29 Jul 13
Originally posted by wolfgang59I believe stirling engines are pretty good.
Going off at a tangent here .... does anyone know the most efficient way of turning heat into electricity?
Just thinking about the "free" energy produced by a heat-pump and if that could be used to generate electricity.
???
29 Jul 13
Originally posted by wolfgang59In power stations they use steam turbines. Are you trying to power your fridge with electricity generated using waste heat from your fridge?
Going off at a tangent here .... does anyone know the most efficient way of turning heat into electricity?
Just thinking about the "free" energy produced by a heat-pump and if that could be used to generate electricity.
???
29 Jul 13
Originally posted by DeepThoughtNot quite. 🙂
Are you trying to power your fridge with electricity generated using waste heat from your fridge?
Heat pumps are being advertised that are 300% efficient. ie they use 3kW
of electricity and kick out 9kW of heat. How much better do they have to
become before the "free" heat can be used to generate electricity? Obviously
that depends on the efficiency of the heat => electricity. Hence my Q.
29 Jul 13
Originally posted by twhiteheadThanks.
I believe stirling engines are pretty good.
http://en.wikipedia.org/wiki/Stirling_engine
Wiki says up to 30% efficiency on temperature differences as low as 0.5C.
So with current technology an efficient heat pump together with an efficient
Stirling engine would be very close to being a "perpetual motion" machine.
When those efficiencies increase it will be free energy!
Thoughts?
30 Jul 13
Originally posted by wolfgang59This is known as a perpetual motion machine - as they offer 300% output it's a more than perpetual motion machine. Because now is pretty much like then, energy is a conserved quantity. This is due to something called Noether's theorem which is probably the single most important theorem in physics. This means you will not get 9kW of heat from something you are only putting 3kW into. They are trying to sell you crap.
Heat pumps are being advertised that are 300% efficient. ie they use 3kW
of electricity and kick out 9kW of heat.
30 Jul 13
Originally posted by DeepThoughtIts a heat pump.
This is known as a perpetual motion machine - as they offer 300% output it's a more than perpetual motion machine. Because now is pretty much like then, energy is a conserved quantity. This is due to something called Noether's theorem which is probably the single most important theorem in physics. This means you will not get 9kW of heat from something you are only putting 3kW into. They are trying to sell you crap.
http://en.wikipedia.org/wiki/Heat_pump
The energy is extracted from the air. (I am aware of conservation of energy!)
(Think of it as a refrigerator in reverse)
btw some heatpumps listed here
http://www.energywise.govt.nz/products/listing/100/heatpump?gclid=CPOJnKSS1rgCFYZMpgodLgQAEg
give out 5 times what they cost to run!!
30 Jul 13
Originally posted by wolfgang59You are confusing work efficiency with COP
Not quite. 🙂
Heat pumps are being advertised that are 300% efficient. ie they use 3kW
of electricity and kick out 9kW of heat. How much better do they have to
become before the "free" heat can be used to generate electricity? Obviously
that depends on the efficiency of the heat => electricity. Hence my Q.
http://en.wikipedia.org/wiki/Coefficient_of_performance
Wikipedia claims electric heating is 100% efficient at the heater:
http://en.wikipedia.org/wiki/Electric_heating#Environmental_and_efficiency_aspects
A heat pump can provide more heating on less power.
30 Jul 13
1 edit
Originally posted by twhiteheadNo I'm not, I was using "efficiency" in a thoroughly unscientific way. .
You are confusing work efficiency with COP
http://en.wikipedia.org/wiki/Coefficient_of_performance
Wikipedia claims electric heating is 100% efficient at the heater:
http://en.wikipedia.org/wiki/Electric_heating#Environmental_and_efficiency_aspects
A heat pump can provide more heating on less power.
Heat pumps give out more heat energy than the electrical energy they
use. (Because they are extracting energy from the outside air) That's not in dispute. (COP figures of 5 for newer models apparently)
I was wondering when (if ever) the output heat could be used to produce
more than the input electricity.😉
30 Jul 13
Originally posted by wolfgang59It's still a perpetual motion machine. Without a really cold thing for heat to run into, the huge amount of energy in the atmosphere you are trying to tap isn't available to do work. Say you have a heat reservoir and a box, initially at the same temperature. You pump some heat from the reservoir to the box, so the box becomes hotter than the reservoir. You then let the heat run back from the box to the reservoir using it to do some work on the way. You will never get more work out in the second step than you put in in the first.
No I'm not, I was using "efficiency" in a thoroughly unscientific way. .
Heat pumps give out more heat energy than the electrical energy they
use. (Because they are extracting energy from the outside air) That's not in dispute. (COP figures of 5 for newer models apparently)
I was wondering when (if ever) the output heat could be used to produce
more than the input electricity.😉
It's not totally ridiculous to set it up, since you will be able to generate some electricity from the waste heat, just not enough to power the heat pump.
30 Jul 13
Originally posted by DeepThoughtBut heat pumps for home use can also use pipes underground that extracts heat from the ground which is usually around 55 degrees F. With a constant input of heat it is theoretically possible to produce more energy than you consume based on the replacement of heat from geothermal sources.
It's still a perpetual motion machine. Without a really cold thing for heat to run into, the huge amount of energy in the atmosphere you are trying to tap isn't available to do work. Say you have a heat reservoir and a box, initially at the same temperature. You pump some heat from the reservoir to the box, so the box becomes hotter than the reservoir ...[text shortened]... ble to generate some electricity from the waste heat, just not enough to power the heat pump.
In this case, geothermal is not from a hotspot like in Iceland, but at a more sedate temperature of the regular underground. The deeper you dig, however, the higher the temperature. I think at 2 miles deep you get something like 180 to 200 degrees F. Bit of a project to go 10,000 feet deep though🙂
30 Jul 13
Originally posted by DeepThoughtMy heat pump works well enough. Lets say I get a newer better one.
It's still a perpetual motion machine. Without a really cold thing for heat to run into, the huge amount of energy in the atmosphere you are trying to tap isn't available to do work. Say you have a heat reservoir and a box, initially at the same temperature. You pump some heat from the reservoir to the box, so the box becomes hotter than the reservoir ...[text shortened]... ble to generate some electricity from the waste heat, just not enough to power the heat pump.
It will give me 10kW of heat output and use 2kW of electricity.
That's just using heat from outside air (at say 5C) and warming my house
to 22C. That's what it does. (And it pumps very cold air back outside!)
Now my question is how can I get 10kW of heat to produce more than 2kW of electricity?