Fault Clusters
Clusters group faults that share a root cause. The trigger is the fault that usually fires first; members refine the diagnosis.
CLU-01 — Simultaneous Heating & Cooling
| Trigger | AHU-0016 |
| Members | AHU-0004, AHU-0005, AHU-0012, AHU-0025, AHU-0029, FCU-0001, AHU-0032 |
| Playbook | simultaneous-hc |
| Prevalence | common |
| Energy impact | 15-40% of AHU energy |
CLU-02 — Missing Reset Strategy
| Trigger | AHU-0023 |
| Members | AHU-0024, AHU-0019, AHU-0031, AHU-0035 |
| Playbook | missing-reset |
| Prevalence | 74% of buildings (PNNL 151-building study) |
| Energy impact | 5-20% of site energy |
CLU-03 — Economizer Failure
| Trigger | AHU-0017 |
| Members | AHU-0009, AHU-0011, RTU-0004 |
| Playbook | economizer-failure |
| Prevalence | 54% of RTUs (Cowan 2004) |
| Energy impact | 5-20% of cooling energy |
CLU-04 — After-Hours Operation
| Trigger | AHU-0018 |
| Members | SYS-0003, SYS-0004, AHU-0026 |
| Playbook | after-hours-operation |
| Prevalence | ~15% |
| Energy impact | 3-16% of site energy |
CLU-05 — Zone Heating & Cooling Conflict
| Trigger | VAV-0006 |
| Members | VAV-0003, SYS-0007 |
| Playbook | vav-min-flow-reheat |
| Prevalence | common |
| Energy impact | 5-20% of zone energy |
CLU-06 — Chilled Water Plant Inefficiency
| Trigger | CHW-0001 |
| Members | CHW-0002, CHW-0003, CHW-0004, CHW-0005 |
| Playbook | chiller-efficiency |
| Energy impact | 5-15% of chiller energy |
CLU-07 — Unnecessary Plant Operation
| Trigger | SYS-0001 |
| Members | SYS-0002 |
| Playbook | unnecessary-plant-operation |
| Energy impact | 100% of plant energy while active |
CLU-08 — Schedule Dysfunction
| Trigger | AHU-0018 |
| Members | SYS-0008, SYS-0004 |
| Playbook | exhaust-fan-schedule-misalignment |
| Prevalence | ~15% |
| Energy impact | 3-16% of site energy |
CLU-09 — Sensor Integrity Failure
| Trigger | SYS-0005 |
| Members | AHU-0028, AHU-0002, AHU-0003, SYS-0006, SYS-0009, SYS-0010, VAV-0010 |
| Playbook | sensor-drift |
| Prevalence | ~15% |
| Energy impact | prevents false alarms; sensor-dependent |
CLU-10 — Condenser-Side Degradation
| Trigger | TOWER-0001 |
| Members | TOWER-0002, CHW-0005 |
| Playbook | cooling-tower-performance |
| Prevalence | unpublished (library-authored family) |
| Energy impact | ~2-4% chiller power per degC of added lift (BEE 2006 §3) |
Tower heat-rejection capability loss and chiller condenser fouling share causes (scale, fouling, airflow/waterflow deficiency) and one investigation path: the tower-side vs tube-side split. Fixing the condenser-side root typically clears the chiller efficiency symptom (CLU-06 overlap via CHW-0005).