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Building Success 101
Q: How deep are the pipes of a ground-source heat pump?
A: For the most part, the temperature of the ground becomes predictable and constant at about 8 feet below the surface. Vertical GSHE piping loops, used in residential lot conditions, are excavated as deep as 400’ to enable an effective transfer of temperature between the ground and the pipe’s fluid.
Q. How many holes are required?
A. The air-condition requirements of the home will drive the number of holes. Our challenge is having enough contact with the 70 degree earth to absorb the summer heat from our homes.
Q. Why are the holes spaces so far apart?
A. The 20’ grid is based on the amount of heat/cold transferred into each hole and how far horizontally that thermal load migrates before influencing adjoining holes.
Improving home energy efficiency and building more sustainable housing is no longer a trend — it’s mainstream. As a professional builder, we feel it’s important to keep up on emerging technologies that will down the line help our clients save money, improve comfort and reduce our impact on the environment.
In the spirit of learning about these new technologies, we profile a rising star in the world of heating and air conditioning: Geothermal (or “ground-source heat exchange” GSHE) heating and cooling systems. Simply, a geothermal system uses the temperature of the ground to condition the air that is distributed through the house using conventional ductwork.
To transfer ground temperature to a Las Vegas home’s central air distribution system, a closed loop of narrow, flexible pipes are installed in 6” holes, 300’ to 400’ deep and spaced on a 20’ grid.
The temperature of the ground in Las Vegas averages 70-75 degrees. Conductive, non-toxic fluid is pumped through the pipes and is heated or cooled (depending on its temperature) by the constant temperature of the ground. When that fluid returns to the surface, it transfers its temperature to the air being blown into the home’s ductwork.
That’s exactly how conventional, air-sourced heat pumps work, except that those systems use the temperature of the ambient outdoor air, which is far less predictable and less constant than underground temperatures.
In winter, for instance, if the thermostat is set at 72 degrees, the heating coils in the pump only need to boost the incoming ground-conditioned, 70-degree fluid by a few degrees to achieve the desired temperature. The outdoor air temperature that day, however, is likely much colder, which requires far more energy from the pump’s heating coils to warm it sufficiently.
Merlin Custom Home Builders’s go-to ground source heat exchange subcontractor is GES Nevada. GES Nevada was recently awarded the contract for installing a geothermal system at the Springs Preserve “Historical Cottage Restoration” project.
Because this type of ground-source system requires far less supplemental heating or cooling measures to achieve desired indoor temperature and comfort levels, it uses less energy. In turn, there’s less wear and tear on the heat pump, allowing it to operate at optimum efficiency for a longer period of time and with less maintenance.
Cost and payback: Until 2016, the Federal Government is offering a 30% tax credit on geothermal systems with no upper limit. This covers both the cost and installation of the units. These credits apply to both new construction and existing homes. The cost to install a geothermal system and the savings vary but with the 30% tax credit a residential geothermal system can be paid off in 7 to 10 years.
People with geothermal systems also report better and healthier indoor comfort, especially in the height of summer or winter when a conventional heat pump has a hard time conditioning the outside air to the desired indoor temperature.
Geothermal heating and cooling systems may not be for everyone or every new-home condition, but they are a proven, energy-efficient option that delivers better performance and lessens environmental impact.