Heat Pumps - Energy Systems Research Unit


Heat Pump


Heat pumps use electricity to move heat from a cool space into a warm space, making the cool space warm and the warm space cool. Heat pumps offer an energy-efficient alternative to furnaces and air conditioners. They require work to move thermal energy from a cold source to a warmer heat sink

(inside the home). There are currently three types of Heat Pump: An Air Source Heat Pump (ASHP) uses the outside air as its cold source, Ground Source Heat Pump GSHP uses the ground as its cold source and a Water Source Heat Pump uses water from a lake or swimming pool as its cold source.

Mechanics of a Heat Pump

A heat pump works in a similar way to a fridge, however with heat pumps the outside source is chilled and the inside air is heated up. The Heat Pump manipulates a refrigerant with a low boiling temperature to move the heat from a colder space to a warmer space. Below is a description and diagrams of the steps a refrigerant goes through:


Refrigerant is compressed to superheated steam. Electrical energy is put into the system in this stage of the process.


Fluid is passed over the refrigerant in a heat exchanger. Latent and Sensible Heat is released by the refrigerant as it reduces in temperature and becomes a liquid. The Fluid passing over it extracts all this heat and is used to warm the house.


The refrigerant then passes through an expansion valve where the pressure abruptly decreases, this causes flash evaporation. The refrigerant is now at a low pressure and mixed water vapour.


The refrigerant is the taken outside where it extracts heat from the outside air to becomes saturated vapour again. Outside source is cooled. At low outside temperatures, below -5 degrees, heat energy can’t be readily extracted by a heat pump and efficiencies fall.

Figure # - The water-vapour cycle of a heat pump Figure # - Schematic of heat pump cycle

Heat Pumps work best with heating systems which are optimised to run at a lower water temperature than is commonly used in UK boiler and radiator systems. As such, they make an ideal partner for under floor heating systems.

Heat pumps are typically measured by their Coefficient Of Performance (COP). This is how much heat energy can be distracted by each unit of electricity put in.

Suitability for using ASHP

The ASHP is a suitable option for heating the houses in this community.

Suitability for using GSHP

The GSHP is not a suitable option for heating the houses in the community. The GSHP requires a cooling load within the house during summer months. This is to put heat back into the ground from where heat was extracted; otherwise the ground is likely to develop permafrost as heat is being continually extracted from it. This is damaging to the ground and effectively stops the GSHP from working. For the climate in Ayrshire, a cooling load is not required during summer months so a GSHP is not feasible.

Suitability for using WSHP

The WSHP is not a suitable option for heating the houses in the community because there are no readily available sources of still water nearby.