From the Depths: Can you harness the power of the earth to heat and cool your home?

story by samantha wittchenWith such high-profile institutions and individuals as the Philadelphia Zoo, Friends Center and even Phillies reliever Ryan Madson all going gaga for geothermal, it looks like there may be a trend in the making for the future of heating and cooling in Philadelphia. Geothermal systems, designed to exploit the fact that the Earth maintains a near-constant temperature throughout the year, offer high efficiencies and big energy savings, but with price tags to match.

Geothermal heat pump systems consist of three main components:
- a ground heat exchanger
- a heat pump unit
- ductwork to deliver the air throughout the house

The heat exchanger is a loop of pipes buried in the ground near the building. Inside that loop is a thermal fluid, such as glycol, that circulates through the system to transfer heat to and from the ground. In the winter, heat is transferred from the ground to the house; in the summer, vice versa. The system uses much less energy than a conventional heating and cooling system because the ground loop allows the circulating fluid to be naturally cooled to the Earth’s temperature of 50 to 60 degrees Fahrenheit in the summer, and naturally warmed the same way in the winter.

The good news: A geothermal system typically boasts energy savings in the 30-60 percent range, says the Department of Energy (DOE).

The bad news: A new geothermal system can costs tens of thousands of dollars to install.  
That seems like a lot compared with the cost of a regular heating and cooling system, but when you consider the potential energy savings and available tax incentives, the payback period is often in the five- to 10-year range, reports the DOE. After that, you’ll reap the savings for a long time before you’ll need to consider replacing system components; typical system life for the inside components is 25 years, and 50 years or more for the ground loop.

Consider the newly completed Hazel House in West Philadelphia ( “Eye for Design,” March 2011), which sports a geothermal system and is seeking LEED Platinum certification. Laura Raymond, an architect and one of the house’s developers and residents, expects the payback for the system to happen in five years. The total system cost about $30,000, including the cost for drilling the hole for the ground loop. She compares that with $15,000 for an equally sized conventional heat pump system, and after $10,000 in tax incentives and grants, the extra cost of the geothermal system was really only about $5,000. Not bad for decades worth of energy savings, right? And, according to the DOE, if you roll the cost of the system into your mortgage, your geothermal system is likely to have a positive cash flow from the very beginning.   

But what about a retrofit instead of building new? If you have ductwork in your house, the payback may still be worth it. Unfortunately, many Philadelphia rowhomes have radiators for heating and no cooling system, so installing the geothermal system will require opening up walls and ceilings to run ducts, which can add thousands of dollars to the overall cost.  

The other big question for both retrofits and new construction is how to run the ground loop. For houses with sufficient land, like those in the Philadelphia suburbs, a closed horizontal ground loop is ideal because deep drilling isn’t required.  The loop is run closer to the surface, and the required piping—typically 1,500 to 1,800 feet for a 2,000-square foot-home—can be laid horizontally in the ground, which keeps the costs down.  For houses on small plots, like those in the city, a closed vertical ground loop is better because the piping is run vertically deep into the ground, requiring less space; the Hazel House’s loop extends 350 feet down and cost $7,000 to drill.

As with any alternative energy system, the key is to first make your house as efficient as possible before you install that fancy new system. The bigger your alternative energy system needs to be to meet your heating and cooling needs, the higher the cost and longer the payback period. So, go ahead and consider that geothermal system, but let your mantra be: Conserve before you convert.  

Is geothermal right for you?

What kind of ground loop can you have?  A horizontal loop requires more room, but will generally be cheaper than a vertical loop, which requires drilling.  A horizontal loop will, however, require substantial excavation. Your property’s geology and local municipal codes are also factors.

Do you have existing ductwork?  Adding ductwork adds cost.

Can you roll the system cost into your mortgage? Ask your bank.

Are there federal, state or local incentives available for the project?  The Database of State Incentives for Renewable Energy (dsireusa.org) provides up-to-date information on state incentive programs. The federal government provides a 30 percent tax credit for geothermal systems in service before Dec. 31, 2016.

Samantha Wittchen is partner and co-founder of iSpring (ispringassociates.com), a sustainability consulting firm serving companies and organizations in the Delaware and Lehigh valleys.