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Heat Pump & Radiant Heating Control: ΔT, Metering & Diagnostics

Heat Pump & Radiant Heating Control: ΔT, Metering & Diagnostics

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Heat pump radiant heating performance becomes predictable when the controller can prove delivery (Flow + ΔT), prove capacity (Compressor/Vdc/Iphase), and prove boundaries (metering + state gating) with complete logs. If any of these evidence chains is weak, COP, comfort, and fault conclusions will be misleading—so the fastest fix is to restore trustworthy sensing, stable control, and actionable snapshots.

H2-1 — Definition & boundary: Heat Pump + Radiant Hydronics

This chapter locks the scope so every later section stays evidence-based and non-overlapping: drives → ΔT/flow proof → metering/COP confidence → remote diagnostics logs.

One-sentence boundary

This page focuses on control and diagnostics for a heat pump feeding a hydronic radiant loop—compressor/valve/pump drives, supply/return ΔT and flow evidence, energy metering and COP estimation, plus remote fault logs—excluding thermostat UX, room-by-room zoning/TRVs, and cloud platform architecture.

Inside this page (must land here)
Compressor inverter drive EEV / reversing valve Circulation pump Mixing valve Supply / return ΔT Flow + pressure proof Electrical-in metering Thermal-out estimate Fault code + event log RS-485/Modbus or Ethernet
  • Drives: what is commanded, what feedback confirms execution, and what “trip signatures” prove a root cause.
  • ΔT & flow evidence: where to measure, what ranges make sense, and what failure patterns look like.
  • Metering: define the energy boundary (AC line vs DC link) and grade COP confidence based on sensor integrity.
  • Remote diagnostics: minimum snapshot bundle + counters so “remote fault” becomes actionable.
Outside this page (do not deep-dive)
  • Thermostat UX / automation rules (schedules, UI flows, app integration).
  • Room-by-room zoning, TRVs, manifold actuator design (end devices and zone logic).
  • Boiler/furnace flame control (combustion safety chain).
  • HEMS / whole-home energy orchestration (panel-level switching, solar/storage system control).
  • Cloud backend architecture (pipelines, dashboards, multi-tenant services).
  • Installation tutorials (plumbing practice, building codes, hydronic balancing procedures).

What this scope enables (reader outcomes)

  • Fast discrimination: separate “not enough heat” into capacity vs circulation/mixing using ΔT + flow evidence.
  • Trustworthy performance: compute thermal output and grade COP confidence instead of relying on misleading single sensors.
  • Actionable remote support: define exactly what to log so the first remote report already contains proof-quality snapshots.
Scope Boundary — Heat Pump + Radiant Hydronics Everything below stays in this page; outside items are excluded. INSIDE (covered) Drives / Actuation Compressor inverter EEV · Reversing valve Pump · Mixing valve ΔT / Flow Evidence Supply / return temps Flow + pressure proof Freeze / defrost state Metering / COP Electrical-in boundary Thermal-out estimate Confidence grading Remote Diagnostics Fault codes + snapshots Counters + event log RS-485 / Ethernet link OUTSIDE (excluded) Thermostat UX Apps · UI · schedules Zoning / TRVs Room-by-room control Cloud Platform Backend architecture Boiler/Furnace Flame safety chain ICNavigator
Figure F1. Scope boundary map: what is inside this page vs intentionally excluded to avoid overlap.
Cite this figure Figure ID: F1 · ICNavigator

H2-2 — Reference architecture: Outdoor unit + hydraulic module + radiant loop

The goal here is not theory—it is a stable “evidence coordinate system” that every later control, metering, and diagnostics section can reference without drifting into thermostat or cloud topics.

How to read the system: four evidence paths

  1. Power → Drive path: AC input to PFC/DC link and inverter current/voltage prove whether trips, brownouts, or ramp limits are electrical/drive-driven.
  2. Refrigerant actuation path: compressor speed, EEV state, reversing valve state explain defrost transitions and capacity behavior without turning into a refrigeration textbook.
  3. Hydronic delivery path: pump + mixing valve + supply/return headers, validated by ΔT/flow/pressure, prove whether heat is actually delivered to the radiant loop.
  4. Diagnostics/log path: fault codes + snapshot bundle + counters convert “remote fault” into proof-quality evidence.

Blocks (and why each matters to control & diagnosis)

  • AC in → PFC → DC link → inverter: defines the electrical-in boundary and explains start/defrost transient failures (DC link sag, current spikes).
  • Compressor inverter drive: provides capacity; phase current + speed command are the quickest discriminators for overload vs control-limit behavior.
  • EEV + reversing valve: must be logged as state during capacity drops/defrost events; “water-side symptoms” can be caused upstream.
  • Hydraulic module (HX/buffer optional): acts as the coupling point between refrigerant-side capacity and water-side delivery stability.
  • Circulation pump + mixing valve: determines radiant supply temperature and ΔT stability; hunting often comes from sensor lag + actuator deadband.
  • Supply/return temps + flow + pressure: are the minimum set to prove circulation vs blockage/air-lock vs sensor error.
  • Remote interface (RS-485/Modbus or Ethernet): used to deliver evidence—fault class, snapshots, and counters—not a protocol-stack deep dive.

