Computer Simulation Solves Cooling Problem in Plastics Plant


Computer simulation was used to solve a difficult problem in a plastics plant that had threatened to damage expensive equipment and materials. The plant includes 52 molding machines that are supposed to be maintained at temperatures no higher than 78° in order avoid damage to the control systems. The computer controls on the machines must be maintained at relatively cool temperatures in order to avoid damage to delicate semiconductors.

When the company built its first plant, temperatures were far too high for the machines and materials, not to mention the people working in the plant. The company called in a representative for Applied Air, Dallas, Texas, to discuss adding cooling equipment to the plant. Using hand calculations, the representative proposed a solution that involved putting two Applied Air IFA 60,000 CFM air turnover systems at either end of the building, blowing air from both ends down the length of the machine rows towards the middle. However, because of the special challenges involved in this application, Applied Air recommended to the manufacturer that computer simulation be performed to evaluate the effectiveness of the proposed solution.

They used Flovent software from Flomerics because it is designed specifically for the building industry. “It’s much easier modeling building problems with Flovent than a general-purpose CFD code,” said Mike Kaler, Application Engineering Manager for Applied Air. “Flovent’s technical support staff specializes in HVAC so they can quickly and easily understand what we are trying to do and provide answers.”

Applied Air engineers began by constructing a box representing the building. They then created cubes in the approximate shape of the molding machines and located them in the appropriate positions. Applied Air engineers entered the surface temperature and power consumption of each machine into the software, which then calculated the effective heat dissipation. The engineers ran a steady-state solution on a personal computer. They viewed the simulation results as particle traces that are often useful in diagnosing HVAC problems. In this case, the particle traces showed that the hot machines were generating strong convective flow straight up to the ceiling. The result was that the machines in the middle of the building received little or no cooling.

This image
adjacent to second row of machines illustrating worst case temperatures near
machines of approximately 75°F. It also illustrates stratification of air as the
air near the ceiling is warmer (redder) than air near the floor.

Based on the diagnostic information that showed the updraft was preventing horizontal flow across the length of the rows, they decided to try a different approach where air was passed across the width of the rows, so it only had to traverse two machines rather than 26. This required switching to DFM indoor units that can be mounted on the longer walls well above the floor. The initial simulation run showed temperatures were at acceptable levels.

Applied Air engineers then re-ran the simulation in optimization mode to determine the minimum configuration that would provide acceptable cooling with a margin of safety. This simulation run showed that 60,000 CFM units provided effective cooling at a very attractive cost. The manufacturer installed the cooling units in the plant and was so happy with their performance that it has standardized on them and is using them for each of its plants during its current expansion drive.

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