I spent 2 days this week working with producers who purchase feed ingredients from a regional supplier. At all of the sites, I was once again shocked by the lack of knowledge regarding the ventilation system. By lack of knowledge, I mean producers who only knew how to change the set point on a controller.
At almost all of the sites, there were improper settings in the controllers that resulted in higher than necessary fuel expenses. A classic example was a farrowing house where the set point for the room was 70F. The furnace was set to turn on at 70F and off at 71F. At the same time the stage 1 variable speed fan began increasing speed at 70F. The obvious complaint was high fuel bills. The solution – reset the furnace so it turned on at 67F and off at 68F.
At the same time, we examined how the variable speed fan for stage 1 operated. In one farrowing room, the fan was at full speed when the controller was set at 50% minimum speed. Below that, a change of 1% on the minimum speed caused enough of a change in speed that we could hear the change. Unfortunately, this controller (over 10 years old) did not have the capabilities of any adjustments to compensate for how the fan responded to the voltage signal from the controller.
In another farrowing room, the controller had user selectable motor curves, but the producer had never been shown how to select them. In this case, the consequence of the wrong operating curve for the fan installed resulted in a very high propane bill.
Another common problem is thermostat settings in pre-heat hallways. Everyone assumes that because heat is often needed in the farrowing rooms and nursery rooms associated with these hallways the temperature of the hallway is relatively unimportant.
In fact, the room using air from the hallway reacts as if outside air temperature is the hallway temperature. When it is 0F outside and 55F in the hallway, the ventilation in the room responds to 55F, not 0F.
To better understand this issue, I modeled the balance point temperature for a farrowing room with a pre-heat hallway. The balance point temperature is the incoming air temperature at which heat production by the lactating sow and litter equals heat loss for the insulated building shell and ventilation system. I used a 22 crate farrowing room with R=30 for ceiling insulation and R=19 for sidewall insulation.
The balance point temperature for a farrowing room full of females and litters that are approximately 2-2.5 weeks into lactation was 45F when the minimum ventilation rate was 25 cfm/crate. This means that when the incoming air was warmer than 45F, the ventilation system in the room would speed up as heat would gradually increase in the room.
I also looked at the impact of various ventilation rates on this balance point temperature. At 35 cfm/crate, the balance point became 50F. That is, when the pre-heat hallway is set to 50F, the ventilation rate in the farrowing room will speed up to 35 cfm/crate to maintain temperature in the room. This means more air must be pre-heated in the hallway, only to go out the ventilation fans at rates higher than the minimum rate needed for moisture control.
This suggests that farrowing facilities that have pre-heat hallways set to 50-55F for worker comfort have higher than necessary fuel expenses due to over ventilation of farrowing rooms.