Why are all the geothermal pumps electrical?

"Am I missing something in my suppositions"

Yes! You can't get more energy out of a system than you put in to it.

" My heat pump is about 300% efficient." is just a joke.

Sorry, over unity is still not possible.

Google: over unity

I realize that I am not running a perpetual motion machine in my basement.

However, what the ground-souce heat pump does, is to pump heat from the dirt about 8 feet under the surface. This amounts to a solar thermal energy collector.

Rather than calling it efficiency, I believe the correct term is Coefficient of Performance. In any case, the system puts out an average (depending on seasonal ground temperatures) of 3 times the heat that would be put out of a purely resistive system drawing as many watts.

My question was (and is) : Could a gas-powered engine run the heatpump more efficiently considering the inherent inefficiencies in coal-fired electrical generation?

An earth-coupled heat pump run off wind or solar is your best bet unless you can develop a hydrogen burning combustion engine or hydrogen fuel cell.

A 7 ton gshp would be 25.5 kW - good sized solar or wind system! The starting current is also rather high for alternative energy type supply. Considering the COP of the heat pump, return on investment for additions to it will be very small. The geothermal site supplied in one reply has nothing to do with the ground source heat pump. That is a different topic. The point about saturating the ground with heat/cold is an open point to the best of my knowledge. It has been talked about but I believe is only a negative in the event a city is using such a system.

1: There has never been a case of ground saturation in a properly designed and installed system.

2: I am all for alternate energy that works. The area where I live, the electrical authority installed a demonstration wind turbine. Due to the wind patterns, either there is too little wind or too much wind for it to operate. This is about 95% of the time. I call it a massive waste as it will take close to 20 years just to recover the capital costs, and rarely produces any electricity.

3: As for solar; great idea, but as I have not seen the sun the last four days, again due too the weather is not viable either.

4: Depending on where you live and the climate, geothermal may be the best option.

Please note that I live close to the southest parts of Canada. I call it the banana belt.

Off topic: There are there things that Canadians will complain about in the following order:

1: the weather

2: their hockey team and, or lack of one, or the one that they do have is pathetic.

3: the government

So, do you want to compare the total energy required to run the heat pump for an hour, let's say on an ICE as compared to electricity?

Then start with exploration, discovery, drilling, pumping, transportation, refining, transportation, storage and finally pumping and transportation of gasoline to run the heat pump compared to the, "inherent inefficiencies in coal-fired electrical generation?" Which one is more efficient?

I don't know.

Or you could just go by what each costs per unit of energy measured. The fuels BTU's per dollar Vs the energy that electricity would have per purchased KWh's per dollar.

When saving money cost per unit of energy is what counts not how many steps it takes to get to that relative cost number.

You make the same error which was done a couple of month ago. The efficiency of a heat pump is measured as the ratio between the power "transferred" (not generated) and the power used for the transfer.

If you look at the cycle you see why the ratio can be >1 without dis-considering the thermodynamic principles.

Do not forget that the latent heat is also used for transfer.

Touch'e.

GA Fred!

About the only way I can see to improve the heat-pump system is to add some solar arrays and maybe a wind charger. It's not impossible to make such a system completely independent of the grid.

Good but as you imply a very different point. Self sufficiency is a valid, laudable goal that greater efficiency can help. But many self sufficient systems will be less efficient than being on the grid.

Northern Minnesota.... well I wouldn't expect too much solar help in the wintertime. How expensive is the methane, is it piped to your house?

I'm hoping to move to West Virginia, where natural gas comes out of the ground, on your property if you are lucky. If I can, I want to put in auxiliary power, methane fueled. I prefer the generator in a separate building, for safety and noise reasons.

Like posted, caring for a powerplant is a full time responsibility. You are responsible to keep the starting battery up and happy. In the basement is asking for carbon monoxide poisoning! Transfer switches are expensive and need to be put in by a qualified electrician.

As a backup or weekend use project, it may be helpful, especially if power goes out in your area.

I would size and wire the generator to power the heat pump and some emergency circuits for the house. That would justify the cost.....Northern Minnesota?...cold!!

Thanks for the enlightening discussion. I can see that my idea, though efficient, is fraught with complications; maintenance, noise, dealing with toxic exhaust etc. No doubt it would be more expensive than a heat pump driven by an electric motor too.

Jeff

Hi, " NotanEngineer"

Do not be disheartened too soon. Technology is available, though currently quite expensive, which does go some way to hitting your goal.

I too have considered a cheaper and more "green" way of powering the heat pump which I would need to heat my house here in Devon England. I have a plentiful supply of low grade heat in a very wet field, so the source is there.

