A comprehensive energy saving concept for the injection moulding shop.

Flow measurement technology is the profession of the Wehrle company in Furtwangen, which emerged from the watch industry. A core area of the traditional company is plastics technology, which today produces precision components with around 70 injection moulding machines, mainly in 2-component technology. In addition to constant innovation in products and production, extensive investments have been made in technologies for the sustainable reduction of energy consumption - in order to be able to continue manufacturing in Germany at globally competitive costs in the future.

Companies with 170 years of successful history are rare in Germany and Europe. Started with the production of trumpeter watches, which can now be admired in the German Watch Museum, the company has always concentrated on precision products throughout its history. Today, the two business units "Metering" and "Precision Plastics", which produce plastic components and assemblies for customers from various industries, form the most important pillars. More than 70 modern injection moulding machines, most of which are equipped for 2K technology, are available for this purpose. The clamping force ranges between 250 and 2,200 kilonewtons, the unit weights range from 0.01 to 600 grams.

The positive development of the company is reflected in the steadily growing number of employees and the new hall that has just been built. On an area of around 11,000 square metres over four floors, the energy centre in the basement, the injection moulding shop on the ground floor, offices on the first floor and the tool construction and social rooms equipped with the latest technology on the second floor have found an attractive new home. The building and interior architecture as well as the individual operating areas were designed for an optimal production process. "As a medium-sized company with traditional roots in the Black Forest, we are committed to our location and to the people who passionately contribute to achieving our goals. For this reason we develop and produce exclusively in Germany. In all our activities, we always keep the topic of energy efficiency in mind in order to make our contribution to the preservation of our environment. For the implementation of an energy concept in our new construction project, we were therefore looking for a partner with extensive experience. After market research and information evaluation of reference plants, we got the energy saving specialist Oni from Lindlar on board. Together we have implemented an energy supply concept that sets standards in terms of economy and ecology," says Georg Herth, managing partner of E. Wehrle GmbH, describing his decision.


Integrating natural resources

If you can use well water as a recooling medium, you have an unbeatably inexpensive cooling energy carrier. Years ago, a well was drilled on the Wehrle site to supply the first spraying plant. This was integrated into the new supply concept and optimised. Today, the available bulk quantity is used in the best possible way within the range of the permissible temperature spread. Thus, supply circuits with different temperatures are connected in series wherever possible. This series connection is made possible by selecting the supply temperatures in the individual cooling circuits. A spread of 25/30 °C was selected for the supply of the injection moulding machines in the hydraulic cooling area, a spread of 15/18 °C for the mould cooling area and a spread of 12/18 °C for the ventilation area. Since the individual circuits are operated separately from the recooling network via heat exchanger units, it is also possible to use the waste heat from the machine hydraulic cooling system for heating purposes.


Security of supply has priority

Compliance with delivery obligations is probably the most important demand made by customers on their suppliers. Particularly when parts have to be delivered "just-in-time" or "just-in-sequence", this requirement is given special emphasis. In order to be prepared for all eventualities, all systems and heat exchanger units at Wehrle in Furtwangen have been designed to ensure double security of supply at all times. Should the well water supply not be sufficient during the summer months or should more power be required for the peak demand, a cooling machine with 310 kilowatts of cooling capacity can be switched on from a standing start.


Cooling saves heating costs

In order to heat a company with several thousand square meters of production, office and storage space in the transition and winter months, a lot of natural gas or heating oil is usually required. The heating energy consumption and the resulting operating costs are therefore considerable. In addition, a boiler house with boiler, burner and flue gas system is required for heat generation and distribution. In order to keep the investment costs and ultimately the heating costs as low as possible, Wehrle first focused on the use of waste heat from all possible areas. The cooling energy supply for the hydraulics of the injection moulding machines and the cooling circuit of the compressed air compressors were identified as particularly attractive sources.

Cooling water with a temperature spread of 25/30 °C and a capacity of 300 kilowatts is provided for the hydraulic cooling of the injection moulding machines in the two production areas. The recooling would normally also run via the well water system during the transition and winter months. Here, however, once the energy has been used, it is simply used a second time by converting the cooling circuit into a heating circuit. This use is made possible by the fact that industrial underfloor heating surfaces have been installed in the new building, which manages with a correspondingly high heating surface density with a flow temperature of 30 °C as the heating water temperature and brings the rooms to be heated to the set temperature. In addition, waste heat with 70 °C is available from the compressed air supply, which is also converted into low-temperature heat via a heat exchanger system and made available for underfloor heating and ventilation systems. This heat recovery process turns free waste heat into valuable heating energy, which replaces natural gas and heating oil and thus prevents unnecessary environmental pollution.


Room air conditions influence part quality

Sensitive production areas, in which high-quality products are manufactured, require defined room ventilation. Unfortunately, practice shows again and again that expensive ventilation systems in companies work energy-intensively, but without the desired effect. Since Wehrle places the highest demands on product quality on moulded parts used in precise measuring instruments, constant production conditions must be ensured under all circumstances. In the area of room air quality and room temperature distribution, Wehrle has opted for a ventilation concept tailored by Oni that is planned and implemented taking into account all aspects of reliability, energy efficiency and functional safety.

Different air outlet systems were used, which were optimally adapted to the room geometry. These include displacement air outlets in the floor area of the production halls and displacement air hoses arranged in the ceiling area. This ensures that supply air volumes arrive where they are needed. Large discharge surfaces also ensure that the supply air is introduced at low flow velocities. Interfering air turbulence and point flows are thus prevented. During the transition and winter seasons, the waste heat from the machines and the compressed air compressors is used to heat the fresh air components that have to be supplied. The use of free waste heat for air heating naturally has an extremely positive effect on the energy balance and ultimately on the company's annual operating costs.


Trust is good, ....

...Control is better. Plausible economic efficiency calculations and exemplary reference projects can certainly be used to make decisions, but it is nice to be able to check the predicted savings and the operating situation of the plant technology at a glance. In the Wehrle case, the company's management wanted to have exactly this opportunity to be able to evaluate your decision for an energy-optimized plant retrospectively and at the same time keep an eye on the plant situation. Therefore, a control system was installed in which all relevant plant data are visualized. The focus is on a PLC module with an energy-optimizing system software developed by Oni which, as a dynamic management system, takes over the organization of energy supply at Wehrle. This is where all information on the system statuses of the entire system converge, are evaluated and from here the system components receive all the necessary commands. For example, the control system immediately detects when a peak load makes it necessary to switch on cooling of the chiller or in which area waste heat can be used. This ensures that only the primary energy expenditure that is absolutely necessary is operated at all times. If heating is required in a company area, the corresponding power is provided by the machine or compressed air cooling circuit. The resulting reduction in recooling capacity in turn results in a reduction in well cooling.


Well positioned

The Wehrle project is an example of how holistic energy concepts can open up the possibility of particularly economical and thus cost-saving energy generation. "We have opted for state-of-the-art system technology in all areas, from cooling systems technology to ventilation and pump technology, and are pleased that the energy concept we have now implemented not only enables us to produce energy efficiently, but also makes a significant contribution to environmental protection by keeping energy volumes in the electricity and gas sectors at a minimum level. Oni's experts were exemplary at our side from the first project discussion to the turnkey handover of the plant and continue to be partners of choice for us when it comes to reliable and energy-efficient plant systems," was Georg Herth's summary of the energy concept implemented in Furtwangen.