In the quality department at the Lafayette plant, Rick Dossett, quality analyst and project manager, recently purchased a Prismo Coordinate Measuring Machine (CMM), an ultrasensitive, highly accurate testing machine which performs in-process engine inspections to verify dimension, form and position. Due to the machine's advanced technology, Dossett needed a clean-area environment to house the machine within the factory. Jim Hennessy, a local contractor with clean-room experience, was called in to prepare a site for the machine. Hennessy learned that the requirements for the Caterpillar room extended the limits of many conventional HVAC systems, particularly concerning temperature and humidity challenges.
"With the sensitivity of the equipment, the room can't exceed 60% humidity," says Dossett. In addition, the CMM manufacturer required a constant temperature of 68 degrees with the gradient of plus or minus one degree. The airflow in the room needed to be even from top to bottom of the 18X12-ft. enclosure with 13-ft. ceilings, with no tolerance for error.
To achieve this, Hennessy tested a high-pressure air handler from Unico, Inc., a St. Louis, MO-based maker of mini-duct central and spot-heating and cooling systems. According to Hennessy, the Unico system provided the uniformity in air temperature the company required. "It's a high-pressure air handler with a large blower," he says, adding that the unit's refrigeration controls enable it to handle numerous air changes. The Unico works on the principle of aspiration. Where conventional systems leave hot and cold spots as well as drafts, Unico's streams of air enter the room and mix with the room's existing air currents. From floor to ceiling, air temperatures are even and drafts are eliminated.
Hennessy installed a two-ton UniSpot System using an air-chilled condensing unit. The air handler unit was placed outside the building for easy maintenance access. The 5-in.-diameter outlets of the Unico system were placed every two feet around the perimeter of the enclosure's ceiling. The outlets in the clean room ceiling allowed ample room for the unobstructed operation of the overhead crane used in the CMM process.
Installed last year, the system's results have been excellent, according to Dossett. "The Unico System is doing an excellent job of meeting our requirements," he says. "It maintains the required temperatures, airflow is even, and the system has helped to significantly reduce humidity levels."
Unico, Inc., 7401 Alabama Ave., St. Louis, MO 63111;