Browse Publications Technical Papers 2019-26-0287
2019-01-19

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

Considering today’s competitive environment in automobiles, the MAC (Mobile Air Conditioning) systems should deliver good cooling performance, be energy efficient and cost effective. In order to optimize MAC’s performance, 1D CAE simulation is preferred to predict vehicle level AC system performance, components sizing and address risks like freezing of evaporator core. Thermistor based AC Cut Off/Cut-In logic is incorporated in MAC systems to prevent freezing of evaporator core at moderate and lower ambient conditions and liquid refrigerant flow to AC compressor. This paper addresses the approach followed to simulate the physical phenomenon of AC Cut Off/Cut-In in 1D CAE. Currently, during AC system performance simulation, we can predict cabin cooldown performance for severe ambient conditions (>40°C, higher solar load) with good accuracy, as AC compressor Cut-OFF/Cut-In due to thermistor doesn’t occur. In case of moderate ambient conditions (~35°C, moderate solar load), compressor Cut-OFF/Cut-In 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 accurately predict cabin cool-down performance even with AC compressor cycling, it is necessary to model AC compressor Cut-OFF/Cut-In phenomenon in 1D CAE. To model the phenomenon described above, a subsystem comprising of logic to control AC compressor operation based on evaporator air outlet temperature and lumped masses to model evaporator inertia are incorporated in existing 1D CAE AC cooldown simulation model. Further, to improve accuracy, the effect of AC compressor speed on refrigerant mass flow rate is also taken into account. The updated 1D CAE model resulted in an improved prediction of cabin cooldown performance for all ambient conditions. The present study will also be helpful to determine compressor cycling rate and suction pressure value which in turn is important to predict compressor clutch life and probability of icing over evaporator coil. Further, the work can be extended to find optimum thermistor location and hence eliminating the need of physical iteration.

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