What is a geothermal system and how does it work?

Every day, the earth absorbs over half of the sun's energy. Geothermal (also known as geoexchange or earth energy) systems rely primarily on this stored solar energy to heat or cool a building and provide domestic hot water. Geoexchange systems use a loop field and a ground source heat pump to concentrate heat from the earth and transfer it into a building in winter, or to transfer heat from a building into the earth in summer, where it is stored for extraction later. Geoexchange uses the same heat pump system for both heating and cooling. A common example of a heat pump is a refrigerator, which concentrates and extracts heat from the interior, and rejects it into the surrounding space.

By transferring thermal energy rather than creating it through combustion or electrical resistance, geoexchange systems achieve very high efficiencies. For each unit of electrical energy consumed by a heat pump, three to four units of heat energy are moved from the earth to your building.

The two basic types of geoexchange systems are open loop and closed loop. Closed loop systems are preferred for their reliability and low maintenance.

Ground source heat pumps use a network of fluid filled pipes to transfer heat to and from the earth. The pipes can be inserted into vertical boreholes, buried in horizontal trenches, or submerged in the ocean, lakes, or rivers.

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What are the benefits?

Geoexchange systems provide superior comfort to building occupants because they provide a steady flow of lower temperature conditioned air or water, eliminating the surges, hot flashes and drafts associated with conventional systems.

The temperature of the ground a few feet below the Earth's surface remains relatively stable between 10oC and 15oC. This constant "thermal reservoir" allows very efficient performance year round.

Geoexchange systems provide extraordinarily low operating costs. Approximately 75% of the energy used in geoexchange heating and cooling is renewable thermal energy from the ground - energy you already own. The remainder is clean electrical energy used to power the pumps and compressors. Dependence on utilities is reduced. Geoexchange also provides a "buffer" between your operating budget and the impact of increasing fossil fuel costs. Geoexchange systems do the work that ordinarily required three appliances: a furnace, and air conditioner, and a hot water heater. They eliminate the outdoor noise pollution and space requirements of an air source heat exchanger. Located indoors, they are extremely quiet and space efficient.

Geoexchange heat pumps are more reliable than conventional systems. Eliminating fossil fuel combustion means no thermal stresses, and equipment has a much longer life span. Geoexchange heating and cooling is an environmentally benign technology, with no emissions or exhaust. The emissions offset by even the smallest geoexchange system is equivalent to taking two cars off the road or planting an acre of trees.

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What is the difference between geoexchange system and a conventional HVAC system?

Geoexchange systems are different from all other HVAC systems due to their ability to store thermal energy: the ground loop essentially acts as a "thermal battery". Heat rejected from a building during summer air conditioning is stored in the earth surrounding the ground loop, and is reclaimed during the heating season. The ability to store and reclaim thermal energy greatly increases geoexchange efficiency when compared to air source heat pumps.

Geoexchange systems don't rely on fossil fuel combustion to produce heat. Instead the ground source heat pump simply concentrates and transfers heat that is already there. This process of moving heat uses far less energy than conventional methods.

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What types of commercial/institutional buildings are best suited for geoexchange system?

Buildings with both a heating and cooling load (also called a balanced load) are best suited for geoexchange systems. This will take advantage of the capital cost benefit of having only one system for both functions, and provide a faster return on investment. (In some applications, a geoexchange system will pay for itself in as little as 4 to 6 years.) A geoexchange loop field designed for a balanced load can also be sized smaller than one for an unbalanced load, since it can function more as a "thermal battery" as opposed to a thermal source.

Used only for heating, geoexchange still provides significant operating cost advantages, increased comfort, reduced ambient noise, and all the benefits of eliminating emissions due to fossil fuel combustion.

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Are you seeing demand growing for this type of technology from ICI sector?

Yes, the biggest growth in the geoexchange industry is in the ICI sector. Typical installations in this sector call for both heating and cooling, allowing the capital cost and operating cost benefits (described above) to be realized.

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What is the average cost of installation?

Installation costs are specific to each site. Factors affecting installation costs include the heating and cooling load assessment, the usage of the system, the inclusion of domestic hot water or not, the type of distribution system used inside the building, and the thermal conductivity of the local soil.

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Although new construction provides an easier opportunity to install a geoexchange system, can they be installed for a retrofit project?

Geoexchange retrofits are possible, though installation costs will typically be higher than in new construction. The distribution system inside the building often provides the greatest challenge. For example, a forced air system designed for a natural gas furnace will require larger diameter ducts, or a radiant floor system designed for a natural gas boiler may require closer pipe centres. The cost of modifying these systems can be prohibitive. A site inspection by a qualified geoexchange engineer will assess the potential for a geoexchange retrofit. As fossil fuel costs continue to rise, geoexchange retrofits will become increasingly viable.

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What is some important information owners and property managers need to know when considering ground source heat pump technology?

The best time to plan for a geoexchange system is during the design phase of your project. Including the geoexchange engineer at this stage can mitigate design obstacles before they arise. Horizontal loop systems are more economic, but a vertical borehole system is very space efficient and can be utilized in applications where horizontal loops are ruled out due to space limitations. When possible, ocean or lake loops are very affordable and efficient.

Though the upfront costs are higher than conventional systems, geoexchange systems are an excellent investment when viewed over the life of the property and when the changes in the global energy market are considered.

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Are geoexchange systems guaranteed?

The heat pumps, circulating pumps, control systems, and pipes used in a geoexchange system all carry manufacturers guarantees. However, the greatest guarantee for the efficient performance of your geoexchange system is the capability and expertise of the designer and installer. Knowledge of the geothermal resource, the handling and care of the design, and an optimized control strategy will ensure that your geoexchange system reliably performs to maximum efficiency.

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Are there any challenges with these systems?

The first thing that comes to mind with a geoexchange system is ensuring that maintenance staff are aware of the operating differences from conventional systems. Incorrectly adjusting the control system could negatively affect geoexchange performance.

As a buyer, the biggest challenge is securing a contractor with the system design and control strategy experience to ensure that your system will meet your expectations for comfort and efficiency.

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