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Old 10-27-2020, 09:53 AM   #71
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Originally Posted by Krbjmpr View Post
Do you have the ability to measure current in and current out? I use several 12 > 6 and then 6 > 12 converters to feed my electronics (router, BR burner, drives, anything with 12v wallwart). This allows me to switch to 6vdc LIFE for extended outrages. I also use 12 > 24 for my winega rd WC3000 booster. I am seeing about an 80%, rated draw, to 90%, light load. I don't have anything that could pad a converter with a 55/60w continuous draw.
Not sure I fully understand the question.

The headlights are a known wattage, and I sized the converts to be nearly twice the needed size to allow them to run cool. Doesn't really consume any extra power having the extra capacity as the headlights only draw what they draw.

The OEM wiring was actually done well, with a totally separate circuit for each of the four lamps. One circuit can go totally out without affecting the others.

Regarding DC appliances in the coach - if there are any capable of running on 12vdc, then I've already got them wired to do so directly. I have eliminated all of the wall warts possible, as they do nothing to add to efficiency.
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Old 01-24-2021, 06:10 PM   #72
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Very helpful read.

My heat & AC struggle so swapping out for Mini Splits is appealing.

Would not mind removing the propane as well
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Old 01-25-2021, 01:39 AM   #73
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QUESTION: How much difference will a higher SEER rating mean to me?

The goal is to be able to run the mini-splits as much as possible on SOLAR and LifeP04 batteries.

One vendor has a 9K BTU unit at 17 SEER, another at 22.8 SEER, another at 23 SEER, another at 25 SEER, and even one at 30.5 SEER.

I even found a 6K BTU unit at 33 SEER. (How many BTU's does a coach bedroom need anyway? (No slides, bedroom accessed by a side-hallway instead of an open bathroom plan)

And, while I am asking, how many BTU's does the front end of the coach need? No slides, 38' DP, adding 1/2" foam insulation to the walls, single-pane windows.

Thanks to everyone who has commented. Our remodeling plan is now much better for it.
Better late than never ...... didn't see this question until these many months later.

SEER is a seasonal energy efficiency rating meaning it tells you relatively how well the unit compares with others if it sits in one place and runs hard when hot and slows down when it's not so hot. So it runs slower before and after the hot summer afternoon and runs slower in the spring months and in the fall months. A full timer might use the system over many months making SEER the important number.

However, part timers or hikers might mostly use the mini split to cool down the RV after returning from a days outing. In that case it will run hard for a few hours (summer) or an hour or two (fall and spring) to cool down the RV. I.e., it won't spend much time loafing at low compressor and fan speed. In this case EER is a more relevant indicator of efficiency. EER is the efficiency under heavy load.

Comparing EER and SEER one finds that some mini splits get higher SEER from a modest EER and some get lower SEER from a higher EER. Best is high SEER and high EER, but that can get expensive.

One of the determinants of SEER is how low the compressor speed can go. Some mini splits can take the compressor throughput down to 30 or 40% of max throughput. I.e., a 9K unit that has a turndown ratio of 3 can only modulate down to 3K. If the cooling demand is less than 3K, the unit must cycle off. That reduces efficiency. Some units can get down to 25% throughput, so will go into cycling less often when cooling demand is low and thus will have a higher SEER relative to EER. The best unit I know of is the Gree 9K Saphire that has a SEER of 38 and has a six to one turndown ratio. It can still modulate at cooling loads down to 1.5K. It has a modest EER but a great SEER because of this. If one is going to have the mini split running lots of hours even if only a bit of cooling is necessary, it's a good unit. The compressor is a bit large and heavy though. The price is good.

For many of us, EER is probably the number to look at. Full timers that will use the mini split throughout the day and night should be looking at SEER.

As to how much cooling is needed, it seems there are a lot of happy mini split users with 9K units covering intermediate sized RVs. A bedroom surely won't need near 6K but mini splits don't come smaller so that one is going to cycle a lot especially since it will be used mostly at night when not so much cooling is needed.

