Ground Source Heat Pumps
What are Ground Source Heat Pumps?
Ground source heat pumps are a proven and well-developed technology that has been in use since the late1940s to utilise the heat that is stored in the ground for heating purposes.
The earth has the natural ability to absorb and store heat directly from the sun, from rain and the air as well as heat from within the earth itself. This stored solar energy is a vast reserve of free low grade heat which heat pumps can extract from the ground and concentrate from low grade heat to temperatures that are high enough to be used for heating water, homes and commercial premises. The systems can also be reversed which makes them ideally suited to cooling in summer, providing the perfect temperature in all seasons.
There has been a misconception that such systems can only be used in cold climates such as Scandinavia, or countries that are perceived as having volcanic/geothermic activity. In fact, they can be installed in most UK properties and are rapidly growing in popularity in the UK as people are realising the financial and environmental benefits of these systems.
How Does it Work?
While the UK can experience seasonal temperature extremes, from warm summers to sub-zero cold in the winter, just a few meters below the Earth's surface, the ground actually remains at a relatively constant temperature averaging between 8C and 10C.
Unlike traditional boilers, ground source heat pumps do not use energy to generate heat directly. Instead the systems only use small amounts of electricity to circulate and compress fluid with an electric pump that upgrades the temperatures drawn from the ground sufficiently for space and hot water heating, as a result, they are a very energy efficient method for heating.
There are different types of ground source heat pumps, but the principle on which they operate is similar. All Green Energy Doctor systems consist of three main components:
Ground Collector
This is a loop of special grade piping that is buried in the ground beside the property and is invisible after installation (see opposite for configurations). A fluid (with a small amount of environmentally friendly anti-freeze) is circulated through the loop, where it absorbs heat energy from the ground. This is pumped through the loop to the heat pump.
Heat Pump / Exchanger Unit The energy (heat) is transferred from the fluid to a refrigerant via a heat exchanger (evaporator) which extracts free low temperature heat and transfers it to a refrigerant that runs through it. The refrigerant has a low boiling point (-10C) and as it absorbing the heat it evaporates into a gaseous state. The gaseous refrigerant is then increased in pressure by a compressor. As the gas is compressed it increases in temperature. The refrigerant gas passes to the condenser (a second heat exchanger) where it cools and condenses as the expansion valve allows the pressure to drop. As it condenses, this enhanced energy is transferred from the refrigerant to the heating system.
Using compression technology similar to that found in your fridge, ground source heat pumps capture and upgrade heat from the ground. 1. Fluid from collector loop, 2. Evaporator Heat Exchanger (heat from ground to refrigerant), 3. Compressor, 4. Condenser Heat Exchanger (refrigerant to heating system), 5. Expansion Valve that releases pressure.
Heating System
You've probably got one of those already in the form of radiators, but ideally, for maximum benefit and efficiency, a heat pump is best used with under-floor heating, but low temperature oversized radiators are also a practical option. For domestic hot water, ground source heat pumps are able to provide this via a modern high efficiency indirect water cylinder.
Types of System
Most heat pump systems use a similar technology in the actual heat pump/heat exchanger (as detailed opposite). However, geological, hydrological and landscape conditions vary significantly around the UK, as does the availability of space. To meet these differing factors, there are a number of different ground collector configurations that are used to obtain energy from the ground:
Horizontal Collector
The heat is extracted from the soil by means of lengths of pipe (ground collector) that are buried in trenches approximately 1.5 metres below the ground and spaced to form a grid. This is a good solution if the property in question has enough land to accommodate the collector.
Vertical Collector
A borehole is drilled to a depth of between 60 and 200 metres, and the ground collector is fed into the hole. A vertical collector is a good solution where there is limited space as the borehole can be drilled on the smallest of plots.
Water Source
If ground water is available, such as a pond, it can be utilised as a heat source and removes the need to drill or dig trenches. However, system efficiencies are likely to be slightly lower because of seasonal variations in the water temperature.
There are three principal configurations of ground collectors for domestic dwellings in the UK. 1. Horizontal collectors (also available as more compact 'Slinky TM' version), 2. Vertical collectors, 3. Water source collectors. Each method has a different energy yield, which will vary significantly based on site location and local geology.
What Are The Benefits?
Reduce Your Energy Bills By Up to 50%
With a properly sized and installed geothermal heating system you can significantly cut your heating bills, which, depending on your current fuel source, may provide yearly savings of many hundreds of pounds. They can be particularly cost effective in areas where mains gas is not available, with an oil-fired boiler costing twice as much to run and electric heating being at least three times as expensive. Even the very best modern condensing gas boilers are more expensive to run than a ground source heat pump, although not to the same degree as oil or electricity.
Improved Efficiency
Unlike traditional boilers that generally create heat through the inefficient combustion of fossil fuels, modern heat pumps are extremely efficient. Heat pump efficiencies are normally quoted as the 'coefficient of performance' of the system; these are typically in the range 3 to 5. In other words, extracting heat from the ground requires just 1kW of electrical input in order to generate 3kW to 5kW of heating output. Heat pump systems therefore, are 3 to 5 times more efficient than fossil fuel boilers and are more than capable of warming a house completely, even during the lowest winter temperatures.
