Chillerless Data Centers: Less is More

Eric Soladay, Integral Group

A new trend in data center management is the relaxation of temperature controls. This is in part due to the hardware manufacturers building more robust equipment, but repeated successful testing of performance in high temperature data center environments is making the industry more comfortable with this trend.

The increase in allowable temperatures has led to a much larger number of 'economizer hours' in a given year. This number can range from a significant fraction to all year round depending on the project location. Pixar, based in Emeryville, CA, recently underwent a full renderfarm renovation totaling 1 MW in system capacity, in which they opted to forgo a chiller on the project. After a thorough system analysis, it was determined that a maximum allowable "extreme" entering air temperature of 95F was acceptable. This enabled the design team to solely rely on water-side economization through the use of oversized cooling towers, which drastically decrease the wet-bulb approach of the system.

This strategy was only acceptable due to the fact that all of the racks in the renderfarm were cooled with either in-row cooling units, or rear door heat exchangers, both of which bring the cooling directly to the rack. A chillerless data center with the same temperature requirement would not have been possible in this climate with a purely air based solution.

By eliminating the chiller, Pixar has significantly reduced the maintenance requirements for this system. Chillers are the single biggest failure point and maintenance requirement of a chilled water system, and by eliminating them, Pixar is saving more than just electricity and capital costs. On the other hand, due to the weather dependency of the system, the renderfarm servers will see varying supply air temperatures on peak days.

Design and construction information will be shared as well as operational data from the first year of live production in the renderfarm. On a typical year, the system operates within "recommended" ranges. For rare warm and humid afternoons, temperatures remain well within the maximum allowable temperature.

The actual energy consumption of Pixar's renderfarm will be compared against other chillerless data centers, such as NREL's ESIF facility. Other sustainable features include reclaimed make-up water for the cooling towers, saving millions of gallons of potable water per year; and highly efficient modular UPS's operating in bypass mode, substantially reducing the electrical losses.

Learning Objectives

  • Understand compressor-free cooling applications and how they're inherently weather-dependent.
  • Enhancing reliability in critical environments by simplifying systems and eliminating maintenance.
  • Latest server environmental requirements.
  • Data collection to verify operation and design intent.


Eric Soladay is an innovative, collaborative and goal-oriented mechanical engineer responsible for the development and delivery of high performance buildings. With a focus on building occupants and end users, and a team approach to executing complex projects, Mr. Soladay's work embodies holistic sustainable design and efficient systems, healthy environments, and maintenance-conscious designs. Mr. Soladay brings a calm and reliable creativity to the art of engineering the built environment.


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