The Case for Geothermal

My father Graham, I’m proud to say, has been a environmentalist his entire life. He started the recycling project in our hometown back in the 1970’s. He put solar panels on his roof to heat his water in the 1980’s, and now he’s put in a geothermal heating and cooling system in his backyard.

     I have to confess that I knew nothing about the geothermal option until my father did this: I thought it was some dodgy, speculative technology that wouldn’t really work. Then I went home last winter, and stayed in my parent’s house over a freezing weekend—and not only was the house warm but the difference in the quality of the air inside the marked. Oil heat works through combustion: it uses up oxygen. Geothermal systems heat the house with ambient air, which makes you feel like you are outside when you are inside. This summer, southern Ontario—where my parents live—has had the same heatwave as the rest of us in the Northeast, and now my parent’s house has been as wonderfully cool as it was warm in the winter.

    So what is geothermal heating? I’ve discovered that lots of people know as little about it as I did, and so I asked my father to write a short description of his geothermal system. Keep in mind that he is a mathematician by profession, which will explain the wonderful technical bits in the middle. Keep in mind, as well, that he is my father, so that any parallels between his beautifully lucid prose and my own are not coincidental. (If you like my father’s post, by the way, I encourage you to check out his latest book—“Inverse Problems in Vibration”—currently ranked 2,149,990th on Amazon.)

    Here goes:

    Geothermal heating and cooling is based on one simple fact: that 6 feet down in the ground the temperature is the same—between 50˚F and 60˚F- the whole year round. This means that it is relatively cool in the summer, and relatively warm in the winter. Geothermal heating is thus quite different from solar heating: solar heating works worst when you most need it--in the cold, cloudy, snowy conditions of winter; the source for geothermal heating and cooling is not affected by the weather.

     For geothermal cooling, all one needs to do is to circulate water in a pipe through the ground to cool it, and use this cool water to cool the air pumped through the house in the heating ducts.

     For heating, there is an extra wrinkle. Most of us prefer the temperature in the house in the winter to be nearer 70˚F then 60˚F, so we need to raise the temperature of the relatively warm air a little. For this we use the gas equation that you may remember from High School Physics: PV=RT. Here P is pressure, V is volume, T is absolute temperature, and R is a constant. If we keep the volume constant, we see that the Pressure is proportional to the Temperature. This means that if we want to raise the temperature of the air a little, then we should increase its pressure a little. To see how much, we must work in absolute temperature, which is 273˚+temperature in Celsius (centigrade) . Take an example: suppose the temperature of the water coming out of the ground were 50˚F; that is 10˚C or 273˚+10˚=283˚ absolute. We want to heat the air from 50˚F to say 68˚F. 68˚F is 20˚C or 273˚+20˚=293˚ absolute. Raising the temperature from 283˚ to 293˚, means that we raise it by (293-283)*100/283 percent, or 3.5 %. That small increase in pressure can easily be done by using a compressor.

      That is the theory. Now the technology. First we have to build a trench in which to place the pipes carrying the water (actually they add some glycol to it, to improve the performance). For our installation we had 3 trenches each 300ft long, 5ft wide and 5ft deep. Each trench had four 4inch pvc pipes in it; 3600 ft in all. Typically the trenches are 5ft deep, rather than 6ft, because all kinds of safety regulations come into play in building a 6ft trench. The 4inch pipes are fed from one large pipe coming from the basement, and they are funnelled back into a large pipe as they return to the basement. The whole system is filled with water and sealed. There is a pump in the basement that circulates the water through the pipes, and brings the warm water back into the basement. The water then goes into a heat exchanger. A heat exchanger does just that: it takes the heat out of the water and heats air that runs through pipes through the water. A heat exchanger is rather like two clasped hands, with the fingers of one hand interleaved with the fingers of the other. One set of fingers carries the warm water, the other carries the air to be heated.

      After being heated by the water, the air enters a compressor where it is warmed further, before feeding it into the air ducts. It is possible to have the pipes running deep down into the ground, rather than running horizontally 5ft down. If there is a lake or a deep river, then the pipes can run through the water, rather than through the ground.

