This was one of our initial ideas for the design, but it boiled down to an airflow concern. There are some products that do this, such as http://www.h-sq.com/products/mprack/index.html
If you look at how the airflow works on that shelf, I think you'll see why I don't have confidence in that solution. The air paths to each system seem to be based on wishful thinking.
We also didn't need to go that dense after considering each host's power draw at full load. I design towards a 208v/3ph/50a circuit on each rack, and 44 Mac Pros at full load (plus a switch) are about 13.5kW in my testing. So we would need to build for 60A circuits, or not completely fill the rack, to make the vertical orientation worthwhile.
That product you linked to isn't all that bad, provided that you run with a front plate to actually block off the rest of the cold isle and force the air to flow to the hot isle. But that doesn't seem to be included anywhere. So I agree that it's wishful thinking.
The reality of the power budget makes the most sense really. There's no point in cramming extra units in if you're going to have to rewire for them. Systems engineering!
H-Squared's product isn't terrible by any means, but I see it as phase 1 of at least a 2 or 3 phase solution. If you were running one shelf of Pros in a rack, it wouldn't matter much -- but at 10 racks of 88 Pros each, you'll run into cooling issues unless you put more work into it.
On the topic of density: our chassis was originally specced to support 6 units rather than 4. I vetoed that because it would require a second top-of-rack switch, and would have been too power dense for our current site design.
44 turned out to be the magic number this time around. The design is also flexible enough that if the specification changes dramatically in future Mac Pros, we can tweak as necessary to achieve ideal density.
If you look at how the airflow works on that shelf, I think you'll see why I don't have confidence in that solution. The air paths to each system seem to be based on wishful thinking.
We also didn't need to go that dense after considering each host's power draw at full load. I design towards a 208v/3ph/50a circuit on each rack, and 44 Mac Pros at full load (plus a switch) are about 13.5kW in my testing. So we would need to build for 60A circuits, or not completely fill the rack, to make the vertical orientation worthwhile.