"Plant"wide Automation

With 3,200,000 square feet (80 acres) of total heated greenhouse production space, Huntersville, NC-based Metrolina is one of the largest single-location greenhouses in the United States. "Greenhouses are measured in terms of plants per square foot, and the more plants you can grow in a small space, the more money you make," says Bill Durkee, Maintenance Engineering. Metrolina uses a series of 500-foot long overhead cage systems-each of which holds about 12,000 hanging basket-type plants-to maximize their growing space. Having resolved the space issue, Durkee sought a reliable and consistent method of controlling the movement of the cages and the greenhouses' different watering systems: drip watering through the plant baskets, sprinklers, and booming "rain" overhead watering for propagation of plants on the floor. He turned to CIMTEC, a Charlotte, NC-based supplier of automation and process control products, solutions, and support services, for help.

Durkee designed and built a control system based on a GE Fanuc Series 90-30 PLC platform. Approximately 35 PLCs located in a 30- acre area of the greenhouse, known as the MX, monitor and control between 20 to 30 I/O points each on the overhead cages and about 480 control valves on the floor watering system. The PLCs are connected via a fiber-optic Ethernet backbone. Four fiber-optic hubs connected to two GE Fanuc Display Stations running numerous CIMPLICITY servers split control of the MX. The fiber optics run through water hoses that feed the cages 25 feet in the air, keeping the cables out of the growers' way.

CIMPLICITY's robust feature set helps Metrolina maintain optimal growing conditions. Using the Action Calendar, for example, growers can select not only when and how plants are watered, they can also move the cage based on sunlight during the day and control grow lights to extend the day at night.