Heat pumps provide central heating by transferring heat from an external source to inside a building, even when the outside air feels cold.
Here's a breakdown of how they accomplish this:
The Heat Pump Process
-
Heat Absorption: The heat pump uses a refrigerant fluid that circulates through a closed system. This refrigerant absorbs heat from the outside air, ground, or water (depending on the type of heat pump). Even on cold days, there's still some heat energy present.
-
Evaporation: As the refrigerant absorbs heat, it evaporates and turns into a low-pressure gas.
-
Compression: The gaseous refrigerant then enters a compressor, which increases its pressure. Compressing the gas also raises its temperature significantly.
-
Heat Exchange: The high-temperature, high-pressure refrigerant gas flows through a condenser coil inside the house. Here, it releases its heat to the air or water of the central heating system (radiators, underfloor heating, or forced-air systems). As the refrigerant releases heat, it condenses back into a liquid.
-
Expansion: The liquid refrigerant then passes through an expansion valve, which reduces its pressure and temperature. This cooled, low-pressure liquid refrigerant is now ready to begin the cycle again by absorbing more heat from the outside.
Types of Heat Pumps Used for Central Heating
Heat pumps come in several types, each drawing heat from a different source:
-
Air Source Heat Pumps (ASHPs): These extract heat from the outside air. They are the most common type due to their ease of installation and lower upfront cost. However, their efficiency can decrease significantly in very cold temperatures.
-
Ground Source Heat Pumps (GSHPs): These extract heat from the ground via buried pipes. The ground temperature remains relatively constant year-round, making GSHPs more efficient than ASHPs, especially in colder climates. However, they require significant excavation for installation, increasing the cost.
-
Water Source Heat Pumps (WSHPs): These extract heat from a nearby body of water (e.g., a lake or well). Like GSHPs, they offer consistent performance because water temperatures are relatively stable.
Key Advantages of Heat Pumps
- Energy Efficiency: Heat pumps are highly efficient because they transfer heat rather than generating it directly, consuming significantly less energy than traditional furnaces or electric resistance heaters.
- Reduced Carbon Emissions: By using electricity instead of fossil fuels, heat pumps can reduce carbon emissions, especially when powered by renewable energy sources.
- Heating and Cooling: Most heat pumps can also provide cooling by reversing the heat transfer process, making them a versatile option for year-round comfort.
Example
Imagine an air source heat pump operating on a day when the outside temperature is 35°F (1.7°C). The refrigerant in the outdoor unit absorbs the available heat from the air, even though it feels cold to us. The refrigerant, now a low-pressure gas, is compressed, raising its temperature to well over 100°F (38°C). This hot gas is then circulated through the indoor unit, where it releases heat into your home's heating system, warming your living space.
