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Old 07-22-2020, 02:05 PM   #1
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Mini split airconditioner

I haven't started my skoolie yet. Counting cost and planning right now.

Who's using a minisplit?

What size?

How successful is that?

How much solar does it have to have?

How was it installed?

Thank you so much!
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Old 07-22-2020, 02:25 PM   #2
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I don't have personal experience, However there are lots of threads on this topic that will answer some or most of your questions. The Heating and Cooling section has a handful of posts on Mini Splits and A/C more broadly.
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Old 07-22-2020, 05:06 PM   #3
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Originally Posted by Samtheman View Post
Who's using a minisplit?

What size?

How successful is that?
Me for one.

9000 BTU unit. (37' bus, front interior unit, rear exterior unit.)


There is a need to circulate air from the front to the back in order to evenly distribute hot/cold air. Also, I insulated quite thoroughly. But yeah, it keeps us warm in winter and cool in summer.



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Originally Posted by Samtheman View Post
How much solar does it have to have?
Lots of variables to this one. Do you want to run it at night, or is only during sun good enough? With 1000W of solar panels, I could run mine all day. I have 3000W on the roof, and nights kill me.


If you want to power AC off of batteries for any length of time, buy the most efficient unit available. You'll spend ~$1200 or more as opposed to $300-$400 cheap units, but you will save money overall as to power the less efficient unit you would need something like double the battery bank.



Mine is 37.5 SEER, again I have 3000W of solar up top, and 10kWh (6.4-7 kWh usable) of battery capacity. I can survive one night of AC but that's about it with all other appliances (fridge, security system, computer, lights, etc) considered.



Panels are cheap, batteries are expensive.



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Originally Posted by Samtheman View Post
How was it installed?
I prepared the environment by mounting the outdoor unit on the back of the bus:
https://www.skoolie.net/forums/f11/k...tml#post356910
https://www.skoolie.net/forums/f11/k...tml#post378461


I ran two lengths of conduit on the roof to go from the rear of the bus to the front for the gas lines:

https://www.skoolie.net/forums/f11/k...tml#post356996



And I made a spot for the indoor unit at the front of the bus:
https://www.skoolie.net/forums/f11/k...tml#post361915



I also prepared a 220V AC breaker at the rear of the bus to power the split.



After all of this was in place ( the indoor unit was not on the wall, just the bracket ), I called the local HVAC guys and asked them to hook it all up. They were able to install and connect the copper tubes, run a vacuum test, release the outdoor unit's refrigerant and supplement it for the two 40' runs.



Ran me about $500 doing all the prep work.





If you have any questions, let me know.
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Old 07-22-2020, 07:20 PM   #4
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also size it accordingly so it doesnt run at 100% all the time if you are going for efficiency such as battery or solar.. these units are desaigned to reach their most efficient peak at 80% of capacity and below.. if you need 9000 BTU install a 12000 BTU unit so it can run at a lower speed.. it will actually be more efficient than a 9000 running at full blast..



in my house i have 2 12,000 BTU units and 1 18,000 BTU unit.. in testing specific airflow CFMs and temperatures, I can produce about 14,000 BTU of cooling with less wattage on that 18,000 unit than I can produce 12,000 on one of the 12,000 units.. all are the same brand,, of course i sized them such that the only time they run anywhere near full blast is when ive had the house opened up and I need a quick cooldown..





-Christopher
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Old 07-24-2020, 04:07 PM   #5
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I'm curious what the reccomended method of determining the proper size heating/cooling system is, and/or determining how much energy a mini-split will consume in practice.

@Kazetsukai I believe I recall you alluding to or outlining your process in another thread, but I don't recall where

@Cadillackid I've gathered you are quite knowledgeable about HVAC. Any pointers on how to 'do the math?

