Applying a heat pump for thr heating of houses and the production of hot water is getting a great deal of attention lately. The technique is very simple: you will extract heat from outside to heat your house withon. In Germany and in the Scandinavian countries, this technique is applied for years and is an integral part of the design of a home. But also in Scotland there is more and more interest in this alternative heat source.
A heat pump is basically a refrigerator that works in the opposite direction. Where a refrigerator take the heat out of the refrigerator and emots it on the back of it, a heat pump installation extracts the natural heat from the outside to the inside. Around the house heat can be used from the air, the soil or the groundwater. In the ground the temperature from a depth of 1.5 metres is for example more than 0°c throughout the year.
How does a heat pump work?
The current generation of heat pumps are usually based on an electrically powered compression technique. Fluid is being pumped in a closed circuit. This fluid is in a liquid form or a gaseous state depending on the pressure and the temperature. It is these changes of state that ensures that the heat is contained and then issued.
A heat pump installation consists of a fluid circuit a pump, expansion valve and two heat exchangers. The evaporator extracts the heat from outside and the capacitor causes the heat again. In steps, the following happens:
Efficiency of heat pumps
A heat pump is pumping coolant around in a closed circuit. To do this, the pump uses gas or electricity. The efficiency of the pump is expressed in the Coefficient Of Performance COP (Coefficient of Performance). This gives the ratio of energy output. A coefficient of performance of 3 means three heat-pump output units are produced out of one unit of electrical need. The COP is always greater than 1 therefore you will always find higher return than 100%. A heat pump is interesting as the power consumption of the pump is more than offset by the win in heat (high COP). This rate of return is determined by the difference and the stability of the temperature between the cold source and the heat source, the efficiency of the heat exchangers and the electricity consumption of the compressor.
Types of heatpumps
Ground source heat pumps
When a heat pump gets its heat from the ground we speak of a geothermal heat pump or ground source heat pumps. There are two systems that are applied. The heat exchanger that goes horizontally in the soil of the garden and the heat exchanger that goes vertically in deeper soil layers.
The sun heats up the earth and this energy can be recovered by a distribution system that runs about 70 centimeters below the surface. If you have a well insulated house then the available land in the garden should be about 1.5 times larger than the heating surface. A poorly insulated house needs has a larger surface area to provide sufficient heat from the ground. Take care of the construction in the garden, as roots can damage the pipes of the heat pump.
It is also possible to dril the pipes vertically in the ground to a depth of 50 to 150 meters. The temperature of the earth is at that depth higher. This heat comes from solar radiation, soil and from surface water as well as heating from the Earth’s core. A vertical pump is ideal for residential houses that have insufficient space for a horizontal placement of the pipe system.
An airsource heatpump heat pump like used at the energy efficient home East Lothian draws heat from the air outside. The evaporator consists of a series of tubes where the coolant flows through. These tubes are in contact with the ambient air. The air can flow around naturally (heat exchanger with static air) or supported by using a fan. The disadvantage of an air heat exchanger is that it is dependent on the temperature of the air, and as everyone knows these strongly fluctuates. The return (COP) of this air heat pumps also varies strongly. As a result, it is usually necessary to combine this system with another heat source in order to be able to switch if not enough heat is generated.
It is also possible to detract heat from the groundwater, a pond or even a river. This technique can be interesting because these sources generally has a relatively stable temperature what benefits the return. However, it is not possible in every situation.
Heat exploitation with heated floors and wall heating
You can utilyse the heat win with a heat pump in different ways. The theory is that the lower the temperature that is used in a hesating system the more efficient the installation works. In other words, the smaller the difference between the cold source and the heat source the higher the return. Low temperature heating is widely applied through underfloor heating and wall heating. Underfloor and wall heating have an even temperature heat distribution by the the large surface area and can be heated whith at much lower temperatures while maintaining comfort.
Heating using with a heat pump is the most suitable for new homes. This means excellent insulation in combination with low temperature underfloor heating. For an existing build a heat pump installation is only interesting after rigorous alterations.