[nebulight]

Awesome, I can't wait to run my heatpump off my inverter, lol! Free heat!!

 

[RV8R]

OK - if he AC actually needs 1500 watts to runs, and the inverter is 85% efficient, then

(0.85) * ACout = 1500, or ACout = 1500 / 0.85 So, ACout = 1764 watts
That is, for the inverter to output 1500 watts, it has to consume 1764 watts with 85% efficiency.

So, the Inverter is wasting 1764 - 1500 = 265 watts.

In BTU this is: 265 watts * 3.412 BTU/watt-hr = 904 BTU

So, I guess both of our first attempts were wrong

This is somewhat conservative in that some inverters (but not too many) do better than 85%, and the AC won't be drawing 1500 watts all the time. But, you can plug in your numbers.

Gary

Even “Victron” publishes their maximum efficiency % ,, Not Average or Mean

My multi shows 93% “max” ,, I just don’t feel that lucky in “real world” 😳

I think 85% is conservative ,, but without actual testng I believe that is the right way to analyze it 👍

 

[RV8R]

OK - if he AC actually needs 1500 watts to runs, and the inverter is 85% efficient, then

(0.85) * ACout = 1500, or ACout = 1500 / 0.85 So, ACout = 1764 watts
That is, for the inverter to output 1500 watts, it has to consume 1764 watts with 85% efficiency.

So, the Inverter is wasting 1764 - 1500 = 265 watts.

In BTU this is: 265 watts * 3.412 BTU/watt-hr = 904 BTU

So, yes you are correct - sloppy math on my part.

This is somewhat conservative in that some inverters (but not too many) do better than 85%, and the AC won't be drawing 1500 watts all the time. But, you can plug in your numbers.

Gary

I suppose it isn’t rocket science ,,, Could be Mrs. RV8R forced me to watch this movie last night “Hidden Figures” (it was a very good movie);

 

[rjcarter3]

To me, AC is a shore power luxury. I'll be getting a cheap portable AC that I can vent out the window. If I lived in the van and actually needed to run it off batteries and wring out every watt of efficiency, I'd have already spent so much money on a lithium battery bank to power it that I'd just take the rest of my lumps on the 12V AC.

 

[tgregg]

I think the real potential benefit for 12v A/C is one with a variable speed compressor. This allows the unit to adjust its output (and power consumption) to match the cooling requirement just like an Espar or Webasto heater does. This eliminates the temperature swings and the frequent starts of a single speed 120vac compressor that typically require up to twice the normal running current.
I recently installed a variable speed heat pump - A/C in my house and it's a night and day difference in comfort, noise and electric consumption.

If somebody makes a variable speed 120vac RV air conditioner that might make a viable alternative but you still have the heat and power loss from the inverter.

 

[Lolaeliz]

i'm with @rjcarter3 . It's a power luxury. In my travels so far, I have never wished for AC. Following the weather is the best way to enjoy what vanlife offers. I love having all the doors and sunroof open with a good fan moving the air around. The AC takes away the outdoor magic a van offers.Now, if I lived in the van full time in a southern/hot climate where I couldn't follow the weather -- I'd have a bigger van, maybe even a skoolie, with a giant battery bank, lots of windows, dc ac and all the other luxury comforts of home.

EDIT: I also hate AC in my house. When I lived in Los Angeles, I almost never used it. In PA, the humidity makes it a necessity.

 

[el Jefe]

I think the real potential benefit for 12v A/C is one with a variable speed compressor. This allows the unit to adjust its output (and power consumption) to match the cooling requirement just like an Espar or Webasto heater does. This eliminates the temperature swings and the frequent starts of a single speed 120vac compressor that typically require up to twice the normal running current.
I recently installed a variable speed heat pump - A/C in my house and it's a night and day difference in comfort, noise and electric consumption.

If somebody makes a variable speed 120vac RV air conditioner that might make a viable alternative but you still have the heat and power loss from the inverter.

