Single slope cold weather coop ventilation question

[a_a_ron]

I wonder if anyone could dive into any more specifics. I’m already sold on the value of ventilation overall, I’m just trying to get a good understanding of how one can use design to influence the function. I’m just the kind of person that has trouble planning out this type of thing without understanding all the facets.

For example, the rule of thumb is 1 square foot per chicken, right? But, that value can be reduced if you put in a fan. So really it’s about airflow, not a static number of open space. And lots of factors have to influence that. I have to imagine 1 cubic foot of ventilation on one side of the building has a much different effect than if we put 1/2 cubic foot on opposite sides.

So, there’s one end of the spectrum with active ventilation and one with passive, but what about in the middle? Can one reduce the amount of opening required by placing it properly?

Can implementing convective ventilation make up for 10% off open vent space? 50%? And are there any data-driven ways to analyze this? Calculate the amount of rise between the two sides? Is it better to have the same amount of open space on the higher and lower sides, or can a configuration be made to pull more air through? Or is it all even more complicated and depend on ambient air temps etc.?

(And of course, if there’s more threads that cover this and I’ve just missed it, apologies, and please pass it on).

 

[3KillerBs]

I wonder if anyone could dive into any more specifics. I’m already sold on the value of ventilation overall, I’m just trying to get a good understanding of how one can use design to influence the function. I’m just the kind of person that has trouble planning out this type of thing without understanding all the facets.

For example, the rule of thumb is 1 square foot per chicken, right? But, that value can be reduced if you put in a fan. So really it’s about airflow, not a static number of open space. And lots of factors have to influence that. I have to imagine 1 cubic foot of ventilation on one side of the building has a much different effect than if we put 1/2 cubic foot on opposite sides.

So, there’s one end of the spectrum with active ventilation and one with passive, but what about in the middle? Can one reduce the amount of opening required by placing it properly?

Can implementing convective ventilation make up for 10% off open vent space? 50%? And are there any data-driven ways to analyze this? Calculate the amount of rise between the two sides? Is it better to have the same amount of open space on the higher and lower sides, or can a configuration be made to pull more air through? Or is it all even more complicated and depend on ambient air temps etc.?

(And of course, if there’s more threads that cover this and I’ve just missed it, apologies, and please pass it on).

The important thing to understand is that these recommendations are MINIMUMS. Don't try to reduce, if anything try to increase.

As @U_Stormcrow always says, a chicken coop needs to be ventilated like a bathroom or kitchen, not like a human house. Birds have very delicate respiratory systems and thus giving them generous ventilation is one of the keys to keeping them healthy.

If you install a fan it needs to be rated for barn use because the dust from bedding and feather dander will clog up a motor and create a fire hazard. Commercial chicken houses have elaborate systems with automatic controls linked to thermostats and ammonia detectors.

That's beyond the scope of most backyarders so we have rules of thumb instead.

 

[U_Stormcrow]

I wonder if anyone could dive into any more specifics. I’m already sold on the value of ventilation overall, I’m just trying to get a good understanding of how one can use design to influence the function. I’m just the kind of person that has trouble planning out this type of thing without understanding all the facets.

For example, the rule of thumb is 1 square foot per chicken, right? But, that value can be reduced if you put in a fan. So really it’s about airflow, not a static number of open space. And lots of factors have to influence that. I have to imagine 1 cubic foot of ventilation on one side of the building has a much different effect than if we put 1/2 cubic foot on opposite sides.

So, there’s one end of the spectrum with active ventilation and one with passive, but what about in the middle? Can one reduce the amount of opening required by placing it properly?

Can implementing convective ventilation make up for 10% off open vent space? 50%? And are there any data-driven ways to analyze this? Calculate the amount of rise between the two sides? Is it better to have the same amount of open space on the higher and lower sides, or can a configuration be made to pull more air through? Or is it all even more complicated and depend on ambient air temps etc.?

(And of course, if there’s more threads that cover this and I’ve just missed it, apologies, and please pass it on).

Yes, there are rather expensive modeling programs that can do the fluid dynamics calculations. There is no "back of the napkin" math, that I am aware of. Particularly with small structures like our chicken houses, full of odd protrusions, you can't do real basic computations like horizontal wind load on a house, or a peak rainfal calculation for gutter sizing. Those are all easy formulas (or at least, simplify down to easy formulas for large relatively flat areas).

So we use thumb rules, and try to follow passive ventilation principles - placing our weather-sheltered 24/7/365 openings at the tops of walls, usually on opposing sides, often supported by a ridge vent (or better - particularly in areas with heavy seasonal snowfalls - where monitor and half monitor roof designs are popular).

Materials, masses, and colors matter, too. A clear, thin plastic roof has no thermal mass to speak of, and doesn't warm up much, but probably allows passive solar to warm the ground or walls when the sun is - depending on building orientation and the sun's elevation relative to the horizon. That will affect which locations show more and less warming of the air. Similarly, a heavy plywood and dark asphalt shingle roof has a lot of thermal mass (relatively), and considerable passive heat gain from the sun, while the area it shades should be much cooler. Larger theoretical temperature differential, faster potential air flow - but if the air can't carry the heat radiating from the roof out as quickly as its generated, the coop heats up inside...

Can think oneself in circles.

Ultimately, we build the best we can the first time with the thumb rules, then experience the coop for a while under our conditions. When chciken math requires that we build a second coop, we (hopefully) take what we've learned and do better.

 

[aart]

Yes, there are rather expensive modeling programs that can do the fluid dynamics calculations. There is no "back of the napkin" math, that I am aware of. Particularly with small structures like our chicken houses

Ditto Dat!

 

[a_a_ron]

Can think oneself in circles.

Ultimately, we build the best we can the first time with the thumb rules…

Indeed you can… No modeling for me! Guess I’ll stick with the rules of thumb for now, give something a shot, and then report on it here so others can learn at least! Thanks all.