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To cool in order to warm  #10 (68) 2008

Heat recovery systems by a German company Reisner AG allow to optimize energy consumption efficiency at manufactures and cut down costs considerably due to use of waste heat in heating systems

Free energy
Energy costs in plastics processing can be compared to a spiral that has been going up for many years. And there is no end to such a growth of costs so far. That is why those who want to bring down production energy costs and keep them at a low level have to search for ways of energy saving.
Use of waste heat plays a greater role in the process.  Indeed, “excessive” in some cases energy is quite necessary for other purposes, and its cost is rather high. The most efficient thing here is individual solutions on heat recovery for every enterprise that are offered by Reisner AG.
Reisner systems use waste heat beneficially, that is why they provide lower energy consumption at manufactures. It is this approach that accounts for Reisner success in the world market.
If in plastics processing water is used for cooling moulds or hydraulic components, most often it should be cooled to a working temperature with the help of a special system that performs as a heat pump. That means that the cooling system collects heat energy where it is not wanted, increases temperature, and after that heat is dissipated at another place. This happens with the help of a condenser which conveys heat to the environment. This is true not only for the energy released in the production process, but for the heat released during work of the refrigerant compressor.
Working on refrigerating systems Reisner specialists concluded that a whole wide range of useful applications for the energy released in the manufacturing process can be found. It is appropriate not to waste it, but to place it at the disposal of the enterprise. That is why for many years Reisner has been offering systems that allow using heat released in the manufacturing process or in cooling process in the cooling system for heating, for example, work rooms. Today the company has developed a completely new concept which allows to make a step forward in existing solutions, thus giving more interesting perspectives.
Using the conventional recuperation method waste heat is directed to a heat loop and released in the rooms by air heating. Due to this method considerable energy saving becomes possible. Using a cooling machine with the cold productivity of 100 kilowatt and the compressor power of 38 kilowatt, a producer can expect a total waste heat flow of 138 kilowatt. With the electric energy consumption of 38 kilowatt hour by the compressor, all in all, we have 3,6 kilowatt hour of heat (138:38) for each kilowatt hour of electrical energy consumed.
Comparison with electrical heating where each kilowatt hour requires 1 kilowatt hour electrical energy shows how profitable it is. Besides, cooling machine is in operating mode, anyway, and waste heat is at the disposal of the producer for free.

New opportunities
Technologies waste heat recovery that have been used so far in this field do not take use of all the possibilities for saving and part of the expensive energy is lost. With the help of these technologies water can be heated to a rather low temperature. It limits production halls heating as well. If a comfortable microclimate in production halls and rooms is to be kept at an appropriate level, then the water should be heated to a much higher level. 
Those who want to use waste heat immediately for manufacturing purposes and apply it in temperature regulation devices need a more heat released during manufacture. This application field is especially attractive because work of devices designed for keeping temperature at the appropriate level is usually based on electrical energy consumption.
Developing their heat recovery concept further, Reisner saw its main task in creating systems that produce hotter water for heating systems. In this case a problem of efficiency may arise depending on the desired temperature: in some circumstances the system should reach a higher temperature of condensation. As a result, the condenser will consume more energy. Thus, not only potential profit from heat recovery will rise, but also costs for the process. This ratio should be taken into account in each case.
The advantages of Reisner systems are based on the ability to control all the thermodynamic processes in the system. Waste minimization and 100 per cent use of waste heat become possible. High temperatures can be also achieved without increasing condensation temperature. It allows to keep energy consumption within the acceptance limits.
Technically, the key role belongs to waste flow centralization. For this purpose a heating loop is installed. It goes through the condenser and receives all the released heat. If the heat is not necessary at the moment (when it is used only for room heating and the external temperature is high enough, for example), a dry cooler diverts it to the environment. Otherwise, central heating stream is accumulated in a special tank. There, the waste heat is ready for use at any moment. A lot depends on the heat exchangers used in the system. They are specially designed for heat recovery and allow to achieve best results.

Solutions for any task
A large number of Reisner heat recovery systems installed at different enterprises show how well the concept works. Dr. Schneider Kunststoffwerke GmbH, Kronach, Bavaria has changed their cooling system for a heat recovery system. This pilot project was subsidized by the Federal Environment Ministry. Deceuninck, a window profiles producer, heats its offices in Russia with the help of Reisner system which provides the necessary temperature  in the premises without additional expenditure of energy even with cold winters. Also, Vollmehrhaus GmbH, Plettenberg that specializes in metal surfaces treatment benefits from free heat produced by Reisner system.
Even in a cooling system with the cold productivity of 155 kilowatt and the compressor capacity of 42 kilowatt that altogether emit 197 kilowatt of energy the volume of recovered heat is enough to heat premises of 2500 m2 during the winter. Recalculation of the saved fuel oil shows that this change is obviously reflected in the balance of energy costs.
Fuel oil has the energy content of 9 kilowatt hour per litre. Thus, 197 kilowatt of emitted heat correspond to 21,9 litres of fuel oil per hour. 1 litre of fuel oil costs 0,6 euro. In this case using waste heat saves 13 euros per hour. Hence, we can assert that investments in a heat recovery system guarantee payback in short periods (one should take into consideration constant price rise of oil products).
Devices controlling temperature in injection molding machines can be exploited using waste heat. However, an especially high heat carrier temperature of 60?C minimum is needed in this case. Such indices cannot always be achieved by using only a waste heat flow. A higher condensation temperature is required here, compressor consumes more energy and power factor becomes lower.
Even in this case using waste heat can be beneficial. If a system with the power of 155 kilowatt is to provide warm water of 60?C, the system capacity is reduced to 123 kilowatt. At the same time, energy consumption increases to 67 kilowatt. Thus, the temperature control device possesses 190 kilowatts. If its work is based on electricity, the ratio of consumed energy to produced heat is 1:1. It turns out that operating costs are reduced almost twice in this case.
Taking into consideration all the possibilities that result from using new heat recovery technologies Reiner AG never forgets that the main function of their systems is cooling. The main goal in the field is achieving better power factor. Finally, in this or that way, a cooling system is necessary in the manufacturing process, and it should be integrated in it as well as possible. While calculating the payback, one should pay attention to this fact. Only additional heat recovery expenses should be taken into account during the calculation.
In any system cooling units with heat recovery should meet the exploiting part’s demands. Then Reisner’s concept will be fully realized: waste heat flow use will reach 100 percent, and energy consumption by the cooling machine will change minimally in relation to a conventional operating mode. It guarantees a high quality supply with cold and heat which will correspond to environmental protection laws getting more and more strict and control the upgoing spiral of operating costs.


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