Previous investigation found that the bypass blending station (BBS) system can potentially reduce in-building pump power by 48% to 97% of the design pump power. However, the BBS pump may work in an unstable zone when it has 100% of the building design flow. This paper investigates the impacts of pump flow capacity and pump control on the pump operation stability and power savings using analytical and numerical methods. The investigation found that the optimal pump design flow depends primarily on the building load and recirculation flow rate requirements. The optimal pump size should be determined based on the re-circulation rate requirements under typical building load conditions. An identical pump should be installed as a backup pump. Under typical load conditions, one pump is used. Under low building load conditions, both pumps should be activated. Optimal pump design and operation control can ensure stable, efficient pump operation. The pump power saving varies from 70% to 97% of the building pump design power depending on the building load.

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