Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: McKay on 20/10/2014 22:03:49

Title: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: McKay on 20/10/2014 22:03:49
I am wondering - can a heat pump system be used to generate electricity from T>0K (temperature larger then 0 kelvin)?
That is - if a heat pump system consumes 1 energy unit and gives back 3 units (that includes the input unit), where the excess energy is taken from somewhere, decreasing that places temperature - using a thermoelectric converter with efficiency of 40%, then 1 unit can be pushed back to repeat the process, 1,8 is lost (non-converted) heat and 0.2 can be harnessed as electrical energy. With the mechanical parts and the compression chamber in the same place, surrounded by the thermoelectric converter system not to loose heat energy at mechanical inefficiency. It almost seems as if a system could be built that just keeps on cooling its surroundings and generating electricity as long as there is T>0K in the surroundings. Cant it?
Title: Re: heat pump system to generate electricity from T>0K?
Post by: chiralSPO on 20/10/2014 22:46:56
Only if there is a 0 K heat sink to connect the heat pump to. The efficiency of a heat pump depends on the *difference* in temperature between the two ends. No useful energy can be extracted from a heat pump that is in equilibrium (same temperature on both ends), and it would require input of energy to move heat from a cool body to a warmer one.
Title: Re: heat pump system to generate electricity from T>0K?
Post by: alancalverd on 20/10/2014 22:55:30
A heat pump doesn't create energy, it moves it from place to place. Given a heat source and sink, there are many ways to extract useful energy from the source, the Stirling engine being one of the most entertaining and more efficient than a heat pump since it does not require any additional input.
Title: Re: heat pump system to generate electricity from T>0K?
Post by: McKay on 21/10/2014 18:06:29
what I mean by a heat pump is the things used in building for heating - they can pull out, as far as I understand, heat energy from outside air, or ground that is colder then the inside, making the house warmer and the outside, ground even colder..
Title: Re: heat pump system to generate electricity from T>0K?
Post by: evan_au on 21/10/2014 21:06:29
An air-conditioner used in winter moves heat energy from the cold outdoors (which must remain at > 0K) into the warm indoors, making the indoors warmer.

But it consumes electrical energy to move the heat energy from outdoors.

For a "perfect" heat pump, it takes just as much energy as you could obtain from a perfect heat engine working between the same two temperatures.

But real heat pumps & heat engines have electrical losses, mechanical losses, energy losses due to turbulence in their fluids, etc. So I'm sorry, but you can't make a perpetual motion machine with an air-conditioner coupled to a Stirling engine...  [:(]
Title: Re: heat pump system to generate electricity from T>0K?
Post by: syhprum on 21/10/2014 21:20:57
Evan_au

Such talk is going to depress the value of the shares in the company I intend to set up to sell heat pump-sterling engine systems.
Title: Re: heat pump system to generate electricity from T>0K?
Post by: McKay on 21/10/2014 22:21:59
It is not perpetual motion I am trying to suggest, dont get me wrong.
Title: Re: heat pump system to generate electricity from T>0K?
Post by: McKay on 21/10/2014 22:31:06
please, explain to me - if there the pump and the compression chamber is in a room, 1 unit of energy is put into the pump and 3 units of energy are released as heat in the compression chamber, energy being taken from outside, how is that not more energy then the room initially had? Then part of that energy could be used to power the pump (1 unit) and collect whatever is left.
If heat pumps dont work by "stealing" heat energy from outside/ ground, then how do they work, if at all?
Title: Re: heat pump system to generate electricity from T>0K?
Post by: chiralSPO on 23/10/2014 19:21:16
There is no "stealing" going on. Heat will naturally move from a warm body to a cold body, if provided a path between the two. A heat engine can extract useful energy when it is the path between two bodies at different temperatures, but there is no energy created, and there is no energy "stolen." The hot body will give up its energy anyway, it's just an issue of putting that energy to use. Does that make sense?

