Winter surprised us this week

The sudden arrival of winter has caught a lot of producers unprepared. I’ve heard of producers who still need to empty pits, but tonight’s -3F predicted low will really drive the frost down. Hopefully next weeks break in the weather will be enough to allow the remaining pits to be emptied.

For many producers I’m betting that this past week’s sudden onslaught of cold weather has meant a return of wet and messy pens as ventilation systems suddenly ramped down to minimum levels. Many assume that the cause of the wet and messy pens is that the minimum ventilation rate is too low and the response is to increase the minimum speed setting in the controller. This may or may not be the correct solution to the problem.

In my experience, messy pens at minimum ventilation are often caused by incorrect inlet adjustment, rather than incorrect controller adjustment. For example, if you have 2-24” fans as your stage 1 minimum and you operate the minimum at 50% (assuming you have the correct motor curve in the controller), the total inlet area into the room only needs to be 7.5 square feet to get the 800 fpm desired inlet velocity.

To tell if you have the correct inlet velocity (and static pressure), in rooms with 7.5-8 ft ceilings you should feed the ‘draft’ in your face when you stand 13-15 back from the inlet (and you aren’t 6 ft 5 in tall). If the inlet ‘draft’ hits you in the face at 4-6 ft back from the inlet, you’ve got too many inlets open and the resulting inlet velocity (static pressure) is less than optimal.

In cold weather fills in situations such as this, I aggressively lock up some (or even many) of the ceiling inlets until I get to the point of reasonably correct inlet velocity. Once I get air in the correct location in a pen, then I evaluate whether the minimum setting in the controller is correct. Until you get inlets set correct, increases in minimum ventilation settings mean greater expenditures on propane, something that may not be necessary to correct the wet flooring problem.

Common causes of too many inlets into a room or animal space include pit lids incorrectly positioned on pump outs, unsealed shutters on unused fans, broken/missing shutters on unused fans, emergency drop curtains with pin-holes from being washed with rotating tips, missing door stops and door sweeps, etc. It doesn’t take much of an opening to influence incoming air velocity (distance traveled) when the total need into a 50 x 196 ft room is only 7.5 square feet!

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