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Switch to geothermal energy improves heating and cooling, and saves money

Our heat pump essentially works like a super-efficient version of those common in many homes, extracting heat from one environment and moving it to another. But instead of having to work with 20-degree air in January or 90-degree air in July, our heat pump gets to draw on the 55 degrees in the water-antifreeze mixture. The pump then uses electricity to bring air the rest of the way to a comfortable temperature, and blows it through the house using our existing ducts.

How the house felt

I'd give our new system's performance an A. Both heating and cooling have proved to be more comfortable and consistent with geothermal. With our old heating system, we had wild temperature swings, and pockets of colder air were common throughout the house in winter. Not so with our new system, which stayed evenly in the range where we're comfortable (66 or 67 degrees). Air conditioning was similarly improved, keeping the thermostat between 72 and 75 degrees.

Furthermore, our indoor air was less humid in summer and less dry in winter than it had been with a traditional system.

Our HVAC experts had told us this would be true, and they offer interesting explanations, involving such factors as the size of the evaporator coil, the volume of air being moved, the super-high efficiency of our heat pump. They're too complicated to include here. But one point that is easy to understand is why our house is now less dry during the winter heating season: There is no combustion involved, since we're not burning oil anymore.

Savings: The bottom line

My grade for savings: B.

The big savings we counted on was eliminating our oil bill, and that was solid. The previous year we'd spent $2,942 for the oil that heated our home and hot water. After geothermal: not a dime.

However, we paid (as anticipated) higher Pepco bills in the winter, because we needed extra electricity to power the heat pump. Some of that cost was offset with lower electric bills during the summer cooling season. In the end, our 12-month electricity outlay went from $3,358 under our old system to $3,890 with geothermal, an increase of $532. Subtracting that increase from the oil savings left us with net annual savings of $2,410.

But those seemed like pretty rough numbers. To get a professional analysis, I went to Sustainable Design Group of Gaithersburg, the company that had conducted an energy audit on our home as part of our original research. John Spears, the company's president, helped us separate our heating, cooling and hot water costs from the costs of running lamps, computers, appliances and anything else that connects to an outlet - the "plug load."

He also adjusted for temperature differences between the 12 months after geothermal and the 12 months before we did the install. Then we figured in the cost of installing and operating a propane-fueled tankless water heater - not part of the geothermal project per se, but something that my family decided to do at the same time.

In all, this more sophisticated calculation gave us a somewhat better result: $2,678 savings for our first year.

I wanted to figure our return on investment - that is, how long we can expect it to take us to recoup the money we'd spent. So I added in some other costs. For example, we paid $1,400 in landscaping to fix what the drillers tore up and nearly $2,000 in costs related to installing that hot water heater. On the other hand, I subtracted the almost $400 we had been spending on annual service contracts on our HVAC. (Service on geothermal units is minimal: replacing a filter once a year.)

Factoring in these variables (plus the extra plug load we incur because we're hosting a foreign exchange student) and assuming our savings continue at the same rate, our system will have completely paid for itself in 4.4 years - a little worse than I'd originally expected, but pretty good.

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