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Author Topic: Rooftop AC  (Read 3182 times)
robertglines1
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« Reply #15 on: May 18, 2011, 07:49:51 PM »

My first coach I built before I was a member here. With very little guidance. A mic 8 with little more than stock insulation. Two 13,500 btu roof top ac were marginal at best. That was 3 conversions ago. Would go with 15,000 heat pumps if budget allows with smaller in bedroom area which should be easiest  to heat being smallest area. Box heaters make good back ups when it gets to cool and power is free. Propane furnace?. If you go with bigger and one lays down you may just get by with one less without terminating your trip. Or driving home in your underware Shocked  Bob PS Just looked at your profile and saw you in northern Michigan. I realize your summers are short but even if you come the 500 mile south to Southern Indiana we get about 4 months of hot miserable humid weather.Just a comment for future travel considerations'
« Last Edit: May 18, 2011, 08:18:05 PM by robertglines1 » Logged

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« Reply #16 on: May 18, 2011, 07:53:09 PM »

Heater quit on me once and I had to dig out the longjohns Bob!!!
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« Reply #17 on: May 18, 2011, 10:28:34 PM »

Dometic Penguins.  Everything breaks and they are more reliable than the others. (OR?)

Go with HEAT PUMPS.

Avoid the heat strips.

Forget that bubble wrap.  R factor is the only way to eval insulation.  The rest is smoke and mirrors OR it performs well in a particular situation.  Now if that is you situation you might consider it as augmentation. R FACTOR.

The spray foam is the most insulation for your thickness you can buy.  It used to be cheaper than anything else in total.  The guys that spray it usually have tools and energy to go through the bus after applying the foam and level everything for you.  might cost beer and then it might cost?  Putting up the fir strips is a superb idea.  Foam also quiets the interior to the extreme.  Some have said they can no longer tell if the engine is running by listening.  Makes the shell stronger....but who knows what that is worth.  You should add a layer to the top of the bays to get a R10 boost for the floor.   You can make this a thermos bottle.  Make sure you are getting the correct type foam. 

Seal up every friggen crack and hole in the front....wire chases....screw holes....everything.  That is another benefit for the foam as it seals up the walls and roof for air penetrations.

Be anal with this part of the conversion.  What you accomplish now will determine your comfort for many years to come and many miles as well.

Incorporate a propane furnace into your design.  Maybe not install it yet but plan for it.  Redundancy and backup.  You will find yourself in the winter hooked to a 30 amp pole and if you are electric heated you have a problem.  All around, propane is the best heat you can do for the money.  heat pump if power is available.

Double pane glass that is the heat and uv rejection.

Two thermostat controlled roof exhaust fans.

Good luck,


John
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« Reply #18 on: May 19, 2011, 02:42:26 AM »

I dont know.... the aluminum foil stuff "might" not work so good in cold weather, I just dont know. But I do know it worked great out here on a real hot day and that is saying a LOT
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TedsBUSted
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« Reply #19 on: May 19, 2011, 03:10:30 AM »

. . .Forget that bubble wrap.  R factor is the only way to eval insulation.  The rest is smoke and mirrors OR it performs well in a particular situation.  Now if that is you situation you might consider it as augmentation. R FACTOR. . . .

I installed some common home-center reflective  "bubble wrap" in an antique car that previously had been like riding in a hot-house and snare drum all in one. Installing just one layer of the insulation on the floor, cowl, and above the headliner  made a terrific improvement. Noise level dropped to modern car standards and the previous high level of heat radiating to the car's interior dropped to an acceptable level.

True, it's probably difficult to scientifically evaluate where it will work and how well, but "bubble wrap" definitely has merit.

Ted
« Last Edit: May 19, 2011, 03:17:35 AM by TedsBUSted » Logged

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« Reply #20 on: May 19, 2011, 04:50:46 AM »

Just for fun, R-Value is measurement of the thermal conductance of a material.  Spray foam is probably one of the greatest at slowing thermal conductance.  Plus the advantages of being an excellent sound deadner.  However, the advantages of bubble/foil/bubble can't be dismissed.  Here in the Grand ol' USA we don't consider radiant energy as much as we should.  Radiant energy can easily be reflected by aluminum foil or other such products.  However, aluminum foil by itself conducts heat energy very quickly.  Hence, the use of the bubbles on each side of the aluminum.  The bubbles only prevent the aluminum from conducting heat directly by contact transfer.  So, the products doesn't even attempt to get involved in the R-Value argument, but to simply reflect heat energy. 
As a side note, heat energy can be reflected in both directions.  In other words, it can keep heat out by reflecting the radiant energy from the outside, or keep heat in by reflecting the radiant energy from the inside. 
I wouldn't use the bubble/foil/bubble by itself.  We need the R-Value of some other kind of insulation, but I wouldn't try to cool any tin box without it either.

Thanks so much for all the input of the air conditioners.  That's exactly what I needed to hear. 
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« Reply #21 on: May 19, 2011, 06:52:27 AM »

This winter, I tracked my energy costs running electric heaters IN FLORIDA, and using a heat pump.   There are a lot of factors. 

In general, no large electric draws, just house refrigerator, pumps, and battery charging   $3/day.

All the general uses plus heat pump above about 40 degrees   $5/day

All general using resistant electric heaters 50-20 degrees  $6-10/day

This last winter sold me on the use of heat pumps.

