Feature Article

High Volume\Low Speed Fans and Sprinkler Operation


In 1896 when the first National Fire Protection Association standard, “Rules and Regulations of the National Board of Fire Underwriters for Sprinkler Equipments, Automatic and Open” was published, the authors could not have imagined the complex issues the standard would come to address. In the current edition of the sprinkler standard1, requirements for such equipment as 19th century steam driven fire pumps have been replaced with the allowance to utilize modern engineering tools. Today’s fire protection engineers use computer fire modeling or full-scale fire testing to obtain design solutions.

Aon Fire Protection Engineering (Aon FPE) is leading the path to engineering- based fire protection system design both as practicing design engineers and in the academic fire research arena. This abstract briefly summarizes the most recent of the many research projects completed by Aon FPE.

A High Volume Low Speed (HVLS) fan can be defined as a ceiling fan which is approximately 6-24 feet in diameter with rotational speed of approximately 30-70 revolutions per minute. HVLS fans are routinely used to condition storage and industrial buildings. There are many advantages to the use of HVLS fans, they are highly energy efficient (producing the highest airflow per watt), quiet, and eligible for Green design credits (aka LEED credits).

The large physical size and air flow capacity of HVLS fans created concerns among the fire protection community regarding their impact on sprinkler performance. These concerns provided the impetus for the Fire Protection Research Foundation (FPRF)2 to commission the research project “HVLS Fans and Sprinkler Operation.

Phase I of this study, completed by Aon FPE, focused on the degree of sprinkler water spray obstruction that fans create, as well as the impact of fan-induced airflow on the rate of fire spread through commodity arrangements.

This initial phase of the research program included laboratory testing intended to measure the degree of sprinkler obstruction caused by HVLS fans through a series of Actual Delivery Density (ADD) tests. Additionally, two full-scale tests were conducted to measure fan airflow effects on sprinkler performance. Due to budget constraints, the focus of Phase I was limited to Early Suppression Fast Response (ESFR) sprinkler technology with standard plastic test commodity in rack storage array.

Data obtained from Phase I work provided a foundation for the second phase of this study. In Phase II, Aon FPE focused on full-scale fire testing to examine the effect of HVLS fans on both ESFR and Control Mode Density Area (CMDA) sprinkler performance. Cartoned, unexpanded Group A plastic was used for all testing. The primary goals of Phase II of the project were as follows:
 
  1. Complete the initial focus of Phase I to analyze the impact of HVLS fans on ceiling ESFR sprinkler performance for rack storage arrays.
  2. Expand the investigation to include HVLS fan affect on ESFR sprinkler performance for palletized storage arrays.
  3. Analyze HVLS fan affect on CMDA sprinkler performance for both rack storage and palletized storage arrays.
Ten full-scale tests were completed, four tests in the Large Burn Lab of the Fire Laboratory at the FM Global Research Campus located in West Glocester, Rhode Island and six tests at Underwriters Laboratories large scale fire test facility located in Northbrook, Illinois.

K14 ESFR sprinklers protecting both rack storage and palletized storage arrays were tested. The boundary condition used for all the ESFR tests was a 40-foot ceiling, the maximum allowed by current design standards. A storage height of 30 feet was used for three of the four rack storage tests, the tallest possible given the required clearance of 5 feet above and below the fan. One rack storage test was also completed with a storage height of 15 feet to test a high-clearance condition, 25 feet from ceiling to top of storage. Cartoned, unexpanded Group A plastic commodity was used for all tests. The ESFR palletized storage tests used a storage height of 15 feet to simulate conditions found within picking and receiving areas where handling of product was the priority, not maximization of storage density.

Review of the ESFR rack storage testing data showed the most challenging fan to ignition location was with the fan hub centered over ignition. This is consistent with the Phase I FPRF work. ESFR sprinkler performance was acceptable when the fan was de-energized 90 seconds after waterflow from the first operating sprinkler.

Review of the ESFR palletized storage test data showed that the location of the fan relative to the ignition location had little affect on the performance of the ESFR sprinklers based upon a comparison of the number of operating sprinklers, sprinkler activation times, ceiling temperatures, and commodity consumed. ESFR sprinkler performance was acceptable in all palletized tests, which is consistent with previous testing of this array.

Three CMDA sprinkler tests were conducted at the Underwriters Laboratories large scale fire test facility located in Northbrook, Illinois. The highest storage and ceiling heights allowed by current design standards, 15 feet and 25 feet respectively, were selected for these tests and palletized storage array was used. CMDA sprinkler performance was acceptable when the fan was de-energized 90 seconds after water flow activation from the first operating sprinkler, from air sampling-type detector activation or at ionization smoke detector activation.

From the fire tests conducted, the following conclusions can be made:
  1. K14 ESFR sprinklers can adequately protect cartoned, unexpanded Group A plastic in double row rack storage array to a height of 30 feet beneath a 40-foot ceiling in the presence of HVLS fans when the fans are de-energized no later than 90 seconds after waterflow of the first operating sprinkler.
  2. K14 ESFR sprinklers can adequately protect cartoned, unexpanded Group A plastic in palletized storage array to a height of 15 feet beneath a 40-foot ceiling in the presence of HVLS fans operating.
  3. K11.2 CMDA sprinklers can adequately protect cartoned, unexpanded Group A plastic in palletized storage array to a height of 15 feet beneath a 25-foot ceiling in the presence of HVLS fans when the fans were de-energized no later than 90 seconds after waterflow of the first operating sprinkler.
These findings have been provided to the NFPA 13 Discharge Criteria Committee for use in the development of a code change to address HVLS fans. It is anticipated the code change will be included in the 2012 edition of NFPA 13.

The complete research report can be viewed at the Fire Protection Research Foundation’s website:
http://www.nfpa.org/assets/files//PDF/Research/RF%20HVLS%20Fans%20Ph2.pdf

After completion of the project, NFPA Journal interviewed Garner Palenske, Vice President, Southwest Region for its article titled “Wind+Water: How much impact do high-volume, low-speed fans have on sprinkler system effectiveness in storage facilities?” This article was published in the March/April issue.

References:

1) NFPA 13- Standard for the Installation of Sprinkler Systems, 2010 edition.

2) The Fire Protection Research Foundation is an independent nonprofit whose mission is to plan, manage and communicate research in support of the NFPA mission.


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View of Sprinkler Discharge, Underwriters Laboratories large scale fire test facility located in Northbrook, Illinois
 
View of Commodity and Fan Orientation, Underwriters Laboratories large scale fire test facility located in Northbrook, Illinois
View of Sprinkler Discharge, Underwriters Laboratories large scale fire test facility located in Northbrook, Illinois