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Old 07-17-2018, 12:29 PM   #1
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Too hot? How about misting the roof?

Just thought I would throw this out there after the recent heat wave.


My single AC unit is not powerful enough to battle direct sun in the 90's on a 27' motorhome. The indoor temp was 100 when I turned on the AC and I can only get down to about 90 deg. after 2 hours. (Yes I know 2 AC units are better than one, but I only have room for one.


I have a 16' misting setup I use for the kids (young & old) to cool of at events I go to. I run it off the rv water supply through a filter and it works nice with very low water usage.

I wonder what would happen if I suspend the misting tubing a few feet above the RV roof, from end to end?
Would it have enough evaporative power on the skin and around the AC condenser to reduce the inside temperature more than the 10 degrees I get now?

Insert opinion here:
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Old 07-17-2018, 01:06 PM   #2
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I can see the possibility that misting the roof, and from there, most of the AS. If the relative humidity in the area is low, it could provide some added cooling.

There is a downside or three:

1) Misting the roof would run the risk of mineral deposits on the roof and all the stuff on the roof as the water evaporates uncontrolled off the metal surfaces. If the water is alkaline, it can easily etch or corrode any unprotected aluminum.

2) Water on the roof is an invitation to find places for the water to leak into the structure wherever it can find a path. It's also a nice way to encourage the growth of algae and mildew if prolonged.

3) It's going to take a LOT of water to get significant cooling. At least around here, we are still in a drought, and the local authorities might take a very dim view of 'wasting' water.

I do see the utility of misting under the awning where the humans and pets hang out--that would be refreshing, and if properly positioned, would not get too much aluminum wet...
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Old 07-17-2018, 01:24 PM   #3
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Umm, park under a tree.
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Old 07-17-2018, 01:31 PM   #4
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I have had it so hot that the AC would not remain on do to excessive head pressure. I had to play water on the condenser coil to lower the head pressure till it was low enough to allow the AC to remain on. The inside temp of the trailer was 107 when I started.
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Old 07-17-2018, 02:20 PM   #5
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We are going to the NY State Fair in August, and no trees will be in the camp area, basically a giant parking lot with hookups.

I am not sure of the water quality there but it will be filtered for minerals, but not PH balanced.

The mist nozzles produce a very fine spray and with 10 nozzles it should use less than 5 gallons per hour, much less than any rain storm or any concern for the water department.

I have tied the misting line to the awning before, and as great as it feels, it does make everything damp after a while. It works best between 2 trees about 3 to 5 feet above your head to allow the mist to cool the air as it flows downward over you. The perfect setup evaporates all the water before it hits the ground. The 150 deg. skin should help with that, but as mentioned, stains may be a problem. The skin on my MH is so oxidized, it wont be noticed.

On the next 90+ heatwave with full sun I think I will try it.

In my mind (whats left of it) I figure to run poles on a rotatable bracket attached to each bumper. The mist line will be bungied between the poles, with someone in the front & back, rotate the poles vertical and lock them in place.

Pause for special news report on TV...

OK I'm back, and I checked my text to be sure I used the word "would" and "wouldn't" accurately.

I think I said what I meant the first time
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Old 07-17-2018, 02:29 PM   #6
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We have a 27' trailer with a single AC.

The late start on cooling after a day of travel is hard to overcome.

We close the divider curtain and cool half the trailer, to get living area cool enough to have dinner. After the sun drops a bit we open the rest and run a fan.

By time to sleep it gets much better.

If parked for a few days, we sleep with it as cold as it will get so the AC has a head start the next day.

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Old 07-17-2018, 03:20 PM   #7
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Iím interested to se how this works or doesnít.

I seem to remember someone asking about suspending a sun shade above their trailer to help with heat. Canít find the thread now but that could work too.
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Old 07-17-2018, 03:46 PM   #8
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Quote:
Originally Posted by jdalrymple View Post
We have a 27' trailer with a single AC.

The late start on cooling after a day of travel is hard to overcome.

We close the divider curtain and cool half the trailer, to get living area cool enough to have dinner. After the sun drops a bit we open the rest and run a fan.

By time to sleep it gets much better.

If parked for a few days, we sleep with it as cold as it will get so the AC has a head start the next day.

Regards,

JD
You mean to tell me Airstream air conditioning has a setting OTHER than "as cold as it will get"? It's a binary thing for me, "off" or "arctic"
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Old 07-17-2018, 03:54 PM   #9
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Glad I opted for 50 amp/dual air. No problem maintaining 72F in recent 95F temps...
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Old 07-17-2018, 04:30 PM   #10
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I have 4 solar panels around the front vent, so there is no room for dual AC units.
Those 4 100 watt panels probably do help a little with keeping the heat down inside with less sun hitting the skin
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Old 07-17-2018, 05:11 PM   #11
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Getting the mister line high above the roof seems to be a good idea. It's worth a try, so please report back on how well the idea worked. Might want to use a piece of nylon rope to help support the mist line tubing and avoid stretching/breaking it. It's usually thin vinyl tubing that needs support.

I live out in a very dry desert, so dampness build-up is not usually an issue. In New York State, I can believe much higher humidity...I've been in Owego in the summer next to the river. Steamy at times!

Please keep us posted on this experiment...
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Old 07-17-2018, 05:30 PM   #12
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Quote:
Originally Posted by rmkrum View Post
Getting the mister line high above the roof seems to be a good idea. It's worth a try, so please report back on how well the idea worked. Might want to use a piece of nylon rope to help support the mist line tubing and avoid stretching/breaking it. It's usually thin vinyl tubing that needs support.

I live out in a very dry desert, so dampness build-up is not usually an issue. In New York State, I can believe much higher humidity...I've been in Owego in the summer next to the river. Steamy at times!

Please keep us posted on this experiment...

The rope is a good idea to keep the mist hose from coming apart.
We are not suppose to hit the 90's for at least a week, but direct sun on the skin can still get the interior over 100.
I will do a test as soon as I can and report the results.
BTW, today's humidity is now down to 87%, it was close to 100% after the rains, that brought the temps down from the 90's to the 80's
Misting probably would not help for those conditions.
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Old 07-17-2018, 06:03 PM   #13
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Misting and evaporative (swamp) coolers usually work best in humidity under 30% relative humidity. Above that, evaporative cooling just gets clammy wet, and the dogs hate it, because they can't pant to properly cool themselves.

Around here, we easily get below that 30% RH in the summer (and darn near any other time).

95% humidity is not going to be easy to handle. The mister will make it hit 100% and not cool much, if at all.
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Old 07-17-2018, 06:40 PM   #14
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Have sprayed the trailer to help with cool down. Worked well. Is not allowed in many campgrounds. But it was very effective.
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