Recommendations and tips from the pros.
For whatever reason—expense, simplicity, space, time constraints—growers may consider upgrading storage facilities over building new. Several experts offered Spud Smart suggestions on improving existing structurally sound facilities for successful potato storage.
Storage facilities that are properly insulated and well sealed will keep temperature and humidity at the desired levels and prevent problems in storage from condensation, such as disease. “Dealing with your building envelope is really important,” says Doug Small of DGH Engineering in Winnipeg. “If you don’t have a good envelope with a high R-value, you are going to get condensation and dripping and that’s going to cause problems with storage.”
Todd Forbush, an engineer with Techmark Inc. located in Lansing, Mich., recommends insulating to a value of R-35. This is equivalent to 250 millimetres (10 inches) of fibreglass or 150 mm (6 inches) of polyurethane insulation. Closed-cell foam insulation board or highdensity, spray-in-place urethane insulation are the most commonly used materials for upgrading storage insulation, says Forbush. “Good insulation is critical to proper storage performance,” he says.
Proper ventilation is crucial to maintaining the correct temperature, relative humidity and air quality in storage, and for managing problem lots and the build-up of carbon dioxide, all of which affect tuber quality. Ventilation systems usually consist of intake doors, fans, air plenums, ducts, exhaust louvers and a control system.
“Over the past 30 years the required air flow rates for potato storage have doubled,” says Small. “If you have high-quality, healthy potatoes you don’t need a lot of air flow—the older rates were fine—but you need the higher air flow rates if you have some problems in the bin,” he says. “The two typical issues are disease or frozen potatoes in the fall. Either way you will need more air flow because in each condition the potatoes are under stress and giving off heat and you have to remove that or the whole pile will heat up and at some point you could lose the whole thing.”
Plains Potato Ltd., a cooperative that stores potatoes for its grower members located at Portage la Prairie, Man., recently completed an upgrade to its storage facility, which included the installation of a new ventilation system designed to double its air flow rate.
The new installation meant incorporating bigger fan housings into the building itself—but according to Cory Smith, manager of Plains Potato, the renovation was worth it. The new system gives Smith more flexibility by allowing him to increase the number of climate zones in the building from four to six. “We now have 21 separate bins across six zones, each with 15,000 bags apiece. Each bin has sensors inside to monitor the heat and relative humidity, so it’s a lot easier to control the conditions in each individual bin,” says Smith.
Poor ventilation and air distribution, caused by incorrect sizing of fans, ducts, air inlets or distribution slots, will lead to inconsistent potato quality and/or potato rot. “As you put more air flow through, if you have an older shed that has an under-designed ventilation system, your ducts are going to be too small and so it is a challenge to get the extra capacity in your air plenums and ducts,” says Small.
And if the potato bin walls also form a part of the actual air ducts in the building structure, replacing those ducts can be extremely problematic. In that case, Small recommends the average grower should consult a specialist.
Power consumption of the main ventilation fan is also crucial in storage upgrades. A variable frequency drive can control the speed of the fan motor, allowing the volume of air moved by the fan to match the needs of the potatoes, saving energy and money.
“It’s important to take the total ventilation system into account when utilizing a VFD,” says Forbush. “Slowing the fan speed can save energy, but may cost quality in the long run if the system is not designed to operate with lower fan speeds.” Although the variable speed fan can reduce energy consumption, it must have a good control system to monitor the need for ventilation, especially when fans are operating at lower speeds.
Smith went with VFD fans, but because the upgrade was just completed this year, he knows it will take a while for those savings to start showing a positive impact on his bottom line. “I know I have saved some money on hydro already,” he says, “The drive can slow down the air flow and the control panel monitors it continuously and adjusts it automatically according to conditions in the bins.”
A qualified ventilation contractor can perform a storage ventilation analysis for a grower in order to determine what is needed to improve the air distribution within a structure.
There are many different types of controls available, from a straightforward single insulated damper that controls the blend of fresh and returning air, to systems that also combine carbon dioxide sensors with humidistats.
Forbush recommends a system that integrates control of fans, air inlet, humidification, refrigeration, heating and air exhaust fans or louvers. This will maximize storage energy usage, while controlling temperature, relative humidity and carbon dioxide in the storage facility. “A storage control review will help the storage manager determine if the existing equipment is sufficient, or if there are benefits that can be obtained using new storage control technology,” he says.
Smith’s state-of-the-art system is a microprocessor-controlled unit called the Agri-Star, made by the Gellert Company in the United States. It monitors and controls the entire environment inside the storage facility through the use of sensors, and adjusts temperature and air flow as needed to maintain temperature and relative humidity, which must be kept above 95 per cent.
Smith is impressed with the features and the capabilities of the system, which comes with easy to use, proprietary software. “The panel itself has a full-size, colour, touch screen display, with on-screen graphing, multi-modes, a carbon dioxide control—and it basically gives plug and play internet ready communications,” he says. “It gives a lot more flexibility and I can monitor everything from my computer. It has really fine-tuned the control system. The older system had a lot of fluctuation and it wasn’t as responsive. You can keep the temperatures exactly where you want them.”
Upgrading an existing storage facility is not cheap: the cost to upgrade its storage cost Plains Potato approximately $700,000. Now, the facility houses 325,000 bags of potatoes. But, at the end of the day, keeping customers happy was a factor in making the decision to upgrade the facility. “One of the big reasons for upgrading was to keep the processors happy,” says Smith. “It’s security for them to see that you are willing to invest in the upgrades so you can do a good job of supplying them with what they need.” Angela Lovell