How a Heat Pump works
The heat pump works on the same characteristics as a standard domestic fridge but in reverse, instead of cooling, it heats. Heating and cooling are achieved by moving a refrigerant through various indoor and outdoor coils and components. A compressor, condenser, expansion valve and evaporator are used to change the state of refrigerant from a liquid to hot gas and from a gas to cold liquid.
- The refrigerant (liquid state) passes through the outdoor evaporator coils at a low temperature.
- The water/antifreeze from the ground loop enters the unit and heat is transferred from this water/antifreeze to the refrigerant. The refrigerant begins to boil and changes to a vapour.
- The vapour is pressurised by the compressor where the temperature is increased to over 100 degrees.
- The vapour then enters the condenser heat exchanger and the heat is given up to the coils. At this point, the heat is transferred to the buildings heating, and hot water systems. As it passes through the coils, it cools and turns back into a liquid.
- The refrigerant which is now cooled liquid at high pressure passes through an expansion valve, which reduces the pressure so that the liquid can re-enter the evaporator and begin the cycle again.
Read More on the Efficiency of Heat Pumps.....
Heat pump efficiency (COP) is obtained by comparing how much energy it consumes in order to complete the heating and cooling cycle. Coefficient of performance (COP) defined as: “The ratio of heat delivered by the heat pump and the electricity supplied to the compressor”
(COP = Kilowatts Delivered) eg. 7.5kw (Output) ÷ 1.5kw (Electrical Input) = 5 COP
Electricity is needed to drive the heat pump, but for every unit of electricity used, it will generate 3 to 5 units of useful heat. The efficiency of a heat pump will depend mainly on the temperature of its energy source and the temperature at which the heat generated is needed. Basically, the higher the temperature of the heat source is and the lower the temperature of the useful heat is, the more efficient the heat pump will be. A Ground Source heat pump using the soil as a heat source (constant temp of 8°C to 12°C) and floor or wall heating (water temp of 35°C to 55°C) is one of the best combinations, with an efficiency in excess of 450%, compared to an oil or gas boiler with an efficiency of 70 – 85%.