Have a look at www.energ.co.uk where thay have good technical details of production CHP units which are ready today. They burn natural gas in a cogeneration engine which provides, say, 10kw of electrical power and 17kw of heat recovery at an overall efficiency (on site) of 84%.

If you then use that 10kw to power your heat pump, then you have provided a heating system for your home which does not (locally) have any carbon footprint.

I just wish that I could afford to install it!

If you're HOPING to move to West Virginia, my friend, I would be afraid to ask where you live now...

I understand this is coming from someone who does not know the subject, but it I have wondered about thermopiles being useful where heat is already available.

Could a thermopile be made in this man's area and drilled deep enough to provide sufficient valuable energy to be used to run his motor? It seems to this green-horn that, although it requires a higher temperature that a heat pump to run efficiently (power output/unit cost), it would require a smaller footprint (hole diameter) than the heat pump's heat source, and would be both safe and reliable, since we are referring to (I think) a simple fixture of bimetallic metals converting electricity, which could be protected fairly well from corrosion, and last for a long time. This way the heat pump could be used to convert the relatively lower geothermal temperature differentials to electricity more efficiently, because it's source, at only 8 feet from the surface, is less expensive to gain access to.

I am imagining a thermopile built 2"-3" in diameter and (many) feet long may be sufficient to run the motor. I also admit I suspect that to get the thermopile to a depth where it is hot enough to provide efficient and sufficient energy may be cost prohibitive. How deep would it have to be set to get at say, 400-700C? (maybe that would burn up the drills?) (And the protection/cost of the wiring to bring the power to the surface?) Maybe I have talked myself out of this idea already! What do you think?

I'm sure this is not a new idea, but could you help me get the practicality of this in perspective?

Though I'm no expert, I have a feeling that it would cost tens of thousands of dollars for just a few hundred watts tops. In most places it would take thousands of feet to get a warmer location underground... unless of course you live near a geothermal location :) I always thought that thermopiles were also made of fairly expensive metals... ie copper, nickel, chromium etc. Plus with the length so long the temperature difference between the individual thermopile stack would probably be very small and have very little potential.

In addition to many good points made about why this would not be a good idea, the additional consideration regarding geothermal is that in most cases they need to be run in cooling mode to "recharge" the ground source with heat during the summer months. There are installations which have become ineffective when ground coupled systems are used for heating only, as over time the heat in the ground will become depleted, as the heat pulled out of the ground is taken at a greater rate than it is recharged, hence reducing the efficacy of the heat-pump. So, in cooling mode, what are you going to do with the waste heat from the methane fueled heat pump... pump it into the ground?

As for running it on wind, solar or another renewable resource this becomes problematic due to the known issues of unreliablity (the sun is not shining or the wind not blowing) so then you need back-up electricity. If you plan on going the renewable route you might as well keep it electric and do a grid-tied solar/wind electrical set-up.

Generally speaking "geothermal" is a mis-nomer (although widely used and accepted), as it really should be applied to installations where the heat captured is at much higher temperatures than 50 to 55F. The term Geo-exchange is the proper term in these lower temperature applications.

Hi notanengineer,

As I understand it you have a heat pump which effectively gives you 'free' power?

Any heat or power or whatever you want to call it cannot be more than 100% efficient, and is more likely to be nearer 20% or 30% than 100%? And most certainly will not be 300% more efficient. ............

However, it could 'generate' 300% more than you could expect to get from the grid, given a certain size of supply, or than the amount of power you can use. But as you say the initial outlay is high, but running costs are very low. Why change it?

Geothermal pumps turn the heat they have to electricity because you do not have a directly 'heat powered' kettle, drill, Toaster, etc.

Electricity is the medium used to transfer the power because pretty much everything is run by a motor or heat exchanger of some kind. Apart from directly heating water through a remote coil, how else would you expect to use any of the heat absorbed by your '7 ton heat engine'?

Apart from the power to perhaps pump the heat if you are heating water all outlets have to be electrical. It cannot be gas. But you do have something that others may die for! It is not about to fail each time you draw power is it, where the grid could and does fail for various reasons.?

Sounds like a pretty good deal to me. Why change it if it 'aint broke', you know?

Can I make a kind suggestion?.

Think a little more about how you phrase a post as at first glance yours does not make sense. It is only after a little thought that we, (If I can talk for others?) can wheedle out of you what you mean?........... No insult intended, OK?

I also use a geothermal heat pump at home and love it. I use it for heating in winter and cooling in the summer. I also dump the summer's heat into my swimming pool to keep it nice for a longer period of time (I live in Montreal, Canada, most people have pool heaters).

