Inlets will not perform without Static Pressure and if you have no negative Static Pressure, you have NO ventilation. Static pressure is defined as “the pressure exerted by a still liquid or gas, especially water or air.” This simply relates to the occurrence of a slight decrease in pressure within a building relative to outside air pressure when one or more exhaust fans are turned on. It’s the force you feel when you open a door to a production unit and you feel resistance (sometimes called a vacuum). If the door closes behind you, you have static pressure. However, if it remains open or opens wider, then you have no negative static pressure. If you see curtains flapping and not drawing up tight to the bird wire, then you also do not have static pressure.
It is important to understand this concept because the use of negative pressure is a necessary form of power to ventilate swine buildings. There are tools available on the market to check your static pressure – the Dwyer Mark II manometer is the most common. Other static pressure tools are the smoke stick, manometer, wind meter, and pressure gauge.
You cannot maintain proper static pressure if have air leaks
Most managers overlook the fact that static pressure is affected by air leakage. Remember, you are trying to pull incoming air in through engineered openings, not through random leaks in the building. Cold air entering through cracks, curtains, or inlets is heavier than the inside warm air. If it does not shoot into the room with sufficient speed at ceiling height, this incoming cold air will immediately fall downward along the sidewalls and endwalls. This results in in pigs being chilled. This is why drafts of air often feel cooler in these areas of sub-standard ventilated buildings.
In buildings under proper static pressure, there will be fewer cold spots, fewer dead air pockets, and no drafts at animal level. By keeping proper static pressure – between 0.05” and 0.08” – you can achieve suitable air mixing. Because the proper velocity of air is coming out of the ceiling inlets, 800 fpm, there is sufficient mixing between incoming and tempered air. Velocity that is too slow will allow the cold air to immediately fall into the pig space.
Wind has a negative effect on static pressure & your heating bill
Wind is a powerful ventilation force that can provide tremendous hot weather ventilation benefit. However, it also can be an enormous hindrance during the heating season. For example, a sidewall curtain with three 4-inch diameter holes, will allow about 40 cfm of infiltration air into the building when subjected to a 5 mph wind. If the situation persists for four months, an additional 80 gallons of propane would be needed to heat the air to an acceptable temperature.
10 to 15 mph wind whirling around the building creates a vacuum in the attic causing you to lose static pressure, which allows hot air to be sucked up into the attic. Hot air contains a lot of moisture and is very damaging to your building’s attic. The attic insulation soaks up the moisture causing it to deteriorate. Insulation that once was 6 inches deep is now much less with minimal R-value. Also, the hot air causes the steel to rust and shortens the life of your building rafters. If the steel plates on trusses are compromised enough, the building could actually collapse under heavy snow.
Check Fan Belts
Fan belts that lose tension are not running cost effectively. These should be checked regularly. You can lose 50% of fan capability with slipping belts.
When operating any air inlet system during the cooler times of the year, it is important to keep in mind that our primary objective is to maximize the amount of fresh air we bring in. This must be done without causing excessive decreases in air temperature or excessive increases in fuel usage. Quite simply, the more air we can bring in without decreasing inside temperature, the fresher the air will be, and the better livestock will perform.
Maintaining a higher static pressure (i.e., 0.08”) by reducing the inlet opening will help direct the cool incoming air to move across the ceiling. As the air moves across the ceiling it will mix with the warm air, heat up and then upon reaching the center of the building, gently move towards the floor. The air temperature at animal level might stay the same or possibly increase, resulting in even better air quality. Again, the goal is not to reduce fan run time/electricity usage, but rather maximize the amount of time fans operate so we can maximize air quality and animal health.