Industrial buildings virtually always have ventilation and exhaust equipment. Due to the nature of work being accomplished in industrial facilities, ventilation and exhaust systems are required to properly maintain a clean and safe indoor air quality, maintain worker comfort and effectively operate building processes.
As ventilation and exhaust systems remove air and contaminants from the building, air pressure will find equilibrium and air will then enter the building in an amount to equal the flow rate of exhaust air whether or not there is a planned system for the air’s replacement.
Make-Up Air units are designed to replace exhaust air by bringing in fresh outdoor air into the space and heating or cooling it to the desired condition and discharge the conditioned or tempered air into the building. At the same time when properly designed, a make-up air system provides building pressure thus eliminating negative building pressure and the problems caused by negative pressure. Make-Up Air (MUA) systems are the preferred HVAC and IAQ design solution in industrial spaces because all industrial spaces use ventilation and exhaust, so make-up air (replacement air) is always needed. Incorporating heating and/or cooling into the make-up air system reduces or eliminates the need for supplemental building heating and cooling, thus reducing overall HVAC equipment and energy costs.
The air being drawn into the building to replace exhausted air has barriers to overcome. Due to this resistance, the ventilation and exhaust systems are not able to operate to overcome these barriers to air availability and performance drops below rated air flow rates. The decrease from the designed exhaust flow rate can be significant. Ventilation and exhaust systems no longer move the correct amount of air needed. The resultant indoor environmental condition quickly becomes undesirable.
The drawing in of outdoor air into the building creates “a negative building pressure”.
When a building is in a negative air condition, air contaminants are not properly cleared and purged through exhaust, often noticed by a haze in the air. This haze (air contaminants) can cause safety, health and manufacturing process problems. Air temperature and humidity becomes uneven as an influx of cold outside air chills the perimeter of the building in winter (or draws in hot, humid air into air conditioned spaces in summer). Workers are subjected to drafts, workspace temperatures are not uniform, and the building heating/cooling system most likely gets overtaxed. Although the air temperature may eventually mix to acceptable condition as it moves toward the building interior, this is an ineffective, uncomfortable and uncontrolled way of transferring heat to the air and usually results in greater fuel usage.
|Negative Pressure Inches of Water
|Adverse Conditions Which May Result
|0.01 to 0.02
|Worker Comfort-High velocity drafts through doors, window and crack openings.
|0.01 to 0.05
|Natural Draft Inoperable-Ventilation through exhaust ventilators, flow through stacks with natural draft greatly reduced.
|0.02 to 0.05
|Carbon Monoxide Exposure-Back drafting of atmospheric burners will take place in water heaters, unit heaters, furnaces and other combustion equipment not provided with induced draft.
|0.03 to 0.10
|Mechanical Ventilation Greatly Reduced-Airflow amounts reduced in propeller fans and exhaust system.
|0.04 to 0.10
|Doors Difficult to Open - Employee injury may result from non-checked slamming doors.
|0.10 to 0.25
|Local Exhaust Ventilation Reduced- Centrifugal fan fume exhaust flow reduced. Exhaust hood source capture zones greatly reduced.
We manufacture both direct fired & indirect fired make-up air units to meet commercial and industrial heating, cooling and ventilation requirements ranging from 1,000 to 150,000 CFM. Our manufacturing capabilities allow semi-customization for additional heat sources: electric, steam or hot water (and cooling coil options). Our HVAC systems have controls options to best suit the specific use of each building or to enhance and support the manufacturing processes of industrial applications. Building temperature and pressurization can be controlled by a direct digital controller (DDC), allowing communication with building management systems via BACNet, Modbus, N2 and LONworks.