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Air Conditioning - Refrigeration R134a R410A Volumetric cooling capacity 0°/40° kJ/m 3 2.050 4.781 Evaporation heat kJ/kg 216 268 Critical temperature °C 101 71 Absolute pressure at 0 ° C(p o ) bar 2,93 8,06 Absolute pressure at 40 ° C (p c ) bar 10,17 24,36 Differential pressure p c - p o bar 7,24 16,3 Pressure ratio p c / p o - 3,47 3,02 Temperature glide K 0 < 0,2 ODP - 0 0 GWP (relative to CO2, 100a) - 1.300 1.720 OEL (occupational exposure limit) kg/m 3 0,25 0,44 The TEWI (Total Equivalent Warming Impact) takes into account the sum of direct (GWP contribution of refrigerant leaks during installation and disposal) and indirect (contribution of CO2 emissions resulting from energy consumption to operate the plant) emissions of greenhouse gases. If the refrigerant loss is minimized, then the influence of the GWP in the TEWI is very low. A comparison of the main physical data is shown in Table 1. Turbo or Screw The semi-hermetical screw compressors are in the power range up to 2200 kW, depending on the refrigerant, the operating conditions and number of compressors. They show a wide range of operation, they can be used with the default configuration; varying flow temperatures of -8 ° C to 15 ° C with cooling water outlet temperatures of up to 55 ° C. The performance adjustment should be continuously adjustable from 25 to 100% of the standard cooling capacity, a flow temperature control is to be considered as prior art. Compressors are started via the star-delta, to reduce the starting current a soft start can be used, more recently, frequency converters are used. McQuay semi-hermetic-turbo compressors are used in the power range from 900 to 4500 kW. Since a maximum of two compressors can be used in a refrigeration circuit, a capacity of up to 9 MW can be achieved. Each turbo chiller is based on a projectspecific configuration; the selection of the main components such as motors, compressors, gears and gear ratios, impeller and heat exchangers is dependent on the operating conditions. For this reason, as well as flooded evaporation, which requires an exact Refrigerant charge, varying operating points Table 1 are not quite as arbitrary as with screw chillers and must be verified for the configuration. The adjustable power control from 10 to 100% is best carried out using the inlet guide vane setting via oil pressure. The turbine can be started via star / delta or soft-start, by mounting an optional VFD (Variable Frequency Drive, frequency converter) corresponding to the starting current, respective to the operating current (Figure 1). Again, the VFD will significantly contribute to an increase in the ESEER / IPLV, through the loss dissipation of the frequency converter; however the 100% EER decreases by about 2.5%. In Table 2 a comparison of different Chillers at different operating points and cooling systems can be seen. Cooling Towers When it comes to cooling towers everyone has probably one of those big steaming power generation plant cooling towers in mind. For a large portion of the cooling tower processes, standard cooling towers are implemented. However, they perform their job in Physical Data for the refrigerants R134a und R410A most instances well concealed and can only be seen when taking a closer look at the roofs. Often, cooling tower issues of are placed in the background, even with respect to: The relatively small cost compared to the cooling system, although the choice of an appropriate process, system, tuning of the refrigeration unit and integration into the overall system has a significant impact on the efficiency of the overall system. Distinction between the methods of heat transfer to the outside Basically, two methods are used to dissipate the excess heat to the environment. Dry cooling transfers the heat to the surrounding air by the temperature gradient of the coolant to ambient air temperature. Accordingly, the high temperature of the cooling medium of approx. 45/40 ° C is assumed when designing for the Picture 1 2.5 MW turbo chiller WSC 100 with free-standing frequency converter of protection IP54 to improve part-load efficiency at decreasing coolant temperature. HLH Bd. 60 (2009) Nr. 10 - October 41
