Geothermal Heat Pumps

- "Would it be possible to put a small turbine and generator after the expiation valve and produce over unity?"

No. Its a fundamental truth of the universe - you don't get something for nothing (aside from theft). In fact, thats exactly what will be happening here - apparent 'over-unity' devices always have a source of energy external to the system - in effect, pinching energy from their surrounds. Geothermal power is commonly used today and viable source of energy, but the total plant is not, and never will be 'over-unity'.

On a personal note, I'm becoming slightly little fed up with all the free-energy questions on CR4 - I think that many people who keep on persuing these 'over-unity' machines are lacking in proper work ethic. King Solomon wrote "every man should eat and indeed drink, and see good for his hard work, it is the gift from God". (Ecc 3:13) Whether you're a man of the bible or not, everyone can agree that when you work to accomplish something purposeful, its much more satisfying than if you attain it for free and with no effort.

A universe where free energy is possilbe would be boring!

Regards,

TinTin

You are NOT 'pulling heat from the earth", unless you are using this for winter heating. The advantage of an earth-coupled heat pump (used as an air conditioner) is that the earth can (at least for a while) more efficiently absorb excess heat than air can.

I didn't bother to investigate, but I very seriously doubt your factor of 20 times more efficient. 20 percent more efficient sounds conceivable; that is 1.2 times more efficient, 20 times, NO WAY!

"No. Its a fundamental truth of the universe - you don't get something for nothing ..."

Normally I'd agree with you, but isn't the Bible you quote full of cases where magic is used to rewrite the rules?

What about calling it "Inexhaustable supply of energy" or "Practically an inexhaustable supply of energy"? It's not free, but there's plenty of it. Isn't there mass being created somewhere from all the energy we're using? If Albert was correct, then, mass equals energy divided by the speed of light squared. This would be a very small number for the energy we're using.

There's only two things in life that are free; love and hate, and either can harm or kill you. PAPADOC

No. It's impossible to produce over-unity .

More than unity wviolates second law of thermodynamics.

Bioramani

In the case of heat pump no heat is generated. Heat available at a lowwer temperature is moved to a higher temperature. The energy for this is less than the heat moved. If electricity (or mecahnical energy) is used to produce heat then the equivalence applies.

Even in a heat pump a bit of the energy (from the compressor) does go waste in friction.

Bioramani

Okay, maybe I used the wrong word (unity) what I meant is more energy than the electricity to run the compressor. A heat pump will pull heat from the ground. A cold liquid (refrigerant) is put into the ground and wormed by the earth that converts to a gas, the gas is then compressed and is shot into the blades of a turbine, then it turns generator. What I'm asking is will the electricity from the gerator be grater than needer too run the compressor?

If you are in a location where there is sufficient energy near the surface, then yes, it will work. We call this geothermal energy.

You don't need a compressor for the gas coming out of the well: the heat of the earth vaporizing the liquid will produce the pressure. You do need a compressor/pump to convert the gas at the turbine output back into a liquid and force the liquid down the well under that pressure. Most turbines can't handle condensation back to liquid inside the turbine, so something else like a Stirling engine might be more efficient.

If the ∆T between the earth and the cool side of the turbine is insufficient, then you may need a refrigeration system to cool the gas back to a liquid (you did say a cold liquid), and there went your free energy (to run the cooling system).

Hi,

You make some good and interesting points, as do other comments. I like this thread it is interesting.

Other heat sources may be utilized, such as concentrated solar. I read in an article about some MIT students converting solar to electricity for under $200 using readily available materials. I think that concentrated solar would be more energy effective than PV's. Especially if you take into consideration energy costs to manufacture PV's, then installation costs are likely lower, although maintenance costs, etc.

Stirling cycles are interesting, I am a fan. Residential co-generation is possible using a natural gas feed. Provides your electricity, heating, cooling, and hot water, all in one. Still need storage tanks.

Speaking of storage, I wonder about conversion of liquid to high pressure vapour, held in large storage tanks for energy conversion and heating later. Is this an efficient or economical way of storing energy? Could this be appropriate with concentrated solar? Industrial applications and cryogenic refrigeration including liquification/separation of gasses such as oxygen, CO2, etc.