I found these two videos helpful (the first on calculating U-value for a wall, the second on calculating heat loss of a building and sizing heating system):

https://youtu.be/jok1QbzAvJo
https://youtu.be/etdpW1yMrIg

I also came across this resource someone else on the forum posted:

Heat Load Calculations

On a related note, I'm still trying to understand SEER and EER. One lingering question I have is whether SEER ratings are more 'gameable' by manufacturers. I bring this up because, when you compare SEER and EER, some of the ultra high efficiency (33+ Seer) units have very high SEER ratings but EER ratings that are roughly in line with apparently less efficient units. I feel its quite likely that I'm misunderstanding something, but I also feel if manufacturers can game the ratings they will. Any insights?
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Old 07-24-2020, 07:46 PM   #6
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Quote:
Originally Posted by dzl_ View Post
@Kazetsukai I believe I recall you alluding to or outlining your process in another thread, but I don't recall where
I'm not doing complex thermal energy transfer calculations, that's giving me way too much credit.

If you want to know my process/rationale for how I decided what to install...



Quote:
Originally Posted by dzl_ View Post
On a related note, I'm still trying to understand SEER and EER. One lingering question I have is whether SEER ratings are more 'gameable' by manufacturers. I bring this up because, when you compare SEER and EER, some of the ultra high efficiency (33+ Seer) units have very high SEER ratings but EER ratings that are roughly in line with apparently less efficient units. I feel its quite likely that I'm misunderstanding something, but I also feel if manufacturers can game the ratings they will. Any insights?
For me, _power draw_ was of the utmost, critical importance. I used SEER/EER to find what appeared to be the most efficient units and then focused solely on their rated current:
https://www.innovair.com/wp-content/...re-English.pdf



Mine: 2.2A cooling, 4.0A heating.


I figured that if these were the maximums and that if my averages were 70% of these figures that the overall draw was acceptable.


If you look at the back of my rig, I left space for a second exterior unit. I planned to install one unit, the first which I chose 9000BTU as it had the lowest energy consumption figures. Upon receipt I would install and measure real world results. From there, I'd size the second unit.


I haven't felt any need for a second unit yet.
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Old 07-24-2020, 09:15 PM   #7
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Quote:
Originally Posted by kazetsukai View Post
I'm not doing complex thermal energy transfer calculations, that's giving me way too much credit.

If you want to know my process/rationale for how I decided what to install...




For me, _power draw_ was of the utmost, critical importance. I used SEER/EER to find what appeared to be the most efficient units and then focused solely on their rated current:
https://www.innovair.com/wp-content/...re-English.pdf



Mine: 2.2A cooling, 4.0A heating.


I figured that if these were the maximums and that if my averages were 70% of these figures that the overall draw was acceptable.


If you look at the back of my rig, I left space for a second exterior unit. I planned to install one unit, the first which I chose 9000BTU as it had the lowest energy consumption figures. Upon receipt I would install and measure real world results. From there, I'd size the second unit.


I haven't felt any need for a second unit yet.

Thanks for the info! I have been looking into that same A/C unit (found through your build thread).



Do you have any indication of whether your A/C is able to keep the Bus cool running at less than full power? I think CadillacKid has stated its best for efficiency and the health of your A/C to size so that you are not using the full capacity normally.



I'm planning to purchase a smaller bus than you, but also don't plan to permanently cover any windows, so its hard to say how similar my situation would be to yours especially not knowing what climate you are in.


If I understand correctly (chances are I don't) the EER rating is a better indication of efficiency/power consumption when the A/C is running flat out right. In which case I don't know any AC A/C that beats yours (18 EER), the 33 SEER Fujitso ties with it, and the 42 SEER Carrier does significantly worse at (15 EER). For reference the DC powered Hot Spot energy A/C claims EER of 19.3, but doesn't list a SEER value (though they say these use the Same compressor as 27 SEER rated units).
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Old 07-24-2020, 09:38 PM   #8
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Do you have any indication of whether your A/C is able to keep the Bus cool running at less than full power? I think CadillacKid has stated its best for efficiency and the health of your A/C to size so that you are not using the full capacity normally.
Well, that depends on what you set it to and what the ambient temperature is, and how well insulated your rig is. Without more information to go on (from what temp to what temp), its hard to answer.



If I set it to 62, the lowest temperature I can, and it is 90 degrees out, it will never reach that temperature and always be pedal to the floor, full power.



