Enhance Hydraulic balance of a District Cooling System with Multiple Jet Pump

Abstract

Due to the small temperature difference between the supply and return water in the conventional district cooling system, the flow rates of the chilled water have to be very large to fulfill the buildings’ huge cooling demands. To save the electricity consumptions of the circulating water, the variable-speed pumps are commonly applied. However, it may deteriorate the hydraulic balance of the pipe network in most circumstances. The variable flow rates necessitate dynamic hydraulic balance in a pipe network. The conventional approaches, which depend on the throttle valves, can hardly adapt the dynamic regulations. Therefore, a new scheme of applying the jet pumps is introduced in this study to enhance the hydraulic balance of the district cooling system. The proposed jet pump has an adjustable jet orifice, which is flexible to adjust the local water mixture ratio. With these jet pumps installed at the entrances of the buildings, the thermal load conditioning for each building can be performed by adjusting the local jet orifice. Then the chiller plant can operate independently without considering the mutual hydraulic influences of the buildings. Furthermore, the electricity consumption of the circulating pump can be saved significantly in the proposed scheme where there are less water flow rates in the main pipelines and lower supply water temperature. The simulation results showed that the dynamic hydraulic balance can be achieved more conveniently by the proposed scheme, in such scenarios as the thermal loads or the hydraulic resistances of the buildings varied a little from time to time. The electricity consumption of the circulating pump can also be saved as much as 10-30%.