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Old 05-12-2005, 04:48 PM   #15
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Dan,

I think you have the air changes done pretty well, but I don't know if you will get the 60-80% recovery in a 4" cube. It just seems a little ambitious for such a small (shortpath) unit.

But it's worth a shot, and I applaud your effort! At the very least, you will have a way to control the air changes that is better than just cranking open a window and cracking open a vent.
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Old 05-12-2005, 05:18 PM   #16
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I'm hoping that the short path through the heat exchanger is compensated by the slow movement of air through it (~10 cfm?) to provide efficiency similar to the full sized units. I don't know how the efficiency rating is calculated, but I assume the inputs to the calculation are the inside and outside ambient temperatures, and the temp of the air blowing into the trailer.
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Old 05-12-2005, 05:28 PM   #17
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I agree that the efficiency is probably based on the inside/outside temperatures.
I'm a little worried about the slow air movement though. While the 'transit time' through the unit may be the same, I think slowing down the flow rate will reduce the heat transfer rate significantly.

To get good heat transfer you need to have a high Reynolds number (very turbulent flow), and I think you may be in more a laminar flow regime.

BUT- I encourage you to try it anyway, I would love to be proven wrong. Do you want to split the cost of the heat exchanger? I'll go halfsies.
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Old 05-12-2005, 10:33 PM   #18
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Quote:
Originally Posted by markdoane
...To get good heat transfer you need to have a high Reynolds number (very turbulent flow), and I think you may be in more a laminar flow regime.
Looks like we have a displaced high-performance sailor!!!
Perhaps some 'tell-tales' along the inner walls will aid in tuning your vents!!!!
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Old 11-27-2005, 07:45 PM   #19
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DMac or others-
Has anyone worked out the thermodynamics of an air-to-air heat exchanger to fit an Airstream? And has anyone tried using one?
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Old 11-28-2005, 08:45 AM   #20
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I have not been able to find an air-to-air heat exchanger for RV's, although it seems like there might be a market opportunity. I have not built one yet, due to my other time commitments.
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Old 11-28-2005, 09:13 AM   #21
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I found a site that lists all the manufacturers of air-to-air heat exchangers. All were too large for this application by a factor of 5. I think you would need to do what Dan was considering in #13.

I wouldn't do any thermodynamic calculations because the numbers (cost savings) won't justify an installation. Rather you should estimate the number of air changes desired and base the design on that.

I think one air change per hour would be sufficient to keep condensation to a minimum and not be to costly in terms of propane. It would be best to have the inlet and outlet at opposite ends of the trailer.
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Old 11-28-2005, 12:40 PM   #22
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Oh Don... opposite ends? This sounds like an application for that infamous idea born years too soon -- the Suspended Ceiling thread: http://www.airforums.com/forum...ngs-18436.html. Maybe people could store their bikes & BBQ grills up there too!
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Old 11-28-2005, 02:52 PM   #23
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Oh Don... opposite ends?
Maybe that's a little bit of a stretch. You wouldn't want the inlet and outlet right next to each other though.

Would you?
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Old 11-28-2005, 04:53 PM   #24
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Air Exhange.
I leave my bathroom fan vent open and assume that there are enough air leaks in the trailer to bring in fresh air. This leaves me with almost no condensation down to about 34 degrees Fahrenheit. What condensation I get is removed with a towel twice a day.
guess what! I have clean windows.
If I close the vent condensation is intolerable.
That's with two people in a 31 foot trailer.
I also leave the bathroom vent open when the trailer is not being used and have never seen any condensation problems.
Al
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Old 11-29-2005, 01:46 PM   #25
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Ive cured the condensation problem. I hung a piece of plastc from the ceiling to the floor right beside thr bed. that keeps all the moister that we breath in one small space. the moister then condences on the bedside window and runs dow to the little aluminum box at the bottom of the window. from that I ran a hose up to the water tank and save most of the water for reuse. with a little work I think I can reach 100% eficancy. I may do the same thing with the moister from the Bath room. Mac
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