Improving Fuel Economy Estimates on a Chassis Dynamometer Using Air Conditioner Correction Factors

Carmakers, regulatory agencies, and consumers share an interest in accurately determining a vehicle’s fuel efficiency under operating conditions that match the expected use. Previous studies have shown that a vehicle’s air conditioning (A/C) system is the most energy-intensive non-propulsive system and significantly reduces fuel economy. This study aims to design and validate a new method of improving fuel economy estimates obtained on non-climate-controlled chassis dynamometers, as such laboratories are limited to measuring fuel economy with the A/C system deactivated. The methodology proposed herein uses a chassis dynamometer to measure the fuel economy penalty caused by the A/C system at different steady-state conditions. The hypothesis is that these penalties can be imposed accordingly for a given drive cycle to obtain an additional fuel consumption due to A/C. To validate the proposed methodology, a vehicle was outfitted with a data acquisition system and was driven 50 times around a predefined route using varying A/C settings. The proposed method was then used to estimate the additional fuel consumption due to A/C usage for each of the runs. Comparing the calculated and actual fuel economies showed an average error of 1.924%. It was concluded that the proposed methodology is a viable alternative to existing procedures.