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and cons and eventually decided to opt for three direct freon pump systems (see photo 1 and 2). Freon R134a is used as the refrigerant. Cofely Refrigeration BV designed and supplied the installation (Project
Working principle diagram 1: Indirect coo- ling system
manager: Henk Tebben). The considerations that contributed to their choice included: • With the indirect glycol installation it was neces- sary to cool one degree colder than with the direct pump system, which used extra energy. They had also experienced some technical problems (glycol corrosion and ice-forming), however this was no longer an argument, as this problem does not oc- cur with the current indirect glycol installations.
• Despite the higher initial cost of a direct pump system, experience shows that the energy con- sumption is substantially lower, partly due to free cooling (cooling with deactivated compressors at external temperatures of 8°C and lower), a method also known as winter operation.
Working principle diagram 2: Direct coo- ling system (electronical- ly controlled direct coo- ling system).
Working principle diagram 3: Direct pump system.
• They were already familiar with the direct pump system and satisfied with its working, particularly in extreme conditions.
• The energy saved by the direct pump system had not been verified in practice, but the energy consumption corresponded to the figures presen- ted in the quotation. The calculations in the quote indicated an energy saving of 20-25 % compared with an indirect cooling system.
• For flexibility and reliability, the chosen option was a cascade configuration with three direct pump systems equipped with multiple compressors.
• To prevent noise nuisance and save energy, low- noise < 49 dB(A) and energy saving EC condenser fans were used.
rature never falls below freezing point. This slightly increases the efficiency of the heat transfer.
Smits-Derks BV Horst The farm owned by Peter Smits and Henk Derks has 17 growing rooms of 850 m2 where mushrooms are grown for mechanical harvesting. They produce to a four-week cropping cycle. The company has its own grading room equipped with the latest in grading line technology, which can process nine grades. A wide number of grades is harvested depending on the current demands of the customers. The climate installation consists of individual climate units with two centrifugal fans. Where possible frequency controllers are used on the fans, motors and pumps. The central energy supply on the farm comprises a steam boiler, two high-efficiency central heating boilers and three direct freon pump systems. This enables maximum flexibility in the cropping cycle.
Choice of cooling system In the past, Smits-Derks had a direct freon pump system and an indirect glycol system. When the company had plans to build new facilities in 2000, they weighed up all their experiences and the pros
Compressors and refrigerant tank.
Practical experience Henk Derks uses the system actively, by both adjus- ting the tank temperature and using winter operation (see photo 3). Depending on the situation, he sets the tank temperature to between 5 and 8 °C, however preferably as high as possible, as each degree hi- gher represents an energy saving of +/- 3 %. He can also set the winter operation temperature (e.g. 8 °C) so that the compressors are deactivated as soon as the external temperature drops below this value. This just leaves the pump active to send the refrigerant around the system. At an outside temperature of 8 °C, the pump pressure will also produce additional coo- ling of some 2 to 3 °C, so that the tank temperature will be at around 5 to 6 °C, which is more than cold enough. Another extremely important factor is the
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