建环毕业设计外文翻译--关于先进的低能耗的超市制冷系统的分析(编辑修改稿)

建环毕业设计外文翻译--关于先进的低能耗的超市制冷系统的分析(编辑修改稿)内容摘要：

iplex refrigeration systems to reduce the amount of charge needed for their operation. Little is known about the operating or energy consumption characteristics of these low charge systems. Without proper design and operation, it is likely that global warming reduction achieved by lowering refrigerant charge and leakage could be negated by secondary global warming caused by increased electrical energy consumption (as measured by the concept of TEWI [Sand et al. 1997]). 13 For these reasons, the . Department of Energy initiated an engineering investigation of lowcharge supermarket refrigeration. The initial work on this investigation involved analysis of distributed and secondary loop refrigeration systems and gave an energy and TEWI parison with multiplex. The results obtained for this analysis were presented in Walker (2020). Work has continued on this investigation including a field test involving two supermarkets with one equipped with distributed and the other with multiplex refrigeration. Analysis was expanded to include lowcharge multiplex and advanced selfcontained systems. This paper presents all analytical results obtained to this point. Previous results are included for pleteness. 1. DISTRIBUTED REFRIGERATION Figure 3 is a diagram showing the major ponents of a distributed refrigeration system. Figure 3 Distributed refrigeration system. Multiple pressors are located in cabis placed on or near the sales floor. The 14 cabis are closecoupled to the display cases and heat rejection from the cabis is acplished through the use of either aircooled condensers located on the roof above the cabis or by a glycol loop that connects the cabis to a fluid cooler. The distributed refrigeration system employs scroll pressors because of the very low noise and vibration levels encountered with this type of pressor. These characteristics are necessary if the pressor cabis are located in or near the sales area. The scroll pressors have no valves and, in general, do not have as high an efficiency as reciprocating units. The novalve feature of the scroll pressors allows them to operate at a significantly lower condensing temperature. The lowest condensing temperature possible occurs at a suctiontodischarge pressure ratio of 2, which, for supermarket systems, means that the lowest condensing temperature possible is on the order of 55176。 F to 60176。 F for mediumtemperature refrigeration and 40176。 F for lowtemperature refrigeration. The use of the 40176。 F minimum condensing temperature was not considered here because of the necessity to have two glycol loops, which may or may not be practical for actual installations. Minimum condensing temperature was, therefore, limited to 60176。 F for this assessment. Scroll pressors also have the potential of providing subcooling through midscroll injection of refrigerant vapor. This particular method has not yet been optimized by the pressor manufacturers and was not included as part of this analysis. The closecoupling of the display cases to the distributed refrigeration cabis has other ramifications to energy consumption. The shorter suction lines mean that the pressure drop between the case evaporator and the pressor suction manifold is less than that seen with multiplex systems, which means that the saturated suction temperature (SST) of the cabi will be close to the display case evaporator temperature. The shorter suction lines also mean that less heat gain to the return gas is experienced. The cooler return gas has a higher density and results in higher pressor mass flow rates, which means that less pressor ontime is needed to satisfy the refrigeration load. The refrigerant charge required for a distributed refrigeration system will be on the order of 900 or 1500 lb when either water or aircooled condensing is employed, 15 respectively. When watercooled condensers are employed, heat rejection from the watercooled condensers is done by a glycol loop and a fluid cooler, usually located on the roof of the supermarket. The use of the glycol loop increases the energy consumption of the refrigeration process due to the pump energy needed and higher condensing temperature due to the added temperature rise of the fluid loop. Much of this energy penalty can be negated if an evaporative fluid cooler is employed where heat rejection can take place at close to the ambient wetbulb temperature. 2. SECONDARY LOOP REFRIGERATION Figure 4 shows a piping diagram of a secondary loop refrigeration system. Brine loops are run between the display cases and central chiller systems. The brine is refrigerated at the chiller and is then circulated through coils in the display cases where it is used to chill the air in the case. Figure 4 Secondary loop refrigeration system. Lowest energy consumption for secondary loop systems is achieved when the display 16 case evaporators are designed specifically for the use of brine, so that the temperature difference between the brine and air is minimized. Brine selection is also of importance, because energy consumption for pumping is a large ponent of。