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Heat Pump - How It Works

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The best way to understand how a heat pump works is to remember that temperature and the concept of hot or cold is subjective. With the coldest possible temperature being absolute zero at -273°C, your average fridge at 5°C could be perceived as hot! Heat is energy, the more intense the energy the higher the temperature produced.

What an air source heat pump does is absorb heat from the outside air and intensify it to increase its temperature. The increased heat can then be used to heat radiators, underfloor heating systems, or warm air convectors and hot water in your property.

An air source heat pump extracts heat from the outside air in the same way that a fridge extracts heat from its inside. It can extract and intensify the heat from the air outside even when the temperature is as low as -20°C, although efficiency decreases at lower outside temperatures. A heat pump will still have some impact on the environment as they need electricity to run, but a pump can produce up to 5kWh of heat for every 1kWh of electricity used to extract it, a ratio of 5:1. And remember the heat they extract from the ground, air, or water is constantly being renewed naturally, so if coupled with a Solar Photovoltaic array to account for the electricity used it is possible to have a Carbon Neutral heated property.

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There are two main types of air source heat pump system:

An air-to-water system distributes heat via your wet central heating system. Heat pumps work much more efficiently when heating water to a slightly lower temperature than a standard boiler system would (60°C). So they are generally better suited to underfloor heating systems. However, an air to water system can work very will without underfloor heating by ensuring a property is insulated to normal building standards and increasing radiator size by an average of 30%. Hot water is also produced and stored in a tank using this system.

An air-to-air system produces warm air, which is circulated by fans to heat your property and look very similar in size, layout and style to air conditioning units. They are unlikely to provide you with hot water as well, but can provide an air cooling mode.

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In Greater detail:

Moving a refrigerant through the heat pump’s indoor and outdoor coils achieve heating and cooling. Like a fridge, a compressor, condenser, expansion valve and evaporator are used to change states of the refrigerant between a cold liquid and a hot gas.

When the liquid refrigerant at a low temperature passes through the outdoor evaporator heat exchanger coils, ambient heat from the air is absorbed and causes the liquid to boil. This boiling or change of state process builds energy as latent heat. The gas vapour produced by the boiling refrigerant is then drawn into a compressor, which further boosts its temperature.

Passing into the building, the vapour enters the condenser heat exchanger coils where it transfers heat to indoor air/water, which is drawn across the coils by a fan/pump. As the vapour cools, it condenses back into a liquid, and releases its latent heat.

Exiting the condenser, the cold liquid refrigerant is under high pressure. The refrigerant passes through an expansion valve, which reduces the pressure, draws in heat and allows the refrigerant to re-enter the evaporator to begin a new cycle.

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