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The Perfect Climate Controller

Ideally, it would tell us the “true” temperature

September 15, 2014
By Shawn Conley

The next step in poultry barn climate control may be controllers that take heat index and evaporative cooling into effect


Regardless of the season and climate, the same factors come into effect when trying to maintain target conditions in poultry barns. Depending on whether your barn is in British Columbia, Ontario, or another country, these factors can figure much differently into your ventilation calculations. Temperature, humidity, and air movement are the three that we’re talking about, and it would be huge progress if we had a climate controller that would truly take all three into consideration to keep conditions ideal. Climate controllers should focus on this in the coming years, taking us into the future of agricultural ventilation.

We hear meteorologists talk about “real feel” temperatures — humidex, or heat index — as well as wind chill in the cooler months. If we think about the inside of a barn as a kind of micro- weather system, we can really see how it impacts the comfort of the birds. For any of us that have spent any time in any of the Gulf States in the U.S. (or the wrong July day in Ontario), even if the temperatures are relatively comfortable — say around 25°C / 77°F — it can feel pretty oppressive when combined with 80 per cent humidity, or even higher as a storm is rolling in. Alternatively, especially in the Western provinces in winter, wind can make the already sub-zero temperatures unbearable, and a little moisture combined with 5°C chills to the bone. I’ve never been colder than the day I was caught riding my motorcycle home in the rain and a temperature drop from 20° C to 8°C.

Combination effects
With the importance of humidity, wind chill, and temperature established, what do we need to do? When it comes to poultry, we know that when the combination of temperature and humidity added together in the barn approaches 160, we are in the danger zone for heat related mortality. Our first line of defense is air exchange — just get the hot air out so the birds can continue to release the BTUs of heat they are generating into the cooler air, and move the moisture they pant (their version of sweating) away. The second is to get that air moving over the birds at a velocity that adds a wind chilling effect to it. In some cases this effect can be 15°F. Our last line of defense is to utilize water to cool even further.

I’ve talked before about a side effect of cooling by evaporative cooling pads or fogging / misting, and the respected ventilation expert; Mike Czarick, has talked about the same problem in his summer ventilation schools. When adding water to the air to reduce the temperature, humidity increases 2.5 per cent for every degree F. The problem here is that a 2.5 per cent humidity increase results in a 0.5 F perceived temperature increase, so we lose half of the ground we seem to gain (this is another case for using the combined calculation to give a true temperature). It would be better to increase air speed, and directly apply water to the birds using a sprinkler system to multiply the wind chill effect and keep humidity 20 per cent lower, according to Yi Liang of the University of Arkansas. I think this sprinkling effect could be incorporated into control systems calculations of wind chill.

So, back to the point, our problem with maintaining ideal conditions is that we are guessing at the actual effect of the changes we are making. OK, it’s clear that reducing the temperature is pretty straightforward, but without knowing the humidity levels, we still have to observe the birds on a hot day to see if they are panting too much or being too inactive, or consuming less feed to tell for sure what that temperature really means. In setting up ventilation and controls, I’ve seen many times where producers didn’t realize that wind chill was too high as well, with young birds huddling, or older birds sitting down due to high tunnel wind speed, leading to breast blister and button problems or hock burn. A controller system that factors these issues in would allow more peace of mind on hot days, especially for farmers who have off farm jobs, are busy cropping, or are managing multiple farms. On cold days, piling that can occur quickly if birds are chilled could also be prevented with a few strategically placed anemometers (wind meters) linked to the controller.

Estimating Variables
With anemometers, humidity sensors, and temperature sensors working in concert to provide continuous feedback, creating a logarithm to take temperature + humidity – wind chill effect should be an achievable goal that can be used to build a new type of target temperature curve ­— maybe we call it the wintempumidity curve? Whatever it is, I think it could be a great way to estimate they interaction of all the variables, and create the optimum growing conditions, allowing us to manage the climate without having to do daily tweaks to our ventilation program. If we could establish that, for example, 80 F + 60 per cent humidity – 15 F wind chill at 600 feet / min – 10 F sprinkler effect = 75 F true temperature (this is not necessarily correct, just a potential example), and we can establish a range of acceptable values for our target curve, this could be an excellent way to know how comfortable our birds really are. The controller could adjust all the variables to reach the target if it knows this “true temperature.”

In a perfect world, we’d have a controller that would take the heat index (temperature and humidity), and the effect of wind chill heat loss into its calculations of perceived temperature, and ventilate / heat / cool based on a combination of all of these. It would involve some complex calculations, and a hefty processor, but I think it can be done, and done affordably enough for producers to justify purchasing a system. It just may the next step in the evolution of poultry barn climate control.