As mentioned earlier, Ground Source Heat Pumps require electricity to operate. However, for every unit of electricity that is used to operate the system, on average, 4 units of heating are generated by the system. This means that the system has a Coefficientof Performance (CoP) of 4 to 1.
The CoP of any single system will vary as each installation is different. Some will be installed in more conductive land materials, whilst others may be installed in water. However, when designing a system the CoP should never be less than 3.
Similarly, the CoP of any single system will vary throughout the year as it is affected by how much energy you need the heat pump to produce. If you require the heat pump to heat the water in the house to around 60 degrees (i.e. in winter), then the CoP is likely to be around 2, whilst heating the water to just 35 degrees (i.e. in Summer) will create a CoP of around 4+. This relationship can be seen in the following chart:
The CoP will also be affected by how warm the ground temperature is, and thus how warm the transfer liquid is when it comes back from the ground loops and into the Evaporator. This is because the warmer the liquid, the less work the Evaporator will have to do to boil the refrigerant liquid and thus the less electricity it will need to work. The relationship between ground temperature and CoP can be seen as:
All GSHP’s are tested as standard with a ground temperature of zero and a heating requirement of 35 degrees Celsius, and it is this test that is used to give the official CoP that is described in the datahseets. 35 degrees Celsius should be more than enough heat for a well-insulated house that uses underfloor heating.
Heat Pumps that are required to provide domestic hot water, which requires a higher temperature than domestic heating (at least 65 degrees Celsius in the UK), will have a lower CoP. That said, more traditional methods of heating, such as immersion heaters, have a CoP of 1 or even less than this (meaning more energy input is required than the outputted heat). For example, Gas and Oil boilers have efficiency ratios of 85%, equivalent to a CoP of 0.85. This is also why GSHP systems are more suited to under floor heating, a system that requires a lower temperature/more continuous flow of water through it (under floor heating generally requires a water temperature of 35 degrees, as opposed to 65 degrees for domestic hot water, and 75-80 degrees for radiator heating systems). This increases the CoP of the GSHP.
Home pages of interest in this section are:
- Ground Source Heat Pumps
Pages of interest in this section:
- What is a Ground Source Heat Pump?
- How do GSHP’s work?
- Types of GSHP
- GSHP Efficiencies
- Sizing a GSHP
- How much does a GSHP cost
- GSHP Planning Permission
- GSHP’s versus ASHP’s
- GSHP’s in conjunction with Solar PV
- GSHP’s and ASHP’s in Practice