     Now the money matters. We live in the country. In the winter of 2004/5 we spent about $2,500 on oil for our oil furnace. If we had kept the furnace, then we would have spent about $3,000 in the winter of 2005/6. The geothermal system has four parts: the pump to move the water around the circuit, the compressor, the heat exchanger, and the fan to blow the air through the house; those cost $18,000. The trench and pipes cost $2,000, and the necessary changes to the electrical system in the house cost another $2,000. We received a rebate of $600 on the items from the Ontario Government, and another $1,400 from a government conservation initiative.

     When the system is running at moderate strength it takes 1500 KWH, about the same as a single baseboard heater; when it is running at high, it uses 2200KWH, and when the fan alone is working, then it uses 500KWH. Our electrical bill has increased by about $150 per month for the winter months.

     We did not have air conditioning before; the air conditioning is set to come on when the temperature in the house reaches 75˚F, which is not often. The biggest difference in the winter months is in the quality of the air inside the house. There is now no combustion, so no loss of oxygen, as there is with an oil furnace. As far as conservation is concerned, we save about 8 tons of carbon dioxide per year!

     A few additional points. Obviously geothermal doesn’t work for everyone. My father has a luxury of a large backyard, so he could fit all that piping easily into shallow trenches. If you don’t have that much room, as he points out, you have to dig down—and that’s obviously more expensive. I’m not suggesting, in other words, that this is going to solve the energy crisis. But surely there are lots of lots of houses—as well as commercial buildings (like malls, with huge parking lots) that could easily install geothermal systems, and even a modest application of technologies like this could begin to make a real difference in our energy problems.

     I think it is also worth noting how absurdly low-tech the system is. It is pvc pipes and a compressor. My father lives in Ontario, where the winters can be vicious, and has thrown out his furnace! The other noteworthy fact is how (relatively) inexpensive the system is. For an investment of $25,000, my father saves, conservatively, $2000 a year (remember; he wasn’t running air conditioning in the summer before this, so the financial benefits of his system are substantially understated.

     One of the frustrating things about the current discussion over our dependence on imported oil is the persistent notion that real solutions will require some future technological breakthrough. I think we have a lot of the answers. We just haven’t made consumers and public officials aware of them.

Comments

[Michael J.]

I ran this post by a friend who is a well-known and well-respected expert in high-performance energy systems and his response was:

"Amazing how much mis-information can be packed into a short article!"

So I think you'd want to get an engineer involved if you head down this path. I agree with the closing point, re breakthroughs, but nothing is without hidden costs and trade-offs.

[Rob_]

It is great to have a post about this technology.

But the terminology may be a bit outdated.

People in the industry now tend to all this technology “Geo-exchange” or “Ground Source Heat Pumps” to avoid confusion with “Geothermal Power” which refers to technologies that extract power from underground heat sources (with temperatures above average ground temperature).

[mike]

why don't we hear more about this? Because the rot starts at the top in this country, for example a VP from the oil industry who terms conservation "a personal virtue" that obviously is not worth trying to persuade people to adopt (as opposed to stem-cell restrictions, which apparently are of critical importance to the survival of the republic)

[S Iyer]

Joel, could you go over what you
used to calculate interest?

Are you compounding the $2000/year
in savings assuming that I invested it in an S&P 500 index traking fund?

What is the depreciation rate of
the initial investment?

I'd argue that after the end of year 5, I probably have about $22,000 (lost $3k due to depreciation) + $10,000 (savings from the system) + the compounded annual interest assuming I invested the $2k savings per year in an S&P 500 index fund. That number is much better than -16.74%.

I'm no financial analyst, so I got no problem if you can point out to me where my assumptions are wrong.

[pat joseph]

The rot may start at the top, Mike, but here's a surprise: Guess who else uses ground source heating and cooling? Would you believe George W. Bush? It seems its part of the design at the Crawford ranch. I had nearly forgotten.

[Sylvia Warren]

Very informative. Thanks to you and your Dad for sharing and delineating the 3-P (profits--i.e., ROI, people and planet) benefits of a home geo-thermal system. The current state of this technology is another indicator that a serious lack of vision keeps the US "addicted" to oil.

[Devon]

I've been thinking about geothermal a lot lately. I'm looking into buying a house, and thinking about the work required to make the conversion. A question I've had, though, is what kind of impact, if any, will wide-spread use of geothermal have on the environment, and on its effectiveness? I'm wondering if anyone has done some modeling of ground temperature when different densities of houses are using geothermal, and considered what impact higher/lower temperatures might have. I just want to make sure that collectively we don't make the same mistake previous generations have made - blithely ignoring the consequences of their actions. Perhaps the research has been done, but I'm just not aware of it. Please let me know if it's out there.

