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Old 05-18-2017, 03:47 PM   #11
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Originally Posted by warewolff View Post
A Mitsubishi getting into 12kBTU+ and I'm looking at thousands into my a/c... This 12kBTU Toshiba looks pretty enticing though.
Go with a $500 chinese system, they're all the same pretty much.
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Old 05-18-2017, 04:00 PM   #12
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Go with a $500 chinese system, they're all the same pretty much.
yep this!!! like I say ive had 3 modified chinese ones in my house since 2009.. i use them for heat and cool and they work just fine.
-Christopher
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Old 05-18-2017, 04:10 PM   #13
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10 or 11 amps/hr is nothing, even on the Chinese systems that are not energy star. However I'm having some difficulty crunching the numbers. THIS 24kbtu mini split has a rated capacity of 6800w, a rated power consumption of 2465w, and running current of just 10.76 amps.

Now ... I can find a 3kw inverter, but a 7kw inverter is going to be tough. Being I'm not an electrician, can anyone explain these numbers to me? if A x V = W, 10.76amps x 230v = ~2.4kW. I would imagine a 3 or 4kW inverter could handle the startup surge. Am I very mistaken?

So even if I go with the lower number, 230/240v at 3kW, I'm looking at about a $1500-2500 investment if I go on the cheap, between the chinese mini split and the inverter? Jeeze... I thought this'd be easier.
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Old 05-18-2017, 04:22 PM   #14
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capacity is deemed by the amount of heat it moves.. that efficiency is determined by a lot of factors, theres no real startup current because these units are running internal inverters with soft start compressors...

my "24k" btu unit slowly starts up adding more and more power.. I see it reach a maximum of 2600 watts when im overloading the CFM of air across its indoor coil in heat mode.. in cool mode I rarely see it pull more than 1800 or so..

-Christopher
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Old 05-18-2017, 04:49 PM   #15
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So do I need an inverter with this unit? If so what specs should I be looking for?

It looks like I can get a 12k btu unit and a 240v 3kW inverter like THIS for under a grand.

Or I can get a 110v unit and maybe not even have to upgrade my inverter. Right now I have a Magnum 1500w, 2200w peak unit. For the most part I haven't seen my power consumption in the bus go over 3 or 400 watts and a 12k BTU unit like THIS uses less than 10 amps at 1180 watts. I assume the 1180 figure is peak, on high. I just might be alright ... Thoughts?
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Old 05-19-2017, 05:26 PM   #16
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Just an update and solution:

I was looking at thousands of dollars to go for a 230/240v unit and also a comparable inverter. I found a 22 SEER Pioneer 9k btu ac/heater for $810 shipped on ebay. It's highly efficient and will only pull ~650 watts total at full load. The best part about it is that it's 120v, meaning I can use my existing 1500w Magnum inverter and still have headroom even running my fridge, televisions, and computers. I'm very happy. All running comfortably off grid on my 1.2kW solar array and 10kW battery backup.

I'll be installing it in the next few weeks. Follow my build thread for updates.
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Old 05-19-2017, 07:49 PM   #17
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9k is gonna maybe keep you from sweating profusely ti just sweating... 650 watts is a pipe dream at full load.. as i mentioned either in previous post or another thread.. mini split inverter units running at full tilt are VERY INEFFECIENT.. they are designed to be most efficient at 30-80% or so of their capacity...

I have 3 of them in my house connected through temperature and energy monitors.. since I hacked the computer protocols in them i can limit them to 85% of capacity so they are always in their efficient range when i choose to...

minisplits are a great way to go in a bus, but as with all HVAC gear it should be sized appropriately for the job at hand...
-Christopher
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Old 05-19-2017, 09:07 PM   #18
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I checked the specs. This is a high SEER unit, which is why it's so expensive. 665 maximum cooling watts, 790 maximum heating watts. Christopher, I'm not trying to be argumentative but do you honestly believe it will draw higher than that at full load? Keep in mind it's rated as a 22 SEER unit. Most are 13-17. That means it draws 30% less power than a 15, which is probably what you have installed in your home. 15 is the norm. That's why this 9k btu unit is pricey at over $800. I spent hours poring over energy specs on the various units and found that most of them are inefficient. I can pull just over a kW more on the inverter before I'm redlining it.

