Analysis of transfer pumping interfaces for stratified chilled water thermal storage systems - Part 2: parametric study

Transfer pumping interfaces are an important component of chilled water storage systems and other open hydronic systems. This paper describes a parametric study of seven interface types applied to a representative chilled water storage application. Interface types considered include indirect (heat exchanger) interfaces, direct interfaces, direct interfaces with energy recovery operated at variable or constant speed, and reversible variable-speed direct interfaces. Annual simulations on an hourly time step were performed using component models described in Part 1 of this paper. Seven levels of static head, varying from 90 ft to 360 ft (27 m to 110 m), were considered for each alternative. Construction costs were estimated and economic performance was described in terms of simple payback period and life-cycle cost. Results of the study suggest that energy recovery for direct interfaces may be feasible for static head as low as 120 ft (37 m) and that indirect interfaces may not be economically superior except at very high levels of static head due to high capital cost.