In both new and remodeled swine production facilities, it is not uncommon to have fans, inlets, heaters and controllers supplied by up to four different companies. While the ventilation controller is the hub for all heating and ventilation system operations, many, if not most, producers rely on their many suppliers and/or builders to integrate the components into a working system.

When construction and/or equipment installation is completed, there is often only a 20-30 minute ‘training’ session on the system and the producers are left to fend for themselves in management of the system. With four or more brands of equipment, there is most likely no detailed explanation of how and/or why the various components were chosen, nor is there detail as to the capacities of the components or verification of the settings most likely input into the ventilation controller by the installer.

For many producers and their employees, ventilation controllers are something to be feared, meaning that operation of the entire heating and ventilation system remains a mystery.

The obvious place to start in understanding your ventilation system is to list the fans, furnaces and inlets installed, and the capacities of these devices. It is not enough to list the fans as ‘24 inch Multifan pit fans’ since that tells potential users of the information nothing about the capacity of the device or specific model number, an important criteria when ordering parts or estimating performance. For example, Multifan has 6 different 24” fans listed in the BESS Labs manual (www.bess.uiuc.edu) with capacities at 0.05 in. w.g. static pressure (1.25 mm w.g.) ranging from 4,520 to 7,280 cfm (7,680 to 12,370 m³/hr). Armed with fan specific information, it is possible to predict how a ventilation system will respond to various pig size during varying seasons and to compare the installed capacity versus recognized ventilation needs (Table 1).

Table 1: Recommended minimum (cold weather) ventilation rates for moisture control in growing pig facilities. MWPS (1990)

Assuming insulation values of R=35 for ceilings and R=20 for side walls, combining pig heat production estimates (Brown-Brandl et al, 2004) with facility heat loss equations (MWPS, 1977) make it possible to create Table 2. The balance point temperature in Table 2 is the estimated incoming air temperature at which heat production equals heat loss via the ventilation system and insulated walls at various combinations of pig weight and room temperatures. Note that the cfm’s chosen represent typical fan ventilation capacities for fully slatted wean-finish and grow-finish facilities in the US. For example, the 10 cfm rate would represent 2 -24 in. diameter pit fans at 100% of rated capacity in a 1200 head room, while the 5 cfm would be the fans operating as variable speed fans at 50% of capacity, etc.

Table 2: Balance point temperature (in C degree) for growing pig facilities

For pigs weighing 23 kg, if the set point of the controller is 22^o C, and the first stage variable speed fan has a bandwidth of 1.1^o C (2^o F) with the minimum speed set to ventilate at 5 cfm/pig, the room is in balance when the incoming air (outside air temperature) is -11^o C. That is, if the incoming air temperature is lower than this, heat must be added to the room or facility, or the room temperature will gradually lower. If the incoming air temperature is higher than this, the ventilation system will gradually increase the amount of air removed (increased cfm), while also raising room temperature. When the stage 1 fan(s) is running at 100% speed (often 10 cfm/pig in US fully slatted finishing facilities), the room temperature is 1.1^o C higher (bandwidth setting in the controller) than the set point and the incoming air will now be approximately 6^o C.

In essence, Table 2 allows producers to develop an expectation of how their ventilation system should operate. When they walk into a room or facility, with pigs of a certain size, given outside air temperature, which fan(s) should be operating, and for variable speed fans, what speed should they be operating at?  For example, with 45 kg BW pigs, if the outside air temperature is near 0^o C, the first stage fans (10 cfm) should be operating at full speed, and the second stage fans (an additional 10 cfm in US facilities) should be cycling on and off. For 91 kg BW pigs, the same outside conditions should mean that stage 1 and stage 2 fans are at or very near to full speed (20 cfm in a typical US facility).

As Table 2 illustrates, one of the biggest ventilation challenges in many production facilities is to get the ventilation rate low enough for 11 kg or smaller pigs. In well insulated facilities, the balance point changes from -17^o C to 4^o C as the ventilation rate increases from 2.5 to 5 cfm/pig for 11 kg pigs. At the 5 cmf/pig rate this means that heat must be added to the system, either as room heat or supplemental zone heat whenever the incoming air is colder than 4^o C.

References

Brown-Brandl, T.M., J.A. Nienaber, H. Xin and R.S. Gates. 2004. A literature review of swine heat production. Trans. ASAE 47(1):259-270.

MWPS. 1997. Structures and Environment Handbook. MWPS-1. Midwest Plan Service, Iowa State University, Ames.

MWPS. 1990. Mechanical Ventilating Systems. MWPS-32. Midwest Plan Service, Iowa State University, Ames.

Photo Caption:  Hog barn-1