Geothermal vs. traditional HVAC

I had always thought we'd install geothermal heating and cooling. It is considered a green technology for its improved energy profile, but I also thought it would just be a cool thing to do.


For those not familiar with it, a geothermal system drills deep holes in the ground into which piping is installed. The depth and amount of piping is sized by the house you intend to heat or cool. A fluid fills the pipes and circulates through the system to heat or cool the interior air as necessary. Ground temperatures are stable, so you start at a warmer or cooler point than a conventional system. You use less energy to achieve a given temperature. I'm told the fans are the largest consumer of power in a geothermal system. Further, geothermal systems typically maintain ambient temperatures within 1-2 degrees. A conventional system sees a 4-5 degree fluctuation before it kicks into gear, so they'll run for a longer period of time. Geothermal systems can produce a good and reasonably speedy payback, depending upon the specific home and where it's located. It's also cool if you want to move closer to being off the grid by using alternative energy like photovoltaics or wind. You just don't need as much electricity.


I was all primed to be sold on geothermal. I was probably the easiest prospect a geothermal guy could have found. Then, I was educated on the inherent energy efficiency of this home. Riverbend said that while we could certainly do geothermal, the payback would be incredibly long, in the 10-15 year range. If true, who knows what technologies will be available then? This and other conversations created a lot of uncertaintly about what an HVAC system should look like for this house. We decided to hire an energy auditor. Our banker Bob Link, stepped up again and named a resource that had the necessary experience. We needed to do this anyway in order to get Energy Star certification, but a part of the service a guy like that provides is to size the HVAC. In our initial bids, HVAC contractors looked at the plans and sized things according to a conventional home. The bids called out the need for 8 tons of total heating/cooling split between two units, one 5 and one 3. The audit called out the need for one 5 ton unit. The auditor said we only needed 4.5 tons, but they don't sell a 4.5 ton unit, so that's how we arrived at a 5 ton solution. A 40-50% reduction in requirements has to be a good thing.


We could no longer justify the expense of geothermal, which is an additional $9-$10K per unit. The one technology I was sure we'd have, is one we sure won't have. So much for preconceived ideas.