With propane at $2/gallon, many producers have begun inserting ‘Tekfoil’ or similar materials between the bird netting and emergency drop curtains in cold weather. The question that needs to be asked – how tight can these emergency drop curtains be sealed and still maintain the emergency ventilation protection?
One way to estimate this number is to examine a curtain sided finishing facility measuring 41 x 200 ft housing approximately 1000 growing pigs. This number of pigs within this building dimension translates into 5 pigs per foot of building length.
A 5 mph wind against the long side of the building is 440 ft/min in velocity. With a 1 ft opening on both sidewall curtains, each 1 ft of length in the building receives 440 cfm of exchange, assuming 100% of the wind velocity is transferred thru the curtain openings. With 5 pigs per ft of facility, this becomes 88 cfm/pig.
This suggests that ‘Tekfoil’ type products, when installed, need to stop a minimum of 6” from the top of the opening in a 40 ft wide facility to ensure emergency relief for any curtain that has an ‘emergency’ drop function (magnetic relay or override thermostat) associated with it’s installation and operation.
In the case of double-wide facilities (80’ wide barns) there are 10 pigs per ft of barn length, so a minimum opening of 12” is needed to maintain an emergency ventilation rate at 5 mph.
For barns with 50 ft wide rooms, the number of pigs per ft of facility length increases to 6.1 for single wide and 12.2 pigs for double-wide facilities. A 1 ft opening on curtains translates into 36 cfm/pig on double wide facilities.
This cfm rate translates into effective heat removal for 50 lb pigs whenever outside air temperatures are less than approximately 65F. At the other end of the weight scale, this amount of emergency ventilation translates into effective heat removal for 200 lb pigs when outside air temperatures are less than approximately 50F.
Because of issues associated with even distribution of the ‘Tekfoil’ materials, etc. in sidewall curtain openings, I suggest that producers who rely on these curtains for emergency ventilation keep at least 12” of curtain open for the emergency function, regardless of building width.