Air Conditioning Refrigerant Of Choice
some European countries was 1 January 1998 banned the use of new equipment HCFCs, HFCs air conditioning makes the significant increase in the proportion of possession. Some major manufacturers have officially announced the selection of HFC-134a with R-407C refrigerant as a new product. According to the findings of IIR, Europe has more than 50 more than the company can provide skilled of HFCs systems, particularly HFC-134a and R-407C refrigerant. Thermodynamic properties of R-407C and R? 22 similar, suitable for large-scale air-conditioning, refrigeration range from 5kW to 300kW, the world has a lot of new R-407C system market, and has been running more than five years. There are also many old systems Dress R-407C is also very successful. In Europe, R-407C is almost fully replace R-22 medium and large air conditioners, air source heat pump system is mainly with rotary, scroll and reciprocating compressors, or water-cooling system with screw compressors. Denied, compared to R-134a and R-404A, R-407C have more worth in-depth study. In principle, the use of its large temperature difference between the characteristics of slip, and to avoid improper installation, should be able to get good results. Used in plate heat exchanger, it can use its advantages of reverse flow, the properties and R-22 close to, if the system optimal design, performance is improved. To calculate the direct expansion of the air-liquid heat exchanger heat exchanger difficult than for larger slip refrigerant temperature, the more need to consider some additional problems, such as air condenser refrigerant distribution of average or not, or heat load distribution uniformity, these will affect the system performance. Shell and tube condenser to be concerned about more problems. The results show that, R-407C condensing temperature will increase by 3 ~ 5K, on the temperature and boreal regions, and will not cause high-pressure high risk, but would increase electricity costs. There are many ways to improve the condensing pressure rise issues, such as the same time accelerate the speed of the refrigerant condenser discharge to cause more than cooler supercooling, or to use other methods to make the top of the gas condenser cooling down faster. Shell and tube evaporator quite suitable for R-407C, but must pay attention to frost protection. Because the evaporator inlet temperature than the R? 22 low, may lead to the formation of ice cold water affect unit performance. Even when the liquid bubble endoscopic totally free, you may have a large undercooling. That is too hot and cold single-phase condenser to increase the exchange area, while the two-phase condensation area of reduction of the condensation temperature. Some of the system in time to stop and start again when the action and shut down because of pressure switch. This is the condenser and evaporator, the gas composition, the need for higher condensing pressure. To avoid this phenomenon, can the compressor starts, the operator into the condenser cooling water to prevent excessive condensation pressure. Sometimes this problem can be MOP valves or suction pressure control valve to reduce the evaporation pressure, the compressor starts to reduce the refrigerant into the condenser capacity. To reduce the system’s failure, the most important thing is to understand the non-azeotropic refrigerant temperature slip characteristics for the analysis of refrigeration cycle and adjust the volume expansion valve and refrigerant filling. Must be in liquid filling system, otherwise the system will not function properly.
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