An air-to-water heat pump works by extracting heat energy from the outside air and transferring it to water, which is then used for heating or hot water production. This process leverages refrigeration principles to efficiently convert ambient air temperature into usable heat.
Here's a breakdown of the process:
1. Heat Extraction:
- The system contains a refrigerant, a fluid that easily changes between liquid and gaseous states.
- An outdoor unit containing a fan draws in outside air across a heat exchanger (evaporator).
- The refrigerant inside the evaporator absorbs heat from the air, causing it to evaporate and turn into a low-pressure gas. Even in cold temperatures, the refrigerant can boil because it has a very low boiling point. This is similar to how a refrigerator extracts heat from the inside.
2. Compression:
- The low-pressure, gaseous refrigerant is then compressed by a compressor, which increases its temperature and pressure significantly. This process adds energy to the refrigerant.
3. Heat Transfer to Water:
- The high-pressure, hot refrigerant gas flows through another heat exchanger (condenser) located inside the unit.
- Here, the refrigerant releases its heat to the water circulating through the system, warming it. This heated water can then be used for central heating (radiators, underfloor heating) or domestic hot water.
- As the refrigerant loses heat, it condenses back into a high-pressure liquid.
4. Expansion:
- The high-pressure liquid refrigerant then passes through an expansion valve (also called a metering device).
- This valve reduces the pressure of the refrigerant, causing it to cool down rapidly. This prepares the refrigerant to absorb more heat from the outside air in the evaporator, starting the cycle again.
Simplified Analogy:
Imagine a refrigerator in reverse. A refrigerator extracts heat from inside the fridge and releases it into the kitchen. An air-to-water heat pump extracts heat from the outside air and transfers it into your home.
Key Components and Their Functions:
| Component | Function |
|---|---|
| Refrigerant | Carries heat throughout the system, changing between liquid and gas to absorb and release heat. |
| Evaporator | Absorbs heat from the outside air, causing the refrigerant to evaporate. |
| Compressor | Increases the pressure and temperature of the refrigerant gas. |
| Condenser | Transfers heat from the refrigerant to the water. |
| Expansion Valve | Reduces the pressure of the liquid refrigerant, allowing it to cool down and absorb more heat. |
| Circulation Pump | Moves water through the system to radiators/underfloor heating/hot water cylinder. |
Efficiency:
The efficiency of an air-to-water heat pump is measured by its Coefficient of Performance (COP). A higher COP indicates a more efficient system. For example, a COP of 3 means that for every 1 unit of electricity consumed, the heat pump produces 3 units of heat. The COP can vary depending on factors like outside air temperature and the temperature of the water being heated.
Air-to-water heat pumps offer an energy-efficient and environmentally friendly alternative to traditional heating systems. By utilizing the freely available heat in the air, they reduce reliance on fossil fuels and lower carbon emissions.
