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There are three important elements to a GSHP:

 

• Ground loop - comprises lengths of polyethylene pipe buried in the ground, either in a borehole or a horizontal trench. The pipe is usually a closed circuit and is filled with a mixture of water and antifreeze, which is pumped round the pipe absorbing heat from the ground.

 

• Heat pump - A heat pump is a powerful refrigerator, the main elements of which are:  

 

Evaporator - (e.g. the squiggly thing in the cold part of your fridge) takes the heat from the water in the ground loop

 

Compressor - (this is what makes the noise in a fridge) moves the refrigerant round the heat pump and compresses the gaseous refrigerant to the temperature needed for the heat distribution circuit.

 

Condenser - (the hot thing at the back of your fridge) gives up heat to a hot water tank which feeds the distribution system.

 

• Heat distribution system - consists of under floor heating or radiators for space heating and in some cases water storage for hot water supply.

 

Key components to a GSHP system

 

Rapid Expansion of liquid into gas at the expansion valve in the refrigerant circuit causes cooling in the evaporator heat exchanger. Thermal transfer within the evaporator heat exchanger causes warming of the cooled refrigerant gas and an equivalent cooling of the ground loop solution.

The “warmed” refrigerant gas now passes through the compressor and is turned back into liquid. The compression of the gas into a liquid causes heating within the condenser heat exchanger. Thermal transfer within the condenser heat exchanger supplies heat to the domestic heating and hot water system and an equivalent cooling of the refrigerant liquid.

The domestic heating and hot water system should be a “wet” system consisting of radiators, underfloor heating and/or hot water tank. This part of the system is essentially the same as for alternative “wet” systems such as gas or oil fired boilers with the heat pump taking the place of the boiler.

The important difference is that the system will be designed for an output temperature of 500C rather than 800C typical for systems fuelled by oil or gas.

 

There are two main types of ground loop that can be used to extract heat using GSHPs. The loop can either be laid in horizontal trenches, or installed in a vertical borehole. A domestic household would require a horizontal ground loop buried between 1.5-2m deep in a 40-100m long trench.

Vertical pipe installations are more suitable for sites with limited land requiring a bore hole of 50-100m but require a specialist boring rig which makes these installations more expensive. The pump itself is a square box similar in size to a fridge freezer.

 

Sizing

 

The length of pipe required depends upon the building heating load, soil conditions, loop configuration, local climate and landscaping. Sizing of the heat pump and the ground loop is crucial to the operation of the system.  At the outset it is a good idea to look at energy efficiency measures such as wall and floor insulation to reduce your heat demand.

When sizing a system it’s important to consult a professional installer for expert advice. A heat pump can be designed to meet 100% of space heating requirements but it will usually only pre-heat domestic hot water so top up heating (e.g. an immersion heater, or solar thermal equipment) will be required.

Air- and Water-Source-Heat-Pumps are less needy of space. The pipe work of a WSHP can simply be sunk to the bottom of a nearby watercourse whilst the coils of an ASHP are self contained inside a compact unit resembling an air conditioning system.

How much maintenance is required?

Heat pumps are highly reliable with virtually no maintenance required following installation. As they don’t have many moving parts they do not require annual inspections or servicing. The underground piping typically carries a 50-year warranty. ASHPs and WSHPs that are sited externally will have a shorter life expectancy (~15 years).

 

 

Please feel free to get in contact with us by email or call 0845 189 9894 to discuss any of your requirements.