Physicists help needed!!! Current technology limitations.

Please pay attention. I never once mentioned the first law.

Look closely at both of those - especially the first which makes it even more clear where it says "spontaneously." What you are failing to recognize is that neither of those statements preclude the ability to apply external power to the system (as with the refrigeration compressor) to reverse the heat flow. Both statements are talking about static conditions - like placing an ice cube in the sun. You cannot do that, they both say, and make the ice cube get colder.

You will eventually understand all this when you get older. I guess you'll just have to wait until then - when you'll also learn why turbines are more efficient, too.

 

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Knock off the cracks about my apparent mental age. What you are not understanding is that I have never objected to the idea that the hot side gets hotter and the cold side gets colder. What I said, over and over again, is that I have been told that the second law says that you cannot do this without expending more energy than you move from the cold side to the hot side. Supposedly, according to several authorities that I have read, it should take more than 100 watts of energy supplied to the electric motor powering the compresser to move 100 watts of heat from hot side to cold side.

 

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That wasn't intended to be a crack about your mental age, just a statement about your actual age. (Which you seem to still be afraid to reveal, by the way.)

And everything that you "supposed" from all those authorities is still incorrect.

 

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Hmmm... And after having just responded, I noticed your final statement more clearly. Are you now talking about standard air conditioners and refrigerators as opposed to heat pumps? It would appear so.

 

I have been told this stuff by people who I have more than a little reason to believe. It is a doctrine that I have found in several books. The doctrine is that the second law prohibits 100 watts of heat from moving uphill unless you spend more than 100 watts pumping it. So doctrine is wrong. I'm just telling you that I was told this thing about the second law. I have also told you more than once that I accept verifiable experimental evidence over theory or doctrine. And actually, until we started this discussion, I assumed that you would be one person who would tell me that you can't get 400 watts of heat for 100 watts of electrical power out of a heat pump or that it didn't mean what I thought it meant. Now I find out that it means exactly what I think it means. Doctrine is wrong and in realworld examples, 1000 watts of electricity moves about 4000 watts of heat uphill a certain number of degrees. This is probably why I used both window units for about half the day each and only spent 40 dollars on electricity. The one in the kitchen is newer and runs during the hot part of the day. The one in the bedroom is only on when I'm home and runs during the cool part of the day, which means it probably draws extremely low power most of the night. (During the summer)

What I have been trying to get at is how the gain occurs. I don't think that using a pure gas with no liquid phase is going to let you pump heat out of an area without spending more energy than you extract. I think that the condensation at the hot side does the job, for reasons I have already explained, and that's how you get gain.

There isn't anything in the Wiki article that explains that there is any difference between a heat pump and a "standard" refrigerator or AC. It would seem like a better heat pump design would make a better air conditioner or refrigerator. The big differences include the fact that if the heat pump and the AC are the same unit, that unit has to be reversible without physically moving parts. That takes some doing to design to work right. The other is that the heat pump can't get away with inefficient design or it will rapidly fail to work as a heat pump. People expect their air conditioners to suck power, but the whole idea of the heat pump is to save electricity, so it actually has to do it.

And another thing about a unit that is expected to conserve power is that if you use a heavier unit, larger compressor, larger reservoir of freon, more fancy tricks, you can get a little more efficiency than you can out of a unit that is compact and has to be less than a certain weight.

 

Well, you've still gotten better but still not quite there yet. The law is NOT wrong at all. What's wrong is the way you are trying to use it. I've already tried to tell you that the law is talking about ONLY the natural tendencies of things WITHOUT the external application of energy.

Let me try and put it in simple terms that you might understand. The laws of thermodynamics can be compared to the law of gravity. Gravity clearly says that water flows downhill - always. Period. It says absolutely nothing about you taking a bucket and carrying the water back uphill. Nor does it say anything at all that forbids you using a pump to send it back up. So is it with thermodynamics. It considers NO pump, no buckets, no nothing - just natural heat flow. I cannot see why you fail to understand something so simple.

And there most certainly IS a difference between a refrigerator and a heat pump. And I've already told you. It's called a 4-way valve, remember? It reverses the flow of the working fluid. The condenser becomes the evaporator and the evaporator becomes the condenser. It only depends on which way you want the heat to go - to the inside or the outside. It would be rather foolish to build that into a household refrigerator since there is never any need to heat it inside.

 

I have not failed to understand that. I know the difference between using a pump to pump heat to a higher temperature and the natural tendencies of heat. I have made it very clear that other people say that it can't be done at a net gain in usable heat, and that I am the one who believes it when I see it. I have also explained more than once that the first thought is that it can be done but it takes more energy to pump it than you get out of it.

