Geothermal Basics
How does a geothermal heating and cooling system work? Outdoor temperatures fluctuate with the changing seasons but underground temperatures don’t. Four to six feet below the earth’s surface, temperatures remain relatively constant year round. A geothermal system capitalizes on these constant temperatures to provide ‘free’ energy.
In winter, a series of fluid-filled underground pipes called a loop absorbs stored heat and carries it indoors. The indoor unit compresses the heat to a higher temperature and distributes it throughout the building. In summer, the system reverses pulling heat from the building carrying it through the earth loop and depositing it in the cooler earth.
Unlike ordinary systems, geothermal systems don’t burn fossil fuel to generate heat; they simply transfer heat to and from the earth to provide a more efficient, affordable, and environmentally friendly method of heating and cooling. Typically, only a small amount of electricity is used to operate the unit’s fan, compressor, and pump.
HOW EFFICIENT IS A GEOTHERMAL SYSTEM?
A geothermal system is over five times more efficient in heating and more than twice as efficient in cooling as the most efficient ordinary system. Because geothermal systems move existing heat rather than creating it through combustion, they provide four to five units of energy for every one unit used to power the system.
All heating and cooling systems have a rated efficiency from a US governmental agency. Fossil fuel furnaces use AFUE. Air conditioners use SEER while heat pumps use HSPF and SEER.
Geothermal heat pumps rate heating efficiencies according to their coefficient of performance or COP. It’s a scientific way of determining how much energy the system produces versus how much it uses. Most geothermal heat pump systems have COPs of 3.0-4.5. Where a fossil fuel furnace may be 78-98% efficient, a geothermal heat pump is about 500% efficient.
For cooling, geothermal units are rated by Energy Efficiency Ratio (EER). EER is a measure of efficiency in the cooling mode when measured at a constant temperature (95F). The higher the EER, the more efficient the unit.
HOW LONG IS THE PAYBACK PERIOD FOR A GEOTHERMAL SYSTEM?
Geothermal systems are so energy-efficient that the payback period is remarkably brief. A study by the Air Force Institute of Technology calculated that it takes on average just seven to eight years to recoup costs.
Your specific payback point depends on factors like local utility rates, excavation/drilling costs, how well your house is insulated, the efficiency of the model you choose, and what incentives your state or utilities provide.
One of the best aspects about geothermal is cash flow. If you install a geothermal system, the monthly savings in operating costs generally offset the additional monthly financing cost, resulting in an immediate positive cash flow, especially in a new home.
WHAT ARE THE COMPONENTS OF A GEOTHERMAL SYSTEM?
The three main parts consist of the geothermal unit, the underground piping system (open or closed loop), and the ductwork. We install vertical closed loop systems. (see illustration below)
Vertical bore holes are drilled into the ground where a continuous loop of special high-density polyethylene pipe is installed in each. The holes are grouted from bottom to top to ensure consistent ground contact with the earth. The piping is then connected to the indoor heat pump to form a sealed, underground loop through which an environmentally friendly antifreeze-and-water solution is circulated.
Closed loop systems, when properly installed, can outlast the building. The pipe is inert to chemicals normally found in soil and has good heat conducting properties. Pipe sections are joined by thermal fusion which creates a joint that is stronger than the original pipe and protects the system from leakage and contamination.