PROJECT
INCORPORATING COLD CHAIN has eight different punnet sizes to cater to specific client requirements. Each punnet has 250g of berry and typically each pallet has 270 to 400kg of fruit. Clients also require the raspberry to be a distinct colour; some want the berry to be a dark red, others want it to be pink and others almost orange. The colour depends on the level of maturity and impacts on the heat of respiration, which the refrigeration plant must handle. All these factors are considered in estimating the cooling load, the air circulation volumes and humidity levels to handle higher volumes and to improve the quality of raspberry at the point of sale – be it London, Johannesburg or Cape Town.
Humidity levels at the pack line was a prime consideration. The dew point of the air must always be lower than the core temperature of the fruit to prevent any condensation on the fruit as this leads to mould forming and rejection by retailers. A further operational issue must be considered in the design. At the start of each day, the air temperature in the pack line must be maintained at 2 ° C or 12 ° C depending on the pulp temperature of the incoming fruit( some fruit may have been held overnight at 2 ° C). Later in the day when the fruit arrives directly from the pickers, the air temperature is maintained at 12 ° C. The switch over of the air temperature controller between the two temperatures is done manually by pack house staff.
A new dual circuit coil in a purpose-built plenum, with a high capacity fan and fabric ducting, was installed to reduce supply air velocity which is key to ensure staff comfort at low air temperatures. The coil of the air handler has a glycol circuit(-5 ° C) and a water circuit for re-heating. Additional plate heat exchangers in the chiller heat the water for the air handling unit with compressor discharge gas.“ The performance of the custom-made Dixell control system to maintain optimum humidity levels, air temperatures and cooling capacity of the
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Berries are grown in netted tunnels. |
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Trees provide a wind break between the netted growing tunnels. |
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Pallets of packed berries are dispatched in refrigerated vehicles. |
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The new holding area in dispatch. |
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Samples are checked for shelf life. |
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36 www. coldlinkafrica. co. za COLD LINK AFRICA • May | June 2017