Optimizing Campus Chilled Water Connections
ASHRAE Journal, April 2020
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Campuses and institutions often use centralized plants with chilled water distribution infrastructure to provide cooling to multiple buildings for the various operational and packaging benefits that come with a central utility plant scheme. The way these buildings connect to the chilled water distribution infrastructure can have a significant impact on the performance of the central plant and on the HVAC systems in the building. Although several articles have been written about this topic over the years, the author has recently observed examples where campus chilled water design fundamentals have been misapplied, so our design community may benefit from a refresher.
Optimizing Pumping Energy Performance
Chilled water distribution pumps located at the central plant are often the largest consumers of pump energy on a campus due to the entire campus chilled water flow moving through them. Inspecting the pump head equation in Figure 1 reveals that an effective way to reduce their power draw and overall energy consumption is to lower their operating pressure requirements. This is where design of campus chilled water building connections comes in. The most efficient campus pumping scheme involves operating the central plant chilled water distribution pumps with just enough pressure to overcome the friction and fitting losses required to pump water through the distribution piping with a small margin of additional pressure to achieve a slight positive pressure delta at the most remote building connections. This approach is described by this author as the “lazy river” strategy and relies on booster pumps to be provided at buildings that require more head pressure than the coincident campus distribution pressure available at their connection.