When I added the supplementary water coils to heat the pool, I placed one on the hot side and another one on the cold side. Why? I would like to run a heat to electricity conversion system some day. (The cold coil is not used for the moment)

All I need is an electricity conversion system better than 40% conversion efficiency operating with 50C and 10C hot and cold source. If I could ever find a thermopile or a heat engine/generator that met this, I could use the ~300% transfer capacity of the heat pump to produce the electricity that it consumes. This would make it self sufficient (or almost depending on how much thermal energy I use for my house). I would still need electricity to start though and when the earth temperature becomes lower at the end of the heating season.

Anybody knows a +40% efficient (30% + some coupling losses) thermal to electricity conversion system?

Another idea, (I am giving it to the world!) is to make a thermally run compressor that would compress the heat pump freon running in parallel with the "starter electrical compressor". After the start period, the electrical compressor would shut down or be slowed down. The heat pump would then operate from the thermal heat gain from the ground.

Of course, this would mean that a much larger ground loop would be needed as the energy to run the system has to come from somewhere. For the moment, the cost of this system would exceed the savings but some day...

Sterling engines have some fair efficiency numbers relating to conversion of heat into mechanical power.

I have in fact pondered on this many times given the realistic efficiency limits of heat pumps and sterling engines do have a theoretical sweet spot where the numbers add up to produce an unlikely and someowhat limited working range but still possible localized heat to mechanical power converter system. Although the device itself would be large and its mechanical output small its theoretically provable I believe!

Hello Mr. Jeff

You are absolutely right. But consider, if the methane would be free, your expenses will be only for the maintenance of the IC Engine plus capital expenses of the investment, compare to the EE bill. Now consider add the methane price and the sum again be lower of that of the electricity bill, your decision will be right. If the expenses are greather than the EE bill, choose the electric motor.

Brockmeyer

Hi notanengineer, you have a point. But instead of an ICE you should (could?) wait a couple of years for the HT-PEM ( http://www.geifuelcells.com/innovation/ht-pem ) to be developed. It converts (burns?) methane or natural gas to hydrogen to electric power using oxygen, and biproducts are heat and water. The heat can be used for heating water and the electricity can run your heatpump. Then your efficiency is high. The fuelcell only uses gas when electric power is used, its a linear function.

May I point out, that efficiency is mesured in percentage, and I feel you are somewhat mixing the terms.

COP is Coefficient Of Performance which compares consumption in watts with output in watts for a heatpump, say when you use 1kW electric power you get 3kW heat, its like comparing apples to bananas, its fruits, but not similar, but nonetheless thats how its done.

The efficiency overall for the system cannot exceed 100%, but the overall COP-factor can be 1 or more. To find the precise COP-factor overall for the system, you need to know the energy-density in the media you want to convert (methane, gas, hydrogen) in watts and compare it to the total output (heat, electric power) in watts, divide the two figures and you have your COP-factor for the system.

The fuelcell has an electric efficiency of 40-60 %, but when wasteheat is recovered, total efficiency is higher. The coalfired powerplant in my neighborhood has a total efficiency of 88%, because wasteheat water is used for heating my house among several thousand others. But there are heat wasted when the hot water is pumped several kilometers in underground pipes, so to use the fuelcell wasteheat on location is more efficient.

The total efficiency of different methods of conversion is a very relevant question to ask when one has to decide what kind of energy supply we should focus/rely on in the future.

Till then,

regards, moe

Hi notanengineer,

Please forgive my presumptuousness in what I said in my first post here.

I had something entirely different in mind when I said what I did.

The site below I find gives some pretty good info and it might have the detail you require, OK?

I think I am right in saying that this site says the best place for geothermal heat pumps is the SW States and California. That is where it is closest to the surface.

Hope it is of use to whom soever reads it.

This site give a whole lot of detail which may be helpful to those no yet making use of heat pumps? Great site!

http://www.ucsusa.org/clean_energy/technology_and_impacts/energy_technologies/how-geothermal-energy-works.html

Though your idea sounds pretty nice, my major concern is, that the co-generated heat will by far exceed the heating requirements of your home and you will not need your heat pump any more. Please refer to the link given below, where you can see an example of a small scale system generating both, electrical energy and heating which has been designed for "home use"

http://www.senertec.de/index.php?id=3&L=1

nudnik

Virtually all things are possible. If you want to spend the money. The Apollo project is a prime example of that.

I have not noticed the mention of an adsorption chiller/heat pump or a Stirling engine.

Again, thanks to all for a discussion that was stimulating and, in most cases, helpful.

Now, if only I could figure out why the cold fusion generator I bought doesn't work...

Jeff

Maybe you shold get the luke warm fusion model.