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ANSI/ASHRAE Addendum 15 c - 2000
Update
In October 2001, in response to questions and concerns raised by the IIAR Membership, an IIAR Membership Alert was prepared advising the Members of the impact of the new ANSI/ASHRAE Addendum 15 c - 2000 on those involved in the design, installation and maintenance of mechanical refrigeration systems. The Addendum was necessary because it was discovered that the formulae and tables used in earlier editions of ANSI/ASHRAE 15 to calculate relief discharge piping sizes and lengths were based on outdated assumptions. In the Addendum, ASHRAE replaced paragraph 9.7.8.5, which dealt with determination of the maximum allowable lengths of the discharge piping installed on the outlet of pressure relief devices and fusible plugs discharging to the atmosphere. A new Appendix H was also added that prescribed the means to determine the allowable equivalent length of this discharge piping.
Many engineers and other practitioners found that when using the ratings and dimensional configurations of many of the existing relief valves and applying the Addendum 15c-2000 changes, calculations of allowable equivalent lengths of relief piping of a size corresponding to relief valve outlet size sometimes yielded negative values.
Relief and Resolution
There was confusion regarding whether it was allowable to "bush up" to larger piping at the outlet of a Safety Relief Valve to meet the revised requirements. Initial consideration of this possibility indicated that it would not be permissible to "bush up" to a larger pipe size because inserting a fitting in the female connection on the relief valve outlet would reduce the flow cross sectional area. This was the reasoning expressed in the October, 2001 Alert.
Two events occurred subsequently that provided relief from the Addendum: First, Safety Relief Valve manufacturers responded by de-rating current valve models and by producing new valve models having larger outlet diameters. Second, in response to a written request for interpretation, ASHRAE appears to approve increasing the discharge piping from a Safety Relief Valve with a reducing adapter or similar combination of fittings.
Therefore, it is permissible to increase the size of the outlet piping of a Safety Relief Valve by using short transition components for the purpose of immediately increasing the Safety Relief Valve discharge piping size, provided that the transition component(s) is/are included in the equivalent length calculation.
It is not the policy of IIAR to publish product offerings or announce changes in products of member and non-member manufacturers. However, volunteer members of various IIAR committees dedicate their time and energy to benefit the overall vitality of the ammonia refrigeration industry. Accordingly, members of the Standards Review Committee wish to notify the Membership of all information learned about the Relief Valve issues since the Membership Alert was first published in October 2001. Names of Standards Review Committee members are published at the front of the IIAR Membership Directory.
Standards Review Committee
December 2003
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