Whenever an exhaust system is installed in a manufacturing facility provisions should be made to bring in the correct volume, temperature and relative humidity supply air necessary to keep the pressure in the building close to a neutral pressure. Picking a volume, temperature and relative humidity of air to bring in is not simple.
Picking Southeastern AirWorks to work all that out is the simplest way and here are some of the reasons why.
Should the make-up air be equal to or be more or less than the total exhaust? The answer depends on many other factors. depending on how the air in the rest of the facility should travel. Should the air in the plant travel from clean to dirty areas? Should the plant air pressure be less than the air pressure in the offices and by how much. If it is too high opening the doors can become a problem.
A proper design must always consider the range of temperatures, air quality, and relative humidity levels that is best for production and technician comfort. There may be multiple processes in the room. Each one requiring a different climate condition. The operators in the room may be able to accomplish their tasks in small zones of conditioned space that can be isolated from the process temperature controlled area. Conditions near the floor will be different than the conditions near the ceiling. Additionally, when dealing with complex systems, air migration from zone to zone should be controlled.
In an air conditioned plant the exhaust air requirements and radiant heat from the process create the greatest load on the air conditioning system from a heating and cooling stand point. Outdoor air will come in to balance the exhaust air. If not the exhaust system will under perform and air quality will suffer. Making up that incoming ambient, seasonal air will bring conditioning challenges to maintain indoor conditions. Some of the most challenging times for proper temperature and humidity control for make up air for exhaust process inside a production facility will be when the ambient air is at its most extreme outdoor conditions. The big question at those times is how important is it to meet indoor design conditions? Is it worth the money to design the indoor conditions to be met 100% of the time – 24/7 – with full 2N redundancy? If not then what percentage will the output of the process accept that is less than 100% perfect indoor conditions?
Humidity variation may also be a concern. Normal incoming ambient air will generate condensation conditions under certain conditions during the Spring, Summer, and Fall – early every morning. Condensation will exacerbate corrosion in places not normally considered. The addition of electronic controls in production areas have made condensation a concern. Most indoor designs for an air conditioned facility expect the RH to be ~50%. That is very expensive to satisfy when conditioning makeup air for exhaust processes.
The humid South requires more drying of makeup air than adding humidity during the year. However, adding humidity to control static or product shrinkage may be critical.
The cleanliness of the make-up air and possibility of introducing contamination from other near-by exhausted processes should be considered. Prevailing winds may bring exhausted harmful, contaminates from near by facilities that are brought in by the makeup air. Wildfires and seasonal tree dander are notable sources that will contaminate makeup air.
Proper industrial ventilation design will always include the supply and exhaust of outdoor air. In occupied, non-air conditioned facilities, dilution ventilation is necessary. It is also recommended for warehousing for mold control. Gravity ventilation systems are the most economical to operate that take advantage of the natural thermal stratification effect. The drawback is that those systems cannot be controlled year round. Wall supply fans and gravity roof exhausters satisfy that concern.
Proper design of the process exhaust will go a long way to reduce the makeup air requirements. Source capture to reduce the amount of exhaust air required and proper hooding is very important and should be part of a complete industrial ventilation system.