Robust sensor fault diagnosis and validation in HVAC systems

A robust fault diagnosis and validation strategy for temperature sensors and ow meters in central chilling plant is developed, which is based on the rst law of thermodynamics. The strategy evaluates soft sensor faults (biases) by examining and minimizing the sum of the squares of concerned mass or steady state energy balance residuals represented by the corrected measurement over a period. It considers systematically all the concerned energy balances and obtains the best estimates of the sensor biases by minimizing the sum of the mean squares of normalized residuals of all energy balances involved. The genetic algorithm technique is employed to determine the global minimal solution to the multimodal objective function, which can be difcult to achieve by traditional gradient-direc ted search methods. Performance of an advanced robust fault detection, diagnosis and evaluation (FDD&E) scheme is compared with that of a sequential scheme, which was reported earlier, in simulation tests. The robust scheme is superior to the sequential scheme in robustness to abrupt sensor faults, such as biases, etc. The robust scheme is applied to a central chilling plant in an existing commercial building, providing satised bias estimates. As a basic method, the sensor FDD&E strategy is of practical value in heating, ventilation and air-conditioning (HVAC) systems as well as in systems where the measurements of liquid ow variables are essential to control and performance monitoring. Nomenclature a Coeffcient b Constant c p Specic heat capacity at constant pressure (kJ/kg°C) d f Relative difference of the best tness values from two consecutive GA runs f Fitness value or tness function I(j) Index denoting operation status of jth chiller (or ow) (0,1) I bp1 Index denoting positive bypass ow direction (0,1) I bp2 Index denoting negative bypass ow direction (0,1) J, k, l Serial number M Flow meter or ow rate (l/s) M(j) Chilled water ow meter or the ow rate of jth chiller (l/s) M b Building chilled water ow meter or the ow rate (l/s) M bp Flow rate or ow meter of bypass (l/s) M bp1 Flow rate or ow meter in positive bypass ow direction (l/s) M bp2 Flow rate or ow meter in negative bypass ow direction (l/s) N Total chiller number in the plant N op Total number of chillers operating simultaneously N pt Total number of sample points r balance residual Sr sum of residuals Sr sq sum of the squares of the balance …