When dealing with winter and cold weather operation a number of problems can occur if proper maintenance and understanding of the ventilation system is ignored.  These may include higher than normal energy bills, poor air quality, too high or low humidity levels, cold air drafts, disease outbreaks, and ultimately poor pig performance.  For example, by resetting his ventilation control from very tight to letting the controller do its thing, a producer with a 2000 plus sows farrow to feeder pig operation and a 1/3 of the pigs being finished, reduced their propane bill in 2006 from $97,000 to $40,000 in 2007.  This reduction occurred even with higher propane costs and a colder winter.   Key items that need attention before winter include:

Fans: Dirty fans (1/8-inch of dust) can decrease airflow up to 40%.  An example of a pit fan that hasn’t been cleaned in five years is shown in Figure 1.  Having poor performing fans will raise electrical costs because more fans will need to run to compensate for the lack of ventilation and could lead to poor air quality and humidity problems due to reduced airflow.  Fans should have:

1. blades and shutters cleaned
2. deflectors and cones in good repair
3. correct tension on belts
4. winter covers on-hand for unused fans.  

Even though this is a winter checklist, fans should be inspected every month. 

Inlets:  Air inlets are critical for gaining proper air distribution in a swine facility.  Common problems noted for air inlets include not enough opening for the required airflow, downdrafts caused by having opposing airstreams too close to each other, and either operating at too low or too high of static pressure.  Operating inlet air speeds and static pressures are shown in Figures 2 and 3.  Inlets should:

1. be in good working order
2. open uniformly throughout the facility
3. have counter-weighted baffles allowing for four inches of movement and not be locked down completely.

Also, all pump ports and all other unplanned openings (holes in curtains) need to be sealed for inlets to operate correctly. 

Soffits:  In order for the inlets to operate properly, soffits will need to be cleaned of all debris.  It may also be a good time to take a look to make sure soffits are allowing enough airflow into the attic space.  Soffit net free area is defined as a minimum of ¾” x ¾” opening, with the amount of airflow being pulled through at a maximum rate of 400 cubic feet per minute (cfm) per 1 square foot of soffit opening.  For example, if 50,000 cfm of airflow is being pulled through the attic to the inlets, soffit opening would need to be 125 square feet.  Figure 4 shows an example of correct soffit construction.

Curtains:  Curtain leakage is a major problem with negative pressure ventilation systems and ceiling inlets. If curtains aren’t tight, air enters from curtain versus ceiling inlets and air distribution is a problem.  Also, having small cracks around the curtain can lead to excessive propane use.  Curtains should:

1. have no sags or gaps
2. have a 2-3 inch overlap at the top plate
3. have holes (anything over ½ x ½ inches) repaired
4. have ropes in place and tight
5. move 2-4 inches per cycle
6. have end pockets repaired.

Furnaces:  Furnaces need to be cleaned and the pilot lights lit.  Also, if the heater is a variable output model and oversized at maximum output, especially with larger pigs in the room, it may be beneficial to turn the output down.  It is easier to maintain a uniform temperature in the room if heaters run longer rather than in short bursts.    

Controllers:  A real benefit can be gained in reducing heating costs if there is a good understanding of controller settings and how it affects the overall ventilation system.  A common problem is heater overshoot of the set-point temperature and variable speed fans ramping up to compensate for the increase in room temperature.  This is caused by either not shutting the heater off quick enough as room temperature reaches the set-point and/or having the bandwidth on the variable speed fans set to tight.  It is recommended that the bandwidth on cold weather variable speed fans be set no tighter than 1.5 oF, preferably 2 oF, and the furnace offset temperature set from 1 to 2 oF.   If the heater is oversized, offset temperature may need to be increased to prevent heater overshoot.  Also, the minimum speed setting on variable speed fans may be set too high causing over ventilation and wasting heat.  If there are two variable speed fans on the circuit, it may be better to shut one off and run the other at a higher speed, until pigs are larger and more airflow is required. 

Emergency Thermostats: High temperature should be set at 90 oF and low temperature set 60 oF.

Temperature probes:  Temperature probes should be cleaned and checked for accuracy.  Since the controller uses the average of all the probes, having a defective probe will have an affect on overall ventilation performance.  Probes should also be placed so that the temperature recorded is a reflection of the pig space and not be in a position where hot air from a heater or cold air from an inlet is affecting the readings.

Figure 1. Pit fan that had not been cleaned in five years

Figure 2. Correctly adjusted air inlet

Figure 3. Air inlet velocity and static pressure relationship

Figure 4. Attic air intake with proper soffit construction