BradKW said:
Even a specially designed for off-grid, soft-starting DC mini split at it's lowest setting still draws 500 watts...and I believe the thing costs about $2000. It's actually pretty sweet and I'd buy it if money was no issue, but paid under $200 for my window unit.
Hot Spot DC Mini Split
While that unit is good, it is not the most efficient mini-split unit available. This one is:
http://www.geinnovations.net/HSAC_Productline.html
Yep, it costs around $2k but only draws 560 watts to produce 12,000 BTUs of cooling. But since the rotary compressor is scalable, (it slows down drawing less power after your space is cool) when you only need 5,000 BTUs of cooling (like a small window unit produces) it draws less than 300 watts. Plus that 440 watt 110v a/c powered window unit needs a 1,000 watt PSW inverter to power it. At best they are 90% efficient (in the $300+ range) the cheaper inverters (in the $150 range - 50% more than your window unit) are around 85% efficient meaning you will be drawing about 520 watts from your battery bank.
If on a budget, the window AC and an inverter is the way to go for only $250 vs $2,000. But that is only part of the cost. You will need about 8 GC-2 golf cart batteries to power the referenced HSAC-12C/C overnight (if that is your goal) at a minimum cost (from Sams) of $85 x 8 = $680 (plus the core charge if applicable for a total of about $800 + tax. Then you need to calculate your charging requirements for both. If using solar, here's a good chart:
http://www.geinnovations.net/solar_panels_required.html . Remember you will need enough solar to both power the AC by day and recharge your batteries for running all night too. Then you need to consider oversizing them a little to account for cloud cover. So according to the chart you would need about 950 watts of solar to run the referenced HSAC-12C/C for 8hrs at night (assuming 5 hrs of sunlight). You would need more than this for your small window AC.
However if you only need to run your AC for a few hours in the peak of the afternoon heat and a few hrs at night to cool things off inside, then you can reduce your battery and solar requirements by half.
I'm planning on full-timing in a Class A in a couple years when I retire and spending most of my time off the grid in warmer climes, so I'm planning on installing a system like I described for cooling off the bedroom at night. With about 1,500 watts of solar I could run it day and night, partially cooling the RV during the day, (as much as its 12,000 BTU output can do), as long as the ambient temp doesn't go north of 85 degrees. I'm planning on 1,740 watts of solar - four 435 watt Sun Power E-20 panels, providing plenty of power for my other needs too. We can always huddle in the bedroom with the door closed to cool off when needed, moving to higher elevations seasonally, as Class A's burn much more fuel moving than an economical van that many of you use. I also can use my RVs onboard generator to run my other AC during peak daytime heat and recharge my batteries when faced with several days in a row of nasty weather. True a system like this will be expensive (I'm budgeting around $5k), but it should easily pay for itself in under 2 years in campground fees and electricity costs. $300/month avg. in a campground (If one could accomplish such a feat) is $3,600/yr, plus another $100/mo avg. in electricity usage means my solar ac system would save $4,800/yr paying for itself very quickly. If the batteries only last around 3 years (my biggest recurring expense) then they would average only about $20/month, and that's easy enough to budget for, even when living off of my DW and my modest social security checks.
Another thing to consider is that the high-efficiency mini-split referenced is also a heat pump, sparing propane use in cool weather (I don't plan on going where it freezes, as I'm used to Louisiana weather) saving not only the cost of propane but reducing the trips into town to replenish my supply.
Food for thought.
Chip
