Analysis of Defogging Performance, Thermal Comfort, and Energy Saving for HVAC System Optimization in Passenger Vehicles

Taro Ono,Shinsuke Kato,Hideaki Nagano,Kenjiro Shimano,Suguru Shiratori,S.I Tanabe,H Zhang,P Wargocki,M.C Gameiro Da Silva,L Mazzarela,G Cao,I Nastase,J Kurnitski,C Inard

doi:10.1051/e3sconf/201911101033

Abstract

The heating, ventilation, and air-conditioning (HVAC) system in a vehicle is used for both defogging the windshield and ensuring the thermal comfort of passengers. A challenge is that energy savings in the HVAC system lead to decreased system performance. The three objective functions, i.e. defogging performance, thermal comfort, and energy savings, these must be considered in parallel to find the optimized control strategy. In the present study, a transient numerical simulation of the in-vehicle environment is performed and the dependency of performance on the air flow rate and supplied air temperature is analyzed. The criteria of defogging performance and thermal comfort are determined as the constrained conditions. The results show a trade-off relationship between the air flow rate and air temperature in defogging performance and thermal comfort; however, their sensitivities depend on the conditions and the time elapsed. As for transient defogging performance, the air flow rate has greater impact than airflow temperature. The air flow rate and the air temperature are comparable in their effects on equivalent temperature, which is employed as the index of the thermal environment. The blowing condition range that fulfills the criteria makes a transition to a low-energy condition with time elapsed. A control strategy for the air flow rate and temperature is derived considering the transient and steady-state conditions.

Highlights

In recent years, electric vehicles (EVs) have been attracting attention as a measure against environmental problems
For the evaluaton of energy savings, only the condition with the lowest energy consumption among the conditions satisfying the required defogging performance and thermal comfort was taken as the condition satisfying energy savings performance
A constraint condition for the thermal comfort evaluation is required; no standard is defined for the equivalent temperature

Summary

Introduction

Electric vehicles (EVs) have been attracting attention as a measure against environmental problems. One problem is a decline in cruising distance when the heating, ventilation, and air-conditioning (HVAC) system is used because it consumes a significant amount of energy from the battery. If the energy of the HVAC system is saved more than required, there is concern that fogging on the windshield or reduced passenger thermal comfort could result. The purpose of this study is to determine optimal conditions for the HVAC system in order to fulfil the three aspects of defogging performance, thermal comfort, and reduced energy consumption. The evaluation of defogging performance is described. This considers performance in terms of removing fog from the driver’s visible area in a short time

Objectives

Methods

Results