Shipping Container solar AC

[SoakedUp]

I have a 20ft HC shipping container that houses some storage, tools, construction material and also a small solar set up. Located in the Southern California Desert temperatures are on the warm side especially from May to October (90-120F ambient, +10-15 degrees inside the container.

The top of the container is almost fully covered with solar panels, 2k watts worth of panels and mostly all four sides are shaded with shade sails.

I need to add some sort of AC to the container to keep the solar equipment cool, mainly the batteries. All I’m currently running is a small fridge, some vent fans, cell booster, and a 4g lte modem and a wifi camera.

All of my storage and solar equipment is in the back 8ft of the container. I was thinking of constructing a wall to block off that back 8ft and then cutting a hole in the wall for a 8k btu window AC unit to just keep the back 8ft cool(under 90F). My question is how efficient would this be dumping the heat into the other 12 ft of the container. I don’t care how hot the front 12ft of the container gets. I was thinking I could exhaust the front unconditioned space through a hole in the floor with a powerful in-line fan. I’m currently exhausting the entire container in the same fashion and it seems to work fairly well.

I’m trying to avoid cutting any holes in the walls of the container at this time for various reasons if anyone is wondering why I don’t just exhaust to outside the container. I know it seems counterintuitive but replacing a small 4-6” hole in the wood floor is easier for me to patch than a 15x24” square cut out in the metal wall. I don’t have a welder at this time.

 

[Rednecktek]

How much airspace is there under the container? A free standing portable unit with 2 hoses plumbed through the floor would probably work well. Get one of the heat pump varieties to keep the power consumption down and you should be fine.

 

[SoakedUp]

How much airspace is there under the container? A free standing portable unit with 2 hoses plumbed through the floor would probably work well. Get one of the heat pump varieties to keep the power consumption down and you should be fine.

I was considering a portable unit with the hoses but then I found this.

Midea 8,000 BTU U-Shaped Smart Inverter Window Air Conditioner–Cools up to 350 Sq. Ft., Ultra Quiet with Open Window Flexibility, Works with Alexa/Google Assistant, 35% Energy Savings, Remote Control https://a.co/d/fGaZ6A9

I figured an inverter type window unit would be way more efficient power wise. All of the reviews say the power range is 100-350 watts. They have inverter type portable units but they are large, expensive and take up a bit of floor space. Costco is selling that Midea window AC right now so I figured if it all doesn’t work out I can just return it since their return policy is pretty good.

There’s about 12” of space under the container. I’m currently exhausting out a 4” hole right in the corner of the container floor and when the 300cfm fan is on I can feel the air being expelled at the outside corner of the container by my feet.

 

[Shimmy]

I would go for a mini-split and not a window unit. Much more efficient in multiple ways, and it actually stands a chance at working in the heat. Not sure what the ratings for EG4's solar hybrid units are in those temperatures but it might be an interesting option. If you can do a hole in the floor anyway no reason to not run refrigerant lines instead.

 

[SoakedUp]

I would go for a mini-split and not a window unit. Much more efficient in multiple ways, and it actually stands a chance at working in the heat. Not sure what the ratings for EG4's solar hybrid units are in those temperatures but it might be an interesting option. If you can do a hole in the floor anyway no reason to not run refrigerant lines instead.

I currently have a 12k btu Mr. Cool mini split in the cabin next to this container. It’s awesome. The problem is its start up power is about 1200-1300 watts for about 3-5 min. I’m using a Victron 12/1200 inverter with my solar which will sometimes power that mini split but sometimes it will trip the inverter. I plan to get a bigger inverter but I’m not there yet. Also a mini split is in the $1000-1500 range plus the bigger inverter to run it. The window unit is $400 and can run off my existing inverter. This window unit essentially is a small mini-split. Inverter technology in a small window size package.

 

[Hedges]

If other half gets hotter than outside air, performance gets worse. I would think dumping heat to shady side of container would work better. Hole in floor or side, fan pull air through that hole and over the coils? Don't want to circulate air in a box and separately transfer air from outside, better direct outside to coils.

Insulate from exterior and from unconditioned half.