Think of it as water that can be a different heights. Water will naturally flow down from a high reservoir to a lower one. This can happen with no useful energy extracted (a waterfall) or it can go through a hydro-electric power station, which will extract some of this energy for use. You cannot connect the hydro-electric power station to only one reservoir, no matter how high it is because the water has to go somewhere. It is only by making the connection between the high water and the low reservoir that energy can be extracted (for heat engine, you need both a hot body and a cold body with the engine in between). You can pump water up from a low reservoir to a higher one, with the input of energy, but this energy will always be greater than the amount of energy one will get back by letting the water flow back down. Similarly, one must expend energy to move heat from a cold body to a warmer one, and this will be more energy than can be taken back by allowing the heat to move from the hot one to the cold one.
Title: Re: heat pump system to generate electricity from T>0K?
Post by: McKay on 24/10/2014 22:34:58
I do understand energy conservation and that one cant get energy out of nowhere, but that doesnt really answer my question - how is using a heat pump for, say, heating a house more efficient then just running the same amount of electric power straight trough an electric radiator? Or are you saying that heat pumps dont work at all?
You do know what kind of heat pumps I am talking about and there is no confusion here, dont you?
Title: Re: heat pump system to generate electricity from T>0K?
Post by: chiralSPO on 24/10/2014 22:42:48
I think I know what you mean, but perhaps you should explain these heat pumps a little more, there might be some confusion...

I know of ways to extract heat from the ground during winter to heat a building and/or put heat into the ground during the summer to cool the building, but this relies on the fact that the ground temperature (a few meters deep) changes much less than the atmospheric or surface temperatures in response to seasonal changes.
Title: Re: heat pump system to generate electricity from T>0K?
Post by: McKay on 24/10/2014 23:07:01
well, there are ground based and air bases heat pumps and perhaps even water (small lake near a house?) based, ground based being more efficient because the temperature in the ground is a bit higher then the subzero air outside, but air bases forks on the same principles.
These pumps are exactly what I am talking about.
They dont rely on temperature difference, do they? Its not like they are just heat-conductive pipes that make the house the same temperature as the sub-surface ground - the system makes the house warmer then the ground and even warmer then it would be if the electric power would be used directly for a electric radiator. And make the ground colder in the process, of course.
Title: Re: heat pump system to generate electricity from T>0K?
Post by: evan_au on 25/10/2014 09:50:31
Quote from: McKay
how is using a heat pump for, say, heating a house more efficient then just running the same amount of electric power straight trough an electric radiator?

An electric radiator generating 1kW of heat consumes 1kW of electricity (plus about 50W more in transmission losses from the power station to your home).

An electric airconditioner generating 1kW of heat consumes around 250W of electricity (plus about 15W more in transmission losses from the power station) plus 750W of heat which it draws from the outside air/ground/water.

The more extreme the temperature difference from outside to inside, the more electrical power the airconditioner needs to pump that heat from the outside. This tracks the increase in power you could generate by a Stirling engine working between the outside temperature and inside temperature as this difference becomes more extreme.

So overall, an airconditioner powered by a Stirling engine will quickly grind to a halt (assuming it is initially started with a source of external power).

But far more efficient (in winter) is to pipe "waste" heat from a nearby power station to heat houses. This has some heat loss in the pipes, but no electrical transmission losses. But nobody wants a power station in their back yard, these days...  [;)]
Title: Re: heat pump system to generate electricity from T>0K?
Post by: McKay on 26/10/2014 11:54:51
So overall, an airconditioner powered by a Stirling engine will quickly grind to a halt (assuming it is initially started with a source of external power).
I am not exactly sure if I understand you - you basically just said that an air conditioner (heat pump?) can generate 1 unit of heat energy requiring only .25 units of electric energy (that can initially come from either the grid or a accumulator pack, btw), taking extra energy from the environment. Why would there be ever (and quickly) increasing temperature difference ? How to ordinary heat pumps dont grind to a halt?
What I am talking about is to basically put some thermo-electric generators around the compression chamber to get some electricity from that. And, if the efficiency is high enough (40% seems to be high enough and doable in the foreseeable future using vacuum gap thermo-electric generators, probably), make the process self sustaining and even have some spare energy left..  or, even better - thermoelectic generators around the compression chamber and the pumping motor(s) to  get back some of that otherwise lost heat.

