The space under the dashboard is precious, and the less that is used for componentry, the more that remains for passenger space in the cabin. But there's one system that presently takes up a lot of space and yet is in the most practical location: the HVAC.
Until the industry moves to another technology, which seems at least a decade or more away, suppliers are focused on downsizing the large cases with heat exchangers, fan, and ductwork that fill so much of the under-dash area. Denso featured its newest approach at the North American International Auto Show (NAIAS)—a smaller, lighter climate-control assembly that saves an estimated 20% in its under-dashboard real estate demand.
The design already is in use by Toyota on a Japanese market crossover, the Harrier, and two Asian market minivans (Noah and Voxy), but prospective installations in U.S. models are still in the "to be determined" stage.
HVAC case center section standardized
The approach is scalable, explained Jason Hendry, Denso North American Director of HVAC Design Engineering, and is based on the concept of sectioning the design of the HVAC case into three parts. The center section is the largest, optimized for efficiency and performance, basically standardized and for most applications fixed in size. The outer (side) sections are "adjustable"—i.e., sized and shaped for extra performance and airflow if necessary to meet requirements of a target vehicle—and configured to connect the case to a car manufacturer's specific cabin ducting.
The center section, therefore, is usable without significant change in a large range of car sizes. However, it also provides enormous flexibility, as it can accommodate a cold-storage evaporator that Denso has available for cars with engine stop-start. The heater core can be replaced with parts that would enable heat pump operation, which could be required for electric vehicles and some plug-in hybrid designs.
For space saving, one might have expected something on the order of a blower motor integrated with the evaporator case, as was done on the Scion IQ, a very small car (10.0 ft/3048 mm). But that aspect of a compact HVAC system did not carry over to larger vehicles, Hendry said. It proved to be an exception for that particular car, as integrating the blower motor into the HVAC case enabled Toyota to clear under-dashboard space on the passenger's side of the IQ. Result: Toyota could curve the dashboard forward, creating extra fore-aft space in front of the passenger. As a result, the passenger seat could be moved forward, which then resulted in a normal size space behind it, producing a seating area for a third adult in the second row.
The separate blower case works better with the conventional cabin layout, where there is a comparable passenger seating comfort requirement on each side. Hendry told Automotive Engineering that this new design reduces the HVAC fore-aft space requirement virtually across the full front by 40 mm (1.6 in). That is equivalent to lengthening the cabin by that dimension to increase passenger comfort.
Sliding door for air-mix
The HVAC case air-mix (temperature control) door is a slider type, and incorporates new forming technology, to make it an ultra-thin design. The standardized mounting requires only a single actuator to operate, vs. the previous design that used several actuators to cover all the typical applications. The new slider design also eliminates the need for specific sliding door sealing. The mode doors are conventional flaps. The evaporator is a nearly vertical installation in the case, which helps promote good drainage of A/C condensate.
The blower fan has redesigned wing-type blades, reshaped for higher efficiency. Denso claims they are about 15% smaller and consume 20% less power than a conventional design.
Although the HVAC shown at NAIAS has a blower case with a single fan, Denso also has developed a case with two blower fans stacked vertically. This enhances horizontal splitting of the outside and recirculating interior airflows.
For improved A/C efficiency (and eligible for an EPA Corporate Average Fuel Economy credit), most new systems minimize use of outside air in an A/C mode, as increased use of recirculation reduces A/C power consumption. The dual fan permits greater precision with this airflow management approach, as the upper fan can be biased to outside air, the lower fan toward recirculation, with an available mix adjustable for either or both.