暖通空調(diào)專業(yè)畢業(yè)設(shè)計(jì)外文翻譯-暖通(存儲(chǔ)版)
【正文】 [1]節(jié)選自 James B. Bradford et al. “HVAC Equipment and Systems”.Handbook of Heating, Ventilation, and . Jan F. Raton, CRC Press LLC. 2020 浙 江 海 洋 學(xué) 院 畢 業(yè) 設(shè) 計(jì) 2 FIGURE A dual chiller application with major auxiliary systems (courtesy of Carrier Corporation). The type of chiller used in a building depends on the application. For large office buildings or in chiller plants serving multiple buildings, centrifugal pressors are often used. In applications under 1000 kW (280 tons) cooling capacities, reciprocating or screw chillers may be more appropriate. In smaller applications, below 100 kW (30 tons), reciprocating or scroll chillers are typically used. Vapor Compression Chillers Table shows the nominal capacity ranges for the four types of electrically driven vapor pression chillers. Each chiller derives its name from the type of pressor used in the chiller. The systems range in capacities from the smallest scroll (30 kW。 whereas, reciprocating chillers have the worst efficiency of the four types. The efficiency numbers provided in the table are the steady state fullload efficiency determined in accordance to ASHRAE Standard 30 (ASHRAE, 1995). These efficiency numbers do not include the auxiliary equipment, such as pumps and cooling tower fans that can add from to kW/ton to the numbers shown (Smit et al., 1996). Chillers run at part load capacity most of the time. Only during the highest thermal loads 浙 江 海 洋 學(xué) 院 畢 業(yè) 設(shè) 計(jì) 3 in the building will a chiller operate near its rated capacity. As a consequence, it is important to know how the efficiency of the chiller varies with part load capacity. Figure shows a representative data for the efficiency (in kW/ton) as a function of percentage full load capacity for a reciprocating, screw, and scroll chiller plus a centrifugal chiller with inlet vane control and one with variable frequency drive (VFD) for the pressor. The reciprocating chiller increases in efficiency as it operates at a smaller percentage of full load. In contrast, the efficiency of a centrifugal with inlet vane control is relatively constant until the load falls to about 60% of its rated capacity and its kW/ton increases to almost twice its fully loaded value. FIGURE Chiller efficiency as a function of percentage of full load capacity. In 1998, the Air Conditioning and Refrigeration Institute (ARI) developed a new standard that incorporates into their ratings part load performance of chillers (ARI 1998c). Part load efficiency is expressed by a single number called the integrated part load value (IPLV). The IPLV takes data similar to that in Figure and weights it at the 25%, 50%, 浙 江 海 洋 學(xué) 院 畢 業(yè) 設(shè) 計(jì) 4 75%, and 100% loads to produce a single integrated efficiency number. The weighting factors at these loads are , , , and , respectively. The equation to determine IPLV is: Most of the IPLV is determined by the efficiency at the 50% and 75% part load values. Manufacturers will provide, on request, IPLVs as well as part load efficiencies such as those shown in Figure . FIGURE Volumepressure relationships for a reciprocating pressor. The four pressors used in vapor pression chillers are each briefly described below. While centrifugal and screw pressors are primarily used in chiller applications, reciprocating and scroll pressors are also used in smaller unitary packaged air conditioners and heat pum
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