In Do You Dig Ground Source Heat Pumps? (Nov/Dec '96, p. 33), Jeff Stein concluded that some ground source heat pumps did not meet efficiency targets. However, his conclusions were based on comparisons to noncentrally heated electric-resistance homes in the extreme North, many (maybe all) with supplementary wood heat.

Similarly, in responding to John Livermore's letter (Give Heat Pumps Their Day in the Sun, Mar/Apr '97, p. 3), you asserted that the EPA's report Space Conditioning: The Next Frontier is based on simulations when heat pumps perform to specifications and ducts don't leak. As the primary author of that report, I know that the analysis assumed a duct leakage rate for all types of energy systems. We wanted to isolate the comparative performance of various electric, gas, and oil technologies by holding all other variables constant. You make it sound like we pumped up the results for geothermal by assuming a different value for the duct systems. Actually, we deliberately disregarded the fact that, on the air-source side, there is an expected degradation of performance due to mischarging and/or leaky charges (this is not a problem with geothermal heat pumps, since the charge is hermetically sealed in the factory). We also disregarded the additional annual maintenance charges associated with gas-fired heat pumps, since we were not aware of the servicing requirement at time of publication.

We don't claim that geothermal systems always perform as advertised. Nevertheless, PV and passive solar advocates prefer geothermal systems because of their low demand and friendly load shapes. You have jumped to a negative conclusion about ground source heat pump technology, showing a very strong negative bias.

Mike L'Ecuyer
Washington, D.C.

Editor's reply :

Mr. L'Ecuyer is correct in describing the problems of comparing heating systems. However, Jeff Stein did in fact adjust energy use to reflect differences in insulation levels. It's more difficult to adjust for differences in inside temperatures, but Stein was able to confirm that the control houses were warm because the inside temperatures were monitored and the occupants were surveyed. The biggest factor affecting energy use is burning wood in wood stoves. Fortunately, most of the control houses did not have wood stoves or fireplaces, and the few that did were paid not to use them during the monitoring period.

I have a friend with a superinsulated house, and he's had serious problems with carpenter ants nesting in the foam board.

Stressed-skin panel manufacturers often add borates to the foam to reduce this problem, but I haven't heard of such a thing for regular foam board insulation.

I live in a heavily wooded area, and I've already had termites and carpenter ants do serious damage to the house. I don't want to make my house even more inviting.

Carl Windnagle
Hudson, MA

Siding retrofitter Paul Fisette, author of Roofing and Siding Rehabs Get an Energy Fix (Nov/Dec '96, p. 25) responds: I don't think that there is an epidemic of ant infestation in foam. However, it is a concern of mine. I have seen several cases where carpenter ants have infested rigid foam insulation. I've seen bags full of material that I thought was cellulose. After closer inspection, I found that it was expanded polystyrene, destroyed by nesting ants.

Ants nest in soft media and leave the nest to forage for food. They nest in wet wood because it's soft and easy to chew; foam is vulnerable for the same reason. If you do not have foam, you most likely have another appealing nesting medium. For example, you may get ant infestation in cellulose or fiberglass. The insulation can be drastically compromised. Since the insulation is out of sight and out of mind, the heat loss may never be visually detected.

Manufacturers of stressed skin panels do add borates to their mix to discourage nesting, but I have not seen evidence that they've been successful. And borates can leach out if your siding leaks. I am also not sure that foam board with borates is readily available.

Given all the odds, I would still use foam in a residing project. What are the alternatives? If you need to upgrade your insulation, foam is often the best choice.

Warren C. Liebold, Director of Conservation/Technical Services
NYC Department of Environmental Protection
New York, NY
 

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