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Old 08-09-2017, 10:39 AM   #1
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Building for Nevada temps. Effort/Investment vs Return on roof insulation

I'm approaching these stages and really questioning how much energy/effort/investment really provides a solid return, when it comes to creating comfort in summer/sun/desert like atmosphere.

The simple question is:

Would you rather have a typically insulated bus in shade, or would you rather have a foam sprayed, roof insulation painted bus in the sun?

Seems to me, in desert like climate, shade is the most effective form of staying cool. So, this means solar radiation through the windows and heating the outer skin of the bus. The bus only has 2 or so inches of roof insulation, and shy of paying for NASA like insulation tech, how much R value can you really get for your money. Seems to me, shade is the better investment.

I am building a lightweight roofdeck that will shield 35% of the roof toward the rear, then solar will cover much of the rest. Solar emits heat, but angled and shades the roof. I have a shade system which will swing upward/outward to shield the windows from sun.

My point is, investing in "shade" (roofdeck, swing up shades), then insulating with pink foam seems the "best compromise" approach, in tandem with a pair of 12k btu mini splits.


This is my theory...if you have experience and HVAC expertise, feel free to tell me how wrong I am, just also tell me why, so I can then agree and change course!
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Old 08-09-2017, 12:07 PM   #2
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I would think that would be a good set up. May be throw another inch of aluminum foam board on top of the bus.

Are you traveling with your set up or stationary?

Desert is dry , depending on water source you could go swamp cooler.

I think most of it depends on your requirement. Do you want to be 74 and couped up inside like most apartment dwellers or do you want to live with nature and just take the edge off?

later J
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Old 08-09-2017, 12:21 PM   #3
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PV panels do not emit heat! They don't get warm as they work. They do however need air to circulate underneath them to prevent them from getting too hot in the sun - heat derates their performance, so folk in Alaska in the winter can sometimes get more output than folk in the normally sunny warmer states.

I built a walkway between my two roof hatches from which the panels are hinged. When down against the roof there is several inches of airgap under them, and air can freely circulate there to keep them as cool as possible. Where the panels and walkway cover the roof I can feel the difference in ceiling temperature compared to where the sun hits the roof. Anything you can do the reduce heatload into the roof will be worthwhile.

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Old 08-09-2017, 12:27 PM   #4
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Well I am in Alabama in August, and the sun is really the least of my problems as I have really shady parking. I am only exposed for about 2 hours per day and my bus stays 2deg cooler than ambient with fan on. I was worried I would need to add air conditioning, but in direct sunlight my factory insulated bus would require 6-8 hours of cooling everyday.

IMO put as much effort into avoiding exposure as you would insulation - the return has to be equal or better?
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Old 08-09-2017, 12:37 PM   #5
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dredman, what causes the temperature drop from ambient. I thought that temp is measured in the shade?

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Old 08-09-2017, 12:44 PM   #6
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Quote:
Originally Posted by joeblack5 View Post
dredman, what causes the temperature drop from ambient. I thought that temp is measured in the shade?

later j
the only guesses I have are difference in probes, or sunlight hitting outside probe. If I turn off the fan during exposure it goes from -2 to +2 inside

Guess I need to do some testing with the probes?
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Old 08-09-2017, 12:51 PM   #7
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shade shade shade.. its common in ohio to have days with alot of sun and then the clouds roll in later.. I can stand inside my carpenter bus and feel within a couple miniutes the ceiling temperature drop a LOT or rise alot as the sun goes in and out of the clouds..
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Old 08-09-2017, 05:00 PM   #8
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Quote:
Originally Posted by Iceni John View Post
PV panels do not emit heat! They don't get warm as they work. They do however need air to circulate underneath them to prevent them from getting too hot in the sun - heat derates their performance, so folk in Alaska in the winter can sometimes get more output than folk in the normally sunny warmer states.

I built a walkway between my two roof hatches from which the panels are hinged. When down against the roof there is several inches of airgap under them, and air can freely circulate there to keep them as cool as possible. Where the panels and walkway cover the roof I can feel the difference in ceiling temperature compared to where the sun hits the roof. Anything you can do the reduce heatload into the roof will be worthwhile.

John
Good to know the heat isn't substantial beneath them, I've read some conflicting info.

The setup you describe is pretty much dead on to what I want going toward. Just keep air moving beneath them, then use them as shade for the roof. In NV, I believe the angle is minimal for peak sun time, like 7 degrees or less.


Another good question to ponder, was stated above. Do you want it to be 74 or do you want the edge off? In honesty, I think about 76-77 ac-only is my target, or at least close to it.

I recall seeing a very "green" structure in Arizona that started as a container. They used slats of metal that from the side couldn't be seen, but that kept the sun from hitting the walls of the structure at any point. Air circulation is a big part of it also, as not allowing trapped heat at the ceiling to escape sometimes worsens the issue.

I think the point of my post, is I am trying to decide how far I take insulating the roof. I am pulling down the panels as we speak, and I'm just trying to figure how far to take it without blowing budget. In reality I can see spending 400.00 at running at 80 degrees, versus spending 1200.00 on insulation and being at 79 degrees...lol.

I have built some structures in the past, and my findings were that if you only have a thin section in a roof for insulation, you're only going to get so far, and throwing money at the problem generally won't solve it.
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Old 08-09-2017, 06:06 PM   #9
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I'll be watching this. I've been thinking about shades and multiple awnings as well.
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Old 08-09-2017, 09:22 PM   #10
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"My point is, investing in "shade" (roofdeck, swing up shades), then insulating with pink foam seems the "best compromise" approach, in tandem with a pair of 12k btu mini splits.
LMAO. Why worry about shade when you have two 12 k btu mini splits?

Just kidding. Shade does help a great deal. I talkled with a couple of Anza Borrego Desert State Park rangers who live in state provided trailers supplied with "ramada" type covers. They say the difference in temp in their abodes is tremendous with the shade as opposed to those without. Jack
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