European turntable for fruit and vegetable
Pfalzmarkt Mutterstadt uses cooling logistics
With production of more than 120,000 tons of fruit and vegetables on an area of more than 12,000 hectares by about 2,100 collectively organised members, the Pfalzmarkt in Mutterstadt is one of Europe’s leading production and distribution centres. Since the demand for fresh fruit and vegetables is continuously increasing because of the expansion of the EU, the storage and operating area that was set up in Mutterstadt in 1987 was recently increased from about 15,500 m² to 45,300 m². About 1/3 of new building no. 2 is used as a storage, loading and unloading area for fruit and vegetables and 2/3 of the building is used by empties and returnable crate provider EuroPool System International (Germany) GmbH.
When the VOB tendering took place, the order for the refrigeration system was placed with Heddesheim company Schulz Kälte- und Klimatechnik GmbH. Although a large number of manufacturers and distributors competed to supply the air coolers, condensers and refrigerant containers, the order went to Güntner. According to refrigeration system constructor Klaus Schulz: “The proposed Güntner products with their specific equipment features were the most suitable for the planned cooling concept.”
First cool the goods, then load them
The collectively organised members of the Pfalzmarkt had already decided to expand the cooled loading/unloading and storage area at the Mutterstadt site before EU legislation 178/2002 concerning the traceability of perishable goods came into force. Decisive for the construction of new building no. 2 was not just the area for loading, unloading and intermediate storage of fruit and vegetables that was so urgently required, but specific cooling of the goods supplied by the surrounding producers during commissioning for the individual customers. Since the EU directive came into force on 1st January 2005, customers and distributors have required the perishable goods to be pre-cooled to a certain core temperature, e.g. 5 °C for fresh vegetables.
Collectively organised fruit and vegetable producers help to make the decision
The topic of cooling has played an important part with the members of the Pfalzmarkt cooperative, even before the new EU legislation came into force. For the majority of agricultural producers, the cooling of their goods is the key to greater value creation. The expectations of the cooling equipment in the new hall were therefore extremely high. Jürgen Hutzler from VR-Bauregie GmbH, Eschborn, as the representative of the clients who are responsible for the construction of the new building, explains the farmers’ situation as follows: “Strong emotions are often in play when fruit and vegetables are being sold. The subject of cooling is a particularly hot potatoe.
Almost every farmer has his own ideas about what should be cooled and how it should be cooled. It was therefore a difficult decision to make. In the past, the quality of the produce was obviously frequently affected by lack of cooling, meaning that it could not be sold.” Thomas Schlich, the managing director of Pfalzmarkt eG, explains the cooling problem as follows: “The products have a wide variety of cooling requirements. Some of them reach their core temperature quickly, such as lettuce and radishes, and others take longer. We need the technology to cool our products to the required core temperature as quickly as possible without causing damage, so that the time between delivery, commissioning and transportation is kept as short as possible."
The formation and support of a work group consisting of six agricultural producers and an expert adviser from the “Dienstleistungszentrum Ländlicher Raum“ (Rural Service Centre – DLR) in Neustadt showed how important the subject of cooling was being taken by the Pfalzmarkt management. However, the results of the work group were more or less the same as those of engineering office that was commissioned to plan the refrigeration system (Brunnenkant, Wiesloch). According to Dr. Holger Kettenmann, the project leader of the engineering office specialising in food refrigeration: “It was important to all participants that optimum use was made of the limited space situation and that enough cooling power for storage and commissioning was available. This is why our ideas were fairly similar.” A multifunction building with the following critical values was created:
- Approximately 11,000 m² of the 15,500 m² building is used by returnable crate provider EuroPool System International (Deutschland) GmbH as a store and for cleaning plastic crates.
- Approximately 4,300 m² of building space is cooled, divided into
- 10 continuous loading rapid refrigeration rooms (width x length x height = 7.25 x 14.5 x 4.5 m) for cooling the goods delivered by the farmers from 30 °C down to 5 °C,
- 10 rapid refrigeration rooms (width x length x height = 7.20 x 8.90 x 7.00 m) for cooling and storing fruit and vegetables from 30 °C to 5 °C,
- approximately 2,400 m² of cooled commissioning area for room temperatures of between 2 °C and 12 °C, depending on what is being stored,
- each with 2 entry and exit locks with high-speed doors.
For lack of space, there are three modified high-efficiency evaporators, model S-GHN 066C/27-E, with integrated 90° air deflection, concealed upwards headers and automatically controlled defrost flap in each of the ten continuous loading rapid refrigeration rooms. They are installed at the long sides of the room, directly beneath the ceiling, so that the maximum storage space is available and the first-in-first-out concept can be adhered to.
The ten rapid refrigeration rooms for the short, medium and long term storage of appropriate types of fruit and vegetables (so-called long turning screw machines) have Güntner SGSN080/ 408 upright evaporators attached to the front. These are made to measure with integrated defrosting flaps and a blow-out channel with a 90° bend. Three 6200 kg insulation coolers that are preferred by the Brunnenkant office and manufactured by Güntner are used for cooling the central commissioning area. These are directly connected to air ducts and provide draught-free, homogeneous and low-noise air distribution over the entire commissioning area using optimised air outlets.
Risk analysis speaks in favour of an R 404A system
Two R404A combination systems, one with 650 kW and one with 720 kW of refrigerating capacity, are used for refrigeration. The original intention was to use NH3 as the refrigerant. However, the client and the planner decided to use R404A refrigerant, which was for safety reasons in order to protect employees and because of the possibility of damage to the stored goods if NH3 escapes. This also means that the BImSchG (federal law for the protection against immissions) approval procedure is not required.