Air Conditioning - Refrigeration Chiller Specifications Unit Proximus Evolution 596.2 XE S T WSC 100 WDC 079 Cooling capacity kW 2.268 2.196 1.933 2.200 2.200 2.200 2.200 2.200 2.200 Power consumption at the terminal box kW 434 461 553 310 352 509 314 352 523 Condenser capacity kW 2.702 2.657 2.486 2.510 2.552 2.709 2.514 2.552 2.723 Cold water temperatures °C 12 / 7 12/ 7 12 / 7 Cooling water temperatures °C 27 / 32 30 / 35 40 / 45 27 / 32 30 / 35 40 / 45 27 / 32 30 / 35 40 / 45 Medium Water 34% Glycol 34% Glycol Water 34% Glycol 34% Glycol Water 34% Glycol 34% Glycol Performance figures - 5,2 4,8 3,5 7,1 6,3 4,3 7,0 6,3 4, 2 special part ESEER-Value - - 5,38 - - 6,21 - - 7,48 - Evaporation dry flooded flooded Number / type of compressors (Units) Quantity 2 / semi-hermetic screw compressor 1 / semi-hermetic turbo compressor 2 / semi-hermetic turbo compressor Capacity control at constant cooling water temperature % 12.5 - 100 10 - 100 10 - 100 20 - 100 5 - 100 5 - 100 20 - 100 Length x Width x Hight mm 4.800 x 1.350 x 2 .550 4.300 x 2.100 x 2 .550 5.600 x 1.800 x 2.550 Refrigerant circuits Quantity 2 1 1 Refrigerant R 410A 134a 134a Refrigerant charge amount kg 2 x 130 636 670 670 884 920 878 Cooling Circuit Technical Data heat exchangers Design temperature Unit ° C Evaporation cooler for an open circuit with centrifugal fans 2 x KD 2/18-28-S2 Evaporation cooler for a closed circuit with centrifugal fans 2 x KI 3/12-28-12 Dual cooling system / hybrid coolers for closed circuit with axial fans 3 x KA VH-09-2x6 Chiller for a closed circuit with centrifugal fans 3 x KA VL-09-2x6 Evaporative c ooling Evaporative cooling / Dry c ooling Dry cooling open c ircuit closed circuit closed circuit wet bulb 21 °C wet bulb 21 °C wet bulb and ambient air temperature 21°C / 18 °C ambient air temperature 32°C Cooling agent Water Water-glycol mixture 34% Water-glycol mixture 34% Cooling water temperature °C 32 / 27 35 / 30 45 / 40 Cooling c apacity kW 2.700 - 2.500 2.650 - 2.550 2.650 - 2.550 2.700 - 2.500 Ventilator shaft capacity max. kW 20,8 48,44 86,4 90,00 Type of water q uality Basis VDI 3803 Basis VDI 3803 Osmotic water - Additional water conditioning necessary - hardness stabilization, corrosion yes yes no - protection, organic load Evaporation water quantity max. (full load) m³/h 4,0 3,9 3,9 - Water discharge reference value m³/h 1, 3 1,3 0,6 - Sound output level with out / with additional sound elimination measures dB(A) 99 / 78 105 / 84 108 / - 99 / - Dimensions Length x Width x Height mm 2 x 5.000 x 3.700 x 2.400 2 x 5.000 x 3.700 x 2.900 3 x 9.300 x 2.250 x 2.400 3 x 9.300 x 2.250 x 2.370 Floor space approx. (without maintenance area) m² 37 37 63 63 Operational weight cooling towers kg 12.800 29.000 24.600 12.900 Table 2 Technical Data of various refrigeration units and heat exchangers typical maximum surrounding air temperatures in the summer of about 32 to 34 ° C in Germany. In wet or evaporative cooling, one takes advantage of the physical effect that for a corresponding change in the aggregate state, vaporization energy is required. Thus evaporative cooling towers have a considerably greater efficiency of heat dissipation because of latent heat. Compared to dry cooling, significantly lower the temperatures of the cooling medium can be achieved, since the ambient air temperature is not critical, but the wet bulb temperature is. Thus cooling media temperatures of e.g. 32/27 ° C can be achieved in an implementation for a wet bulb temperature of 21 to 22 ° (Fig. 2). Dry or glycol coolers are often given preference over evaporative cooling, because it avoids the hassle and cost of water consumption and water treatment. For decentralized and relatively small plants dry cooling may be the choice, but in large and centralized systems, evaporative cooling is to be preferred. 42 HLH Bd. 60 (2009) Nr. 10 - October
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