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Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
I don't want to argue over semantics here. The energy used to turn the fan blades is not wasted either, it ends up as heat in the room. You can't destroy the energy, it has to go somewhere.
A heat pump isn't bringing air from the outside to the inside, it is a closed system. A compressor pumps gaseous refrigerant into a condenser, where the room air is used to extract the heat and the refrigerant condenses into a liquid. This flows outside where a metering device, either a simple orifice or a TXV lets it into an evaporator coil where the ambient air provides the heat to boil the liquid refrigerant back into a gas. Even very cold ambient air is still quite warm compared to liquid refrigerant. This gaseous refrigerant now contains the heat it took out of the outside air and the cycle repeats.
A space heater with a stopped fan produces exactly the same amount of heat as one with a working fan, and the eventual result will be the same. The heat will flow from warmer areas to cooler areas and eventually heat the room. That is not to say this is a good arrangement, you will have one pocket of very hot air and a room full of much cooler air, while to be comfortable you want the heat spread out evenly in the room. The fan does this, rapidly spreading the heat around, but it does not impact the efficiency of creating the heat. You're welcome to disagree, but you are arguing against the laws of thermodynamics.
You guys are taking the wording far too literally. Yes the heat comes from outside, yes it comes from the sun, no it's not LITERALLY over 100% efficient, but again, EFFECTIVELY, as in as far as it matters to the end user, you are getting more heat into the room than you are putting into it in electrical energy, the part that you pay for. Resistance heat turns all the electricity you put in into heat, a heat pump does too, with the added bonus that it harvests additional heat that is otherwise wasted outside.
Dollars spent on electricity vs BTUs of heating the air in the room is all that's really relevant here.
Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
James wrote ...
I don't want to argue over semantics here. The energy used to turn the fan blades is not wasted either, it ends up as heat in the room. You can't destroy the energy, it has to go somewhere.
A heat pump isn't bringing air from the outside to the inside, it is a closed system. A compressor pumps gaseous refrigerant into a condenser, where the room air is used to extract the heat and the refrigerant condenses into a liquid. This flows outside where a metering device, either a simple orifice or a TXV lets it into an evaporator coil where the ambient air provides the heat to boil the liquid refrigerant back into a gas. Even very cold ambient air is still quite warm compared to liquid refrigerant. This gaseous refrigerant now contains the heat it took out of the outside air and the cycle repeats.
A space heater with a stopped fan produces exactly the same amount of heat as one with a working fan, and the eventual result will be the same. The heat will flow from warmer areas to cooler areas and eventually heat the room. That is not to say this is a good arrangement, you will have one pocket of very hot air and a room full of much cooler air, while to be comfortable you want the heat spread out evenly in the room. The fan does this, rapidly spreading the heat around, but it does not impact the efficiency of creating the heat. You're welcome to disagree, but you are arguing against the laws of thermodynamics.
James -- I think the confusion began when you made the statement: ".....effectively greater than 100% efficient". I've read way too many claims from the Free Energy whackos who make claims of over-unity and such silly things, and that's why I jumped right on it. I read that link you provided to Wiki, and I copied a portion of it to print here: "When comparing the performance of heat pumps, it is best to avoid the word "efficiency" which has a very specific thermodynamic definition. The term coefficient of performance (COP) is used to describe the ratio of useful heat movement to work input. " The COP rating makes much more sense, and it shows how very efficient (oops!) a heat pump truely is.
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
Yes, I was hoping "effectively" was suitable wording. I too have read a lot of crud from free energy whackos, and I agree that they are nuts. The difference here is that we know where the "extra" energy is coming from, it's not "free" in the sense that it's coming from nowhere, but it's free in that we don't have to pay for it. We're not getting something for nothing, just moving something from a place where we don't need it, and concentrating it somewhere that we do. The end result is that you get more heat where you want it for the same amount of electricity consumed. I agree that COP is a better way of describing it, although I still prefer BTU's per Watt.
I suppose you could also say a heat pump is more efficient at converting money to warmth in the room, which is all the end user cares about.
Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
James wrote ...
Yes, I was hoping "effectively" was suitable wording. I too have read a lot of crud from free energy whackos, and I agree that they are nuts. The difference here is that we know where the "extra" energy is coming from, it's not "free" in the sense that it's coming from nowhere, but it's free in that we don't have to pay for it. We're not getting something for nothing, just moving something from a place where we don't need it, and concentrating it somewhere that we do. The end result is that you get more heat where you want it for the same amount of electricity consumed. I agree that COP is a better way of describing it, although I still prefer BTU's per Watt.
I suppose you could also say a heat pump is more efficient at converting money to warmth in the room, which is all the end user cares about.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
It is absolutely true. A good heat pump will deliver 3kW of heat to your room while consuming 1kW of electricity. One of the kilowatts came from the electricity, the other two were got by refrigerating the outside world.
If you have to use electricity for heating, that's how to do it: you can think of it as compensating for the low efficiency of the power station, giving you a result almost as good as if you burnt the power station fuel in your home in the old-fashioned way. Admittedly this is not easy when the power source is hydro or nuclear.
What the Second Law says is that you can't use heat pumps to heat the power station's boiler from its cooling water and sell the leftover free energy.
Electric heaters are 100% efficient as electric heater salesmen love to point out. But in these days of environmental consciousness, the efficiency of the power station and electric grid should be taken into account, since the fuel burnt at the power station is what determines the carbon footprint.
Fuel burning heaters are less efficient as some of the heat escapes up the flue along with the fumes. A log fire is about 25%, a modern design of central heating boiler maybe 70%.
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
Or think of it as active insulation. You consume some electricity to keep pumping heat back into the house as it leaks out through the walls instead of making new heat by just burning up electricity.
Or like using a pump in a collection pan to keep a leaky bucket full. It takes less energy than pumping new water all the way from the reservoir.
At any rate I installed a heat pump in my house a few years ago and love it. I have a 92% efficient gas furnace as backup heat, but with our cheap hydro power the heat pump is cheaper to run down to about 30F outside. Usually I have it switch over a bit sooner though to avoid the unpleasant defrost cycles.
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Induction Space Heater
