Air source heat pumps are more efficient than oil, gas, and electric resistance heating in mild climates but they are less efficient than ground source heat pumps because a ground source heat pump draws energy from the ground which is warmer than the external air in winter. However, air source heat pumps are cheaper to install than ground source heat pumps as they avoid the cost of installing a ground loop. An air source heat pump is a type of heat pump which uses the outside air as a heat source or heat sink to heat or cool an interior space. Domestic hot water storage can also be provided.
An Air Source Heat Pump uses the refrigeration process and transfers low temperature energy to a refrigeration loop, compresses the refrigerant to a high temperature, and transfers this heat to the hot water and heating distribution system, or, in the summer, removes it. A heat pump transfers energy in the form of heat from a cooler location to a warmer location. Systems normally range from a single 4kW unit to multiple units with a single controller producing around 300kW.
Air Source Heat Pumps - Bullet Points
- Reduced Carbon Emissions / Lower Heating Costs
- Utilises approximately 25% – 35% of the electricity of a standard electrically heating system for the same amount of heating, reducing utility bills. This typical efficiency compares to 70-95% for a fossil fuel powered gas boiler
- Few moving parts, reducing maintenance requirements
- As an electric system, no flammable or potentially asphyxiating fuel is used at the point of heating, reducing the potential danger to users, and removing the need to obtain gas or fuel supplies (except for electricity)
- May be used to heat air, or water
- The same system may be used as a cooler in summer, as well as a heater in winter
- Can be utilised in conjunction with Underfloor Heating Installations, Solar Panel Technology and other Eco Friendly Heating & Hot water systems
Air Source Heat Pumps - The Technical Points
In the outdoor unit the refrigerant meets the outdoor air in the evaporator (heat exchanger). The air is drawn through the evaporator by a fan located on side of the Air Source Heat Pump. The refrigerant, which is in a liquid state absorbs free energy from the air and evaporates in this process. A sensor in the expansion valve ensures that the liquid refrigerant collects the correct amount of the ‘free energy’ before the refrigerant (now in a gas state) is led into the compressor. The compressor increases the pressure of the refrigerant. The temperature of the vapour reaches approximately 100°C. The warm gas is then led into the condenser. The condenser is the heat pump’s heat emitting part. In the condenser, which is a fully brazed heat exchanger in stainless steel, the refrigerant (gas state) meets the water from the heating system (radiators and/or floor coils). When the warm gas is cooled by the circulating heating water, it condenses into a liquid state.
Energy is emitted in this process to the heating system or the hot water. After the condenser, the refrigerant, which is now in liquid form, continues through a drying filter. The drying filter is used to collect any moisture in the system. After the filter it continues on to an expansion valve. The refrigerant pressure is lowered in the expansion valve. This also causes the temperature to drop. When the refrigerant has left the valve and passes the evaporator it changes to vapour again. This completes the refrigerant circuit. The expansion valve is equipped with a sensor (bulb) just before the compressor. The sensor controls the amount of fluid entering the evaporator.
Air Source Heat Pumps - Applications
Air source heat pumps do not incur any ground works cost for the installation and laying of pipe. The cost of ground works can be significant for ground source heat pumps. Air Source Heat Pumps provide a low cost solution for space heating and hot water. Return on investment against oil and LPG heating systems can take as little as five years. Air Source Heat Pumps are also suitable for hot water and comfort cooling for both domestic and commercial use.
Air Source Heat Pumps - Anything Else?
Air source heat pumps also provide hot water from a pressurised system up to temperatures of 55°C which is suitable for domestic and business requirements. It may be appropriate to couple traditional heating technology to an air source heat pump to boost temperatures above 55°C. The fan intake system (outdoor air handling unit) is fixed to the outside of a building and requires no annual maintenance.
For commercial and large spaces a row or bank of air source heat pumps (air handling units) will be required along with internal heat pump and pressured hot water tank for water supply. Air source heat pumps can be used where land space is restricted. Air sourced heat pumps can be used for room heating using the same distribution system as a ground source heat pump or a traditional system.
Air source heat pumps have no major parts outside exposed to the elements, the organ’s compressor and circulation pumps are all internal. The intake fan is the only feature which is external and kept at optimum working temperature with the support of an internal defrost cycle system ensuring operation in all seasons. The internal defrost system uses the hot water collected by the air source heat pump as opposed to direct electric. Air source heat pumps should last for over 20 years with low maintenance requirements.