Acoustic Nozzles to Mitigate Risk in Data Centers

Nov. 2, 2018

When using inert gas fire suppression in data centers, it’s critical to measure and understand the level of acoustic noise to determine its impact on HDDs.

Data centers are used by a wide range of industries to store and disseminate information to the connected world. Perpetual uptime of data centers is critical to maintaining normal business operations. Any amount of disruption can cause significant loss to companies.

Hard disk drives (HDDs) are a primary means of information storage in data centers. As technologies advance, evidence has shown that HDDs are increasingly sensitive to noise, including noise generated by inert gas fire suppression systems. Recently, several large businesses have suffered significant data and monetary loss caused by data center downtime.

Agent discharge nozzles that are part of inert gas fire suppression systems are sources of sound that can momentarily interrupt or damage HDDs, causing loss of data. When the agent is released from pressurized cylinders it moves through the pipes at a high velocity. Upon exiting through the nozzles into the data center, the agent generates high sound pressure levels (SPLs). When this noise reaches the HDDs, it causes vibrations, which in turn compromises the HDDs read/write performance.

Studies have shown that once the SPL reaches 110 dB of any one-third octave (OTO) band, HDD performance can realize a 50 percent performance reduction. Some drives experience severe degradation in read/write performance after exposure to SPLs as low as 85 dB. Therefore, when using inert gas fire suppression in data centers, it’s critical to measure and understand the level of acoustic noise to determine its impact on HDDs.

Understanding Sound Measurements

The sound output of fire suppression systems is dependent on several factors, including discharge duration, peak agent flow rate and valve technology. When investigating noise control issues in data centers, companies should consider the Source-Path-Receiver (SPR) Paradigm, which provides insight into the measurements necessary to define and address acoustic issues that can damage HDDs.

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This method of measurement includes the:

  • Source: The system or component that’s generating the noise)
  • Path: Any combination of acoustic or structural paths the sound can take to travel from source to receiver
  • Receiver: The instrument or object affected by the noise

Results determined by acoustic calculations can help designers select the appropriate nozzle and its placement as well as the optimal room configuration/materials to achieve desired sound pressure levels. Using the SPR Paradigm helps data center operators understand how sound is generated as sound power at the source, and altered through the room paths to be experienced as sound pressure at the receiver such as HDDs.

Acoustic Nozzle Solutions and Performance

The standard discharge control method for inert gas suppression technology has been metering orifices, which have proven to successfully suppress fire. However, one characteristic of this orifice flow technology is high peak agent flow rates that generate elevated noise levels. Testing has determined the nozzle sound power of orifice flow system discharges can exceed 145 dB, thereby greatly reducing the read/write performance of HDDs.

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A solution was needed to lower the sound power of agent discharge nozzles to prevent HDD degradation. Acoustic nozzles with innovative noise-reducing features can greatly lower sound power levels and subsequently the SPLs to reduce the risk of damage to HDDs. UL Verified Sound Power provides confidence in the acoustic nozzle noise reduction. Extensive testing of these new acoustic nozzles with a variety of enterprise model HDDs in various data center configurations helps determine their fit for market performance.

Calculating Acoustic Levels

Every data center protected by an inert gas fire suppression system will yield varying sound path absorption properties. Data center operators should conduct room acoustic calculations to ensure the fire suppression system installation meets sound performance requirements. This helps reduce the risk of HDD degradation if the inert gas fire suppression system discharges.

Once calculations are performed, the estimated HDD sound pressure level can be compared to an HDD acoustic noise performance curve to determine the data center noise specification or applicable HDD manufacturer’s data. This allows system designers to determine the necessary suppression system nozzles, HDD placement or room path material modifications to greatly reduce the risk of damage to HDDs in the event of a fire suppression system discharge.

Derek Sandahl is global product manager for Engineered Systems at Johnson Controls.

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