Data center cooling efficiency improvement

Cold aisle
Data center cooling
Data center operations
Hot aisle
A reader wrote in with this question: 200 kVA is the load in our 25+ year-old 6,800 sq. ft. "data center" as measured from the UPS. · What should the theoretical cooling requirement (in tons of cooling) be using downdraft CRACs? · By what factor or amount might that cooling requirement increase due to: A. Only a 12" plenum/raised floor B. 33% blockage due to power and data cabling I sense that we have sufficient cooling capacity, but I want to confirm my math. My theory is that continuation of my plan to optimize the space by continuing the hot aisle/cold aisle layout, removing as much cabling from under the floor, properly sealing the floor and possibly segregating the hot and cold aisles above the racks with a thermal barrier/curtain are better solutions than adding another CRAC unit.

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One area of significant cooling loss is related to loss of underfloor pressures due to openings that are not sealed. It is very common for the facilities guys to cut the floor tiles so the IT crew can pass their cables through.

What frequently happens, especially in older data centers, is that holes are not plugged or closed up around the cables which results in cooling going to the wrong places. In my experience, I have been to many data centers where there just old tiles with cut outs in them sitting around the data centers.

You can stuff the hole with a fire retardant material or there is a product called Kold-Lok (developed by the guys at Uptime I believe) that can be used to close things off. As the prior answer indicated, you could have a CFD analysis completed for your raised floor, which will cost several thousand dollars and confirm your suspicion.

You can use the soft fire proof bags that are used to seal wall penetrations. These can be purchased in different sizes and can also be squashed in around the cables etc. While these are a very fine covered bag and will not allow the fire proof fill to escape care needs to be taken to ensure the tiles do not have sharp edges. If continually removed for adding cables etc careful observation needs to be taken to ensure tear’s or worn areas do not occur.

Simple tin plate can also be used if it’s under racks and you won’t be standing on the cover.

OK, as I understand it, the panel on your UPS indicates the OUTPUT of the UPS is 200 kVA. Servers generally have a power factor of one, and all server input power is considered converted to heat that must be removed. Then

200 kVA x 1.0 p.f. = 200 kW converted to heat.

200 kW x 3414 BTUH/kW x 1 ton/12,000 BTUH = 56.89 tons of cooling required to remove heat of servers (+ PDU + switches + appliances + routers + storage etc).

Remember, if the data center roof is also the roof of the building and/or the data center walls are the outside walls of the building, you must add additional cooling to remove the solar load. I don’t hae a rule of thumb for what that will be (you really should hire a consulting engineer to size the system).

Neither the raised floor nor the cabling will increase the cooling load, they will increase the fan static pressure required to deliver the conditioned air to the servers.

Yes, sealing holes in floor, instituting hot aisle-cold aisle arrangement, using thermal barriers to prevent mixing of room air with hot air, etc should improve system efficiency.

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  • Bobkberg
    Good suggestions on cooling leakage - I learned from it. . A few other factors should be mentioned here - Spend some time looking for cables that don't go anywhere. In any cable cleanup operation I've been involved in, there are always a lot of cables that don't connect to anything anymore. - Spend some time re-laying out cables (may have to be done after-hours) to minimize the spaghetti effect - which blocks airflow. Example, 4 2"x2" openings have 16 square inches of passage, but offer more resistance (friction) than a single 4" x 4" opening. - Vacuum out the plenum space below the floor. Dust buildup also blocks air flow, AND can act as an insulating blanket. - If at all possible, take the servers out once a year and blow them clear with CLEAN compressed air (not the stuff in the cans) - Add better filtering (HEPA style is good) to keep dust out in the first place. . Bob
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