Energy Facts

Heat pumped from the ground and extracted
from the air

 

In the UK, the earth just a few metres below our feet is at a constant year-round temperature of between 11°C and 12°C.

Systems known as ground source heat pumps are able to capture this heat and transfer from ground and into a building to provide space heating and, in some cases, domestic hot water.

A similar concept enables air source heat pumps to absorb heat from the environment.

However, air source heat pumps are less efficient than ground source heat pumps, yet they need less space and are easier to install as they do not need buried loops of piping to work.

Heat from the ground

The system that extracts heat from the ground typically has three key elements.

Systems such as ground source heat pumps run on electricity that captures the low grade heat from the ground. The heat pumps works much like a fridge in reverse mode to provide both space heating and hot water much more efficiently than conventional systems. They work best in new houses which are designed with their installation in mind, including a low temperature heating system using under-floor heating or oversized radiators, a building with high thermal mass and large hot water storage facilities.

As this liquid is piped around the loop it absorbs heat as it passes through the section of pipe buried in the warm earth.

Just as a fridge uses loops of piping filled with pumped refrigerant to absorb the heat from the inside the fridge, keeping your food cool, so a ground source heat pump extracts heat from the ground. The difference is that whereas with a fridge the heat gathered is lost as waste and dispersed from the back of the fridge in a network of piping, the heat pump uses that collected heat to warm the home.

The heat pump features an evaporator, which absorbs the heat from the water and antifreeze liquid. The gaseous refrigerant in the evaporator expands. It is compressed and circulated around the system by the compressor. This has the effect of raising the temperature of the refrigerant which is then passed through the condenser. Here it releases the heat to the central distribution system within the house.

The heat is distributed around the home using underfloor heating or radiators for space heating. In some cases the system can also heat water for a hot water supply.

Heat from the air

Air source heat pumps taking warmth from the air work on exactly the same principle as a pump system taking warmth from the earth.

There are two types of air source heating systems. Air-to-air systems provide warm air, which is circulated to heat the building. Air-to-water systems heat water to provide heat through radiators or an underfloor system.

The benefits of air source heat pumps are similar to ground-source heat systems. Both systems offer maximum environmental benefit when run on low carbon renewable electricity.