Mini splits do have the losses of the copper lines between the indoor and outdoor units, but that's about 1% per four feet. That's far less than the duct losses in a ceiling unit. I'd say this explains why 9K mini splits seem to replace a 13,500 conventional ceiling unit with no problem.

IMHO.
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Old 02-21-2021, 08:23 PM   #74
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And, while I am asking, how many BTU's does the front end of the coach need? No slides, 38' DP, adding 1/2" foam insulation to the walls, single-pane windows.[/B]
This question bothered me since it was posted .... so I had to finally look into it. I generated a simple spreadsheet to calculate BTU/Hr requirements in an RV. I had to make some assumptions and educated guesses, but here's what I came up with for my 30' 5er.

Note that in this example I'm assuming 75F inside and 95F outside or 80F inside and 100F outside .... i.e., a 20 degree difference. See the notes. I believe the results are somewhat pessimistic.

The spreadsheet provides steady state heat flow into the RV from the ambient. I.e., if you come back from a hike and the RV is 90F inside, it's going to take a while to cool down. What you see below is "steady state" after cool-down.

I'd say this calculation pretty much confirms why folks do fine with a 9K mini split.

PM me if you'd like a copy of this spreadsheet so you can insert your own numbers.

Here's what it looks like .......

Click image for larger version

Name:	RV BTU Estimate.JPG
Views:	6
Size:	291.3 KB
ID:	318839
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Old 02-22-2021, 06:38 AM   #75
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Originally Posted by hclarkx View Post
This question bothered me since it was posted .... so I had to finally look into it. I generated a simple spreadsheet to calculate BTU/Hr requirements in an RV. I had to make some assumptions and educated guesses, but here's what I came up with for my 30' 5er.



Note that in this example I'm assuming 75F inside and 95F outside or 80F inside and 100F outside .... i.e., a 20 degree difference. See the notes. I believe the results are somewhat pessimistic.



The spreadsheet provides steady state heat flow into the RV from the ambient. I.e., if you come back from a hike and the RV is 90F inside, it's going to take a while to cool down. What you see below is "steady state" after cool-down.



I'd say this calculation pretty much confirms why folks do fine with a 9K mini split.



PM me if you'd like a copy of this spreadsheet so you can insert your own numbers.



Here's what it looks like .......



Attachment 318839
Where are the calculations for the greenhouse effect at the front? In my experience, there is interplay between windows/windshield that goes beyond how much thermal load there would be with the same amount of glass spread out over a long wall.
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Old 02-22-2021, 07:59 PM   #76
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Where are the calculations for the greenhouse effect at the front? In my experience, there is interplay between windows/windshield that goes beyond how much thermal load there would be with the same amount of glass spread out over a long wall.
See the "windshield" entry near the bottom. Increase it if you think it's too low. Not sure about the "interplay between windows/windshield" you mention. Seems both are exposed to the outside temperature and one or the other is hit with radiant heat from the sun (or both at 45 degrees). Note that I did double heat pickup along one wall assuming radiant from the sun on that wall.

Personally, I'd drape something across the windshield to slow heat gain there. Maybe some other windows as well. And foam inserts in ceiling vent fans.
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Old 02-22-2021, 08:08 PM   #77
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See the "windshield" entry near the bottom. Increase it if you think it's too low. Not sure about the "interplay between windows/windshield" you mention. Seems both are exposed to the outside temperature and one or the other is hit with radiant heat from the sun (or both at 45 degrees). Note that I did double heat pickup along one wall assuming radiant from the sun on that wall.

Personally, I'd drape something across the windshield to slow heat gain there. Maybe some other windows as well. And foam inserts in ceiling vent fans.
I guess what I was getting at is no matter how careful we all are about shielding our cab areas, they tend to pick up much more heat than expected.

When on the road this gets even worse as there is no way to block the sun from the windshield and front side windows while driving, so my question also related to this. If you're taking out the generator from a coach, unless you've got OTR a/c which can keep up you'll need to run one (or two) of the house units to keep the interior comfortable.

