I’ve had so much fun with air exchangers I would like to throw a heat pump into the stew. I have a heat pump that starts diminishing in capacity at or around -4 Deg C. (And let me hold the patent on this if if works), Can I build a glass / Plexi-glass shelter around my heat pump and use the passive solar heating (Sun-room effect) to boost its efficiency during a cold but sunny winter day? Obviously would have to be ventilated or removed for cooling in the summer. Any thoughts?
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How much volume are you thinking of enclosing? I think you would need an awfully big shelter (bigger than your house) to give the air to air heat exchanger enough air to work with.
Jon Blakemore
RappahannockINC.com Fredericksburg, VA
I am just thinking that since the freon is flashed off or vaporized by the latent heat contained in the outside air, in the reverse cycle that gives me heat in the winter, that air flow is not actually needed. A fridge takes the latent heat from the food and uses it to flash off the freon. This freon is sent to the compressor, cooled and compressed into a liquid again. So by simply enclosing the Heat pump with a solar heated enclosure am I not accomplishing the same thing? Could I even add thermal mass such as rocks or stone to soak up the heat and radiate it back during the nighttime? No air exchange is actually needed here. When I am in cooling mode, there has to be air flow across the coils outside to dissipate the heat, but air flow is not required in the outside coils in the winter is it?
I just recently had a 17 seer HP with puron installed. The salesman told me the backup heat would probably stay off down to about 0 degrees F if it was sunny. Sounds like he's saying your theory is sound.http://www.quittintime.com/ View Image
OK you get 10% of the profits.
Actually, this came up because had asked about shading the unit. One of my shop windows is near it and I've been toying with the idea a building an awning of some sort over the window because the winter sun blinds me when I'm at my brake. Thought I might incorporate what ever I did to the window to also cover the HP. His theory was that the sun shining on the HP when it was cold would benefit more than shading it when it was hot.http://www.quittintime.com/ View Image
Seems a removable shade is needed here. It would give you the sun in the winter and shade in the summer. I might do that myself.
> When I am in cooling mode, there has to be air flow across the coils outside to dissipate the heat, but air flow is not required in the outside coils in the winter is it?Air flow is required. Otherwise the outside coil would just get colder and colder.
The only function of economic forecasting is to make astrology look respectable. --John Kenneth Galbraith
Not in a sun room continuously heated by the sun
Yes, even there. Something's got to be carrying the heat in as rapidly as the inside circulating fan is carrying it away.
The only function of economic forecasting is to make astrology look respectable. --John Kenneth Galbraith
The problem is that your shelter, in its simplest form, would prevent air movement, and the exhaust air (which is cold) would end up being recirculated back to the intake.
So you need a "shelter" that just contains the incoming air, which means that the warm air is being sucked out of the shelter rapidly, and you need a large (greenhouse-sized) shelter to produce enough heated air to do much good.
You do not need air flow to pass latent heat to the liquid freon. It is called an air to air heat pump because it uses the latent heat present in the air to heat or cool depending on which side of the system you are using (heating or cooling). I could enclose the heat pump and heat the space with an electric heater. That heat would cause the freon to flash off, but would defeat the purpose and cost me more money. but If I use free solar heat from the sun-room effect it should work???maybe. The outside coils do need air circulation in the summer to operate in cool mode though. The coil in the furnace and the coils outside simply switch jobs.
Yeah, right.
The only function of economic forecasting is to make astrology look respectable. --John Kenneth Galbraith
"It is called an air to air heat pump because it uses the latent heat present in the air to heat or cool depending on which side of the system you are using ..."
No, it does not.
Latent heat means the heat of vaporization or condensation when referring to most physical phase change processes including refrigeration cycles. In regards to comfort air systems, the space being heated or cooled has two components of a "load" (i.e. the heating or cooling requirement) which includes sensible heat and latent heat. In heating applications, the primary concern is sensible heat.
Only In cooling and dehumidifiying indoor spaces is where the "latent heat present in the air" is applicable. The latent heat part of the equation is simply the cooling load required to remove the moisture from the the air to maintain a reasonably compfitable relative humidity level, hopefully 50% or less.
The air that cools the condenser coil in the heat rejection (i.e. air conditioning) mode of an ATA heat pump absorbs sensible heat only. The air that gives up heat to the evaporator coil in the heating mode (same coil, the outside one) gives up only sensible heat, unless it condenses and/or freezes.
Thanks for the correction.
I meant to explain, not to correct. General terminology maybe good enough for general conversation, but when you get into discussing technical details, the terminology must be precise. It helps when everyone understands the meanings of the words used. Actually, it is the only way technical discussions can be conducted that have any use whatsoever.
Take the term ventilation. To most people it simply implies air moving or blowing, i.e. open the window for some ventilation. To an HVAC engineer ventilation very specifically means: outside air introduced into a space for the purpose of diluting contaminants. So, as you can imagine from my perspective (I am an HVAC engineer), the term latent heat has a very specific definition.
That is right up there with the term air conditioning, to me it means humidifying, de-humidifying, cooling, heating (Conditioned air being the result). To most people it means cooling. Very good point
Plot the enthalpy, temperature, and pressure onto the Mollier curve for your system and observe the thermal transfer relationships.
Then you will know the realities of vapor recycle mechanics.
