ASHP - HOW THEY WORK & BENEFITS

ASHP - HOW THEY WORK & BENEFITS

An air source heat pump (ASHP) is a device that transfers heat between a building and the outside air. It operates on the principles of thermodynamics, similar to how a refrigerator works, but in reverse. The basic science behind an air source heat pump involves the transfer of heat using a refrigeration cycle that can either heat or cool a space.

Here’s how it works:

1. Heat Transfer Mechanism

• Evaporation: The heat pump contains a refrigerant fluid (a substance that has a low boiling point). The process begins when this refrigerant evaporates outside the building (in the evaporator coil), absorbing heat from the ambient air, even when it’s cold outside. The refrigerant becomes a gas as it absorbs heat.

• Compression: The refrigerant gas is then compressed by a compressor. This increases the gas pressure and temperature, making it much hotter than the air inside the building.

• Condensation: The hot, high-pressure refrigerant gas then flows through a coil inside the building (the condenser coil). Here, the refrigerant releases its heat to the indoor air, causing it to condense back into a liquid state. This heat is what warms up the inside of the building.

• Expansion: The refrigerant, now in liquid form, passes through an expansion valve, where it loses pressure, cools down, and returns to the evaporator coil to start the cycle over again.

2. Reversibility (Heating and Cooling)

• In heating mode, the heat pump absorbs heat from the outside air and transfers it indoors, as described above.

• In cooling mode, the cycle is reversed. The heat pump will absorb heat from the indoor air and release it outside, working like an air conditioner.

3. Efficiency: Coefficient of Performance (COP)

One of the main benefits of an air source heat pump is its efficiency. The Coefficient of Performance (COP) measures the amount of heat the pump delivers compared to the amount of electrical energy it uses. For example, a COP of 4 means that for every unit of electricity consumed, the heat pump provides 4 units of heating or cooling. This efficiency is why heat pumps are considered much more energy-efficient than traditional heating systems like electric resistance heaters or boilers.

4. Heat Extraction from Air

Even in cold weather, the outside air still contains some heat, though the temperature might be low. Heat pumps can extract heat from air temperatures as low as -15°C (5°F), though they become less efficient as the temperature drops. At very low temperatures, an auxiliary heating source may be used to support the heat pump.

5. Environmental Impact

Air source heat pumps use electricity to run the compressor and fans but do not burn fuel like gas or oil. Therefore, they can reduce carbon emissions if powered by renewable energy sources (like solar or wind). They also have a lower carbon footprint compared to traditional heating systems.

Summary

The air source heat pump works by extracting heat from the outside air, compressing it, and transferring it inside to heat a building, or reversing the process to cool it. It’s a highly efficient, eco-friendly system because it uses renewable heat from the environment, and its efficiency improves as it moves heat rather than generating it directly.