Widespread Use Of Geothermal Energy?

cheese63 asks: "I was reading an article in the New York Times about the usage of geothermal energy for homes. Does anybody out there use this type of energy? If so, how viable is it in reality?"

How Does it work

[Marc Boucher]

ClimateMaster [climatemaster.com] has a nice article [climatemaster.com] on how it works.

Iceland

[scotpurl]

Remeber reading an article a while ago about Iceland, where they hope to have enough geothermal powered/heated greenhouses to be self-sufficient in about a decade or two.

The article mentioned how they generated power from steam, then piped the "waste heat" as if it were a public sewer, and instead heated homes with it.

Expensive and limited in location

[Matt_Bennett]

Registration-Free Link [nytimes.com]

As the article points out, they are pretty expensive to install and you need a *large* open space to put it in. Most of these schemes exploit the fact that the earth is a pretty good heat sink and stays at a remarkably constant temperature. To maintain this, you have to have a "low impedance" path to send your heat away- which is why you need lots of land. A traditional air conditioner uses a "higher impedance" path to get rid of the excess heat, by blowing it into the atmosphere.

In some areas (like central Texas, where I live) it would be especially expensive to put in one of these systems because about 6 inches below the topsoil is limestone, which you would have to grind through and many $/foot. I'm guessing that a geothermal field like this would have to be maintained clear, like a septic field, since the roots of the plants could wreak havoc with your heat exchanger, and finding the leak would be particularly hard if the field is spread out over an acre or so. Drilling straight down can be similarly expensive.

Some areas have natural hot springs that they exploit for heat and power generation, but there aren't too many places like that.

If you can afford it, and you live in the right location, it can be great. Looking at it from a purely economic standpoint, your money is probably better spent with more traditional measures, like good insulation, high efficiency A/C, thermal windows, etc. Geothermal systems are the path of the person with a lot of money that wants to make less of an impact on the environment. But if you do this, please don't take the money you save and buy an SUV.

Geothermal Heatpumps

[EABinGA]

This is probably not what you are looking for. But this is the most common use of geothermal energy.

Presenting the Geothermal Heat pump!

Heat pumps work by moving heat, rather than by converting chemical energy to heat like in a furnace. Every heat pump has three major subsystems or parts: a geothermal heat pump to move heat between the building and the fluid in the earth connection, an earth connection for transferring heat between its fluid and the earth, and a distribution subsystem for delivering heating or cooling to the building. Each system may also have a desuperheater to supplement the building's water heater, or a full-demand water heater to meet all of the building's hot water needs.

In heating mode, heat is extracted from the fluid in the earth connection by the geothermal heat pump and distributed to the home or building -- typically through a system of air ducts. Cooler air from the building is returned to the geothermal heat pump, where it cools the fluid flowing to the earth connection. The fluid is then re-warmed as it flows through the earth connection.

In cooling mode, the process is reversed. The relatively cool fluid from the earth connection absorbs heat from the building and transfers it to the ground.

Geothermal heat pumps basically work like their air-to-air counterparts, only they save even more power, due to fact that the ground temperature usually is constant all year round.

The energy efficiency of heat pumps can be compared by looking at the rated COP or Coefficient of Performance of the unit. COP is the ratio of energy output to energy input thus a higher COP rating indicates a more efficient unit.The COP of an electric furnace is 1, since each watt of electricity put into it produces the equivalent of 1 watt of heat energy out. The COP of a typical unit is 3 or greater. Each watt the heat pump uses to run it's transferring mechanism enables it to draw 2 or more from the earth thus giving a total of 3 or more units out for every 1 unit put in. The heat pump supplies more than 2/3 of your energy requirement from free energy stored in the earth and reduces your heating cost by at least 66%

One of the common features of heat pumps are their ability to provide "free" hot water during summer operation. Btu output actually increases during hot water making cycles and the recovery rate is similar to that of a 40 gal. electric hot water heater. Hot water is also provided during winter operation at a saving of 65-70% less than the cost of heating the water with an electric hot water heater. A typical homeowner can expect this feature alone to save him 20 to 30% of his present electric bill.

Consider the cost of money and politics

[human bean]

I live in an area where geothermal energy potential abounds, ranging from simply "it's twenty degrees warmer in that well than it should be" to "Liquid magma fifty meters beneath your tootsies". Regular energy sources (nat. gas, coal, oil, electricity) are hard to transport here, even though we have plenty. Many folks here want to live "off the grid", just because that is the kind of people they are (the warrants don't help any, either). With all of this, you would think that small or stand-alone geothermal would be making a serious dent in the energy needs of our population. Not so. Consider:

The cost of money. I can go out and up-front the money needed to install a heat pump to use low-grade underground heat (or whatever...) and it will cost me about twenty grand and maintenance costs over its lifespan, which will be about twenty years. Or, I can call the gas company, they will run the pipe to my property, install the meter, and they take care of all maintenance up to and including the pressure reducer. I have to buy the furnace and get it installed. About two grand up-front, and I get this bill for, say, a hundred dollars each month (it's cold here.) If I stick the difference between up-fronts in the bank (or don't have to wait until I earn it) then it starts to look real attractive to use the gas, and not the heat pump. Plus, I don't have to take care of the damn thing. I'm not interested. All I want is to turn up my thermostat and get more heat.

