I would like to respond to the replies to my comments [There are easier ways to improve energy efficiency, Viewpoints, Nov. 15] on the payback time for a geothermal system installed in Oak Park [Opting for geothermal HomeFront, Nov. 1; Geothermal options is worth the upfront investment, and Geothermal payback time is shorter than you think, Viewpoints, Dec. 6].

Both respondents correctly noted that the true cost of adding a geothermal system in Don Batterson’s case is the total cost ($55,000), minus the cost of a new conventional system ($25,000), leaving $30,000 in additional expenses. However, neither respondent took into account the savings provided by the improved efficiency of the house and neither provided realistic payback figures. I have consulted with John Porterfield at www.energydetectives.com to assist in a detailed reply.

By choosing a geothermal system, one is switching the energy source from natural gas to electricity. That electricity drives a motor-driven compressor in a heat pump. Geothermal is not four times more efficient than high efficiency natural gas heating. It takes more than three units of energy at a generating facility to get one unit of electricity to the site. The “source” efficiency of electric heating is about 30 percent of the labeled efficiency and at 4.2 COP, high-efficiency geo is about 33 percent more efficient than high efficiency gas at 95 AFUE.

Now how do the costs of heat from geothermal and gas systems compare? Using local costs per therm for natural gas of $0.85, the cost of electricity of 0.09/kWh, and the assistance of the Dept. of Energy’s Heat Calculator at www.eia.doe.gov/neic/experts/heatcalc.xls, one arrives at $6.13 per million BTUs for geo and $8.95 for gas (assuming 95 AFUE for gas and 4.3 COP for geo). If air-conditioning, the geothermal unit will also cost less to operate than a SEER 13 unit.

Let’s get back to Don Batterson’s case, where a recent decision by ComEd, “grandfathered in” those receiving the discounted Rate 14 for “all electric heating” at the end of 2006. The special rate is $0.03734/kW for use above 400 kWh/month during winter, which gives us $2.55 per million BTU for geo.

Mr. Batterson is saving 72 percent for geo versus a gas heating system. Making an educated guess that in his well-insulated 5,900-sq.ft. house, he might have spent $200 per month on average with a 95 AFUE gas furnace–saving $143/month average for 7 months with geothermal, and saving perhaps $250 in the summer–the total annual savings is $1,250. The $30,000 geothermal investment pays off in 24 years. The same investment in 2007–without discounted electricity–pays off in about 43 years.

When four bungalows on the 6400 block of South Fairfield were remodeled and rehabbed in 2001-2002 with various energy efficient building techniques and equipment utilized, it is noteworthy that the geo house had the longest payback as compared to the three gas equipment houses (“The Chicago Green Bungalow Project,” by Paul Knight, Home Energy July/Aug 2004, p. 24-30). The payback times for the actual combined building and equipment costs over the typical rehab energy costs were 12.2 yrs for the geo house and 5.4 yrs for the high-efficiency gas house.

Improved building tightness and insulation levels in new construction and in older homes are not “small, simple steps.” They require architects, engineers, and builders to work together for improved performance. While I applaud Don Batterson for his efforts to conserve energy, let’s be realistic about geothermal’s payback time, and let’s not forget the humble house.

California has seen a 40 percent energy savings since 1978, when it set tight energy conservation standards for commercial and residential construction. Why not follow that lead here in Illinois? (“Chicago can be greener” Jan 1, 2007 Crain’s Chicago Business, www.chicagobusiness.com.).

Join the discussion on social media!