At a producer meeting in northwest Iowa yesterday, Steve Pohl and I got into a discussion with the audience about bubble wrap versus 6 mil poly to tighten up curtain sided finishers in cold weather.
A common problem with curtain barns in cold weather is there are too many inlets due to leakage around the curtain ends and all of the little holes that happen in curtains over time. To give you a better idea of how these leaks impact minimum ventilation, let’s look at a 1200 hd room that has 2 24” pit fans. If the fans are model APP24F without discharge cones (a common fan in Iowa and southern Minnesota), the rated cfm at 0.05” static pressure is 5820 cfm. If 2 fans are on stage 1 variable speed, and the controller is set correctly, 50% minimum speed will be about 5800 cfm.
The desired inlet velocity from ceiling inlets is 800 fpm (feet per minute). This corresponds to 0.05” static pressure. The total inlet area needed for the 1200 head room becomes:
5800 cfm = 800 fpm x 7.25 sqft
The sum of the area of all holes and planned openings to the room needs to be only 7.25 sqft. If it is more, the inlet velocity will drop. To give you an idea of how small an area 7.25 sqft is, think about a 3 ft wide entry door to the facility. With a height of 6ft-8in, the total area of the entry door is 20 sqft. This means the total area need for air entry into the room from all entry holes is equal to the bottom 29” of the entry door.
This isn’t much and explains why ceiling inlets often don’t appear to function correctly when barns are operating at minimum ventilation in stage 1. Too many inlets are open, especially in curtain barns with older curtains.
Using 6 mil plastic or bubble wrap makes curtains tight by stopping air leaks at the curtain. Plastic is easier to install (just staple it to the studs on the inside). However, with no insulation value (other that the air space between the curtain and the plastic, moisture in the room condenses on the plastic and drips, meaning wet floors along the outside wall.
There isn’t much R value in bubble wrap, but compared to 6 mill plastic, it is enough that curtains side walls that have bubble wrap installed don’t have condensation (or as much condensation) compared to side walls with plastic. If bubble wrap is used, be sure the reflective foil side is towards the pigs. The foil reflects radiant heat from pigs back to the pigs so the curtain with bubble wrap will feel warm to the pig as it won’t be letting radiant heat loss occur as rapidly as a curtain with plastic.
Whether you use bubble wrap or plastic to tighten a curtain barn, be sure you don’t make the barn so tight the emergency ventilation safeguards don’t function. If the curtain has a magnetic curtain drop, you need to leave space at the top of the plastic/bubble wrap for the curtain drop to function. If you disable the north curtain drop in cold weather so you can put bubble wrap to the top of the opening, be sure the south curtain can drop 2 ft.