Experimental analysis of the thermal stability of the pressure control method for a variable flow air-conditioning water system

In this study, we investigate the stability of a pipe network for differential pressure (DP) control of a variable flow air-conditioning chilled water system. First, the hydraulic properties of the pipe network and the thermal properties of the terminal air-conditioning equipment are presented, and the thermal stability is defined to serve as an indicator of the impact that flow regulation in the active branches has on the energy supply capacity of the passive branches. An evaluation indicator of the thermal stability is also developed for online applications. Second, dynamic changes in the hydraulic and thermal properties of the passive branches of a primary pump variable flow dual loop air-conditioning water system were experimentally studied during an active branch regulating valve action stroke cycle using an uncontrolled hydraulic pump, constant DP control and variable DP set-point control. The feasibility and energy savings of various DP control strategies were evaluated in terms of the thermal stability and energy savings for hydraulic pumps. The results show that using a variable DP set-point control strategy produced significant energy savings; however, the thermal stability must be considered when setting the step size in adjusting the DP set-point.