Interface evidence table (what to measure, what it proves)

Signal / Node Sensor / Method Typical range (field) What it proves Failure signature (common) Logging rule
Supply temp
Radiant supply pipe		 NTC / PT1000 clamp
or immersion well		 Low-to-mid temp water for radiant floors
(system-dependent)		 Confirms delivered water temperature at the loop entry; used with return temp for ΔT and thermal output estimation. Loose clamp: noisy steps; poor insulation: drift with ambient; slow response causes mixing valve hunting. 1–2 s
Return temp
Radiant return		 Same as supply Usually below supply; gap depends on load and flow Enables ΔT; rising return temp with low ΔT often indicates high flow or insufficient load pickup. Thermal coupling errors make ΔT appear “too small/negative,” breaking COP estimation. 1–2 s
Flow rate Hall/turbine flow sensor
or inferred from ΔP		 Varies by loop size and pump curve Proves circulation actually occurs; required to distinguish “capacity issue” vs “delivery issue.” Intermittent pulses: sticking rotor; flow reads OK but ΔP abnormal: sensor misread or bypass path. 1–2 s
ΔP / pressure
Across filter/loop		 Pressure sensor(s)
or ΔP transducer		 System-dependent; used as trend evidence Separates clog/valve restriction/air-lock from normal flow; validates whether “flow” reading is believable. High ΔP + low flow: blockage; normal ΔP + low flow: pump issue or closed valve; noisy pressure: cavitation/air. 2–5 s
Pump RPM / tach EC motor tach output
or driver estimate		 Varies by pump type Confirms actuator execution; essential when remote diagnosis claims “pump running.” RPM present but flow missing → air-lock / closed valve; RPM unstable → supply/driver issue. 1 s
Mixing valve position Stepper position
or analog feedback		 0–100% (normalized) Explains supply temp shaping and hunting; validates whether control action matches measured ΔT trends. Deadband/stiction: repeated small commands with no temp change; overshoot: sensor lag or wrong loop gain. 1–2 s
DC link voltage Divider to ADC Tracks input line and PFC state Proves brownout/UVLO behavior; ties transient faults (start/defrost) to power integrity evidence. Sag during defrost/start → resets / derating; spikes → OVP trips; ripple rise → capacitor aging. Event snapshot
(200–500 ms)
Inverter phase current Shunt + amplifier
or Hall sensor		 Load-dependent Separates “control-limited” from “hard overload”; supports OCP/root-cause classification. Current spikes aligned with valve transitions; high RMS for same capacity → mechanical or refrigerant-side issue. Event snapshot
(200–500 ms)
Ambient / frost state NTC + logic state Climate-dependent Explains defrost entry/exit and capacity derating triggers; prevents misdiagnosing “heat drop” as water-side only. Frost sensor drift → excessive defrost; missing state in logs → remote diagnosis becomes guesswork. 5–10 s
+ state changes

Note: “Typical range” is intentionally described as field-dependent to avoid false precision across different loop sizes, pump curves, and regional design temperatures. The diagnostic value comes from trends and cross-checks (ΔT vs flow vs ΔP).

Reference Architecture — Outdoor Unit + Hydronic Radiant Loop Evidence paths: power/drive · refrigerant actuation · hydronic delivery · diagnostics/log Power / Drive Path AC In PFC DC link Inverter + Current Sense Refrigerant Actuation Compressor EEV step/coil Reversing Valve (State) Hydronic Delivery HX / Buffer (optional) Pump Mix Valve Radiant Loop Supply · Return · Headers ΔT + Flow + ΔP proof Controller + Sensors + Logging Sensors Supply / Return Temp Flow + Pressure (ΔP) Ambient / Frost State MCU control loops state machine Logs fault codes snapshots counters Diagnostics I/F: RS-485 / Modbus or Ethernet → evidence delivery (not protocol deep dive) ICNavigator
Figure F2. Reference architecture: power/drive, refrigerant actuation, hydronic delivery, and diagnostics/log evidence paths.
Cite this figure Figure ID: F2 · ICNavigator

H2-3 — Control loops that matter (and how they couple)

This chapter defines a practical control coordinate system: what each loop controls, what evidence proves it is behaving, and how defrost/freeze-protect states override setpoints so faults are not misclassified.

Loop selection rule (keep it evidence-based)

Every loop below is defined by a controlled variable, an actuator, and 2–3 proof signals. If a claimed “loop issue” cannot be proven by these signals, treat it as a measurement integrity or override-state problem first.

Key loops (what controls what)

Loop A — Capacity

Compressor speed loop (capacity control)

  • Controlled variable: delivered capacity proxy (speed/power trend), not abstract thermodynamic quantities.
  • Actuator: inverter → compressor (BLDC/PMSM).
  • Proof signals: speed command vs speed estimate; inverter phase current; DC link voltage/power trend.
  • Common failure signature: command rises but current/power does not → derating, protection limit, or measurement error.
Speed cmdPhase currentDC link
Loop B — Refrigerant-side actuation (high-level)

EEV control (state-driven stability)

  • Controlled variable: stable EEV state consistent with operating mode (heating/defrost transitions).
  • Actuator: EEV step/coil driver.
  • Proof signals: EEV position/step count; driver status; mode/defrost state bits.
  • Common failure signature: frequent state changes with weak system response → mechanical stiction, drive undervoltage, or missing logs.
EEV positionDriver statusMode state
Loop C — Water delivery

Pump control (flow/ΔT stability)

  • Controlled variable: flow (or flow-derived stability) and its impact on ΔT trend.
  • Actuator: EC pump speed/PWM.
  • Proof signals: pump RPM/tach; flow reading; ΔP/pressure trend (if available).
  • Common failure signature: RPM present but flow missing → air-lock, closed valve, or bypass path.
Pump RPMFlowΔP
Loop D — Radiant supply shaping

Mixing valve control (supply temperature shaping)

  • Controlled variable: radiant supply temperature (and/or ΔT target stability).
  • Actuator: mixing valve position (stepper or analog feedback).
  • Proof signals: valve position; supply temp response; sensor lag/filtered sampling window.
  • Common failure signature: valve hunting usually indicates sensor lag + deadband + loop gain mismatch, not only a “bad valve.”
Valve positionSupply tempFilter lag
Loop E — Overrides

Defrost / freeze-protect interactions (what gets overridden)

