Investment in a new system at this so-called Plastics Technology Centre was necessary because the old closed system employing a hybrid evaporative cooler was reaching the end of its service life after 25 years. In the old Miele system, the water had direct contact with the ambient air, resulting in contamination of the prepared make-up water. In addition to the continuous loss of water through evaporation, the circulating water had to be filtered and conditioned with water additives in a rather complex process. The whole situation required extensive monitoring due to the increased risk of contamination, such as with legionella and other bacteria which, in turn, required extensive maintenance.
The new solution can provide 30°C water even at a high ambient temperature of up to 35°C.
Closed free cooling systems, which release heat into the environment by way of an air/water heat exchanger, are an alternative to open cooling systems. These systems come within about 5 Kelvin of the outside temperature. This means that if a water feed flow temperature of 30°C is required, these standard systems work correctly up to an outside temperature of 25°C. If the outside temperature is higher, additional cooling must be ensured, for example by spraying, the addition of tap water or an additional refrigeration unit, in order to keep the feed flow water at 30°C.
A special feature of the new Reisner solution is its combination with a pad system, which enables cooling at high ambient temperatures thanks to moistened honeycombs. As a result, Miele not only saves time and money, but also meets its own demand for high-quality solutions. Alexander Wibe, head of production engineering, said: "We were looking for an energy-saving solution that leaves nothing to be desired in terms of our technical requirements. The cooling system had to be of excellent quality and include components of renowned suppliers. A reliable and efficient low-maintenance solution with 24/7 customer support in the event of malfunctions – that is the package that we were trying to find."
The Warendorf location supplies all of the Miele production sites. Its product portfolio includes complex assemblies such as washing machine doors or dryer screens, multi-component parts and parts with high-gloss surfaces, for example the outer shells of vacuum cleaners. In addition, the facility, which was founded in 1975 and has a workforce of approximately 300 persons, supports and assists the Miele plastic part production sites in Uničov (Czech Republic), Dongguan (China) and Ksawerów (Poland).
The closed system incorporates a V-shaped, self-draining free cooler. The honeycomb structure of the pad system will only be moistened with tap water when this is necessary due to high outside temperatures of 25°C or higher. When air flows through this pad system, it cools down through adiabatic cooling. Then, the process heat is transferred to the cooled air by way of a Cu/Al heat exchanger (not by evaporation).
"The decisive factor here is that the spraying water does not come into contact with the heat exchanger," explains Günter Sareyko, head of sales of Reisner Cooling Solutions. Reisner has physically separated the second step, that is, the process heat transfer, from the first one. "The heat is dissipated nearly completely through the air, so that Miele now has a reliable and cost-efficient cooling solution," adds Sareyko. The special design enables a considerable reduction of the operating costs.
The new system offers a cooling capacity of up to 500 kW and reliably ensures the correct process temperature at an outside temperature of up to 35°C. Maintenance is another factor where Reisner has developed an excellent solution. The easy replacement of the pads, which have a service life of 3-5 years depending on the area of application, has been as important as a minimised water consumption and the use of durable materials.
The fail-safe double-pump system with a volumetric flow rate of up to 87 m³/h, and the 14 fans with EC motors are all speed-controlled. The humidification system has a multi-stage design, while the integrated return flow filter works completely without pressure and can be changed during operation. As a result, Reisner was able to reduce the required energy to a minimum during every step of the process.
The system has been in use since October 2020. Alexander Wibe is more than satisfied: "The fast turnaround and the fact that we were able to integrate the system into our running production without having to resort to renting interim cooling solutions were big pluses." The company also handled the provision of the control cabinet in line with the Miele specifications.
Alexander Wibe is not yet able to precisely quantify the cost and time savings. However, he is very optimistic after the first phase. "We noticed early on that the energy consumption has drastically decreased. The system is extremely reliable and we were able to completely forgo the use of chemicals."
Miele's high standards are also reflected in the decision to use an additional filter solution and chemical-free water preparation system. After a very brief period of use, the water preparation system, including a full-flow filtration solution in the return flow, resulted in steadily improving water quality. The system dissolves limescale and corrosion compounds by way of low-frequency electromagnetic fields. Then, they can be filtered out of the water.