Sustainable Heating Solutions

Heat pumps

As with most technologies in everyday use, the basic principles of how a heat pump works are fairly simple but – in the case of heat pumps – can require a vast amount of words to explain!

The following information is therefore intended to provide basic details rather than go into too much technical detail.

Our environment contains heat – even on freezing cold days. The purpose of a heat pump is to transfer heat from one place where it is plentiful (but of little use) to another location where it can be used for space or water heating.

Useful heat can be found in the air outdoors, in the ground, and is present in water, rivers, lakes and the sea. Even on the coldest winter days, sufficient heat is present to warm our homes and offices – what’s more, it’s free. All we have to pay for is the technology to recover it and the cost of the energy to power that technology.

At the heart of a heat pump is a refrigeration system. Paradoxically, the refrigeration cycle is an efficient provider of heat as well as cooling, and the basics of its operation are fairly straightforward.

The mechanical refrigeration cycle consists of an arrangement of heat exchangers; one that absorbs heat, the other that rejects it. The absorbed heat is transported through a sealed system of pipes by a fluid (the refrigerant) which is circulated by a compressor. The refrigerant is a fluid that has a low boiling point.

The ability of the refrigerant fluid to boil from a liquid to a vapour and then to condense back into a liquid is used in order to absorb and release the heat into and from the refrigerant. This is a continual process while the compressor is running and circulating the refrigerant.

High pressure liquid refrigerant is fed through the evaporator heat exchanger where it evaporates into a vapour by absorption of heat from the heat source (air, water, ground, other) passing through the heat exchanger.

The relatively cool return vapour is drawn back to the compressor. The cooled return vapour from the evaporator is passed over the compressor motor windings within the heat pump, thus cooling the windings of the motor.

Much of the energy absorbed by the electric motor driving the compressor is absorbed into the refrigerant.

The combined heat from the source, plus much of the waste energy from the electric motor is then compressed to a high temperature vapour and enters the condenser heat exchanger where it is cooled and condensed into a high pressure liquid ready to begin the cycle again.

The heat released during the process of condensing the refrigerant to a liquid is rejected via the heat exchanger directly into air or transferred to water to heat the building. The air or water temperature at this point could be anywhere between 43oC to 60oC, depending on the design of the system.

This air or water is then distributed throughout the property in order to provide space heating.

It is the fact that heat pumps can only produce a maximum temperature of around 60oC that is their biggest limitation. In order to use water at 60oC to heat a property requires a huge surface area to transfer the heat – which means massive radiators. This problem is commonly overcome by using heat pumps in conjunction with underfloor heating, but in poorly insulated properties it can still be difficult to achieve a comfortable temperature on a cold day – it is a race to generate and distribute heat around the property faster than it is lost through walls, windows, etc.

Heat pumps work well in well insulated, modern properties with low heat losses, and whilst there is a common perception that you need acres of land to run extensive ground loops, this isn’t necessarily the case.

Air to air heat pumps can however provide an excellent source of supplementary heating in an older property – reducing dependence on fossil fuels and heating costs by working alongside existing heating systems.

If you feel that a heat pump is right for you, please contact us to discuss your needs and we will advise you on the most appropriate system to meet your needs.

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