When all that glass up front gets sun shining through and bouncing between the two other windows up there it tends to magnify the heating effect, just like in a greenhouse. A straigthforward calculation based on the sq footage alone won't account for this.
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Old 02-23-2021, 12:29 AM   #78
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I guess what I was getting at is no matter how careful we all are about shielding our cab areas, they tend to pick up much more heat than expected.

When on the road this gets even worse as there is no way to block the sun from the windshield and front side windows while driving, so my question also related to this. If you're taking out the generator from a coach, unless you've got OTR a/c which can keep up you'll need to run one (or two) of the house units to keep the interior comfortable.

When all that glass up front gets sun shining through and bouncing between the two other windows up there it tends to magnify the heating effect, just like in a greenhouse. A straigthforward calculation based on the sq footage alone won't account for this.
Good points!! My calculation is for stationary operation. I should have mentioned that.

Driving is a whole other ball game. Sun as you mention, and a "force cooled" box. I.e., a convection cooled RV. Driving through 90+ F air is going to mean much more BTU/Hr coming into the RV than near still 90F outside air. A single mini split isn't going to hold 75 under that condition. Do "motor homes" have a condenser on the engine with automotive type A/C? If not, a larger mini split might be in order. My son's solution is a curtain that contains the mini split output to the forward area. And, surely that mini split run really hard ..... with possibly a second alternator helping keep the battery up.

My own unit is a 5er and the mini split will often run while driving, but we are in the truck with it's ample A/C.
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Old 02-23-2021, 05:44 AM   #79
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Good points!! My calculation is for stationary operation. I should have mentioned that.

Driving is a whole other ball game. Sun as you mention, and a "force cooled" box. I.e., a convection cooled RV. Driving through 90+ F air is going to mean much more BTU/Hr coming into the RV than near still 90F outside air. A single mini split isn't going to hold 75 under that condition. Do "motor homes" have a condenser on the engine with automotive type A/C? If not, a larger mini split might be in order. My son's solution is a curtain that contains the mini split output to the forward area. And, surely that mini split run really hard ..... with possibly a second alternator helping keep the battery up.

My own unit is a 5er and the mini split will often run while driving, but we are in the truck with it's ample A/C.
Some motor homes do have an engine powered compressor for dash air. Our coach has OTR (over the road) a/c designed to keep the entire coach comfortable, so we're fortunate in this regard. Even with this though, the front few feet of the coach are the warmest while on the road in the summer due to the glass.

The curtain behind the cab area does make a huge difference if using dash a/c - there is no way it will keep up if trying to cool the whole coach but just the cab area is usually manageable. Won't work for everyone though.
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Old 02-28-2021, 02:16 PM   #80
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Good points!! My calculation is for stationary operation. I should have mentioned that.

Driving is a whole other ball game. Sun as you mention, and a "force cooled" box. I.e., a convection cooled RV. Driving through 90+ F air is going to mean much more BTU/Hr coming into the RV than near still 90F outside air. A single mini split isn't going to hold 75 under that condition. Do "motor homes" have a condenser on the engine with automotive type A/C? If not, a larger mini split might be in order. My son's solution is a curtain that contains the mini split output to the forward area. And, surely that mini split run really hard ..... with possibly a second alternator helping keep the battery up.

My own unit is a 5er and the mini split will often run while driving, but we are in the truck with it's ample A/C.
Oops. I said "convection cooled" in the above. Since we are talking about cooling, I should have said "convection heated." I.e., driving at 60 through 90F air will keep the outer skin of the RV very close to 90F even though it's cooler inside. And warmer yet on any wall that is getting direct sun. And maybe warmer still from friction of the moving air.

Even when sitting still there is some convection heating of the outer skin from a breeze or just air flowing downward along the skin because the skin is cooled somewhat from the cooling going on inside. But, for the most part, when sitting still, the outer skin will be a bit cooler than the outside temperature as heat is pulled in through the wall and dispensed by the A/C unit. Only direct sun on a wall can take it above outside ambient. Thankfully that only occurs on one wall (or to a lesser extent on two walls depending on sun angle).
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