This paper focuses on the development of the centralized air flow system S-FLOW (Energy Saving Air Flow Control System). The S-FLOW system directs thermal energy to each seating position in the vehicle based on occupancy, thus prioritizing the energy usage based on the particular scenario.
The thermal environment in a vehicle's cabin is non-uniform. If the climate control system is used to direct airflow exclusively to any one region of the cabin, without special considerations, comfort may be adversely impacted. To solve this concern, a non-uniform evaluation method was developed to evaluate comfort at each body region of the occupant using the SET* (Standard new effective temperature) method. SET* is a parameter that combines the effects of temperature, airflow velocity, humidity, and other parameters to quantify thermal comfort. Next, a method was established that correlated each body region's SET* value to the occupant's overall thermal comfort. Using this method, a technique was developed to efficiently apply thermal energy exclusively to body regions which require additional thermal treatment to maintain comfort. This control method, combined with a new advanced HVAC module, makes up the S-FLOW system.
The 2013 Lexus GS Hybrid is the first vehicle to adopt the S-FLOW system. Through this system, the energy consumed by the air conditioning system is reduced. Based on in-house testing, this leads to an estimated 4% decrease in annual fuel consumption. As an additional benefit, HVAC noise was reduced due to the lower blower level used to condition the space during S-FLOW operation.