Engineered Systems NEWSCase in Point

AC Drives Meet Unique Challenges for Mice — and Men

The Jackson Laboratory (Bar Harbor, ME), an internationally recognized research center and leading provider of genetically defined laboratory mice, presents unique challenges in designing environmental control systems. Each year, the laboratory distributes nearly two million laboratory mice to universities, medical schools, and research laboratories throughout the world.

Twelve thousand research institutions in 56 countries depend on the laboratory to provide more than 2,400 varieties of genetically pure mice. Founded in 1929, the nonprofit organization occupies nearly 50 buildings in a campus-like atmosphere and employs more than 1,000 people.

Rigorous Quality Controls

Rigorous quality controls ensure the standardization, health, and genetic definition of the mice. State-of-the-art hvac systems provide the optimal environment for raising the mice and maintain the working environment for staff.

Breeding and raising healthy laboratory mice requires constant temperature and airflow 24 hours per day, seven days a week. On the other hand, laboratories and offices for Jackson staff function most efficiently on an advanced vav system,which can deliver optimum comfort during working hours and energy savings during evenings and weekends.

The hvac system, as designed, installed, and maintained by John Fitzpatrick, P.E., manager of engineering and technical services for Jackson Laboratories, and Mark Levesque, senior engineer for AC Electric (Auburn, ME), achieves control of these dissimilar environments through application of Yaskawa Electric America Inc.’s (New Berlin, WI) GPD ac adjustable speed drives. According to Fitzpatrick, the adjustable-speed drives provide control in the “macro” environment of approximately 50,000 sq ft in several laboratory buildings, and in the “micro” environment of the separate animal rearing cages.

In the “micro” environment, supply and exhaust plenums actually serve as frames for the cages. The drives control fan speeds on both the supply and exhaust sides of air handlers feeding these plenums. Ensuring optimum rearing cage conditions on a 24-hour-a-day schedule revolves around maintaining constant discharge pressure, according to Fitzpatrick.

One of the unusual elements that he must address is the heavy biofiltration designed into the hvac system. Such filtration is necessary to provide biologically pure, fresh air to the animal cages. This intense filtering requires that drives and motors run hard, Fitzpatrick says. In fact, drives and motors have been oversized by about 15% to accommodate the exceptional filter load.

“Office Side” Savings

The same drive/motor installations that maintain constant discharge pressure in the cage areas also provide energy savings in the administrative and laboratory spaces, or “office side,” as Fitzpatrick calls it. Electrical energy savings greater than 20% are easily realized in Jackson lab and office areas where Yaskawa GPD drives are also used to provide vav heating and ventilation control. “We consider this an extraordinary result, since we program a minimum of 12 air changes per hour instead of the normal six, and use 100% fresh outside air instead of recycling inside air,” Fitzpatrick says.

AC Drives Reduce Power Consumption

In a typical building, maximum heating or cooling capacity is required only about 10% of the time. Ninety percent of fan operating time requires only 40% to 70% of maximum volume.

The adjustable-speed drive delivers its savings by varying the motor speed so that it drives the fan only fast enough to maintain the desired air volume. Thus, the same system that requires 100% of full power to produce 100% of volume needs only 28% of full power to deliver 60% of volume. Significant savings are achieved by the drive’s ability to reduce fan speed during the 90% of the day when full system capability is not required. Additionally, office spaces are programmed for automatic system setbacks during unoccupied hours.

Adjustable-speed drives also provide accurate temperature control and the ability to reduce peak demand and usage charges. Additionally, they cut maintenance costs by delivering “soft starts” to accelerate and decelerate motors and mechanical equipment smoothly, eliminating the mechanical stress of starting across the line.

The laboratory installed its first Yaskawa adjustable-speed drive in 1992 and presently has more than 50 GPDs in operation in various campus facilities. Working with Fitzpatrick, AC Electric installed the Johnson Controls Metasys “communications option on four GPD 506 adjustable-speed drives to demonstrate how drives — and therefore, control and monitoring of the building environment — can be achieved from a central point.”

The GPD 506 drives with Metasys cards and bypasses have been installed in Jackson’s “Annex Three” production facility for more than a year. By linking the drives and related equipment (boilers, chillers, air handlers) to a PC or other monitoring device, the Metasys system provides effective control from a single point.

As installed at Jackson, the Metasys systems acts as a monitoring, alert and control system, while the adjustable-speed drives regulate fan speed and air volume to match flow requirements. System information fed back into the communication network also provides information to help maximize energy savings. Jackson and AC Electric are presently evaluating operation of the Metasys installation, with an eye toward converting the remainder of the campus to a communications-controlled drive architecture. ES

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