Real funny; Will it improve the efficiency or not? I realize I will not heat my home for free, just need to know if it will up the efficiency a little bit. You appear to have the knowledge base to answer the question, thanks
Edited 11/13/2008 12:51 pm ET by losh
That was not a "funny" answer, but maybe a little sarcastic (in as much as if you knew what any of those things were you would probably know the answer). What he meant to say was - No, your idea will not work.
Edited 11/13/2008 1:46 pm by Tim
It was a sarcastic "funny", and you are quite right, if I knew the answer I would not have asked it. What I have gathered from the discussion is that the sun would not re-heat the air in the enclosure fast enough, so a method of introducing fresh air in, after or during a cycle, would have to be incorporated in an economical fashion, would only work during sunny days and for as long as the sun is shining on the enclosure. It is staring to sound like a folly. Thanks
Think about it this way: How much heat will your little Plexiglas hut capture? How much heat is coming out of the inside unit of your heat pump? If the former isn't more than the latter then the hut will get colder and colder. TANSTAAFL.
The only function of economic forecasting is to make astrology look respectable. --John Kenneth Galbraith
I'm jumping into the fray here, expanding on what the others have said, at the risk of offering more detail than wanted.In house heating mode (winter), the liquid refrigerant is evaporated in the outside coil at some pressure low enough that the temperature is below that of the outside air. Heat flows from the air to vaporize the refrigerant. Refrigerant gets vaporized, and the outside air gets colder.The air must be kept moving, or within seconds it would be cooled to the temperature of the vaporizing refrigerant, and no further vaporization would occur. If you built a glass box around the outside coil, the vaporizing refrigerant would quickly cool down all the air within the box to the point where no further heat would flow out of it.As heat is extracted from the outside air, the supply of heat to pump into the house must be replenished by keeping the air in motion and pushing the air already cooled away from the coil. The same air can't be simply recirculated past the coil again unless it gets rewarmed by some means to ambient air temperature. If this source of heat were to be the sun, then indeed a greenhouse-sized enclosure would be required, so that the total sunlight falling on the greenhouse, less the heat lost through the glass to the air, equals the heat pumped into the house.The source of heat (the sun) disappears at sunset. As long as there is plenty of air outside to be moved past the coil, and the temperature isn't too cold, the heat pump can extract heat and move it into the house. Anything you do to enclose the outside coil will have a negative impact on the efficiency, because it will interfere with movement of "new" air past the coil.
Edited 11/13/2008 2:00 pm ET by DickRussell
Thanks. I liked your answer, straight and to the point; I am not an HVAC Technician as the Navy does not give us the refrigeration portion of the training, other than a basic refrigeration cycle. (Or I would not have asked the question) We take over from the marine engineers after the chilled water has left the chiller; But I don't give up that easy. What if I were to pipe air in to be reheated by the sun after every cycle via auto dampers powered from the existing relays on my ETS (Electro Thermal Storage) system. It does have the capability to do this. I read the instructions; I know, pretty silly thing to do, but I did. What do you think?
Edited 11/13/2008 2:11 pm ET by losh
Presuming your ETS is inside the house, it will be more efficient to circulate inside air through it to extract heat. If you move outside air through it, just to get rewarmed air to move past the outside coil, you'd lose some heat to the surroundings.If you are talking about placing the ETS within the proposed enclosure around the outside coil, that's less efficient as well. First, any heat you extract from the ETS will have been put into it at electric power rates, so you haven't got any "free heat" from the outside at all. Second, some heat will be lost to the surroundings. Finally, the idea of an ETS is to be able to store electric energy at cheaper night time electric rates, then release it for comfort when the daytime rates would be higher.The whole idea of a heat pump is to use "X" units of energy to lift 2X or more heat from a source at some lower temperature to a destination at a higher temperature. There is thus "leveraging" of the energy you pay for (electricity) to move some multiple of that into the house. This is better than electric resistance heating, where you get only "1X" of heat for each "X" units of electrical energy. The ETS is just another "1X" device.
I just meant that the ETS which is inside the house, would control a fresh air damper inside the outside enclosure. This would bring in outside air into the enclosure, not actually into the house itself.
Oh. But if all that does is funnel outside air through a damper, so it can go past the coil and out of the enclosure somewhere, then nothing has been gained, the free flow of air past the coil has been impeded, and efficiency has been lost.
The damper would be controlled by the relay on the ETS unit, preventing a free flow of air across the enclosure. But I have given up on this as it appears to be a useless endeavor. I would still like to shield the heat pump from the northern wet snow that we get up here. It gets stuck up in the fins and freezes there. Making the heat pump useless. Any suggestions?
Conversely, I have a friend who was telling me that he set up system to spray mist on his AC compressor during the summer to improve the efficiency through evaporative cooling. Jay
I did that with our old unit, when it was on its last legs. Used an ag spray nozzle. Made a unit that could barely produce cold air chill the house like gangbusters. If I'd needed it for more than a few days in the worst of summer I'd have rigged a lawn sprinkler valve to it to switch the spray on and off with the compressor.In theory the same thing would work in winter, except that it would likely freeze up unless very carefully balanced.
The only function of economic forecasting is to make astrology look respectable. --John Kenneth Galbraith