JC Dill <jcdill.lists@gmail.com> writes:
Why do you believe that it is proper to deliver the cooling "top down"? Heat rises! The cool air needs to be delivered to the bottom (raised floor) or front (alternate row cooling) so that it flows over/thru the computers on its way to the hot air intakes which should be located above the back of the cabinet (above the "hot row") or top of the room (for raised floors).
This would be true if the computers were all mounted within several inches of the floor, but they're not.
Just as heat rises, cold sinks. Discharging cool air up high in a data center will cause it to end up where it needs to be for all computers in a rack, not just the ones in the bottom.
In theory, this should work. In theory, there is no difference between theory and practice. In practice, there is.
Visit any Equinix for an example of this principle in action
I disagree, and I've been in several Equinix locations. Computers produce heat / hot air, and this hot air rises. As the hot air rises and moves away from the computers, new air has to circulate in from *somewhere*. There isn't a vacuum of "no air" between the cold air sinking/sitting at the bottom of the room and the hot air rising up to the ceiling. :-) When you have cold air entering the bottom and/or front of a rack, and hot air exiting out the back (and then up) then you don't have cold air mixed with hot air circulating in the room before it gets to the computers. The fans located in the building's hot air intakes, the action of the rising hot air, and the fans blowing the cold air into the data center all create the air flow that pulls the "heavier" cold air up into and across the computers. When you have cold air coming down in the same area with hot air going up, it just mixes up into warm air, and truly cold air never gets to the bottom - you get warm (or hot) air flowing across the bottom computers in the racks. This is not an efficient air flow, and not a good way to keep the hot and cold air separate so you can get cold air (not warm air) flowing over the equipment. It works great for offices full of people (where you want an even temp everywhere in the room) but isn't great for computers (where you want cold air entering the equipment for maximum cooling effect and hot air being removed as quickly as possible.) I've never been happy with the room temps or equipment temps in any data center that used this "blow cold air from the ceiling" approach. But hey, if it works for your equipment, more power to you. I encourage all my competitors to do this. jc