Same with heat, if I set it to 80F and it is 20 degrees out, it will struggle but likely never reach its target.


Let me just give a few examples of real world performance:


I set it to 70F throughout the winter. Ambient ranged from 50F to 10F. Cabin temperature stayed constant at 68F. Observing the system, power draw varied from 200W-1000W. It did "spin down" (idle) during winter. Also when heating, the exterior unit has to defrost from time to time (a puddle of ice forms on the ground near it from condensation).



Cooling, its been up to 96F around here, and we've set it to around 76F. Set lower the front of the bus gets uncomfortably cold. You can hear the exterior unit's _very_ low hum go silent quite often to idle. Average draws are between 200W - 500W, right now its 300W.


If you truly, truly care about efficiency, replace those windows. They're too drafty. Not sure how it will affect performance in your bus. I think the real insulation killers are _any_ exposed metal surfaces. All I have for exposed metal is small sections of the skylights, the front door/cabin area and the emergency doors.


Real world testing destroys theory on a regular basis, don't put absolute faith in the numbers, you will be disappointed.
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Old 07-24-2020, 10:24 PM   #9
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Well, that depends on what you set it to and what the ambient temperature is, and how well insulated your rig is. Without more information to go on (from what temp to what temp), its hard to answer.

If I set it to 62, the lowest temperature I can, and it is 90 degrees out, it will never reach that temperature and always be pedal to the floor, full power.
I was referring to your experience with your particular situation, so whatever your conditions and usage has been.

Quote:
Let me just give a few examples of real world performance:

Perfect just what I was looking for, I should've read the full response before starting my reply Thanks.

Quote:
If you truly, truly care about efficiency, replace those windows. They're too drafty.
Yeah I feel you
, I wish there was a decent drop in replacement. Ditching the windows completely is a dealbreaker for me based on my current thinking. Its one of the things that most draws me to skoolies, love the look, love the openness, love the light.

However if I could find double paned windows (I know they are out there, just rare) afford custom windows (I know of one company that will do this, but its not cheap). I'm also pondering many different options for window insulation like sliding insulation panels that could be raised and lowered.

The other option is to just not try to fight the climate and focus on insulation and airflow and opting not to use A/C at all. In all likelihood this is how I will start off. I'm out west so heat is limited to the summer months and its dry heat.

Quote:
Real world testing destroys theory on a regular basis, don't put absolute faith in the numbers, you will be disappointed.
Yeah, I feel you, I just want to try and get a ballpark, I know the margin for error would be super super high especially with something as irregular as a Bus.
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Old 08-01-2020, 03:54 PM   #10
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Thank you for such a thorough answer and reference to other links. We removed my old AC unit and heat unit. Temporary measure didn't work in high desert of CA so I now have my bus in storage until I can figure out how to do the mini split. Again, thanks.
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Old 08-01-2020, 04:07 PM   #11
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We're running a 12,000 btu minisplit on our 26' transit bus. Like someone said, insulation and having additional airflow is key. I have the indoor unit mounted in the front of the bus and the outdoor unit mounted to the vehicle frame under the rear of the bus. The outdoor unit needs ample space to exhaust hot air to remain efficient. For us, its exhaust vents through retractable stairs. Inside, we have a ventilation fan in the rear of the bus that draws in cooler air near the floor and blows it near the rear ceiling of the bus to keep air moving. The indoor units tend to have weaker fans. They have the cooling and heating capacity but need help with the airflow.

We don't have solar but my unit draws anywhere from 400w-1kw 120v AC depending on how hard it's working to cool the bus.