Finally, one poster touched on energy gradients in their informative reply to the OP's question. This is the situation where very efficient energy conversion may occur. External water sources are effective cooling systems, either natural bodies of water, or other man-made open water sources. I would rate ground-coupled systems second, and air systems third. All can be appropriate, depending on restraints or availability of the installation.

When considering the installation, then a good LCC analysis should be performed for all the scenario's, and some systems may require redundancy of diverse systems for back-up.

Of course the advantage of PVs is the absence of moving parts, including fluids. I have recently done just a bit of experimentation with concentrated solar using earth cooling, but haven't learned anything earth-shaking yet...

I have over the years thought quite a bit about Stirling, but have never found the time to do any real experimentation. It sounds like the best thermal alternative for low ∆Ts.

Large high pressure storage tanks are expensive and dangerous. That's why butane and propane are so widely used - they can be converted to ambient temperature liquids with only modest pressures, and yet converted back to gasses using only ambient air as the heat source (except in very cold climates). Safety and the large volume changes reduce the usefulness of liquid/vapor transitions. Solid/liquid transitions don't store as much energy, but they do so much more safely!

Hello Duane:

I thought you and the others might be interested in a thread that was done a couple years ago along this line. My opinion then as now is that it might be possible to utilize a low-grade heat source such as geothermal or even ambient air for that matter utilizing a heat pump into a viable source of electricity.

http://cr4.globalspec.com/blogentry/4247

I did a quick off the head calculation and a COP of about 4.5 would be required to just about breakeven. I have recently seen a raypack heat pump pool heater that I believe had a COP of about 5.5.

Of course are a lot of factors to consider but you never know someday it might become practical.

Hi RR,

Have we crossed paths before? Perhaps on CL or Alt.HVAC? Anyway, I did a quick perusal of the thread you posted, and I need time to review it, but there seems to be some interesting things there.

As a thought experiment, the idea of using a heat pump to generate electricity is a good start in the right direction. Really, to achieve best results you need to use specific equipment designed for purpose, and they have developed this with the ORC. I would envision this type of unit to be more industrial, institutional applications where the payback for installation could be very quick. What would be the savings yearly on say a University Campus steam plant, where you can save 3 to 5% on their fuel costs, or more? Anyone have a feel for the operating budget for institutional or industrial settings?

My gut tells me that for the smaller applications the stirling engine would have the greatest chance for success to generate electricity as it is not restricted by operating temperature ranges of a refrigerant. Economy of scale and simplicity.

I have found that in the last 10 years I have come look at any new theory with open-mindedness (enough even to be considered radical by some), and give thought to the possibilities. However, there is caution as well, since in my experience you can get burned even when the theory is sound, and the salesman appears kosher.

Cheers,

Duane

Hello again:

I don't think we've crossed paths, it's a pleasure to meet someone on the radical side. I've gotten into protracted discussions regarding the potential uses for heat pump type technology.

It seems to be a losing battle, there are some extremely intelligent members here on CR 4 whose opinion I respect, but they do not seem to be able to grasp the concept that we are not talking over unity or perpetual motion when discussing theoretical possibilities regarding heat pumps. Rather we are discussing a heat concentration device , it still requires an energy source.

Rather than re-post the information I thought you might be interested in a system I saw in operation, so two more links.

You might also be interested in Honda's Cogen unit, the only reference I could find was to a 1 kW generator/3 kW hot water supply. I believe it operates at about 85% efficiency.

Hopefully there will be more developments similar to Honda's idea, as you said it's going to take ground-up engineering to make these applications practical.