No, a refrigerator is a heat pump and so is an air conditioner. It is just that those are not readily reversible to move heat the other direction and they don't need to be. The problem with trying to reverse the action of a heat pump is that for optimal efficiency the hot side and cold side are physically different. Larger gauge tubing on the cold side lets the liquid expand better. Smaller gauge tubing on the hot side gives better compression. I would have to look for specific designs to see how they handle that because it looks to me like if you make it reversible from the control panel one side or both will be inefficient.

 

You misunderstand me. Those "other" people (assuming they are smart enough) should also know that it's possible. I believe you are misunderstanding them - just as you did me.

In the strictest sense, yes, a refrigerator does pump heat. However is does NOT qualify for the term "heat pump" because that name refers to a specific type of reversible unit. So your statement is incorrect.

Yes, you are right about the efficiency angle. But that's what engineering is all about. Certain compromises have to be made but they can be done in such a way that the efficiency doesn't really suffer an appreciable amount. It's still better than having to supply one unit just for heating and another just for cooling in many cases. Especially in the apartment example I gave and were you get rate breaks for having an all-electric home. It also depends on your climate as well.

 

Actually, I think that it's convention to call it a heat pump when it can heat the inside of the house whether it is reversible or not.

It may be better to supply one unit for heating and one or several units for air conditioning when you are getting COPs of 3 or 4 and that would be reduced. The cheap window units seem to be very efficient. This of course is something I need to actually calculate out. The window unit in the kitchen would use a lot less power if I could keep it out of the sun, but it doesn't use much as it is. The setup using a reversible heat pump seems really vulnerable to getting a COP of 3 or 4 in one mode and less than 1 in the other. Or you have to split the difference between both sides, which increases the expense of using either side. Unless I can find some numbers showing me equal efficiency either way, I would rather use a dedicated heat pump for heat and window units for AC because the window units that I am using seem to do a really good job without spending a lot of money.

 

This really is a serious issue, too, when you realize that design compromises might double a utility bill from $150 a month to 300 a month or worse.

 

No, absolutely not true at all. That's just what you think it is and you are incorrect. Refrigerators, air conditioners, freezers and the like were in use for many, many years before the device and the term "heat pump" ever came into use.

While it's certainly true that those devices do pump heat, trying to apply the term as you are doing is still not correct. For example, you could call an airplane a "car" because it's perfectly capable of driving along the surface of a road. But that doesn't make it a car. It's capable of doing more (flying) and so is the device we call a heat pump (it's reversible).

 

Once again, as you so often do, you are simply talking without the benefit of actually knowing any facts. The actual compromises are very small - nothing like you are assuming !

You are good at thinking, but unfortunately your thinking isn't very good.

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You still need to learn the importance of getting facts before speaking.

 

How about, forewarned is forearmed? Technology has both real and potential faults that are predictable when you think them through. I would want to see the ratings that show me that I am better off buying a piece of machinery that is a compromise design, or a compromise of a compromise, and that includes figuring out the initial cost of the plant.

 

Well, guess what? Those ratings are posted right on the machines! It's required by law. (See? There's two more important things that you didn't know.)

 

What makes you think I didn't know that? You assume too much.

 

Well, silly one, it's precisely because you said: "I would want to see the ratings that show me that I am better off buying a piece of machinery that is a compromise design, or a compromise of a compromise, and that includes figuring out the initial cost of the plant."

So I simply pointed out that what you "want to see" is right there waiting for you to look at it!!!!!!!!!!!

And you don't have to "figure out the cost", it's also posted right on the unit. And if you mean before "compromising", there is no such silly data available. They are designed exactly as they are designed - not modified.

So just how is that "assuming?"

(Yeah, I know. You learn something and then come back acting like you knew it already. You've done that several times before - and it isn't very smart of you.)

 

Heat pumps work. Except one time in a Holiday Inn in South Bend, Indiana in mid January when the temp was 10 F. No go.

I should be able to take one of my window unit AC and turn it around and heat my inside of my house. Efficiency? Well, maybe not tops. But, it should work.

Perhaps a ( very ) crude but effective science experiment for anyone doubtful about life, the universe, and heat pumps.

 

Yes, it would work fairly well until/unless you encounterd the low temperatures you mentioned. Just don't forget to drain the condensate outside and also keep it away from the condenser coil where it's normally used to remove some of the heat.

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You teach class that way, don't you? No wonder we're all going to have to learn Chinese in a couple of decades.

 

At least reading this thread is entertaining...