Enthalpy-based automatic temperature control for automobiles

This paper studies the temperature control for an automobile air-conditioning (AC) system, especially the control of air flow rate in the circulation. Based on energy balance and mass conservation laws, the control strategy is proposed by analyzing the heat exchange between heat gains form outdoor environment and the AC equipment. To be more precise, sensible heat exchange characterized by room sensible heat factor (RSHF) responses to the change in temperature; whereas latent heat exchange characterized by apparatus sensible heat factor (ASHF) responses to the variation in humidity. The problem of temperature control is to assess not only the sensible heat transfer, resulting from the mismatching between RSHF and ASHF while the system attains its equilibrium state, but also the extra cooling load while the system is on the transient stage. Simulation results show a good agreement that the car compartment condition will converge into the comfort zone defined by ASHRAE Standard, regardless of initial conditions.

I. Introduction

A good automobile air conditioning system enhances not only human thermal comfort but also driving performance, as well as safety in different weather conditions [1]. Comparing to residential air-conditioning (AC) system, the challenge of designing control strategies for an automatic temperature control (ATC) is to automatically maintain thermal comfort, regardless of time-varying weather conditions. Basically, the ATC system consists of a refrigeration sub-system and an air distribution sub-system. Nowadays, most researches for ATC focus on the efficiency improvement for the refrigeration sub-system [2], rather than on the thermal comfort control for the air distribution sub-system.