For building professionals, the name Hilti stands for reliability and safety. The company has achieved a leading position among the world's largest manufacturers of equipment and systems for the construction industry. The economical use of energy also contributes to the sustainable success of the company in its core business of top-class products. In addition to efficient products and systems, this also includes the efficiency of the company's own energy systems in production.
The Hilti Group, headquartered in Liechtenstein, supplies the construction industry worldwide with technologically leading products, systems and services. Today, the company is successful in more than 120 countries around the world with innovative solutions for professionals in the construction industry. Hilti also occupies an outstanding position among the major manufacturers of construction equipment with regard to optimized energy efficiency. For years, an offensive energy-saving policy has been pursued. With a view to the future, the company is thus responding to the expected continued rise in energy prices in order to improve its own competitiveness and thus further expand its market position. At the same time, the aim is to show that the responsible use of primary energy is not only worthwhile from an economic point of view, but also makes a significant contribution to active environmental protection. The cooling energy supply at Hilti Kunststofftechnik GmbH in Nersingen, where fastening elements and device components are manufactured from plastic, has recently been brought up to the state of the art in 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 started up with cooling water via two separate networks. A classic dual-circuit cooling system is used to supply the injection moulding machines. For mould cooling, a cooling water temperature of 12 °C is provided all year round and for hydraulic oil cooling, a cooling water flow 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 technology.
The system design as a dual-circuit cooling system and the selected temperatures in the network circuits ensure that extremely efficient energy-saving measures can be implemented in both areas of cooling energy generation.
An essential approach can be found in the area of cooling water supply for mould cooling. The cooling water for mould cooling and the building services area is usually generated via cooling machines. In order to make this energy-intensive form of cooling water production as economical as possible, it was decided to use particularly energy-efficient, water-cooled chillers. However, since further energy saving potentials were also to be exploited in this area, following energetically optimised chiller operation, an energy-saving circuit was planned for the transition and winter months to relieve the load on the chillers. Another area that is ideally suited for the successful use of energy-saving measures is machine cooling. Here, the energy used in the transition and winter months can be used several times by using heat recovery.
Chiller operation at minimum level
Cooling water with a flow temperature of approx. 12 °C is required all year round for the cooling of the injection moulds with the highest possible security of supply. Today, electrically driven chillers are still used in many cases throughout the year to generate the cooling water, which leads to considerable cost burdens due to high power consumption. In addition, the operating costs for a cooling system exceed the acquisition costs of the system many times over over the service life. If even a moderate price increase for primary energy sources is taken into account, the share of energy costs in the total costs becomes a significant and serious factor. In order to effectively counter this problem, Hilti's project managers set out from the outset the demand for particularly energy-efficient cooling water generation.
For this reason, the decision was made to opt for a system solution that is inherently particularly energy-efficient and also largely dispenses with the energy-intensive use of refrigeration technology throughout the year. For this reason, particularly energy-efficient, water-cooled chillers were used to generate the cooling water for the moulds of the injection moulding machines in Nersingen. The water-cooled design of the machines achieves an extremely high degree of efficiency and thus very low energy consumption, even under permanent full load operation. The cooling water supply for the cooling machine condensers is provided by a closed recooling system, which as a composite solution also provides the cooling water supply for the machine cooling.
Although the operation of the chiller has already been optimised from an energy point of view by this design variant, the remaining energy consumption was to be reduced to an economically justifiable level by additional measures. The aim was to ensure that the system technology used would ensure that the operation of the chiller would be limited as far as possible to the summer months and a short period during the transition period. The cooling machine system for the tool circle was equipped with a so-called ONI winter relief. This system technology takes over the cooling water supply of the mould cooling circuit instead of the chillers in the transition and winter time. With this technology, the ambient air available free of charge is used as cooling medium. As soon as the required cooling water temperature can be provided with the outside air, the cooling machines are simply switched off and no longer consume electricity. The electrical energy required for winter relief is reduced to a value of approximately two to three percent for a refrigerating machine. This eliminates the need for chillers for more than 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 with energy-optimizing system software. This ensures at all times that the refrigeration system is operated with the lowest possible energy consumption. In addition, it ensures that the winter relief remains active for as long as possible because every hour the chiller remains switched off is worth cash for the operator.
With the cooling can be heated free of charge
Plastics processing is inherently extremely energy-intensive. In this respect, it is understandable and comprehensible if the plastics processor wants to reduce his energy costs as much as possible. Ideally, this can always be achieved if one is in a position to be able to use the necessary amounts of energy several times at the same time. The cooling energy supply of the injection moulding machines at Hilti in Nersingen offers this optimal approach.
Due to the heat exchanger geometry of the oil coolers in the injection moulding machines, a cooling water temperature spread of 33/38 °C could be selected. This increased system temperature pair, compared to a normal temperature spread of 30/35 °C, offers several advantages at the same time. On the one hand, the cooling water supply of the machines will manage without peak cooling via secondary systems even at the highest summer temperatures. In addition, the cooling water return with a temperature of 38 °C supplies waste heat from the machines, which can be excellently used for heating purposes via a heat recovery system. In this specific case, the waste heat with an output of around 1400 kilowatts is used for several applications at the same time. These include underfloor heating, ventilation and air heating systems for heating offices and social rooms as well as a logistics center and toolmaking. This turns waste heat, which previously had to be recooled at high cost, into valuable heating energy that replaces natural gas or heating oil. As a result, heating costs are reduced by up to 95 percent.
This low-temperature technology also offers a particular advantage in terms of heat distribution in the room. Heating heat emitted by conventional heating systems naturally migrates by the shortest route to the ceiling of the room or hall, where it is not normally desired. Heating heat on a low-temperature basis mixes much faster with cooler room air, so that ultimately the heating heat reaches where it is really needed.
Multi-effect per economy and ecology
In hardly any other area does the implementation of an energy-saving measure have such a strong effect as in the supply of cooling water. The right choice of system technology and temperature spread ensures low costs in primary cooling water generation right from the start. By using heat recovery, heating costs are massively reduced because free waste heat replaces expensive primary energy sources such as heating oil or natural gas. At the same time, heat recovery ensures that no separate recooling of the cooling water is required during waste heat recovery. At the same time, of course, the costs for recooling are eliminated. Through the use of particularly energy-efficient chillers and an attached winter relief, the electricity input for the cold water supply of the mould cooling system is reduced to a minimum value.
All in all, the consistent implementation of the requirements defined by Hilti does not only result in the energy cost share being reduced to a minimum. With this energy concept planned and implemented by ONI experts, KTO-engineering and Hilti, Hilti is at the same time setting standards with regard to active environmental protection. Economy and ecology therefore benefit ideally from the use of energy-saving measures, especially in the plastics processing industry.