The seasonal variations in the earths’ ground temperature disappear at a depth of below 10 meters, whilst the upper most 10 feet of the earth maintains a relatively stable temperature all year round – between 10 and 15 degrees Celsius, meaning that heat can be extracted from this level during the winter months and cooler air during the summer months. This extraction is done through a Geothermal Heat Pump (GHP – also known as a Ground Source Heat Pump or GSHP) and these can be used anywhere in the world, in essence providing a household with its domestic heating during the winter months.
A Geothermal Heat Pump consists of pipes buried in relatively shallow ground within the proximity of the property for which they apply. In winter the heat from below the surface is pumped directly into the house via a heat exchanger, whilst in the summer months the heat from the house is pulled into the heat exchanger and pumped back into the ground (or used to heat water). Thus the GSHP helps heat the house in the winter and cool the house in the summer.
This is a very efficient and green source of obtaining heating for households and businesses. However, the GSHP’s do need to use electricity to operate the pumps and therefore the efficiency of the heat pump is essential. A mid-range pump with good ground conditions will generally provide 3 to 4kW of heat energy for every 1kW of electricity used to generate the heat (a Coefficient of Performance of around 4:1). Therefore it has an energy efficiency of some 400%.
The advantages of geothermal energy are that it is efficient and available 24 hours a day, 365 days a year, anywhere in the world (even in snowy regions such as Sweden and Norway). Meanwhile, GSHP’s are easily installed, reliable with little maintenance requirements, and make next to no noise in energy production. However, the disadvantages of GSHP’s are that they can be costly to install and will be needed to run alongside traditional boiler systems (although reduced energy bills will mean that the system pays for itself over future years), and they do require a lot of land mass for the pipe network to be laid (more on this later).
The temperature at a depth of 1 meter below the ground surface is affected by the outside air temperature that prevailed approximately 6 months previous. That is, the temperature of the ground at a depth of meter below the surface is actually a factor of the outside air temperature that prevailed in the previous July. The ground temperature at a depth of 1 meter in July will be a result of the air temperature at the surface in the previous December! The added advantage of this is that when you are trying to extract the most heat from the ground (i.e. during winter) you are actually extracting it from a source that has been determined by the summer weather! That said, the temperature at a depth of 1 meter only ever varied by 1 or 2 degrees! Hence the variation between summer and winter is actually minimal!
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