Reduce Your Impact On The Environment
With almost 40% of all UK carbon emissions coming from 24 million dwellings in the UK there are many opportunities to install heat pumps to help reduce these emissions. Fossil fuel use has a particular detrimental effect to the environment as burning fossil fuels releases carbon dioxide into the atmosphere contributing significantly to global warming. Heat pumps can extract around 75% of usable heating energy from the environment and can generally reduce carbon emissions compared to gas central heating systems by approximately 50%. These savings are even greater when compared to other fuels such as oil. For a particularly environmental solution, green electricity can be purchased to provide the electricity needed by the system.
Reduce Your Dependency On Fossil Fuel Imports
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 as a result of foreign government actions or the prevailing economic climate.
Easy To Use As A Fossil Fuel System
Modern ground source heat pumps are compact units that offer similar levels of convenience to oil and gas boilers. A typical heat pump unit for a domestic dwelling is about the same size as a large fridge, with some smaller units able to be fitted under work surfaces in areas such as the utility room.
Lower Maintenance And Servicing Costs
The technology inside a heat pump works on similar principles to those of a domestic fridge, but in reverse. Unlike fossil fuel systems there is no need for regular servicing or annual safety checks and maintenance is minimal. This means that the actual running costs are reduced further when compared to fossil fuel systems.
Is It Suitable For My Requirements?
Because shallow ground temperatures are relatively constant throughout the UK, ground source heat pumps can be effectively used almost anywhere. However, the specific heating requirements of your household and the geological, hydrological, and spatial characteristics of your land will be important factors that Green Energy Doctor will take into consideration, when designing a system.
The following gives a good indication of some general principles:
Insulation of the property and heating requirement
Ground source heat pump efficiency demands a properly insulated house: insufficient insulated walls, floors, ceilings or attics and basements may make the system less effective. 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 the system installation. Money spent on upgrading insulation levels can save a considerable amount on the system cost. However, for some properties the cost of making the building sufficiently energy efficient to use a modern heating distribution system might be cost prohibitive.
Heating System
Ground Source Heat Pumps work best with heating systems that are optimised to run at a lower water temperature than is commonly used in UK boiler and radiator systems. As such, they make an ideal partner for underfloor heating systems or oversized radiators sized for the typical 45C to 50C water temperatures obtained from ground source heat pump systems. For homes without such modern additions, ground source heat pumps can still work. Green Energy Doctor will be able to advise on the suitability of your current system and any potential changes that would be required to make the system suitable.
Geology:
Factors such as the composition and properties of your soil and rock (which can affect heat transfer rates) require consideration when designing a ground loop. For example, soil with good heat transfer properties requires less piping to gather a certain amount of heat than soil with poor heat transfer properties. The amount of soil available contributes to system design as well, areas with extensive hard rock or soil too shallow to trench may require a vertical ground loops instead of horizontal loops.
Hydrology
Ground or surface water availability also plays a part in deciding what type of ground loop to use. Depending on factors such as depth, volume, and water quality, bodies of surface water can be used as a source of water for an open-loop system, or as a repository for coils of piping in a closed-loop system.
Land Availability
The amount space you have available, the layout and the location of underground utilities also contribute to your system design. Horizontal ground loops are typically used for buildings with sufficient land. Vertical installations or more compact horizontal 'Slinky TM' installations are often used for existing buildings because they minimize the disturbance to the landscape. The size of ground area required for trenches will vary with the location, the property and the output required. As a very general guide, for a newly built 3-bedroomed house of around 120 m2 in area with a heat loss of around 6kW, two trenches of 30-40 metres in length would probably be required.
There are very few projects where we are not able to come up with a satisfactory solution. That is why the Green Energy Doctor is on hand to help and advise you on the best course.
Please feel free to call us, send us an email or send us a drawing of your specific project.
How Much Does It Cost?
As a general rule it costs between �1000 and �1600 per 1 kW of heat output. So the typical cost for a professionally designed and installed domestic 8kW system would cost between �8,000-�12,800 plus the price of the distribution system. This can vary with property and location but a system using horizontal ground loops will generally cost less than a system with vertical loops.
Even though the installation price of a geothermal system can be several times that of conventional heating and cooling systems of equal capacity, it is more efficient, thereby saving money every month. Therefore the additional costs are returned through energy savings in 5 to 10 years if you were to purchase one. When included in a mortgage, your GHP will have a positive cash flow from the beginning as the energy cost savings will easily exceed that added mortgage amount over the course of each year.
With a system life is estimated at 25 years for the inside components and 50+ years for the ground loop you will continue to make savings long into the future.
Once the technical survey has been carried out, all Green Energy Doctor prices will be given as fixed prices.
Government grants are available for these technologies; please contact us to find out more information.
How to Get Started...
To organise a no obligation site visit or to start moving your project forward contact the Green Energy Doctor today on:
T: 0845 009 5652
E: info@greenenergydoctor.co.uk