Hilti Group: Curbing energy costs with a proactive energy-saving strategy
Among construction professionals, the name Hilti stands for reliability and safety. The company has earned a leading position among the world’s largest manufacturers of equipment and systems for the construction industry. In its core business, energy efficiency also contributes to the company’s long-term success. This includes not only efficient products and systems but also the efficiency of its own energy infrastructure in production.
The Hilti Group, headquartered in Liechtenstein, supplies the construction industry worldwide with technologically leading products, systems, and services. With innovative solutions for construction professionals, the company is now successful in over 120 countries around the world. But Hilti also holds a leading position among major construction equipment manufacturers when it comes to optimized energy efficiency. For years, the company has pursued an aggressive energy-saving policy. This proactive approach addresses the rising energy prices that are expected to continue, with the aim of improving the company’s competitiveness and thereby further expanding its market position.
At the same time, however, the company also aims to demonstrate that the responsible use of primary energy is not only economically beneficial but also makes a significant contribution to active environmental protection. Recently, at Hilti Kunststofftechnik GmbH in Nersingen, where fasteners and equipment components made of plastic are manufactured, the cooling energy supply was upgraded to the latest energy-efficient technology by the energy-saving specialist ONI from Lindlar.
At the Hilti plant in Nersingen, production is divided into two areas and is supplied with cooling water via two separate networks. A conventional dual-circuit cooling system is used to supply the injection molding machines. For mold cooling, a cooling water temperature of 12 °C is provided year-round, and for hydraulic oil cooling, a cooling water supply temperature of 33 °C is sufficient due to the selected heat exchanger geometry. In addition to the production machines, the cooling system supplies various areas of the building services.
The system’s design as a dual-circuit cooling system and the selected temperatures in the circuits ensure that highly efficient energy-saving measures can be implemented in both areas of cooling energy generation.
A key approach is found in the area of cooling water supply for mold cooling. Typically, the cooling water for mold cooling and the building services area is generated by chillers.
To make this energy-intensive method of cooling water production as cost-effective as possible, the decision was made to use highly energy-efficient, water-cooled chillers. However, since the goal was to tap into further energy-saving potential in this area—even after optimizing the chillers’ energy efficiency—an energy-saving circuit was designed for the transitional and winter months to reduce the load on the chillers. Another area ideally suited for the successful implementation of energy-saving measures is machine cooling. Here, the energy used during the transitional and winter months can be utilized multiple times through the use of heat recovery.
Refrigeration system operating at minimum capacity
In order to cool the injection molds, cooling water with a supply temperature of approximately 12 °C is required year-round, with the highest possible level of supply reliability. In many cases today, electrically powered chillers are still used throughout the year to generate the cooling water, which leads to significant cost burdens due to high electricity consumption. Furthermore, the operating costs for a cooling system exceed the system’s acquisition costs many times over during its service life. Even if one considers only a moderate increase in the price of primary energy sources, the share of energy costs in the total costs becomes a significant and serious factor. To effectively address this issue, the project managers at Hilti specified from the outset the requirement for particularly energy-efficient cooling water generation.
For this reason, the decision was made to implement a system solution that is inherently highly energy-efficient and, furthermore, largely avoids the energy-intensive use of chiller technology throughout the year. To generate the cooling water for the molds of the injection molding machines in Nersingen, highly energy-efficient, water-cooled chillers were therefore selected. The water-cooled design of the machines achieves extremely high efficiency, ensuring very low energy consumption even during continuous full-load operation. The cooling water supply to the chiller condensers is provided by a closed recirculating cooling system, which, as an integrated solution, also handles the cooling water supply for machine cooling.
Although the operation of the chillers had already been optimized from an energy efficiency standpoint through this design variant, the goal was to reduce the remaining energy consumption to an economically viable level through additional measures. The aim was to ensure that the system technology employed would limit chiller operation as much as possible to the summer months and a brief period during the transitional season. To this end, the chiller system for the tool circuit was equipped with a so-called ONI winter relief system. During the transitional and winter periods, this system takes over the cooling water supply to the mold cooling circuit in place of the chillers. This technology utilizes the freely available ambient air as a cooling medium. As soon as the required cooling water temperature can be achieved using the outside air, the chillers are simply shut down and no longer consume any electricity. The electrical energy consumption for the winter relief is reduced to approximately two to three percent of that of a chiller. As a result, chillers are not used for approximately 65 percent of the operating time. This saves a great deal of energy and money.
The associated energy management is handled by a dynamic control system developed by ONI, featuring energy-optimizing system software. This ensures that cooling is operated with the lowest possible energy consumption at all times. Furthermore, it ensures that winter load relief remains active for as long as possible, because every hour the chiller remains shut down is worth real money to the operator.
You can heat your home for free using the cooling system
Plastics processing is inherently extremely energy-intensive. In this regard, it is understandable and reasonable for plastics processors to want to reduce their energy costs as much as possible. Ideally, this is achieved whenever it is possible to reuse the energy that is absolutely necessary multiple times. The cooling energy supply for the injection molding machines at Hilti in Nersingen offers this optimal approach.
Thanks to the heat exchanger geometry of the oil coolers in the injection molding machines, a cooling water temperature spread of 33/38 °C was selected. This increased system temperature pair, compared to a standard spread of 30/35 °C, delivers several advantages. First, the machines’ cooling water supply can manage without peak cooling via secondary systems even during the hottest summer temperatures. Furthermore, the cooling water return at a temperature of 38 °C carries waste heat from the machines, which can be excellently utilized for heating purposes via a heat recovery system.
In this specific case, the waste heat—with a capacity of approximately 1,400 kilowatts—is utilized simultaneously for several applications. These include underfloor heating and ventilation or air heating systems for heating offices and common areas, as well as a logistics center and the toolmaking department. As a result, waste heat—which previously had to be recooled at great expense—is transformed into valuable heating energy that replaces natural gas or heating oil. Consequently, heating costs are reduced by up to 95 percent.
This low-temperature technology also offers a particular advantage in terms of heat distribution within the room. Heat emitted by conventional heating systems naturally travels along the shortest path to the ceiling of the room or hall, where it is typically not desired. Low-temperature heating mixes much more quickly with cooler room air, ensuring that the heat ultimately reaches where it is truly needed.
In almost no other area does the implementation of an energy-saving measure have such a significant impact as in the cooling water supply. Choosing the right system technology and temperature spread ensures low costs in primary cooling water generation right from the start. The use of heat recovery drastically reduces heating costs because free waste heat replaces expensive primary energy sources such as heating oil or natural gas. At the same time, heat recovery ensures that separate recooling of the cooling water is not required during the period when waste heat is being utilized. Naturally, this also eliminates the costs associated with recooling. By using highly energy-efficient chillers and an integrated winter load-shedding system, electricity consumption for the cold water supply to the mold cooling system is minimized.
Overall, however, the consistent implementation of the requirements defined by Hilti does more than just minimize energy costs. With this energy concept—planned and implemented by ONI experts in collaboration with KTO-engineering and Hilti—Hilti is also setting new standards for active environmental protection. Economy and ecology therefore benefit ideally from the implementation of energy-saving measures, particularly in the plastics processing industry.
