Geothermal Basics

Most commonly used for medium sized systems in the 100 to 1,000kW range, although we have installed both smaller and larger systems in the UK. 125mm bore holes are drilled and a pair of 32mm pipes are grouted into place. A typical grid of 3 to 6m is used between the holes and depths are typically between 50 and 150m below ground level. All headers are completed at least 1m below finished level and are simply buried under the finished surface.

Most suited to: medium to large projects in all areas.

These can be used in any piled building and with any common piling method. They can typically cover about 50% of the building load and offer a very economic installation proposition. An important consideration is to minimise the impact of the inclusion of the pipes on both the pile design and installation program. This gives a very low additional cost over conventional equipment and the lowest possible extra over cost for the piling contractor. Our association with Cementation Foundations Skanska has  given us a lead in this market in the UK.

Most suited to: new buildings with piles and little external space.

If land is available 1.5m deep trenches can be used to install the closed loop. Various trenching methods and pipe geometries are used. At Geothermal International we prefer straight pipes rather than the slinky variety you may have seen used by other installers. This offers a more efficient collection of energy from the ground and makes the most of every meter of pipe installed. Horizontal systems do require a significant amount of land and for this reason systems up to 150kW are most common although where land is plentiful, larger systems can be considered and have been installed.

Most suited to: small to medium projects with access to land.

These are a particularly efficient method of ground sourcing and can cover practically any size of load, systems of many MW are common. They offer excellent installation costs. A constant water depth of 2 to 3m is required and as a guide 9m2 of surface area is required per kW of system capacity. Either stainless steel plates or polyethylene pipes are simply submerged below the surface and again water / anti-freeze solution is circulated through them.

Most suited to: any sized project with access to surface water.

An abstraction and rejection pair (or pairs) of water wells are installed as the source. The water is piped into the plant room and through a heat exchanger where heat is either taken or added to the water. The water is then returned to the ground, chemically unaltered. Open loop water well systems are best suited for larger projects and, provided water is available, any size of project can be undertaken. There is a risk element to water well drilling, in that water yields cannot be guaranteed. In order to mitigate this risk, which is borne by the client, we produce detailed hydro-geological studies to quantify the risk involved.

Most suited to: large projects in built up areas.

Where surface water is available, but closed loop is impossible, we can use this as a source by taking water through a similar system of heat exchangers to that outlined above. Filtration isthe main issue with these systems and can constitute a significant maintenance requirement.

Most suited to: medium to large projects with limited access to surface water.

When a cooling load dominates over heating, as is common in many commercial buildings today, the addition of dry coolers on the ground loop itself provides a cost effective alternative to increasing the ground loop size.

Most suited to: projects with large cooling loads.

Closed-loop systems should only be installed using high density polyethylene or polybutylene pipe. Properly installed, these pipes will last for many decades. They are inert to chemicals normally found in soil and have good heat conducting properties. PVC pipe should not be used under any circumstances.

The only acceptable method for joining sections of the special pipe used for the closed-loop systems is electro fusion. Pipe connections are heated and fused together to form a joint stronger than the original pipe. Mechanical joining of pipe for an earth loop is in some restricted applications an accepted practice. The use of barbed fittings, clamps, and glue joints is certain to result in loop failure due to leaks.

The net results in operating cost and efficiency are virtually the same. Which system to choose depends mainly on whether you have an adequate groundwater supply and means of disposal. If you do, an open-loop can be used very effectively. If not, either a horizontal or vertical closed-loop system is your best choice. Over a period of years, a closed loop system will require less maintenance because it's sealed and pressurised, eliminating the possible build-up of minerals or iron deposits.

