Heat pumps use the reverse cycle of a refrigeration plant to heat water. In effect, it transfers heat from a source such as air which is sucked over the condenser by means of an electric fan. This fan has large area blades so as to maximize the volume of air moving across the condenser coil. The latent heat energy of the air is transferred to the gas within this condenser coil which pre-heats the gas and in this way reduces the work that the compressor has to finally do. The compressor increases the pressure and the refrigerant gas is heated as a result of the increased partial pressure. This heat is passed on to the water circulating in one channel of a double walled heat exchanger with the heated gas in the other. The coefficient of performance, or COP, is a measure of the performance of a heat pump. A typical value for COP is 4. This implies that the heating capacity is 4 times the amount of electrical energy that is required from ESKOM. So, if the heat pump is powered by 1 kW of ESKOM power then the heating capacity will be the equivalent of a 4 kW heating element. The saving is therefore 75% to the consumer.
As in other refrigeration equipment, the heat pump system employs an evaporator, a compressor, a condenser, refrigerant gas, and an expansion valve as its main components, forming a closed heating circuit. A dedicated controller allows the user to set operational times and desired water temperature. Some factory pre-set values, and on board error codes, ensure safety to the end-user. Hot water temperatures normally range from ,55-0 .C to, 60-0 .C, controlled by a thermostat integrated with the controller functions.
In the case of a typical domestic heat pump, two types of configurations can be found. In the first case the entire system is contained in one unit that consists of a storage tank and a heat pump. In the second configuration the tank is separated from the heat pump. Domestic heat pumps are typically mounted on the outside walls of buildings under the eaves or at ground level depending on the configuration of the system. Commercial heat pumps are installed in the boiler rooms, near the buffer tanks. Noise pollution is minimal as is maintenance, due to few moving parts.
