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Sounding Board: Letters to the Editor, July 2017

Reader comments on the article "Dynamics of Tall-Building Riser Design, Part 1 of 2"

Tall-Building Riser Design

In a letter (Sounding Board, January 2017) in response to “Dynamics of Tall-Building Riser Design, Part 1 of 2” by Marty Rogin, PE (October 2016), we inadvertently omitted some important information regarding copper’s use in tall-building riser design.

“Arrangement for anchoring copper-tube stack passing through concrete floor” is a typical detail for supporting vertical drainage, waste, and vent risers where very small temperature differentials, delta-Ts, are expected because of the nature of the flow characteristics in sanitary drainage systems.

That detail is acceptable for anchoring vertical copper-tube risers where much higher temperature fluctuations, delta-Ts, are expected. What was inadvertently overlooked in our response was text suggesting measures must be employed to allow and compensate for the expansion and contraction of the tube during normal operating conditions of systems with high delta-Ts (as in hot-/chilled-water supply and return systems). In most cases, compensation for expansion and contraction is accomplished with the use of expansion loops where accessible.

Mr. Rogin’s calculation of expected expansion in the 10-ft section of tube between floors was correct, and the expected expansion of 0.147 in. would, in fact, produce excessive strain in the vertical piping beyond what would be acceptable if it was anchored at each floor penetration. Further, anchoring at each floor as shown in the detail probably would compromise the integrity of the vertical stack piping.

We apologize for any confusion this omission may have caused.

Copper Development Association Inc.

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