Aerovent Solves A Smokey Problem with Swingout Roof Exhauster
An industrial manufacturing facility contacted Aerovent’s local representative to solve a ventilation problem. There were 12 existing 48″ 7.5 H.P. commercial grade upblast roof exhaust fans manufactured by a competitive company. The fans were intended to exhaust smoke and heat from four large canopy hoods over four large press machines. But, the building was constantly full of heat and smoke making it difficult to see or breathe.
Two years ago, a design-build HVAC contractor sold the customer a “pressure gravity” system to solve the smoke problem. It consisted of large commercial grade wall supply fans and a small continuous gravity roof ventilator. The theory was to introduce a larger volume of fresh outside air at floor level, pressurize the building, and force the air out of the gravity roof ventilator. The system never worked properly. During the winter months, the outside air was too cold and the employees wouldshut off the new wall supply fans and close the doors. During the summer months, there were too many open doors, fixed blade wall louvers, and hood exhaust fans to “pressurize” the building. The wall fans required extensive maintenance due to loose belts and inoperable dampers.
The initial fan survey revealed smoke escaping from the canopy hoods. Using the existing fan manufacturer’s catalog data and hood dimensions, Aerovent’s rep was able to demonstrate that the hood capture velocity was less than half the level recommended by the Industrial Ventilation Manual. The exhaust ducts between the hoods and roof exhaust fans had large holes that were cut by the customer in an attempt to exhaust the stratified smoke from the ceiling cavity. These holes short-circuited the canopy hoods and because several of the existing fans were inoperable, the smoke would bleed out these openings under the ceiling. Because of the heat, smoke, and roof conditions, the existing fans were very difficult and unsafe to maintain.
The first part of the solution was to replace the existing fans with new fans sized for the proper hood capture velocities. Working with a sheet metal/roofing subcontractor, The proposal scope included removing the existing fans and furnishing and installing new industrial Aerovent fans. The initial proposal included twelve 60BD40C-15HP fans rated for 720,000 CFM, with swingout construction, premium efficient severe mill and chemical duty motors, hot dip galvanized construction, stainless steel hardware, custom curb adaptors, and NEMA 4X disconnects.
The customer then requested “competitive” pricing from the original installing contractor. They quoted commercial fans. The contractor actually told the customer that Aerovent industrial fans are too expensive and strongly recommended using the commercial fans. After researching both proposals the customear found substantial difference in the “competitive” commercial products offered by the contractor and those manufactured by Aerovent.
Because the roof was so large and was in very poor condition, the installation required special considerations. The roof felt like walking across a weak trampoline. The fans were located in the center of the roof and were too far from the wall to use a crane. A helicopter could not be used because the plant would have to shut down for insurance and safety requirements. The proposed solution included a custom fabricated rolling crane with pneumatic tires to remove the existing fans and install the new fans in pieces. The combined weight of the fans and crane was almost that of a small truck. Heavy ¾” thick plywood sheets were used to reinforce the pathways from the edge of the roof to the roof openings. Each worker and the rolling crane had to be tied off for safety requirements. For additional safety, the area inside the building under the fan was restricted during the installation. The roofing and curbs had to be repaired before installing the new fans with heat and smoke continuously exhausting through the uncovered roof openings. Only three fans could be shut down at one time because of the smoke inside the building. The work had to be closely coordinated with the plant’s electrician to minimize downtime.
The customer was very pleased, the project was completed safely, and on schedule. They maintained full production during the installation of the new fans. The smoke was gone and the working conditions were greatly improved. During the final inspection, the customer’s Maintenance Manager demonstrated the easy swingout access. He said, “it was as easy as opening a car door.” He also stood a 4″ lag bolt on the top of the motor cover to show how smooth the fans were operating. The bolt didn’t even move.
The customer needed to solve a problem. The competition was only selling price. The customer paid a premium for the Aerovent products and is very happy with the quality and performance… and its decision.
Tags: Axial Swing-Out, Roof Exhauster, Swing-Out Design, Swing-Out Fan