Batteries have thermal mass, but 8' of container is a large volume compared to that. Additional thermal mass, maybe a cage filled with large gravel?
Cooling will of course be best accomplished when outside air for heat exchanger is cooler, and sun is on the panels.

 

[Shimmy]

I currently have a 12k btu Mr. Cool mini split in the cabin next to this container. It’s awesome. The problem is its start up power is about 1200-1300 watts for about 3-5 min. I’m using a Victron 12/1200 inverter with my solar which will sometimes power that mini split but sometimes it will trip the inverter. I plan to get a bigger inverter but I’m not there yet. Also a mini split is in the $1000-1500 range plus the bigger inverter to run it. The window unit is $400 and can run off my existing inverter. This window unit essentially is a small mini-split. Inverter technology in a small window size package.

The window unit is going to be lower efficiency though (at ideal conditions), and by exhausting the heat into an adjacent 115F (starting) space the efficiency is going to drop significantly lower. All it will really do is make the situation worse.

I know the cost is a big delta. FWIW, the EG4 units have direct solar input so you don't necessarily need to upgrade the inverter to accommodate the mini-split-- just some dedicated panels. The other option is going for a swamp cooler (preferrably indirect).

 

[Bluedog225]

Sounds like a cool setup. I’d love to see pics of the panel attachments.

I’m in the process of super insulating my conex. Mylar with spacers, 5” polyiso on the roof and 2.5” on the walls, tyvek to keep cool air from leaking to the hot walls, and 5/8 fireguard sheet rock. all on the first 10’. That will be a little air conditioned room for the solar stuff. The rest of the conex will be lightly insulated and a little hotter.

I decided to get the Midea portable unit from Costco. Just got it. Hole in the floor seems like better security. The thing is a beast as well. I’m going to run it here for the summer and see if it is reliable. And costco returns policy gives me a lot of peace of mind. Cheaper than a split and easy install through the floor.

 

[SoakedUp]

The window unit is going to be lower efficiency though (at ideal conditions), and by exhausting the heat into an adjacent 115F (starting) space the efficiency is going to drop significantly lower. All it will really do is make the situation worse.

I know the cost is a big delta. FWIW, the EG4 units have direct solar input so you don't necessarily need to upgrade the inverter to accommodate the mini-split-- just some dedicated panels. The other option is going for a swamp cooler (preferrably indirect).

I did look at the EG4 units. I like them. I’m pretty remote though so getting hvac guy to come out to vacuum pump the lines could be an issue. I could buy the tools and do it my self but $$. That’s why I got and like the Mr. Cool units. 100% DIY with no vacuum pump.

I know there are better ways of doing this. I understand the way I’m suggesting isn’t the most efficient just trying to figure out if it will be efficient enough for now. I’m typically a do it right the first time, but once, cry once kinda person. I just haven’t fully figured out how I’m going to configure the container yet and need a quick fix. A portable unit with a hose feeding the hot air out the floor might be my best bet.

 

[SoakedUp]

Sounds like a cool setup. I’d love to see pics of the panel attachments.

I’m in the process of super insulating my conex. Mylar with spacers, 5” polyiso on the roof and 2.5” on the walls, tyvek to keep cool air from leaking to the hot walls, and 5/8 fireguard sheet rock. all on the first 10’. That will be a little air conditioned room for the solar stuff. The rest of the conex will be lightly insulated and a little hotter.

I decided to get the Midea portable unit from Costco. Just got it. Hole in the floor seems like better security. The thing is a beast as well. I’m going to run it here for the summer and see if it is reliable. And costco returns policy gives me a lot of peace of mind. Cheaper than a split and easy install through the floor.

View attachment 146967View attachment 146968

That’s almost exactly what I was thinking of doing to insulate the back 8’ of my container. Get some of the 4x8 foam panels like that and screw magnets onto the backs so I could just stick them on to the walls and ceiling. I might end up getting the portable AC and use the existing vent hole in the floor I have. Seems like the easiest way to go.

Here’s the roof of my container. I have since covered the edges with trex deck boards for full coverage. I used 4x4s on the ends of the container bolted down at the corner iso attachment points. A 2x6 in the middle with 2x4s connecting in between. I used unistrut on top of the 2x4s to bolt the panels down too.

