CHW Fault Rules
Chilled-water plant fault detection rules (CHW-*). CHW-0001..0006 originate
in HVAC FDD Reference v1.0 ch.13 or close its cited approach-rule gaps.
CHW-0007..0009 are library-authored control/protection extensions grounded in
public plant guidance and verified graph precedents. The family now separates
efficiency and reset performance from per-machine tracking, proof, and cycling.
Point dictionary: points/chw.points.json.
Supplementary deep-read sources (paraphrase-and-cite only, per the licensing
rule): G36 cooling-plant AFDD document, ASHRAE RP-1043 chiller FDD review,
and the chiller-plant entries in the project’s internal research triage (licensed sources; not distributed).
Index
| ID | Name | Sev | Method | Status |
|---|---|---|---|---|
| CHW-0001 | Chiller efficiency (kW/ton) degradation | 3 | statistical | verified |
| CHW-0002 | CHWST reset not functioning | 3 | statistical | verified |
| CHW-0003 | CHW loop DP reset not functioning | 3 | statistical | verified |
| CHW-0004 | Chilled water low delta-T syndrome | 3 | rule | verified |
| CHW-0005 | Chiller condenser approach high | 3 | rule | verified |
| CHW-0006 | Chiller evaporator approach high | 3 | rule | verified |
| CHW-0007 | Chilled-water supply temperature tracking failure | 3 | rule | verified |
| CHW-0008 | Chiller proof-of-operation failure | 2 | rule | verified |
| CHW-0009 | Chiller short-cycling | 2 | rule | verified |
Severity and method per the reference’s ch.13 cards. CHW-0005/CHW-0006 are the approach pair resolving the reference’s dangling CHW-FC-008/009 playbook citations (mentioned there, never defined): condenser side and evaporator side of the same verify step, tube-side discriminators for CHW-0001.
Relationships
- CHW-0002/CHW-0003 are the plant-side siblings of AHU-0023/AHU-0024 (SAT/DSP reset) — same detector shape (setpoint range flat over a window while the load moves), same RetuningOpps lineage, and the same CLU-02-style “reset never programmed” root cause one system further upstream.
- CHW-0004 (low delta-T) is the plant-level symptom of coil-side defects the library already detects locally: fouled/leaking coil valves (FCU-0004, AHU-0014), three-way bypass, dirty filters — tied together by cluster CLU-06 (trigger CHW-0001).
- CHW-0001’s baseline follows the HP-0001 host-fitted pattern — the reference specifies a Ridge regression over load/CWST/CHWST; the graph carries the fitted coefficients as set_param placeholders.
- CHW-0007 complements CHW-0001/0005/0006: tracking direction is useful evidence during an approach or efficiency finding, so none suppresses it.
- CHW-0008 stays relationship-only. Its fail-to-start direction makes tracking non-evaluable, but its unexpected-run direction can still be loaded and meaningfully fail tracking. Current metadata cannot encode only one lane.
- CHW-0009 and CHW-0007 are related because low-load overshoot can produce cycling, but neither implies the other and no graph state is shared.
Per-machine binding boundaries
| Point | CHW-0007 | CHW-0008 | CHW-0009 | Plant/loop use |
|---|---|---|---|---|
chiller_cmd | — | Final command for this machine | — | Plant enable or cooling demand is invalid |
chiller_status | This machine | This machine, independent proof | This machine | A fleet OR hides lag-machine starts |
chiller_load | This machine | — | — | A documented plant maximum remains valid only for plant-level gates such as CHW-0004 |
chwst / chwst_sp | Same controllable leaving-water target | — | — | Common header is conditional, not automatically per-machine |
On parallel plants, prefer each chiller’s evaporator outlet plus the final active target delivered to its controller. A mixed-header measurement/setpoint may be used for CHW-0007 only when the deployment proves the staged machine(s) actually control that same point. An OR of statuses or maximum of loads is not a weaker per-machine proxy; it changes the question.
Ontology and cluster decision
The PR 04 point additions pin ASHRAE 223 to the inspected public-review
artifact 1.0.0-ppr.2.1 (SHA-256
1f156f9938c0be430d2216e01e31bb183c438ba318d8d4a23d2f074ebcd6f573),
replacing the former unverified v1.0.0-2026 label. The migration also
replaces legacy Water/Refrigerant and free-text aspect shorthands with
artifact-defined local names such as Water-ChilledWater, Fluid-Water,
Constituent-Refrigerant, and Aspect-Setpoint. Brick 1.4.4 provides exact
generic Start_Stop_Command and Run_Status classes on a Chiller.
CLU-06 is not broadened. Tracking, proof, and cycling improve diagnosis but do not share one trigger/fix with the existing efficiency-reset-approach cluster.