| Sprinkler, the most important component in automatic sprinkler system, is a device which will operate in a predetermined temperature range and intend to distribute water in a specified pattern and flow rate. The Response Time Index (RTI) which is a parameter of sprinkler actuation represents the thermal time constant for the heat-responsive element of an automatic sprinkler and the square root of the associated gas velocity.It is normally considered that the sprinkler actuation mainly depended on the heat release rate during the fire. However, a lot of test results have indicated that conductive heat loss from the heat-responsive element to the sprinkler support may also influence sprinkler response. This report describes the conductive heat loss in an existing thermal response model for sprinklers,and the heat loss is proved in the fire tests correspondingly. Conductive heat loss is represented by a conduction coefficient, C, which is a companion parameter to RTI and can be measured from the prolonged-exposure test by a hot-air tunnel. The conduction coefficient C then is used with actuate time and air temperature as well as air velocity to calculate RTI.The study of the conduction coefficient C, in prolonged-exposure tests revealed that it was only slightly dependent on variables of the sprinkler fitting, such as absence or variations in mounting torque, depth of thread engagement, material, and the type of sealant for the sprinkler thread. However, flowing water past the sprinkler waterway increased the conduction parameter significantly. The result of this study has been used in modification of the dynamic heating performance and test methods in China national standard for sprinkler, GB5135-1993 Performance Requirements and Method of Tests for Automatic Sprinkler. The mounting plate for this study has been accepted by The National Center for Quality Supervision and Test of Fixed Fire-extinguishing Systems and Fire-resisting Building Components, and will be used for testing.
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