And since I am talking about electric power generation, then actual heat might not be the priority and it doesnt even  have to work in very cold weather..
Title: Re: heat pump system to generate electricity from T>0K?
Post by: evan_au on 26/10/2014 18:17:45
Quote from: McKay
How to ordinary heat pumps don't grind to a halt?
Ordinary heat pumps do grind to a halt within about a second of turning off the electrical power source (I have also seen some refrigerators that work by burning an organic fuel: getting cool by producing heat!).

Quote from: McKay
It is not perpetual motion I am trying to suggest, don't get me wrong.
Quote from: McKay
self sustaining and even have some spare energy left
This is the definition of a "perpetual motion machine of the first kind (http://en.wikipedia.org/wiki/Perpetual_motion#Classification)".
Title: Re: heat pump system to generate electricity from T>0K?
Post by: alancalverd on 26/10/2014 20:01:21

I am not exactly sure if I understand you - you basically just said that an air conditioner (heat pump?) can generate 1 unit of heat energy requiring only .25 units of electric energy

No, the heat pump doesn't generate a unit of heat energy, it moves one unit of heat from A to B and uses 0.25 unit to do so. 
Title: Re: heat pump system to generate electricity from T>0K?
Post by: McKay on 29/10/2014 13:29:04
exactly, it moves the energy that is already there. In the end of the day, the system provides a home (the compression chamber) with 1 unit of energy while  consuming 0.25 units from the electric grid (or whatever).
Title: Re: heat pump system to generate electricity from T>0K?
Post by: McKay on 29/10/2014 13:31:40
Quote from: McKay
How to ordinary heat pumps don't grind to a halt?
Ordinary heat pumps do grind to a halt within about a second of turning off the electrical power source (I have also seen some refrigerators that work by burning an organic fuel: getting cool by producing heat!).

Quote from: McKay
It is not perpetual motion I am trying to suggest, don't get me wrong.
Quote from: McKay
self sustaining and even have some spare energy left
This is the definition of a "perpetual motion machine of the first kind (http://en.wikipedia.org/wiki/Perpetual_motion#Classification)".

But its not what I mean - it is supposed to take (move) that extra energy from the outside world heat that already exists.
Title: Re: heat pump system to generate electricity from T>0K?
Post by: McKay on 02/11/2014 21:53:24
Answer me this, please - is the fluid of a heat pump, just after compression, hotter than it could be if the same amount of electric energy was put directly to heating that fluid?
Does a house require less electric energy to heat it up using heat pump than it would require using simple radiators? Because from what you guys are saying, it seems like heat pumps are a hoax and dont work as a heating element.
Title: Re: heat pump system to generate electricity from T>0K?
Post by: syhprum on 02/11/2014 23:02:49
They are certainly not a hoax they really work but the only snag is the capital cost rather like that other free lunch solar panels.
Title: Re: heat pump system to generate electricity from T>0K?
Post by: McKay on 08/11/2014 18:55:58
Ok, so they work - using them, the house gains more heat energy taking less electric energy from the grid (or wherever), right? How much more?
Title: Re: heat pump system to generate electricity from T>0K?
Post by: alancalverd on 09/11/2014 00:30:17
Depends on the outside temperature, but I get about 3:1 from an airsource pump feeding a low temperature (30 degC) underfloor heating coil, and a bit less efficiency when heating the hot water tank (50 degC). Costwise it works out about the same as heating with gas or oil, but it's better than anything else for frost protection of a large open-plan area, where wallmounted radiators would just produce hotspots and electric underfloor heating would have required more mains supply capacity than was available - and cost 3 times as much to run!   

Title: Re: heat pump system to generate electricity from T>0K?
Post by: evan_au on 09/11/2014 02:48:50
Quote from: McKay
is the fluid of a heat pump, just after compression, hotter than it could be if the same amount of electric energy was put directly to heating that fluid?

Yes, the refrigerant would contain more heat from the outside world than if you obtained it from an electrical heating element.

However, depending on the boiling temperature of the refrigerant, and temperature/pressure operating conditions of the airconditioner, the temperature of the refrigerant may not change significantly, but it might change from gas to liquid.
Title: Re: heat pump system to generate electricity from T>0K?
Post by: SisGhidir on 29/06/2015 09:31:27
McKay,

Don't know why these guys don't grasp your concept. In theory your idea could work, but in practice there seem to be some complications.