A hypothetical scenario would be to drive a small 1 ton or so heat pump with this Cogen, the Cogen itself approaches the efficiency of many furnaces, so for a hypothetical scenario you could potentially reduce the amount of natural gas required for your hot water and heating needs by 75% or so. Of course costs and maintenance are an issue however the payback could be rather dramatic.

http://world.honda.com/news/2004/c041020.html

http://cr4.globalspec.com/comment/421444/Re-Efficiency-of-5-to-10-KW-Gasoline-Generators-for-Residential-Use

YWRoadrunner,

I happen to think that one of the most efficient platforms for HVAC is a reversible heat pump system, particularly in the moderate temperature climates. In these climates when it's to hot the heat can be pumped down into a moderately isolated below ground heat reservoir. Whet it's too cold the below ground heat can be pumped back up. In this approach it would be tempting to think that energy would be stored below ground, but this approach leads to an obvious problem of trying to balance the power in/out ratio. I believe that this is not necessary, for the thermal mass of the crust of the earth significantly dwarfs that of a single dwelling.

Hello redfred:

I certainly believe that heat pumps are a underutilized technology. Of course expense is one of the major drawbacks.

As I'm doing this post, I'm also doing the laundry. It's about the time of the morning that my air conditioner is going to fire up, sure would be useful to have a water cooled condenser to dump the waste heat into my dryer but again complex.

If I ever get out of this condominium I may get a chance to play with some of these energy recovery ideas.

Actually I was thinking of all the heat energy under a freeway or road system producing electricity from 54 degree ground tempature.

Has anyone put any iteration of this into practice.

I have been thinking about it for a while and would like to chat with anyone who has done this.

Hi Stolly,

No, not that I'm aware of, if you are referring to the use of a refrigerant to drive a turbine. Thanks for reminding me of this post, I forgot I even posted this.

Personally, I'm seriously considering going back to do my M.Eng in energy systems, and this would make a great Master's project for study.

Cheers,

Duane

Machines that use refrigerant cycles to drive turbines are commercially available from a number of manufacturers. They are generically called ORC (Organic Rankine Cycles) and the most basic of them are actually transformed chillers.

Everyone seems to be all tied up in the over unity issue. I am just looking to give my heat pump a leg up, thereby saving on heating and cooling. Not to mention the LEED credits on my building.

Understanding that i am not trying to create the perpetual motion machine, will this practically save $ on my utility bills over 20 years?

You say building... so this is larger than a residence? Think waste heat as a source. I've thought of many schemes for recovering waste heat in commercial buildings in my years as a mech eng. Sanitary drainage would be a good source of waste heat. If you have a parkade requiring exhaust, you could couple the exhaust fan to a coil to recover the heat from the building substructure. Running loops around the perimeter of the building where the perimeter drain tile is located. Tie up a few of these ideas together and with a small boiler for backup on those real nasty days, and add some water storage you could likely provide your building with all the heat and hot water it needs. Just a few ideas off the top of my head.

Cheers,

Duane

Man, that's what i'm talking about. I know that I am over simplifying but if the mean temp down below is ~65F and I put that through the heat pump, the differential would be so much closer.

Like I said, I am not looking for this thing to run itself but there are a myriad of possibilities that if all added together would likely save loads of dough over the long haul. oh yeah, tax credits too.

These are the things that occupy my mind when it's not required elsewhere!

You can run modern extended range heat pumps very low, close to freezing water in fact. Apparently they are using open source water systems in Sweden to heat buildings during the winter.

That's the beauty of the refrigeration cycle, but of course warmer is better, but consider that 15ft into the ground you reach a steady state temperature of between 45 to 55F, so the ground coupled systems are using that ground temp to heat buildings.

Electricity from refrigeration with the placement of media at a different temperature allowing heat to move (as it does by itself, not "us moving heat") interfaced with EARTH :

Only mentioned to me by Dr john Jones, of Jones Heating, then 1980, Dayton , Ohio, that he and PE ME: Michael Rice and others had interests in what first appeared as 7% resultant usable electricity from all energy / Earth interfacing/ - all inputs::: but

the low pressure submarine-turbines required near 0f in 54f Dayton soil interfacing, and deeper Earth-Coupling to 18 ft; and in part also as he taught at the GeoThermal Heat Pump seminar (charging $300./ person in June 1980) ---

What appeared near 7% was more likely 1.7% efficiency, -- and "if" , to just keep "wheels turning"

These were the same who pointed out things like in a 2ft ditch of decent conductivity, two 3/4" lines of PE well piping had nearly as much use as 2) x 1.1/4" lines, because of the expenses to the pumping for turbulence required of the 1.1/4" to hit Reynolds #'s was not necessary with 3/4" having OEM I.D. inside deformations allowing for tiny pumps and much more heat moving in/out of the media (mink oil and silicone oil, etc., to methanol 16% by vol, then experimenting) they circulated for heat absorption to rejection to the Earth-Coupled Source.

