[HVACman]

Its possible they have discovered the need for more cooling system surface area, I have noticed my Hummer with the clear roof panels, on a hot day, and after DC charging, has trouble keeping the interior cool. I have tried to figure out if this is related to the HVAC system, or the solar radiation that gets through the roof panels? My recommendation to people like @azbill living in AZ or other hot areas, avoid those clear roof panels a lot of heat comes in through those, much more than our Audi, or Tesla which both have large glass roofs (heavily tinted).

This larger patterned front panel also could be updated aero decision. Some recent aero studies have shown that a full-patterned type fixed panel in the front stagnation area actually creates less drag than a smooth panel. It "trips" the boundary layer and improves attached air flow, something similar to the golf ball dimple effect. Also, I think Audi dimpled the e-tron's bottom panels for a similar effect. I believe all of GM's new Ultium-based EVs have some sort of patterning on their large front grille panels, usually styled in the specific brand's design language.

Also, most current-generation EVs now pull all their TMS air flow from a narrow long grille just above the bottom-front air dam. This grille will have motorized active shutters behind it to throttle or close off the opening as dictated by the TMS logic. This is an aerodynamically-ideal location to put it, as then the TMS, when active, captures some of the air that would otherwise flow under the vehicle and increase drag. Zooming in on that image, there appears to be some openings in that area on either side of the front license plate. @Nebula1701 , did you happen to notice which "grilles" actually were air grilles which were "fake"?

 

[HVACman]

Its possible they have discovered the need for more cooling system surface area, I have noticed my Hummer with the clear roof panels, on a hot day, and after DC charging, has trouble keeping the interior cool. I have tried to figure out if this is related to the HVAC system, or the solar radiation that gets through the roof panels? My recommendation to people like @azbill living in AZ or other hot areas, avoid those clear roof panels a lot of heat comes in through those, much more than our Audi, or Tesla which both have large glass roofs (heavily tinted).

That is probably related to the DC charging. The AC system shifts almost all of the refrigerant to the glycol chiller to bring the pack's cell temperatures back down to a more normal level. The pack requires about 15-20 kW of cooling just for the pack, which is over 5 tons when thinking about typical household cooling. And you have about 2,000 lb of cell thermal mass, which will take some time to get cooled down. Now add a glass roof on a hot day for the cabin HVAC. That's about 3.5 tons of cooling. You'd need a large commercial AC type system to make all that work at the same time, which is too much even for a Hummer-sized vehicle to handle. When you get that worst-case scenario, quickly duck into the mini-mart and hang out a while sipping Slurpee's.

 

[HVACman]

Maybe this RST has the MAX tow package... so it requires more air?

That could be. I'm thinking perhaps GM routes cooling air for the glycol radiator fed directly through the main grille, as that radiator could see up to 40 kW of glycol heat load with the motors ramped up on a high-speed climbing while towing. The refrigerant condenser would optimally have its own outside air source and would only see about 10-15 kW max of refrigerant heat load, so could be fed from the smaller bottom grille.

This could explain why GM's heat pump patent diagram shows the glycol radiator and refrigerant condenser with distance from each other rather than back-to-back on the same air flow stream. I had a assumed that was just for diagrammatic clarity, but perhaps they actually do have separate flow streams.

The Hummer EV might also use this concept. Any Hummer owner who might feel like popping the frunk tub from their EV and taking a look at how the cooling air actually flows through their glycol and refrigerant coils could probably help resolve this question.

 

[HVACman]

Feel free to look at my improperly filmed short video and see if you can determine that yourself.

Hummer under Frunk tub

www.youtube.com

If not, can't say I didn't try.

View attachment 3208

Oops, I must have missed that April message. Thanks for the video post! What I see is a single stacked glycol/refrigerant coil assembly with a shared radiator fan. Glycol connections on the passenger side, refrigerant connections on the driver's side. So that shoots down my two-air-source theory. I also saw the 3-way and 4-way glycol spool-valves referenced in the patent. From my thermal-engineer's perspective, confirming GM actually used spool valves is the most interesting revelation from your video. I've never seen that type of valve used in a glycol flow control application. Normally, linear push-pull spool valves are used in heavy-duty hydraulic controls and automatic transmissions. They are a lot simpler and more compact than the rotary type normally used, such as in Tesla's Octo-valve assembly. Kudos to GM's thermal engineers for a little slice of outside-of-the-box valve engineering embedded in their larger heat pump patent.