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Heat Pumps

A heat pump is a device that transfers heat energy from a heat source against a temperature gradient. Heat pumps are designed to move thermal energy opposite the direction of spontaneous heat flow. A heat pump uses some amount of external high-grade energy, typically electricity but sometimes gas to accomplish the desired transfer of thermal energy from heat source to heat sink. As part of the process a large volume of low grade heat is converted in to a smaller volume at a higher temperature.

A common household example of a heat pump is a fridge taking heat from within and expelling it at the rear. On a larger scale a residential heat pump operates in a similar fashion taking low grade heat from the environment and putting this energy into the building.

Heat pumps often quote their Coefficient of Performance (COP). The COP of a Heat Pump is calculated by the ratio of the heat delivered divided by the power consumed to run it.

Ground Source Heat Pump

A Ground Source Heat Pump (GSHP) extracts heat from the ground. This method takes advantage of the moderate ground temperatures in the UK to give a constant efficiency. This is achieved by burying a collector pipe 2 metres below the earth’s surface (below the frost line) in horizontal trenches, or if space is limited, in boreholes.

Air Source Heat Pump

An Air Source Heat Pump (ASHP) extracts heat from the atmosphere outside of the building and transfers it to the interior of the property.

ASHPs are harder to size than GSHP as the CoP will vary widely with air temperature resulting CoP in the coldest months being lower than expected.

Water Source Heat Pump

A Water Source Heat Pump (WSHP) uses water as the medium for the heat transfer. Water is a much more efficient heat transfer medium than air due to its density - it takes four times more energy to move a quantity of heat with air than water.

WSHPs generally use open loop collectors, where river/stream or underground water is circulated through the pipes. However in the Hybrid Solar Solution the WSHP is connected to the PV-T array and uses this as its heat source. This has two main benefits: firstly in the day time the panels provide a high temperature heat source, and secondly by removing the heat from the panels and keeping them cool the panels are able to produce more electricity than standard PV panels.

Multi-stage Heat pump

A multi-stage heat pump has two or more gas cycles. The first loop uses a gas that is appropriate for medium temperatures. When higher temperatures are required this first loop then feeds the second which is filled with a gas which is appropriate for higher temperature applications. This means that the multi-stage heat pumps can reach temperatures of up to 80 degrees and as such can be fitted to standard existing high temp radiator systems. One key disadvantage however is that the higher temperature differential between the source temperature and the target temperature the heat pump will run with a lower CoP than a single stage heat pump.

Multi-source Heat pump

This heat pump is able to use two or more heat sources to provide a more consistent and efficient heating. At Newform Energy we see this as a key area for growth in the future. We have just won the Rushlight award for our Hybrid Solar Solution combined with boreholes. This solution utilises a multisource system at its core in order to create a very low carbon heating and hot water solution. The heat pump chooses the hottest source between PV-T panels and borehole in order to achieve maximum efficiency. This also means that when there is no demand for heating the panels can be used to thermally recharge the borehole and in return keep the panels cool to maximise the electrical efficiency. At Newform Energy we are also currently developing a multi-source heat pump which uses PV-T and air as its two sources for applications where there is not enough room for boreholes or they are cost prohibitive.

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