Creating Positive Air Flow in a Large Roof-Vented Facility

Operations such as steel/iron works, glass/ceramic production and die casting often experience issues with employee comfort and morale due to high temperature. Redesigning building configurations can be cost-prohibitive, particularly if the issue is only present a few months out of the year.

With this in mind, Trace Die Cast Inc. (Bowling Green, Kentucky) sought help cooling its personnel working at aluminum die casting stations by implementing a solution that would improve positive air flow toward the roof vent. The facility has a natural airflow system with fan-driven vents, a pitched ceiling, and no HVAC.

The production rooms are four separated, unconfined areas that share a central passage in two rows, leading to openings on either side of the facility. The walls of the building have vents with slowly churning fans that draw air into the 350,000 ft3 (9910 m3) space and a 150 ft2 (14 m2) pitched roof vent on the ceiling that exhausts the hot air.

Trace Die Cast Air Pressure

Wind passing over a vertical shaft will pull lower pressure air up through the pitched roof vent.

Typically, the temperature outside is around 10°F cooler than inside the facility. However, during the summer the ambient temperature at the workstations can be as high as 110°F (43°C). With an upper roof vent temperature of approximately 140°F (60°C). Kentucky summers also can include periods of low wind speeds.

Wind is one of the essential elements of creating positive airflow in rooftop venting systems. The action of horizontal wind pressure across a vent is expressed in Bernoulli's principle of flow dynamics, which explains how air exhaust can induce the compression and expansion of air inside the facility.

In this application, Bernoulli's principle describes how higher pressure horizontal air (wind) passing over a vertical shaft will pull lower pressure air within the facility up through the pitched roof vent. The pressure difference results in a net force, which causes an acceleration of the internal air upward.

The Factory Cooling Solution

In Trace Die Cast's facility, the absence of consistent air flow across the vertical roof vent during the summer created a negative pressure situation. Heated air would build up at the ceiling, causing the pressure on the inside to exceed that of the outside and preventing it from being properly exhausted. This allowed stagnant air to get trapped in pockets, raising the ambient temperature throughout the facility.

"A local colleague of mine had a similar issue in his smelting operation," said Kent Guthrie, vice president of facilities. "I checked out his solution using fan-driven atomized mist cannons with the water function shut off, and it worked so well for him that we called BossTek and rented two KoolBoss units.

The machines are designed to atomize a water supply into millions of tiny droplets, which are propelled by a powerful fan forcing air through a cone-shaped barrel. By turning off the water, a dry air stream is created, allowing operators excellent control over the airflow.

The fan runs at 9200 CFM (260.50 CMM), and creates a long, directed airstream which then slowly disperses in the same general direction. The long-ducted fan enhances airflow and control, which standard open-face fans don't.

Most industrial fans on the market are engineered with a short outer shell large enough to house the motor and sizeable fan blades, protected by a mesh cage on either end. Some models do away with the metal shell altogether and only have a mesh cage. These units disperse air in a wide pattern, creating a breeze over a large area. This method is effective for generating broad circulatory airflow or cooling when directed at specific stations, but has difficulty precisely directing airflow over extended distances.

Trace Die Cast set cannons at both entrances and pointed them at each other to create an airstream down the central aisle. That created positive flow from the ground.

Trace Die Cast Factory Cooling Solution

The cannons were located at opposite ends of the facility, directing air flow down the central aisle.

The KoolBoss is designed with a powerful 7.5 horsepower fan, set in the rear of a specially engineered cone-shaped steel barrel, with the fan blades shielded by a heavy mesh guard. The unit draws air from the wide opening in the tail and forces it down the cone toward the narrower mouth in front, where the shape increases the air velocity and directs the discharge.

Either mounted on a mobile carriage or a square steel tube skid, the golf-cart sized unit weighs approximately 800 lbs. (363 kg) and can be relocated where needed.

The units were run 24/7 over a three-month period, without disruption and with only the occasional position adjustment. The units pulled air from the entrances and delivered a strong airflow that extended down the length of the work aisle and prevented hot air from forming into pockets, boosting positive flow out of the roof vents. The circulation lowered the overall temperature of the facility and created a more controlled and comfortable work environment. That raised morale and made work stations more pleasant.

The warmth of the summer started earlier and ended later than predicted, so operators report their rental period would have been even longer if the forecast had been more accurate. Trace Die Cast's satisfaction with the results led them to purchase two KoolBoss units for permanent use.

CUSTOMER
Trace Die Cast Inc.

LOCATION
Bowling Green, KY (USA)

CHALLENGE
Prevent heat-related illnesses from taking place while working at aluminum die casting stations.

SOLUTION
Two KoolBoss™ units directing air flow toward the roof vent.

RESULTS
The units were run 24/7 over a three-month period. The circulation lowered the overall temperature of the facility and created a more controlled and comfortable work environment. At a later date, Trace Die Cast purchased two KoolBoss units.

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