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Entropy Exchange Dehumidifyer

Pre-cool air before chilling.
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(+3, -2)
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In a conventional dehumidifiyer (the type using a heat pump,) air from the room enters the machine, is chilled to it's dew point, and is then cooled further.

That "further" cooling results in condensation of water from the air.

The air then passes through the hot part of the heat pump, bringing it to just above it's original temperature, and then it leaves the machine, going back to the room.

What I propose is very similar, but with one key difference:

Air enters the machine, passes through an entropy exchanger (where it loses heat and gains both absolute and relative humidity). The air coming out of the entropy exchanger has a relative humidity of nearly 100%.

The air then goes through the cold part of the heat pump. Here, the air is chilled, of course, but since the air is nearly at 100% humidity, we don't need to pre-cool the air much before condensation begins. After this, the *absolute* humidity has decreased, but the *relative* humidity is 100%.

Then the air passes through the entropy exchanger a second time. Naturally, since it's cold, it will be in good condition to absorb heat from the other flow of air through the exchanger. Less obviously, since the relative humidity is 100%, it is in good condition to transfer humidity to the other flow of air. This is because entropy exchangers absorb or release moisture based on relative, not absolute humidity.

After the air leaves the entropy exchanger, it's temperature will be close to, but lower than, the original air's temperature, and of course it's humidity will be close to, but less than, the original air's humidity.

Then, as in a conventional dehumidifiyer, the air passes through the hot part of the heat pump, and goes back to the room.

goldbb, Jul 20 2009

Adding an intake/exhaust heat exchanger to an A/C system to improve dehumidification. http://wiki.answers...tioning_system_work
The heat pipes in the article merely act as a heat exchanger between the pre-cooled air and post-cooled air... I'm sure this could easily be accomplished without heat pipes. [goldbb, Dec 17 2009]


       do these entropy absorbers defeat conservation of energy? So in effect you saturate the air, then you condense the water back out of it. Brilliant. The bit about one air mass transmitting its moisture to the other air mass is a little mystical but surely possible using these new thermodynamics ignoring "absorbers".   

       I must argue however that if you propose a mystical way to do things that assails both math and science it is better to make it more effective, rather than less effective, than the physics-respecting current state of the art.
WcW, Jul 20 2009

       Last week while driving (LOTS of driving) My sinuses wished I could cool the air without pulling all the moisture out.
normzone, Jul 20 2009

       I invite anyone who desires to know more about the reality of "entropy exchangers" to simply google the phrase.
WcW, Jul 20 2009

       This wont work:   

       Conservation of energy (It's the law)
MikeD, Jul 22 2009

       This doesn't necessarily break any laws; there is inefficiency in the need to reduce the temperature to the dew point before any water is removed, and this seems to address that. You could also gain some efficiency with a simple heat exchanger between the cooled air and the inlet air. Again, no laws broken.
spidermother, Jul 22 2009

       It is the very definition of inefficiency to add more moisture to the air before we try to dehumidify it. And if by doing so we saved energy then, yes, we would also be violating thermodynamic laws. It's like saying that supersaturated air will absorb less energy getting dry then air with a R. Humidity of 50% because the wetter air gets down to business immediately, rather than waiting to get colder.
WcW, Jul 22 2009

       Also, after a few reads I suspect that the author simply intends to make the room hotter using his heat pump, thus reducing the R. Humidity.
WcW, Jul 22 2009

       //no laws broken//   

       Yes, if this mythical entropy exchanger adds energy to the equation, you would be correct.   

       But your not.
MikeD, Jul 22 2009

       If water were added to the incoming air from another source then efficiency would obviously be reduced, but here the water to be added to the incoming air is from the outgoing air - some of the dehumidifying uses the potential of the incoming air to absorb water up to its dew point (assuming the incoming air is not already saturated). The cooling part gets to work with saturated air, and therefore proportionally more of the energy is used in removing the heat of condensation rather than cooling the air to its dew point.   

       I would like some explanation of this "entropy exchanger", and I'm not convinced of any greater efficiency improvement than a simple heat exchanger would provide (since that would also reduce the energy cost of the cooling to dew point) but I'm not yet ready to side with the naysayers.   

       (later) I think this could be achieved by a long trough of brine, divided laterally into several sections, above which is a matching air duct, divided lengthwise into two such that two counter-current air streams contact the brine, but not each other. The brine in each section would allow heat and humidity to pass from one air stream to the other but prevent the air streams from mixing. The temperature and concentration of brine would gradually increase from one end to the other.   

       There are probably better ways to do it.   

       It increases efficiency by allowing both heat and humidity to move at close to equilibrium, rather than across large changes, so the efficiency can come closer to the maximum thermodynamic efficiency. No magic involved.
spidermother, Jul 23 2009

       can you explain why moving humidity from the intake to the exhaust side would improve efficiency? Why not simply blend the air at a lower recycle rate?
WcW, Dec 18 2009

       Who is suggesting moving humidity from the intake side to the exhaust side?
goldbb, Dec 20 2009

       Needs more bolts, man...
4whom, Dec 20 2009

       "passes through an entropy exchanger (where it loses heat and "gains both absolute and relative humidity)"   

       I think it would be easier on my brain if you said "strip of cloth, acting as a wick...running into a water reserve" instead of "entropy exchanger"..as that would seem to do what the entropy exchanger does? Give it a go, try it. X-rays from sticky tape, who'd have though that?   

       Or..this is one that crept across from a Half-bakery in a parallel universe.. Maybe we should just get everyone on here to describe their local physics and go compare..<sound of evil laughter> and so gain control of the world using our pooled knowledge and exploiting cross-worlds physics variations </sound of evil laughter>   

       //This wont work:   

       Conservation of energy (It's the law)// ([MikeD])   

       You may have missed, in the original post, //The air then goes through the cold part of the heat pump// and //the air passes through the hot part of the heat pump//.   

       Energy is added by the heat pump. I'm persisting in defending this, because is is a valid idea, which obeys conservation laws; energy is used to drive the heat pump, just less energy than without the exchanger because efficiency is improved.   

       I seem to be the only one to have carefully read and understood this idea before commenting!
spidermother, Dec 09 2010


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