The temperature of the outside air is what affects the comfort of indoor spaces in all buildings. Unlike shallow earth temperatures, outdoor air displays a great range from day-to-night, and across the seasons. This results in heating, ventilating, and air conditioning (HVAC) equipment always opposing the influence of outdoor air during extreme temperature swings.
HEATING—COOLING AT THE WRONG TIME
For all buildings with standard air conditioning and those with evaporative-based chillers (cooling towers) the HVAC equipment is called upon for cooling the interior space just as the outdoor temperature has become its warmest in a 24-hour daily cycle. That’s because a building’s defense via insulation has finally failed to maintain interior comfort. Air-based cooling equipment is therefore working at a time that reduces its rated efficiency.
UNDERGROUND IN THE SHALLOW EARTH
As anyone who’s visited a cave in the height of summer’s heat or winter’s cold will tell you, the cave’s temperature is far cooler than above ground in summer and far warmer than above ground in winter. If a standard electric air conditioner or air-source heat pump could reside inside such a cave, they could dump their waste heat into cooler air during summer. An air-source heat pump installed inside that cave could benefit in winter, too—but neither can be located in a cave for that stable, narrow temperature range.
GEO HEAT PUMPS WORK WITH DIRT
However, the geothermal heat pump (GHP) operates continuously from a cave-like stable temperature band and it benefits during both heating and cooling by using a circulated fluid “ground loop” that acts as a heat exchanger. This ground heat exchanger (GHEX) not only resides in a narrow temperature range, but it is capable of connecting to underground thermal energy as if the underground formation was a battery—capable of absorbing heat energy as well as exporting it. There are a number of GHEX styles that tap underground dirt or rock, and bodies of water—anywhere renewable thermal energy can be borrowed and/or re-deposited. Examples can be found in the Geo Basics menu of www.CaliforniaGEO.org.
—Bill Martin, President CaliforniaGEO
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