[Joel Schopp]

It turns out I'm no finanical wizard either. I forgot to count that the savings from the system would also earn interest. I feel a lot like consumer reports double counting depreciation of the Prius. My bad.

So the geothermal system does beat the bond, here is the (revised) amount of time it takes for the geothermal system to win out at the various rates of return on investment.

5% - 21 years
7% - 31 years
10% - never

[happyjuggler0]

Some things to note before taking into account the various cost savings or returns on investment (or lack thereof).

The higher the price of oil relative to electric costs, the more it makes sense financially. The opposite holds true too.

It simply must be cheaper in a new home than retrofitting an old one, not even taking into account the sunk cost of the oil heater or air conditioning.

The more extreme the heat or cold where you live, assuming no start-up or other operational problems due to extreme temperatures, the more the savings. Along the same lines, if you face both hot summers and cold winters you ought to do better than someone who lives in a location that is more moderate year round, such as a southern area with a coastal breeze during the summer.

Finally, it is hard to quantify the air quality issues the author mentioned. How do you put a price on that? If it is "well known" that the air quality is better, your house's resale value may well outstrip the capital costs themselves in an expensive real estate market, and be worth little in the boonies.

In short, your mileage will vary.

[Dane]

In chinese rural areas,people have already been talking about,or even adopting this technology,only that they don't call this "geothermal" system or something technical like that,but rather "rudimentary or primitive" air-conditioning.And they barely know the principles and innerworking of this systme either when asked about it.i THOUGHT it was just a fake science experiment and hoax,but after raading your old man's lucid exposition of this technology,I begin to realize what a great thing those chinese peasants are doing.and for a country oil crisis has begun to loom very large,like China,this shouldn't just be conducted in rural areas and confined,a wide public awareness campaign is what I'M thinking.By the way,Malcolm,your suggestions for urban adaption of this technology,such as the mall parking lot exploitation stuff,are truly insightful and clever.
We need more things like this one,the world over.Any take?

[Mary_C]

Malcolm Gladwell, you remain one of my heroes.

http://www.zaadz.com/people/heroes/Malcolm+Gladwell

And, I'm going to have to add your dad to my list! :)

[Alexander Karelis]

Your writing is elegant in both style and content. Thank you for suggesting new ways for me to think.

[Graham Gladwell]

Yes, KWH in my description should be replaced by watts,
I am sure that my description is faulty in many other respects. Is there not an expert out there who can give an accurate description? Remember that I am just a mathematician. My wife once stated that I regularly talk authoritatively about things I know nothing about. That way I can fool most of the people all of the time. Remember too that I am Malcolm's Dad!

[Sarah]

You don't necessarily need a football field to do geothermal, but I suspect in the absence of space, you need a lot more money:

http://inhabitat.com/blog/2006/02/12/geothermal-manhattan-townhouse/

[JP Elverding - the Netherlands]

whatever the engineering integrity, it's the example and explanation that make it very worthwhile to read. A point proven by the reactions I'd say.

Will see what is done over here although, when I start digging, I'll get my feet wet at 2", that might make some difference.

Thanks!

[Kevin]

I wrote the finance guy at my high school and he wants to install this at my school. I was wondering who to contact that would install geothermal heating at my high school. We are a small private school in Northern California Please write me or boboxen@pacbell.net if you have information.

[stephanie]

I was thinking of putting an inground pool in an inground basement and it occurs to me that if you can put the water pipes thru a lake or river, you could probably put them in the bottom of a pool about 12 feet or more underground and cool your house and heat your pool water at the same time?

[Bruce]

I heat my house in Eden Prairie, Minnesota with a geoexchange heat pump. My system was designed to heat my house to 23 below before backup (electric resistance) heat is needed. I have done considerable analysis, and a smaller system, one that would heat my house to zero before backup heat was needed should have been installed, but the point is the system can be designed to handle the whole load, it is just more expensive. As for financials, I calculate the operating cost to be equivalent to using a 95% efficient furnace with natural gas at $4.60 per million btu and electricity at $0.054 per kwh. Our local utility has a 'WindSource' program where we can pay $0.02 per kwh extra to get electricity generated by wind(above and beyond what the state requires). I buy all of my electricity through this program, costing me an extra $150 per winter, but I have the satisfaction of knowing that I put nothing into the atmosphere to heat my house, and my heating dollars stay in the state. For a more detailed analyis, see the Minnesota Department of Commerce website, edocket 04-820.11. The reponses to my petition by our local utility and the Department of Commerce are absurd and misleading.

