TECHPAPER_ATD_ContCooling.pdf

8/14/2019 TECHPAPER_ATD_ContCooling.pdf

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U P T I M E I N S T I T U T E , L L C

Accredited Tier Designer Technical Paper Series:

Prepared by Uptime Institute Professional Services, LLC

Copyright 2011 by Uptime Institute, LLC

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Continuous Cooling

This Technical Paper supplements Data Center Site Infrastructure Tier Standard: Topology.


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UPTIME INSTITUTE ATD Technical Paper Series: Continuous Cooling

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This technical paper clarifies the requirements for Continuous Cooling in the context of the Uptime Institutes Tier Standard:Topology. Tier IV is the only Tier that requires Continuous Cooling. Additionally, this paper serves to recommend ContinuousCooling at densities beyond 4 kilowatts (kW)/rack, regardless of Tier.

As the power densities in the data center increase, the need for Continuous Cooling becomes more profound. The risk ofthe loss of cooling during a UPS ride-though event can be catastrophic to a business. IT equipment may fail or becomewounded.

However, depending on the cooling or UPS technology deployed, the definition and requirement for Continuous Cooling

can widely differ. This paper clarifies the definition of Continuous Cooling and details its deployment with varying types oftechnology choices.

Regardless of technology, Continuous Cooling is defined as the ability to provide stable cooling to the IT and UPSenvironment without any interruption. Continuous Cooling provides this stable cooling capability for the duration of theUPS ride-through time. For example, for a static UPS system with 15 minutes of battery, the Continuous Cooling will needto provide stable cooling for 15 minutes. Note, however, that if there are redundant modules and battery strings available,the 15 minute ride-through time could become 30 minutes or more (depending on redundancies). Careful considerationshould be taken by the owner to determine if the stated ride-through time or the available ride-through time should be therequirement for the Continuous Cooling solution.

The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), in concert with major ITequipment manufacturers, established Thermal Guidelines for Data Processing Environments that includes recommendedcomputer equipment inlet air temperatures necessary to enable reliable operation of servers, storage, and network devices.As of 2010, the ASHRAE guideline (accepted on a global basis) recommends that the device inlet be between 66-81F(18-27C) and 20-80% relative humidity to meet the manufacturers established criteria.

As a point of reference, Uptime Institute conducted a demonstration on a 6-kW/rack average computer room. Intake airtemperatures in computer rooms will exceed the top value in this range within 60 seconds after a loss of cooling or evenair movement.

Consider the scenario of a utility failure, during which the UPS continues to power the IT devices, but mechanical plantoperation is interrupted. Depending on the technology of the cooling deployed, this interruption may continue for severalminutes. During this time, elevated temperatures in the computer room may damage IT equipment. Continuous Coolingprovides the bridge to enable stable cooling to continue until the mechanical or other cooling resumes.

TIER STANDARD: TOPOLOGY REQUIREMENTS

Tier IV is the only Tier that requires Continuous Cooling.

Continuous Cooling for a chilled water system is generally accomplished with thermal energy storage (TES) capability(also known as chilled water storage). Secondary pumps and computer room air handlers (CRAHs) are required to be onUPS. This can be the IT UPS or a separate, Concurrently Maintainable and Fault Tolerant, mechanical UPS system. If thecooling system is in a primary-direct configuration, then the primary pumps are required to be on UPS.

Continuous Cooling for direct exchange (DX) systems requires both the computer room air conditioners (CRACs) and theexternal condensers to be on a Concurrently Maintainable and Fault Tolerant UPS system. The same requirement exists forsplit- system air conditioning units.

Continuous Cooling for 100% outside air systems that can provide cooling throughout the year require the fans (or thesystem that delivers the air to the computer room) to be on UPS.

When rotary UPS systems are deployed as the IT UPS, then the cooling system must be on the no-break bus. This allowsprovision of cooling throughout a UPS ride-through event. If there is a chilled water system deployed in tandem with arotary UPS with no batteries, typically no TES is required. However, each specific case should be reviewed to ensure stablecooling is provided during a loss of power event.

Regardless of any of the cooling or UPS technology deployed in a particular data center, consideration must be given tothe time required to restore mechanical cooling. For example, in a chilled water system, although the engine generatorsmay assume the electrical load within seconds after loss of utility, the result of the momentary loss of power to the chillersmay require a restart cycle lasting up to 15 minutes or even more. Although manufacturers are reducing the restart times,


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UPTIME INSTITUTE ATD Technical Paper Series: Continuous Cooling

the interval between the loss of power and a resumption of the systems ability to produce stable cooling needs to beincorporated as a data point in the ride-through time. For example, if a UPS ride-through time is set at 5 minutes, yet it takes15 minutes to resume stable mechanical cooling after a loss of power, then the TES must be able to provide 15 minutes ofchilled water storage.

Providing thermal stability to the IT and UPS environment during the transition from utility outage to engine-generatorpower, Continuous Cooling ensures that a utility event does not result in costly heat damage to IT hardware or criticalequipment. A requirement only for Tier IV, but justifiable for average densities above 4 kW in light of potential damage tofacilities and IT investment.

RELATED PUBLICATIONS

Tier Standard: Topology Accredited Tier Designer Technical Paper Series: Engine-Generator Ratings Accredited Tier Designer Technical Paper Series: Makeup Water

Further information can be found at www.uptimeinstitute.com/resources.

Documents

TECHPAPER_ATD_ContCooling.pdf