 

[sunshine_eggo]

That’s almost exactly what I was thinking of doing to insulate the back 8’ of my container. Get some of the 4x8 foam panels like that and screw magnets onto the backs so I could just stick them on to the walls and ceiling. I might end up getting the portable AC and use the existing vent hole in the floor I have. Seems like the easiest way to go.

Cool idea.

 

[Bluedog225]

Pretty slick. The magnet idea is intersting. I had a time wrassling those sheets into place. Two people would help.

Where did you find a 20’ coolaroo sun shade? Or is that another brand?

 

[Hedges]

Insulation on the inside preserves external mechanical and shipping characteristics, but loses volume and in the event of fire releases toxic gasses inside. Sheet rock of course helps protect against that.

How about exterior insulation? What surface treatment would you use for weather protection?

I wonder if the "self adhering" feature of this roll roofing would work as well as it sounds?

GAF Liberty 3 ft. x 34 ft. (100 sq. ft.) SBS Self-Adhering Cap Sheet Roll for Low Slope Roofing in Hickory 3730395 - The Home Depot

LIBERTY SBS Self-Adhering Roofing Systems are applied without torches, open flames, hot asphalt, or solvent-based adhesives and are suitable for many primed substrates. LIBERTY SBS Self-Adhering Cap Sheet

www.homedepot.com

 

[SoakedUp]

Pretty slick. The magnet idea is intersting. I had a time wrassling those sheets into place. Two people would help.

Where did you find a 20’ coolaroo sun shade? Or is that another brand?

Colourtree 18x22’

ColourTree 18' x 22' Grey Rectangle Super Ring Sun Shade Sail Canopy Structure, Super Durable Heavy Duty, Reinforced Corners, Edges & 260 GSM Permeable Fabric https://a.co/d/1h5Q5tt

 

[SoakedUp]

Insulation on the inside preserves external mechanical and shipping characteristics, but loses volume and in the event of fire releases toxic gasses inside. Sheet rock of course helps protect against that.

How about exterior insulation? What surface treatment would you use for weather protection?

I wonder if the "self adhering" feature of this roll roofing would work as well as it sounds?

GAF Liberty 3 ft. x 34 ft. (100 sq. ft.) SBS Self-Adhering Cap Sheet Roll for Low Slope Roofing in Hickory 3730395 - The Home Depot

LIBERTY SBS Self-Adhering Roofing Systems are applied without torches, open flames, hot asphalt, or solvent-based adhesives and are suitable for many primed substrates. LIBERTY SBS Self-Adhering Cap Sheet

www.homedepot.com

I’ve considered exterior insulation and is probably ideal. Protecting the insulation from the elements is the only hassle. Luckily I’m in a very dry climate and there is minimal rain. The main problem with insulating the inside with anything other than spray foam, is the risk of condensation build up on the metal walls and then mold. Any insulating on the inside would be temporary and again with how dry it is in my region I’m not to terribly concerned with condensation.

 

[Hedges]

Magnet attach inside allows a path for drying air.
Sealed volume should keep inside humidity from reach cold walls in winter. Foil duct tape?. Dessicant could also help.
I understand this is an issue with how walls are insulated and vapor barriers used. Sounds like blown-in insulation for house can cause rotted sheathing.

 

[Bluedog225]

My new one trip strangely came with eight vents. My older 40 foot high cube only had two vents total. I’ve left space all around those vents so they can can communicate with the gap between the mylar on the outside metal. Also, the air conditioner should produce a fairly dry inside environment.

I’ve taken a piece of Polyiso and held a propane torch to it. It did not propagate flame. I’m hoping it will not be a contributing factor in a fire. But Sheetrock anyway.

 

[FilterGuy]

How about exterior insulation? What surface treatment would you use for weather protection?

Others have reported that insulating the outside is far more effective than insulating the inside. Even just shading the outside makes a big difference.

 

[Hedges]

First order theory, I wouldn't think order of layers would matter.
Main differences I can think of are absorption of solar energy by different surfaces, and thermal mass inside of insulation moderating temperature changes.

Certainly shading helps.
I've always noticed it was hot underneath ground-mount panels; they may not be as good a shade as something else.

 

[sunshine_eggo]

Haven't seen @Guda in awhile, but that's the route he went: