That's the first I've heard of 'tube in ground' cooling. Clever idea.
As for ventilation, I have a primitive nomadic style yurt 16 feet in diameter. No power, I don't live in the yurt. It's permanently set up on our property about 50 yards from the house, so everything I know about yurts is from having that set up year round.
I have a low and middle rope encircling the yurt, in addition to the high tension band. To cool it in the summer, I pull up the low edge of the wall cover until it is snug against the lowest tension rope, and tuck it behind the middle tension rope encircling the yurt wall. That leaves a foot high gap between the deck and the cover all around the yurt.
When the roof ring is wide open, convection pulls the the cool air from ground level up and out the ring. It is actually very effective. Laying in there on my cot in the shade with a breeze blowing over me and I'm out in a minute. I've pretty much found naps is why I built the yurt. lol
The age old way to keep sun from
tents is to erect a tarp above the tent. That also stops rain and premature aging of the fabric. It's also a debris barrier keeping cinders and ash off the tent fabric. The tarp (fly) doesn't particulary look good, but it is effective. Good luck.