Better designs of ECL Earth-Coupled Loops are at over 24 tons per circulation hp through all piping and fittings (usu under 22ft TDH-w including GTHP, but not using circuit setters) and all, again with the GeoThermal Water Source Heat Pumps, GHP, GTHP.

Process cooling of say 30-tons with 85- to -95f usable ranges needed:

1.1/2 hp was sufficient to off set 25 hp of chillers at a savings of 84% plus savings with completely accounted-for (censored): reduced RFG-Chiller tech calls and related high mechanical costs.

If I didn't get it wrong, you intend to use waste heat to drive a turbine and feed the heat pumps generating the waste heat with the electricity thus produced. While geothermal heat pumps may achieve very high COP's, they'd never be able to: 1. supply the necessary temperature levels for turbine operation (even considering low-temperature Organic Rankine Cycles) 2. even if they did, the COP they'd attain would never be able to compensate for the 5% electrical efficiency of small ORC's. and as pretty much everyone has said - it wouldn't be "over unity" - you'd be taking heat from earth (the rate at wich you take it determines if this may or may not be considered a renewable energy source)

Thats up to 20 times more than other heating systems.

Archer,

Your original post sounds like a question on "perpetual motion", or getting more energy from a closed system than you put into it. If this is what you are asking about, then the previous answers and the quietly-stated frustrations with topics posted to CR4 are all correct. No, you can't.

However, I think your question is really asking about a non-closed system (an open system)--in other words, a system in which the energy input is somewhere outside of the portion you are looking at. Geothermal energy is an open system. Your question is about moving energy from the ground to some other form or location.

You correctly note that geothermal has a much higher COP for comfort heating than most other methods for heating or cooling. Lets look a little more carefully at this:

1. The efficiency of the refrigeration cycle is inversely dependent on the temperature difference between the evaporator and condenser sides of the cycle.The greater the temperature difference, the more energy used to move the same amount from one side to the other.
   
2. The ground temperature (before you consider the removal or addition of heat to it by your geothermal system) depends on the air temperature above, the depth below the surface, and geological features of your area such as water table, soil types, etc. Depending on where you are in the world, this average ground temperature can be low (think permafrost areas) or fairly high.
   
3. Over the season, the ground temperature in your location will vary by perhaps 10 °F. If you are deeper in the ground and have a good thermal connection between the ground and your evaporator coil, with a large surface area for thermal transfer, this temperature variation will be less; if you are closer to the surface (such as only a couple feet down) or have a poorly-designed system, this temperature variation will be more.
4. In contrast to the fairly stable ground temperatures, an air-source heat pump's evaporator side is the outside air at a temperature that varies from 60 to -30 °F.
5. Therefore, a heat pump is seasonally more efficient if it is using the ground for the heat source instead of the air because for any geographical location the air temperature will always get colder than the ground.

If you are trying to extract heat from the ground and convert it to some other form of energy, the losses mentioned at the start of this post are not all. Converting thermal energy to electricity is no more than 40% efficient at the very best and many large power plants have thermal efficiencies closer to 30%.

World-wide, there are many places where geothermal heat it being used for electrical generation, but typically this is where the temperature of the geothermal source is much higher because of local volcanic heating, hot-spots, etc. None of these can be considered "over unity" because you are always dealing with an open system.

Friends I have worked with over the years have made a couple good points: use sources of energy with high energy density (such as fossil fuels) for applications where a high energy density is needed. Where low energy density is needed (such as for comfort heating or cooling), low-density sources are quite sufficient (such as ground-source heat pumps). Solar can be either high- or low-density, depending on how it is collected. The same is true for wind. The same is true for geothermal (the source temperature determines the "energy density"). Efficiency and wisdom is in matching the source to the use; we have often been lacking in these.

