---

Jump to:

Choose... About ground source heating Boreholes for ground source heating How it works... Case history Morgans in action...

---

About ground source heating

Renewable energy options

Ground source heating is probably the most dependable, reliable and cost-effective form of renewable energy that is accessible to domestic and small commercial users.

Wind turbines are notoriously expensive to install, and unless huge-and hugely expensive-don't produce much power. And on a still day they won't work at all. Siting them can be problematic, and planning permission is likely to be required: installing a 20 metre mast in a domestic area is not likely to gain approval.

Photovoltaic cells convert daylight to produce relatively small amounts of power, and won't work at night time. They are extremely expensive to install, so any payback period is very long term. Planning permission would certainly be needed to install panels to any listed building.

Ground source heating works 24/7/365 regardless of weather conditions, and it is highly unlikely that any planning permission will be needed. Although they need electricity to power the heat pump with is at the heart of the system, for each kilowatt-hour of electricity used, you get a return of up to 4 kilowatts of heat for your building.

Getting heat from the ground

For a heat pump to operate, it is necessary to install a heat collection system in the ground.

There are two main ways to gain access to ground heat:

A horizontal system, involves digging a trench 1 or 2 metres deep, then burying pipes. A wide trench needs to be dug, and coiled plastic pipe, coiled into 'slinkies' is buried. On average 10 metres of trench is needed for each kilowatt of power. This is likely to mean digging at least 100 metres of trenchwork - a considerable earthworks exercise.

A vertical system involves drilling one or sometimes more boreholes. Our compact drilling machine is set to work, and requires very little space to operate. When it departs, and the installation is completed, there is little or nothing to see! In a domestic situation, boreholes are often created beneath a front drive, or in a garden. The borehole drilling exercise is often completed within two days.

Why boreholes are the best source of ground heat

We'll admit to being biased! But as you will see, borehole systems bring major advantages:

Far less disruption: it eliminates the need to dig and re-cover massive trenches. Trenching is a major exercise, and in many instances-for most domestic properties, and many commercial premises-the space is simply not available.

Far less mess: and we drill using fluids rather than using compressed air, so that arisings from a borehole are contained, and can be readily disposed of, either on-site or carted away.

Better consistency and efficiency: Unlike trench systems the underground temperature is consistent, and heat is extracted more efficiently.

Payback in relative few years.

The cost of oil has risen steeply, and is predicted to continue to rise. And of course the price of oil and gas governs the cost of most forms of power, including electricity generation.

The electricity used to power the heat pump is likely to produce 3 or 4 times its energy output from the ground source, the economies are clear.  For each kilowatt hour of electricity powering the ground source heat installation, you can get a return of up to 4 kilowatt hours.

For many installations, ground source heat pumps are very competitive over their expected life when compared with oil, electricity and LPG.  Unlike conventional boilers, once installed a ground source heat pump installation requires no regular maintenance.

As each installation is different, and costs depend on variables such as site conditions and the amount of heat required, it is not possible to provide a pricelist for a complete heat pump installation.

Obviously, it is best to design a property in the knowledge that ground source heating will be used: for example

 

Renewable Energy is in every sense a hot topic, and the reasons are clear: Energy costs continue to rise, and there is an ethical move to reduce the use of carbon-based fuels.

Legislation is helping drive things forward, Part L of the latest Building Regulations sets higher standards for energy conservation.

Best of all, renewable energy can bring attractive economic benefits—ground source heating and cooling bring the promise of ‘something for nothing’, often delivering four times more heat than the electric energy used.

This is proven technology, ground source heat systems have been successfully and extensively used worldwide for many years, and the benefits demonstrated.

These include environmental and economic factors due to very low operating costs compared to fossil fuel systems. CO2 emissions are reduced—attractive with the possibility of a CO2 tax being introduced. And as an incentive to go green, Government grants may be available towards these installations.

The ground can be used either as a source of heat or for ‘coolth’ to provide cooling. Underground temperature is constant, so air temperature has no effect on a system’s efficiency.

Either way, heat is taken from or disposed of into the ground via boreholes or trenches.

Heat is made available to the building using a heat pump. Configurations range from simple under floor heating and domestic hot water, to reverse cycle pumps for heating and cooling; and sophisticated systems for simultaneous heating and cooling.

There are three main ground source heat systems:

Vertical closed loop systems incorporate one or more boreholes with a single U-shaped HDPE plastic pipe loop that circulates water with an antifreeze, usually brine.

The finished borehole is sealed with special heat-conductive grout from top to bottom.

The solution extracts heat from the borehole and delivers heat to the heat pump. Heat is extracted from the water before returning it to the ground.

A closed loop system has no direct interaction between the solution and the groundwater or rock mass. There is little risk of contaminating the ground and is not subject to Environment Agency licensing formalities, although larger schemes may be regulated via planning consents

One advantage of a vertical loop is that it does not require a large area of ground, so is ideal where the site is smaller: often a single 150mm diameter borehole—perhaps with another one located 5 metres away where demand is higher—is all that is required. Typically a 100m borehole provides 5kW of energy.

Horizontal closed loop systems work on the same principle as the vertical closed loop system. A pipe is coiled and placed in a 1 to 2m deep trench.

It will typically supply 1kW of power for every 8 to 12m of trench. The pipes are often referred to as ‘slinkies’ and are easy to install—although they require a large area.

