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Old 05-24-2018, 10:03 AM   #1
Mini-Skoolie
 
Join Date: Jun 2017
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Insulating the "cab" area

Hey all. I've been racking my brain on thermal calculations, and I thought I'd externalize my madness and include you.

After doing some math, I realized just how severe the heat transfer through the driver section will be, compared to my insulated walls and floors. Here are some numbers to give you an idea:
2.5" spray foam walls and ceiling: 22.5 watts/ deg C
3" rigid insulation floor: 6.8 watts/ deg C
9 double-pane RV windows: 16.4 watts/ deg C
Windshield, door and driver window: 34.8 watts/ deg C
Dash and driver floor: 67 watts/ deg C

This is for an 11 row front-engine flat-nose with an 18" roof raise. You can see my efforts to insulate in the list above. I am assuming the exterior surface is at ambient temp and I am excluding heat from solar radiation, because my roof will be shaded by decking/ solar panels. Also, for the dash area I assumed an R-value of around 0.5. With all that being said, it will take around 10,000 BTU to cool the interior ~25 deg F (I live in FL).

When you consider that mini-splits should be oversized by 150% to 200%, I'm looking at an 18k BTU system. No thanks, I think I can do better. Obviously, the point of focus is the cab area. Not much can be done about the windshield. I could install a new door, but I really want to keep the original. So my question to you all is:

What have you all done in an effort to insulate your dash areas??

Also, if anyone is interested in my thermal calcs (including solar radiation) I will be happy to share more detail.
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Old 05-24-2018, 10:14 AM   #2
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I have a push, but i removed tbs whole dash. Spray foam where i could, and plastic from the outside. There was a lot of wind coming in. It list heat quickly and made driving uncumfortable. It's a lot better, but it can always use improvements.
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Old 05-24-2018, 10:54 AM   #3
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I use a snap in partition to isolate the "cab" area in my little bus. It is made of the clear plastic used in convertible tops and has a zippered door way. I also have an old fashion roll up shade above the windshield that when lowered provides trapped air insulation as well as privacy. Not very sophisticated but it sure slows the heat loss. Jack
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Old 05-24-2018, 11:03 AM   #4
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A thermal curtain you can pull over the entire width behind the driver's seat, is a common solution.
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Old 05-24-2018, 11:07 AM   #5
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Quote:
Originally Posted by Twigg View Post
A thermal curtain you can pull over the entire width behind the driver's seat, is a common solution.
I like that idea and may use it myself.
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Old 05-24-2018, 11:11 AM   #6
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I like that idea and may use it myself.
A local seamstress should be able to sew one up for a reasonable price.

It's one area where I might have Reflectix sewn in, and you can get the top curved to fit the ceiling profile.

A couple of layers of cotton duck or light canvas, with Reflectix in the middle, should do a decent job.
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Old 05-24-2018, 11:50 AM   #7
Mini-Skoolie
 
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Thermal curtain is a great, easy to employ, solution. My only reservations with the curtain are that it will make the space feel smaller. The cab area may be unusable as living space, but it still lends to the impression of openness, as does being able to see out the windshield. Maybe I can add a window with the "convertible top window material mentioned by Jack. Hmm....
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Old 05-26-2018, 10:12 PM   #8
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I'm interested in the OP's thoughts since we're doing a reverse-layout (bedroom in front) build.

I plan to delete the front door, extend the floor over where the door stairwell was, turning the stairwell into under-storage. On top of that will be pink panther 1.5 inch firm insulation under plywood, with vinyl floor on top of that in the entire cab area. I'm going to also cover the existing metal walls with 1.5 inch insulation and wood walls, so the only original exposed surfaces will be the main window area...

I think I could get away with a thermal curtain over the windows only... thoughts?

Also, I'm keeping the original ceiling panels- my thermal imager showed the problem points to be where the ribs contact, so I may put something over the existing ceiling if I can afford the room.
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Old 05-27-2018, 08:21 AM   #9
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Kazetsukai, if your bedroom is going to utilize the front entryway, does that mean you are deleting the driver area? ...making the bus immobile? What config is your bus- FE, RE, dognose?

My personal outlook is there's no such thing as too much insulation, but I want to be able to climate control off-grid in extreme conditions. Windows are tricky, really the only option is to cover them when you need the insulation. Some people use curtains, others make removable inserts with rigid foam insulation. I'm going as far as to replace them all together with RV windows. The thorn in my heel is the dash, likely 80% of the insulation work for only 20% of the gain. That rule never fails...

The conditions are very variable bus to bus, and depending on your needs. My best advice is do some rough calcs and see where you stand. Calculate the heat transfer in watts for each section (roof, windows, metal walls, floor) and see where the most heat is being transfered. You can also sum the numbers for all surfaces and it will give you a good idea how much A/C or heat you will need.
Q = U * Area * delta T
Watts = (Watt / m2*degC) * (m2) * (degC)
where U = 1 / R and, delta T = difference between inside and outside temps.

Yes, that's the R-value advertised on so many insulation products. Keep in mind- many R-values are "per inch", thickness matters, and to convert American R-values to (W/m2*degC) divide by 5.678. For single pane glass- you can use an R-value of about 0.14 W/m2*degC.

There's also solar irradiation... that's a bitch. White roof paint goes a long way, as does anything you will mount on the roof with an air-gap underneath.
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Old 05-27-2018, 09:41 AM   #10
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Quote:
Originally Posted by paulnack View Post
Kazetsukai, if your bedroom is going to utilize the front entryway, does that mean you are deleting the driver area? ...making the bus immobile? What config is your bus- FE, RE, dognose?
RE flatnose. I'm deleting the door (sheet metal over it, framing under that, insulated with R13 fiberglass, maybe reflectix), the stairwell (covering it wth sheet metal level with the floor, 1.5 inch R7 firm insulation over that, then plywood + vinyl flooring).

Quote:
Originally Posted by paulnack View Post
Windows are tricky, really the only option is to cover them when you need the insulation.
I'm in the process of deleting all of the windows, I expect to finish putting the sheet metal over them today, then I'll frame and insulate over them (same R13 fiberglass as in the walls, maybe reflectix).

Quote:
Originally Posted by paulnack View Post
The thorn in my heel is the dash, likely 80% of the insulation work for only 20% of the gain. That rule never fails...
Really. I had to redo the internal coolant loop for the defroster (the original owner removed the heaters when he removed the seats- leaving not evne the defroster). On a side note, I had enough BTUs pumping out with the 3 replacement heaters I installed that even in 30 degree weather with no insulation on the walls, or windows, after about 40 minutes it would get uncomfortably warm. I'm guessing there's some overkill there... I might want to isolate that loop from the engine coolant loop with a heat exchanger for the warmer weather.
Anyway, it _looks_ fairly simple to frame over and insulate underneath/behind the dash... I'm going to be covering most of everthing though.

Quote:
Originally Posted by paulnack View Post
There's also solar irradiation... that's a bitch. White roof paint goes a long way, as does anything you will mount on the roof with an air-gap underneath.
I can speak to this... Installed Henry's tropicool (stole that from ROLL WITH IT) before it got cold last year- before the ceiling would get too hot to touch in the sun, now it is cool to the touch. Major difference.
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