  • Controlled variable: system safety and survivability states (freeze avoidance, stable transitions).
  • Actuator overrides: compressor/pump/valves may be forced to preset actions during defrost or freeze-protect.
  • Proof signals: defrost/freeze-protect state bits; override reason; start/end timestamps; affected setpoints.
  • Common failure signature: “heat drop” during defrost misread as water-side fault when override states are not logged.
Defrost stateOverride reasonSetpoint rewrite

Loop coupling map (if X changes, check Y)

  • If mixing valve hunts (rapid position oscillation): check supply sensor response time (contact + insulation) and filter window; confirm valve deadband/stiction before changing gains.
  • If ΔT collapses while supply temperature looks “fine”: check flow (pump RPM vs flow) and return sensor integrity; verify ΔP trend to rule out bypass/air-lock.
  • If compressor command rises but heating performance does not: check inverter current/DC link evidence; then cross-check hydronic delivery (flow + ΔT) to separate capacity from delivery.
  • If frequent defrost coincides with heat delivery drops: check defrost state transitions and overridden setpoints; ensure snapshots include valve states and DC link during entry/exit.
  • If pump RPM is stable but ΔT is noisy or negative: suspect ΔT measurement integrity (placement/lag) before concluding “loop instability.”
Loop Coupling Map — What Controls What Signals are chosen for proof: command → execution → measured response → logged evidence MCU Control loops · states · limits Loop A: Compressor Speed Speed cmd Phase current DC link Loop B: EEV State EEV position Driver status Mode state Hydronic Delivery Evidence Loop C: Pump Pump RPM Flow ΔP Loop D: Mixing Valve Valve position Supply temp ΔT Integrity Supply / Return temps Loop E: Overrides Defrost / Freeze-protect Logs (Proof) Fault codes · snapshots · counters ICNavigator
Figure F3. Loop coupling map: commands, proof signals, and override states that must be logged to avoid misdiagnosis.
Cite this figure Figure ID: F3 · ICNavigator

H2-4 — ΔT capture: sensing chain, placement, accuracy, and sampling strategy

ΔT is the evidence currency for this topic. If ΔT is wrong, diagnostics and COP estimates become untrustworthy. This chapter treats ΔT as an integrity problem: sensor choice, placement, lag, and field validation steps.

Sensor options (NTC vs PT1000/RTD) — choose by failure signatures

  • NTC clamp sensors: cost-effective but sensitive to contact quality, self-heating, and ADC reference stability; poor contact often appears as step noise and drift.
  • PT1000/RTD: better linearity but more sensitive to lead resistance and installation method; incorrect wiring or contact can bias ΔT and break COP estimation.
  • Selection rule: prioritize the option that yields repeatable trends under insulation and contact constraints, because trend integrity matters more than a single absolute value.

Placement pitfalls (most field failures originate here)

  • Stratification / non-mixed points: measuring too close to mixing junctions can read blended water rather than true supply/return.
  • Pipe contact errors: loose clamps create noise and “teleporting” temperature steps.
  • Insulation missing: ambient air affects the pipe sensor; return readings often drift more, creating a fake ΔT shrink.
  • Response time mismatch: slow supply sensor response introduces phase lag, causing mixing valve hunting and overshoot.

Sampling & filtering (avoid lag that destabilizes control)

  • Over-filtering risk: smoothing reduces noise but adds delay, which destabilizes mixing valve and pump coordination.
  • Recommended pattern: a slow trend channel (1–2 s) for steady-state analysis plus a fast event snapshot (200–500 ms window) on defrost start/stop and trips.
  • Cross-check rule: if supply temp changes but return temp shows no coherent delayed response, treat ΔT as untrusted until placement/contact is verified.

Two “first measurements” to validate ΔT quality in the field

  1. Co-located cross-check: place a second probe or contact thermometer at the same pipe point and compare trend alignment. Large divergence indicates contact/insulation issues.
  2. Small step response test: apply a small controlled change (pump speed or mixing valve position) and observe whether supply and return temperatures respond with a reasonable delay and direction. Lack of coherent response indicates lag/placement problems.

Deliverable checklist: ΔT sanity checks + symptoms of bad ΔT

ΔT sanity checks (proof-oriented)
  • ΔT should not cross zero repeatedly in stable heating; frequent sign flips suggest contact/placement or filtering artifacts.
  • Supply and return should move coherently with return lagging; return moving “first” often indicates ambient coupling or sensor error.
  • ΔT trend should correlate with flow changes; if flow increases and ΔT stays random, at least one sensor chain is untrusted.
  • Cross-check ΔT with ΔP/pressure trend when available to rule out bypass/air-lock misreads.
Symptoms of bad ΔT (common misdiagnoses)
  • False “capacity loss” diagnosis when return sensor drifts or is ambient-coupled.
  • False “pump insufficient” conclusion when supply sensor lag compresses ΔT.
  • COP estimate jumping wildly due to ΔT noise dominating thermal-out calculation.
  • Mixing valve “unstable control” blamed when the real cause is sensor phase lag and deadband interaction.
ΔT Measurement Integrity — Make ΔT Trustworthy Placement · contact · insulation · sampling → ΔT compute → logs/COP confidence Supply / Return Pipes Supply Return Correct Contact Insulation Stable trend Wrong Loose clamp No insulation Lag / drift Sensing Chain Sensor ADC Filter lag risk ΔT Compute Supply − Return Logs / COP confidence grade Field Validation (First Measurements) 1) Co-located Cross-check Second probe on same pipe point Compare trend alignment 2) Small Step Response Change pump or mixing valve slightly Check coherent supply/return response ICNavigator
Figure F4. ΔT integrity: correct placement and sampling prevent false diagnoses and stabilize mixing control.
Cite this figure Figure ID: F4 · ICNavigator

H2-5 — Flow & pressure sensing: proving circulation vs guessing

“Not enough heat” must be separated into a delivery problem (circulation/valves/air-lock) versus a capacity problem (compressor/derating). This chapter treats flow and pressure as proof signals that cross-check ΔT.

