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.)
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.