[Rick P]

"the persistent notion that real solutions will require some future technological breakthrough"

Not surprising when you take into account the money that is made on research that produces nothing.
For a energy researcher a solution means the end of their job. Just as a cure is a brings death to the cash flow of a medical research lab.

Also it real hard to corner the market with technology that is covered by an expired patent.

This is why scams like the Hydrogen Economy and Ethanol are the ones that get promoted.

[Greg]

For those figuring the payback for installing a ground-source heat-pump so far in this thread, I've only seen the payback figured in today's energy costs.

Here in the northeast U.S., since 2000 my heating fuel K-1, has risen by 60% while my electricity has only risen by about 15%. Past performance does not assure future performance but the evidence is mounting that we are reaching the limits on how much more oil and natural gas can be pumped out of the ground. Our ability to generate more electricity is only limited by free market return on investment and our own self-imposed regulations.

The math here tells me that in my lifetime, we will be living in a heat-pump dominated society for heating and cooling needs.

I do work for a heat-pump manufacturer and am familiar with some cutting edge companies in the same field.

Big strides are being made to improve air-source heat pumps for cold climates. There are machines on the market now that can extract heat below 0 F without relying on electric strip back-up heat which most of today's heat pumps commonly use. For more on these systems, follow this link:
http://www.nyletherm.com/spaceheating.htm
(I do not work for this company)

If you are intersted in how heat-pumps are used to efficiently creat hot water, follow this link:
http://www.aers.com/casestudies.html
(I do work for this company)

Heat pumps have also been succesfully used in clothes dryers and to extract drinking water out of humid air, but these uses are more "Popular Science-neat-things-you-can-do-with-heat-pumps" than commercially viable uses of the technology-- the kind of stuff that tickles my geek sensibilities.

[Jessica Stone]

Gladwell for president.

[portsmouthliz]

This is really cool. I wish my apartment building had this kind of system - in the sweltering heat and mugginess of Washington, DC I get so sick of having the a/c on all the time. It's gross to think of how little fresh air we get when it's really hot. What a difference it would make to people's health to avoid the wild swings between too much heat in winter and too much a/c in summer!

And excellent point about Bush's notion that some kind of technological breakthrough is needed - completely false. It just takes the will to apply what already exists.

[dave]

Thanks for this post. I'd never realized that geothermal heating could be implemented on a personal level like this before.

--

Doug,

The first point you made is dead on: "Iceland is a great example of the use of geothermal energy." Iceland is a paragon of the benefits of geothermal heating. The entire country, "the land of fire and ice," has converted 90% of its energy to hydroelectric power and 70% of its heating to geothermal. And this is really something, given the length and strength of Icelandic winters.

It is truly revolutionary in this near total transformation.

But I'll have to disagree with your second point: "They have none of the pollution difficulties that we have."

The economy is dependent on fossil fuels: fishing, automobiles, and planes (as a hub for constant flights between the USA and UK). As a result, Iceland produces more greenhouse emissions per capita than any other nation in the world - even considering their transition to hydroelectric energy and geothermal heating.

This reliance on fossil fuels is especially damaging to Iceland, which lacks natural oil resources of its own. The country must import oil to maintain its fishing industry (which accounts for a whopping 70% of exports).

Oil imports have damaged the economy. Because of the detrimental effects, Iceland has started efforts toward another transformation. The plan is to convert all fossil fuel use into hydrogen fuel cells within the next twenty years.

--

But thanks again, Malcolm, for this interesting post.

[David Neubert]

Thanks to Dad. I want to build one of these now. I always thought it was much more complicated.

[Brandon Keepers]

I live in Holland, MI, which uses a "hydronic snow
and icemelting system"--water pumped through tubes under the street and sidewalk--to melt snow in the winter. Best of all, it uses excess heat from the local power plant, so it uses very little energy, and probably saves the plant from pumping 90 degree water into the river. Right now, it only runs through a few blocks of the downdown, but I hope they expand it to cover more of the city.

This is the only link I could find about it: http://www.wirsbo.com/includes/get_docs.php?id=68