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Drilling boreholes at The Carrier

posted 2 Jun 2014, 05:18 by Graham Knight   [ updated 6 Jun 2014, 05:29 ]


Many people have asked about the recent drilling rig which was located outside ‘The Carrier’ in the centre of the village.

Firstly, please accept our apologies for the noise, and especially for the short term loss of water pressure to some residents.

The drilling rig was there to drill two boreholes down to some 125 metres depth. These are to supply heat recovered from the ground to supply a ground source heat pump which will be installed shortly in our home.

A technical explanation follows:

Each borehole has a loop of plastic pipe inserted, through which a glycol/water mixture, similar to anti-freeze in cars, is circulated. This is called a ground loop, and one can be seen in the following picture, awaiting later connection to the pipes to the house.

A temperature increase within the ground loop fluid of just 3˚C or 4˚C is all Ground Source Heat Pumps require. The returning warmed liquid is fed into a Heat Exchanger / Evaporator.
The diagram below demonstrates how the heat pump compresses heat and passes it through to the heat distribution system:

The Evaporator

The purpose of the Evaporator within the heating pump is to take the collected ground source heat out of the ground loop liquid and return it cooled to the pipe for the next cycle. It does this by using a refrigerant that boils at approximately -10˚C. The act of boiling turns the refrigerant into a vapour which is then moved into the Compressor.

The Compressor

The Compressor does exactly what the name suggests: the vapour is compressed in volume and as its volume reduces, the temperature increases to levels of between 75˚C and 125˚C. The gas is then fed through a Heat Exchanger within the heating pump.

The Heat Exchanger

Feeding the hot gas through a condenser allows the refrigerant to turn back into a liquid. As it condenses, its heat is passed into the Heat Exchanger which supplies the domestic hot water and powers the central heating system using the ground source heat extracted originally.

The Expansion Valve

To complete the closed circuit of the Ground Source Heat Pump, the only thing which needs to be done is reduce the pressure of the condensed liquid. This is achieved via the Expansion Valve.

Pros of ground source heat pumps

  • Ground source heat pumps generate less CO2 than conventional heating systems.

  • The Energy Saving Trust (EST) says that a 'typical' ground source heat pump could save you between £395 and £2,000 a year depending which existing heating system you are replacing. 

  • You can get financial help towards the cost of a ground source heat pump. The Renewable Heat Incentive scheme provides payments to householders who have a heat pump, estimated to be between £2,325 and £3,690 a year for an average four-bedroom detached home.

  • You need to use electricity to power the pump which circulates the liquid in the ground loop, but for every unit of electricity used by the pump, you get between two and four units of heat – making this an efficient way to heat a building.

  • Cheaper Economy 7 electricity tariffs can be used to lower the cost of electricity to power the heat pump, and special heat pump tariffs may be available from some electricity suppliers – alternatively consider solar photovoltaic panels or a wind turbine (if you live in a suitable area) for a greener source of electricity.

Cons of ground source heat pumps

  • Installing a ground source heat pump is expensive

  • Ground source heat pumps are not always suitable for properties with existing gas/oil -fired central heating as the technology works at lower temperatures, making it better suited to homes with underfloor heating. A survey at the outset is advisable to confirm this.

  • The groundworks required to dig the trench can be expensive and disruptive. Ground source heat pumps tend to be better suited to new-build homes as they can be planned as part of the construction process.

  • You still need to use electricity to drive the pump, so a ground source heat pump can’t be considered completely zero-carbon unless this is provided by a renewable source, such as solar power or a wind turbine.

How green is a ground source heat pump?

A ground source heat pump system can help to lower your carbon footprint as it uses a renewable, natural source of heat – the ground. According to the EST, a heat pump with mid-range efficiency uses a third of the energy needed in an average gas or oil boiler to produce the same amount of heat.

A heat pump also requires a supplementary source of power, usually electricity, to power the heat pump, so there will still be some resulting CO2 emissions. 

Malcolm Ingham