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2021 Promaster 136 HR (if I can actually buy one)
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I was thinking you were really about to be dissappointed until I got to the last part of your post. My experience with my well insulated van is that the 5000 BTU air conditioner can just barely handle it when the temperature is 100 degrees and 70-80% humidity when I am parked in partial sun.

The solar load is very important here. In theory you can insulate really well, but if you are parked in the sun that is a significant additional thermal load that has to be accounted for. White vans are better for this, but they all have metal heat conducting ribs. I have added some additional insulation in some critical areas since my last test, but the van will never be perfectly insulated. I have r10 in a lot of areas, but I still have the cab area with windows (which if not covered is basiacally a greenhouse capturing heat).
Absolutely right. I've been really surprised to see many builders meticulously insulating their walls, floor, and ceiling and then leave the cab essentially uninsulated and expect to manage their heat gain with fans. Here's a little understood fact about R values. Equal square footage of R-1 and R-10 give you a blended R value of 1.8. That's because what you average are the U-values. So U of 1 and U of .1 average to 1.1/2 = .55 with and R-value of 1/.55 or 1.8. AND, then if you let solar rays actually enter the van, you have to deal with radiant heat from the sun. What you have to do is isolate your temperature controlled area and surround it with ambient temperature air using fans and then insulate to a high level like R-9. Very few people are doing this. In your case, if it's possible, you might want to first use windshield heat deflectors, then run a fan in the cab to exhaust the super hot air, and then a thermal curtain between the cab and your well-insulated areas. I would bet your experience will improve with that.
 

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The best bang for the buck I’ve ever found to reduce air conditioning load during day is to cover windshield and front windows on the outside. I’m not willing to curtain off the cab area routinely during day because vans are too small already, and at night it’s not as critical for A/C. I’ve used a cab curtain a few times mostly at night in winter to sleep, but only once during day in summer to air condition when we left our dog in van. I prefer the extra visual space/room over cooler temperature.
 

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2018 3500 EXT Camper Conversion in CT (TX for now due to Covid)
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In your case, if it's possible, you might want to first use windshield heat deflectors, then run a fan in the cab to exhaust the super hot air, and then a thermal curtain between the cab and your well-insulated areas. I would bet your experience will improve with that.
I was saying in general. I already cover my windows from the inside, plus where the test was conducted the sun was not on my windows directly. I have a pull down shade between the cab and rear as well. If I was really attempting to use the air conditioner during the heat of the day, I would defintely cover them from the outside.

The test was conducted mostly for the benefit of everyone here to show a 5000 BTU air conditioner can work, even during the day in the Texas heat. I don't spend days inside the van. I have no problem sitting outside the van with a cold beer when its 100 degrees (although I will do it in the shade). I use my air conditioner in the evenings only under normal circumstances. (but I understand other people have comfort or health issues).
 

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2021, Promaster 159 HR 2500, Silver
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Discussion Starter #44
I truly appreciate all of the great information. It is very clear that you all are very knowledgeable and I am studying all of the posts to try to come up with a solution. For now the solution is not to sell the house until I can make sure I have an alternate solution (teleworking from Alaska, a place to plug in and charge overnight, or a bazillion amp hour batteries).

The weather has actually been too cold for me to even get started insulating since some of the initial steps require adhesives. But with the 3 day weekend I may have to plug in a heater out there and get going.
 

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2021, Promaster 159 HR 2500, Silver
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Discussion Starter #45
The air conditioning unit that you linked to is a single-hose exhaust model. That means that it draws outside air into the van, cools down the air in the van, and then exhausts hot air out. Unfortunately, because it continually draws in hot air from outside, this technology has very low energy efficiency. Also,, it's rated at 7.6 BTU/watt, which is a very poor efficiency to start with. If you use a dual-hose model of a portable air conditioner you can get an efficiency of up to 12 BTU/watt, which is similar to what the best roof-top air conditioners offer. The best window air conditioner for efficiency is the Midea U, which is rated at 15 BTU/watt, just about double what the TOSOT is going to give you best case.

Insulation of your van needs to have a very good blended R-value for air conditioning on battery to be feasible. This is actually pretty hard to achieve unless you create a closed-off area in the van that is insulated from the front cabin area. So let's start by thinking of creating a box within the van and insulating it to R-9 or better. Then air condition and ventilate that space. Here's the math: a 6x6x10 foot box has 312 square feet of surface area. R-9 translates to a U-value of .1111. So BTU/hr per degree F will be 312 x .1111 or about 35 BTU/hr per degree of temperature difference between the inside and outside. If it's 100 outside and you want it 70 inside that is 30 degrees of difference, so 30 x 35 = 1,050 BTU/hr. And then if your air conditioner has an efficiency of 10, that would be 105 watts. So you can cool that space with nothing in it for 12 hours using 1,250 watt hours of electricity.

That is before you ventilate it, which could add as follows: 20 CFM x 1.08 x 30 degrees = 648 BTU/hr. Again, with an efficiency of 10 that is 64.8 watts, and then for 12 hours that is 778 watt hours.

Then if you have two people (or the equivalent) in that space, they will generate about another 682 BTU/hr of hear. At an air conditioner efficiency of 10 that is 68.2 watts, and over 12 hours that is 818 watt hours

So, total is 1,250 + 778 + 818 = 2,846 watt hours by the end of 12 hours. This is a bit of a back-of-an-envelope level as the temperature varies throughout the day, and we have not factored in humidity, but it's going to be in the right ballpark for your planning.

Most vans do not really create a controlled environment. You will have to be obsessive about this to use an AC on battery.

My quick thought on your build plan: Solar needs to be at least 660 watts for it to make much difference. Lithium batteries need to be at least 4,000 watt hours and topped up every night. Insulation should be at R-9 for a space of no more than 312 cubic feet. Air conditioner should have an efficiency of at least 10 BTU/watt.

A Honda 2200 generator at 1,800 watts should top up your batteries in 3 hours of run time on about one gallon of gas. This is assuming that you only air condition for 12 hours per day. Plan on maybe $100 per month to run the generator, but less if the weather isn't bad.

I've been working on the possibilities of running an air conditioner on batteries. It's fairly daunting but not impossible. Very, very few van builds include a truly controlled environment and consequently the effective R-Value will be closer to 4, and the square footage will be closer to 500. In that situation 500 square feet x .25 (U-value) gives a cooling load of 125 BTU/hr per degree of temperature, which is about 3,750 BTU/hr just to deal with the space cooling when it gets to be 100 out, so the totals almost double and then it starts to seem ridiculous.
jkmann,

Thanks for the math! I've had several semesters of college physics (and calculus) but it was a long time ago! Your post has been the most helpful in figuring out logistics. The air conditioner you mentioned seems to be a window unit. Do you think there are any portable dual hose models that would be equivalent?
 
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