Split System Air Source Heat Pump
The refrigerant is heated across the heat exchanger in the outdoor fan unit and then passes inside the building where it is compressed in an indoor heat pump unit transferring heat to water for space heating and domestic hot water.
Air to Air Heat Pump
The refrigeration cycle takes place in the outdoor heat pump unit and hot gas (or cold gas when cooling) is passed inside to a fan convector mounted on the wall or in the ceiling. Hot or cold air is distributed into the room via the fan convector. Air to air heat pumps do not heat water and are not eligible for the RHI.
During operation, the fan contained within the external unit does omit some noise, therefore the location of the heat pump needs consideration – not located near bedrooms, for example. Having said that, higher quality units tend to be quieter. Also, when the heat has been extracted from the ambient air, cold air is expelled, which again requires some consideration in terms of locating the unit. Also, drainage needs to be considered under the external unit to take care of condensation from the heat exchanger. An air source heat pump is more efficient when ambient temperatures are higher, but it is important to look at the energy performance calculation for the year when doing comparisons with other systems.