You're right that a decent household heat pump will deliver heat at a ratio of about 1:4 to electrical input. This heat is transferred from outside, and is replenished by environment heat (no going to 0K).

A decent power plant will run at an efficiency of about 60%. So (in theory) you could use 42% of the electricity generated (=25% of the original energy input) by the power plant to resupply it with enough heat to keep it running. And all that with 58% of the electricity for other uses. This is neither magic nor a perpetual motion machine. It's a power plant that uses environment heat as a "fuel" source and would be a very nice way of combatting global warming.

The main problem however is that (i) heat pumps work at low output temperatures and their efficiency decreases sharply when requested output temperature goes up, whereas (ii) power plants require high temperature output to be able to generate electricity efficiently. The output temperature problem is less one of environmental heat decreasing (could easily be tapped from stable underground sources) but of the coolants used to operate heat pumps and extra efforts required to increase the temperature differential between input and output.

If you could design the right heat pump, this could work. But that won't be all that easy...

Hope this makes sense,
Sis
Title: Re: heat pump system to generate electricity from T>0K?
Post by: SisGhidir on 29/06/2015 10:11:04
Just to nuance myself after thinking this over for another 10 minutes: designing the right heat pump would not just be difficult, it would be impossible. It would be an impossible carnot cycle and violate the 2nd law of thermodynamics...

Too bad.
Title: Re: heat pump system to generate electricity from T>0K?
Post by: jccc on 29/06/2015 16:51:49
Just to nuance myself after thinking this over for another 10 minutes: designing the right heat pump would not just be difficult, it would be impossible. It would be an impossible carnot cycle and violate the 2nd law of thermodynamics...

Too bad.

not bad at all.

the law stands, everywhere, any time.
Title: Re: heat pump system to generate electricity from T>0K?
Post by: AL-azzeh Tareq on 28/02/2016 18:55:25
I believe I have developed a system where green, renewable and free energy is possible, but before I go any further, let me introduce myself and list my credentials in order to substantiate my claims.
My Name is Tareq Al-Azzeh, I am a mechanical engineer with more than 17 years of electromechanical, Maintenance, Construction, and Management experience. Holder of
B.Sc. Degree in Applied Engineering major in Mechanical Engineering Minor Hydraulic and Thermal Machines from Amman University Collage for Applied Engineering (1992 –1997) I am a Member of Jordan Engineers Association and a member of Project
Management Institute PMI Working as Chief Engineer Movenpick Hotel and Resorts worked as MEP coordinator in China State Construction Engineering Corp. in Abu Dhabi, worked as MEP Coordinator in Emirates Falcon Electromechanical Co.LLC and worked as chief engineer in Oasis Hotel Casino Resort, and InterContinental Hotel

The system I have theorized, and it is at present just a theory, involves the unlimited potentials of the refrigeration cycle

The result, should my theory work as I expect, would be green, free and renewable energy. It would “capture” the wasted energy used during the cooling processes and harvest the condensate water for use elsewhere.

The first application of the theory is to use the cycle for heating and not for cooling, the process will still have a cooling effect

Using the simple cycle as a boiler for heating water instead of burning fuel; fuel burners for heating purposes should have been obsolete long time ago. It is my opinion is that the heat pumps (refrigeration cycle) has been used commercially less than 2% of its potentials. If 1% of the monies spent on other forms of energy are directed towards the development of my theory, the world would solve its energy problems and produce potable water as a byproduct.

That was a simplified application of the theory, a complicated, more detailed description of the theory and how it will produce electrical power, heating, cooling and water production for free is shown in the sketch below.

When my system is adopted it will change the world and the way of life of its inhabitants, its heating and cooling systems will change, it will become totally self sustainable, both now and in the future. Public transportation will cease using fossil fuels to run, instead they will use electric motors because electrical power will be more economic and readily available.

My theory is a revolution that will change almost everything thermodynamics, global warming, pollution, power production, heating, cooling, water production, agriculture and public transportation, the list is almost endless. This system is not consigned to the future, with a little funding and development, it is available now. I am dedicating my life to this theory.