Circulation proof rule (ΔT + flow + pressure must agree)

A single sensor can lie. Circulation is proven only when ΔT trend, flow evidence, and pressure/ΔP evidence form a coherent story across mode transitions and pump commands.

Flow sensing options (choose by diagnostic strength)

Option A — Hall / Turbine
  • Best for: low-cost trending and “flow exists / not exists” proofs.
  • Typical artifacts: intermittent pulse dropouts from bubbles, stiction, or debris.
  • Proof pairing: always compare with pump RPM/tach and ΔP trend to avoid false confidence.
Pulse continuityRPM cross-checkBubble signature
Option B — Differential Pressure (ΔP inference)
  • Best for: blockage evidence and resistance change detection.
  • Typical artifacts: pump cavitation shows as noisy ΔP and unstable ΔT.
  • Proof pairing: combine with valve position and pump command to separate “restriction” vs “forced bypass.”
ΔP trendRestriction proofCavitation noise
Option C — Ultrasonic
  • Best for: stable long-term flow trending and low-maintenance sensing.
  • Typical artifacts: air entrainment can reduce accuracy; treat “unstable readings” as evidence of bubbles.
  • Proof pairing: validate against ΔT response to small pump steps (coherent response matters).
Stable trendingAir evidenceStep response
Pressure sensing (head / blockage / air-lock)
  • Pump head evidence: outlet pressure and ΔP across loop correlate with commanded RPM.
  • Blockage evidence: ΔP rises while flow drops (or inferred flow drops).
  • Air-lock evidence: unstable ΔP + flow pulse dropouts + ΔT coherence loss.
Head vs RPMΔP vs flowNoise patterns

Failure signatures (what the evidence looks like)

  • Bubbles / air-lock: flow pulses intermittently missing, ΔP noisy, ΔT becomes erratic or flips sign during transients.
  • Clog / restriction: ΔP rises, flow falls, ΔT can inflate (heat stays “in the water” but delivery weak) or collapses (if circulation becomes intermittent).
  • Stuck valve / wrong valve state: normal pump RPM with abnormal ΔP/flow correlation; supply looks “OK” but return response is delayed or absent.
  • Wrong pump curve / insufficient head: pump command increases but flow barely changes; ΔP stays low; ΔT can grow (low flow) while comfort stays poor.

Discriminator table (symptom → ΔT trend → flow/pressure evidence → likely cause)

Symptom ΔT trend Flow evidence Pressure / ΔP evidence Likely cause First confirmation
Supply temp looks OK, rooms still cold ΔT small or unstable Flow low or intermittent; RPM may be normal ΔP noisy or inconsistent with RPM Air-lock / bubbles; intermittent circulation Check air purge behavior and pulse continuity during small pump step
Heating slow; short bursts of warmth then fades ΔT flips or drifts Flow pulses drop out; flow reading sporadic Pressure signal noisy; ΔP spikes then collapses Bubble entrainment / cavitation events Correlate events with pump RPM and valve position changes
System trips into protection when demand rises ΔT may collapse abruptly Flow does not increase as commanded ΔP rises sharply at higher RPM Restriction/clog or partially closed valve Inspect filter/strainer state and valve commanded state
Comfort poor; pump command higher does not help ΔT grows (low flow) Flow barely changes with RPM ΔP remains low even at higher RPM Wrong pump curve / insufficient head Compare head evidence versus expected RPM response; check bypass paths
ΔT looks “great” but feels wrong ΔT large but inconsistent across time Flow reading stable but mismatched with return response ΔP contradicts flow or shows abnormal noise Flow sensor bias or placement artifact Cross-check with ΔP inference or secondary flow method

Note: Diagnostic strength improves when flow and ΔP are evaluated as trends against pump commands and mode states (e.g., defrost transitions).

Flow & Pressure Proof Map — Circulation Evidence Use flow + ΔP + ΔT coherence to separate delivery faults from capacity limits Radiant Loop Supply Return Pump RPM / Tach Mixing Valve Position Filter Valve Flow: Hall/Turbine Flow: Ultrasonic Flow: ΔP Pressure Pout / Pin ΔP across loop ΔT Supply − Return Signatures Air bubbles Clog Stuck valve Wrong pump curve ICNavigator
Figure F5. Flow and pressure proof map: cross-check flow, ΔP and ΔT to confirm circulation and isolate restriction or air-lock signatures.
Cite this figure Figure ID: F5 · ICNavigator

H2-6 — Drives & power chain (only what supports control + evidence)

Drives are included only as they impact stability, trips, and remote diagnostics. Each drive block is paired with the minimum signals required to confirm trip class and isolate whether the fault is electrical, thermal, or state-driven.

Drive evidence rule (trip class must be provable)

A trip label is actionable only when it can be confirmed by a time-aligned snapshot: DC link + current sense + driver status + temperature + state bits (mode/defrost).

Compressor inverter (evidence points that matter)

  • Gate driver status: driver fault/UVLO flags distinguish power-stage events from control derating.
  • Current sense: phase current peaks and trend confirm true OCP and identify pre-trip spikes.
  • DC link monitoring: sag/spike evidence supports UVLO/OVP classification and correlates with resets.
  • Mode coupling: defrost entry/exit often changes operating constraints; snapshots must include the state bits.

Valve & actuator drives (state + execution confirmation)

EEV stepper/coil
  • Log: position/step count, enable, driver status (and drive current if available).
  • Evidence goal: distinguish mechanical stiction from undervoltage or disabled drive.
Reversing valve coil
  • Log: coil ON/OFF with timestamp, mode state, transition counters.
  • Evidence goal: correlate transitions with capacity drops and defrost cycles.
Mixing valve actuator
  • Log: target vs actual position (if available), supply temperature response, sensor lag marker.
  • Evidence goal: separate “stuck valve” from “ΔT / placement artifact” and control lag.
Pump drive (BLDC/EC)
  • Log: PWM/command, tach/RPM, optional power/current trend.
  • Evidence goal: prove execution and correlate RPM-to-flow consistency (ties back to H2-5).