I benchmarked it on a few 100 degree days a couple weeks ago with the bus sitting in direct sunlight(0% shade lol), the outdoor temp was between 99 to 102F and inside was 82 in the rear and 78 up front. The air coming out of the indoor unit ranged from 37F to 42F on those days....Brrrrrr. To note, I didn't have my windows covered(side windows and massive windshield not covered) so a ton of radiant heat was pouring into the bus. If i covered them up, it would have easily stayed around 75. What's also helping is we recently coated the roof in Henry's Tropicool silicone roof coating. The difference was night and day. Outdoor roof temp dropped from 124F down to 82F in direct sunlight. Water on the roof from a storm a few days ago won't evaporate because the sun can't get the roof hot enough to dry off.
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Old 08-01-2020, 05:04 PM   #12
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I have two 12,000 btu minis. They are about 6 years old I think seer was about 12 don't really remember. Bluebird factory insulation, buskote on roof. and awnings on both sides. Solar panels shade about 2/3 of the roof. They cycle high and low even when sitting in the sun in 100°. When running full each one draws about 7 amps. Inside temp stays at what ever I set it at, me 75° wife more like 70 or 72°.
Last weekend, Indiana high humidity and nite time temp about 80. Bedroom stayed quite cumfy well, I needed a blanket. Next AM I still had 75% left in the battery bank. After using the Keurig, microwave, hair curler and still the AC, had 69%.
This is the first time I used the front ac driving. The hour long drive kept us cumfy and had about 65% battery when we got home. We were in shade over the weekend so the drive home we got some sun on the panels, don't know how much since it was partly cloudy.
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Old 08-01-2020, 07:05 PM   #13
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Bluthebus00- how do you power your AC?
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Old 08-01-2020, 07:46 PM   #14
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That's awesome!
We only have 200AH of lead acid batteries. 100AH usable
We used to have a wheelchair lift so I'm going repurpose its left-behind high current 12V line from the alternator/engine battery to power my inverter when driving for simple things like the fridge, and a TV while driving down the road. Battery isolator is ready for the second 12V power source



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I have two 12,000 btu minis. They are about 6 years old I think seer was about 12 don't really remember. Bluebird factory insulation, buskote on roof. and awnings on both sides. Solar panels shade about 2/3 of the roof. They cycle high and low even when sitting in the sun in 100°. When running full each one draws about 7 amps. Inside temp stays at what ever I set it at, me 75° wife more like 70 or 72°.
Last weekend, Indiana high humidity and nite time temp about 80. Bedroom stayed quite cumfy well, I needed a blanket. Next AM I still had 75% left in the battery bank. After using the Keurig, microwave, hair curler and still the AC, had 69%.
This is the first time I used the front ac driving. The hour long drive kept us cumfy and had about 65% battery when we got home. We were in shade over the weekend so the drive home we got some sun on the panels, don't know how much since it was partly cloudy.
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Old 08-01-2020, 07:58 PM   #15
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We have a 120V minisplit. We're not full-time in our bus so we don't have a ton of house battery capacity nor do we have solar(yet) We power our unit with a standard 30 amp RV hookup.

My main 2 circuit breaker box splits the 30amp circuit down the middle. 15 amps dedicated to the minisplit AC and the other 15 amps feeds another breaker box that houses my circuits for all 120V accessories and appliances.

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Bluthebus00- how do you power your AC?
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Old 08-01-2020, 08:29 PM   #16
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Bluthebus00-what do you use to cool inside while you are driving? Or when you are away from RV hookups?
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Old 08-01-2020, 08:40 PM   #17
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While driving, the bus has a transit bus rooftop AC unit that runs off the engine. We haven't gone anywhere without hookups yet Our plan is to run on a generator when we eventually get one for those situations if needed.


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Bluthebus00-what do you use to cool inside while you are driving? Or when you are away from RV hookups?
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Old 08-01-2020, 11:52 PM   #18
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Bluthebus00-thank you. Right now I have no AC. But I do have a generator. I have seen which mini-split should be ok for my 24 ft shuttle (insulated) I have a Maxx Fan that should help circulate the air when I get my mini-split installed. I just need to start saving for the batteries for my solar. I know they are the most expensive part.
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Old 08-02-2020, 12:23 AM   #19
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Has anyone thought about a split 12 VDC truck ac unit?

Just to show you the kind thing of I'm talking about: https://www.alibaba.com/product-deta...79ebMCgRJ3&s=p .
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Old 08-02-2020, 05:57 AM   #20
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According to their specs those are 24 volt and less than 7000 BTU. Even though the title says "12V 24V".
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