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What Causes Hot Spots?

December 4, 2012 By Leave a Comment

The single issue that every facility manager hates most is hot spots.  They are like a disease.  You cannot see them and you only become aware of them by observing their symptoms.  And be aware when you do.  Hot spots that continue for extended periods of time can cause poor server performance and, in the most extreme cases, server failures.  Since the number one job of a facility manager is to prevent server failure, hot spots needs to be diagnosed and treated early.    This post will examine why hot spots exist and why the industry’s current solution for mitigating them may actually make them worse.

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The Farmer’s Dilemma

July 19, 2012 By Leave a Comment

A story about temperature vs. pressure in cooling management

Once upon a time long long ago, in a valley just south of the San Francisco Bay, a large truck pulled up to a farmer’s house and dropped off a thousand boxes, each of which was the same size and weight.  The farmer was puzzled to find that in every box was a toaster each with the same set of instructions.  The instructions indicated that the farmer must construct a way to ensure that, when these thousand toasters were turned on, they would not overheat and burn up.

Said the instructions, if even one toaster burns up, the farmer will have failed and be damned for eternity.  If, however, the farmer succeeds at this challenge, he will be rewarded and praised in all the land.  This was quite an odd request, but the farmer took it seriously and consulted with his smartest group of friends.  The group was comprised of the three people: a toaster expert who knew the heat output of every type of toaster ever invented, a building engineer who had designed cooling systems for office buildings, and a PhD who just happened to be the farmer’s neighbor.  The team deliberated for a few weeks and came up with a brilliant design.

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How cool should my data center be?

February 20, 2012 By 6 Comments

How cool should your data center be?  The answer to that question depends on who you ask.  If you ask the customer they will say: “cold enough so the equipment doesn’t fail.”   If you ask the IT equipment manufacturer they will say: “cold enough not to void the warranty.” If you ask an energy consultant they would say: “shouldn’t be that cold!”  Thanks guys…very helpful.  Luckily, the reason that the American Society of Heating Refrigeration and Air-Conditioning Engineers (ASHRAE) exists is to be able to provide an unbiased answers to questions like this.

However, their answer to the question will be: “well, it depends.”  Fortunately it is ASHRAE’s job to define ‘it depends’ and they have done just that in their 2011 Thermal Guidelines for Data Processing Environments.  This post summarizes those thermal guidelines.

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Underfloor Air Distribution System

August 31, 2011 By Leave a Comment

Most large data centers use an underfloor air distribution (UFAD) system to cool IT equipment. Why are UFADs commonly used in data centers and not in typical building environments? Building cooling systems typically use duct distributed ventilation, versus under floor systems. Understanding the benefits and drawbacks of a UFAD and why they are commonly used in data centers can shed light on how to make them more efficient. The following are some key features, along with some pros and cons of using a UFAD system.

  • Open Space Layout
    • Pros     Because a data center is one large open space, individual ducts aren’t needed to deliver air to specific zones or rooms (like you’d find in a building). Air delivered via a UFAD can provide cooling to the entire space. Also, tiles allowing ventilation can be self-configured to provide cooling only where needed (such as cold aisles).

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Power Densities

August 16, 2011 By Leave a Comment

I stumbled upon this listing of data center real estate developments from Symphonic Investments.  The list is here, but these are some highlights with energy densities that I added.  Just for reference, building energy densities are ~20 – 30 watts/sqft.

Dupont Fabros
Size: 85,000 sqft
Load: 18.2 MW
Power Density: 214 watts/sqft
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CRAC vs CRAH

August 11, 2011 By 6 Comments

Yes they are different and yes the difference matters.

Ever since I have entered this industry I have heard the acronyms CRAC and CRAH used interchangeably.  Industry professionals, user manuals, and even colleagues of mine have either incorrectly used the wrong acronym to describe a cooling unit in a data center or referred to them collectively as “CRAC/CRAH” units.  The difference is simple and it is time we start getting it right.
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