Design constraints (minimal rugged note)

  • Surge/EFT risk: DC link spikes/sags and MCU resets can mimic “random trips” if snapshots are missing.
  • EMI risk: tach/flow pulses and ADC readings may glitch; use counters and plausibility checks rather than trusting a single sample.

Deliverable: trip taxonomy (OCP/OVP/UVLO/OTP) + confirmation signals

Trip class What it looks like Must-log signals Fast discriminator Typical root causes (scope-safe)
OCP Immediate shutdown or rapid derating during load increase Phase current peak; gate driver fault/status; timestamp; mode/defrost state Current spike aligned to trip edge Mechanical load anomaly, short transient, incorrect current threshold, power-stage fault
OVP Trip coincident with voltage spike; may happen at transitions DC link spike snapshot; driver status; line/rectified trend (if available) DC link exceeds limit before trip Surge event, regen transient, clamp insufficiency, measurement bias
UVLO Reset, brownout, or forced low-power mode under demand DC link sag; MCU reset reason; driver UVLO flags; load/current context Voltage sag with reset reason Weak supply, inrush, PFC limit, wiring drop, excessive load step
OTP Gradual derating then shutdown; repeatable after warm-up Thermal sensor(s) trend; derating state bit; fan/pump states; timestamp Temperature crossing threshold with derating flag Insufficient cooling, blocked airflow (unit-level), sustained overload, sensor placement error
Drives & Trip Evidence Map — Minimal Signals Power chain + actuators + proof signals → trip taxonomy → snapshot logs Power Chain (Compressor) AC In PFC DC link Vdc Inverter Vdc sense Iphase sense Driver fault Compressor Actuator Drives (Log execution) EEV drive position + status Reversing coil ON/OFF + time Pump drive cmd + tach Mixing valve actuator target/actual + supply response Trip taxonomy OCP OVP UVLO OTP Snapshot logs time-aligned proof set: Vdc + Iphase + driver status Temps + mode/defrost state Valve/pump execution signals ICNavigator
Figure F6. Drives and power-chain evidence map: minimal signals required to classify OCP/OVP/UVLO/OTP and support remote diagnostics.
Cite this figure Figure ID: F6 · ICNavigator

H2-7 — Energy metering & COP estimation (electrical-in vs thermal-out)

Practical performance measurement requires two coherent stories: electrical input and thermal output estimate. COP is meaningful only when ΔT and flow are trustworthy and operating states (e.g., defrost) are properly labeled.

Boundary (device-side, not HEMS)

Metering is limited to equipment-side signals (AC line or DC link, ΔT, flow). Results are for engineering diagnostics and trend verification, not utility billing or whole-home energy management.

Electrical input: where to meter (AC line vs DC link)

Option A — AC line metering (system input)
  • What it proves: true equipment input including auxiliary loads (controls, pumps, valve drives).
  • Accuracy tradeoffs: PF, harmonics, phase error; low-power segments require careful sampling windows.
  • Best use: whole-unit trend, validation of “energy-in” across modes and transitions.
System-level inputPF / harmonic riskTrend-friendly
Option B — DC link metering (compressor-side proxy)
  • What it proves: inverter-side energy that correlates tightly with capacity commands and trip evidence.
  • Accuracy tradeoffs: excludes front-end losses and some auxiliary loads; boundary must be labeled.
  • Best use: capacity diagnostics, derating correlation, and trip analysis (ties to H2-6).
Capacity correlationBoundary-sensitiveTrip-friendly

Thermal output estimate: ΔT × flow × fluid heat capacity

  • Thermal-out estimate: heat output can be approximated from ΔT and flow with an assumed Cp for the working fluid.
  • Calibration note: fluid mixture and sensor scaling create systematic offsets; trend coherence matters more than a single absolute number.
  • Sampling note: ΔT and flow must be evaluated in the same time window; asynchronous sampling creates artificial COP spikes.
  • State note: defrost/freeze-protect segments must be labeled or excluded to avoid mixing incompatible regimes.

COP estimate: when it’s meaningful, when it lies

Meaningful Engineering COP trend
  • ΔT passes sanity checks (stable sign, coherent supply/return dynamics).
  • Flow is consistent with pump RPM and/or ΔP evidence (no pulse loss patterns).
  • Metering boundary is explicit (AC-input COP vs DC-link proxy).
Lies Common false COP patterns
  • Bad ΔT: poor contact/insulation or heavy filtering causes lag and oscillation artifacts.
  • Bad flow: bubbles, stiction, or bypass paths break coherence between RPM, ΔP and flow.
  • State mixing: defrost segments included without labeling corrupt averages and trends.

Deliverable: COP confidence checklist (High / Medium / Low)

Confidence level Required conditions Automatic downgrade triggers How to use the COP number
High ΔT sanity checks pass; flow correlates with pump RPM and/or ΔP; defrost state filtered or labeled; metering boundary explicit (AC or DC link). Flow pulse loss, ΔT sign flipping, sensor error flags, or unlabeled defrost segments. Use for performance trend, comparative commissioning checks, and remote verification of stability changes.
Medium ΔT and flow mostly stable but partial evidence missing (e.g., no ΔP); DC link metering used with boundary label; occasional missing samples tolerated. Increasing noise metrics, rising retry counters, or inconsistent RPM-to-flow response. Use for trend direction only; avoid absolute claims; prioritize additional proof signals in snapshots.
Low ΔT or flow not trustworthy (noise, drift, dropouts); defrost state not available; sampling windows not aligned; metering boundary unclear. Frequent invalid flags; counters indicate missing/CRC errors; state mixing suspected. Do not interpret COP; first repair measurement integrity (ΔT/flow) and logging schema (H2-8).
COP Evidence Map — Electrical In vs Thermal Out COP requires coherent metering boundary + trustworthy ΔT and flow + state labeling Electrical input AC meter P, PF DC link meter Vdc × Idc Boundary label: AC-input COP vs DC-link proxy Thermal output estimate ΔT Tsupply − Treturn Flow L/min or kg/s Thermal-out ≈ ΔT × Flow × Cp (fluid) Calibration: Cp/mixture + scaling + time alignment COP estimate COP ≈ Thermal-out / Electrical-in Use consistent windows + state filters Confidence levels High Medium Low Drivers: ΔT valid · Flow coherent · Defrost labeled · Sampling aligned Downgrade on: pulse loss · sign flips · CRC/errors · state mixing ICNavigator
Figure F7. COP evidence map: choose a metering boundary (AC vs DC link), estimate thermal-out from ΔT and flow, and attach confidence levels.
Cite this figure Figure ID: F7 · ICNavigator

