Humidity in the coop and frostbite

[dacjohns]

I don't have a problem with humidity in my coop. It is probably over-ventilated but so far no problems.

This has been a good discussion and I hope it continues.

Just a quick recap. I asked the original question, which has since been refined, because of the plethora of posts on other threads saying "high humidity" contributes or causes frostbites. The thing is, "high humidity" as used in those threads was a subjective term that was not defined.

We have come close to defining it.

I guess for the purposes of the typical small flock chicken raiser (small flock meaning roughly other than commercial) keeping the humidity not high would mean your coop is not sealed so tight that you have poor ventilation with a resulting rise in humidity causing condensation inside the coop and frost forming on the combs and wattles of your chickens. Quantifying it, I don't know yet. Maybe a difference of +X% above the outside relative humidity.

 

[ivan3]

dacjohns wrote: Need numbers and a frame of reference. Relative humidity or actual amount of water vapor in a given volume of air and at what temperature? The term "high" is subjective. How high is high?

I think I mentioned this in my first post (specific humidity). The relative humidity is simply a handy guide (am not going to go swinging a wet bulb thermometer around my head) If it reads 98% at 10°F and the door and vents are closed on the chooks who will dump even more into the coop continuously, then the vents will be adjusted.

Insofar as `high' is subjective, well we are talking about a clinical situation and not an academic exercise. The health of the roo, previous cold injury, diet, etc. can be as important a contribution to the development of frostbite as the temp and humidity. Too `high' is the point at which the air exchange is inadequate and the roo develops frostbite (all other variables being held constant, e.g., diet, etc.)

There is no hard and fast combination of temp/humidity that will predict a particular individual's response. The fisherman of Nova Scotia apparently are so well acclimated to shoving their hands into freezing water (and heat transfer from hands to water is thirty two times as great as the transfer of heat from the hands into air of a similar temp), that blood flow into their hands is enhanced by the capillaries near the surface of skin dilating instead of constricting.

I would be willing to perform a rather off-the-cuff experiment if you would like. It is currently 4.3°F with a RH of 63% outside. In the coop it is 16° with a RH of 75%. I'll go out and completely close the lower and upper vents and, if you are willing to pay any resulting vet bills, I'll be more than happy to proceed.

If you run down any research on, let's say, a single breed, experiment I'd be happy to look at it.

I believe I covered the particulars of why humidity, as one variable, contributes to frostbite in my earlier post.

thanks for the thread, needed more coffee, but fun

 

[RocketDad]

This has been a good discussion and I hope it continues.

Yeah, it has me googling like mad. I have several calcs, 5 browser tabs and a periodic table open on the screen all at the same time, trying to wrap my head around some pretty abstruse concepts.

I don't think moisture can condense on the chickens' combs, by the way, since the skin will always be dumping body heat. The body heat may not be able to keep up with heat loss, but it shouldn't ever be colder than the air in the coop. Condensation will always be on a surface colder than ambient. Like windowpanes, nailheads... surfaces dumping interior heat to the outside.


Thus, if there is any validity to the theory that higher humidity leads to greater risk of frostbite, it's an atmospheric cause, not a skin-surface cause.

Here's a comment from an AC guy's site:

# Sensible heat, is defined as the heat of dry air. It is the "dry heat" from anything that has the temperature above 0 Kelvin

# Whereas latent heat is the heat contained in the water vapour, carried by the air. The higher the water vapour content, the higher the latent heat

http://www.air-conditioner-selection.com/air-properties-and-air-conditioners.html

I think the moisture pulls more heat (or dumps it, at higher temps) to the skin than the dry air, from this and other things. I'll keep looking.

 

[ivan3]

dacjohns wrote: causing condensation inside the coop and frost forming on the combs and wattles of your chickens.

The the temp. of the surface of the roo's comb can fall to the ambient temp. of the coop, but to get it any lower would require energy from somewhere. What damage is done has to do with the fact that the heat capacity of humid air is twice that of dry air (with provisos, of course).

That said, anyone with a pic of a roo standing in the coop with hoar frost on his comb, please, post it up.

ed: clarity​

 

[dacjohns]

Moisture condensing on the comb and wattles. What was I thinking? That's what comes from posting before thinking through something.


