Unreasonable air conditioner plan?

[B and C]

You also have to remember that you have to charge the batteries the next day.

 

[XERTYX]

True. But I think the last proposal was to scale up to 1800 watts of solar. The surge on the air conditioner was 900 watts last they reported it. Maybe still doable. Idk. They have it running until 9pm I think they said to get an average of the watt hours.

 

[VanFan]

The air conditioner is at the rear, mounted below the fan, the front sticks though a cut out in the moving blankets...

Another question?  Assuming the entire unit is inside, is the condensate drained into a bucket?  (I don't mean to hijack this thread, but am very interested in the concept of "zoning".)

 

[mjbeam64]

I haven't had to deal with any condensation yet. If it becomes a problem there are a few factory holes through the floor in the back with rubber caps on them that I could run a drain line through. I have an Econoline (E-250) van.

 

[VanFan]

I haven't had to deal with any condensation yet.

Thank you.  You have encouraged me to experiment a bit more with some of my "unreasonable air conditioner plans."  Stay cool .

 

[Malamute]

Okay, I just reset the wattsup with the unit until 2100 tonight as we have grid power in our plave.  I have the a/c set at "eco"and 75F.  I'll report my results  when I have them.

Unfortunately,  my son would not be willing to live with a smaller unit.  Especially when Mumsy comes to visit and she can't tolerate such high temperatures....that would mean I couldn't ever visit him in the Summer during the day.
Ted

 How big is the cabin? Any construction details or type you can share?

 Why is he fixed on a 12kbtu unit?

I have a 6k btu window AC in my 14x18 log cabin. It has a dark green metal roof, moderately well insulated roof with live ventilation, and 8-10" log walls, which act as a heat sink, radiating heat in through the night that they absorbed in the daytime. I run the AC 24/7 when its warm out and it stays very comfortable, to the point of feeling cold if Im not covered up at night. Summers often get in the 90s to 100 occasionally, with a 30-35 deg drop at night being common.

If I didnt have the heat sink issue with the log walls, i could probably turn the AC off at night and open windows. Thats my spring/fall routine anyway, when AC isnt really needed. If his cabin has decently insulated walls and roof, he probably wont need the AC 24/day like I do.

 

[highdesertranger]

if you have four 6v batteries and you want 24v you need to wire two pair in series and then in series again. so the ah rating stays the same 225ah's.

oopsy i see you guys already have it. carry on

highdesertranger

 

[WalkaboutTed]

Update:

It took exactly 3.25kw for the nine hours of air conditioning (on eco mode at 75F), so I figure, with the inverter inefficiency and more fudge, at least 500w an hour (with a 70w fan blowing on him). If he doesnt run the a/c at all after the sun sets, his system (1800w of panels, 225ah battery) should run it, am I right?

Malamute,
It's a 10' x 16' Tuffshed, the same size as ours, but his will have the barn roof ceiling, that's why he needs the higher powered a/c. Hubby and I were able to put in R35 insulation in our ceiling, and R13 in the walls. My son will only be able to put R13 in both his ceiling and his walls. It's not enough insulation for the desert of Southern New Mexico, but will have to do. So his usage will be greater than ours, but hopefully not too much more, since he likes the room temp 7-8 degrees higher than I do.

We spent the afternoon together and talked about the options. He likes to keep the a/c in the low eighties and is fine turning it off and opening the windows at dusk. He was planning to get a generator for running power tools and is open to using it if absolutely needed, though he is a hard-assed Marine and says "Mom, I spent a year sleeping on bricks on the ground in Iraq, I can stand a little discomfort". I told him that the discomfort in ignoring his battery health will be in his wallet. He promised that he would never run the air conditioner except on the timer, so as not to accidentally run the batteries down too low. I need to set up some kind of alarm/mechanism for low voltage, just in case.

So for now, we'll use the batteries we have, he'll get 1800w of panels with the two Victron 100/30 charge controllers. At least I have a baseline. Hopefully that will get him through the rest of the summer. If (when) he kills this first set of batteries, he'll put in a much bigger battery bank. But by then he will be settled into his new job and it won't break the bank too much.

Please, more comments/ suggestions are still welcome. Thank you,
Ted

 

[tx2sturgis]

Update:

It took exactly 3.25kw for the nine hours of air conditioning (on eco mode at 75F), so I figure, with the inverter inefficiency and more fudge, at least 500w an hour (with a 70w fan blowing on him). If he doesnt run the a/c at all after the sun sets, his system (1800w of panels, 225ah battery) should run it, am I right?

Making corrections so the math can work out:

3.25kwh (or 3250 wh) (added h) for the nine hours is in the ballpark of my previous guess as the range that A/C might use in a full day of operation...

Quoting myself in #10 above:  

If it is pulling 900 watts for 10 hours....nope. But if the duty cycle is say, 30%, that's like 300 watts for 10 hours...much more likely to work well.

300 watts pulled for 10 hours would be, 3.0 kwh (or 3000 wh). Close to your results, at 3.25 kwh (or 3250 wh).

So now we are in the ballpark. Again, adding inverter inefficiencies, yeah, maybe 500 watts draw. It may not be that bad in actual use. 

At any rate, an 1800 watt solar array will not put out 1800 watts continuous all day unless it is actively tracking the sun...so we have to de-rate the system...by how much? Well, a lot of factors are involved, (panel angle, controller efficiency, ambient heat loads, dust on the panels, wire sizes, battery state of charge, other loads, etc) but if the panels are on a ground mount, with airflow, and tilted at about the right angle, and are not moved all day long as he is asleep, lets put a 'best guess' on this and say, 1000 watts AVERAGED continuous output for the day. 

Some controllers will track the kwh produced, yours may or may not have that function.

But with an assumed and AVERAGED output of 1000 watts, and a known AVERAGED draw of about 500 watts, then I think you are gonna be able to power that A/C unit during daylight hours....but there might not be much surplus on cloudy and hot days...

Anyway, let us know how it works out.

 

[Malamute]

Malamute,
It's a 10' x 16' Tuffshed, the same size as ours, but his will have the barn roof ceiling,  that's why he needs the higher powered a/c.  Hubby and I were able to put in R35 insulation in our ceiling, and R13 in the walls. My son will only be able to put R13 in both his ceiling and his walls. It's not enough insulation for the desert of Southern New Mexico,  but will have to do. So his usage will be greater than ours, but hopefully not too much more, since he likes the room temp 7-8 degrees higher than I do.

 Is that due to the thickness of the ceiling and using fiberglass batt insulation?

 Ive used foam board insulation where space was limited, he could also add depth to the bottom of the existing roof rafters/framing. Foam boards have higher R value, theres various levels of R values in differing types. Cheapest being white styrofoam, like cheap coolers, to various types in different colors etc. 

 Getting some ventilation in the roof may help also for heat. Ive added small wood strips as spacers to the edges of the rafters, then put in foam board insulation, the space allowing ventilation from the eaves to the ridge, which was vented (can be done retroactively).

 Just some thoughts, its not required to simply live with small rafters and not much R value for the roof/ceiling.

 

[bullfrog]

Don’t over look the value of shade and roof coatings. Even if solar is mounted on the roof raising the panels several inches will allow them to work better and keep the roof cooler. A trellis or sun screened porch on the south east side will keep morning sun off those walls making it stay cooler inside.