H2-8 — Remote diagnostics: what to log so you can actually debug

Remote diagnostics works only when logs contain time-aligned proof signals. This chapter defines an event-first logging model with snapshot bundles, counters, and communication reliability evidence—without drifting into platform architecture.

Remote diagnostics rule (event + snapshot + counters)

Every actionable fault must be supported by timestamped events, a snapshot bundle captured at the fault edge, and counters that turn intermittent issues into measurable evidence.

Event log structure (make faults self-explanatory)

  • Required fields: timestamp, sequence ID, fault code, trip class, operating state (heating/defrost/freeze-protect), snapshot ID.
  • Why sequence ID matters: reveals drops, reordering, and overwrites that otherwise look like “random missing data.”
  • Why state bits matter: defrost and protection overrides change setpoints; events without state are not diagnosable.

Snapshot bundle (minimum useful set)

Hydronic delivery proof
  • Tsupply, Treturn, ΔT
  • Flow
  • Pump RPM (tach)
  • Mixing valve position
Capacity & electrical proof
  • Compressor speed
  • Inverter current (Iphase)
  • DC link voltage (Vdc)
Environment & state proof
  • Pressures / ΔP (if available)
  • Ambient / frost state
  • Defrost state and transition markers
Validity flags (stop bad inference)
  • ΔT_valid, Flow_valid
  • Sensor CRC / error flags
  • Pulse-loss / missing-sample indicators

Counters (turn intermittent faults into statistics)

  • Defrost counters: defrost count, defrost duration histogram (if feasible), entry/exit timestamps.
  • Trip counters: count by class (OCP/OVP/UVLO/OTP), plus “last trip timestamp” per class.
  • Retry counters: restart attempts, compressor retry, comm reconnect.
  • Sensor integrity: ADC out-of-range count, CRC error count, flow pulse-loss count.

Communications (RS-485/Modbus or Ethernet) — reliability evidence only

RS-485 / Modbus evidence
  • CRC error count, frame timeout count, retry count
  • bus idle time anomalies, re-init count
  • sequence gaps (if events are polled)
Ethernet evidence
  • link up/down count, reconnect count
  • socket reset / keepalive timeout
  • packet drop indicator (if available)

Deliverable: minimum viable log schema (MVLS)

  • Event record: timestamp · sequence_id · fault_code · trip_class · mode_state · snapshot_id · comm_status_summary (optional)
  • Snapshot record: Tsupply · Treturn · ΔT · Flow · Pump_RPM · MixingValve_Pos · Compressor_Speed · Vdc · Iphase · Pressure/ΔP (opt) · Ambient/Frost · Defrost_State · validity_flags
  • Counters: defrost_count · trip_count_by_class · reboot_count · retry_count · comm_crc_err · comm_timeout · comm_retry · link_flap · flow_pulse_loss · sensor_crc_err
  • Trigger strategy: on_trip · on_defrost_enter/exit · on_flow_drop/pulse_loss · periodic baseline snapshot
Minimum Viable Log Pipeline — Event + Snapshot + Counters Remote debugging requires time-aligned proof signals and comm reliability evidence Signals (sources) Tsupply · Treturn · ΔT · Flow · Pump_RPM MixingValve_Pos · EEV_Pos (opt) Compressor_Speed · Iphase · Vdc Pressure/ΔP (opt) · Ambient/Frost Defrost_State · Mode_State · Validity_Flags Sensor CRC · Pulse loss · Error counters Event detector on_trip / on_defrost / on_flow_drop event = timestamp + code + state + snapshot_id + sequence_id Snapshot bundler time-aligned bundle (proof set) include validity_flags + counters for confidence gating Event log ring buffer sequence gaps Counters trip_by_class defrost_count Comms RS-485/ETH Reliability evidence: CRC_err · timeout · retry · link_flap ICNavigator
Figure F8. Minimum viable log pipeline: event-first records with snapshot bundles, counters, and comm reliability evidence for remote debugging.
Cite this figure Figure ID: F8 · ICNavigator

H2-9 — Protection & safety logic inside THIS controller (keep it local)

Protection is actionable only when it is expressed as controller-local triggers, deterministic actions, and mandatory proof logs. This section keeps safety tied to heat pump + hydronics behavior, not certification theory.

Local safety scope (what “local” means)

Local protection reacts using available sensors (ΔT, flow, pressures/ΔP, Vdc, Iphase, ambient/frost, state bits) and local actuators (compressor inhibit, pump force, mixing valve clamp, alarm/event logging).

Freeze protection (conditions → actions)

  • Trigger candidates: low ambient/frost state, low Tsupply/Treturn, or persistent near-zero ΔT while flow exists.
  • Primary actions: force pump to circulate, clamp mixing valve to a safe position, and mark state as freeze-protect.
  • Escalation: if flow is absent or sensors invalid, upgrade to alarm + lockout with evidence snapshot.

