Consulting-Specifying Engineer - April 2008 - (Page 27) Commissioning BY DAVID SELLERS, PE, Senior Engineer, Facility Dynamics Engineering, Portland, Ore. hen practitioners in the buildings industry think of campuses—college universities, resorts, industrial complexes, etc., they envision large, expansive systems that perform exotic HVAC processes to support cutting edge research and systems that provide a comfortable working environment for the leading thinkers of the day, all served by central plants with big pipes, big conduits, and big machinery. And, while that picture generally is correct, the trick to making these systems perform ideally and achieve their best efficiency often lies in the smallest of details. Below, several mini case studies analyze small details that were root causes behind commissioning issues on campus chilled or condenser water systems. While the stories are framed in the context of several different large campus systems, most of the lessons learned apply across the entire spectrum of the building stock. After all, physics is physics. Cooling tower piping symmetry Central plants with water cooled chillers are common in campus facilities and the words “water cooled” typically are synonymous with a cooling tower. On the surface, cooling towers appear to be fairly simple machines exploiting on campus The smallest details can be root causes of large issues on commissioning cases. The author presents four case studies that analyze commissioning issues on campus chilled or condensed water systems. W evaporation. However, there are some fairly complex phenomenon occurring in cooling towers1. Consider the following example from a project at the University of California, Berkeley. The towers on this project are part of the central plant serving the Doe library, which houses rare collections, including the Tebtunis Papyri and Mark Twain’s papers. Cooling and the related dehumidification processes are critical for the long-term care of these artifacts—so the central plant is the focus of scrutiny in the commissioning process to ensure that the design intent is realized. During a construction observation visit before much piping was in place, the commissioning team noticed clues that indicated the field configuration for the piping might end up being different from the design configuration. Specifically, the drawings showed a symmetric piping arrangement (see Figure 1), but it appeared as though the mechanical contractor was about to install a nonsymmetric piping arrangement. The symmetric piping arrangement depicted on the design documents would be preferable because it ensures uniform flow distribution through both tower cells under all operating modes. This in turn: Consulting-Specifying Engineer • APRIL 2008 27
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