Approach to Model Thermistor Based AC Compressor Cut-OFF/Cut-IN Phenomenon in 1D Simulation of Mobile Air Conditioning 2019-26-0287

This paper documents the approach followed to simulate the physical phenomenon of thermistor based AC compressor Cut-OFF/Cut-IN (AC compressor cycling) in 1-Dimensional Computer Aided Engineering (1D CAE) to enable Mobile Air Conditioning (MAC) performance prediction at different ambient conditions. Thermistor based AC compressor cycling logic is incorporated in MAC systems to prevent ice formation at evaporator core and liquid refrigerant flow to AC compressor. Currently, during MAC system performance simulation over a transient drive cycle, the 1D models are able to predict cabin cooldown performance for severe ambient conditions (>40°C, high solar load) with >95% accuracy, as in these cases AC compressor cycling due to thermistor doesn’t occur at higher ambient. In case of moderate/low ambient conditions (~20-40°C, moderate/low solar load), AC compressor cycling takes place and the simulation model is able to predict the cabin cooldown performance only till first event of compressor Cut-OFF in line with physical test. Hence, to predict cabin cool-down performance with AC compressor cycling, it is necessary to model the same phenomenon in 1D CAE.

To model the phenomenon described above, a logic to control AC compressor cycling operation based on evaporator air outlet temperature and lumped masses to model evaporator thermal inertia are incorporated in transient MAC performance simulation model using 1D software KULI. Accuracy of >95% in average cabin temperature prediction has been achieved at moderate ambient condition after incorporating AC compressor cycling model, which confirms the robustness of the simulation model. Frequency of AC compressor cycling phenomenon (i.e. number of cycling events in a minute) in the proposed simulation model is observed to be higher as compared to real world physical test which affects the prediction of AC compressor power consumption, further work is required to address this gap. The present work can be extended to determine optimum thermistor location through 1D CAE, thereby eliminating the need of physical testing for the same.