Hoses are installed that will eventually be attached to the geothermal heating system for the renovation of Sheep Dog Hollow, a 1902 farmhouse in Connecticut.
(Joanne Ciccarello/Staff/The Christian Science Monitor)Photos (1 of 1)
Drawbacks of geothermal heating systems
By Alexandra Marks | 11.05.09
I’m sold on geothermal heating. Just check out my previous blog post. But being trained as a journalist, I can’t help but strive for at least some kind of balance. And so, I’ve felt it necessary to outline some of the various problems associated with geothermal residential heating.
First, let’s start with the very basics – the word geothermal itself. Several helpful readers have noted that there’s a bit of confusion about just what it means. So let’s get that cleared up.
Geothermal, as the word is traditionally used, refers to harnessing “energy from ‘hot spots’ in the earth’s crust, and can only be employed in locations where these exist,” according to the website Lighthouse.
On the other had, geoexchange, as Lighthouse notes, “uses the relatively constant temperature of the ground to simply moderate a building’s temperature.
For example, in the winter, the ground temperature is usually warmer than the air temperature, so heat is pumped from the ground to help heat the building. In the summer, the opposite is the case, and the building can be cooled.”
So, technically, we’ve been talking about a geoexchange system. (I’m still sold on it, even if it does have a different name.) But, like much in the English language in America, meanings evolve and specificity sometimes gets lost.
As it turns out, the “geothermal” is now commonly used as a catchall for both traditional geothermal systems and geoexchange systems, at least according to the International School of Well Drilling.
There are two types of geothermal energy, it explains in one of its training documents [pdf]:
1. High Grade – High-grade geothermal energy is the heat of the earth’s pressure which turns water into steam. Old Faithful at Yellowstone National Park is an excellent example.
2. Low Grade – Low-grade geothermal is the heat within the earth’s crust. This heat is actually stored solar energy.
We will use the terms “low-grade geothermal” or “geothermal” throughout this presentation because it’s the most commonly used.
So, forgive me for being common, but I’m going to continue to refer to the heating system that we’ve chosen as “geothermal,” even though the technically minded are welcome to quibble with me.
Now on to some of the more pedestrian problems with a geothermal heating system:
1. First and foremost, at least from my perspective, are the high upfront costs. The internal works – the heat pump, ducts, electrical, etc., cost about the same as a top of the line, highly efficient traditional oil or gas heating system. But on top of that, you have to add the cost of drilling the wells. In our case, we’re talking an additional $20,000. But, fortunately, there are tax breaks and longterm savings to offset those drilling costs.
2. The second big drawback is that every geothermal system needs a back-up heat system, according to our geo-man Tony Silverio, who says:
The second stage heating system has to be there for one simple reason. The heart and soul of your geothermal system is based on a compressor – like you have in a traditional air conditioning system.
If the compressor in an air conditioner goes out, no big deal; you don’t have air conditioning for a couple of days while you wait for the mechanic. In a geo-system if a compressor fails you need heat immediately – especially if it’s a real cold day. And if a compressor is going to fail, it’s going to be when the weather is the coldest and it’s working the hardest.
So what happens then, is the second stage heat kicks on automatically and you have heat until someone comes and fixes the compressor. That’s the whole logic of second stage.
Some geothermal systems, though, which are less expensive and less efficient, also need a back-up system that can kick in when it drops below 25 degrees F. to augment a system that may not be able to handle really frigid temperatures.
3. The final big drawback I’ve been able to gather concerns maintenance. Every seven to 10 years, the pipes in the system have to be “purged and flushed.” That costs about $1,500. Every year, air filters have to be changed as well. If you choose to hire a company to do it twice a year, add another $200 annually. But that does not deter me. Considering that I now pay about $230 a year for a service contract for my oil burner, and thousands every year for oil, I still think geothermal is a cost-effective – to say nothing of environmentally responsible – choice.
I’m sure that many of you know much more about this than I do, and if I’m missing some big problems that I and others should be aware of, please, comment away!
In the meantime, in my next post, I’ll be writing about the windows we have decided to use.
Editor’s note: Alexandra Marks will be blogging twice a week about her green and budget-friendly restoration of a 1902 farmhouse in Connecticut. See a photo gallery of the early days of the project by clicking here. You can read all she’s written about the project so far by clicking here and then looking for Sheep Dog Hollow under Topics on the right side of the page.
You’ll find numerous articles about the environment at the Monitor’s main environment page. Also, check out our Bright Green blog archive and our RSS feed.
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2. Ted K | 11.06.09
Ms Marks:
Geothermal is the latin for ‘ground heat’. ‘GeoExchange’(tm) is a trademark owned by the Geothermal Heat Pump Consortium, an industry lobbying group. The word is actually a trademark for the same technology.
I am not aware of the “international school of well drilling” materials you cite but scientists to my knowledge usually divide the heat in to three types, including a medium-enthalpy (heat), by degrees Centigrade. The definition you cite is further inaccurate in that the earth’s crust is actually between five and 25 miles deep (!), while the ‘trapped solar energy’ penetrates usually to a depth of about 100 yards, depending on density and saturation of the soils.
You are absolutely correct that the various usages are confusing, and in fact this conversation is confusing. One of the key barriers we have identified to the future growth of our industry in Canada is information - reliable, clear, and useful information.
