Renewable energy - Heat Pumps

renewable energy - heat pumps

A heat pump works in the same way as a refrigerator, but in reverse. Solar heat is stored in the ground, water and air and is available all year-round. Heat pumps transfer this heat from one medium to another.

As solar heat occurs naturally it has no cost or carbon impact. A heat pump transfers this free energy by mechanical means, using some electrical energy.

The design of your property will dictate the size and type of your heating system and therefore the size and type of heat pump to use - we can help you with this.

How a heat pump works?

Remember the heat pump in your house - your refrigerator?

This has a metal grille on the back and the motor you can hear is the compressor. The only difference between your refrigerator and a heat pump for the heating system is that your refrigerator is pulling heat from inside your fridge and dumping it into your house through the grill. This is an air-air heat pump. You’ve probably never questioned how it works?

The cycle of a heat pump can be best be explained in four basic stages:

The liquid refrigerant absorbs energy from the heat source (ground, air or water) and changes its state into a gas.
The gas is compressed increasing its temperature, condensing it into liquid and releasing heat energy.
The heat energy is transferred (via heat exchanger) into the heating system.
The liquid under pressure passes through an expansion valve lowering its pressure reverting back to its original state (liquid refrigerant).

The cycle then starts over again.

Heat Pump Efficiency

The efficiency of a heat pump is expressed as a Coefficient Of Performance (COP). This is the energy that can be transferred using one unit of energy. For example; a heat pump with a COP of 4.5 will transfer 4.5kW's of heat/energy from one medium to another using only 1kW of energy to do so. In summary it is 450% efficient.

Domestic Hot Water

Generally we advise that hot water is maintained at a temperature that the heat pump an efficiently achieve with the added protection of a sterilisation cycly where the heat pump uses an additional source such as an immersion heater or auxiliary boiler to raise water temperature in the tank to a point which sterilises the tank and water iside it.

Ground Source Heat Pumps (GSHP)

Ground Source Heat Pumps (GSHP) extract heat from the environment using a water/brine mix in loops of pipe and transfer the heat into a water-based heating system.

The pipe loops can be buried in trenches in the ground, sunk in boreholes or placed at the bottom of lakes or canals.

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Air Source Heat Pump (ASHP)

An Air Source Heat Pump doesn't need any borehole or ground collector. Instead it uses solar energy stored in the air and transfers it to the water based heating system (even when the outside air temperature is below freezing).

They are effective with outside air temperatures down to - 20° C, but the efficiency reduces at colder temperatures.

The advantage of this type of heat pump is that there is no collector pipe required and they are ideal where space and access is limited.

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Heat Recovery Heat Pumps (HRHP)

These work in a similar way to an Air Source Heat Pump but recover heat from inside a property. This heat is made up partly of solar energy but also heat generated internally from lighting, people and domestic appliances.

Not only does this type of heat pump provide heating and hot water, it also delivers whole house ventilation.

Ventilation is a basic requirement for living in a healthy house. Controlled domestic ventilation with heat recovery helps you re-use the energy from within the property.

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