The local meteorologists came through and delivered an especially hot day yesterday for my A/C testing. Here's my report.
The bus was parked facing due east in full sun all day long. I set a window A/C unit on a stool inside against the north wall about 1/3 down the length of the bus and hung a tarp (folded in half, so it's double-layer) to separate the front from the back. Note that I was mistaken on the capacity of this A/C: it's actually a 10000 BTU unit; earlier I had reported it was just 8000. I closed the doors, windows, and roof hatch in the front portion of the bus. In the back portion I opened the window beside the A/C, the roof hatch, another window, and left the rear doors hanging wide open to provide ample opportunity for the hot air off the A/C condenser to find its way out. I finished the setup and turned on the A/C around 10:00 am and left it for the day.
Temperatures were checked at a few times in the afternoon and evening with a "type K" thermocouple attached to my multimeter:
4:30 PM - 103 in the sun outside; 86 in the breeze in the front seat ahead of the A/C
6:20 PM - 99 outside in the shade; 91 in the middle of the conditioned front area inside. Evaporator discharge 59, condenser discharge 151, hottest area near the back window of the bus was 112. The headboard (?) surface above the windshield was plenty hot!
8:00 PM - 89 outside in the shade; 76 inside. Condenser discharge 137 and warmest point in the rear 96.
Because of the orientation of the bus the solar heat gain through the windshield grew as the afternoon wore on. By 8 pm the windshield was fully shaded by a nearby building and the interior air temperature corresponds to that.
Sooo, I learned a few lessons: don't drive east in the morning or west in the afternoon. Removal of most of the side windows and tinting of what remains will help keep gain while pointing north or south under control. Heat gain through the windshield is brutal. Not sure how I'm going to control that.. I wish there were a solar control window film, like the Solar Gard I used in my last bus, but in a static cling form instead of permanent installation so that I could easily stick it up inside the windshield for just a few hours while it's needed and then remove before driving in the dark.
Fighting that solar gain 10000 BTU didn't go very far. Probably the back portion of the bus, after I remove most of the windows and insulate like a madman, will need less than this. But for the front passenger area I'm not sure what I'll do. Probably will end up finding a way to make a bigger generator acceptably quiet so that I have electric power budget to run a larger A/C up there. Sure would be nice to shave off that direct sun peak, though -- once the sun quit shining on the windshield temperatures inside got pleasant really fast.