Introduction
Green, free and renewable energy is a dream, and this dream is now closer to reality than ever. My theory will explain how that can be achieved. It is based on the refrigeration cycle which in my opinion should be more accurately called a heat pumping cycle.

The Theory
In a refrigeration cycle, the heat ejected to the environment is the sum of energy given to the refrigerant by the compressor plus the heat extracted in the evaporator. In lay mans terms, energy ejected into the environment will be at least 4 times more than the electrical energy which runs the compressor
Based on my theory, a system that will produce green free and renewable electrical power, cooling, heat and water at only maintenance and initial cost, is possible, hard to believe but if my theory hold out, possible.

Heat extraction -rejection cycle
1- Evaporator where the refrigerant will extract Heat =Qev
2- The compressor will compress the refrigerant to high pressure and high temperature this means it will give the refrigerant energy (heat) Qcom
3- The condenser will reject the heat to the environment Qc=heat rejected
4- Qc=Qev + Qcom
5- Qev= 3Qcom as per actual systems that exist in the market

The results of the system are
1. Free electrical power (7)
2. Free cooling (1)
3. Free heating power (5)
4. Free Condensate water (1)

 


P.S please don’t hesitate to contact my at any time for any clarification

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2F&hash=3cd4f4119996b42d10f5ed9eb0e8d712)
Title: Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: syhprum on 28/02/2016 23:56:28
For a heat pump system to extract energy from the environment you need both a source of heat and a source of cold that is why power stations spend a lot of money building cooling towers. 
Title: Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: McKay on 23/05/2016 13:07:40
For a heat pump system to extract energy from the environment you need both a source of heat and a source of cold that is why power stations spend a lot of money building cooling towers. 

Did you mean that for thermoelectric effect (or steam engine or something the likes) to work you need a temperature difference? Sure, of course.

But a heat pump actually work the best when both source temp and target temp are the same (and it works to make one cooler and one hotter), doesnt it?

*Input = 1 unit
*Hot side = 3 units ->> generate anything >1 unit using thermoelectric/ piston/ whatever generator.
*Cold side = -2 units ->> is replenished to 0 from environment.

Sorry, I just cant let this thing go :D
 
Title: Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: agyejy on 23/05/2016 21:31:13
For a heat pump system to extract energy from the environment you need both a source of heat and a source of cold that is why power stations spend a lot of money building cooling towers. 

Did you mean that for thermoelectric effect (or steam engine or something the likes) to work you need a temperature difference? Sure, of course.

But a heat pump actually work the best when both source temp and target temp are the same (and it works to make one cooler and one hotter), doesnt it?

*Input = 1 unit
*Hot side = 3 units ->> generate anything >1 unit using thermoelectric/ piston/ whatever generator.
*Cold side = -2 units ->> is replenished to 0 from environment.

Sorry, I just cant let this thing go :D
 

Simply put what you are attempting to do violates the second law of thermodynamics. The validity of which is well established.

https://www.ohio.edu/mechanical/thermo/Intro/Chapt.1_6/Chapter5.html <- discusses the conected heat engine/pump secenario and why it violates the second law
Title: Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: McKay on 24/02/2017 17:18:38
Question 1 : Are there heat pumps that work with effective efficiency of 300% + (that is - 1 kwh of input electricity produces 2kwh loss of heat on one side and 3 kwh influx of heat on the other) ?
Question 2 : Are there thermal generators (steam, peltier, w/e) that work at 35% + efficiency?

I really dont want to sound like a crack-pot, but, ... ughhh. What do I need to do to build this myself? A working heat pump + the thermal generator = rather expensive. I am really not in a position to play around with money like that. Then I could see exactly what happens.
Title: Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: industry7 on 02/03/2017 19:34:11
Question 2 : Are there thermal generators (steam, peltier, w/e) that work at 35% + efficiency?

An electric heater is essentially 100% efficient.  Think about it.  Normally when you talk about inefficiency, you're talking about waste heat.  Some friction somewhere that's bleeding off some useful work as non-useful heat.  Well if you have a heater sitting in the room that you're trying to heat, even "waste heat" is doing "useful" work.  It's heating the room, which is what you wanted.

