FPB Fault Rules
Fan-powered terminal rules (FPB-*) cover series and parallel fan-powered VAV
terminal units, also called fan-powered boxes, fan-powered terminal units, or
FPUs. Ordinary VAV boxes remain in vav; fan coils remain in fcu.
Point dictionary: points/fpb.points.json.
Brick 1.4.4 provides only generic Terminal_Unit; ASHRAE 223 PPR2.1 provides
exact FanPoweredTerminal. Series/parallel identity is deployment topology.
| Concern | Series FPB | Parallel FPB |
|---|---|---|
| Fan location | In the primary/discharge path, generally continuous when occupied | Parallel plenum-air branch, often heating/low-flow operation |
| Primary airflow | Through primary damper | Through primary damper |
| Reheat coil | Typically downstream of fan | In fan/reheat branch before mixing, per actual unit topology |
| Fan proof rule | Applicable when commanded | Applicable when commanded |
| Airflow tracking | Primary airflow only | Primary airflow only; does not prove fan-branch airflow |
| Reheat delta-T binding | Direct coil inlet/outlet | Must remain branch-local or use a validated derived point |
Excluded: ordinary single-duct VAV boxes without terminal fans, FCUs, induction units without commanded fans, dual-duct boxes without explicit compatibility, and electric-reheat-only units for the hydronic valve rule.
Index
| ID | Name | Sev | Method | Status |
|---|---|---|---|---|
| FPB-0001 | Terminal fan proof-of-operation failure | 2 | rule | verified |
| FPB-0002 | Primary airflow tracking failure | 3 | rule | verified |
| FPB-0003 | Reheat valve closed with unintended temperature rise | 3 | rule | verified |
| FPB-0004 | Terminal fan airflow degradation | 3 | statistical | verified |
| FPB-0005 | Primary airflow sensor disagreement | 3 | meta | verified |
| FPB-0006 | Reheat-coil heat-transfer degradation | 3 | statistical | verified |
Minimum telemetry tiers
| Tier | Points | Supported rules |
|---|---|---|
| Basic | fan command/status, primary flow/setpoint | FPB-0001..0002 |
| Reheat | + valve and coil inlet/outlet temperatures | + FPB-0003 |
| Performance | + fan airflow/expected airflow and expected coil delta-T | + FPB-0004, FPB-0006 |
| Sensor redundancy | + independent primary airflow reference | + FPB-0005 |
Expected/reference points are host-derived contracts, not guesses. Each deployment records known-good fit data, model/version, inputs, accuracy, same-path scope, freshness, domain checks, and update/freeze policy. A model using the point it is supposed to check is circular and invalid.
Source and validation posture
The LBNL simulated FPU dataset (DOI 10.25984/1881324) documents PFPU/SFPU topology and publishes HVACSIM+ cases spanning 365 days at one-minute resolution, 109 points, fault-free cases, and ten fault categories. It is a future validation source, not evidence for the library-authored thresholds in this slice; the adapter is deferred to PR11.
Relationships
- FPB-0001 supplies direction-sensitive fan-proof context; no whole-rule suppression is safe for FPB-0002/0003.
- FPB-0002 is the primary-stream sibling of VAV-0004 and relates upstream AHU static/reset signatures without claiming their causes.
- FPB-0003 is the coil-local leakage sibling of FCU-0005/VAV-0009; FPB-0006 asks the opposite full-command performance question. Neither joins CLU-01.
- FPB-0004 separates proven operation from delivered fan-path airflow. FPB-0001 remains direction-sensitive context, not a whole-rule suppressor.
- FPB-0005’s ambiguous adjudication reports disagreement without automatically choosing the physical sensor or host reference as the failed member.