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Author Topic: How much AC in a class A and spray foam?  (Read 352 times)

unclean

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How much AC in a class A and spray foam?
« on: July 22, 2017, 03:46:18 AM »
I'm trying to buy a 36' class A with 0 slides and only the one side door.  It's an older model so single pane windows but I want to fix that.

I keep reading about RVs with 2-3 AC units but not the circumstances or performance.

How many watt hours will I need to run AC in 100 weather with no shade and a thermostat setting of 80?

I assume the third AC units are for RVs with a bunch of leaky sliders.

I assume my insulation will be pretty basic.  Plan A is to photograph the interior with a Flir thermal camera and inject spray foam in the leaky spots but I'm not familiar enough with RV wall construction to know if that is practical or a good idea.

My end goal is AC that can run off of solar during summer.  I'm planning a 1kw array with about 5kwh of lithium ion batteries.

Plan B which I intend to do either way is to find somewhere cooler to spend the summer and early fall.  I want to travel mostly around the South West USA and figure out a loop that avoids steep long climbs, tornado season, humidity, high heat and freezing cold.

If anyone has a route to suggest, let me know.

Plan C is to remove the interior to add spray in foam thoughout.  If anyone has tried full spray foam and dual pane windows in a class A with no sliders, I would love to hear how it worked out.

I have seen some bus conversions that seem close to what I may do but they usually have more windows and very few people attempt solar powered AC.

Larry N.

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  • Westminster, CO
Re: How much AC in a class A and spray foam?
« Reply #1 on: July 22, 2017, 07:10:45 AM »
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I assume the third AC units are for RVs with a bunch of leaky sliders.

Nope! The 3rd one is because the rigs around 45 feet need it for adequate cooling because of the added internal space with slides extended. Rvs in general are not as well insulated (even with double pane windows) as a stick house, and the sun can heat them quickly. The slideouts do provide extra floor space which needs cooling, but they're not generally "leaky."

About performance -- my previous coach was a 45 footer with 3 air conditioners and in very hot, sunny weather it needed them, but stayed pretty comfortable with them all on. In lesser heat, or when cloudy, two were adequate.

Running even one A/C from solar needs, as you evidently realize, a lot of power, a very large battery set, a LOT of solar panels and a rather large inverter. Then you hope you get enough sun.

Sorry I can't give you the engineering details, but if you mention the coach brand and model someone here with solar experience might have some thoughts on it.

As far as the foam/extra insulation, be sure you know what that will do to your weight, whether it will leave you with appreciably less load capacity, since some coaches are marginal in their capacities.

Quote
Plan B which I intend to do either way is to find somewhere cooler to spend the summer and early fall.  I want to travel mostly around the South West USA and figure out a loop that avoids steep long climbs, tornado season, humidity, high heat and freezing cold.

Good luck on avoiding long, steep climbs in the southwest. You'll be avoiding a large portion of the desirable areas.
Larry and Mary Ann N.
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Gary RV_Wizard

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Re: How much AC in a class A and spray foam?
« Reply #2 on: July 22, 2017, 07:39:04 AM »
There are several reasons that RVs require a lot more a/c than a typical residence, starting with relatively thin walls (modest insulation), a proportionally high amount of glass in the walls (e.g. windshield), no attic, hot air under the floor, etc. etc. Further, RVs have a high rate of heat gain, especially in full sun. Basically a box lying in the sun that heats up quickly. Every wall is an exterior wall, so occupants are rarely more than 3-4 feet from a warm exterior wall and local hot spots abound.   In full sun or temperatures above 90 it is common for the a/c units to run non-stop to stay abreast of the heat gain.  In 100 degree temps with no shade, my guess is the a/c's will run non-stop and still may not be able to maintain a consistent 80 degree internal temperature. However, external color is a factor - white coaches fare better than those painted with elegant but darker colors.

Coaches above about 30 ft need two a/c units of 13.5 or 15k btu each, and coaches over 40 ft need three.  Each 13.5 or 15k btu RV a/c units uses 1300-1400 watts per hour in hot weather. Your 1 kw solar and 5 kwh battery bank are only a drop in a bucket.

RV sidewalls are already insulated, usually with foam board sandwiched between the inner and outer skins. Typically only 1.25"-1.5", since the entire wall thickness is probably no more than 2". The better quality rigs have the available space pretty well-filled, but some brands may have a sloppy fit with gaps. Getting at those gaps to fill with something may be challenging, though. Most newer rigs (say post-2002) have pretty decent floor and ceiling layers & insulation, but again it varies by the original price point. Skimping on construction quality under the covers is a common way of keeping the price point down.

It's often possible to make improvements in RV heat gain, sometimes dramatic ones, but it's still a hot box. The area around the windshield and front cap in a motorhome is often fruitful grounds for improved insulation.
« Last Edit: July 22, 2017, 07:41:31 AM by Gary RV_Wizard »
Gary
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Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

Drifterrider

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Re: How much AC in a class A and spray foam?
« Reply #3 on: July 25, 2017, 06:51:44 AM »
There is a good video on YouTube made by Gonewiththewynns.  They have a large coach and run their A/C off batteries.  They  have a LARGE bank of batteries (much money) and a LARGE solar panel assembly (much more money) but they tell you how they did it.  It is worth watching.  They also mention a "soft start" system for their A/C so you don't damage the equipment.

Gary RV_Wizard

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Re: How much AC in a class A and spray foam?
« Reply #4 on: July 25, 2017, 10:19:20 AM »
gonewiththewynns near always has sound practical advice. They also cover RV solar and AC on their website - see http://www.gonewiththewynns.com/off-grid-solar-rv-air-conditioning
Gary
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Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

RedandSilver

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Re: How much AC in a class A and spray foam?
« Reply #5 on: July 25, 2017, 10:58:09 AM »

If anyone has a route to suggest, let me know.


Yes buy a different coach.

MOST people will tell you a coach with no slides is not as nice as a coach with slides.

Running AC and Solar in the same sentence should be avoided.


AC running off of Solar will disappoint you even after spending big bucks on batteries and the like.

Trying to re-insulate a coach is more than likely going to give you a very very small amount of benefit vs. all the work to do it.

You would gain more benefit from parking under trees then doing a lot of work and still being too hot.
2002 Rexhall Rose Air  Cummins 8.3  350hp

 

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