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Especially true in your case, Knight Rider. ♠😎

I did some "testing" this week that was not exactly on a GaryBIS level. It finally got warm and sunny here so I closed up the van in direct sunlight. It was 83 degrees outside and 96 in the van. The 1" Polyiso on the ceiling was hot to the touch and radiating heat into the van. The 1.6" Thinsulate covered walls seemed to be barely warm, and the bare metal floor was about ambient.

Because of this I swapped out the 1" foam that was going to go under the plywood out for 1/2" so now the floor is going to be a 1/2" XPS & 1/4" plywood glued up and the roof is going to be 1" Polyiso, glued to 1/2" XPS, glued to 1/4" plywood. That sun radiating on black metal is no joke.

The tinted plastic windows don't seem to radiate heat as much as you would expect.

Even without the extra insulation on the still hot roof and a bare metal floor the Pioneer HP dropped the temp and humidity in the van to what I would call comfortable in 15 minutes.

The hunch that everyone had about the roof being important and the floor not so much was dead on.

I'm still hoping they are wrong about keeping the 1,200ah battery charged haha!

 

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In case some of you are not following the old thread about it I cut the van up and put the heat pump in today. It’s the quietest air conditioner I have ever experienced in an RV and that’s without the ductwork or bed…

Pioneer 9000 BTU Floor Mounted Heat Pump

When I was planning our build I wanted to avoid things on the roof that would kill MPG and have a very quiet HVAC system that would be able to run on batteries. I had experience with a Dometic Cool Cat and was looking for a modern replacement...

www.promasterforum.com

 

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I purchased a 12 | 3000 | 120 Multi in late 2018 & it is still collecting dust ( my fully electric van days ). I have also never been able to get close to gasoline mileage that Auto Manufactures present ,,, 🤔.

I will probably throw my “Multi” into my remote Cabin in the woods. Someday if we want “real” juice up there I might do that & switch to a bigger bank of lithiums. What is our biggest “need”? Air conditioning. So far we “deal”, but last July we “bugged out” as temps were bumping up to 40C 🥵. Other than the noise (& carbon footprint), the gasoline generator can deal with an air conditioner.

80% efficiency is a far cry from 93% ,,, That sucks ,,, So do Vacuums.

The 21 MPG that we are getting out of the van is one of the big reasons that I went with the under bench heat pump. Well, that and drive throughs!

 

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For the climates where you need AC in a van I don't think the variable speed compressors are much of a benefit when it comes to power consumption. If you only need 2-3k BTU to maintain the temperature the battery capacity problem gets really easy to solve. It does help a lot with noise and humidity though. I'm not sure if RV roof AC's are even using TXV's yet...

As far as inverter efficiency, everyone is spot on. Even Victron overstates their efficiency, plus the standby is closer to 30 watts when the inverter is ON. Real world is around 85% at 12v when you account for all of the losses. Our 9,000 BTU heat pump pulls between 825 and 875 watts depending on temperature and uses 950 to 1000 watts from the batteries. If we are also heating water and running the Nespresso machine the efficiency drops to around 80%. The batteries, wiring, and inverter share a space with the heat pump so that 400 BTU of waste heat goes straight to the return air of the heat pump and is not felt in the van. Compared to the windows its a fart in the wind, but it definitely cuts down on the overall efficiency.

 

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There is actually less flexibility since there is an internal unit you have to find room for. This is way harder in a van than sacrificing roof space. Why give up storage space when you don't have to? Id be curious to know how fast they get destroyed under a van. Or at least getting so dirty that efficiency dives. Like driving on dirt roads must just make those fins filthy.

I meant compared to the under bench I have. You give up a cubic foot or two on the interior but it can be anywhere you want. The thing I can’t get past is it sounds like an electric leaf blower.

Nothing beats sticking the AC on the roof for interior space and the new ones are pretty quiet.

 

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Since there's good discussion going.
How about "a dream system" - it is expensive, but has benefits.

12/24/48 Volt DC Air Conditioners..Battery Powered..Solar Powered..Hand Made In Arizona Since 2010<br/> — Battery Powered Air Conditioners 12/24/48 Volts DC

We manufacture DC powered air conditioners in various voltages for various applications..... Off grid living, solar powered, energy efficient...... Made in Arizona.... Custom applications welcome.

www.cruisencomfortusa.com

It doesn't take any space on roof
It doesn't drip on your head
Only coolant lines go through the floor, means

• flexibility with placement
• no need for a huge hole

It is efficient

cons:
the pricetag
need to run ducts (although, can mount it in a cabinet up high = no floor space sacrificed and no ducts needed)

I was looking at them 10 years ago when I put the battery powered AC in our boat. It seemed like a good solution but the high cost drove me to a 120v AC and Inverter. They got their start in go-fast boats where you want the cabin to stay cool but don't want a bunch of weight or an inverter. I looked at them again for the van but this time the noise and chances for refrigerant leaks drove me back to a packaged unit again. If it was not so loud I would have gave it a shot, especially since I already have the tools for the refrigerant line install.

