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Old 05-27-2015, 11:53 AM   #61
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Just a thought for the original problem
If you could used a high volume, low velocity fan of some sort to circulate the warm air down from the ceiling you might get better cooling. While hanging a big Casablanca ceiling fan might not work so well, that's the same idea and it works in my house both summer and winter



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Old 05-28-2015, 08:48 AM   #62
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You might want to Crack open the roof vent just a little to let the hot air out and th r n the A/C can fill the trailer with cooler air.


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Old 05-28-2015, 11:24 AM   #63
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I have checked, sealed, and double checked everything. Exhaust air completely sealed and doing its job. Cooled air recirculating and doing its job. Functionally, it should work.

It was 88 outside yesterday and I couldn't get the trailer lower than 83. The air is getting all the way to the back of the trailer and it is cool. The air exits the unit at 55 and re enters at 79. I've even tried a fan which made it worse.

I'm testing one more theory by shading the windows that are getting direct sunlight. For now, I taped cardboard outside, if it works I'll use reflectix and suction cups.

All of the thoughts and suggestions were considered and tested.
I still think the unit is under sized for our desert heat. I'm at a loss otherwise.
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Old 05-28-2015, 12:04 PM   #64
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For that A/C setup and everything you've tried, short of a larger A/C in my opinion, shade is your only answer.

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Originally Posted by Whs View Post
I have checked, sealed, and double checked everything. Exhaust air completely sealed and doing its job. Cooled air recirculating and doing its job. Functionally, it should work.

It was 88 outside yesterday and I couldn't get the trailer lower than 83. The air is getting all the way to the back of the trailer and it is cool. The air exits the unit at 55 and re enters at 79. I've even tried a fan which made it worse.

I'm testing one more theory by shading the windows that are getting direct sunlight. For now, I taped cardboard outside, if it works I'll use reflectix and suction cups.

All of the thoughts and suggestions were considered and tested.
I still think the unit is under sized for our desert heat. I'm at a loss otherwise.
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Old 05-28-2015, 12:10 PM   #65
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How could you use the vent fan to just pull the hottest air out? In other words, the fan sucks the air up that is directly under it rather than the hottest air which is along the entire length of the ceiling.

Short of putting a drop ceiling in, I don't see any way to trap the hottest air for exhausting. I don't know how big a temperature difference occurs between the ceiling and floor, but I bet it's substantive.
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Old 05-28-2015, 12:35 PM   #66
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The hottest air will be at the top of the camper and will also be where most of the heat from the sun will be.
Don't run the fan, just Crack open the vent. The hot air will be drawn out by convection. The fan may remove more than you want.
The idea is to replace the hot air with air cooled by the A/C. Think of filling a bottle with water from the bottom. The cold air is heavier than the hot and will displace it if there is a place for the hot to go.
Of course if the A/C is not capable of making up enough there you will need more btu's.
On my mini - split unit I am mounting the air handler high in the back so that it will pull in that hot air and cool it better.

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Old 05-28-2015, 05:10 PM   #67
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Your temp differential 55/79 is good and shows that the a/c unit is doing what it should.


And you can't just vent the hot air out the top without letting some more hot air in. To work, your inside air has to be a complete closed circuit. I agree, if the return air is already at 79 you will never get cool with the surface area and insulation you have. A bigger a/c that can recirculate more air faster is about the only answer other than improving your insulation, and the reflectix over the windows is known to help a lot.


Now, if you could only wrap the entire camper in reflectix, with a 4" air space between ?????



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Old 05-29-2015, 06:34 AM   #68
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The insulation in these campers is minimal, so its important to maximize the effect of the AC you have. Park it in the shade any way you can. Minimize any openings. there is a reason the MAX AC on your car recirculates the air. If you have removed a lot of insulation, put it back. And get some heavy curtains and keep them shut. Those big windows are not exactly the best insulators. Seriously.

I like the reflectex idea.
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Old 05-29-2015, 08:20 AM   #69
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Quote:
Originally Posted by Whs View Post
I have checked, sealed, and double checked everything. Exhaust air completely sealed and doing its job. Cooled air recirculating and doing its job. Functionally, it should work.

It was 88 outside yesterday and I couldn't get the trailer lower than 83. The air is getting all the way to the back of the trailer and it is cool. The air exits the unit at 55 and re enters at 79. I've even tried a fan which made it worse.

I'm testing one more theory by shading the windows that are getting direct sunlight. For now, I taped cardboard outside, if it works I'll use reflectix and suction cups.

