Analysis of Transfer Pumping Interfaces for Stratified Chilled Water Thermal Storage Systems—Part 1: Model Development

This paper describes methods for modeling the performance of transfer pumping interfaces used to connect open chilled water thermal energy storage tanks to closed chilled water systems. Indirect (heat exchanger) interfaces and direct interfaces are considered. Treatment of direct interfaces includes the use of energy recovery with centrifugal pumps serving as hydraulic turbines. Of the seven interface types considered, only three (constant-speed direct, constant-speed direct with energy recovery, and constant-speed indirect) have been previously discussed in the literature. Characteristics of interfaces with variable-speed pumping and a novel reversible direct interface with energy recovery are described quantitatively for the first time. Models of interface components are derived and assembled to simulate the performance of interfaces operating at both constant and variable speed. Representative examples of performance for moderate and large adverse static pressure differentials are presented and discussed. It is shown that the power vs. flow characteristics of the interface types investigated differ greatly and that these differences are affected by the value of the static pressure differential at the interface. The models presented in this paper are of practical value in the design of pumping interfaces for all types of open systems.