ground within a series of energy absorbing pipes, known as ground arrays. As heat naturally flows from warmer to cooler places, the anti-freeze mix circulating around the array is constantly warmed by the ground’s low grade heat.
  • Having increased in temperature, the anti-freeze mixture is fed into a heat exchanger called the evaporator.
  • Within the secondary sealed side of the evaporator heat exchanger is a refrigerant which acts as a heat transfer fluid. When the water anti-freeze mixture enters the evaporator, the energy absorbed from the ground is transferred into the refrigerant which begins to boil and turn into a gas. The refrigerant never physically mixes with the water anti-freeze mixture. They are separated like sandwich layers by the plates of the heat exchanger which permit the heat transfer.
  • This gas is then fed into a compressor. The pressure of the refrigerant gas is increased in the compressor, which makes the gas temperature rise. The hot refrigerant gas then flows into a second heat exchanger, called the condenser, which features an identical set of heat transfer plates.
  • The condenser delivers water hot enough to serve the space heating system and, if required, the property’s hot water needs.  Having transferred its heat, the refrigerant gas reverts to a liquid.
  • This liquid is then passed through an expansion valve at the end of the cycle to reduce its pressure and temperature, ready to commence the cycle all over again.
Watch the video

Improving efficiencies

The lower the flow temperature required in your heating distribution system, the less work your ground source heat pump will need to make, therefore making it even more efficient, and possibly even reducing the size and cost of pump required.

To achieve as low flow temperatures as possible, insulation is the first place to look.

better insulation = lower flow temperature = less work & more efficient heat pump

I think ground source is the future of energy generation and everyone should embrace this this technology.

Alistair Mackintosh, Selfbuilder