All of the thoughts and suggestions were considered and tested.
I still think the unit is under sized for our desert heat. I'm at a loss otherwise.
That is discouraging. I too am at a loss. From the above it sure seems like you would get more than a 5 degree difference. Shading may be the best and least expensive solution. If the cardboard works, consider window awnings. Outside shade is more effective than inside the rig shade, plus you get light. I think I would consider some kinda "white rain fly/canopy" rather than throwing more kilowatts at the issue.

A nice tree would be best but would take some time to grow. ;-)

john
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Old 06-01-2015, 10:13 AM   #70
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Interesting weekend discovery. It got up to 101 this weekend and my scamp was in direct sunlight on the side of my house. I turned on the air inside my scamp, the starting interior temp was 107 and it got down to 84 within an hours time.

I'm only using an air deflector on my ac unit. I noticed that a fan blowing around actually hurts my situation.

Still debating on upgrading from 6000 btu to 8000 btu.
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Old 06-01-2015, 10:20 AM   #71
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Has anybody tried cracking the vent? One of the guys here cooks on the Bar B Que circuit and he says it helps get the super-heated air out and replace it with cooler air.
It won't cost much to try.
We did the same thing with a industrial electrical room with 5000 hp AC drives to reduce the heat load and it helped up out. Our main problem was filtering the dust that was drawn in with the make up air. Filters and fans took care of that.
Oh yeah the original A/C was (and are) dual 65 ton (780000 BTU for the purists among us) units. They keep up now which they did not before the change. (BTW this was for a single unit since with this application if you need one 65 tons you need the second if the first one fails to keep the drive running!)
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Old 06-01-2015, 10:26 AM   #72
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Originally Posted by redbarron55 View Post
Has anybody tried cracking the vent? One of the guys here cooks on the Bar B Que circuit and he says it helps get the super-heated air out and replace it with cooler air.
It won't cost much to try.
We did the same thing with a industrial electrical room with 5000 hp AC drives to reduce the heat load and it helped up out. Our main problem was filtering the dust that was drawn in with the make up air. Filters and fans took care of that.
Oh yeah the original A/C was (and are) dual 65 ton units. They keep up now which they did not before the change. (BTW this was for a single unit since with this application if you need 65 tons you need the second if one fails to keep the drive running!)

Since when are A/C units rated in tons. The standard is BTU (British Thermal Units).
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Old 06-01-2015, 10:45 AM   #73
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OK if you insist they are rated 780,000 BTU. 65 ton is easier to remember.
Since I am old I think in terms of old things and old ratings. That doesn't mean I can't think think in terms of "new" units. ( I have added the BTUs above).
Tons have been used by HVACR professionals probably since Willis Carried invented the process in 1902 (I was not there contrary to popular belief).
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Old 06-01-2015, 10:46 AM   #74
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With my roof-mount unit, we've ALWAYS ran with the Fantastic fan unit "cracked" a bit along with a couple of the windows (kitchen/bath). Now mind you, I dont camp in 0 deg weather (heat unit on A/C) and wont if I can help it. In cooler weather where we ran heat, we still crack the vent/windows.

As far as the A/C's concerned, we've stayed in 90+ deg weather in the sun and never had an issue. 9K BTU's though.


Quote:
Originally Posted by redbarron55 View Post
Has anybody tried cracking the vent? One of the guys here cooks on the Bar B Que circuit and he says it helps get the super-heated air out and replace it with cooler air.
It won't cost much to try.
We did the same thing with a industrial electrical room with 5000 hp AC drives to reduce the heat load and it helped up out. Our main problem was filtering the dust that was drawn in with the make up air. Filters and fans took care of that.
Oh yeah the original A/C was (and are) dual 65 ton units. They keep up now which they did not before the change. (BTW this was for a single unit since with this application if you need 65 tons you need the second if one fails to keep the drive running!)
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Old 06-01-2015, 10:48 AM   #75
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My home central unit is a 2 ton unit w/A/C & Natural gas furnace. In my area they judge what "ton" unit you need by the sq. footage of your home that will be heated/cooled. Typical window units I've seen are rated by BTU's only.

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Originally Posted by redbarron55 View Post
OK if you insist they are rated 780,000 BTU. 65 ton is easier to remember.
Since I am old I think in terms of old things and old ratings. That doesn't mean I can't think think in terms of "new" units.
Tons have been used by HVACR professionals probably since Willis Carried invented the process in 1902 (I was not there contrary to popular belief).
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Old 06-01-2015, 10:59 AM   #76
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Quote:
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Your temp differential 55/79 is good and shows that the a/c unit is doing what it should.