I really dont want to sound like a crack-pot, but, ... ughhh. What do I need to do to build this myself?

I don't understand what you're trying to build.
Title: Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: syhprum on 02/03/2017 20:06:37
where ever you have a thermal gradient similar to a gravitational gradient you can extract power from it I feel that a combination of a heat pump and a Peltier junction is an over complex way of doing it.
Title: Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: yor_on on 27/03/2017 15:14:44
I'm not sure I'm following your argument AL-azzeh Tareq? You state that " In lay mans terms, energy ejected into the environment will be at least 4 times more than the electrical energy which runs the compressor."

I assume that this 'energy' means the same going in, and out? If that is correct then what you say is that you found a way to extract four times the energy you put into a system. That's even better than a perpetual machine. If not, where would the extra 'energy' come from?
Title: Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: McKay on 21/04/2017 07:41:13
Question 2 : Are there thermal generators (steam, peltier, w/e) that work at 35% + efficiency?

An electric heater is essentially 100% efficient. 

Not thermal generator as a device generating heat, but a device generating electricity from temperature difference (peltier generators, Stirling engines and the like)
Title: Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: alancalverd on 21/04/2017 08:03:41
An efficiency factor of 3 is pretty standard for airsource heat pumps working around room temperature and 0 - 15 degC ambient. I have a 2 kW system that delivers around 5 - 6 kW into underfloor heating and a hot water tank.

The "magic" is that it doesn't generate more energy, it just squeezes it from the garden into the workshop. 
Title: Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: McKay on 21/04/2017 08:08:58
I understand, but what happens if I put a 35% efficient thermal-electric engine on a 3kwh heat source (the output of the heat pump) ? It generated 1.05 kilo watts of electricity, doesnt it?
Title: Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: Bolvan on 05/06/2017 08:23:17
McKay!
Yes, properly designed heat pump system will create sufficient delta T to run Stirling engine or Thermoelectric device. And, yes, it will be self-sustaining and generate "extra" for our use.
Source of energy in this case will be ocean or ground or air.
Perfect example of already existing device of this kind is so called "Drinking bird".
It perfectly converts ambient heat into mechanical work and probably knows little about 2-nd law of Tdynamix.
Title: Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: Bolvan on 06/06/2017 04:05:56
To correct my statement eventual source of energy is so called big band... formation of stars burning hydrogen.... shining stars storing the energy in air, ground or water on our planet. 
Title: Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: Bolvan on 07/06/2017 02:37:41
Corrections: Big Bang is initial source of energy.
Every following reciprocation like mass-energy- and back with derivatives MUST be viewed as energy storage IF BB theory is correct.
2nd law does not include such calculus. Hence, all mistakes of interpretations. 
Title: Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: Walterhurley56 on 10/06/2017 13:18:15
Corrections: Big Bang is initial source of energy.
Every following reciprocation like mass-energy- and back with derivatives MUST be viewed as energy storage IF BB theory is correct.
2nd law does not include such calculus. Hence, all mistakes of interpretations.
Agree
Title: Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: Dary on 11/08/2017 19:15:46
Congrats OP. There's a patent (US20080127657A1) describing exactly what you were trying to explain.

* Screen Shot 2015-11-14 at 10.53.56 AM.png (207.95 kB . 894x623 - viewed 3027 times)

* US20080127657A1.pdf (533.81 kB - downloaded 192 times)
Title: Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: McKay on 26/08/2017 09:37:40
Congrats OP. There's a patent (US20080127657A1) describing exactly what you were trying to explain.

Woah, cool. But, apparently, nothing has come from it in the 10 years since its was filled. Either it really, fundamentally, doesnt work or its hard to get efficient enough thermo-electric generators or no one has tried, or both. I am sorry that I cannot explain my thoughts better, I am not smart.

Hmm, but if there is a patent and I, or someone else, actually build it and it does work as suggested - does that mean I would be braking some laws or something?
Title: Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: Fredrik on 03/09/2017 12:38:16
Say that you have temperature T1 on the outside and temperature T2 on the inside of the house.

The efficiency of a heatpump is given as (coefficient of performance, ideal carnot cycle): Heat out / Work in  = T2/(T2-T1).

