In-situ validation of a fault tolerant control strategy for VAV systems

In variable air volume (VAV) systems, conventional control strategies reset the supply air static pressure based on the opening degrees of all the VAV dampers. However, such methods are not robust because the supply air static pressure set-point will gradually increase to its high limit in case some VAV terminals are abnormal. Such abnormal happens quite often as a survey reported that 20.1% of the VAV terminals were ineffective in the field. This study provides a practically applicable fault tolerant control strategy for VAV systems. Instead of using VAV damper positions which contain limited information of space thermal comfort, the developed strategy utilizes other available information for the optimal control. A statistical method is also used in this strategy. After a throughout in-situ test, the strategy has been permanently implemented in all office floors (142,000 m²) in a high-rise building since July of year 2014. Although there are some statistical based optimal control methods have been reported, the permanently application of such methods at large scale is rarely seen in literature. This paper presents the details of the fault tolerant control strategy as well as its in-situ test results. Supported by the test data, the new control strategy is compared with the conventional strategy which was originally implemented in the building. The supply air static pressure is reduced significantly resulting in 33.6% power saving while the space thermal comfort was still maintained.