【正文】 have two glycol loops, which may or may not be practical for actual installations. Minimum condensing temperature was, therefore, limited to 60176。 Advanced selfcontained INTRODUCTION Supermarkets are the largest users of energy in the mercial sector. A typical supermarket with approximately 40,000 ft2 of sales area consumes on the order of 2 million kWh annually for total store energy use. Many larger superstores and supercenters also exist that can consume as much as 3 to 5 million kWh/yr. One of the largest uses of energy in supermarkets is for refrigeration. Most of the 11 product sold is perishable and must be kept refrigerated during display and for storage. Typical energy consumption for supermarket refrigeration is on the order of half of the store’s total. Compressors and condensers account for 30% to 35% of total store energy consumption. The remainder is consumed by the display and storage cooler fans, display case lighting, and for antisweat heaters used to prevent condensate from forming on doors and outside surfaces of display cases. Figure 1 shows the typical layout of the refrigerated display cases in a supermarket. All refrigerated fixtures in a supermarket employ direct expansion airrefrigerant coils. To reduce noise and control heat rejection, pressors and condensers are kept in a remote machine room located in the back or on the roof of the store. Piping is provided to supply and return refrigerant to the case fixtures. Figure 1 Layout of a typical supermarket. Figure 2 shows the major elements of a multiplex refrigeration system, which is the most monly used configuration in supermarkets. Multiple pressors operating at the same saturated suction temperature are mounted on a skid, or rack, and are piped with mon suction and discharge refrigeration lines. The use of multiple pressors in parallel provides a means of capacity control, since the pressors can be selected and cycled as needed to meet the refrigeration load. An aircooled condenser is most often 12 employed for heat rejection from the refrigeration system. As a result of using this layout, the amount of refrigerant needed to charge a supermarket refrigeration system is very large. A typical store will require 3,000 to 5,000 lb of refrigerant. The large amount of piping and pipe joints used in supermarket refrigeration also causes increased leakage, which can amount to a loss of 30% to 50% of the total charge annually (Walker 2020). Figure 2 Multiplex refrigeration system. With increased concern about the impact of refrigerant leakage on global warming, new supermarket refrigeration system configurations requiring significantly less refrigerant charge are being considered. Examples of lowcharge refrigeration systems include distributed, secondary loop, and advanced selfcontained configurations. Modifications have also been made to multiplex 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 s