Imagine an HVAC and water heating system that can save 20% to 50% on a building’s energy costs while minimizing CO2 and carbon emissions. Imagine a system that is more reliable, is 2.5 to 4 times more efficient, provides the lowest life cycle cost, and a high degree of design flexibility.
Where can you find such a system? You need look no further than right under your feet. The earth is a huge energy storage device that absorbs 47% of the sun’s energy. When combined with the constant upward flow of heat from the earth’s red hot interior, the result is geothermal energy. Geo = earth, Thermal = heat. This clean, renewable energy is stored in masses of rock in the upper six miles of the earth’s crust. In nearly every state of the Union, there is sufficient geothermal energy to heat, cool and provide hot water for all types and sizes of buildings.
Temperatures near the earth’s surface remain relatively constant all year round – warmer than outside air in the winter, and cooler than outside air in the summer. Geoexchange systems (or ground coupled heat pumps) extract the earth’s heat during the winter and release it to the building interior. In the summer the process is reversed, drawing the hot air from inside the building and transferring to the earth. Nearly all geoexchange systems on the market can also provide low cost hot water – further increasing their operational efficiency
According to the EPA and DOE, geoexhange systems are the most energy efficient, environmentally clean and cost-effective space conditioning systems available. They rate the systems 40% more efficient than air source heat pumps 48% greater than gas furnaces and 75% greater than oil furnaces. Though geoexchange units do require a power source, they have a much greater energy efficiency ratio. In heating mode, the system will move at least three units of solar energy from the ground for each unit of electricity used.
There are three principal components in a geoexchange system: The ground loop, the heat pump unit and the heat distribution channel:[ad#half-post]
For most buildings, the connection to the geothermal heat source is made via a ‘closed’ loop configuration. A series of flexible, high-density polyethylene pipes are installed beneath the ground in horizontal trenches or vertical holes. A fluid (water or a mixture of water and environmentally benign antifreeze) is circulated through the loops, absorbing the earth’s heat as it passes through the pipes and transporting it to the geoexchange unit inside the building. In cooling mode, the building’s interior hot air is absorbed by the unit, transported back through the loops and absorbed into the surrounding earth. Post-installation the holes or trenches are backfilled, then covered with native landscaping, grass or even parking lots.
Horizontal trenching is usually the most cost effective configuration when adequate space is available and trenches are easy to dig Vertical drilling is used when the land area is limited, or where the soil is too shallow for horizontal trenching. The loops should be installed by professionals who follow procedures established by the International Ground Source Heat Pump Association (IGSHPA), and are either certified by IGSHPA or can prove equivalent training by manufacturers or other recognized authorities.
Geoexchange Heat Pump
The most commonly used unit is the single package water-to-air heat pump, which combines heat exchanger, refrigerant piping, control valve, compressor, air coil, and fan, in one single enclosure about the size of a small gas furnace. The single package design is a major advantage over the “split” system used for air- source heat pumps. There are numerous manufacturers, brands and models of heat pumps available. They are rated by the Air Conditioning and Refrigerant Institute according to their respective Coefficient of Performance (heating) and Energy Efficiency Ratio (cooling). ENERGY STAR qualified geoexchange pumps consume 40-60 percent less energy than a standard heat pump.
Heat Distribution Channel
Conventional ductwork is generally used to distribute heated or cooled air from the geothermal heat pump throughout the building. A well-designed geoexchange system allows building occupants precise temperature control by room or by zone, with ideal humidity levels. The system requires no flue or chimney. There is no rooftop equipment or chilling towers that add weight to the structure or limit alternative roof styles such as vegetated roofing. Their compact size requires significantly less interior storage space. The heated water coursing through the system can be utilized for additional building uses, such as heating swimming pools and spas, melting sidewalk and parking lot ice and snow- even providing water for a car wash!
The largest commercial geoexchange system in the world is the Waterfront Office and Galt East Hotel complex in Louisville, Kentucky. This 1.7 million plus square foot complex is fitted with a 2,700 ton capacity geoexchange system, at a cost of $1,500 per ton. The project manager estimates that a conventional HVAC system with centrifugal chillers, cooling towers and insulated pipes would have cost from $2,000 to $3,000 per ton. Using Geoexchange technology freed up about 25,000 square feet of additional commercial space that would otherwise have been used for conventional equipment rooms. Energy savings are estimated at $25,000 per month while allowing individual temperature control to each room or suite. Annual maintenance costs are about 5 cents per square foot versus much higher average costs with standard HVAC systems.
Best of all, complaints about heating and cooling “have been virtually non-existent, whereas before we had frequent comments about lack of adequate comfort”
Daniele Loffreda is Managing Principal of Plateau Enviro Associates, a consulting firm specializing in green building, sustainable communities and marketing communications. He serves on the Board of Directors of the U.S. Greenbuilding Council Colorado Chapter, and is a Leadership in Energy and Environmental Design (LEED) Accredited Professional
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