Humidity in the coop and frostbite

[RocketDad]

http://www.sp.uconn.edu/~mdarre/NE-127/NewFiles/psychrometric_inset.html

A good discussion of the psychrometric chart and how it relates to livestock and greenhouse management. Reading now...

 

[Mac in Wisco]

I've read that. It does a good job explaining the physics of ventilating a barn, but not so much on the physiological aspects...

 

[chookchick]

Mac, your right, the lack of evaporative cooling probably pretty much cancels out the additional cooling from conduction...

Rocket Dad--nice article! Very good explanation of winter ventilation, now I wonder how much heat has to be added to get this effect--e.g. can you get this effect from the heat of the chickens alone, with a solar heat sink?.....

"The heated air entering the building is dry enough to be useful in absorbing moisture from the plant or animal environment. (Verify that the heated air at point B continues to have a dewpoint of 34oF and humidity ratio of 0.0042 lb moisture/ lb dry air.) The heated air, with its lower relative humidity, can be mixed with moist, warm air already in the building. As fresh air moves through an animal environment, it will pick up additional moisture and heat before it reaches the ventilation system exhaust. We might measure the exhausted air conditions at 75oF (dry-bulb) and 70 percent relative humidity, represented by point C in Figure 4. Note that in this exhausted air, the humidity ratio has tripled to 0.013 lb moisture/ lb dry air. This means that a lot more water is ventilated out of the building in the warm, moist exhaust air than was brought in by the cold, high relative humidity incoming air. This is one of the major functions of a winter ventilation system: removal of moisture from the plant or animal environment."

 

[ivan3]

I'd guess a pretty good proxy for a poorly ventilated coop, (saturated air) rapidly cooling, is what happens when one steps into a walk-in freezer on a warm day. If the temp. hovers near or just below freezing (for a long period of time) and, if the amount of water vapor in the air continues to be augmented, then the enhanced cooling of the comb of the rooster due to the higher heat capacity of humid air will continue. As the temp continues to drop less water vapor will be available to act as a heat sink (temp. then rules the roost) until, as dacjohns mentioned, the water vapor exhaled by the chooks goes through an immediate phase change to ice cystals. Humid air, slightly above freezing temperatures, for an extended period of time, certainly contributes in a big way to getting the process going.

Now, as to whether this is the process that resulted in the Navy's conclusion, I don't know.

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

 

[chookchick]

So what you're saying is that keeping the temperature at or near freezing is much more likely cause a problem (with a lot of water vapor present) than letting the coop cool quickly to a lower temperature--

This would fly in the face of what many here try to do--which is keep their coop near that temp. in order to keep the water unfrozen (yeah, I've done that). If they put a heat source near the water, temp over the roost is likely to be colder. It would be REALLY helpful to know if this practice is likely to cause problems with frostbite!

I'm not getting the relationship to your quote (dry cold?)--and I'm thinking that those temperature findings are human specific.

 

[ivan3]

I would guess that it is the extended exposure to high humidity levels slightly above freezing that puts the greatest stress on the chooks. Once the temp begins to drop the `heat carrying capacity' of humid air, is simply a relatively minor player that adds insult to injury.

If I was living further south where the currently extremely cold temps are dipping into I'd add heat and watch the temp/humidity levels of the coop and try to keep it slightly above freezing and vent excess moisture (no time for the poor chooks to acclimatize so would have to intervene ASAP). I'd be more concerned about the cold stress making them vulnerable to illness.

We are probably going down to -10°F this thurs/fri with wind chills of -20-30°F. I'll be adding heat lamps for the chooks and turks for those few days, but that will just be to take the edge off (they are acclimatized - pretty cold here since october).

ed: oh, we use heated dog water bowls.

 

[Mac in Wisco]

Quote:
It's hard to say if it does or not. With the very small amount of water in the air, you'd think conduction wouldn't be a big deal. Yet the same could be said for the evaporative effect. The difference in the amount of actual water from near zero to saturated at cold temperatures is small, but may not have much of an effect on the evaporation rate given a much warmer bird. The moisture will go into the relatively dry air anyways given that it is heated by the birds.

