I'm no expert on this, but: I think it can be said that the available geothermal heat used to heat buildings (with heat pumps) is of a low grade compared with that which is exploited, in various countries, as an electrical-energy generating method.

But you are correct that the high-level heat available in certain specific places can be utilized to power turbines.

Joel

Here is a link that might be useful: Wiki Geothermal Energy entry

Joel is right. Geothermal energy refers to system like they use in Iceland, which tap into hot water and steam in a volcanic region. Heat pumps use and do not produce energy.

Ziggy

Yes, I agree, after having done a bit more research on ground-source heat-pumps. In fact, it seems they are a bit of a scam, capitalizing on the relatively cheap price (for now) of electricity, and the complexity of the energy equation involved. It turns out that about two-thirds of the potential energy in the fuel used in electrical generating plants is lost in generation and transmission. So an increase of 3.5 times in the energy value of the electricity used to run a heat-pump system is scarcely better than breaking even.

I have an acquaintance who spent about $20,000 putting in a ground-source heat-pump for a sizable rural house he bought. The payback period for his investment may be 15-20 years. But, depending on how you look at things, he's now reaping advantage due to the cheap cost of hydro-electricity in our region. The advantage is that he does not have to cut or buy all the firewood that many people in our region use to heat their home (an alternative, popular about 15 years ago and more, was the oil-fired central heating system).

I don't know the details, but it may be that a savings in the investment in such a system could have been made if it had been installed when the home and homesite were originally built. Retrofits can be a little complicated and expensive.

Joel

You two seem to be comparing energy efficiency and economic efficiency. A heat pump is more efficient than most conventional heating and cooling set ups under most conditions, but it will always use energy and not produce it.
Three physical laws are at work in a heat pump.
1. When a gas is compressed, it gets hotter.
2. When a gas expands (is uncompressed) it gets cooler.
3. Temperature always moves from hotter to cooler.

When it is cold, a refrigerant is compressed to a higher pressure and gets hotter, it is routed into your house. There it gives heat to the house and in return is cooled and condenses into a liquid. This presurized liquid is then sprayed into a low pressure coil, underground, where the expanded refrigerant, which is now cold absorbs heat from the ground and evaporates into a gas again.
In summer, the cold expanded gas is routed into the house to absorb heat and the hot high pressure side is underground.
Nothing is burned and the ground is fairly stable in temperature. Unlike an air conditioner using outside air to cool the high pressure side of the refrigerant, a heat pump uses the cooler ground, and is more efficient. In the winter, a heat pump is like a window AC unit put in backwards, but due to the soil being much warmer than the air in winter, this works to heat the house. The pump or compressor will always use electricity though. I hope the explanation helps. It is hard to simplify without writing a small book.

Ziggy

Hi, Ziggy. In my second post on the thread, I was only addressing the investment/payback aspect. Your points are good ones.

Yeah - by now, a lot of people understand the environmental advantages of alternate enrgy sources. What holds many people back from developing small-scale alternative energy-source installations in their homes, farms, private offices is the up-front cost of installation. So I think it's realistic to bring it into the conversation.

Joel

Yes, I understand a heat-pump is not a net producer of energy (if it was, our energy crisis would be solved).The way the proponents of heat-pumps present the data makes it seem like it, though. I think it's intentionally misleading.

What I'm getting at is, what is the embedded energy cost of a heat-pump intallation? And does it pay back in terms of energy, not just dollars? Fossil-fuel energy, as we know, is absurdly under-priced, and consequently so is electricity.

It's a question we have to ask of all the alternative technologies: are they a net gain, when the whole energy cost is taken into account? Ethanol is not a gain, with current practice. Hydrogen fuel cells do not seem to be a gain, with current technology. Recently I bought an expensive, well-made solar-powered outdoor light. I wonder: if the total amount of fossil-fuel used in it's manufacture were instead burned in a gas-fired lantern, for instance, would it be less light or more than that which the solar light will emit in it's total lifetime? Will the hybrid cars pay back the embedded energy cost of the huge battery packs and other expensive elements? They work out ok for the consumer in terms of dollars, but I'm guessing that toyota et al are eating some of the increased energy cost.

IOW, in the post fossil-fuel world, will we possibly be able to afford and sustain these kinds of high-tech gadgets? When all of industry has to operate on alternative energies? It seems very unlikely to me at this point.

The 350% number you are getting is based on the moving the heat using the heat pump versus directly generating the heat from the electricity in an electric radiator.

So if you plug in a resistive heating element and run X electricity through it you get a certain amount Y of heating.

Take that same X electricity and run it through a properly installed ground heat pump system and you get 3.5 times Y amount of heating. This is because you are using electricity to move heat from the ground into your home, instead of directly creating the heat from the electricity.

As for actually realizing a net gain, depending on how you define your boundaries it is relatively impossible. Since we generally consider the sun as free energy there is hope.

Kyle

Thanks, Kyle. Good explanation. I had essentially figured that out after I first started this thread.

And to further your xy explicate: to get that X electricity to your house from a power plant will on average require 3X amount of energy in the form of the fuel that the plant uses. In the case of hydro or nuclear fueled plants being the supplier to a given home, then perhaps the significant cost of a heat-pump system installation is justified; in the case of natural gas or coal fired plants I'm not sure.