Air-cooled condensers preferred
It was relatively easy to decide what kind of condensers to use to recool the refrigerant. Kettenmann: “Because of the problems with the existing evaporative condensers, the client was clearly in favour of air-cooled condensers.” The following arguments were decisive for the solution that was implemented:
– No need for water treatment
– Performance remains constant, since little soiling occurs.
– Hygienic operation without the risk of water vapour or legionella incidence
– Extremely low maintenance costs compared to cooling towers.
A total of four Güntner axial condensers from the new product line are installed with Güntner support profiles. Two devices of type GVH 090.1 A/2x5-N(D), each with 500 kW capacity, and two GVH 090.1 A/ 2x6-N(D) with 625 kW are installed above the machinery house. All condensers have epoxy-coated fins.
Because of the space-saving base of the refrigerant receivers with a capacity of 1,200 litres, all condensers are supported on 1,400 mm legs, which differs from the standard version. Since the four S-GBH 1200 refrigerant receivers are also supplied by Güntner, the structural coordination of neighbouring components was provided by a single source. For service purposes and in the event of unforeseen breakdowns, the refrigerant receivers can handle the entire refrigerant volume of the respective refrigeration circuit. The Güntner switch cabinet system beneath the equipment has also been integrated into the locality in a user-friendly way. All condensers have the modular switch cabinet system GWS 50-70 beneath them, each with a GDRD 87U digital controller module, including a GSW 4003/F pressure sensor for independent fan control depending on the condensation pressure.
When the order was sent to Schulz with the objective of starting installation within no more than four weeks and completing the work four weeks later, it became clear to managing director Klaus Schulz that such tight delivery deadlines could only be met in collaboration with a partner such as Güntner. “The order was placed with Güntner at the beginning of March 2005 and the units were on site at the beginning of April, exactly on the specified dates and at the required times. With a total of 15 trucks, 11 of which arrived on one day alone, it was a real masterly performance.“ The refrigeration system constructor found Güntner’s option of supplying the equipment ready for installation to be particularly efficient, meaning that the air coolers could be directly unloaded from the trucks using a fork lift or special fork lift and installed and secured in the planned location immediately. “It only took 10 minutes to install an aircooler. This delivery service from Güntner saved us a great deal of time, of course,” remarks Klaus Schulze appreciatively.
Insulated cooler with independent controller
More and more insulated coolers are being used to cool large areas in fresh produce logistics. In combination with ventilation ceilings or air ducts with optimised air outlets, they are far superior to other types of aircoolers with air throw nozzles with regard to thermal comfort. In order to make installation as easy as possible, Güntner insulated coolers are now supplied with preinstalled, tested switch cabinets. They are fully equipped with an energy supply, power units and all of the necessary control components. The control system is independent, but external control values can optionally be used. User guidance is provided in plain text, and is available in German, English, French and Spanish. Up to 24 coolers can be interconnected in one or more control circuits (refrigeration rooms). The internal exchange of data between the coolers takes place via a CAN bus system. The following bus systems are available for communicating with a building control system or other higher-order systems.
- Profibus DP/V1 (Siemens S7 etc.)
- Ethernet TCP/IP 10 Mbit
- Ethernet TCP/IP 100 Mbit
- CAN open
- LON-BUS (BACnet-kompatibel)
The Pfalzmarkt system is incorporated into the higher-order MSR system (TECO, Wurm) via the CAN bus.
Which air cooler for which product?
Each type of fruit and vegetable has its optimum storage temperature and humidity. For example, tomatoes become damaged at a storage temperature of 0 °C, but at 2 to 3 °C there are no problems. Lettuce should have a core temperature of 5 °C before it is transported. There is an optimum storage temperature for almost every fruit or vegetable that can only be exactly controlled in exceptional cases, since the refrigeration rooms are used for a mixture of the above items. The humidity also plays a part in the quality assurance of fruit and vegetables. Whereas the ideal relative humidity for fresh vegetables is about 95 %, apple skins tend to start rotting at this value.
Onions and potatoes prefer a relative humidity of 80 %, which is even dryer. The Pfalzmarkt always attempts to use temperatures that provide the best possible conditions for all stored and commissioned produce. In order to prevent vegetables that have been heated by the sun during delivery from drying up, farmers often use a water hose. The produce is also wetted by “eye judgement” in the new hall, i.e. each batch is individually assessed and wetted using spray nozzles that are built into the ceiling. Since the cooling store has to be used for different items, there is no point in having an evaporator that is specially tailored to a particular item. The following generally applies to fruit and vegetable storage:
- Evaporators with large surfaces and a low Dt do not remove as much moisture from the air, therefore preventing the produce from drying out.
- The evaporating temperature for the fresh produce area should not be less than -8 to - 10 °C.
- The air throw should be adapted to the geometry.
- Electronic expansion valves should be used if possible to control the cooling area temperature as accurately as possible. This will allow the design-based hysteresis of thermal expansion valves to be reduced to ± 0.5 K (Danfoss AKV20/1 electronic expansion valves are used in the Pfalzmarkt).
- The air in cooling buildings containing large numbers of employees should be provided via air ducts if possible.
- Slow air speed / no draughts
- Less noise emission for employees
- More agreeable climate despite low room temperatures
- Good air distribution
- Produce does not dry out as much
- Central treatment of cooled air in insulated coolers that are installed outside the rooms that are being cooled; therefore easier maintenance outside the storage area