Your "hot spot" problem may be due to several things, but getting the maximum amount of cool air to the locations that most need it will certainly be part of the solution. Few Data Centers today have enough cooling capacity to begin with, and an amazing amount gets wasted through unblocked holes in the raised floor. This kind of air leakage contributes nothing to the cooling of the equipment, while it also reduces the static pressure of the air under the floor, which means less air gets pushed through the perforated tiles. It's something of a "double jeopardy" situation.
Gaps and air leakage can occur in lots of places. You want to look anywhere there is a penetration of your raised floor, not just where cables come through. The photos below show two very common places where air leakage occurs, and these are easy to block.
Simple cutouts of metal or Masonite, caulked into place, are an easy and inexpensive way to close around pipes and the like. People have even taped cardboard cutouts into place, as shown in this photo. I can't recommend that as a permanent solution, but it does work. The important thing is to stop unwanted and useless air flow wherever it is found. This can be a little more difficult around Air Conditioners and PDU's because you may need someone to properly cut the floor tiles, but simple neoprene gasketing, the same as you buy at the hardware store for weather proofing, will seal those gaps as well.
We've also seen situations where partitions didn't go all the way to the slab, or weren't sealed to the slab, under the raised floor. This is a major problem that often goes unnoticed because it is hidden, but the wall cavity acts like a chimney, literally sucking large volumes of cold air from under the floor and pulling it upward into the ceiling cavity due to the severe pressure differential between the two levels and spaces. We've seen a 20-Ton air conditioner rendered virtually useless by just one wall condition like this, so it's worth looking in to.
But the biggest concern, and the one that is generally most prevalent, is all those cable holes under racks and cabinets. We don't generally recommend specific products but, in our experience, the best solution is the "KoldLok" Cable Grommet by Triton Technologies (www.koldlok.com). Products are available that can install in new cutouts, or around existing cables. Its is a "self sealing" product that makes it easy to add or remove cables, and it works around both small and large cable bundles, as can be seen in the photos. However, this may be what you are calling an "expensive option." If so, there aren't many commercial alternatives, especially for existing situations, so you're probably going to need to improvise.
Again, you can cover holes with homemade gaskets cut from rubber or foam, pressed around the wires and caulked to the floor. Just be sure that the material you use will not flake or deteriorate, as this would put particles into the air stream and, hence, into your equipment. Hand-cutting seals is certainly a cheaper solution, however it takes a lot of your personal labor, and it is relatively inflexible if you have to add or remove cable. But it can definitely solve your air leakage problem.
A more commercially available alternative is to look at standard Fire Stop products. Intumescent Pillows, which come as small as 9.6" x 4" x 3", can be pressed around cables in many situations, or intumescent sheets can be cut out around cables. These materials are really designed to expand and fill in gaps around wires when they get hot, in order to prevent fire spread, but if you press them into position they will seal the vast majority of your air. The small pillows, in particular, are easy to remove and replace, but the key word here is "replace." It's really easy to take any of these improvised seals out and not put them back. And, of course, you can always caulk around everything, preferably with a Firestop Putty or Sealant that's designed to go around wires. This will really seal things, but it obviously hurts your flexibility. (www.nelsonfirestop.com)
Hopefully, sealing these holes will resolve your "hot spot" problem. It should certainly help. But if it doesn't do the job completely, you will need to look at the myriad other things that can degrade cooling performance. That may take a professional assessment.
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