“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.

This sophis­ti­cated system keeps the temper­a­ture in the ware­house at a constant three degrees Celsius and the humidity at 90 to 95 percent. The green light keeps the pota­toes fresh longer. (Photo | ebm-papst)

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.