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Ventilation for Tiny Shipping Container

 
pollinator
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Location: OK High Plains Prairie, 23" rain avg
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Ideally, there ought to be a forum for Ventilation/Condensation/Humidity Control in the Building forum as proper ventilation can make or break a building and the health of those living in it. I believe many self-design/builders do not understand the importance of moving air through a tiny house, or any house. I myself am behind the eight-ball in this department.

I'm designing a 20-foot shipping container tiny house. I'm not sure if I will have electricity or not. The 5-day winter storm we are having has me considering changing the location of the container so that instead of having electricity which necessitates facing North, I will face East instead but be off-grid. Moving on...

I am insulating the container on the outside to limit toxic gick and mold sources inside. That leaves me with a metal box interior. It's all open floor plan except the bucket toilet room. I will have a shower, washer/dryer, stove/oven and other humidity-making appliances. The stove will have it's own vent which exhausts out. My plan is to have a mini-split but they do not bring in fresh air, only circulate and dehumidify existing air. I am in Western Oklahoma which qualifies as a Mixed-Humid Climate. We have more cooling days than heating days so I was looking at an ERV, but all the ones I find are for ductwork which I don't have or need. The other issue is I am located in the middle of a gas field and two miles from an open pit disposal for fracking fluids and other smelly-bad-for-you chemicals. The wind doesn't blow from that direction most of the time, but it does sometimes so I need to be able to filter the air coming in or close it off.  From the reading I have done that I somewhat understand it looks like two or three separate systems (1. AC-heat minisplit, 2. air intake and exhaust, 3. dehumidifier if needed) are better than one. I've attached my readings below.
So, two questions: 1.If I have electricity what are my options for bringing in outside air and filtering it if needed, and exhausting stale air? 2. Same question but with solar or wind electric?

Balanced Ventilation Systems: HRVs and ERVs

Building Science Corp. Ventilation This one shows my zone and talks about different systems which are more complicated than I need but might be good info for others.

Do Mini-splits bring in fresh air?
 
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What is  ERV, please?
Can I ask why you bought land so near to the stuff you speak of?

I cannot imagine what you can get that would be practical in your situation.
 
pollinator
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Energy recovery ventilator.  It has a gore tex heat exchanger so it balances heat and humidity as it exchanges air.  

Panasonic makes a really good one, super low power draw. I would run it 24/7/365 there or not to keep the place from getting musty. Easy to run from small solar.

NOBODY that I can find talks about this for mixed climates! I can find out for Minnesota or south Texas, but not Midwest.  Matt Risinger is a high end builder in Austin and talks about ervs quite a bit on his YouTube channel, one of the best laymen level resources I have found.  

I think code for an unventilated attic is two or three inches of foam to prevent condensation in your climate (don't quote me) so your external insulation should be enough to prevent bulk condensation IF you haven't added too much humidity from cooking/heating/breathing. Be careful of heating with ventfree propane, they add a LOT of humidity. Best to heat with wood or a sealed combustion furnace that exhausts outside if you do more than the mini split.





 
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If you insulate the outside you may end up having the metal sweat on the inside with just the humidity and body heat a person throws off. I used to live in a converted school bus and I had issues with condensation on the inside of the sheet metal. I built my house to draw air naturally because I knew I'd be off grid eventually. I suggest you put a couple roof vents on it that you can close when its cold and lots of windows with screens that you can open. You could even build a Cupola on the top and paint it dark to draw air upwards.
 
denise ra
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R Scott, Can you please include a link to the Panasonic ERV you mention? I won't have any ductwork so does it go thru a wall? Matt Risinger's Build YouTube channel is full of information, yes. Perfect Wall says I need 8" of roof insulation, we'll see. Thanks!

Joh C Daley, It was my great-grandparents homestead, still in the family, and it needs some attention. It's been continuously grazed by tenants for decades and I will switch it over to rotational grazing next year. It's the prairie and it's lovely. I've gotten used to the gas pads and when it smells bad I will go inside until the wind switches direction. If you've never seen one, look up Wind Rose.
 
R Scott
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https://na.panasonic.com/us/home-and-building-solutions/ventilation-indoor-air-quality/energy-recovery-ventilators-0

They need ducting like a bathroom fan needs ducting, not necessarily tied to an HVAC system.  Pull the exhaust from the bathroom and kitchen, deliver fresh air to the bedroom is the normal way to do it.
 