I do believe you that the 9k unit might not cool enough. I figured worst case scenario I could wall off my bedroom and make it as airtight as possible so I have a space to cool off, leaving the rest of the bus with fans. I'm concerned about energy consumption as I'm completely off grid and don't want to stress my inverter/batteries. As for the the comparable 12k unit ... it's selling for $100 dollars more at ~$910, which is not the issue. Manufacturer states that the 12k btu unit at the same 22 SEER rating pulls, MAXIMUM, 960 watts for cooling and 1120 watts for heating. I could make it work, but it's going to be tight with my solar array. Again, those specs are direct from the manufacturer and generally I find my appliances never reach the maximum stated power consumption.

Also you stated yourself that there is no surge as the inverters are internal. So I shouldn't have to worry about overhead space, right?

Thoughts? I trust your opinion ... just wanted to present all the facts.
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Old 05-19-2017, 09:28 PM   #19
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My units are 21 seer from 2009 which is the most I could get they were brand new then.. in my hvac lab downstairs I have a Fujitsu which claims to be 26 seer but I have yet to take it out of the box.
they aren't supposed to draw more than their rated load but they will run over capacity ..
there is no surge current so you don't need a honking large inverter to account for that .
Mine are rated at 12000 btu but actual capacity is 5000 through 14500 as listed in the book. Since I can manually command my units capacity I have watched useage vs commanded capacity .. and once I reach 80% or so I am at around 1050,watts.. this is 90 outside and 75 inside and 55 wet bulb .. now when I then command 100% my usage jumps to 1450 watts or so... you can see the loss in that I've jumped over 35% power to gain 20% command ..
granted it's not truly scientific but enough so that I force my blower speeds and temperature deltas so that the unit never commands above 80%. You have a chance of attempting that by never turning your indoor fan on high as it will always have a cold enough cool temp to stay at low command .. unless your bus is so hot that it runs flat out all the time...
I don't know what. Linage you are going to live in or if you are going to let the unit run all day where it stands a chance of running 50% capacity as a maintainer .. or if you want to let the bus boil when you are not in it and then expect it to cool down.. the latter scenario is where you will waste efficiency ...
I don't pretend to know how to live off grid as I'm the opposite . I am an in grid city boy type that only lives off grid when lightning hits the power lines..
all I know is what my experience and experimentation on hvac design have brought... I built a computerized zone system in my house from scratch that has features which high end commercial buildings don't yet use...

If all you have for power source is solar and a small inverter then 9k may be all you can run.. but for efficient operation calculate your climate, heat load, and methods of how you plan to run the unit and what temperatures and humidity levels you want in the bus and also how much insulation and how dark and cave like you want the bus ( less windows less heatpoad)..
if your design shows that much of the time your unit runs flat out then you may be more efficient to run a bigger one ...
it's something to think about
Christopher
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Old 05-19-2017, 09:43 PM   #20
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Thank you. Really appreciate the response. It helps to know you are running a 21 SEER unit. If you don't mind my asking, have you ever checked the specs on your units to see what the manufacturer says the max wattage consumption is? Then you can compare that with what you're actually seeing and put an end to my obsession. I'd be curious to know if the specs are actually inaccurate, low balling, or if maybe the units are little more efficient today.

My bus is pretty heavily insulated now with 1 1/2" through all the walls and floors but I think what's happening is the sun is beating down through the remaining windows (I've got 6 in the front open and 2 in the rear), heating up the bus like a greenhouse as the heat can't escape through the insulation. Adding insult to injury, the compressor on my fridge is blowing hot air, the 12 solar panels are absorbing heat that I would assume is transferring into the roof at least a little, and the charge controller/inverter/battery array are giving off heat. Temp today was 98 degrees in the bus. I couldn't even work. This is with reflective elastometric roof paint too. Once I frame the windows I'm going to design window inserts to reflect the sunlight / insulate the bus, but that's a few weeks down the road. Hopefully that will help a lot.

I think I will spring for the 12k unit. Maybe we can meet up sometime and you can share these hacks with me. I might have to add another set of batteries in series but I think I'm close to being able to handle leaving the a/c on all the time. Worst case scenario I can set it to the low setting and close the bedroom door. Voila, problem solved. While I definitely have the headroom on my inverter I am just worried about topping the batteries off before night time. Pulling a 1kWh load with a total available incoming of less than 1.2kWh is like trickle charging an 860aH battery bank.

Anyway, thanks. I'm going to buy the 12k unit and see how it goes.
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