Over-temp / floor safety (mixing valve + pump response)

  • Trigger candidates: Tsupply above floor safety limit or rapid temperature rise with stable pump command.
  • Primary actions: clamp mixing valve to reduce supply temperature; keep pump running to remove residual heat.
  • Stability note: apply hysteresis/hold time to avoid oscillation between comfort control and protection.

Dry-run / no-flow protection (prove circulation)

  • Trigger candidates: pump RPM present but flow ≈ 0 (or pulse-loss pattern), or ΔP signature indicates blockage/air lock.
  • Primary actions: stop or limit compressor demand, force pump purge window, and capture “no-flow” proof bundle.
  • Discriminator: differentiate “true no-flow” vs “flow sensor failure” using RPM↔ΔP↔ΔT coherence.

High-pressure / low-pressure trip evidence mapping

HP High-pressure evidence
  • Pressure rising trend into limit + compressor speed/current correlation.
  • State bits (heating/defrost) captured to avoid mislabeling transitions.
  • Action: compressor inhibit + fault event + retry policy with lockout timer.
LP Low-pressure evidence
  • Pressure falling/unstable + capacity command present + mode state captured.
  • Check sensor validity flags and sampling window alignment.
  • Action: compressor inhibit + fault event + conditional restart after stabilization.

Leak / abnormal ΔP detection (hydronic)

  • Abnormal ΔP: ΔP increases while flow does not increase → likely restriction/clog; ΔP noise spikes → bubbles/cavitation patterns.
  • Leak tendency (local evidence): pressure decay after pump off, unexpected refill behavior, or persistent mismatch between RPM and delivery evidence.
  • Action goal: downgrade capacity demand and preserve evidence snapshots; avoid “silent failure” without logs.

Deliverable: Protection action matrix (trigger → action → what you must log)

Trigger (local condition) Immediate action (actuators) Lockout / recovery rule Must-log bundle (snapshot + counters) Why it matters here
Freeze risk: ambient/frost low + Tsupply/Treturn below threshold Force pump · clamp mixing valve · set Freeze-Protect state Exit only after temp margin holds for N minutes; prevent rapid toggling Tsupply/Treturn/ΔT · Flow · Pump_RPM · Mixing_Pos · Ambient/Frost · Mode_State · defrost_count Prevents freezing while preserving proof signals for remote verification
Over-temp: Tsupply above safety limit or rapid rise Clamp mixing valve down · keep pump running · reduce compressor demand Hysteresis + minimum hold time; log exit condition Tsupply/Treturn/ΔT · Flow · Pump_RPM · Mixing_Pos · Compressor_Speed · Vdc/Iphase Floor safety depends on valve+flow coupling, not a single sensor
No-flow / dry-run: Pump_RPM present but Flow≈0 or pulse-loss Inhibit compressor · purge/force pump window · raise alarm event Retry limited; lockout escalates if repeated within time window Flow · pulse_loss_count · Pump_RPM · ΔP/pressure (opt) · ΔT trend · trip_count_by_class Separates delivery failure from capacity failure and prevents damage
HP trip: pressure rising into limit with correlated Iphase Compressor inhibit · fault event · controlled restart policy Restart only after stabilization; backoff timers; class-based counters Pressure · Compressor_Speed · Iphase · Vdc · Mode_State · fault_code · sequence_id Evidence mapping avoids false blame on ΔT/flow when root is capacity-side
LP trip: pressure falling/unstable with demand present Compressor inhibit · fault event · conditional restart Require stable pressure window; invalidate COP during LP fault Pressure · Compressor_Speed · Vdc/Iphase · validity_flags · retry_count · fault_code Prevents misleading COP and supports remote root-cause narrowing
Abnormal ΔP: ΔP↑ while flow not rising; or ΔP noise spikes Reduce capacity demand · keep circulation as needed · log anomaly Clear only when coherence returns (RPM↔flow↔ΔP) for N samples ΔP/pressure · Flow · Pump_RPM · Tsupply/Treturn · comm_crc_err (if relevant) Hydronic restrictions and air patterns are diagnosable only with ΔP evidence
Protection Map — Trigger → Action → Must-Log Evidence Controller-local safety logic tied to hydronic delivery + compressor evidence Local triggers Freeze Ambient/Frost + Tsupply/Treturn Over-temp Tsupply limit + rise rate No-flow / dry-run RPM↔Flow↔ΔP mismatch HP / LP Pressure + Iphase + Mode Abnormal ΔP / leak ΔP trend + decay Validity flags sensor CRC / pulse loss Safety logic trigger classify + hysteresis action = actuator commands + log requirements Actions Compressor inhibit Pump force / purge Mixing valve clamp Alarm + lockout Must-log evidence (snapshot bundle) ΔT · Flow · RPM Pressure · ΔP Vdc · Iphase Mode/Defrost/Frost state · Fault code · Sequence ID · Counters ICNavigator
Figure F9. Protection map: local triggers feed safety logic that commands compressor/pump/valve actions and enforces must-log evidence bundles.
Cite this figure Figure ID: F9 · ICNavigator

H2-10 — IC/function selection map (with example part categories)

The selection map is organized by function blocks and the evidence/control needs of this controller. It provides procurement-ready requirements without turning into a brand catalog.

Selection principles (tied to this page’s evidence chain)

  • Diagnosability first: time-aligned snapshots (ΔT/flow/pressure + Vdc/Iphase + state bits) must be feasible.
  • Stability first: sensing latency/noise influences mixing valve control and COP confidence.
  • Recoverability first: log memory write strategy determines whether remote debugging is possible after trips/resets.