Say that you use an ideal Stirling engine to transform back the heat energy to mechanical energy/work.
Then you get an efficiency of (Carnot cycle): Work out / heat in = (T2-T1)/T2

Total efficiency for the ideal system is then: (Heat out / work in) * (work out/heat in) = work out / work in= (T2*/(T2-T1)) *((T2-T1)/T2) = 1.

That is, you get as much mechanical work out as you put in. This is for an ideal system. If you look on real systems and also introduce that you have to transform electricity to mechanical work in the heatpump and mechanical work to electricity from the ideal Stirling engine, you'll end up with an efficiency below 1.

Your example assumed a thermoelectric converter. This device also requires a temperature difference to work and is limited in similar ways as my example above.

Would assume this is why we don't have selfpowered heatpumps. I got exactly the same idea as you this morning, found the thread and thought a little bit about it myself before writing my answer above. Maybe the idea would work if we introduce more heatsinks? For example take the heat from T1 and run the heat to electricity converter against heatsink T3 (the house is kept at temperature T2)? It would work if T3 is sufficiently lower than T2. Don't know if it's feasible in practise though. Not always that you have access to multiple heatsinks with different temperature directly outside the house.
Title: Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: lalathros on 13/09/2017 07:54:23
I have been thinking about the same idea in the last 3 days. I'm installing an Air-source Heat pump for hot water in my house and my mind has been blown by the COP of this system which is around 4. I've checked online that there are heat pumps with COP of 5 currently in the market.

I'm not an expert in any way, I have basic knowledge in Thermodynamics and science in general. After reading bit, I've been wondering, like McKay, why this system hasn't been made yet. I would love a discussion on how I could be wrong and understand what could be done to make a system that could use Ambient Heat energy.

Earth is warming up. We've been dumping CO2 into the atmosphere for so long that these molecules are trapping a large amount of heat, which is causing massive global catastrophes like the recent Hurricanes Harvey and Irma, melting of polar ice caps etc.

Using Solar PV converts incoming light energy to electricity. While this offsets equivalent generation of electricity from fossil fuels, it doesn't reverse the process of climate change that was done till now in any way. The case is the same with Geothermal, in my opinion. We are harnessing free clean energy, yes, but we are not reversing the effects of human activity of climate change. To do that, we should either absorb the CO2 in the atmosphere or reduce the average global temperature using some other method.

This is how I stumbled upon the idea of using this heat energy trapped into the atmosphere which we have dumped into the atmosphere in the first place.

A heat pump which generates hot water at 80°C that has a COP of 5, i.e. Input 1kW to Output 5kW, which is coupled with a steam generator that has a liquid with low boiling point which generates electricity with an efficiency of 40%, could give us approximately 5kW*40% = 2kW of electricity. (I'm aware I'm possibly wrong with a lot of things here, I would love if someone could explain how)

As for what Fredrik posted, the ground is an excellent heat sink. At a depth of 5-10 feet, we get a constant temperature all year round at 10-15°C. There would be no need to use extra energy to have a temperature difference for the heat sink.

Thanks for reading this. I've been meaning to post this but never had the courage to type it out thinking I was the only one with this idea. Its amazing to know that there are other people with the same idea and there is a patent as well!

Title: Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
Post by: drmp3 on 29/05/2018 14:27:55
I was thinking about this too - if we have a 400% efficient way of heating something, surely we can make a power generator?

Sadly as mentioned in other posts thermodynamics rules this out. The same thing that means your heat pump can be 400% efficient also means that your Stirling engine (or whatever you use to generate electricity from the heat) can only be 1/400% = 25% efficient. Multiply the two together and you'll get 1 (or less than one in the real world). ie you'll lose more energy than you put in.

Basically the hotter the input to your electric generator, the more efficient it is. But the hotter the output of the heat pump, the less efficient it is. The two will always cancel out.

If this could work, you could e.g. use the electricity output to make a flywheel go faster and faster. Eventually you'll cool the world and the universe down to 0K and concentrate all the energy of the universe in the flywheel (you've reversed the big bang!). The 2nd law of thermodynamics says that energy always spreads out, and this is the opposite, so it's impossible, no matter how you tweak your heat pumps or generators.