This research invloves heat pump technologies that may be used for minimising energy requirements in commercial building heating and cooling. It also shows how space conditioning water usage can be minimised or eliminated altogether, and how systems can be used to generate electric power for local use or for sale to the grid. Savings in greenhouse gas emissions and electricity grid augmentation may also be realised.The ultimate aim of the implementation of these technologies is to produce buildings that are greenhouse neutral, or better. This is achieved when the energy generated by the building’s energy system is equal to, or greater than the energy used by the building itself.

There are outstanding research and development opportunities that need to be addressed to realise the potential of these technologies.

Conventional Heat Pumps

A heat pump is a device that uses energy, usually electricity, to move heat from a cold place to a warmer place. Typical examples are a refrigerator and an air conditioner.

Energy is consumed in the heat pump in driving a compressor. The compressor effectively removes heat from the evaporator, adds further heat, and delivers the total heat to the condenser, hence the term “heat pump”. The compressor does this by circulating a fluid called a refrigerant.
The efficiency of heat pump systems is measured by its Coefficient of Performance (COP) which is defined as the amount of heat moved divided by the energy consumed by the heat pump in moving that heat. Since the energy put into a heat pump appears on the hot side of the device, the heating COP is always greater than the cooling COP. The COP decreases as the temperature difference between the heat source and sink increases, as one might expect.

A good way to increase the performance of a heat pump is thus to decrease the temperature difference between the heat source and heat sink. This applies equally to heating and cooling modes. A performance comparison based on a heat pump with evaporating (cold side) temperature of 5°C and a condensing (hot side) temperature of 45°C is illustrated in Figure 2. In both summer and winter modes, the heat pump COP doubles with a heat sink and source temperatures of 20°C as opposed to using ambient air for heat exchange. The winter air is assumed to be at -5°C and summer air at 35°C.

Ground Coupled Heat Pumps

The addition of a ground heat exchanger (ghx) allows heat to be extracted from the ground on cold days and rejected to the ground on hot days. It usually consists of vertical pipes in the ground to a depth of about 100m, although horizontal pipes nearer the surface can be used if excavation costs are lower than drilling costs. Since the ground is very stable in temperature at depths exceeding just a few metres , a heat pump using a ground heat exchanger can be made to work much more effectively. Such a system is called a ground coupled heat pump (gchp).

The properties of the soil are very important to the operation of the ground heat exchanger and this requires careful management The ground heat exchanger can be made much smaller with the use of phase change materials as energy storage in the system.

Conventional heat pump

Performance improvement with ground heat exchange

Using PCM and GHX in cooling mode

Using PCM and GHX in heating mode