Tapping the Earth: Geothermal Heating & Cooling

The earth offers the perfect exchange medium for warmth in the winter and coolness in the summer.

To tap this free source of energy, a central geothermal heat pump will supply heating and cooling for our new building – reducing HVAC system costs by 50% (based on energy models) in lieu of using existing plant utilities at the college. Each student room will come equipped with a heating/cooling/outside air unit connected to this central unit via a 4-piped system. Geothermal energy will also pre-heat water for all daily uses (showers, sinks, washing machines, etc.)

Our geothermal system uses the earth as a heat source and heat sink. Despite summer highs in the upper 80s and winter lows that drop below 30 in Berea, the ground temperature remains relatively constant – between 50° and 60°F (10°-16°C) year round – just a few feet below the surface. By circulating water through piping in the earth, the lower or higher ground temps transfer into the fluid and then via a heat pump into the building – boosting space heating or cooling according to season. Construction of this system began in January 2013 with crews drilling 50 geothermal wells, each 4.5 inches in diameter, 375 deep and spaced 20 feet apart within the footprint of the new parking lot (directly east of the building).

HOW IT WORKS

Geothermal (a.k.a. “geoexchange”, “ground-source” or “earth energy”) technology relies on the ground – or ground water – as a thermal energy source to warm the air in a building; in hotter weather, it serves as a thermal energy sink to provide cooling. Ground loop systems therefore play a critical role. There are four types: horizontal, vertical or pond/lake closed loops (circulating fluid through plastic tubing) and an open loop, which is basically a water well. The optimal system will depend on water quality, soil conditions, environmental regulations and even the amount of space available. Given all these factors, the design team decided a vertical, closed loop configuration offered the best approach.

Above ground, it’s the work of the heat pump to transfer that thermal energy from one place to another. Our system features a water-source unit, using a refrigerant to move heat from the ground, via the heat exchanger, and into the building’s indoor air delivery system – making it warmer in winter; in summer, the reverse occurs by moving heat from inside the building to the ground. Water-source heat pumps can achieve high efficiencies (300% to 600%) on the coldest winter nights, compared to 175% to 250% for air-source heat pumps on cool days.1 And while total costs (drilling, etc.) are typically higher for a geothermal heat pump system, high efficiency and energy payback in just 5 to 10 years makes this a smart, long-term investment for the college.

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