Heat Pump

Heat pumps offer a most energy-efficient way of providing heating. Even at temperatures, which we consider to be cold, the air, ground and water can contain useful heat that’s continuously replenished by the sun. By applying a little more energy a heat pump can raise the temperature of this heat energy to the level needed. The great majority of heat pumps work on the principle of the vapour compression cycle.

 

The main components in such a heat pump system are the compressor, the expansion valve and two heat exchangers referred to as the evaporator and the condenser. The components are connected to form a closed circuit. A liquid known as refrigerant, circulates through the four components. In the evaporator the temperature of the liquid refrigerant is kept lower than the temperature of the heat source, causing heat to flow from the heat source to the refrigerant, and the refrigerant evaporates. Vapour from the evaporator is compressed to a higher pressure and temperature. The hot vapour then enters the condenser, where it condenses and gives off heat. Finally, the high pressure refrigerant is expanded to the evaporator pressure and temperature in the expansion valve. The refrigerant is returned to its original state and once again enters the evaporator. The compressor is driven by an electric motor.

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Geo-thermal ground water energy

If sufficient ground water is available close to a house it may be used as a heat source. Open or closed systems are used to tap into this heat source. In open systems the ground water is pumped up, cooled and then reinjected into the ground. Open systems should be carefully designed to avoid problems such as freezing, corrosion and fouling. Closed systems can be direct expansion systems, with the working fluid evaporating in underground heat exchanger pipes, or water/antifreeze loop systems. This system is particularly appropriate when using under floor heating coils in a house. Geo–thermal heating systems have a higher installation cost than the conventional fossil fuel using heating systems.

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Geo-thermal ground energy

If the ground around your house is suitable and has sufficient area then a heat pump system may be considered. This system is also very appropriate when using under floor heating coils in a house. Heat is extracted from pipes laid horizontally or vertically in the soil and both direct expansion and water/antifreeze systems can be used. The thermal capacity of the soil varies with the moisture content and the climatic conditions.

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Air to air

Ambient air is free and is a common source of energy for commercial heat pumps when summer cooling is also required. The economics of applying air-to-air heat pumps to home heating should be examined carefully to evaluate all considerations such as the energy required to defrost evaporators during low ambient air temperature periods.