Buying an Air Source Heat Pump – All You Need to Know

Heat pumps are machines that can take heat from one place and then deliver that heat to another place at a higher temperature. Your home refrigerator is similar to a heat pump. The difference is that the refrigerator does not compress the refrigerant gas to raise the temperature, it just draws the heat from the contents of your fridge and dispatches that heat through the heat exchanger (the grill) at the rear of the fridge.Heat pumps extract renewable energy from the ground, water or air (which has been heated from the sun) and transfer it to your home at a ratio of 1: 4 or more. Let's say for every 1 KW / h of electrical energy that you use to drive the heat pump, around 4 KW / h of heat will be produced for use in your home.
There are three different types of heat pumps:

  • Ground source heat pumps (GSHP)
  • Water source heat pumps (WSHP)
  • Air source heat pumps (ASHP)

This article gives information on air source heat pumps.
The advantages of air source heat pumps are that they are:

  • Cheaper to purchase than other heat pumps such as ground and water source heat pumps
  • Easy to install – can be installed in apartments
  • More energy efficient than traditional non-renewable energy systems
  • Capable of having reverse-cycle, ie. has a heating and cooling mode like all geothermal heat pumps
  • Available as 'Reverse Cycle chillers' capable heat pumps that offer additional heating and domestic hot water options
  • Energy efficient and result in reduced annual fuel bills

The disadvantages of air source heat pumps are that:

  • They are not as efficient as other heat pumps, such as ground and water source heat pumps
  • The performance and efficiency of air source heat pumps can be affected by:
    • Sustained temperatures below freezing
    • High or no wind conditions
  • Can be noisy although some systems are quieter than others
  • Can be intrusive although slim-lined models are available

When Choosing An Air Source Heat Pump , consider the following points:

  • Choose a heat pump that has defrost control. Basically this reverses the heat flow to defrost the external coil which will reduce the supplementary electrical energy use for heating by the heat pump.
  • Remember that fans and compressors make noise. If at all possible try to locate the outside unit away from windows and from any windows in adjacent buildings. Noise can be further reduced by mounting the external unit on a sound absorbing base. All external units should have a sound rating – try selecting units that have a sound rating of 76 decibels or lower.
  • Make sure that the outdoor unit is protected from high winds as this will affect the efficiency of the heat absorption process. The right fencing and planting can achieve this. There are in development 'Cold Climate Heat Pumps' that have a two speed two-cylinder compressor, and a back-up booster compressor. These features allow this system to operate efficiently in temperatures as low as -9 o C.
  • If you are going to use the heat pump more in the heating mode rather than the cooling mode then installing the indoor unit in a low wall posistion is better as this will increase its heating efficiency. This is because warm air rises. However, if you are using the heat pump more for cooling, then install the unit high on the wall as this position will increase its cooling efficiency.
  • There are slim-lined indoor heat pump units available. They can be recessed into the wall to make them less intrusive in the room.