N - 1, A different Approach to Redundancy for Laboratory Exhaust Systems

Keith Lins, M. K. Plastics Corporation

Redundancy for equipment and systems whose operation in critical environment control applications is common, good design practice. The "n + 1" concept has been traditionally employed. But there is an alternative redundancy design concept. That is "n - 1". This presentation will explore the differences in a laboratory exhaust scenario, contrasting equipment selection, first cost, operating cost, total connected power, and control stability and compatibility with second tier control hierarchies. Using examples, this presentation reveals the advantages associated with the "n - 1" redundancy concept.

Learning Objectives

  • There is an alternative to n+1 redundancy for critical systems;
  • Implementing "n-1" vs. n+1 in critical lab exhaust systems often results in the reduction of fan size by at least one fan increment. Smaller footprint; lower first cost;
  • Implementing "n-1" vs. n+1 in critical lab exhaust systems typically results in a system which is easier to control, having a faster, more linear response to emergency condition; and
  • Implementing "n-1" vs. n+1 in critical lab exhaust systems typically results in a system which can significantly improve operating efficiency. without increasing connected motor power. In fact, connected motor power may decrease.


Keith T. Lins, Senior Advisor, M.K. Plastics Corp. Mr. Lins has 42 years experience in the HVAC industry, as a senior executive with, and advisor to, two major manufacturers of fans for severe duty and critical service applications. He has managed the design of fans and blowers, and has served on and chaired several working committees for AMCA International, presently on the Standard 260 and Fan Regulation committees. He has a B.S. in Business and Administration, and is an active ASHRAE member.


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