A heated-cooled seat integrated with the vehicle's HVAC system has been developed jointly by Lear and Delphi. The system lowers electric power consumption of the climate-controlled seat by 66-84%. And it reduces compressor energy use, which alone improves fuel economy by 0.5%, said project engineers Karl Kennedy of Lear and Ned Wolfe of Delphi at a recent SAE International meeting in Phoenix on alternative refrigerants.
Another possible fuel-efficiency benefit could accrue if the seat system were used to eliminate the fuel-fired heaters installed in cold climates on diesel-equipped vehicles. The faster, lower-power approach to climate control also could be helpful on hybrids, they said.
The seat control system uses zoned resistance heating mats in the seatback and cushion, with a novel heating strategy that provides warmth in specific areas only as long as necessary to produce a warm sensation but not long enough for the body to adjust to it. Heat then is applied to adjacent areas in what is called a "chase" approach, which contributes to the electrical power savings while providing overall body comfort.
The seatback and cushion resistance mats have three in-line zones each. The mats provide almost instant heat in the rear zone of the seat cushion and the mid-upper zone of the seatback. An optional Peltier-junction thermo-electric device (TED) adds extra warmth to the scarf area (shoulder and neck). After enough time for a mat zone to provide a warm sensation—41ºC (106ºF)—the seat computer switches the circuit to an adjacent zone, allowing the first zone to cool, and then switches to the third zone.
When engine coolant temperature is high enough (after about 6-7 minutes), heated air from the HVAC floor duct enters the seat through an added flexible round duct for distribution from a bag-like plenum, through channels, and out perforations in the seatback, cushion, and scarf area vent. Because the resistance mat is above the plenum, it was designed to not interfere with HVAC airflow.
Initial cooling (with airflow through the plenum, channels, and perforations) is from two TEDs plus the optional scarf TED. After about two minutes, HVAC cool air is added.
Unlike typical climate-controlled seats produced industry-wide today, the TEDs in the Lear-Delphi application are configured basically for cooling. That is because other means (resistance heat) are much more efficient and faster for heating.
When hot or cool HVAC air is available, as quickly as possible the power is reduced to the resistance heaters, TEDs, and fans to save energy. The driver can, however, keep the heating or TED cooling fully active if desired.
A control-module algorithm can add a small amount of seatback heat for lower back muscle comfort in the cooling mode.
The computer-directed comfort approach allows more time for the HVAC to reach the point where it is integrated. In cooling mode, this type of climate-controlled seating is what helps reduce compressor work. Integrating the HVAC with a TED/resistance seat system adds only the cost of the flexible duct, assuming that spare memory in control modules is used for the algorithms.
Each of the climate-controlled seats has an occupant sensor, so in a luxury car with four such seats and only a driver, power would be applied only to the driver's seat, saving energy.