All types of heating and cooling systems have a rated efficiency. Fossil fuel boilers have a percentage efficiency rating. Natural gas, propane and fuel oil boilers have efficiency ratings based on laboratory conditions. To get an accurate installed efficiency rating, factors such as flue gas heat losses, cycling losses caused by over sizing, blower fan electrical usage, etc., must be included. Geothermal heat pumps, as well as all other types of heat pumps, have efficiencies rated according to their coefficient of performance or COP. It's a scientific way of determining how much energy the system produces versus how much it uses. Most geothermal heat pump systems have COPs of 3.5 - 4.5. WaterFurnace units have typical COPs of 4 to 8. That means for every one unit of energy used to power the system; four or more units are supplied as heat. Where a fossil fuel boiler may be 50-90 percent efficient, a WaterFurnace geothermal heat pump is about 600 percent efficient. We use computer programs to accurately determine the operating efficiency of a system for your home or building.

No. There are different kinds of geothermal heat pumps designed for specific applications. Many geothermal heat pumps, for example, are intended for use only with higher temperature ground water encountered in open-loop systems. Others will operate at entering water temperatures as low as -4°C which are possible in closed-loop systems.

Most goethermal heat pumps provide summer air conditioning, but a few brands are designed only for winter heating. Sometimes these heating-only systems incorporate a groundwater cooled coil that can provide cooling in moderate climates. Geothermal heat pumps can also differ in the way they are designed. Self contained units combine the blower, compressor, heat exchanger and coil in a single cabinet. Split systems allow the coil to be added to a forced-air boiler and utilize the existing blower.

Modern systems are very energy efficient. For each kilowatt of electricity used to run the heat pump, three to four kilowatts of heat are delivered to the building.

Around the world, particularly in the USA and several parts of Europe, the use of GSHP systems is common. The ground source heat pump was actually invented more than 50 years ago, and continuous development has greatly improved its efficiency and reliability. It is now a proven, cost-effective, safe and environmentally friendly alternative to fossil fuels.

A typical heat pump unit for a domestic dwelling is about the same size as a large fridge.

Yes. Some domestic systems are able to heat domestic hot water via a modern high efficiency indirect water cylinder. An immersion heater can then boost the temperature which can be done at night using off peak rates.

Yes. There are reverse-cycle heat pumps that can deliver both heating and cooling.

Can I use a standard domestic electricity supply?

Yes. There are a number of heat pumps that have been specifically designed to run on a standard UK single phase supply. However, if you do have access to a three-phase supply, which is essential for the larger units, then this is a preferable option.

Yes, absolutely. All new houses in the UK must be able to meet or exceed Building Regulations, and from April 2002, these are now the new higher standards for part L2. These mandatory regulations have been designed to conserve fuel, reduce heat losses and ensure greater energy efficiency, and so will ensure that all modern properties will lose less heat and need less heating. This means that the size of heat pump is smaller, will need smaller ground loops and will therefore be less expensive.

Yes. Ground source heat pump systems are ideally matched to modern low temperature underfloor heating.

Yes, you can, but your building must be well insulated for you to gain most benefit. The cost of a system is directly related to its size and with heat losses being fairly high from older buildings, this can add substantially to the capital cost of installation. Money spent on upgrading insulation levels can save a considerable amount on the capital cost. Regrettably, many older buildings can never be made sufficiently energy efficient to use a modern heating distribution system such as low temperature underfloor heating, or low temperature radiators.

Yes, they can, but you will need larger radiators, sized for the typical 45° C to 50° C water temperatures obtained from GSHP systems. If your house is really well insulated they may be suitable, but check to see how big they would have to be and the space they would take up. There is now available a wide range of very stylish Italian die cast aluminium, high output radiators. These are very efficient and smaller than conventional radiators. Upstairs is usually less of a problem as bedrooms are normally kept at lower temperatures.

Yes. There is generally no problem in doing so and it normally means the pump is nearer to the pipe connections on your ground loops, which often makes the whole system easier to connect. Some home owners have made up a small, well insulated, external enclosure for the pump unit.

Yes, provided you can physically dig the trenches, a moderate downward slope is not a problem. Consideration needs to be given to purging air from a system with ground loops higher than the heat pump.

Yes, wet land is better at conducting heat so, as long as you can physically dig a trench, its ideal.

