Refrigeration / Fruit and vegetables storages

The Polish vegetable cooperative Carota Sp. z o. o. in Dzierzoniów in the Lower Silesian Voivodeship delivers fresh carrots and onions throughout the year. With subsidy from the EU, the company has built a new refrigeration and production hall for this purpose. The large warehouse and sorting capacities are an indispensable prerequisite for rapidly and reliably serving existing customers and developing new markets in Europe. The few large retailing groups active in Europe need suppliers and trade partners who can deliver large quantities just-intime at a consistently high quality to fill their supermarket counters. The newly built Carota cold-storage warehouse consists of twenty cold rooms – sufficient for 17,000 tons of carrots and 8,000 tons of onions. The refrigeration engineering was delivered by GEA Refrigeration Poland. The carrot and onion warehouses of Carota Sp. z o. o. are climatically separated from each other, because the two sorts of vegetables demand completely different warehousing climates.

Whereas onions must be stored in large, well-ventilated, dry heaps at 4 °C, carrots require a uniformly moist climate with about 95 to 98 % relative humidity at 0.5 to 2 °C and a maximum temperature fluctuation of ± 0.25 K. The carrot harvest takes only a few weeks in September and October. The entire harvest yield of all participating partners in Carota goes into Carota warehouses. Directly after delivery, a cooling tunnel lowers the temperature of the carrots to 5°C within eight hours. The carrots are subsequently stored in wooden boxes in 14 cold-storage rooms at 0.5 °C and about 98 % relative humidity. A special temperature sensor monitors the temperature. A nozzle system that produces a fine water spray under high pressure ensures the preset humidity in the coldstorage room. This technology is more efficient than steam wetting. The carrots are cleaned with ice water, sorted, and packaged.

The onion harvest comes to an end in September. The bulbs are first dried and then cooled at 4 °C, spread loosely over a perforated floor in six storerooms, and kept well-ventilated. Free cooling with a freshair supply is installed in the onion storage room, supported only by an Air Cooler during the drying phase and at the end of the season in the spring. Air exchange with forced draft ventilation through the piles of onions, 4.50 m tall, is about 100,000 m³/h. The onions are sorted, partially peeled, and packaged only just before delivery. During harvest time, the refrigerating system operates mostly at full capacity. Outside season, cool storage requires less cooling capacity, due to outside temperatures as well as low rotation of stocks. For this reason, Carota Sp. z o.o. specified an air conditioning and refrigerating system that also operate effectively under part loads. Three Kelvion Air Coolers from the SG (HB) range are employed for each carrot storage chamber. For the onions one unit of the same range is used. If required, heat exchangers can be defrosted by hot gas.The evaporating temperature is -8°C for cooling the carrots to storage temperature. During storage operations, the temperature rises to -2 °C.

The individual temperatures required for the ammonia are centrally – and hence energy-efficiently – controlled by the compressors to precisely maintain the temperature set in each cold-storage room. Only for low cooling demand, compressors switch to energysaving part-load operational mode. This feature represents a significant difference from traditional systems in which the compressors always operate in full-load level and cooling is regulated by energyconsuming pressure valves. Part-load operation likewise ensures that air velocity over the product remains low. If the air is only slightly moved in this way, a boundary layer with high humidity forms around the carrots. The carrots lose less water and thus remain succulent longer in the moist protective atmosphere. 2.2 MW frequency controlled refrigeration capacity, condenser fans, units cooler fans and refrigerant pumps run throughout the year on demand and cover particularly partload operation. Carota Sp. z o.o. is well prepared for doing business in Europe thanks to its new production and storage technology. The demand for carrots and onions from Lower Silesia has also grown in the course of last year. Over the middle term, the cooperative reckons with a market quantity of 25,000 to 30,000 tons of vegetables per year.