Ed Roelle
Flint, MI/Williston, FL
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JohnEd
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« Reply #22 on: May 19, 2011, 08:37:15 AM »

Just for fun, R-Value is measurement of the thermal conductance of a material.  Spray foam is probably one of the greatest at slowing thermal conductance.  Plus the advantages of being an excellent sound deadner.  However, the advantages of bubble/foil/bubble can't be dismissed.  Here in the Grand ol' USA we don't consider radiant energy as much as we should.  Radiant energy can easily be reflected by aluminum foil or other such products.  However, aluminum foil by itself conducts heat energy very quickly.  Hence, the use of the bubbles on each side of the aluminum.  The bubbles only prevent the aluminum from conducting heat directly by contact transfer.  So, the products doesn't even attempt to get involved in the R-Value argument, but to simply reflect heat energy. 
As a side note, heat energy can be reflected in both directions.  In other words, it can keep heat out by reflecting the radiant energy from the outside, or keep heat in by reflecting the radiant energy from the inside. 
I wouldn't use the bubble/foil/bubble by itself.  We need the R-Value of some other kind of insulation, but I wouldn't try to cool any tin box without it either.

Thanks so much for all the input of the air conditioners.  That's exactly what I needed to hear. 

T,

You have pretty much summed this argument "for and against" up into its salient points.  And did it well.  Search on this subject and you will re-read your words over and over.  You get the nod of the wisdom of this collection of true experts and experienced Knuts.  I am only repeating them, in part, as well in my comments.  Nothing new here.

Continuing, and not contradicting a single word, consider a common tarp as an insulator.  It has not a single digit of insulating R value.  String it up across the bus on a 80 degree day and the bus will go from sweltering to comfortable due to the bus now being parked in the shade.  That tarp would be the greatest payback on performance for the buck we could make. For sunlight heat rejection alone.  Not practical to "carry" our shade so its out and further more it won't do a single thing to help us out when we are dealing with "cold".  Seeking a spot on the north side of a tree or building while in the 110 degree Phoenix sun is a no brainer.  Along those lines is color: white is the best performing and, like shade, it has incredible heat reflectivity.  A pure white roof is essential to efficient cooling in direct sun and, here again, does nothing for heating. 

Were you to install two inches of foam around you in the perfect bus, one where only the skin was a consideration for heat loss /rejection, I don't think you could find the improvement that bubble or even white roofs would contribute.  You could paint your roof black and sit in the sun and three ac units would do fine.  As a previous post noted, ac costs were $10 a day in very cold weather so the message there is do every thing you can at the construction phase as energy costs are an ongoing thing and investment in insulation gives you the biggest bang for the buck. And like the Energizer Bunny, it just keeps on keeping on.    And, like luggage, it lasts forever.

For me its awnings on every window for the max shade I can carry with me.  White roof coating of the highest grade automotive paint I can find.  2 inches of foam in the walls and 4 + inches in the ceiling and floor and reflecting metallic interior surface to the insulation or bubble wrap, double pane reflecting glass in all windows.  All the insulation in the world won't overcome significant air permeation any more than you can compensate for an open door or window.  Every improvement adds something....all of it does.  You just have to decide where you are going to put your money and sweat.

Don't think for a moment I am talking down to you or anyone.  Have to consider the education and experience of all the readers in an answer.  If you can.

Thank you for bringing this up again.  There is an obvious need to rehash the subject periodically.  Notice the posters have a short history.  There must be 20 people here that have more experience with this topic than I and have credentials.  They fatigue of the exercise, understandably, but given the history of the topic and the knowledgeable new Knuts that keep bring it up....it needs to be aired
 periodically.

John
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Seville
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« Reply #23 on: May 19, 2011, 10:12:29 AM »

JohnEd,
Very well said. I am one of those new bus knuts that wants to talk about this subject.
For example, when I started my conversion I was not aware of this forum.
I had no knowledge of foam insulation. I would have gone that route had I known.
Instead, I used Rollboard on the floor, walls and cieling.
Im happy with the results but I would have prefered foam insulation.
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« Reply #24 on: May 19, 2011, 11:32:39 AM »

It is to bad Carrier left the market they made the best roof top of any of the brands IMO

good luck
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« Reply #25 on: May 19, 2011, 05:13:56 PM »

We used one layer of Lowes 1/2" foil backed styro over the sprayed in foam-worked great. Take one of those foil backed panels in the sun and reflect the sunlight at you-you'll feel the heat!
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JohnEd
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« Reply #26 on: May 19, 2011, 07:57:43 PM »

JohnEd,
Very well said. I am one of those new bus knuts that wants to talk about this subject.
For example, when I started my conversion I was not aware of this forum.
I had no knowledge of foam insulation. I would have gone that route had I known.
Instead, I used Rollboard on the floor, walls and cieling.
Im happy with the results but I would have prefered foam insulation.

Seville,

It is always a secret dread that I will disappoint someone for whom these opinions and advice are OBE.  There have been precious few that posted here that didn't show a similar concern.  Mine doesn't show all that much to most.  Thank you for your sensitive and encouraging comments.

Your friend,


John 
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"An uneducated vote is a treasonous act more damaging than any treachery of the battlefield.
The price of apathy towards public affairs is to be ruled by evil men." Plato
“We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light.”
—Pla
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« Reply #27 on: May 19, 2011, 09:22:12 PM »

JohnEd,
You very welcome sir.
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