Supply and Exhaust Air ventilation

[NetBooks]

I know ventilation is a reoccurring topic, but I have not come across any discussions about supply and exhaust ventilation. I am not talking about exhaust fans. I found info about this on websites like this one https://en.farmforage.com/20597-ventilation-in-the-hen-house-what-is-it-for-what-typ.html; https://bz.farmforage.com/14598-features-of-the-installation-of-ventilation-in-the-he.html; https://en.decorexpro.com/saraj-dlya-kur/ventilyacija-svoimi-rukami/ and here is a diagram

My coop is an enclosed trailer, so this design appeals to me because it doesn't require me to negotiate for roosting space and drafts along with the extra humidity I get from the nearby rivers. I am already fighting frostbite and this seams to be an efficient way to pull out humidity from where they breath without causing drafts.

 

[U_Stormcrow]

@NetBooks , can you update your Account with your location (as much, or as little, specificity as you are willing to share). Click on your user name at the top bar, right (next to the mail symbol), then Account Details in that menu, scroll down just past Birthdate, and there's a spot to record your location. While not critical to this discussion, it may be more relevant to others.

As to the subject of this thread, many of us do so without specifically identifying that we are doing so. One of the most popular roof designs for our coops involves large under-eave (soffit) vents for intake, which then exhausts thru a ridge vent, center. That helps draw cooler, drier air up above the birds, so as to avoid drafts, which then combines with the warmer, moister air being generated by our birds, and also radiant heat from the roof itself (metal roofing is very popular here, but so are dark shingles) which then exits at the top of the coop.

In the case of my coop, that is combined with an off the ground approach in which my hens have a "U" shaped floor oriented around a central shaft, the whole thing on posts 3' off the ground. This creates a cool area under the coop (where my ducks sleep, and the chickens often play during hot days which draws in air from three sides (the fourth is shared by a barn wall), that then rises up the central shaft (where it can't create a draft on roosting birds) before joining the soffit to ridge vent current and exiting the house. That's supported by a large gable vent, and a high window to allow more air passage.

Others design monitor and half monitor roofs, where the clerestory area thus created serves similar purpose but allows additional air movement - something I may well do in my next build - and is less prone to being blocked by heavy snowfalls (not a concern for me).

So while many of our chicken owning builders may not know why, exactly, they are building that way, these principles are being respected in the final project.

Tube designs, such as that you offer, are interesting in theory, but handicapped by one very significant concern. Free Ventilation Space. The "rule of thumb" is 1 sq ft free venting per bird. A 4" metal vent pipe provides only about 1/10th of one sq ft of vent space. Much larger than 6", and you won't find a cap to help waterproof the entry, off the shelf - and even that is less than 1/4 sq ft ventilation per penetration. Which is why you will see few such designs in use here.

 

[NetBooks]

This is my coop for the most part https://www.backyardchickens.com/articles/enclosed-trailer-coop.76228/. I have general updates, but am focusing more on the ventilation. The reason why I am considering this design is because we have cold winds frequently when it comes winter. I don't have a pitched roof and I can't simply put it under eaves because I don't have any. If I have this design, it will prevent wind from getting in directly. We also can get heavy snow and are due for two snowstorms this week. Also I live in Prescott, WI.

 

[Ridgerunner]

I use two different principles for ventilation. One is when the wind is blowing. I have opening on all four walls at the top of the walls. Some are under overhang, others are closer to gable vent style. The idea is that if the openings are over the birds' heads when the chickens are on the roost, any breeze will be over their heads and not hitting them directly. This does generate some turbulence in the air below but not enough to ruffle their feathers. They stay warm by trapping tiny bits of air in their down and feathers, that provides insulation. As long as the wind is not ruffling their feathers they can stay warm. That gentle turbulence stirs up the air enough so that bad air gets replaced by good air.

Warm air rises. When the wind is not blowing, as long as you have openings warm air will circulate out as long as heavier cooler air can replace it. In summer it can help to have an opening in the shade so the cooler air there can replace warmer air in the coop. The principle still works in winter. Warmth can come from their breath, their poop, or maybe thawed water. Your trailer is raised so you won't get the benefit but with a coop on the ground the ground acts as a thermal mass in a cold snap and provides warmth. Warm air holds more moisture than cold air so if you can get the warmer air out you can keep humidity down even when the wind is not blowing.

Some people think an opening needs to be low to let in cooler air. Physics does not support that. In many cases, in summer especially, a low spot is beneficial but elevation is not the diving force, temperature difference is. As long as the air outside is cooler than some of the air inside and you have openings gravity will cause an air exchange. In Wisconsin in the summer an inlet low down on the north side in the shade is probably your best spot for the inlet. In winter an opening down low might help cause a breeze over the birds when they are on the roosts, depending where the openings and roosts are located.

It was interesting that they said 20 cm (8") was the maximum size for the pipe. The way I read that you only need one pipe low and one high. I'm not real comfortable with that. The driving force is the difference in temperatures of the air inside and out but the bigger your openings the more air can pass. I don't believe in those magic numbers as to how many square feet you need, to a large extent that depends on the temperature differences as the more temperature difference the more the force. In many cases more is better than less.

I think they omitted one thing about ammonia in the article I read. Ammonia is lighter than air. You don't need turbulence or air flow to get rid of ammonia, you need openings up high. Gravity forces ammonia up as long as there is heavier air to replace it. The bigger the openings the more ammonia can pass but it really doesn't take a lot because ammonia is lighter than air. If you smell ammonia what is probably going on is that the coop bedding is too wet and needs to be changed but make sure you have an opening up high.

Several people from up north on this forum have solved frostbite issues by providing more ventilation, not by sealing up the coop and trapping moisture inside so I think you are on the right track. As people that live up north like you probably know moisture can be a huge factor in frostbite. If you go outside with wet hands you are in much more danger than with dry hands. Getting moisture out of the coop can really help with frostbite issues.

Good luck with it.