Truth is, after harvest, potatoes and onions are taken and stored as quickly as possible in large warehouse-like facilities near the growing fields. Temperature and humidity control of the storage environment is crucial to the quality and safety of the vegetables. Preserving these vegetables as nearly as possible to their pristine state is a priority because it helps ensure farmers can earn better pricing for their crops when they are ready to sell them to market.
The average American consumes 134 pounds of potatoes and 18.5 pounds of onions per year. That's big business for the economies of the states where these vegetables are grown. For example, in Oregon, Washington, and Idaho, onions contribute over $125 million to the economy annually, and the impact of potato production for the same three states is even more significant - upwards of $1 billion annually. Maintaining quality in the raw vegetable product is vital to the success of the industry. Demand is ensured, in large part, by the quality of supply.
A crucial component in JMC's systems, ABB ACS550 motor drives with Ethernet communications, are used to control fan-motor speed and airflow, which directly monitors and varies to precise settings the temperature and humidity. By achieving and maintaining optimal control settings, these drives, in turn, reduce energy costs and help maximize farmers' sales margins.
Joel Micka and his wife Michele founded JMC in 1998. "We've had to gain the trust of the farmers and processors," said Micka, who is no stranger to agriculture, having been raised in a potato farming family in Oregon.
"They put a lot of trust in people like us, because of the value of their crop. It's not only the storage and expense of the ventilation and controls, but the value of the raw vegetable products they're putting in the building. Our systems are solely responsible for maintaining a temperature and humidity environment that allows food storage for up to 12 months. These farmers are entrusting us, literally, with their potential wealth.
"Part of what our system has to do is to deliver a certain amount of air - typically, about 20 cfm per ton for potato storage," said Micka. "In the state of Washington, our average-size storage is 10,000 tons. So we would be supplying 200,000 cfm of air."
To move the air, JMC uses 54-inch custom fans with 15-25 horsepower motors in complement with ABB drives to control the fan speed. Drives are able to vary the speed of motors infinitely, and to adjust fan speeds in this case to meet preset set points for temperature and humidity.
Micka explained that each potato and onion variety has its own temperature and humidity requirements for optimum quality.
"For potatoes, we generally want to hold about 95 percent to 98 percent relative humidity," Micka noted. "So there also will be supplemental humidification that our controls are responsible to turn off or on. We're generally shooting to hold a temperature control plus-or-minus a tenth of a degree. We want to hold the temperature at a very, very accurate setting."
"In years past in our industry, we've only used traditional motor contactors. During the last four years, there has been a big shift because of the energy savings provided by reduction of fan speeds at times that are allowable on the vegetable storages," said Micka.
Incorporating drives enables the fans to run more efficiently by matching air volume precisely to demand. When air demand decreases, the variable-speed drive slows the motor down, saving energy.
The University of Idaho recently studied the impact of variable-frequency drives (VFDs) on potato storage facilities and reported an average annual fan-energy savings of 40 percent, and average mass-loss (shrinkage) savings of 0.81 percent. They also found that color, sugars, and other quality characteristics are not impacted by VFD use.
Micka agreed that the power savings could be significant, offering an example of one customer's onion storage facility. "The system has six 25-horsepower fans that supply 55,000 cfm at 100 percent speed (or 60 Hz), and each one is using approximately 19.2 kWh," he said.
"If the fans are reduced to 50 percent speed (appropriate for winter months when storages are down and the temperature outside is cold), each of the fans uses approximately 2.8 kWh."
All six fans at 50 percent speed use less energy than one fan at 100 percent speed. If the six fans are kept at 50 percent during a one-month period, that adds up to a savings of 70,848 kWh or $5,667 per month. (Note: Savings were calculated using an average commercial energy rate for the Northwest of 8 cents per hour including demand charges. Energy costs vary according to region and other factors.)
Controlling the air supply also helps reduce mass loss (shrinkage) for potatoes. "Typically farmers get paid by the weight of their potatoes, and the potato is about 80 percent water," explained Micka.
"To maintain high humidity, we use the drive to slow down the fan at certain times of the year to supply less air to the potatoes and, in turn, reduce shrink loss. If you have 10,000 tons of potatoes and you reduce the shrink loss by 2 percent, and they are valued at $150 per ton, there is significant money to be saved."
There also are benefits related to applying additives. "For potato storage, there are chemicals that are applied to keep the potatoes from rotting or sprouting," said Micka. "We'll use the drives to slow down the fans, so we can inject the chemicals into the airstream to deposit the proper amount on the potatoes."
"You compromise product quality if the air temperature and humidity aren't where they're supposed to be," Micka said. "In the fall, when you're storing potatoes, you have to supply ventilation to cool them down. If you don't cool them down, they will rot, and you've just lost several million dollars worth of potatoes."
With current technology now in place, Micka described a new scenario, "If we have a motor that is over-amping and the drive hits a fault, with the Ethernet communications, we are able to remotely monitor it, either through a modem or via the Internet. We can see which drive is not operating and why it's tripped out. We can reset the fault and reprogram the drive remotely; restart it and get it up and running." Furthermore, the communications can be set up to send an alert via e-mail to operators to warn them the second such a fault trip occurs."
Tom Carmody, a manufacturer's representative for ABB, introduced JMC to the concept of using drives and remote monitoring in 2003. "If it wasn't for Tom Carmody and ABB's beta test unit, we may not have known about this technology for years. This is really new technology for our industry. It is the stuff of dreams for farmers who rely on managing these crops all the way from field to market," said Micka.
"It's a whole new way of controlling these very critical fan motors - through communications rather than through signals. We are able to pull information out of the drive that we never could before - motor amps, rpms, etc.; to â€˜see' without being on site."
Micka noted that with millions of dollars of raw product on the line, his customers depend on his ability to design and install systems that operate flawlessly. "We're relying on all of these electrical components to work synergistically," he said. "We now have 24-hour monitoring and, yes, rely on this system to call out via text message or e-mail to the appropriate people when there is a system problem."
Depending on the project size and whether any incentives are provided by the energy supplier, drives installed in potato and onion storages pay for themselves in one to three years. "Even institutions that are lending farmers money to build new buildings see the value of this, because they're also on the hook. If the grower loses an entire storage of product, then they don't get paid either," Micka said. "The drives are an essential management tool, and if properly installed and maintained, they will perform for years. They are now in the landscape as essential tools."
Publication date: 04/10/2006