For the millions suffering through the recent heat waves blanketing the United States, geothermal heating and cooling systems may be of interest. Although such systems are by no means new, they have experienced tremendous growth recently. Last year alone, 50,000 new systems were built in the United States, increasing the total number of U.S. geothermal heating and cooling installations to 150,000.
The frequent and extreme heat waves and cold spells of the past decade have put utilities under greater pressure. Just last week, three regional transmission organizations (RTOs) set all-time highs for daily electricity demand. Unfortunately for electricity consumers, rising electricity demand also translates into rising electricity prices. So what does this have to do with geothermal energy? For home and building owners, geothermal systems offer an opportunity for cleaner and cheaper heating and cooling services.
What services can a geothermal heating and cooling system provide?
As the name might suggest, geothermal heating and cooling systems provide heating and cooling for buildings. Less obvious is that these same systems can also provide humidity control and water heating services. This means that installing a geothermal system lowers the demand on furnace, air-conditioning, and water heating units.
How does a geothermal heating and cooling system work?
The three components of a geothermal heating and cooling system are the heat pump, the ground heat exchanger, and the air delivery system. Geothermal heating and cooling systems rely on the simple fact that the ground is cooler than ambient air in summer months and warmer than ambient air in winter months. In general, the Earth remains between 50° and 60°F throughout the year just a short distance below the surface. Geothermal heat pumps work very much like regular heat pumps, with the major difference being that geothermal heat pumps use heat from the ground instead of the air.
When cooling is required, a cold liquid (known as a refrigerant) moves through an indoor coil. As it does so, it absorbs the heat from the warm and humid air passing over it. The surrounding air therefore becomes cooler and drier and is circulated through the room by a fan.
Next, the refrigerant passes into a compressor. The compressor pressurizes the refrigerant, turning it into a warm gas.
This newly-transformed vapor then moves to the condenser (a set of underground loops). Because the ground is much cooler than the warmed refrigerant, the refrigerant releases heat into the ground and once again becomes a cool liquid. Since the refrigerant is still highly pressurized, it must go through an expansion valve. Here the refrigerant is depressurized and the cycle begins again.
When heating is required, the roles of the indoor coil and underground loops are simply reversed. The indoor coil now acts as a condenser while the underground loops act as an evaporator.
Do the economics really make sense?
In short, yes.
Geothermal heating and cooling systems save money on maintenance and operating costs. Because the systems are more efficient than typical heating, ventilation, and air conditioning (HVAC) systems, buildings using geothermal heating and cooling systems normally experience 30-60 percent energy savings compared to an HVAC system.
Typically, installing a geothermal heating and cooling system costs $2,000-$4,000 more than installing a new HVAC system with ductwork, or around $7,000-$10,000 total. With 30-60 percent energy savings, all costs associated with building a geothermal heating and cooling system are recovered in 5-10 years. And because the systems last for 25 years on average (the underground coils often last more than 50 years), they are a valuable long-term investment.
Introducing a desuperheater to the system can increase savings even more. A desuperheater is a heat-recovering system that can be used to heat up to 60 percent of a home’s hot water. It works by capturing heat that is removed from a room through the geothermal heating and cooling system and by directing it to the home water supply. This waste heat can be used to heat all of a home’s water for free during the summer.
What are the environmental benefits?
For the average home, using a geothermal heating and cooling system instead of a typical HVAC system would save 14.7 metric tons of CO2 per year, or 367 metric tons of CO2 over a 25 year lifetime. This is the equivalent of driving 880,000 fewer miles in a typical passenger car.
What are the greatest obstacles to success?
High upfront costs and land availability.
As discussed above, capital costs for geothermal heating and cooling systems are greater than those for typical HVAC systems. Capital costs can also vary greatly depending on the loop type installed, soil or rock type, ground temperature, and even drilling contractor expenses.
Land availability can be an obstacle too. The cheapest geothermal heating and cooling systems use horizontal ground loops. In this system, loops ranging in size from 100 to 500 feet are laid horizontally 4 to 6 feet underground. As one can imagine, this requires a large yard or open space.
Buildings with less available land, therefore, often use vertical ground loops, which can add costs to installation. In this system, 6 inch diameter vertical holes are drilled about 100 to 300 feet down into the ground. These are the most common systems built in residential settings.
What incentives exist?
The federal government has incentives stipulated under the American Recovery and Reinvestment Tax Act of 2009 (ARRA) that cover 30 percent of residential installation costs. ARRA also provides a tax credit for 10 percent of commercial installation costs. These incentives run through December 31, 2016. Many states also have their own tax incentives for installing geothermal heating and cooling systems.
The growth of geothermal heating and cooling systems appears to be a sustainable trend. As consumers continue to learn about the tax incentives and long-term savings associated with geothermal heating and cooling systems, they will likely steal ever more market share from conventional HVAC systems.