Geothermal energy means energy derived from the heat within the earth. People have made use of geothermal energy in the form of hot springs for centuries (i.e. the ancient romans used geothermal energy to heat their baths), however, the first attempt to generate electricity from this energy source did not occur until the 20th century.
The production of electricity from geothermal energy sources can be a highly efficient means of delivering clean and renewable electricity to many people. Location is of key importance for the development of an efficient geothermal power station and therefore, economically viable levels of electricity can only be generated in certain areas of the world. Currently geothermal power heats 89% of the houses in Iceland and over 54% of the primary energy used in Iceland comes from geothermal sources. However, there are only a handful of locations across the world that are capable of producing viable and efficient levels of electricity from geothermal energy sources and as a result of this, in 2007, less than 1% of the world's electricity supply was produced from geothermal sources.
Generating electricity from geothermal energy requires an industrial system which is by no means suitable for a home. An alternative means of harnessing geothermal energy in a bid to receive a source of clean and renewable energy is through a ground source heat pump. This is a environmentally friendly way to heat your home and heat water.
Throughout the year, almost 50% of the sun’s energy is absorbed into the earth where it maintains a consistent temperature just a few feet below the ground’s surface. Geothermal heat pumps consist of two parts: a circuit of underground piping outside the house, and a heat pump unit inside the house. These systems can either be an open loop system or a closed loop system.
Closed loop systems are when the same fluid (usually water and anti-freeze) always flows through the collector pipes. In a closed-loop system, a loop is buried horizontally or drilled vertically in the earth around the home, or laid in a nearby lake or pond.
Open loop systems draw well water for use as the heat source or heat sink, and after use, return the well water to a drainage field or another well. New water is always being pumped through the system when it is in operation. It is called an open-loop system because the ground water is open to the environment.
A ground-source heat pump uses the earth or ground water or both as the sources of heat in the winter, and as the "sink" for heat removed from the home in the summer. This combination of high performance technology allows us to tap into the earth’s natural heating and cooling properties to consistently and evenly distribute warm or cool air in your home throughout each season.
Using a heat pump alone to may not meet your full heating / cooling needs. Unlike gas and oil boilers, heat pumps deliver heat at lower temperatures over much longer periods. You will notice that radiators won't feel as hot to the touch as they might do when you are using a gas or oil boiler. During the winter they may need to be on constantly to heat your home efficiently. However, used in conjunction with a supplementary form of heating, such as an oil, gas or electric furnace, a heat pump can provide reliable and economic heating in winter and cooling in summer.
If you already have an oil or electric heating system, installing a heat pump may be an effective way to reduce your energy costs. Heat pump systems can also be used in conjunction with under floor heating. Under floor heating is an ideal distribution system because high temperatures are not required (the larger the surface area discharging heat, the lower the temperature needs to be). Under floor heating uses a large mass of concrete (your floor) to store the heat, and this storage effect means the heat pump will not cycle (frequently switch on and off) which can shorten the life of the unit.
The main advantage of geothermal ground source heat pumps is that they can be used in many locations. Even ground source heat pumps installed in colder regions such as Norway and Sweden see significant results. A geothermal heat pump system can be highly effective at reducing the energy you require to heat water and therefore reducing your energy bills. While residential geothermal heat pump systems are usually more expensive initially to install than other heating and cooling systems, their greater efficiency means the investment can be recouped in two to seven years. After that, energy and maintenance costs are much less than conventional heating and air-conditioning systems.
How it works
Heat pump systems are typically made up of the following main components:
Collector (system used to collect heat from the surroundings)
Heat pump unit and associated components
Heat distribution system (under floor heating or equivalent low temperature distribution system)
Control system (weather compensation, thermostats, timers etc.)
Heat pumps don’t make electricity but reduce the need for electricity for heating and cooling. They move hot water from the ground outside into the house.
A heat pump is an electrical device that extracts heat from one place and transfers it to another. The heat pump is not a new technology; it has been used in Canada and around the world for decades. Refrigerators and air conditioners are both common examples of this technology.
The geothermal heat pumps consist of two heat exchanger coils. A substance called a refrigerant carries the heat from one area to another. When compressed, it is a high temperature, high pressure liquid. If it is allowed to expand, it turns into a low temperature, low pressure gas. The gas then absorbs the heat. In one coil, the refrigerant is evaporated at low pressure and absorbs heat from its surroundings. The refrigerant is then compressed en route to the other coil, where it condenses at high pressure. At this point, it releases the heat it absorbed earlier in the cycle. This is how we heat the home and heat water for showers etc. All heat pumps have an outdoor unit (called the condenser) and an indoor unit (an evaporator coil).
