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Methodology to Quantify the Undesirable Effects of the Localized Inefficiency of Heat Pick-Up in Suction Line on an Automotive Air Conditioning System
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on August 29, 2020 by SAE International in United States
The automotive application places very special demands on the air conditioning system. As is the case with any other process, system efficiency is very important and the automotive air-conditioning application is no exception.
While the characteristics of all the major components in the air conditioning system like compressor, condenser, evaporator and blower contribute to overall system efficiency, localized inefficiencies do play a part and so must be kept to a minimum, especially in this day and age when extra emphasis is being laid on sustainability.
One such phenomenon that contributes to the system inefficiency is heat pick-up in suction line. Since the temperature at the evaporator-outlet is quite lower than ambient and also its surroundings (steering system pipes and hoses, engine, air intake pipes and so on), the refrigerant picks up heat as it moves along the suction line up to the compressor inlet. This heat pick-up is detrimental to the overall system performance.
Even though most of the automotive HVAC engineers are fairly aware of the undesirable effects of heat pick-up in suction line, many a times the heat picked up in suction line is seen only in terms of °C rise in temperature from evaporator-outlet to compressor-inlet and thus we are not able to visualize or quantify the extent of its impact on other parameters. With the help of case studies, this paper aims at providing a methodology for determining and arriving at the conservative estimate of the impact of heat pick up in suction line on parameters like compressor-outlet temperature, refrigerant mass flow rate, work of compression, refrigeration effect and COP. The results thus obtained provide a greater understanding of the said undesirable effects of heat pick-up in suction line, so that necessary actions could be taken to address the same.