How Do Air Source Heat Pumps Work?

how do air source heat pumps work
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    Simply put, a heat pump is a device that transfers thermal energy from one point to another. A common example of this can be found in our refrigerators where the evaporation and cooling of a liquid is used to lower the temperature of the storage compartment. Nowadays, this technology can also be used to extract the potential thermal energy in the air outside, or even from the ground, feeding it directly into your home where it is compressed and the heat transferred using a series of coils. It sounds like magic but the science behind it is relatively simple… Although they use a small amount of electricity to run, heat pumps are considered highly efficient and clean because they don’t depend on the burning of fuel to create heat. They perform well in moderate climates such as the UK and can provide heating during the winter, even at temperatures of -20 degrees Celsius. There are two main kinds of heat pumps depending on the type of medium they extract heat from, namely air or ground/water. Heat pump technology has become much more widespread in recent years, and will no doubt continue to grow in popularity once the ban on gas boilers for new builds comes into effect in 2025. how do air source heat pumps work

    How air source heat pumps work:

    So we’ve learnt that air source heat pumps don’t generate heat for themselves, but extract it from the atmosphere/air, but how?
    1. Outside air is drawn into the unit and passed over the evaporator fins with the fan.
    2. Electrical energy is provided by the grid, or a renewable source such as solar PV or batteries – this is what powers the fan and compressor.
    3. As the name suggests, the evaporator is where the refrigerant gas boils and evaporates (heated by the energy in the outside air.
    4. The gas passes into the condenser where it passes its heat to the heating system flow. As it releases its energy, it cools, condenses, and returns back to a liquid.
    5. The heating flow is heated by the hot, compressed refrigerant gases and is pumped around your heating system.
    6. The liquid refrigerant passes through an expansion valve, reducing its pressure and temperature, and the whole cycle starts over.
    This cycle is continuous, with refrigerant at all different stages of state (gas, liquid etc) at any given moment. It is this cycle that enables a heat pump to provide more energy than it consumes.

    What Is The SCOP And Why Is It Important?

    SCOP stands for Seasonal Coefficient Of Performance and is the official figure assigned to all air source heat pumps. It is the ratio between the input/output energy. To be eligible for the Boiler Upgrade Scheme (BUS), heat pumps need to have a minimum SCOP rating of 2.8.

    What Is The Minimum Temperature ASHP’s Work?

    Most air source heat pumps operate down to around -15°C, however, are more efficient at temperatures of 0°C and higher.

    Are Air Source Heat Pumps Noisy?

    This is a common misconception with air source heat pumps. Most air source heat pumps operate at between 40-60 decibels. We often compare the noise levels to that of a domestic microwave. how air source heat pump heats hot water

    How Does It Pump Heat My Hot Water?

    Heat pumps are more efficient, when commissioned at lower temperatures (the SCOP value is increased), and as such, this means that we want to design your air source heat pump system to operate at the lowest temperature possible. We generally design our systems to operate between 35°C – 45°C for underfloor heating systems, and 50°C – 55°C for radiator systems. This presents an issue when it comes to heating your hot water, which must be stored at 60°C, or greater, to avoid the risk of legionella. As such, the heat pump will rely on the electric immersion heater to top its cylinder up from its flow temperature, to that required by your hot water system

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    Picture of Dan Loveridge
    Dan Loveridge

    Dan is the managing director at Cinergi, a renewable energy company based in southern England specialising in air source heat pumps and EV charging solutions.

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