Rocket Dad--nice article! Very good explanation of winter ventilation, now I wonder how much heat has to be added to get this effect--e.g. can you get this effect from the heat of the chickens alone, with a solar heat sink?.....

It depends upon the stocking rate. At some point you reach a heat balance where the heat generated by the birds equals the amount of heat lost through the structure and ventilation to produce a given temperature in the barn. If you want it any warmer than that you have to add supplemental heat.

I have a stocking rate of around 1.75 sq ft per bird for 2500 birds.

4 lb layers put out around 40 BTU per bird. So I figure I have bird heat of 100,000 BTU per hour.

The barn is well insulated so I figure I only lose about 5 BTU per sq ft of wall and ceiling regardless of outside temperature (the loss does vary a little with temperature, 5 BTU is a good average). For my barn that equals about 30,000 BTU.

So I have a surplus of 70,000 BTU right? No, we still need to ventilate to remove moisture, carbon dioxide, ammonia and dust. If the ventilation were to ever fail though the birds would be in serious trouble just from overheating.

So, I found at an inside temperature of 65 F, that I needed about 1300 CFM of ventilation to keep the humidity at 80% with an outside air temperature of -10 F. (This ventilation rate increases rapidly with a rise in outside air temperature. It takes little of this very dry air to remove the moisture generated in the barn).

How much energy does it take to warm that air?
(1300 CFM * 60 Minutes * 75F rise in temp) / constant of 55 = 106,363 BTUs

So my heat load is 106,000 BTUS + 30,000 lost through the structure = 136,000 BTU

The birds only produce 100,000 BTU so to maintain 65 F I need an additional 36,000 BTU an hour.

I have an 80,000 BTU radiant heater to make up the difference. Propane gives 90,000 BTU per gallon. So I can figure 36,000 / 90,000 = .40 gallons of LP per hour.

That's the general math behind it. In those conditions I actually burnt less propane than that. The numbers involved are highly variable. I could have been taking in less air than I figured, the birds could have been producing more heat, the insulation may have less losses than I figured...

The biggest demand on the heat is the air for ventilation. I can burn obscene amounts of propane by setting the ventilation rate just a little too high. The whole point of heating this barn is to keep feed costs down. If they eat ad libitum in cold temperatures they can easily eat 25% more feed (they eat $1000 a week anyways). The money saved in feed buys a lot of propane which I can use to provide a better winter environment for the birds. There is a point of diminishing returns though.​

 

[ivan3]

chookchick wrote: I'm not getting the relationship to your quote (dry cold?)--and I'm thinking that those temperature findings are human specific.

The primary differences between a rooster comb and a human finger is the degreee of vascularization near the surface of the roo's comb and the insensible perspiration of the fiinger (try to maintain a 70% humidity level, in a very narrow margin, just above the skin). The percentage of electrolytes in the blood doesn't differ that much - `salt' water freezes at a lower temp. than fresh - in humans the actual temp. at which freezing commences is 28°F. However the more rapid loss of heat from the comb owing to the greater surface to volume ratio of the comb might offset the normally higher temp of the comb (cycling through vasodilation/vasocontriction in response to temp. and external factors that speed the cooling further).

What ressearch the Navy relied on to draw their conclusion that frostbite will begin with extended exposure at temps lower than 14°F if the humidity is lower?

Edited to correct info. for those who don't read entire thread.
(thanks to RocketDad for proofreading)​

 

[RocketDad]

What ressearch the Navy relied on to draw their conclusion that frostbite will begin with extended exposure at temps lower than 14°F if the humidity is lower?

I've run into the Navy data before. They compiled medical information from years of having sailors on the decks in all weather. The military uses information like this to run ops, and to manage work-rest cycles. If there's one thing the military can be counted on, it's having meticulous paperwork for anything. Sometimes it's even useful.

They also have data on how long a person can be in water of various temperatures. There is a point at which a downed-pilot or sailor-overboard is no longer a rescue but a recovery.​

 

[RocketDad]

The primary differences between a rooster comb and a human finger is the degreee of vascularization near the surface, and the temp. (more extensive vascularization and higher temp. in a comb). insensible persperation is probably similar (try to maintain a 70% humidity level, in a very narrow margin, just above the skin).

Chickens don't sweat. Perspiration on the comb is nonexistent.​