“Mmmm! Today, we’re having Jansson’s frestelse!” The children in the schools of the Swedish towns Östersund and Krocom are always very happy when the typical potato casserole with onions, anchovies and cream is what’s for lunch. The potatoes in it are always fresh and delicious. And this even though they may have been stored for months. After all, the potatoes from Stocke Gård Farm, which has been supplying the two regions since March 2019, remain fresh for a long time due to their good storage.
“We have high standards for the quality of the potatoes. We can only fulfill these with the right potatoes, careful harvesting and optimal storage conditions.”
Magnus Larserud, farmer
Magnus Larserud took over Stocke Gård with his family in 2016 and since then, he has produced 450 tonnes of potatoes each year. One of his first investments was to modernize the potato warehouse in Jämtland. “This was an important and necessary investment,” says Larserud. “We have high standards for the quality of the potatoes. We can only fulfill these with the right potatoes, careful harvesting and optimal storage conditions.” In addition to quality, there was another important reason for the modernization: “We wanted to reduce our energy costs with modern fans and control options,” says Larserud.
Outside air used for cooling
For this project, he commissioned Pencraft Services AB. Their energy experts develop solutions consisting of advanced ventilation systems, efficient cooling machines and a control system that adapts the temperature to stock levels. The principle of the Pencraft system is based on the so-called “Alf Johansson system,” which is used throughout Europe. Here’s how it works: If it is cold enough outside, outside air is sucked into the warehouse and distributed via a duct. The duct runs along the long side of the warehouse. The potato crates are in rows towards the wall. The air ducts, which convey the incoming air further into the warehouse, are by their feet.
A fan supplies the floor with cooled air, which then rises upwards. The principle of the ventilation system is that the air heated by the breathing heat of the potatoes rises upwards. This produces a chimney effect that draws the cooler air from the floor and cools the potatoes. The right fan for the system comes from ebm-papst. Pencraft has been working with the fan specialist for several years already and also brought it on board for the modernization of the warehouse in Jämtland. ebm-papst supplied an EC axial fan with integrated control electronics. It is energy-efficient and so powerful that one fan is sufficient to ventilate the entire warehouse.
Constant three degrees Celsius
This sophisticated system keeps the temperature in the warehouse at a constant three degrees Celsius and the humidity at 90 to 95 percent. Both of these factors are crucial for ensuring that the potatoes are still delicious when they are served: “At three degrees, the potatoes are inactive,” explains Magnus Larserud. “When the temperature is lower, the potatoes absorb energy; when it is higher, they germinate and start to sprout. The humidity must be high so that the potatoes do not shrink during storage.”
“I estimate that the energy savings are at least 30 percent.”
Magnus Larserud, farmer
The web-based control and monitoring system from Pencraft now allows Magnus Larserud to monitor and control his warehouse ventilation remotely. It also saves energy: “I didn’t have a system to compare it with before, but I guess it’s at least 30 percent!” Other customers of Pencraft Services and ebm-papst will also enjoy this solution in the future: It is estimated that there are around 600 potato warehouses in Sweden with several thousand tons of potatoes – many with storage solutions that are not ideal for long-term storage. The two companies want to change this with further warehouse projects. So that students in all Swedish regions can enjoy perfect potato casserole in the future.