Balancing Poultry Housing Moisture Levels – Part 2

As discussed in Part 1 of “Balancing Poultry House Moisture Levels,” one of the primary objectives of a minimum ventilation system during cold weather is to manage house moisture levels. If we get rid of too much moisture, a house will become dry and dusty, which can lead to respiratory issues. Conversely, if we don’t get rid of enough moisture, our litter will become wet and cake over, and ammonia levels will rise, which can lead to a reduction in bird performance, health, and welfare..../>
During cold weather, moisture will be removed from a house every time an exhaust fan operates because the outside air will always contain less moisture than the air inside, even if the outside relative humidity is 100%. This fact becomes apparent when we concentrate on the inside/outside absolute humidity (a measure of how much moisture is actually in the air - Figure 2) and not inside/outside relative humidity (how full of moisture the air is - Figure 1).

For instance, during the first ten days of the flock illustrated in Figure 2, the air outside the poultry house only contained approximately 4 ounces of water per 1,000 ft3, while the air inside the poultry house contained roughly 20 water ounces water per 1,000 ft3. Every time an exhaust fan operated and exchanged 1,000 ft3 of inside air (20 ounces) for 1,000 ft3 of outside air (4 ounces), approximately 16 ounces of water were removed from the house.

For any poultry house, if we know the inside/outside absolute humidity, which can be determined using the Minimum Ventilation Calculator in the Poultry411 App, and we know the amount of air exchanged over an hour or day, it is a relatively simple process to calculate how much moisture the fans are removing each hour or day. For instance, we can calculate how much moisture is removed from a house when a single 36" fan (10,000 ft3/min ) is operating on an interval timer one minute out of five:

- Inside conditions (Figure 2):
Inside absolute humidity= 20 ounces/1,000 ft3
Outside absolute humidity= 4 ounces/1,000 ft3
- Moisture removed each timer cycle:
(20 oz - 4 oz) X 10 (thousand cfm) = 160 oz
= 1.24 gals
- Moisture removed each hour
12 cycles per hour X 1.25 gals per cycle = 15 gals

- Moisture removed each day
15 gals per hour x 24 hours =360 gals

To manage house litter moisture levels, the goal is for the moisture removed from a house each day to be equal to the moisture added by the birds, thus maintaining a constant level of litter moisture. Remove more than 360 gallons; litter moisture levels will tend to fall. Remove less than 360 gallons; litter moisture levels will tend to increase.
Figure 3 illustrates the moisture being added and removed from a house hourly over the first ten days of the flock. The amount of moisture removed by the minimum ventilation fans is increasing each day because, though inside/outside moisture levels are relatively constant, the minimum ventilation fan runtime is being automatically increased by the house’s environmental controller from 45 seconds out of five minutes on placement day to 90 seconds out of five minutes on Day 10. From a moisture management perspective this type of controller feature is beneficial because it continually increases minimum ventilation rates to reflect the continually increasing bird water consumption.

The concern in this instance is that the moisture being added to the house by the birds was increasing faster than the rate at which water was being removed from the house by the minimum ventilation fans. By day seven, the birds were adding more moisture to the house than the fans were removing. If this trend were to continue, litter moisture levels would increase over time, resulting in caked litter and increased ammonia production. This is far from a rare occurrence and is the reason that on most farms the litter starts to cake just prior to turning the chicks out into the full house.

Minimum ventilation fan operation comes down to a simple fact: If we want a constant level of litter moisture, we need to set minimum ventilation fan runtime so that whatever moisture the birds are adding to the house each day, the minimum ventilation fans are removing it.

Of course, calculating each day whether the minimum ventilation fans are removing more or less moisture than birds are adding is not realistic. The good news is that it is not necessary. A relative humidity sensor can provide essentially the same information. If the relative humidity is increasing day after day, then chances are the birds are adding more moisture than the fans are removing. If it is decreasing, the fans are removing more moisture than the birds are removing. The goal is to simply maintain a relative humidity somewhere between 40 and 60%.

Here are a few things to consider when it comes to balancing house moisture levels:
1) Be proactive not reactive. Don’t wait until the litter cakes over before increasing minimum ventilation rates.

2) Use the Minimum Ventilation Calculator in the Poultry411 app to provide an estimated moisture balance minimum ventilation rate based on your bird water consumption and your specific inside/outside conditions.

3) Check your relative humidity first thing in the morning. Ideally, it would be no higher than 60% over the last few mornings. If it is trending upward, for instance, from 55% to 60% to 65%, it is a sure sign that litter moisture levels are rising. With near market age birds a maximum RH of 70%-75% is often considered acceptable due the generally higher air exchange rates and higher levels of air movement within the house.

4) The more moisture is removed during the day, the less moisture needs to be removed at night. This doesn’t necessarily mean that timer settings should be decreased at night; rather, they can be increased during the day when it costs less to bring in fresh air because it is warmer. In general, it costs approximately 30% less to bring in a cubic foot of air during the day than at night.

5) Though you can still remove moisture from a house on a cold, rainy day the fact is that it is going to take roughly 50% more air because the outside air contains more moisture than it does on a dry day. With that in mind you might want to consider increasing minimum ventilation fan settings before or after cold rainy weather sets in to remove any excess litter moisture when the air is dryer and it will be less costly.