PDF-Download - Kältetechnik aircool GmbH

Recommendations

Info

Air Conditioning - Refrigeration A comparison of space and power consumption can be seen in Table 2. However, in any case the choice between dry / evaporative cooling, the impact on the chiller should also be taken into account. The example of the turbo chiller WSC 100, the clamp power consumption when using a dry cooler is 509 kW, when using an evaporative cooling tower, however, the power consumption is only 310 kW: Thus just by the choice of implementing another cooling process the electrical energy used by the chiller can be reduced by 40%! Distinction based on the cooling medium system Here one can also distinguish two basic systems. Certainly the oldest and best known method is that heated water is exposed directly to the ambient air, and by way of evaporation of part of the water, cooling of the same is achieved. Cooling towers where the water is directly exposed to the ambient air are designated as open cooling towers (open cooling water circuit). The earliest cooling towers emerged at the beginning of industrialization in the form of natural draft cooling towers which were relatively simple wooden structures. Graduation houses are in use today for another purpose but operate on the same principle. The most efficient heat transfer is achieved by way of direct contact of water with the ambient air. However, the water is exposed to contamination in the air and adds to the impurities such as water dissolved minerals are thereby concentrated, since only pure water in its vapor phase may leave the circuit, this should be taken into account in plant design, e.g. through a impurity factor in the chiller. If this qualitative change in the water can not be accepted, protection may be achieved by separation of the circuits to be cooled machine / system from the influence of the polluted water. If it is realized directly in the cooling tower loop separation, usually by the installation of a tube bundle heat exchanger), it is known as a "closed cooling tower" (closed cooling water circuit). Which is the cooling tower that you would like to have To begin with, this question can not be answered here. If the end-user / operator wants to have an efficiently operating system, the cooling tower manufacturers will be happy to provide a detailed consultation. In recent decades, a wide variety of different types of cooling towers for various applications have been developed, which are described below. Open cooling towers with centrifugal fans They are well suited by their compact design for use in a small space, are of low weight and move large amounts of heat with as little energy as possible. The centrifugal fans offer the ability to mount additional silencers, so that even demanding noise requirements can be met. Because of the mode of operation it is obviously not possible to use dry cooling, which means that over the entire operating life one must expect correspondingly high water consumption. However, open cooling towers may be used at sufficiently low temperatures for "free cooling" (i.e. cooling without refrigeration machine operation). The minimum cooling water temperature usable with free cooling, however, is limited due to the risk of ice formation at below10 degrees C. Closed cooling towers with centrifugal fans The tube bundle heat exchangers of the cooling water circuit is protected from pollution, but the required space, weight and energy requirements are higher than for an open cooling tower. Silencers can be mounted, as well as the operation for free cooling. Additionally, it is possible to run the cooling tower in dry mode. In observance of the cooling water temperatures and the ambient air temperature, the tube bundle heat exchanger in dry operation, can dissipate approximately 10 to 20% of the designated capacity of the chiller in operation. An application example is the air conditioning of a building, which in the transitional period and in the winter only one server room needs to be cooled. HLH Bd. 60 (2009) Nr. 10 - October 43
Air Conditioning - Refrigeration Dual heat exchangers or hybrid coolers special part The aim of these units is to combine the benefits of evaporative and dry cooling in one device. Thus it is possible on the one hand, to reach the low temperatures of an evaporative cooling, and on the other hand through the rational selection of the switching point between wet and dry operation of approximately 15 to 18 ° C to achieve considerable savings of water. Lower set points worsen the water savings and thus the cost savings. The devices are designed so that even at the switchover point, the full cooling tower capacity is available. These systems with intelligent and effectively controlled equipment also have their price. Dry coolers or "glycol" These devices have a relatively simple structure, consisting of a tube bundle with slats designed to achieve the greatest possible heat transfer surface area. Fans provide the necessary exchange of air. Of course you do not need any extra water, but usually have higher electric power consumption than an evaporative cooler and, as already mentioned, the higher coolant temperatures have a negative impact on the performance numbers of the chiller. Advantageous is the ease of installation, the closed cooling circuit and the high potential for free cooling capacity. Water preparation and treatment for evaporative cooling towers Evaporative cooling towers can fulfill their purpose, only when the water quality is good. The best cooling tower will fail, if insufficient attention is paid to the manufacturer's guidelines for water quality. The currently available equipment e.g. for water softening, desalination are relatively easy to handle. When designing the system, specialized firms will provide appropriate guidance. Energy-efficient operation of cooling towers Because a cooling tower is usually designed for the highest summer temperatures (e.g. wet bulb temperature of 21 ° C) it is at all lower temperatures actually oversized. The resulting Picture 2 h-x diagram, a representation of the process of dry and wet cooling. In the initial state at the entry point of the air is the same. Through the various processes involved the corresponding line results. "extra" power is not really needed. The performance adjustment can be effected by regulation of the airflow through the cooling tower. For a long time, the fans were operated with motors having 2 or sometimes even 3 switchable speeds. Thanks to the fact that the frequency converter which is only slightly more expensive than the contactor control circuit for a speed switch, they are frequently implemented and for energy-efficient operation they are the best choice. In connection with the control of the chiller by use of a frequency converter, a continuously variable cooling water temperature can easily be achieved. Conclusion A blanket statement, which system version should be implemented is not possible, the project relevant factors such as capital and operating costs, efficiency, redundancy, reliability, setup time and situation, plant layout, ambient temperatures, and noise standards, as well as (to name but a few) must be taken into account. To find the ideal chiller / cooling tower combination on the basis of investment and operating costs, in preparation a load profile must be created, which also provides information on the required partial load performance of each unit. Frequency converters provide low starting currents and high ESEER / IPLV values, and at constant cooling water temperatures the operating cost savings are not so great. Basically, it is necessary to determine whether heat recovery and / or free cooling can be implemented, the performance numbers (benefits / costs) which can thus be realized, cannot be achieved by any of the most efficient compression refrigeration machines! 44 HLH Bd. 60 (2009) Nr. 10 - October
Page 1 and 2: Air Conditioning - Refrigeration Ch
Page 3: Air Conditioning - Refrigeration Ch

PDF-Download - Kältetechnik aircool GmbH

Create successful ePaper yourself

Delete template?

Save as template?