Optimizing chilled water plants.
In September's "Optimizing Design & Control of Chilled Water Plants, Part 2: Condenser Water System Design" by Steven T. Taylor, P.E., in Figure 5 on the chilled water side of the heat exchanger, I suggest a bypass valve be added at the primary chilled water pump suction side (between chiller return and supply lines), so that during full economizer (no mechanical cooling needed), chilled water return doesn't have to be pumped through chiller evaporators after leaving the heat exchanger. This bypass valve functions differently from the bypass valve at the chilled water pump discharge side, whose main function is to maintain minimum flow through the chiller evaporator. This approach will further improve the chiller plant efficiency during water economizer cycle.
Dawen Lu, P.E., Member ASHRAE, Glen Allen, Va.
The Author Responds
I agree, and in fact we always include this bypass on our projects to improve efficiency and also to allow chiller isolation and servicing when on water-side economizer only. Leaving it out was an oversight. The bypass is shown clouded in the corrected schematic below and is included in the online version of the article.
Steven T. Taylor, P.E., Fellow ASHRAE, Alameda, Calif.