Heat Pumps are widely misunderstood even amongst plumbing and heating specialists who still often refer to them as “boilers” or “heaters”. However, no combustion of any form occurs inside a Heat Pump and they are actually “heat scavenging” devices.
The principles of operation of Heat Pumps are widely misunderstood even amongst plumbing and heating specialists who still often refer to them as “boilers” or “heaters”. However, no combustion of any form occurs inside a Heat Pump and they are actually “energy conversion” devices.
What is a Heat Pump?
In simplistic terms electrical energy is used to power the unit which then converts significantly more heat energy from the surroundings than the electrical energy being used to power it. This seemingly impossible increase in energy output vs energy input is known as the “Coefficient of Performance” (CoP). For typical domestic and commercial heat pumps this CoP can range from around 2 to 5, i.e. heat pumps are between 200% and 500% efficient when compared to using the same electrical energy for heating via a conventional electrical heater or storage heater.
The principles of operation of a Heat Pump are closely related to those of a domestic fridge. In a fridge the heat is extracted from the produce inside the fridge and transferred to the outside of the unit via the condenser (the black matrix structure on the back of the fridge). This is why the interior of the fridge gets colder and the back gets hotter, i.e. the heat energy has been transferred or “pumped” from one place to another. In a heat pump the heat is extracted from the ground (Ground Source) or the air (Air Source) and transferred/pumped to provide heat energy into the property via a conventional water or air-based central heating system. Underfloor heating systems are ideally suited to the temperature characteristics of a heat pump.
Ground Source & Air Source Heat Pumps – the differences….
Heat Pumps generally obtain their energy from the sun and extract this solar energy either from the ground or from the surrounding air. As a consequence there are two main types of heat pump, Ground Source and Air Source.
Ground Source Heat Pump:
Ground Source units are usually located inside the property and rely on the relatively constant temperature of about 10Deg at around 1.5m underground. As such their performance is almost constant all year round.
Ground Source systems require heat collection pipework to be buried around the property (typically plastic pipes around which an antifreeze solution is pumped) and the heat energy extracted from the ground is converted to high temperature water by the internal unit. Deep vertical bore holes into which heat collection pipework is placed can also be used to extract geothermal energy.
For properties where horizontal or vertical heat collection pipework can be relatively easily installed, Ground Source Heat Pumps provide a very efficient source of inexhaustible low-cost heat energy all year round.
Air Source Heat Pump:
Air Source Heat Pumps are usually located on an outside wall of the property and utilise the solar energy stored in the surrounding air. This is achieved using a fan to force the surrounding air across a heat exchanger from where low grade heat energy is extracted. This energy is then upgraded via an indoor or outdoor unit into hot water at up to 90Deg for circulation around the property. Modern Air Source Heat Pumps can work at temperatures below -15Deg.
As the outside air temperature varies throughout the year Air Source units have varying levels of efficiency throughout the year as they have to use air at lower temperatures to extract the heat in the colder months. This affects their efficiency. As the performance of an Air Source unit will vary across the year it’s Coefficient of Performance (COP) is often taken as an average across the year and is known as the “seasonalised” CoP. This typically ranges from 3 to 5.
Air Source Heat Pumps are very efficient in the summer months as they are operating in higher ambient temperatures. Hot water production using an Air Source unit can therefore be very cost effective and the latest Air Source Heat Pumps have seasonalised efficiencies approaching those of Ground Source systems.
The latest Air Source Heat Pump designs operate extremely quietly and are highly unlikely to cause any noise disturbance in or around a property.
