Proper refrigerant charge level is critical for vapor-compression cycle refrigeration systems to operate efficiently and safely. The current practice of accurately determining charge levels is very time consuming and costly. Technicians must stop and evacuate the system, weigh the removed charge, and add the correct amount of charge to the system using a scale. This paper presents a method for obtaining accurate estimates of refrigerant charge level using noninvasive temperature measurements obtained while the system is operating. The method could be used as part of a permanently installed control or monitoring system to indicate charge level and/or to automatically detect and diagnose low or high levels of refrigerant charge. It could also be used as a stand-alone tool by technicians to determine existing charge and during the process of adjusting the refrigerant charge. The accuracy of the virtual refrigerant charge sensor is evaluated using laboratory data for seven different systems and over a wide range of operating conditions with and without the presence of other faults. The evaluation and demonstration verify that the virtual refrigerant charge level gauge has very good performance in terms of accuracy and robustness and can be easily implemented and installed in terms of both hardware and software.
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