For example 880 metres of trench is needed to provide a heating capacity of 80kW for a floor space of 1600 square metres. The horizontal slinkies for this would need an area 50 x 50m

Vertical open loop systems Groundwater is abstracted and circulated directly through the heat pump. Due to the conductive nature and specific heat capacity of groundwater, an open loop system can deliver a large amount of energy from a single well.

Water is abstracted from the borehole, passed through a heat exchanger/pump system, and then either used as part of a greywater supply system or discharged to a surface water system, or back underground.

A second borehole may be required if discharge to groundwater is used. Both abstraction and discharge require consents and licences.

A borehole producing 10 cubic metres/hour can supply 80kW. Sometimes energy loadings in excess of 500kW are possible.

Risks

The use of the ground as a source of heating or cooling has inherent risks. With closed loop systems, in major schemes the largest risk is excessive heating or cooling of the ground around the boreholes. This can occur if they are too close together, or too heavy a demand is put on the system. This would affect system efficiency—but is most unlikely to be a problem with domestic and smaller scale projects under 50kW.

In open loop systems, demanding too high a volume of water from a borehole can exhaust its supply. Otherwise, thermal breakthrough can occur, where the intake pulls warmed water back in. Then there are thermal plume migration issues too—an impact on other boreholes, or the surrounding environment.

For open loop schemes, and closed loop schemes over 50kW, specialist advice should be sought.

While existing buildings can often be successfully adapted to use ground source energy, the most efficient systems are designed into the building from the start. Liaison between building and systems designers, hydrogeologists and thermogeologists will ensure that any risk factors are taken fully into account and eliminated.

Something for nothing is always appealing, and having paid for the installation, you’ll reap the benefit of low-priced heat for years to come.

For more information, visit www.jdih.co.uk

What is a heat pump?

At the heart of a geothermal heating system is the heat pump. How does it work?

Think of it like a fridge, but in reverse—it takes the heat out of groundwater and concentrates it for use in the building. The opposite of a fridge which takes heat out of the appliance and dumps it into the air. 

Leading waterwell driller WB&AD Morgan Limited have taken delivery of a versatile new drilling rig, the Beretta T151.

‘Our decision to purchase this equipment’ says managing director Brian Morgan, ‘was to improve our capability: Increasingly we are being asked to drill geothermal boreholes, and these often involve us working in confined sites. Also the T151 is proving it worth in our core business of drilling waterwells, particularly where space is limited.’

Built in Milan by Beretta Alfredo srl, the T151 is a compact tracked rig powered by a 98kW Deutz engine, it has a small footprint, and can even be operated remotely by radio control if needs be.

Drilling to a diameter of 324mm its dual head system contrarotates the outer casing, with the result that achieving terminal depth is faster, particularly in unstable overburdens.

There is a triple-clamping system for surface casings and drill rods, and the centre clamp has a 30 tonne jack-up system—exceptionally powerful for this size of machine—essential to retrieve stuck surface casings.

Environmental issues are fully addressed, as a fitted preventer system discharges arisings horizontally through a pipe into a skip, helping keep the site clean.

WB&AD Morgan drill wells throughout mainland UK, and have established themselves as a national leader in the field, tackling many borehole projects in sensitive situations, including for water bottling purposes. Says Brian Morgan: ‘We see our continued investment in high quality plant as one of the keys to our reputation and success: This Beretta unit joins other recent additions, including a high capacity purpose-built mud shaker, and the state-of-the art Klemm KR709 W01 drilling rig which brings immense capability.’ 

Today traditional techniques and craftsmanship merge with the computer age to create houses with a very special quality, meeting and exceeding all current demands and legislation.

Based near Hereford, Oakwrights is a national leader in oak framed house design and construction. Founder Tim Crump is passionate about his company’s products, and to demonstrate just how good living in one of his bespoke homes can be, has built a unique show home. This is sited on a compact plot in the attractive Herefordshire village of Kenchester.

Drilltalk met him on site to discuss this house’s special features.

‘Green issues are paramount,’ he says, ‘and I want to show what can be achieved. In particular our focus is on low running costs and a minimal environmental impact.’

As you’d expect, the home is highly insulated and energy-efficient, incorporating both hemp and wood fibre insulation in its structure. A forced ventilation system recovers heat from air in the house and recycles it.

Under the garden is a 4500 litre tank which harvests rainwater, pumped to service the WCs and washing machine.

But one particularly impressive feature is its closed-loop geothermal heating system. The system is operated by electricity—but amazingly each kilowatt of electricity used returns an incredible four kilowatts of heat energy.

Working throughout the year it supplies domestic hot water, and heats the house when needed through an underfloor heating system.

Because of the limited plot size it was not sensible to install a horizontal heat collector, which would involve excavating trenches over a considerable area, so heat is drawn from two vertical geothermal wells drilled in the driveway.

Welldriller WB&AD Morgan drilled these boreholes 5 metres apart to a depth of 65 metres, and after completion the wells were fully sealed. ‘Because of the space limitations, this was an ideal application for our new self-propelled Beretta rig’ says Brian Morgan.

The underground pipework connects to an Ice Energy ground source heat pump inside the house

Tim Crump was delighted with the way that Brian Morgan’s team handled this project: ‘Drilling took three days, and was done very effectively. Now, there is nothing at all to see outside the house, as the boreholes and pipework are completely hidden beneath the driveway blocks.’

The entire project is an impressive demonstration of how a handsome property can combine with the latest in technology to benefit both the householder and the environment.