Data center facilities pro

Nov 6 2008   7:45PM GMT

27 tips for good data center design

Mark Fontecchio Mark Fontecchio Profile: Mark Fontecchio

Last month, Techtarget held its Data Center Decisions conference in Chicago, and the second-day keynote was given by Ken Brill, the executive director and founder of The Uptime Institute. One of the things Brill said was that there are 27 points to a good hot/cold aisle design, and that most data centers only implement a handful of them.

So that got me to thinking: What are those 27 points? I got in touch with Robert “Dr. Bob” Sullivan, a staff scientist at Uptime that came up with the hot/cold aisle design back in the early 1990s. Earlier this year he wrote a paper on good data center design, and included 27 points. Not every one directly involves hot/cold aisle, but they’re all worth checking out. Aside from one general point, I’ve separated them into five groups: raised floor and overhead space, hot/cold aisle, power and cooling equipment, perforated tiles, and cabling.

Hopefully this can serve as a practical checklist for those users out there designing a new data center or retrofitting an old one.

It’s important to note that a lot of these points refer to a subfloor cooling environment, rather than overhead cooling. Here is the first general point, followed by the five groups:

1) Monitor and manage the critical parameters associated with equipment installation, by area of the computer room (no more than two building bays):

  • Space: number of cabinets and rack unit space available vs. utilized
  • Power: PDU output available vs. utilized
  • Breaker positions: available vs. utilized
  • Sensible/redundant cooling capacity available vs. utilized
  • Floor loading: acceptable weight vs. installed cabinet and equipment weight plus dead load of floor and cables, plus live load of people working in area. Compare the actual floor load with the subfloor structural strength.

Raised floor and overhead space

2) Create a raised floor master plan

3) Establish minimum raised-floor height

  • 24″ if the cabling is overhead, with no chilled water or condenser water pipes under the floor blocking the airflow
  • Recommend 30-36″ if there are airflow blockages

4) Establish a minimum clearance of 3′ from the top of the cabinets to the ceiling

5) Seal all penetrations in the subfloor and perimeter walls under the raised floor and above the dropped ceiling

Hot/cold aisle

6) Install computer and infrastructure equipment cabinets in the cold aisle/hot aisle arrangement

  • 14′ cold aisle to cold aisle separation with cabinets 42″ deep or less
  • 16′ cold aisle to cold aisle separation with cabinets > 42″ to 48″ deep

7) Utilize proper spacing of the cold aisle

  • 48″ wide with two full rows of tiles which can be removed
  • All perforated tiles are only located in the cold aisle

8 ) Utilize proper spacing of the hot aisles

  • Minimum 36″ with at least one row of tiles able to be removed
  • Do not place perforated tiles on the hot aisles

9) Ensure cabinets are installed with the front face of the frame set on a tile seam in the cold aisle

10) Require cabinet door faces to have a minimum of 50% open perforation – 65% is better

11) Prevent internal hot air recirculation by sealing the front of cabinets with blanking plates, including empty areas in the equipment-mounting surface, between the mounting rails, and the edges of the cabinets (if necessary)

Power and cooling equipment

12) Put PDUs and remote power panels in line with computer equipment cabinet rows occupying cabinet positions

13) Place cooling units at the end of the equipment rows, aligned with hot aisles where possible

14) Face cooling units in the same direction — no “circle the wagons” aka, uniformly distributed cooling

15) Limit maximum cooling unit throw distance to 50′

16) Create appropriate cooling capacity, with redundancy, in each zone of the room (zone maximum is one to two building bays)

  • Install minimum of two cooling units even if only one is needed
  • Install one-in-six to one-in-eight redundant cooling units in larger areas

17) Use only sensible cooling at 72F/45%rh when calculating the capacity of cooling units

18) Place chilled or condenser water pipes in suppressed utility trenches if the computer room is built on grade

19) Ensure all cooling units are functioning properly

  • Set points and sensitivities are consistent
  • Return air sensors are in calibration – calibrate the calibrator
  • Airflow volume is at a specific level
  • Unit is functioning properly at return air conditions
  • Unit produces at least 15 degree delta T at 100% capacity

20) Be sure the cooling unit’s blower motor is turned off if the throttling valve sticks (chilled water type units) or if a compressor fails (air conditioning type unit)

21) Adjust chilled water temperature to eliminate latent cooling

Perforated tiles

22) The maximum number of perforated tiles is the total cooling unit airflow divided by 750cfm = maximum number of perforated tiles to be installed

  • Install only the number of perforated tiles necessary to cool the load being dissipated in the cabinet/rack in the area immediately adjacent to the perf tile
  • Turn off cooling units that are not required by the heat load (except for redundant units)

23) Do not use perforated tile air flow dampers and remove all existing dampers from the bottom of perforated tiles (reduces maximum air flow by 1/3, the often close unexplainably and they potentially can produce zinc whiskers)


24) Seal all cable cutouts and other openings in the raised floor with closures

25) Spread power cables out on the subfloor, preferably under the cold aisle to minimize airflow restrictions

26) If overhead cable racks are used, the racks should run parallel to the rows of racks. Crossover points between rows of racks should be located as far from the cooling units serving the area as practical

27) Place data cables in trays at the stringer level in the hot aisle

4  Comments on this Post

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  • Keithward5166
    It may be useful to some to list those items which are generic to any cooling delivery design; above or below. Some of these are basic best practices.
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  • Jim52993
    Excellent and timely article! I'm in the process of renovating my organization's datacenter, and I was extremely gratified that my plans are in accordance with these design tips; however, could someone expound on tip #6? What is meant by 14' separation between cold aisles? Where is this measured from? Warmest Regards, Jim
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  • Mark Fontecchio
    Keith: I figured that, for the most part, people could parse out which were specific to overhead or underfloor, but that's a good point. And it never hurts to list best practices for anyone who might need them. Jim: Cold aisle separation can be measured from the middle of one cold aisle to the middle of the next cold aisle.
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  • EdChu001
    Oddly, a good design is worthless if it is not kept up. I have seen many "well-designed" data centers become "poorly designed" because they were not designed to be maintainable by the business. The thing to remember is that best practices are meant to be general. Advanced Data Center design concepts may contradict some items here but are meant to do more than cover the basics of space. power and cooling support. Care must be taken when intentionally going against these guidelines.
    25 pointsBadges:

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