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Heat Pumps and how air source heat pumps get free energy from the air around us

Our environment is full of energy, even at sub-zero temperatures there is plenty of energy available.

Heat pumps use conventional refrigeration technology to extract the sun’s energy stored in the environment and raise it to a temperature suitable for heating purposes.This principle works even in the middle of winter at temperatures as low as -25°C.

Heat pumps are among the most efficient heating and hot water systems available today. Approximately 75% of the energy needed for heating comes from the environment. This means that for every 1kWh of electricity used to power the heat pump compressor, between 3 and 4 kWh of heating energy are produced, giving the heat pump an efficiency of 300-400% or higher.

The heat pump’s “efficiency” is know as it’s “Coefficient of Performance” (CoP). This is simply a ratio between the proportion of the total energy supplied that can be extracted from the environment and the amount supplied by electricity to run the heat pump compressor. The higher the CoP, the more “free” environmental energy the heat pump is using.

This helps result in:

• Lower heating system carbon dioxide emissions
• Lower heating system running costs

A heat pump heating system consists of 3 components: the heat source, the heat pump itself and a heat distribution and storage system. Heat pumps are able to produce more energy than they consume by using the conventional refrigeration cycle to absorb heat from the environment and raise it to a suitable level for heating.
 

1. A large quantity of low grade energy absorbed from the environment is transferred to the refrigerant inside the heat pump (evaporator). This causes the temperature of the refrigerant to rise (even at sub zero temperatures) causing it to change from a liquid to a gaseous state.
2. The refrigerant is then compressed, using an electrically driven compressor, reducing its volume but causing its temperature to rise signifcantly.
3. A heat exchanger (condenser) then extracts the heat from the refrigerant to heat water for central heating, underfloor heating or domestic hot water.
4. After giving up its heat energy the refrigerant turns back into a liquid and after passing through an expansion valve can once again absorb energy from the environment, allowing the cycle to begin again

Heat pump CoP is affected by a number of factors, most importantly:

• Temperature of the heat source (eg the air)
• Heating water temperature

As these factors vary throughout the heating season, the CoP will also continually vary. CoP will be at its highest when:

• The heat source temperature is high – a high amount of “free” energy is available from the environment
• The heating water temperature is low – the heat pump has to do less work to raise the temperature of the heating system

• Heat pumps are by their design extremely suitable for systems employing underfloor heating as a lower flow temperature means a higher CoP.

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