The Myth of Geothermal Heating Efficiency?
Geothermal heat taps the Earth's heat "for free." An example of a passive system is a vertical tube driven below the frost line so the constant non-freezing temperature beneath most populated areas rises through the tube--simple to keep cattle's outside water trough from freezing. However, the typical home would use an active system:
- Boosting the ballpark 50-ish-degree* earth temperature to typical room temperature and hot-shower temperature requires heat pumps/compressors to add heat--so you still need some type of "furnace" *(Edit: I had already mentioned the hotspot variance but here's more detail: Geothermal temperatures vary from hotspot hot springs like Yosemite park to permafrost like Alaskan tundra--and the contiguous 48 U.S. states vary in broad bands of 37-77 degrees F from north to south; it is better if your area has "room temperature" geothermal heat but unfortunately the lowest heats generally are in the north where you need heat most).
- A typical home needs a vast underground radiator of tubes to "mine" the Earth's heat. This outdoor system is an additional up-front capital cost not needed by conventional heating systems (compare the vertical loop to well-digging and the horizontal loop to septic/sewer excavation to get some idea of cost).
- A typical home still needs some type of indoor HVAC system to circulate the geothermal heat.
I read somewhere that a syndicated home energy show designed an HVAC system with:
- a Marathon water heater
- a geothermal heat system
- a heat exchanger so that the geothermal heat pump's heat would provide supplementary heat to the hot water
Rough comparative indicators of heating system efficiency suggest that geothermal costs 50% less than conventional annual HVAC to operate but geothermal costs 50-100% more to install. If you don't pay an extra $10,000 for geothermal installation in new construction and instead put the cash in a 5% money market account, the interest will pay $500 per year (before taxes). The $20,000- $30,000 cost of geothermal-converting an existing home instead put into a 5% Money Market would pay $1,000-$1,500 of your conventional HVAC--and you'll still have the principal cash as an emergency fund (your doctor or car mechanic might not accept geothermal tubes as payment). If you lack cash, borrowing the higher installation cost makes geothermal even less of a bargain. The government might subsidize a geothermal home system but government subsidy could be yet another telltale sign of active geothermal's inherent inefficiency.
Even though commercial geothermal systems might reach their break-even point after a decade or two (when net operating savings finally exceed the initial premium in constant dollars), I fear that the good geothermal idea fell victim to conventional, expensive thinking but with superficial appeal to gear heads, penny pinchers, and tree huggers (the new Green "Glam").
This article's title is a question, not an answer, but those are my concerns. I would like to see comparative data with a passive geothermal tube design, and also an earth-sheltered design without external tubing (with only the Earth against the walls as the passive geothermal heating system). Given a walkout-basement-style earth-sheltered design, what is the most cost-efficient heating system (initial and operating costs including risk of broken equipment) to maintain 65 degrees for room temperature?