Ground Source Heat Pumps (GSHP)

Ground Source Heat Pumps (GSHP) are stand-alone units that normally sit inside your house, alongside your hot water cylinder. They are roughly the same size as a fridge freezer unit.

They work by drawing heat from the ground via pipes filled with brine into a heat exchanger and then transferring that heat to your cylinders to provide you with your heating and hot water.

The pipes can either be laid in ground loops about 1m deep or dropped in verticle boreholes up to 200m deep. They can also be fed into a lake or aquifer.

The pipework is in some ways similar to underfloor heating in that the loops return to a manifold chamber close to the house and there is then a flow and return to the heat exchanger in the heat pump itself.

They are incredibly efficient because even when the outside temperature is below 0˚C, the ground temperature is generally about 8˚C all year round. This makes them slightly cheaper to run than air source heat pumps, however, the capital costs are much higher due to the groundworks needed.

The most common configuration is horizontal ground loop. This loop is laid in a straight line, spaced at least 1m apart. A good deal of land is needed for the heat pump groundwork. A good rule of thumb being 4 times the amount of floor space you are looking to heat.

Water source heat pumps

Ground source heat pumps can use water as their heat source if you have a large lake or boreholes into an aquifer below your property. This is the most efficient of all heat pumps as the temperature of the water in winter is normally warmer than that of the air or the ground.

To discuss the pros and cons of ground source heat or to arrange a quote for ground source heat pumps installation please contact us.

Is air source or ground source best for me?

Much depends on the property to be heated but in smaller, well-insulated houses, it is hard to justify the extra cost and upheaval of installing a ground source because the difference in running costs between an air source heat pump or ground source heat pump would be small and not justify the large capital output. In general, installing a ground sourceheat pump is more suitable for larger houses and businesses.

Advantages of Ground Source Heat Pumps (GSHP)

The main advantage of installing a ground sourceheat pump is the greater efficiency during winter, meaning lower running costs. That is because the ground temperature is constant and maintains its heat evenin the middle of winter. Whereas for air to water heat pumps the efficiency drops in winter as the outside temperature drops. The greater efficiencies also mean lower running costs as they use electrical energy and lower carbon emissions, meaning they can be much cheaper to run than fossil fuel boilers.

Disadvantages of Ground Source Heat Pumps (GSHP)

The main disadvantage of installing a ground source heat pump, whether using trenches or vertical boreholes, is the cost, often more than twice as expensive as installing an air source. Also if digging long trenches a large amount of land is required for a ground source heat pump and the work can be disruptive, making a mess of your lawn which may take time to recover. Drilling vertical boreholes needs much less land and is not as disruptive but they are even more expensive. You also need a suitable position forthe heat pump (heat exchanger) inside the house.

Advantage of Air Source Heat Pumps (ASHP)

Air source heat pumps are far easier andcheaper to install, and the heat pump itself  would be sited outside the house. This is advantageous for smaller houses where space is at a premium. Also there are no parts buried in the garden - in case anything goes wrong they are easily accessible.

Apart from the depths of winter a good air-to-water heat pump can be just as energy-efficient (same running cost) as a ground source and use less electrical energy and be more efficient than a GSHP in spring.

So, for example, installing a ground source heat pump may cost £35k. while installing an air source heat pump may be £17k. In a small property with a £1,000 a year bill for electrical energy the ground source, being 20% more efficient, may be £800 in running costs, saving £200 a year. There’s a lot of £200s to recoup the additional £15k spent installing a ground source heat pump.

That is even more relevant now that the government incentive for installing a heat pump – the Boiler Upgrade Scheme (BUS) grant – is a flat £7,500 for installing an air source heat pump or for installing a ground source heat pump. It used to be much more generous under the old Renewable HeatIncentive (RHI).

In a much larger property, where two or more air source heat pumps may be needed the capital outlay may be £30k, whereas installing a ground source may be £40k. Still a £10k difference but the ground source may be saving £800 a year in running costs (20% of a £4,000 per annum bill) meaning the “payback” makes sense in the long term. And again there is a greater reduction in carbon emissions.

Disadvantages of Air Source Heat Pumps (ASHP)

At the coldest times of the year, the efficiency of the air-to-water heat pump is at its lowest. This is just the time when maximum output is required. That said, the best and newest models can operate fairly well in very cold conditions, especially good quality European heat pumps built for our climate.

The unit will still need some outside space which is not always available, for instance in a terraced house – although it is far less than required for a ground source heat pump. The operating noise is very low on good quality European heat pumps but may be still be unwelcome for some. Also the heat pump is standing outside in all weather, so may not last as long as installing a ground source heat pump where the heat exchanger is sitting in a nice dry plant room. Having said that they will still last twice as long as a fossil-fuel boiler.

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