Your comment of "up to 20 times more than other heating systems" is wrong. For a geothermal system in heating mode, its best COP is about 7. Comparing this to a gas fired furnace of 90% efficiency, you are between 7-8 times more thermally efficient. Comparing it to an electric furnace, you are 7 times more efficient. Only if you include the thermal efficiency of the electric power plant, can you approach the 20 times you state. (Although the theoretical efficiency is even greater than the 7 times I mention, when the temperature difference between outside and inside gets smaller, the design compromises and choices for a heat pump do not allow better than this 7 times.) In cooling mode, a ground-source heat pump can give a thermal performance (EER) of 20 times the input energy because it is actually moving the energy across a negative temperature gradient. If you consider the life-cycle thermal efficiency, which nobody is doing, all these numbers are off. Then you would have to include the energy used in the mining, well drilling, transportation, construction, maintenance, and all the other factors.

As an aside, a well-built well-insulated home with high thermal mass can be heated with an air-source heat pump running only at the hours of day or hours of week when the air temperature is highest. When you compare the installation costs for air-source and ground-source for this type of house, the ROI for ground source can be 20 years or more.

--John Mueller

Your numbers are probably better than mine, But. The cost of drilling the holes has been the BASIC problem all along. I was quoted $22,000 to 26,000 to install a HP system, About 6,000 for the equipment and the rest holes in the ground. Another well driller quoted me $17 ?per foot (400 feet ). I can drill the holes for $2.50 / per foot.

Archers Arrows

Archer,

Yes, the well costs are the biggest portion of the expense. A few of my friends have and swear by the relatively low cost and comfort they have from a ground-source heat pump. But, if you are trying to install such a unit in an urban environment, good luck! Although ground-source is more efficient, I am tending to look for other alternatives.

--John M.

Cogeneration, under the current discussions sound like Tesla in action. If the "wise useage model" of geothermal heat pumps cool, during the summer, and heat during the winter they are obtaining expiation. Learning is an occupation of terrestrial humanity, then teaching can be an act of atonement. Sharing/cogenerating thoughts that compound synergistically to challenge human laws of Energy dynamics opens the door to a heaven full of opportunity, that was restricted by our own ignorance.

I'm not much of an engineer but aren't we talking about a heat differential between the sun and the earth. If the earth therefore is not a closed system due to the receipt of solar energy, than the heat differential has huge potential for capturing energy for work by absorbing solar radiation in geothermal function, and cooling potential as well. It could be like playing roulette while manipulating global temps.

Hi YWRR,

LOL!, you are very diplomatic to the OP's last comment.

I composed a couple of responses, then trashed them.

The way you put it about "I managed to design the world's most complex coffee warmer" really sums it up nicely. Sure, the idea may work, but is very complex and not practical.

The last place you want to place piping is under a road. What happens when your system fails? There is nothing wrong with throwing ideas out there to see what comes back, this is called brainstorming. Sometimes really good solutions come from crazy proposals. That being said, most ideas are generally thrown away. I guess the OP doesn't have any such experience with BS'ing.

One of the better ideas I've seen lately is from France where they are proposing to use the big transmission towers for wind power generation. This is a good example of getting more with existing infrastructure.

Reminds me of an idea I had many years ago about being able to tap into the geothermal potential of the domestic water supply. In most cities the domestic water supply system is laid out as a geothermal grid, and in large cities will equalize to the ground temperature. Even at the low water temperatures, one could conceivably be able to use an extended range heat pump to provide your heating and domestic hot water needs for buildings. This idea would work, and I believe it has even been tried. However, there are other issues, such as protection of the water supply from any cross-contamination, etc. Unlikely to generate any electricity, but would save you from having to lay out geothermal piping or drill wells, not to mention fuel savings.

I could go on, but my coffee is getting cold. I need a stirling engine driven solar powered coffee warmer!

Cheers,

Duane