A glimpse into renewable solutions for your home

Nowadays, in the UK one may observe an installation boost of domestic renewable heating technologies. Thanks to the Renewable Heat Incentive or RHI, a governmental financial subsidy, alongside with chances to lower energy bills and reduce carbon footprint – all these make the renewables a promising alternative to conventional fossil fuel systems. Among the four main types of green solutions, namely solar thermal, biomass, ground source and air source, the latter seems to be the perfect option, especially in off-gas areas.

What kind of air source heat pump is to choose?

Since there are two kinds of air source heat pumps – air-to-air and air-to-water, people often get puzzled which one is suitable for their domestic property. We have a definite answer for you - since an air-to-water type is the only one that is eligible for the RHI, it would hardly be a wise decision to deprive yourself of a pleasure of getting paid for 7 years. This being so, let us have a closer look at the functioning principles of air-to-water heat pumps.

How do air source heat pumps work?

An air source heat pump runs on electricity, though the heat it utilises is renewable. A high coefficient of performance or COP is one of the most prominent advantages of air source heat pumps. It accounts for 300-400%, meaning that for one unit of power it consumes, it generates up to 4 units of renewable energy. Heat pumps function much like an ordinary refrigerator in your kitchen that gets heat from the inside. An air source heat pump acts in a reversed way - it extracts heat from the outside ambient air and uses it for indoor heating. Its external unit looks similar to the air conditioner and usually is fitted at the back wall of your house. The surrounding area must be open for a fan inside the unit to always draw in warmth from the air flow.

How the heat is extracted

Depending on the make of a certain heat pump, they may vary in design and power capacity, still the core components remain the same. An average air source heat pump has an outside unit, a pump itself and a water storage and distribution system. The air from the environment is drawn through the outside heat pump unit by a fan. The heat is transferred and transported by virtue of a refrigerant. This special -purpose substance flows over the heat exchanger coils in two forms – gaseous and liquid states. Inside the heat pump unit, there is a closed-looped system that has evaporation and condensation cycles for a refrigerant to go through. When the heat gets into the loop it is carried by a refrigerant to the evaporation point. Once the refrigerant is vaporised it then goes to a compressor where the temperature of the absorbed heat is significantly increased by means of high pressure. The high-temperature vapour is brought inside the second coil by a condenser to be released via water storage and distribution system to warm your home. When the refrigerant cools down, it turns back into a liquid state and the cycle starts over again.

Do air source heat pumps work in winter?

When it comes to subzero degrees, one may presume that an air source heat pump fails to work at lower temperatures as there is no heat as such to be absorbed in wintertime. This conventional wisdom must be upended – the temperature of zero degrees ℃ means only the water’s freezing point with absolute zero being at minus 273 ℃. Thus heat pumps perform properly in usual winter climate in the UK under the temperatures as low as minus 15-20 degrees ℃.

Seasonal Performance Factor (SPF) for an air source heat pump

You should consider, however, that the actual coefficient of performance may vary. This is known as Seasonal Performance Factor or SPF. It is defined as the ratio of renewable heat generated to electricity consumed as an average over a year. The SPF mostly depends on the region you live in, your home insulation improvements, and the overall area of radiators and underfloor heating. Make sure your heat pump has at least an SPF value equal to 2.5 as it is a minimum value to be eligible for the RHI scheme.


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How does an air source heat pump work?