Politics also intrudes. In our state (Alaska) geothermal energy is highly regulated and is considered a scarce natural resource. As such, anyone using or tapping it must apply for a permit, and make royalty arrangements of up to fifty percent of value with the Department of Natural Resources. This applies even if it is on (under?) land you own. Also consider that most geothermal waters (the easiest source of energy to tap) are also highly mineralised, and under some circumstances considered toxic waste and must be dealt with as such. You certainly can't just dump them in the local watershed.

Even so, the local power companies have given it a go, and were balked by corrosion problems and lack of expertise.

Now, having said all that, I think I will get up and drive out to Chena and sit in the hot springs. Scootch around in the mud a little. Does you some good, you know?

The people across the street

[Elm Tree]

The people across the street from me have a pipe running several hundred feet into the ground, water is pumped through and it's supposed to come out at about the same temperature year round. There was a massive initial investment, but it's extremely cheap on a year to year basis. They've also got a small heater and air conditioner to allow for greater control of temperature.

Please use the can before leave

[Camel Pilot]

I knew a guy that installed a copper coil heat exchanger in his extra large septic tank which he connected to a water source heat pump. He also installed a temperature probe so that he could monitor the internal temperature so that during the heating season he would not drag temperature too low to stop the biological action. During the cooling months that tank really churned.

After visiting he would always encourage you to use the facilities and make your contribution to energy conservation.

It is amazing how inventive and resouceful folks can get given a small economic incentive and it is sad that all G.W. Bush can come up with to confront the upcoming energy crisis is to drill more oil wells which will contribute to global warming and reduced the available resources of our future citizens.

Re:Expensive and limited in location

[Dr. Dewpoint]

So called geothermal heat is of course the ground-source heat pump, and as such, you have the performance limitations of a heat pump.

Let's say you get a coefficient of performance of 3.5, electricity costs 9 cents/kwHr, gas costs $1.10 a therm (ouch, it was only 55 cents/therm last year). A kwHr supplies 3400 BTU times COP of 3.5 or about 12000 BTU. A therm is 10^5 BTU. Your heat pump therm costs 75 cents while your high-efficiency gas furnace therm (96 percent) costs $1.15. So I guess there is a considerable saving, but that is only because gas has doubled in price, and it is not clear that the electric won't get more expensive because a lot of the new electric generators are gas-fired.

What does the ground-source unit gain over a air source heat pump (essentially central AC switched over to heat pump mode)? You can get air-source units with COP of around 3.5, but that COP falls off as the outside temperature reaches freezing (32 F, 0 C), and much below that you are essentially using resistive heat with a COP of 1. What the ground source unit buys you for digging up your yard is the ability to operate tha heat pump when it is colder outside.

But wait. My house needs roughly 500 BTU's per degree F differential per hour. My high-efficiency gas furnace on the quiet, low-electricity using 600 CFM blower setting supplies about 50,000 BTU's/hr, giving me enough heat down to 30 below. Now 50,000 BTU's out of a heat pump needs a hurricane of about 2500 CFM's (a heating/cooling ton is 12000 BTU/hr and you need 400 CFM/ton for AC/heat pumps)-- if it takes a 70 W blower to push 600 CFM's through my ducts, it will require about a 5 kW motor to blow 2500 CFM's (power goes as the cube of air velocity), and I don't know if I can stand the racket.

So I think the ground-source heat pump probably has a narrow climate zone of applicability, where it gets cold enough to have an advantage over the air-source unit yet not too cold that you run into capacity limits on the air handler.

A few types...

[stienman]

First, the note from someone about geothermal use in alaska concerns mainly the use of it as an open loop. You suck water from an underground well, lake or other natural resource into your system, extract heat/insert heat, and then dump it back into the ground (drain, well, lake, etc). Many geothermal systems (If not most) are closed loop, and do not touch underground aquafers (rivers, wells, lakes, etc) and so are considered much less of a danger to the environment, and therefore suffer fewer regulations.

I've not dealt directly in geothermal energy, but I've studied it through the years. It has a low user base, and is very expensive initially (it almost always pays for itself in under 1/2 of it's lifetime). It falls under a lot more regulation than gas/electric systems for several reasons, but mainly that it involves tearing up land, burying pipes (which may or may not leak), and is still considered expirimental by the general public (ie, go to a town meeting and few people will understand that it is a good, safe, well tested method). It should also be kept in mind that the gas and electric companies encourage this extra regulation, and the misconceptions about price/performance/maintenance/etc.

-Adam

Trepanning? I need that like I need a hole in my --- Hey...wait a minute!
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