by Helen Rudd

Created on: June 08, 2009   Last Updated: June 10, 2009

Air, earth and water have always been considered the three most important elements of our life, but in future their significance will become even greater as they are immense sources of free, renewable & thermal energy. Solar radiation from the sun heats the air, earth and water, and heat pumps are capable of extracting this heat and transferring it to a medium (gas or liquid) suitable for heating our homes. A heat pump can save you a lot of money on your heating and cooling bills.

How does a Heat Pump Work?

To help you understand the process, just think about water as it turns to steam (evaporates) at 100 degrees Centigrade. It is still possible to add heat to this steam by superheating it and then pump it somewhere else to extract the added heat. When the heat is removed, the steam turns back to water (condenses). The water is then pumped back to be reheated and turned back to steam again.

In a heat pump the liquid is called a 'refrigerant' and this boils at a temperature of minus 35 degrees. It is pumped under pressure through the system heat exchanger, where it picks up heat from the surrounding air, boiling as it turns into a gas, just like steam, and this boiling, gaseous refrigerant is then pumped around the system and de-pressurised, where it changes back to a liquid and gives off the picked up heat.

Applications for Heat Pumps

Heat pumps are used to create a comfortable temperature inside the house as well as supplying energy for the hot water system and they are most efficient when supplying low temperature systems such as hot water, warm air ventilation, underfloor heating and radiators, although these would have to be larger than domestic boiler powered systems.

The flow temperature of the warm water is typically between 35 & 45 degrees, much lower than achieved by a domestic boiler. The pumps are perfectly capable of generating higher temperatures, but the CoP (Coefficient of Performance) suffers, meaning the economic and ecological benefits maybe affected. Keeping the temperature at the lower end of the scale keeps the system operating at maximum efficiency.

The efficiency of an air source heat pump is measured in CoP. A CoP of 4 (typical for heat pumps) means that for every kilowatt of electricity you put in, you get 4 kilowatts of energy in the form of warm water.

An air source heat pump should cover the heating requirements of a well insulated property in all but the most extreme conditions. When used in combination with an immersion heater,

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