The heating cycle
Heat from the ground is absorbed at low temperatures into a fluid inside a loop of pipe (a ground loop) buried underground. The fluid then passes through a compressor that raises it to a higher temperature, which can then heat water for the heating and hot water circuits (showers) of the house. The cooled ground-loop fluid passes back into the ground where it absorbs further energy from the ground in a continuous process as long as heating is required.
The cooling cycle
The cooling cycle is basically the reverse of the heating cycle. The direction of the refrigerant flow is changed by the reversing valve. The refrigerant picks up heat from the house air and transfers it directly, in DX systems, or to the ground water or antifreeze mixture. The heat is then pumped outside, into a water body or return well (in an open system) or into the underground piping (in a closed loop system). Refrigerators and air conditioners are both examples of heat pumps operating only in the cooling mode.
Different types of geothermal pumps
Geothermal heat pump systems are usually not do-it-yourself projects. To ensure good results, the piping should be installed by professionals who follow procedures established by the International Ground Source Heat Pump Association (IGSHPA). Designing the system also calls for professional expertise: the length of the loop depends upon a number of factors, including the type of loop configuration used; your home’s heating and air conditioning load; local soil conditions and landscaping; and the severity of your climate. Larger homes requiring more heating or air conditioning generally need larger loops than smaller homes. Homes in climates where temperatures are extreme also generally require larger loops. The type of soil around your home is also an important factor. The following are a list of the different geothermal pump options.
Closed loop systems
Horizontal loops are the most common type of loop system, and are commonly used in home where an adequate land surface is available (rural areas). An excavator will dig several trenches about six feet deep in the ground, each one up to 300 feet long. Our green geothermal pipe is placed in the trenches which are then backfilled with soil.
Vertical loops are primarily used in areas with a limited land surface area (urban areas). A specially designed geothermal drilling rig bores vertical holes into the ground each ranging from 180 to 540 feet deep. Our green geothermal pipe is inserted into each vertical bore and then the holes are filled with bentonite grout.
Pond or Lake Loops
On properties that have a nearby lake or pond that is appropriate in size and eight feet deep, a loop system can be submerged at the bottom of the body of water. A single trench is excavated from the home to the water and typically two pipes are inserted into it. These two pipes connect to several green geothermal pipes that are submerged at the bottom of the lake or pond. This type of loop design may be the most economical when a home is near a body of water such as a shallow pond or lake. Fluid circulates underwater through polyethylene piping in a closed system, just as it does through ground loops. The pipes may be coiled in a slinky shape to fit more of it into a given amount of space. Since it is a closed system, it results in no adverse impacts on the aquatic system.
Open loop systems
Open loops are most commonly used on rural properties that have existing high capacity water wells. Ground water is withdrawn from an aquifer through a supply well and pumped into the heat pump, while discharged water from the heat pump is redirected into a second well and back into the same aquifer.
Could geothermal work for you
In 2010 Maurice Stanley wrote a thesis titled “An analysis of the viability of geothermal heating in residential housing in Ireland” and as part of his research he conducted a literature review, case study, and also sent out a questionnaire to 11 people who use geothermal energy in their homes.
He discovered from his research that the average cost for using geothermal heating for one year averaged under half of the price of oil heating. His case study suggests a payback period of just over 7.5 years, while his questionnaire responses suggest an average payback period of 10 years; with some systems having a life span of nearly 25 years the savings which can be made are very reassuring.
Over all the results from the questionnaire were very positive with a massive 82% of geothermal heat users were happy with their systems. 46% of the users would not even consider switching from their geothermal system. This positive result points out that the majority of people who rely on ground source heat pumps for their heating needs are pleased with the chosen method of heating.
He also discovered that out of the eleven users questioned, only two use complementary heating systems namely in the form of a gas boiler and a wood pellet stove. This result demonstrates that the majority of users of geothermal heating systems do not require any additional heat source. According to this, the ground source heat pumps seem to be a sufficient way of heating a home in Ireland.
From the primary sources of information gathered by the author it is clear that such heating systems are economically viable and an excellent solution for domestic home heating in Ireland, and potentially many other locations as well!
For information about other renewable energies in your home please visit our articles on Solar Energy, Wind Energy, and stay tuned for more!
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Sources: Geosmart Energy, Energy Saving Trust, Geothermal-heat-pump-resource, SEAI, Consumer Energy Center, NRCAN, Clean-energy-ideas, CANGEA, Geothermal_energy, Renewable_energy_in_Iceland, Geothermal Int, “An analysis of the viability of geothermal heating in residential housing in Ireland” by Maurice Stanley, BSc (Hons) Quantity Surveying, Edinburgh Napier University