Variable Frequency Drive Improves Greenhouse to Make Quality Grow at Len Busch Roses

Water and sunlight are well understood for being essential to plant growth. But one of the largest nurseries for cut-stem flowers in the central U.S., Len Busch Roses in Minneapolis, Minn., knows there is an additional factor: air. In fact, airflow is so important to the growth of LBR's flowers, the company recently turned to Danfoss to provide a variable frequency drive (VFD) to power the fans used in its largest greenhouse.

— Monday, September 29, 2014 By Danfoss Solutions Magazine

"As plants grow, they not only consume water; they also expire water," explains Rene Vahk, senior technician for Len Busch Roses. "All the water vapor and heat make greenhouse plants very sensitive to rapid changes in humidity and air temperature. In fact, small differences within the plant microclimate throughout the greenhouse will limit the size of blossoms and stems. Air that is too humid can also condense on leaves and petals, causing disease problems.”

“That’s why we want temperature, humidity, and airflow to stay within a range so our plants are more uniform and more marketable,” according to Tom Nass, grower at Len Busch Roses. “So when I discovered a Danfoss variable frequency drive could improve airflow, I was very interested."

Growing flowers requires flowing air and water

The family-owned firm of Len Busch Roses has been growing flowers since 1965. Today, its Minneapolis greenhouse complex covers over a half-million square feet — about the area of 100 football fields — where they grow roses, lilies, tulips, gerberas, snapdragons, alstroemeria, and more. One of the largest greenhouses, which spans 100 by 250 feet, grows snapdragons.

"This particular greenhouse was ventilated with 13 fixed-speed, 42-inch diameter exhaust fans," says Vahk. "They were arranged in three banks. A sensor wired into our automation system would turn on one bank of fans, then another and another until the setpoint was reached. But as each bank of fans turned on, it would create a huge difference in airflow. Humidity could fluctuate by as much as 50 percent throughout a single day. On top of that, the fans required a lot of maintenance due to the constant on/off cycling of the equipment. The fan belts would squeak so much, the neighbors in the residential development nearby would complain."

When Brian Peterson of Schwab, Vollhaber and Lubratt, Inc., (SVL) in Shoreview, Minn., heard about these problems, he suggested that Danfoss variable frequency drive technology would solve the airflow and noise problems.

"Rene was already familiar with Danfoss VLT® Drives, because I had installed some VLT® AQUA Drives for pumps on their water wells and irrigation systems," says Peterson. "Being able to vary pump speed to prevent uneven pressure solved a lot of problems related to water flow. When I heard about the noise with the fixed-speed fans, I thought a Danfoss drive would provide smoother startup and variable speed fan control to eliminate the airflow issues."


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