Online robust control of chilled water systems of buildings for energy performance enhancement

This paper presents two enhanced robust control strategies for building chilled water systems in order to enhance their overall energy performances. A fault-tolerant control strategy for secondary chilled water pumps is proposed to avoid the low temperature difference syndrome and deficit flow problem. This strategy employs the flow-limiting technique that can ensure the water flow of secondary loop not exceed that of the primary loop while still maintaining highest possible delivery capacity of cooling to terminals. This paper also presents an adaptive optimal control strategy for complex chilled water systems involving intermediate heat exchangers. This optimal control strategy determines the optimal settings of the heat exchanger outlet water temperature (hot side) and the required operating number of heat exchangers and pumps in order to minimize the total energy consumption of pumps under varying working conditions. Results show that both of the two strategies have enhanced control robustness and reliability, particularly in avoiding deficit flow problem. Significant energy of chilled water pumps is saved when compared with conventional methods.