Air source heat pumps are heating and cooling systems that use air from outside as a heat source.
It can capture heat from the air even when the temperature is as low as -15 °C (-59 °F). This heat can be used for heating warm air convectors, underfloor heating systems, heat radiators and hot water for domestic purposes.
Based on the principles of vapor compression refrigeration, an air source heat pump employs a refrigerant system that includes a compressor and a condenser for absorbing heat from one place and releasing it at another place. Air source heat pumps are usually known as reverse-cycle air conditioners when it is used as a space heater.
Heat pumps may create some environmental impact as they require electricity for operation. However, the heat extracted from the air, water or ground will be constantly renewed naturally. When used for domestic purpose, they can absorb heat from outside air and release it inside the building during winter, and can do the reverse in summer. Air source heat pumps can provide a full central heating solution and hot water up to 80 °C (176 °C) for domestic purposes.
How do Air Source Heat Pumps Work?
Air source heat pumps operate more like a refrigerator. Each heat pump consists of an evaporator, expansion valve, compressor and condenser for changing the state of the refrigerant from a liquid to hot gas and a gas to cold liquid.
In the air source heat pump, liquid refrigerant is passed via air coils at a low temperature. The air driven by an external fan enters the unit and the heat is transferred to the refrigerant. As a result, the refrigerant boils and vaporizes.
The vapor is now passed into the compressor to increase the pressure and temperature of the gas. It is then drawn into the condenser, the vapor is then transferred to water, used for heating the building.
The vapor condenses back into liquid as it cools and releases latent heat to water passing via the heat exchanger. The refrigerant, which is a cold liquid at high pressure, passes through an expansion valve for reducing the pressure so as to allow the cold liquid to re-enter the evaporator and start a new cycle.
Benefits of Air Source Heat Pumps
The key benefits of air source heat pumps include the following:
- Carbon dioxide generated by air source heat pumps is lesser than conventional heating systems. The heat pump can save 5 t of carbon dioxide a year by replacing electric heating and 4.6 t for solid fuel heating.
- They are highly energy-efficient and have the potential to produce two and a half times the electricity they consume for their operation.
- They require very less maintenance.
- Easy to install.
- They are inexpensive than ground source heat pumps.
- They can produce both space and water heating.
Limitations of Air Source Heat Pumps
Some of the major limitations of air source heat pumps include the following:
- They have relatively high installation costs, but less expensive than most of the ground heat pumps.
- Their efficiency turns down as external temperature falls below 5 °C (41 °F). Therefore, an additional heating source is required during cold weather.
- They require electricity to drive the pump, and hence they cannot be considered completely zero-carbon unless the energy is produced by a renewable source like wind turbine or solar power.
- They require extra space for an external condenser unit.
- External condenser unit could be noisy.
Advanced Technologies of Air Source Heat Pumps
Reverse Cycle Chiller
One of the most efficient innovations in air-source heat pumps is a reverse cycle chiller (RCC) as it offers choices from a wide range of heating and cooling distribution systems. The RCC may be the least expensive heating source of all other heating choices, based on other fuel rates.
It includes 12 SEER, single speed, air-source heat pumps connected to an insulated tank of water that is cooled or heated. Most systems employ a fan coil having ducts for storing water to heat or cool the air and distribute it inside the house.
The RCC heat pump can be operated at peak efficiency even at low temperatures. Therefore, the RCC offers great comfort and economy without using the electric resistance auxiliary heating coils.
Cold Climate Heat Pump
The cold climate heat pump features a plate heat exchanger for enhancing the performance of the heat pump, a two-speed, two-cylinder compressor for efficient operation, and a back-up booster compressor for allowing the pump to operate efficiently at temperatures below -9.4 °C (15 °F).
All-Climate Heat Pump
An all-climate heat pump is another promising technology that can be operated during winter in the absence of supplemental heat so as to maintain comfortable indoor temperatures even when the outdoor temperature falls below zero. It can reduce the heating and cooling costs by 25 to 60%.
Sources and Further Reading