- Economic advantages of depression technology
Until 1990 the banana ripening rooms in Europe were built for box ripening by manual handling. The boxes were loaded manually into the rooms and piled in a honeycomb arrangement, leaving space between boxes for air circulation. In every box the sealing PVC was cut on the upper side and somewhere the carton box cover was removed. The evaporator fans were sized to push and circulate air through the boxes; steam producers were installed to avoid weight losses, mainly during the heating cycle.
Where correctly implemented, that technology led to a fairly good ripening quality at the expense however of demanding labour for box handling.
In the recent years, the technology shifted towards pallet ripening, pushed by operator request to reduce labour and handling costs.
Banana boxes are shipped directly onto pallets from the country of origin; in the past time, they were eventually palletised in the receiving seaport. In any case the ripener receives nowadays banana boxes already on pallets.
Before introducing the pallets into the room, the ripener cuts the banana plastic in every box from the accessible side. The pallets are stored in the room along two rows, creating a central corridor and two side ones. The ripening systems generate depression in the central corridor, to let air travel from the side corridors, across the pallets, and into the central corridor. The steam producers are not necessary anymore.
Since the beginnings, two different technologies have been adopted for pallet ripening. The curtain method, originally used by Del Monte, is actually implemented and recommended by Micheletti Impianti, please refer to the ripening description. The rooftop method, originally used by Chiquita, is also popular in Europe and implemented by several providers of ripening systems, please refer to their documentation.
In the curtain method, dedicated fans, put in a depression box, do generate pressure difference, while in the rooftop method, the depression fans are located inside the evaporators, put over the central corridor. In any case the central corridor is kept at a lower pressure respect to the side ones.
Where correctly implemented, both technologies for pallet ripening do produce better results and more uniform ripening, compared to the older box technology.
For a ripening operator, the total sales and the profit margin are linked to the ripening quality, that is why following requirements are relevant:
- maximum uniformity of ripened bananas
- minimum ripening time
- minimum top temperature during ripening
Those requirements are particularly critical where the market pretends yellow bananas.
When correctly ripened, the bananas do resist in the shops two more days and create more value for the shopkeeper. A perfect ripening system can be compared to the travel agent, since it brings bananas exactly where the ripener desires and all of them at the same stage of ripening.
A box of good quality bananas can be sold up to 1 EUR more than a bad one, hence considering 50 ripening cycles per year, in a room of 24 pallets and 1152 boxes, it is possible to get a price difference up to 1 (EUR/box) * 1152 (box/room) * 50 (cycle/year) = 57600 euros per room per year. That is why also a small difference in banana quality can make a big difference in the long run earnings.
A big chunk of the electric consumption in a ripening system is due to the depression fans.
A 24 pallet room from Micheletti Impianti uses three fans during the ripening cycle to produce a 150 Pa depression and an air flow of 30000 m3/ h, with a power input of 2.7 kW. During the storage, instead, the ventilation is reduced at 13000 m3/ h, with a power input of 1.0 kW. Most of the depression created in the curtain system is used through the pallets, since the pressure drop of the air path is small elsewhere. By contrast there is an additional 0.7 kW consumption due to the evaporator fans, which are switched on during refrigeration only, i.e. 30% of working time. Considering in a year 365 days of operation, of which 300 for ripening and 65 for storage, the total consumption is 300 * 24 * 2.7 + 65 * 24 * 1.0 + 365 * 24 * 30% * 0.7 = 22840 kWh per year per room.
In the rooftop system there are several smaller fans located inside the evaporators. To get the same depression and air flow, by blades of smaller size, there is a minor efficiency, which may be estimated at 10%. Moreover there is a slight pressure drop in the evaporator, due to the evaporating coil and to the air flow bending, that may be estimated at 5% of the total depression. Usually the ventilation can not be reduced during the storage so the total consumption may be estimated as 365 * 24 * 2.7 * 1.15 = 27200 kWh per year per room.
Hence the total difference in electric consumption, considering 0.15 EUR per kWh, is about (27200-22840) * 1.40 * 0.15 = 916 euros per year per room, where the 1.40 coefficient is to take into account the refrigerating system consumption due to higher refrigerating load.
In the recent years scroll hermetic compressors have gained some acceptance in Europe as replacement of traditional semi-hermetic compressors, mainly in commercial refrigeration. Indeed scroll compressors ensure smooth operation, low noise level, and a cheaper purchase cost, compared to traditional semi-hermetic compressor. However the use of scroll compressors in industrial refrigeration raises some doubts, where reliability is paramount and energy costs are taken into account.
To compare fairly the two products it is extremely convenient to stick to the data from Copeland, the leader manufacturer in Europe, which produces both of them. The following table resumes main data from Copeland Selection Software, Version 7.40 / 40654 (04/11).
|capacity||28.9 kW||29.8 kW|
|power in||9.35 kW||10.65 kW|
|max op current||20.5 A||28.2 A|
|net weight||164 kg||65 kg|
Considering 365 days of operation per year, with refrigeration running 30% of the time, for discus compressor, there is a consumption of 365 * 24 * 30% * 9.35 = 24572 kWh; for scroll compressor, proportionally, the consumption is 24572 * 3.09 / 2.81 = 27020 kWh. Hence the total difference in electric consumption, considering 0.15 EUR per kWh, is about (27020-24572) * 0.15 = 367 euros per room per year.