We’ve put in two geothermal systems in the past two years for clients in Minneapolis, both remodels, and with mixed results. For anyone considering geothermal, understand it is not an inexpensive up front option (say, $20,000 and up for an installed system sized for a 1,600 square foot well-insulated home). Geothermal installers often talk up the green aspects of the systems, but we feel the green advantages are not so clear. A few things are worth noting if you’re thinking geothermal.
Just in case you’re not familiar with how these systems work, I offer the following three-sentence, grossly simplified summary. Geothermal systems exchange heat with the ground via liquid – usually a glycol solution – flowing through sub-grade tubing loops (like a radiant floor but in the ground). The tubes are placed at least 5′ below the ground surface, in vertical wells or horizontal fields, where temperatures remain relatively constant at about 50-55 degrees. A heat pump, which operates much like the compression/expansion loop on your refrigerator (but can run both ways), extracts heat from the ground in heating months and dumps it when cooling. If you are looking for the science behind all of that, it’s available on the web; I’ll just say that geothermal systems have potential for obvious environmental benefits.
The downside? The heat pump – the brawn of the system – uses a fair amount of electricity. Remember the refrigerator comparison? The frig is usually the biggest electrical draw in a house, other than the air conditioner, which also runs on a similar loop. In MN, we generate the majority of our electricity from burning coal, so the environmental advantages are not so obvious. If you can run a geothermal system at your place with wind energy, your own wind turbine, or photovoltaic panels, and you have the funds to purchase all this green tech, I’d say go for it.
Some of the local installers for geothermal in the Twin Cities boast payback times of 7-10 years on a properly sized system, but this is only the case for “dual-fuel systems.” Translation – you have to have a gas furnace or boiler as backup, such that when the electric utility chooses to turn off your heat pump, you still have a way to heat your home. The utility’s ability to control your heat delivery method allows the utility to offer you discounted energy rates, often half of the normal kWh rate everyone else is paying. This may make financial sense, but it doesn’t necessarily make strict environmental sense.
The other thing to consider is use. If you’re building a large building housing racks upon racks of computer servers that will need cooling year-round, geothermal is not a good option. It works best in buildings that will heat part of the year and cool part of the year, such that the heat in and heat out is somewhat balanced.
The recommendation we make to our clients is to spend cheap money first. For heating and cooling, the cheapest money to spend is on insulation (consider up to R-50 walls and R-70 roof). If you still have money in the budget to spend on energy efficiency, think about geothermal and solar thermal systems (see an upcoming post on Solar Thermal systems). In many cases, we’d recommend solar thermal first, and then geothermal, but our recommendation would be heavily impacted by site and building orientation.
Twin Cities Geothermal Contact
Maple Plain, MN