I think this system gives up a little efficiency and is noisy because of the evaporator and condenser fans. Moving the air quietly is trickier than you would think and where the foam boxes really shine.

The packaging with this system is a huge win though.

 

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The houghten unit on that sprinter has never pulled more than 20 amps @56 volts from the battery pack, and it is I believe 13K BTU. Most of the time it pulls 1/2 of that or less.

To be fair, the systems you put together are far more efficient than the 12v ones most of us are using!

I figured I would optimize efficiency on the charging side and give up some on the 120v conversion but my error was assuming that Victron was honest about their inverter efficiency. I was never able to get close to that 93% number. I figured that it would be right in the middle of the power curve and running the inverter at 40% would get me as close to the number as possible and keep the wiring losses low. If I knew it was in the mid 80% range and that the new Sterling 1500w 12v to 48v charger was available I would have went 48v. I felt like 24v was just compromising on both ends.

 

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Hi,
That seems quite reasonable to me.
A dark colored roof in direct sun is going to be really hot - its basically how you build the back of a solar thermal collector.

So, for cooling, having more insulation on the roof seems like the way to go.
Also, maybe paint the roof white? Can't really see the roof from the ground anyway.

I'm a believer in insulating both ceiling and roof well for heating (winter). The testing I did on this tends back this up for heating. I looked at the roof losing more heat on a clear night because the warm roof radiates to the cold sky, and there ends up being some truth to that, but in the daytime the sun would warm the roof and reduce heat loss out the roof (and a black roof would be better )

Do you have one of those IR gun thermometers? They have gotten dirt cheap.

Gary

The roof is being covered with flexible solar panels so paint is not an option. I debated putting some sort of thin insulation between the panels and the van but then I’m sacrificing the solar output for thermals. I figure the panel must be converting some of the solar energy to electricity and it can’t be any worse than the black metal. When it gets hot again I’ll throw some panels up there and see what happens.

I do but it’s at work. I do most of my tinkering there 👍

 

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And starting with a properly insulated cargo van with minimal windows matters a whole heck of a lot more than 10% efficiency gains from different systems! I don’t kid myself that the compressor will ever shut off during the daytime, I just sized the system to run constantly in order to keep humidity down.

On the boat throwing a couple beach towels over the outside of the large forward facing windows would actually let the 7k BTU AC start to cycle. With the windows uncovered on the outside and shades drawn on the inside it ran constantly to maintain 75 degrees.

 

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An exception would be if you camp mostly during days at campgrounds with shore power, and can therefore power A/C with 30A service so installing a larger unit makes sense; but at same time occasionally boondock at night and need to power A/C from batteries (with or without inverter).

Some units that can operate down as low as around 30% of rated capacity by use of variable speed also gain efficiency by running much slower, similar to mini-splits. I’m interested in 8,000 BTU/hr dual inverter window air conditioners because they are inexpensive, and EER are +/- 15. It also means SEER rating for nighttime use should be even higher.

That’s pretty much how we roll. We are either driving and run the AC during overnight stops or parked where we can plug in. I just wanted to make sure that we could get through a weekend road trip without needing water or power. Quiet and small were the things I optimized for.

 

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Sorry, but that's a pet peeve of mine. It's "watts", not "watts per hour". Watts are power, which is already energy per unit time.
Watts per hour would imply some sort of load that starts out at a low power consumption, and over time increases its power consumption at a steady rate - it starts out at 100W, then in an hour it is 1100W, then an hour later its 2100W, etc.

Yup, it should have been written watt-hour or converted to amp hours of battery power but I was trying to make it easy to read.

 

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I looked at it from a “how can I run AC without shore power” POV and not just the amp draw that they DC promoters like to show with the system ramped down making 2,000btu.

I went 12v to maximize alternator charging efficiency but if if you plan on doing a lot of solar charging the 24 or 48v inverters are quite a bit more efficient. Real world numbers to convert 12vdc to 120vac are around 87% efficiency with a Victron MultiPlus. The inverter and a Houghton are about the same money as an RTX2000 or Mabru and I’m not sure it’s even fair to count the cost of the inverter since most people spending $3k on an AC are going to go all the way and have a decent 120v system also.

 

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I'll have real world numbers soon with the 9000 btu heat pump running on a 12v Victron MultiPlus. You are exactly right, there is no free lunch and if you want to cool a van it's going to take close to 1,000 watts per hour to do it unless you gave up some interior room for serious insulation. Getting an actual EER of over 10 in a van is not really practical with the space available. 1,000 watts will move about 10,000 BTU. When someone claims efficiency drastically better than that it's time to look behind the curtain and start asking questions.

Remember, this guy has a huge condenser and evaporator to move 18,000 btu and has an EER of 12.