And Trane, who makes some **** efficient nifty equipment, says we are years away from efficient equipment suitable for something the size of a van. R&D is working on units with dual and variable speed compressors for larger RV's.

 

[Dekkars]

We got sold on the 12v benefits, and got a Dometic RTX 2000.

Tested it on some hot muggy days last summer, and even kept our half insulated van pleasant with ~700w power usage. Our solar was pulling 680w, so our effective runtime was days at that point. Since then, we've added an insulated curtain at the back and ceiling insulation (which we didn't have yet!) so I'm excited to see how it does.

It does get loud in boost, though you really can't hear it from inside the van. Outside it sounds like a drone (on boost, normal is fine)

 

[Wowbagger]

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.

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.

 

[dog_house]

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.

 

[dog_house]

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.

 

[RamVanGuy]

Interesting views all round on the AC units. For us folks in the southeast it's a must-have rather than nice-to-have. Here the temp is less of an issue than humidity so I don't think variable speed (even if available) will be useful.

For selecting a unit it's like the old project manager's dilemma: there are four important variables and you can only optimize two..... For RV air conditioners these variables are :

• BTU cooling capacity
• Noise
• Price
• Size - ie weight and height on the roof

Bigger units are inherently quieter since they have more space to direct air flow which is what creates noise. Compact units - often are too low a BTU capacity and/or too noise... etc.

Note that 12 V vs 120 V is not even one of the main variables - the other four govern and 12V loose on price every day!

Everyone's use is different but I would opt for the larger Rec Pro because it works, is quiet and relatively affordable. The smaller Rec Pro is a second place but is less capacity in a compact casing and therefore noisier and less efficient.

 

[Chance]

Everyone's use is different but I would opt for the larger Rec Pro because it works, is quiet and relatively affordable. The smaller Rec Pro is a second place but is less capacity in a compact casing and therefore noisier and less efficient.

Since a lower-capacity air conditioner does not need to move as much air flow, and heat exchangers don’t need to be as large, doesn’t it follow that a 9,500 BTU/hr unit can be much smaller than a 13,500 unit while still having similar sound and efficiency performance? I’m not that familiar with RecPro efficiency data yet, but expect smaller size doesn’t necessarily mean extra noise or less efficiency when cooling capacities are much different.

I helped install two 9,500 recently and know they are fairly quiet compared to most common RV units. If 13,500 is even quieter, that would be great, though probably difference would not be that noticeable. The 9,500 is so quiet that there’s not as much room for improvement.

 

[Chance]

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...

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.

 

[dog_house]

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.

 

[dog_house]

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

 

[HarryN]

Darn Parasites on the wrong side of cold 👿 ,,, 85% efficient pulling 1500 watts ,,, I have not looked very close at this but I always assumed 1500/85% would require 1765W from the battery so 265 watts going mostly into added heat from the inverter ,,, is that wrong?

When considering all electronics with heat sinks ,,, solar chargers, transformers (boost/bucks), & other equipment like isotherm or other HWT I think about the possible added heat as we got no AC.

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.

 

[rjcarter3]

This is basically a window air conditioner with a reversing valve in a foam box.

That's pretty cool, no pun intended.

I don't really have room for this thing and already have heating covered anyway, but I could fit something smaller. I'd love to find a cleaner way to install an inexpensive window AC that didn't involve cutting a hole in the side of the van. Not saying I'd do this, but would it even be possible to lay a window AC flat on the floor leaving the bottom to hang over a similar square hole in the floor then build an insulated box around the top and sides of the vents to keep all the hot air going out the bottom of the van? Seems like it could work, although having it blow cold air that low in the van is less than ideal. Maybe there'd be other problems with rainwater splashing up from the road into it.

I wouldn't have the nerve to try it anyway and would just end up replacing my Maxxfan with a 12V AC before doing this, but just a thought.

 

[dog_house]

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.

 

[RV8R]

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.

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.