Modeling of temperature and humidity ratio in an automobile passenger compartment for automobile air conditioning systems

摘要

This study investigates thermal dynamic modeling of a passenger compartment in an air conditioned automobile equipped with HVAC (heating, ventilation, and air conditioning). In particular, dynamics of temperature and humidity ratio, both critical to passenger comfort, in the passenger compartment are examined. By analyzing enthalpy change during an automobile air conditioning circulation cycle on a psychrometric chart, heat exchange between outside environment and the passenger compartment can be modeled as functions of operation settings of the HVAC. With enthalpy content decomposed into sensible heat and latent heat, changes in heat content can be attributed to the changes in the corresponding temperature and humidity ratio, respectively. Consequently, impacts resulting from the mismatch between two heat characteristics on temperature and humidity ratio can be formulated accordingly: room sensible heat factor (RSHF) of the passenger compartment and apparatus sensible heat factor (ASHF) of the HVAC. A Matlab/Simulink simulation is implemented to verify the proposed model under several control policies that either maintain constant enthalpy or maintain constant temperature in the passenger compartment. With these two temperature and humidity ratio models derived, further research on designing control policies to achieve better passenger comfort for general automobile air conditioning systems can be derived and tested.