Yes. In the UK, there is now a strong move towards alternative technologies that are sustainable and environmentally much more acceptable. It has been calculated that 40% of CO 2 emissions are derived from the heating of buildings. By using renewable sources of energy to heat your property you can help to reduce these emissions, particularly when compared to burning fossil fuels such as oil. Most electricity suppliers are now offering 'clean green' electricity from a renewable energy source and, if you use this to power your heat pump, your property will be totally heated from renewable energy with zero carbon emissions.

There are no hazardous gas emissions, no flammable oil, LPG or gas pipes, no flue or chimney and no unsightly fuel tanks. GSHP systems have absolutely NO site emissions. There is no need for regular servicing or annual safety checks and maintenance is very low.

It depends what you are comparing. In a modern, well insulated house, a Ground Source Heat Pump system can offer very high efficiency and moderate running costs. An oil-fired boiler would cost considerably more to run, and electric heating would be at least three times as expensive. It is true that the very best of the modern condensing gas boilers may only be a little more expensive to run but that is on current gas prices, which are set to rise. Also, all fossil fuel boilers need regular servicing and maintenance.

The initial purchase costs of a ground source heat pump system will be quite a lot more than a conventional oil or gas fired boiler. The initial one-off expense is offset by the lower running costs, lower maintenance and low servicing requirement. There is also the security of knowledge that the majority of your heating and cooling energy comes out of your ground, is under your control and will not increase in price.

The heat pump is not designed or sized to provide the greatly increased heat demand during the initial drying out of a newly constructed building. During this period, and until the building is completely finished, supplementary heating may well have to be supplied by the owner/builder using separate equipment.

A.The term "closed-loop" is used to describe a geothermal heat pump system that uses a continuous loop of special buried plastic pipe as a heat exchanger. The pipe is connected to the indoor heat pump to form a sealed, underground loop through which an antifreeze solution is circulated. Unlike an open-loop system that consumes water from a well, a closed-loop system re-circulates its heat-transferring solution in pressurized pipe.

That depends on land availability and terrain. Most closed-loops are trenched horizontally in land adjacent to the building. But any area near a home or business with appropriate soil conditions and adequate area will work.

Trenches are normally 1.5m deep and up to 150m long, depending on how many pipes are in a trench. One of the advantages of a horizontal loop system is being able to lay the trenches according to the shape of the land. As a rule of thumb, 20 to 35m of trench are required per kW of system capacity. A well-insulated 150 m² home would need about a 9kW system with 50 to 150m of trench.

Normally, a run of pipe is laid at 1.5m then looped back over itself at three feet once the bottom pipe is covered with soil. This allows more length of pipe to be put in one trench and has no adverse affect on system efficiency. Other loop designs use four or six pipes and allow for shorter trenches if land area is limited.

Closed-loop systems can also be vertical. Usually, a hole is bored to about 50 to 65m per 3.5kW of heat pump capacity. U-shaped loops of pipe are inserted in the holes.

Closed-loop systems should only be installed using high density polyethylene or polybutylene pipe. Properly installed, these pipes will last for many decades. They are inert to chemicals normally found in soil and have good heat conducting properties. PVC pipe should not be used under any circumstances.

The only acceptable method to connect pipe sections is by thermal fusion. Pipe connections are heated and fused together to form a joint stronger than the original pipe. Mechanical joining of pipe for an earth loop is never an accepted practice. The use of barbed fittings, clamps, and glue joints is certain to result in loop failure due to leaks.

No. Research has proven that loops have no adverse effect on grass, trees, or shrubs. Most horizontal loop installations use trenches about six inches wide. This, of course, will leave temporary bare areas that can be restored with grass seed or sod. Vertical loops require little space and result in minimal lawn damage.

No. An earth loop will reach temperatures below freezing during extreme conditions and may freeze your septic system. Such usage is banned in many areas.

It's not recommended. In addition to thermal fusion of the pipe, good earth-to-coil contact is very important for successful loop operation. Non-professional installations may result in less than optimum system performance.

Yes, if it's deep enough and large enough. A minimum of 2m in depth at its lowest level during the year is needed for a pond to be considered. The amount of surface area required depends on the heating and cooling load of the structure.