More likely to see frost forming on feathers from the bird exhaling.

I realize specific versus relative humidity. Relative just seems to be an easier term to use since it is more commonly used.


I think we've done a pretty job with this unless someone stumbles upon something else.

Thanks.


ivan, do you have a hygrometer? Wonder how you know the humidity where you are?

 

[ivan3]

dacjohns wrote: ivan, do you have a hygrometer? Wonder how you know the humidity where you are?

The one made of Cass' hair and fishing wt. (put together for oldest grandson's `project') is pretty much a cat toy.

So, (a few miles south, but it'll do): http://agebb.missouri.edu/weather/realtime/mizzou2.asp Coop humidity? cheap digital for RH - from that and the info. from Sanborn I can make a pretty good guess (tell everyone it is `inferential physics'

didn't see a bear but saw the tracks ).

I try to emulate E.Fermi's method in these matters (a hero of my youth - and still in awe of his style of calculation).

Only quote somewhat appropos for this thread (listen up you whippersnappers - math and physics!):

"From reading many detective novels, I know that a body will cool by about 10°C in 6 hours. If we consider the body to be a 100 kg bag of water, then this heat loss corresponds to 1.5°C/min or 1°C/40s. We know that a calorie is the amount of heat required to raise the temperature of 1 g of water by 1°C, so we have 100 kcal/40s. This gives 4180 J/40s or 104 J/s. So we can deduce that a human puts out about 100 watts of heating power."

He was right.

Stay warm, you hear?

John​

 

[RocketDad]

LOL Thanks

 

[chookchick]

Quote:
Okay, I should be asleep, or working on coop page at least, but two points--

"Condense" is the wrong word, I know I've used it incorrectly--but water vapor can settle on surfaces, like when fog creates icy roads, right?

I am still not convinced that the skin-surface (or comb-surface) itself is not contributing to the cooling effect by having a microscopic layer of moisture on it. Skin is constantly losing moisture, that's why we use moisturizers (and perhaps part of the idea of using vaseline?) This layer would evaporate off and not contribute to cooling by conduction if the humidity was low, and with air movement. Still just a theory, I'm trying to figure out why I feel more comfortable in dry cold.

 

[RocketDad]

Still just a theory, I'm trying to figure out why I feel more comfortable in dry cold.

It gets complicated . . .

http://www.air-conditioner-selection.com/psychrometric-chart-air-conditioner-sizing.html

. . . but I believe the short answer is "because you are not warming water with your body."

I'm still researching this trying to find a simple answer, but I suspect I'm trying to find a 10 cent answer to a 2-dollar question.​

 

[Mac in Wisco]

Quote:
I doesn't settle, the moistest air is going to be in the warm air at the top of the coop. That's why you see frost at the top of the walls and slowly working it's way down when it's extremely cold outside.

I am still not convinced that the skin-surface (or comb-surface) itself is not contributing to the cooling effect by having a microscopic layer of moisture on it. Skin is constantly losing moisture, that's why we use moisturizers (and perhaps part of the idea of using vaseline?) This layer would evaporate off and not contribute to cooling by conduction if the humidity was low, and with air movement. Still just a theory, I'm trying to figure out why I feel more comfortable in dry cold.

There are two different effects at work here. Conduction to a layer of moisture on the skin and evaporation. It takes energy to evaporate moisture and it cools the skin. That's why we sweat to cool off, it extracts heat from the body. If it's humid it reduces the evaporation rate and keeps us warmer (or too warm in the summer).

In a humid coop it's possible that a layer of moisture on a bird's comb help to cool it off, but at the same time a humid coop reduces evaporation of that moisture. At very low humidities the amount of evaporation (and additional cooling) can be significant. Where these two effects balance each other I don't know... It would seem to me that a higher humidity should keep you warmer, up to a point, but if you follow the common wisdom here, at some point it becomes detrimental. I still haven't found anything definitive as to the exact reason humid air wold promote frostbite. Most texts just give generalities. Some go as far to say that it reduces the insulating properties of our clothing. Articles that talk more in depth are few and far between.​