What is an air source heat pump?
An Air Source Heat Pump is the best replacement for an existing boiler. The heat pumps extract heat from the air outside, similar to a fridge extracting heat from its inside. No matter what the outside temperature is (can be as low as -20°c,) heat can be extracted. As they need electricity to run, Heat pumps do still have an impact on the environment, however, the heat they do extract from the surrounding elements is constantly being renewed.
The technical part:
The fan at the top of the outdoor unit draws in air.
Refrigerant within the unit – which at this stage is in a liquid state – absorbs energy from the air and evaporates. A sensor ensures that the liquid refrigerant collects the correct amount of the ‘free energy’ before the refrigerant (now in a gas state) is led into the compressor.
The compressor increases the pressure of the refrigerant. The temperature of the vapour reaches approximately 100°C. The warm gas is then led into the condenser.
The condenser is the heat pump’s heat emitting part. In the condenser (which is a fully brazed heat exchanger in stainless steel), the vaporised refrigerant meets the water from the heating system (radiators and/or floor coils). When the warm gas is cooled by the circulating heating water, it condenses back into a liquid state. Energy is emitted in this process to the heating system or the hot water. After the refrigerant has been through the condenser, it continues through to a drying filter.
The drying filter is used to collect any moisture in the system. After the filter, the refrigerant passes through a sight glass. The sight glass is used to check the level in the system. There should be no bubbles in the sight glass during normal operations. However, there might be bubbles when the heat pump is started and stopped or during defrosting. After the sight glass, the refrigerant continues to an expansion valve.
The refrigerant pressure is lowered in the expansion valve. This also causes the temperature to drop. When the refrigerant has left the valve, it passes the evaporator and changes to vapour again. This completes the refrigerant circuit. The expansion valve is equipped with a sensor (bulb) just before the compressor. The sensor controls the amount of fluid entering the evaporator.