How do Air Source Heat Pumps Work?
An air source heat pump (ASHP) is a system used both for heating and cooling buildings by exploiting the thermal energy available in the air outside. It operates on the same basic principles as a refrigerator but in reverse, moving heat from the outside air into a building to warm it, or from inside the building to the outside to cool it. Here’s a simplified explanation of how it works:
1. Absorption of Heat from the Air
The ASHP begins its cycle by pulling outside air into the system. It uses a liquid refrigerant, which circulates through an outdoor coil and absorbs heat from the air. Even if the air outside is cold it still contains enough thermal energy for the refrigerant to absorb and turn from a low-temperature liquid into a low-pressure gas.
2. Compression
This low-pressure gas is then compressed by an electric compressor that sits within the heat pump. Compression increases the temperature of the refrigerant gas significantly, turning it into a high-temperature, high-pressure gas.
3. Heat Transfer to the Indoor Space
The hot gas flows through a heat exchanger (indoor coil) inside the building. As indoor air or water runs across this coil, heat from the refrigerant is transferred to the air or water to produce warm air or water to run radiators and provide hot water. The refrigerant cools down as it transfers its heat and condenses back into a liquid.
4. Expansion
Afterwards, the liquid refrigerant passes through an expansion valve, reducing its pressure and temperature and readying it to absorb heat from the outdoor air again. This process continuously cycles to heat the building.
Cooling Mode
For cooling, the system operates in reverse. It absorbs heat from the indoor air and expels it outside cooling the building interior. This works by reversing the flow of the refrigerant, often through a device called a reversing valve.
Efficiency and Environmental Impact
ASHPs are considered energy-efficient and environmentally friendly compared to traditional heating systems that rely on fossil fuels. They use electricity to move heat rather than generate it, which means they can produce several times the energy they consume in electricity. Their efficiency is often measured by the coefficient of performance (COP) for heating and the energy efficiency ratio (EER) or seasonal energy efficiency ratio (SEER) for cooling.
This technology is especially effective in moderate climates but is also increasingly being designed to work efficiently in colder regions. It represents a sustainable option for heating and cooling by reducing greenhouse gas emissions and reliance on non-renewable energy sources.