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I've got one of those conex boxes for storage and certain times of year I get condensation inside, I've had thoughts of elevating it on blocks and putting a corrugated metal roof over it, but that's both expensive and a lot of work that might have little effect on the condensation problem when season and temperatures change. the idea of vents on top might work well in summer but not sure what effect might have in winter and cutting any holes into it opens up possibility of leaks from rain and snow.
makes me wonder about all the awesome home builds ive seen on internet and how they have dealt with and made out with condensation problems if any at all. but then again this old pre civil war house of mine has moisture and mold problems of its own being in a hot wet area of country and also being in bottom of a valley probably doesn't do a lot to help either.
 
denise ra
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I went to the specs and I am in Zone B on Panasonic's map for the WhisperSonic ERV. Zone B: Unit can perform optimally March through November. I called Panasonic and they say it will run on Defrost Mode in winter. This exhausts moisture out but does not bring in fresh air. Their next model up will bring in fresh air in winter but minimum ACH is 50; way to much for tiny house. I wonder if there is some simple vent which is adjustable to allow air in in winter, smaller than a window? To use this I will have to build a box of some sort inside the house to hold the ERV box. They would hook this up to ducts but I'm guessing I can just leave it ductless?
Panasonic's zone map for their products
 
denise ra
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The brochure, technical specs, and other info for the Panasonic WhisperComfort ERV are at this site for others who would like to understand how this ERV works and what it does.
https://na.panasonic.com/us/home-and-building-solutions/ventilation-indoor-air-quality/energy-recovery-ventilators-0
 
R Scott
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You will want some separation between in and out, but that can be a piece of 4"flex like dryer vent.  Or a piece of pvc painted to match stuck in the corner.   Hide the unit up high above a cabinet or in the dead corner kitchen cabinet.

The sizing problem is a problem, I don't know of any for tiny houses.  Really, a couple computer fans are big enough.  
 
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denise ra wrote:I went to the specs and I am in Zone B on Panasonic's map for the WhisperSonic ERV. Zone B: Unit can perform optimally March through November. I called Panasonic and they say it will run on Defrost Mode in winter. This exhausts moisture out but does not bring in fresh air.

t

Thanks for this info. We're building a "small home" not tiny but at 24' x 24' with a loft, it's small enough that most appliances are way overkill.  Only comment about this is that March through November I can open a window.  In the northeast, once we burn wood for heat, moisture isn't a problem anymore but some additional fresh air would be welcome.

We permitted the building as a residence which means in our State we have to have it pass the "blower door test". So we were planning on putting as few holes as possible through the walls and roof until we passed all our inspections.  Then we'd add a vent for the kitchen stove and one for the bathroom.  We're also putting in a "cool cupboard" in the kitchen.  We have the big culvert pipe into the slab done which will eventually connect and open into a root cellar for the cool air intake, but have the end buried for now and won't vent that out until later too.
 
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Denise, check out:

http://vents-us.com/cat/704/

This is a very simple HRV/ERV that is ductless (goes through the wall) and is for a single room. It has a ceramic heat exchanger and a fan that you set to alternate between blowing inside air out and outside air in. I have a regular size house, not a tiny house, so I have four of them installed all around the house, but for a tiny house one will suffice. I use the HRVs in winter months for ventilating my house that has radon seeping in, so I don't have to keep windows open in frigid temperatures. It can also be set for just blowing air out or blowing air in. Comes with filter. I'm very pleased with these units. As I recall, they cost about $150 per unit. It may be a bit more because I got a discount for getting four of them.
 
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It sounds like it is cold enough to use an HRV instead of an ERV. You will get some humidity control, especially in winter. If your only humidity problems are in summer, use the ERV. You could add a passive ventilation system with a long 4" or 6" duct placed below frost line in the ground, a trick from greenhouses.  Another humidity control is to put a 1-2" layer of rock wool or, even less embodied energy: Homasote sound board, behind thin wood paneling inside your metal shell. It will absorb moisture and later release it when it is dry inside. Nicer surface than the metal also!
 
denise ra
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Wally Jasper, thanks for this info and link. This product might work. Do you know about the filters? In one place it says The twin fresh has a Merv 5 filter, in another place it says GA3 I believe. Will the twin fresh work with a better quality filter? The tiny house will be near a gas well pad that is stinky sometimes. Also, did you get the model s or the model r which is for retrofits? Do you think the model you got will be a good one for the shipping container? I'm insulating on the outside with at least 4 in of foam board plus siding.
 
That is a really big piece of pie for such a tiny ad:
177 hours of video: the Permaculture Design Course and Appropriate Technology Course
https://permies.com/wiki/65386/hours-video-Permaculture-Design-Technology
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