Typically hvac engineers remedy this common production plant problem with a chiller, air handler, and metal ductwork solution that can easily surpass $1 million in equipment costs, not to mention high operating overhead.

SPOT COOLING

However, mechanical engineer Smiley El-Abd, P.E., sales engineer, G.F. Morin Co., a design/build contractor in Laurel, MD, had a better idea. Hi Tech already had a chiller cooling its

18 molding machines ranging in size from 200 to 1,800 tons in Plant 2. Since the chiller typically was used to only 60% capacity, Hi Tech engineers and El-Abd targeted the remaining chiller capacity to spot cool workers at their 100-sq-ft stations instead of cooling the entire plant.

While this method saved more than $350,000 over the purchase of a new dedicated chiller and piping to cool the plant, it was the team’s innovations that made the project successful as well as energy efficient.

Metal ductwork was impractical because the metal building roof was already at its total load bearing capacity. Instead, fabric duct, from FabricAir, Inc., Louisville, KY, made the project possible because it is 90% lighter than metal duct and it didn't affect the roof load.

Another factor making metal duct an impossible solution in this project is its immovability. Like many plastics manufacturers, Hi Tech sometimes moves an injection molding machine into a different location in its production line, which may require the disassembling of duct lines.

The two lines of fabric duct, however — a 292-ft-long, 64-in.-dia run and a 256-ft-long, 52-in.-dia run — can be readily unzipped, capped off, and relocated by the in-house plant maintenance staff.

El-Abd's air distribution design spot cools each operator station with several hundred in-duct, high-velocity nozzles each with a 7- to 21-cfm throw of approximately 12 ft. Using the existing 200-ton chiller, manufactured by Multi-Stack Chillers, West Salem, WI, EI-Abd used a pressure independent valve by Flow Control Industries, Woodinville, WA, on the chilled water supply lines to harness and control the excess capacity.

Sizing the cooling load of plastic injection molding machines is usually calculated to include the worst-case scenario of every machine in production. In typical operating schedules, though, only 60% of the machinery is drawing from the chilled water, which is supplied through a pressurized manifold.

“What's sent to the air conditioning coil is based on not exceeding the chiller’s maximum demand,” explained El-Abd. “With a valve that’s not pressure independent, it’s possible to overload or create safety failures on the chiller.”

APPLYING EXCESS CAPACITY

The excess chiller capacity supplies one Rapid Engineering Inc., Comstock, MI, Series 4000 makeup air handler with 100% modulating outdoor air. Because of the roof’s load bearing capacity and the lack of floor space in the plant, the air handler was installed outside.

The aesthetically designed 8- by 8- by 8-ft wooden plenum is covered with aluminum sheeting that feeds the two fabric duct trunk lines. Return air is taken from the ceiling area and mixed with cooler outside air before entering the cooling cycle again.

Instead of the stale indoor air quality that’s typically associated with plastics manufacturing plants, workers now breathe a healthier mix of approximately 5.5 air exchanges/hr in occupied zones. And with all outside doors shut and locked, Hi Tech has improved its security measures as well.

The system is expected to pay for itself in increased productivity. “Absenteeism on hot days was as much as 10 percent of the workforce,” said Xenides. “Now workers are experiencing more comfort as well as better indoor air quality.”

Publication date: 01/07/2002