We continue on from where I last left off in part 1 of our geothermal home project. Before settling on a geothermal heating systerm, we wanted to do due diligence and looked at another type of system in addition to those mentioned in the last post.

We were intrigued by a new air-to-air heat pump, the Acadia system by Hallowell, that is sort of like geothermal but it sucks heat out of (chills) the air instead of the earth -- and this includes further chilling the already very low-temperature winter air!  Most folks who have heard of heat pumps are in the southern climates, where conventional units have been used for years. Such units generally don't work well in the frigid northern climates, below about 40 degrees F outside temperature. The Acadia is specially designed for cold climates, maintaining its efficiency well. I visited an acquaintance who had a system, and he gave me a convincing tour, complete with a season's worth of diminutive electric bills.

So we created our own spreadsheet, analyzing the payback on all of these alternatives (as I'm sure you remember from part 1, this included a wood or pellet stove, an oil- or propane-fired furnace, or electric baseboard heaters) in terms of money saved vs. our existing wood heating. We computed the net present value of the expected cash outflows over 20 years, building in figures for general inflation and energy inflation. Of course you start out with a negative return because you're laying out big bucks on the front end. We added the cost of air conditioning (using room-sized AC) in order to even the playing field with geothermal, which offers AC by its very nature.

We needed to assess the costs associated with the two alternatives - the air-to-air heat pump and the geothermal heating cost (or geothermal heat pump cost). To compare these alternatives, you need to compare apples to apples. (Green apples, of course.) How much gas, propane, oil, or electricity would we need to replace our wood heating? To get that, we needed figures on heat per unit (gallon, kilowatt-hour, cubic foot) of the various alternatives, compute total energy needed for the year, and then multiply total units of energy by the cost per unit to get the fuel cost of each alternative. Divide by your height in furlongs, multiply by your weight in drachmas, round off to the nearest whole number and then play that in your state lottery.

The official way to figure out how much energy you need is a calculation called "Manual J", created by ACCA (Air Conditioning Contractors of America; not to be confused with Abba) which evaluates your house in great detail. But if you have heating fuel bills for your house and family, that's a pretty good starting point. To figure our minimum annual heating energy consumption we used the heat potential of the 3.5 cords of firewood, multiplied by the estimated efficiency of our old wood stove -- about 60%. (Newer stoves are closer to 80%.)

In the end, the geothermal system was the winner. We hovered between the Acadia and the geothermal for a while because the Acadia did not require putting in wells or a field of pipes, and the capital cost was considerably lower as a result. It appears, however, that the Acadia does not qualify for the full 30% tax credit. (This is really an unfortunate oversight in the economic recovery tax rules that shows you just how unique the Hallowell design is.) Moreover, if we ever were to sell the house, "geothermal" is more widely recognized and accepted than "air-to-air heat pump", at least at this time and in this neck of the woods.

The type of geothermal system we're looking at is called "closed loop" because a fluid is circulated in a continuous loop of piping in the earth. This is why it is sometimes referred to as ground source heating. You can alternatively use "open loop" technology, where you pump water from the ground, suck its heat out, and return the water to the earth. This is not going to work well in states where water is so scarce that people shoot each other over water rights, but can work well in the east where we have absolutely buckets of water. More than buckets, even. The problem is water quality, and ours stinks. It's loaded with minerals that would gunk up the system faster than you can... oh, read the Encyclopedia Britannica in the original Greek, for instance.

To be continued...