Enhancing the performance of large primary-secondary chilled water systems by using bypass check valve

Large primary-secondary chilled water systems often suffer from low chilled water temperature difference (i.e., known as low delta-T central plant syndrome) during operation. This paper presents a detailed study to investigate the feasibility and potential benefits related to the use of a bypass check valve in the chiller decouple line to solve this operational problem and hence, to improve the overall system operating efficiency. The objective of this study is to provide some guidance and necessary confidence as well as the awareness of potential problems that may arise when a bypass check valve is considered to handle the low delta-T syndrome. Based on testing the effects of the low delta-T syndrome, the performances of the systems with and without the bypass check valve are then evaluated by using a simulated virtual system. In the tests, the low delta-T syndrome was introduced through air-side fouling by changing the air-side thermal resistance coefficient in the cooling coil model. The results show that, if the chilled water system suffered from 20% air-side fouling, about 6.77% total energy of the chilled water system studied can be saved when a bypass check valve is used, as compared to that without the bypass check valve.

Research highlights
► A bypass check valve can be used in the chiller decouple line to solve the low chilled water temperature difference in large primary-secondary chilled water systems.
► An approach for investigating the system operational performance with a bypass check valve through simulation tests.
► The overall system performance can be enhanced by using the bypass check valve when the operation of chilled water systems suffers from the low delta-T central plant syndrome.