An air source heat pump (ASHP) is a device that heats and supplies water to a home by moving heat rather than generating heat by burning fuel. It works a bit like a refrigerator running in reverse.
This is the core idea, step by step.
Basic Principle: Move Heat, Not Create It
Even the cold air outside contains heat energy. ASHP extracts low-temperature heat and concentrates it into a higher temperature available indoors.
It does this using a refrigeration cycle with four main components:
1. Evaporator (outdoor unit coil)
2. Compressor
3. Condenser (indoor unit coil)
4. Expansion valve
Refrigerant circulates through these components, changing between liquid and gas.
Step by step function
1. Heat absorption (outdoor unit)
* Very low pressure liquid refrigerant flows into the outdoor evaporator coil.
* Since it has an extremely low boiling point (e.g. -40°C), it absorbs heat from the outside air and evaporates into a gas, even when the air feels cold.
2. Compression
* Gaseous refrigerant enters the compressor, and the compressor squeezes it.
* Compressing gases drastically increases their pressure and temperature (e.g. to 70–80 °C).
3. Heat dissipation (indoor unit)
* Hot high pressure gas flows to the indoor condenser coil.
* Here, it transfers heat to your home's heating system (air, water, or underfloor) and condenses into a liquid.
4. Extension
* As the liquid passes through the expansion valve, the pressure drops sharply.
* This will cool it down and prepare it to absorb heat again.
* The cycle repeats itself.
its role in your home
1. Space Heating: Condensers heat air (air to air) or water (air to water) for radiators, floor heating, or fan coils.
2. Hot water: Many systems also heat domestic hot water cylinders.
3. Cooling (optional): A reversing valve can swap the roles of evaporator and condenser, so the system extracts heat from the room and discharges it to the outside (air conditioning).
4. Defrost Mode: In cold, wet conditions, frost may form on outdoor coils. The system was briefly reversed to melt it.
why it works
1. Because it transfers heat rather than burning fuel, the ASHP can provide 2-4 kWh of heat for every 1 kWh of electricity used. This ratio is the coefficient of performance (COP) or seasonal COP (SCOP).
2. As the outside air gets colder, efficiency decreases because less heat is extracted and defrost cycles become more frequent. But modern cold climate models can still work well below freezing.
Main limitations
1. Performance degrades in extremely cold conditions (although models vary widely).
2. A suitable outdoor location with good ventilation is required.
3. The output temperature is lower than a gas boiler, so it is best suited for larger radiators, underfloor heating or well-insulated homes.
4. Even if the efficiency is high, electricity and natural gas prices will affect operating costs.
In one sentence
Air source heat pumps use a refrigerant cycle to extract free heat from the outdoor air, concentrate it through a compressor, and release it indoors, providing more heat energy than the electricity it consumes.
An air source heat pump (ASHP) is a device that heats and supplies water to a home by moving heat rather than generating heat by burning fuel. It works a bit like a refrigerator running in reverse.
This is the core idea, step by step.
Basic Principle: Move Heat, Not Create It
Even the cold air outside contains heat energy. ASHP extracts low-temperature heat and concentrates it into a higher temperature available indoors.
It does this using a refrigeration cycle with four main components:
1. Evaporator (outdoor unit coil)
2. Compressor
3. Condenser (indoor unit coil)
4. Expansion valve
Refrigerant circulates through these components, changing between liquid and gas.
Step by step function
1. Heat absorption (outdoor unit)
* Very low pressure liquid refrigerant flows into the outdoor evaporator coil.
* Since it has an extremely low boiling point (e.g. -40°C), it absorbs heat from the outside air and evaporates into a gas, even when the air feels cold.
2. Compression
* Gaseous refrigerant enters the compressor, and the compressor squeezes it.
* Compressing gases drastically increases their pressure and temperature (e.g. to 70–80 °C).
3. Heat dissipation (indoor unit)
* Hot high pressure gas flows to the indoor condenser coil.
* Here, it transfers heat to your home's heating system (air, water, or underfloor) and condenses into a liquid.
4. Extension
* As the liquid passes through the expansion valve, the pressure drops sharply.
* This will cool it down and prepare it to absorb heat again.
* The cycle repeats itself.
its role in your home
1. Space Heating: Condensers heat air (air to air) or water (air to water) for radiators, floor heating, or fan coils.
2. Hot water: Many systems also heat domestic hot water cylinders.
3. Cooling (optional): A reversing valve can swap the roles of evaporator and condenser, so the system extracts heat from the room and discharges it to the outside (air conditioning).
4. Defrost Mode: In cold, wet conditions, frost may form on outdoor coils. The system was briefly reversed to melt it.
why it works
1. Because it transfers heat rather than burning fuel, the ASHP can provide 2-4 kWh of heat for every 1 kWh of electricity used. This ratio is the coefficient of performance (COP) or seasonal COP (SCOP).
2. As the outside air gets colder, efficiency decreases because less heat is extracted and defrost cycles become more frequent. But modern cold climate models can still work well below freezing.
Main limitations
1. Performance degrades in extremely cold conditions (although models vary widely).
2. A suitable outdoor location with good ventilation is required.
3. The output temperature is lower than a gas boiler, so it is best suited for larger radiators, underfloor heating or well-insulated homes.
4. Even if the efficiency is high, electricity and natural gas prices will affect operating costs.
In one sentence
Air source heat pumps use a refrigerant cycle to extract free heat from the outdoor air, concentrate it through a compressor, and release it indoors, providing more heat energy than the electricity it consumes.