And you can't just vent the hot air out the top without letting some more hot air in. To work, your inside air has to be a complete closed circuit. I agree, if the return air is already at 79 you will never get cool with the surface area and insulation you have. A bigger a/c that can recirculate more air faster is about the only answer other than improving your insulation, and the reflectix over the windows is known to help a lot.


Now, if you could only wrap the entire camper in reflectix, with a 4" air space between ?????
Cracking the vent works well when using a low mount A/C. No measurable hot air is let in through the roof vent if it is opened only enough to let the hottest ceiling air escape thereby allowing the cabin to fill with cold air by displacing the hotter air which rises.

Still... roof mount A/C remains the best solution for RV trailers.
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Old 06-01-2015, 11:09 AM   #77
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Still... roof mount A/C remains the best solution for RV trailers.

If you don't mind the cost. weight high on top of the trailer, form drag and increased height for clearance under carport. Oh yeah the noise for some of the units.

Other that those possible drawbacks the roof mount is definitely the best solution for RV trailers.

Plus features. All in one design. Cools the hottest air at the top. Made for RVs. Directs the air where you probably want it. Not bad either.

Of our little trailers they are probably too large and the weight is a larger percentage of the total and shifts the Center of Gravity higher to the detriment of handling.

The window unit is not a bad compromise if it can be made to work in your locale.
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Old 06-01-2015, 03:26 PM   #78
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For what it's worth, none of the drawbacks really affects my 13' Scamp that I can feel. NOW, if I was to try and park it in a garage, yes.

I get 20 mpg...cant really argue with "drag" on that one...but it DOES affect it- to that I will agree. In the aviation world, it's considered "parasitic" drag. But it sure beats letting in the parasites at night! And with the weight on top, I'm sure it can affect the infamous rivets where it has to do with structural strength (side to side movement when traveling) etc.

One thing you didnt mention as a plus I really like - besides the excellent cooling quality- is the room it saves over taking up space in a closet or floor if mounted there. Both is "GOLD" in a 13' trailer . And, the weight...though heavier on top....IS centered left/right/fore/aft over the axle so it doesnt affect the horizontal balance of the trailer....as would adding a heavier rear window unit would tend to.

Just some more thoughts....

Quote:
Originally Posted by redbarron55 View Post
Still... roof mount A/C remains the best solution for RV trailers.

If you don't mind the cost. weight high on top of the trailer, form drag and increased height for clearance under carport. Oh yeah the noise for some of the units.

Other that those possible drawbacks the roof mount is definitely the best solution for RV trailers.

Plus features. All in one design. Cools the hottest air at the top. Made for RVs. Directs the air where you probably want it. Not bad either.

Of our little trailers they are probably too large and the weight is a larger percentage of the total and shifts the Center of Gravity higher to the detriment of handling.

The window unit is not a bad compromise if it can be made to work in your locale.
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Old 06-01-2015, 08:25 PM   #79
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Quote:
Originally Posted by redbarron55 View Post
Still... roof mount A/C remains the best solution for RV trailers.

If you don't mind the cost. weight high on top of the trailer, form drag and increased height for clearance under carport. Oh yeah the noise for some of the units.

Other that those possible drawbacks the roof mount is definitely the best solution for RV trailers.

Plus features. All in one design. Cools the hottest air at the top. Made for RVs. Directs the air where you probably want it. Not bad either.

Of our little trailers they are probably too large and the weight is a larger percentage of the total and shifts the Center of Gravity higher to the detriment of handling.

The window unit is not a bad compromise if it can be made to work in your locale.
The cost is of course an issue but it takes no usable space inside and can be fitted with a heat strip. Mine is a Coleman Mini-Mach 7200BTU it is shorter in height and is fitted with a faring... result no appreciable drag. Short carport could be an issue though. My shop has a 9ft door, I can't imagine building a new house without an eight foot door, but they still do. a new scamp won't fit into a seven foot door with or without A/C.
The mini mach is at least as quiet as any wall unit which we have installed.
Affecting the handling is really such a non-issue.

The drawbacks of the window units now available are build quality and the fact that they were really designed for stationary installation, also they are not rechargeable or repairable.
I would compare them to using a "Dorm Fridge" in place of an RV fridge.
They are of course economical and can serve the purpose. I have installed many of them with satisfactory results.
I still stand by my statement which you quoted.
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Old 06-01-2015, 09:14 PM   #80
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I read no mention of thermostat location. If the window unit is 10" above the floor, then so is its thermostat. I doubt any AC is going to cool well if the thermostat is not up higher in the trailer. Is it possible to control a window unit with a remote thermostat?
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