At the Canadian national association for this technology, we have published six new training courses in the past four years, have run a series of advertisements on the Weather Network, issue a quarterly magazine with a technical and market-development focus, run a national quality program to help protect and inform consumers, are compiling this industry’s first-ever reliable industry-wide statistics, and will issue a Consumer’s Buyer’s Guide by the end of the year. Sadly, we have no US counterpart as of this writing.
Regards,
Ted Kantrowitz
Vice President
Canadian GeoExchange Coalition
3. B.Farrell | 11.06.09
I haven’t seen reference to the choice of ‘open’ and ‘closed loop systems in your explanations, design of a closed loop system I believe drastically reduces the need for the periodic system cleansing identified in the article.
4. Dave | 11.06.09
If you want to save a little money you can easily change the filter yourself. They sell them at Home Depot for about $30, e.g. http://www.homedepot.com/Building-Materials-Heating-Venting-Cooling-Air-Filters/Honeywell/h_d1/N-aq3nZ1xr5Zqr/R-100476729/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053
Of course the service guy may do other cleaning & inspections as well.
5. Dom Durbin | 11.07.09
Thanks for writing about geothermal heat pumps. I do not care what you call them as long as you write about them. They have been around for many years but have just taken off in the last 10 to 15 years, so they need all of the help they can get.
Two things about your article.
1. Everything should have a back up plan where practical. The best Geo designers design loop fields on systems so the back up does not come on unless there is an extreme event. Some larger systems or dominant heating loads can be coupled with other forms of back up, like natural gas or solar. That is the best practice even though it can mean drilling deeper or more boreholes.
2. Whoever says a system will need re flushed every seven to ten years has not installed a modern system. With polyethylene pipe, proper first flushing, self purging flow centers, anti freeze inhibitor packages, and reducing pipe size header design all being improved over the last twenty years, this is a solved problem.
It is just my humble opinion but the biggest downside to geothermal or ground source heat pumps is the fact that we really do not have any major add campaigns or public outreach efforts on a large enough scale to educate people what they are and how they work. This is why some people shy away and some regulators come up with crazy notions about codes regarding this “new” technology.
6. Simon | 11.07.09
I’m an environmental planner who’s been following building science, energy efficiency, solar design and related issues for 30 years. Based on the information I’ve seen and talking to a number of professionals in the field in this region (Hudson Valley in NY State), I am very skeptical about using geothermal systems in single family homes and other small buildings in most situations. Even if they are designed, sized and installed properly, the upfront cost is very high, as you have noted, so the payback period is fairly long. Many systems, moreover, are reportedly not being designed and/or installed well, at least in this region. One consultant I know has a lot of business fixing systems that aren’t working right. I’ve been told there’s a tendency to undersize the wells because of their high cost. It’s not uncommon for people to install geothermal and perhaps PV without investing in basic energy efficiency for the building envelope, which has a far better payback. Anyone considering geothermal should understand that you’re paying for a central air conditioning system as well as a heating system, so if you don’t want central AC it’s definitely not the right choice from an economic perspective. On balance, I recommend investing in an energy efficient envelope, efficient lighting and appliances, maximizing the use of passive solar energy, installing solar hot water systems, and then if you have the money installing PV. If a home is highly energy efficient and uses passive solar design, the backup heating system can be a pellet stove or efficient oil, gas or propane system. For new homes geothermal may be somewhat more cost effective but all these other measures should come first, in my opinion. In any case, if you decide to use geothermal it’s a good idea to have an engineer involved in the design. For larger buildings things are very different and geothermal systems start to make a lot more sense.
8. Robert S | 11.12.09
I was investigating “ground loop” heat pump systems recently. What I discovered is that here in Florida, heat is a waste stream. In the far north of my state, a geo-exchange heat pump would dump twice as much heat into the aquifer during cooling as is removed during the heating system. You can look at “degree days” or “equivalent full load days” data to see about your location.
The second thing I learned was just what a great insulator our earth is. Transient heat flow analysis shows just how slowly heat moves in the earth. When the water temperature in the aquifer rises, the unit efficiency and savings both fall. Of course, if you want, you can just withdraw the clean groundwater, use it to condition your house, and throw it away. But first, please read about the world-wide fresh water crisis.
Don’t misunderstand, I am an environmentalist and support conservation where ever possible. But if you think of the impact of thousands of these ground loop heat pumps, there are questions to be considered.
9. LindaS | 11.13.09
You were using oil heating in a farmhouse. Many of those systems were designed to work without electrical power. How often do you lose power? Have a generator which can drive your heating system?
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1. Ted K | 11.06.09
Great topic - and thank you for it! If readers are in the market for a new heating or cooling system, you may want to check out the Canadian GeoExchange Coalition, the national association for geoexchange (a.k.a. geothermal heat pumps, ground source heat pumps, or earth energy systems) in Canada. We do have several US members listed, and a full list of quality program members (about 330 firms nationwide) and about 1,500 accredited professionals. Each of these individuals has agreed to work to a common code of conduct, execute the system according to national standard C-448-02, and has been trained to relevant standards. There is no national standard, nor is there a national quality program in the United States, and we in Canada have no true partner south of the border. I would therefore recommend using only a trade professional fully licensed in another trade, such as plumbing, pipefitting, refrigeration, an engineer, etc.
Best of luck!
Ted