Humidity in the coop and frostbite

[dacjohns]

We're getting somewhere. We're defining what high humidity and cold are in regards to chicken frostbite.

 

[ivan3]

A poorly ventilated coop, loaded to capacity with chooks. Temp is 0°F inside and out. I'm guessing the specific humidity would be the problem. I think that evaporation and condensation don't depend on the relative humidity but on how much water vapor exists in a given area of the air in the coop.

 

[PurpleChicken]

Relative humidity and humidity in general can be very counterintuitive.

A problem for chickens would be the following situation:
It's 50 degrees during the day and the floor temp rises to 45 degrees. As the day ends and the temp drops the air will hit the dew point and water will condense on the pine causing wet conditions. The condensed water will now conduct the heat from the birds feet easier and as the air temp continues to drop frostbite can occur. The lower the humidity, the less condensation, the less heat loss, and the warmer bird.

Now it's morning and things warm up. The water that condensed on the pine now melts and the pine becomes damp. As this cycle repeats more and more water accumulates in the bedding.

Right now the pine in my coop is frozen solid thanks to this series of events.

I hope this makes a little sense.

 

[Mac in Wisco]

Obviously high humidity feels warmer to us because we are losing less moisture to the air which cools us. Even in cold temperatures we lose less moisture to respiration and perspiration if the humidity is higher. Do chickens sweat?

A lot of the texts I read said that high humidity can accelerate frostbite because of increased conduction losses. Even in moderate temps above 0 F. The reason is that the moisture infiltrates the insulation of our clothes, decreases the evaporation rate of our perspiration, and the excess moisture from perspiration decreases the insulating value of our clothing. How that correlates to a bird, I don't know.

 

[Mac in Wisco]

Quote:
Condensation doesn't occur on the warmer surface. It occurs on the colder surface. If the ground cools faster than the air then the moisture in the air will condense on the ground. It will not condense on warm birds either (another reason that humid air really shouldn't increase conduction losses in birds). Birds should be at roost anyways and shouldn't spent the night on the ground. I have a lot of birds, 2500 hens. They all roost at night, either on slats or on the feed trough. I only catch a couple on the ground at night. If the floor were cold and damp I doubt even those last few would be on the ground.

 

[RocketDad]

Humid air has a higher density than dry air, and the heat from the chicken will have to heat more molecules, and heavier molecules. The heat capacity and the heat conductivity of the air is higher when it's moist.

A dry sauna at 170 degrees isn't as "hot" feeling as a steam sauna at 120. Same thing in reverse, but the chicken is the heat source.

Or to put it another way, the moist air is a better Heat Sink than dry air.

 

[Mac in Wisco]

Quote:
I've been doing a lot of reading and can't put my finger on anything definitive.

A few points I've run across:

While people tend to associate damp weather with being chilly and cold, higher humidities, even at low temperatures, actually feel more comfortable because of reduced heat loss due to reduced evaporation of moisture from the body. (The same effect that makes us overheat in hot temperatures). Since high humidities are dangerous to chickens in hot weather because of reduced heat loss, I can only assume that a higher humidity also reduces heat losses at lower temperatures.

Wind chill indices do not include the effects of relative humidity because the weather services have found that any increased thermal conductivity due to humidity is negligible because of the very low moisture content of air at temperatures below freezing.

An increased feeling of chilliness or increasing risks of frostbite in people due to high humidity in low temperatures is attributed to increased conductive losses of moisture laden clothing, not the increased thermal conductivity of the air itself.

 

[chookchick]

Mac--I found many references to high humidity and increased chances of frostbite (this was on human skin) on the actual skin, not just due to chilling from moist or wet clothing. I've pasted below one explanation for this that I found--

# conduction = transfer to another object by direct contact (water or metal). In the presence of cold water, heat is transferred 32 times more than to the air;

Okay this is still a thought in progress, and I'm getting toooo sleepy.....

ETA--It's morning, had the chance to think about things. Perhaps the small amount of moisture on the skin, perspiration if you are exerting any effort, will conduct heat out of your body faster. With drier air, this effect would not be as pronounced. Maybe chicken combs stay fairly moist on the surface--they look like they would. A dry shrunken comb could be another way of protecting against frostbite. It seems to me that I feel colder when it is damp out, but I can't back this up with any evidence.

 

[PurpleChicken]

Quote:
Condensation doesn't occur on the warmer surface. It occurs on the colder surface. If the ground cools faster than the air then the moisture in the air will condense on the ground. It will not condense on warm birds either (another reason that humid air really shouldn't increase conduction losses in birds). Birds should be at roost anyways and shouldn't spent the night on the ground. I have a lot of birds, 2500 hens. They all roost at night, either on slats or on the feed trough. I only catch a couple on the ground at night. If the floor were cold and damp I doubt even those last few would be on the ground.

Yup, had that one reversed. They don't call in morning dew for nothing.

Correction: As the morning air temp rises above the ground temp water will condense on the ground/bedding resulting in damp bedding which causes all kinds of problems.



This is a headache thread but a good one.

 

[ivan3]

I'll take another crack at this: It is currently 7.9°F with a RH of 63%. In the coop it is 18°F with a RH of 72% (5'x7'x7', heated waterer. one 15w light, and 5 chooks). This is acceptable.

What I don't want to see is a reading of 90%+ in the coop. Yes, colder air can't transport as much water vapor, but the saturation point is lower as well. So, without effective air exchange the amount of water vapor from chooks/waterer would rise to the roof peak and begin to build down toward the roosts (ever see hoar frost form a specific ht. on walls in coop?). Layering and pooling of nearly saturated/saturated air is a sure sign that air exchange is lacking.

As has been mentioned, the heat capacity of humid air is higher than that of dry air. The roo's comb has a high surface to volume ratio (like fingers/toes/ears/and other appendages). It cools and can be cooled more rapidly because of that. Basically, the water being transported in the air `sucks' heat from the surface of the comb, vasoconstriction begins in earnest and goodbye comb tips. Granted, radiative and evaporative cooling are tough to beat in dry conditions, but a high humidity level, at roost ht., in freezing temps, contributes to frostbite.

Another contribution to cold injury in a poorly ventilated coop is the resp. stress generated by ammoniacals and the like that `hang-on' in humid air rather than dissipating. A couple of weeks of that kind of insult and one might begin to see respiratory injury resulting in circulatory problems leading to a less than robust perfusion of the comb (even quicker onset of frostbite).

Just a couple of quotes from folks who know way more about humid conditions than I want to:

2. Humidity. Cold injury is due, in part, to the effect of low temperatures on moisture in or on the body. The higher the moisture content, especially on the skin surface, the more rapid the heat loss. As humidity rises, the temperature at which cold injury can occur also rises

b. Freezing, dry cold injuries are associated with extended exposure to subfreezing temperatures, usually 14 degrees F. or lower when the humidity is low

http://safetycenter.navy.mil/osh/ground/coldinjuryprev.htm

PatandChickens info. is very useful, but every coop/barn/house has it's own vagaries and quirks and only careful observation of what is actually occurring will keep your chickens engaged in philosophizing about the meaning of it all and out of the freezer: