C. Hübner GmbH: Energy Efficiency for Premium Plastic Products
For successful companies, the ongoing optimization of their production environment is a top priority alongside their core business. One example of this is C. Hübner GmbH in Marktoberdorf. As a manufacturer of premium-quality plastic products for the automotive, sanitary, and consumer goods sectors, the company has carved out a leading position in the industry.
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Produce energy-efficiently with proper airflow
Reusing energy once it has been utilized while ensuring a high level of supply reliability, along with a heating concept for the injection molding facility that features uniform temperature control and low air velocity—this is what C. Hübner has achieved as part of a company expansion. The Marktoberdorf-based company continuously invests in modern technologies and expanded its production facilities by 5,300 square meters in 2018. In the field of injection molding from 1K to 3K, C. Hübner GmbH offers services ranging from mold design and multi-component injection molding to surface finishing on automatic electroplating systems.
In addition to production technology, the company’s management also keeps a close eye on energy efficiency and process optimization. This means they are monitoring the continuous rise in energy prices—and responding to it. “For us as an energy-intensive company, it is clear that energy costs are becoming increasingly important, and that we can only remain competitive if we reduce energy consumption to a minimum,” explains Managing Director Thomas Hübner. Specifically, the company participates in the Ökoprofit program, an ecological project for integrated environmental technology. The demands on refrigeration technology, heating, compressed air, and HVAC systems are particularly high. When designing and implementing the system technology, the goal is to achieve the highest possible efficiency, consistency, and safety. Systems specialist ONI was brought on board as a partner to implement the energy and utility supply concept for the new Siemensring construction project in Marktoberdorf.
Single-circuit cooling water supply
Using 19 injection molding machines with clamping forces ranging from 350 to 3,500 kilonewtons, Hübner produces technically sophisticated plastic parts, including those for optical applications and visible components. Crucial to their quality and production efficiency is a reliable year-round supply of cooling water at a stable temperature—both for the machine hydraulics and for recooling the water-cooled chiller, which ensures the supply of air-conditioning cooling to various operational areas. Instead of cooling towers with their typical water quality issues and the complex handling of chemicals, Hübner uses patented, dry-running free coolers. These recooling units impress with their ability to adjust output to actual demand while consuming very little electricity. The units, equipped with a so-called adiabatic system, are capable of ensuring the cooling water supply even at higher outdoor temperatures in the summer.
A particular advantage of this open-loop cooling system used by ONI is that it is glycol-free. While glycol provides frost protection, it also reduces the efficiency of the heat exchangers. Since cost-effectiveness and safety are of paramount importance, glycol-free systems were selected.
Experience shows that plastic processors have opportunities to reuse energy in several areas. One example is the use of waste heat from hydraulic injection molding machines. To dissipate this waste heat via recooling systems, expensive electricity must be used once again as drive energy.
However, the thermal energy from the hydraulic oil cooling system can also be used for heating purposes. This allows part of the electrical power drawn by the injection molding machine to be utilized twice, thereby saving the additional energy required for the otherwise necessary recooling. The waste heat from the machine cooling circuit and the recooling circuit of the water-cooled chiller is available at 35 degrees Celsius and is ideal for heating office, workshop, warehouse, or production areas via underfloor heating or specially designed air heaters.
Hübner uses the waste heat to heat office spaces, the tool shop, and storage areas. In addition to significant savings, this low-temperature technology offers another advantage: heat emitted by conventional heating systems naturally rises along the shortest path to the ceiling of the room or hall, where it is typically undesirable.
Low-temperature heating mixes much more quickly with cooler indoor air, ensuring that the heat reaches exactly where it is needed. In addition, the low-temperature waste heat is used to power air curtain systems, which largely prevent cold outside air from entering the heated operational areas during the winter.
The compressed air compressors are also equipped with heat exchangers for heat recovery. They supply waste heat at 70 degrees Celsius, which is buffered by a stratified heating water storage tank and then also made available to the heating system.
Facilities requiring a hygienically safe drinking water supply can ideally utilize the waste heat from the compressed air compressors via so-called storage tank charging systems. This ensures that, in conjunction with a stratified storage tank, drinking water at a temperature of 60 degrees Celsius is fed into the supply network.
A prerequisite for the multiple use of energy from the machine cooling circuits is closed, glycol-free cooling circuits that are recooled via free coolers as self-draining systems. This ensures consistently high water quality in the cooling circuit and frost protection even in the event of a power outage.
Sensitive manufacturing areas where high-quality products are produced require a defined ventilation system. The demands placed on the design, installation, and operational safety of such HVAC systems are correspondingly high. Unfortunately, experience repeatedly shows that costly ventilation systems in industrial facilities are energy-intensive yet fail to achieve the desired results. When developing the concept, the operational and functional reliability of the ventilation systems takes center stage, though low construction and operating costs are closely tied to this requirement. Accordingly, energy costs for heating the fresh air supply during the transitional and winter months should also be kept as low as possible.
To ensure the required indoor air quality with uniform room temperature distribution, Hübner implemented a ventilation concept tailored by Oni that takes into account factors such as reliability, energy efficiency, and operational safety. To ensure high energy efficiency of the ventilation system, the large central ventilation unit in the injection molding shop, with an air flow rate of approximately 65,000 cubic meters per hour, is equipped accordingly. In the first stage, the unit uses the waste heat from the exhaust air to preheat the supply air. For this purpose, the unit features a thermal mass in a two-part duct. In one duct, the exhaust air is directed, and in the second duct, the supply air is directed according to the counterflow principle. Before the exhaust air is discharged into the atmosphere, it must pass through the air-permeable heat transfer medium or thermal mass, where it releases heat depending on the temperature difference and residence time.
After the air has passed through the exhaust air duct, it enters the supply air duct, where it transfers the heat absorbed from the exhaust air to the supply air. The heat recovery coefficient, or thermal efficiency of the heat recovery system, reaches up to 80 percent.
The additional energy required to heat the supply air to the setpoint is provided in a second step by a heat exchanger located in the supply air stream. Cooling water is used as the heating medium; this water is loaded with waste heat after the actual cooling process in machines and systems. Through the use of this heat recovery system, free waste heat is converted into valuable heating energy that replaces natural gas or heating oil. The central ventilation unit for toolmaking, with an air flow rate of approximately 17,500 cubic meters per hour, is equipped with a cross-flow heat exchanger for heat recovery from the exhaust air.
The energy-optimized treatment of the supply air is complemented by its – individually – optimal distribution into the premises. In this context, thermal conditions, influenced for example by machines, systems, and processes, must be taken into account. To achieve the highest possible efficiency, Hübner uses supply air outlets in the floor area of the production halls. They direct the supply air to where it is actually needed. The low flow velocities largely prevent disruptive air turbulence and localized drafts, resulting in a homogeneous temperature distribution.
Expertise is in demand
“You need the right people at the table for consultation and project planning, and on-site for smooth project implementation! If you consider the time from the initial consultation to the turnkey handover of the entire system, add in the smooth project execution and the impressive energy-saving results, you end up with an outstanding outcome that speaks volumes about the excellent collaboration with the experts at Oni. Together, we have implemented a project that, through the use of modern, energy-saving technology, ensures that our energy costs remain at an absolute minimum, thereby helping us secure our competitiveness to a certain extent. Furthermore, the completed project demonstrates that energy savings and environmental protection—that is, economy and ecology—can indeed complement each other perfectly, even in the industrial sector,” concludes Thomas Hübner.
