Fault mechanism and comprehensive analysis of the hydraulic-thermal effect of valves used in flat plate solar collectors

Valve faults significantly threaten the reliability of solar collector fields (SCFs), yet their impact characteristics under transient solar conditions remain poorly quantified. This study investigates five typical faults in gate valves (GVs) and automatic exhaust valve (AEV) using a hybrid simulation-experimental approach. A coupled MATLAB-TRNSYS model, validated with high accuracy against experimental data, simulated unidirectional impact faults (e.g., inlet GV blockage/leakage), whereas a dedicated experimental platform analyzed faults with bidirectional thermal-hydraulic interactions (e.g., outlet GV blockage/leakage, AEV blockage). The results uncover a strongly nonlinear severity-impact relationship, with critical thresholds identified at 50 % blockage and 10 % leakage. For instance, a 50 % inlet GV blockage causes a 31.68 % reduction in pressure drop and an 8.45 % degradation in useful energy gain, surging to 65.49 % and 20.90 %, respectively, at a 70 % blockage. Similarly, a 10 % outlet GV leakage leads to a 25.45 % thermal performance loss, jumping to 50.89 % at 15 % leakage. The proposed comprehensive evaluation index (ECP) further demonstrates that the impact mechanism critically depends on fault location, with inlet faults posing a greater overall risk. This study provides a quantitative database and thresholds essential for developing predictive maintenance strategies, thereby enhancing the operational reliability and efficiency of the SCF.