Looks like the truck may be ready tomorrow and not today. Oh well. Been spending lots of time thinking about insulation values. My generator can't power my air conditioner after all, at least reliably. But perhaps it's a bigger air conditioner than I need...
My initial living space plan is to insulate and seal off the bedroom portion of my trailer. And spin it around so the door is facing north, not south. I've been using a figure of an 8 foot cube, so 64 square feet of living space. Viewing video footage of it, I'm not sure if the space is even that. Most likely, a hair under 7' ceiling, slightly less than 8' width, and maybe 7' in length. Smaller than I'd like but it's a start. Unfortunately in one perspective, not small enough that I can order less material without planning to cobble it together. I've been expecting 4x8 foot sheets of insulation foam board and plywood to work with.
I've had an inner debate about buying R5 1" foam board or R10 2" foam board. $20 vs $30 a sheet. I'll need 12 sheets, same goes for the plywood. I was wondering about if I really need the R10 or not. A basic answer is kind of obvious, the R10 is twice as insulating as the R5.
To try an put things into perspective, the smallest A/C units I've seen are rated at 5,000 BTU. They say they are good for 100-150 square feet. I was curious about what kind of thermal losses my structure would have as even 2x4 stud walls seem to have R19 insulation in them and at first glance I am clearly using less insulation. Now since the size of the space is smaller, less insulation shouldn't be as big if an issue.
Anyway, I found what looks to be a decent calculator for R values corresponding to BTU: http://www.calculateforfree.com/insulation.html
So I plug in the numbers. 64 square feet, R5. Looks like only gaining or losing 300 BTUs per hour. Wow! Something seems off...
The space's volume doesn't matter, it's the area. And not just the living space square footage which is what I put in. The whole exterior area. So this is 64 square feet times 6 for all of the sides, 384 square feet even if I only have 64 square feet to put my feet on. That bumps up to 1,920 BTUs per hour. Still seems well within the capacity of a very small window unit.
Of course, that's assuming a tightly sealed space with no doors or windows. Most doors are R2-3. Most windows are R1-2. 6 square feet of R2 window accounts for 75 BTUs an hour. Not terrible, but I can see why showrooms with whole glass walls get so hot in the summer.
Another thing to account for is that all of your electronics inside will produce some kind of heat. And you produce heat as well, something like 300 BTU/hour/person.
A pretty fair compromise might be to use extra insulation on the south wall, the floor, and the ceiling. Thinking this through now, it's obvious why I was so cold back in December -- the vent had come off and I only could have it partially covered up top. I was losing most of my heat to that vent.
It now makes perfect sense why RVs are often so poorly insulated. They have such small spaces to install the insulation at all. And when you have an RV with probably 12 single pane windows in it, the little insulation value it has in the walls quickly gets drowned out. I believe most 28 foot RV trailers like mine have 13,000 BTU A/C units. Might normally be enough for 400-500 square feet. But in a 28x8=224 square foot trailer, it's barely enough.
Now realizing that if I build a properly insulated space (and not even all that properly), I really don't need my 9,000 BTU, 9 amp A/C unit. A 5,000 BTU unit is fine for me. This is great because finding a generator to run it is a whole lot easier.
Honda makes the EU2000i which sounds like a great generator. However, it seems to have a timing belt and a plastic camshaft of sorts. I'm sure they make it work well but I find the EU1000i a lot more appealing for having a timing gear, push rods, and what looks like a traditional steel camshaft. This will push 900 watts continously or 1,000 at peak from just a 50cc motor. It's very quiet and the fuel requirements are so low I'm betting I could power a minimum of electronics (maybe a laptop or two) and an A/C unit 24 hours a day and use at most 3 gallons of fuel, likely even 2 gallons. This should be $5-7 a day, so $150-210 for electricity effectively. Obviously it could be less but in the summer months that may be as bad as it gets and spring/fall could be $50 if you turn it off frequently.
Running that A/C unit off of an inverter is another possibility. Let's say we have a 200 amp hour 12V battery charged up during the day. At night we would be pulling about 5 amps at 120V for the A/C unit. This translates to 50 amps on the battery and more likely 60 amps given inverter losses. So it almost gets us through half the night, but not quite. If we get four of them I could see this working out quite well.
I'm also suspecting you could get away with fewer solar panels if being mindful of insulation and A/C units. I've generally thought solar to be a bit overpriced but 6 or 8 200 watt panels might do the trick. Possibly for $2,000-3,000 you could be sitting comfortably in your 8' cube and be air conditioned all year. Van Horn has a lot of sunshine hours per year so solar would likely be quite great.
Anyway, it seems like R10 could be overkill for me but it wouldn't be drastically overkill. So I may go with either the R5 or R10. I'm thinking drywall is a bad idea for this because I will be mounting the foam and then interior "wall" material to uneven surfaces. But my initial idea of 3/4" plywood may be overkill, perhaps 1/2" is quite fine since it's already in an existing structure. And maybe with the trailer spun around and having one door and one window facing north I can ignore most of that side. I suspect the ceiling and hallway walls to be the most critical initially.
Thanks for listening to me ramble. The good news is that I think this will translate into adequately comfortable structures. I can see a livable, self-contained shipping container being self-powered, insulated, and cooled for $10,000 or less at your property.