Deliverable: compact selection table (category-level MPN types)

Function block Key specs (what to require) Why it matters here Example MPN types (category-level)
MCU / Control SoC motor-control PWM resources; multi-channel ADC; fast capture window for events; safety IO (fault pins, watchdog); comm interfaces (RS-485 UART, Ethernet MAC/PHY support). Enables MVLS snapshots and protection actions without timing drift; supports state bits and counters at fault edges. Motor-control MCU class · Industrial MCU class · MCU + external ADC architecture
Gate driver (inverter) robust fault reporting (OC/UVLO/desat class); compatible with power stage; fast fault response; clear fault pin/status readability. Trip taxonomy requires proof (driver fault + current + Vdc) to distinguish real power-stage faults from control derates. 3-phase gate driver family · Half-bridge driver family · Intelligent power module driver class
Current sense path shunt/Hall options; bandwidth for trip capture; dynamic range; noise immunity; optional isolation where needed. OCP classification and “spike vs sustained” evidence depends on capture fidelity around trip edges. Shunt amplifier family · Hall current sensor IC class · Isolated current sense amplifier class
DC link monitoring stable divider/reference; ADC range and sampling strategy; ripple/undervoltage event capture capability. UVLO/OVP evidence and correlation with compressor demand is only credible with Vdc snapshots. High-voltage ADC front-end class · Precision reference family · Supervisor/monitor IC class
Energy metering (optional AC input) real power + PF handling; harmonic tolerance; line-voltage/current sensing interfaces; calibration support. Enables AC-boundary COP and system-level energy-in trend; avoids ambiguous “DC-only” energy claims. Single/3-phase energy metering IC family · Isolated metering AFE class
Temp sensor interface (NTC/RTD) low-noise excitation/reference; wiring error detect; linearization support; sampling/filter knobs for loop stability. ΔT quality controls COP validity and mixing valve stability; bad ΔT creates false diagnostics and oscillations. RTD interface IC family · Precision ADC + front-end class · NTC AFE class
Pressure / ΔP conditioning ratiometric conditioning; protection against transients; noise filtering without excessive lag; diagnostics flags. Abnormal ΔP/leak evidence depends on stable trends; laggy filters hide bubbles/clog signatures. Instrumentation amplifier class · Sensor AFE class · Pressure interface ADC family
EEV stepper / coil drive step control + stall/oc detect (if available); position tracking; fault reporting; thermal robustness. Remote debugging needs “command vs position vs effect” evidence to separate actuator failure from sensing errors. Stepper motor driver family · Coil driver / smart switch class
Mixing valve actuator drive H-bridge/stepper/servo interface (by actuator type); position feedback capture; fault detect. Over-temp protection and supply shaping rely on deterministic valve response and measurable position evidence. H-bridge driver family · Stepper/actuator driver class · Position feedback interface class
Pump drive interface PWM/analog command support; tach capture; optional current/power trend; EMC-hardened input filtering. No-flow discrimination requires RPM evidence and coherence with flow/ΔP; without tach the diagnosis collapses. BLDC/EC motor controller class · Tach capture timer + driver interface class
Nonvolatile memory for logs endurance; power-fail robustness; ring-buffer strategy; write amplification control; fast commit for events. MVLS needs reliable preservation of “trip edge” snapshots; without robust NVM, remote debugging fails after resets. FRAM family · SPI NOR flash class · EEPROM class (limited endurance) · Wear-leveling strategy
RS-485 / Ethernet physical layer (optional) robust transceiver; ESD protection capability; error counters visibility; link status reporting. Remote diagnostics requires reliability evidence (CRC/timeouts/reconnect) to separate comm faults from system faults. RS-485 transceiver family · Ethernet PHY class · Isolated transceiver class

Note: Example MPN types are intentionally category-level. If concrete part numbers are needed, request “List concrete MPNs by function block”.

IC / Function Selection Map — Evidence-Driven Controller Select blocks that enable snapshots, protection actions, and reliable logs Sensing + AFE ΔT sensors (NTC/RTD) → Temp AFE/ADC Flow → pulse/ultrasonic/ΔP inference Pressure/ΔP → conditioning + ADC Vdc monitor → divider/ref + ADC Iphase → shunt amp / Hall sense State bits → frost/defrost validity MCU / Control SoC PWM + timers (pump/valves/inverter) ADC capture windows + fault pins Event detector + snapshot bundler Counters + validity gating NVM for logs FRAM / SPI NOR / EEPROM (strategy) Actuation + drives Inverter gate driver + power stage EEV stepper / coil driver Mixing valve actuator driver Pump interface (PWM + tach) Optional Energy metering · RS-485/ETH ICNavigator
Figure F10. Function selection map: sensing AFEs feed the MCU for control + snapshots; logs persist to NVM; actuator drives execute protection actions and stable control.
Cite this figure Figure ID: F10 · ICNavigator

H2-11 — Validation & commissioning test plan (bench → loop → field)

A repeatable commissioning plan must prove control integrity, hydronic delivery, metering credibility, and remote diagnosability using pass/fail signals.

Staging model

Bench: rails + sensing + actuators Loop: ΔT/flow/mixing stability Field: transitions + robustness + logs Always: fault injection → log completeness

Each stage uses a checklist and acceptance metrics tied to controller-visible signals (Tsupply/Treturn/ΔT, Flow, Pump_RPM, Mixing_Pos, Compressor_Speed, Vdc, Iphase, State bits, Fault codes, Counters).

Bench bring-up (prove rails, sensing, and actuation)

B1Power rails & reset integrity
  • Measure: Vdc + low-voltage rails (3.3V/5V as applicable), reset reason, reboot counter.
  • Pass: no reset loops; rail dips do not coincide with false trips; reboot_count stays stable.
  • Fail signals: Vdc sag events without load change; repeated reset_reason patterns; log gaps.
B2Inverter current sense calibration
  • Measure: Iphase offset/gain at known points; trip-edge capture window; driver fault pin status.
  • Pass: stable offset; gain error within target; trip-edge snapshots include Vdc + Iphase + fault pin.
  • Fail signals: drifting offset; clipped peaks; inconsistent Iphase vs commanded compressor speed.
B3Valve actuation tests (EEV / reversing / mixing)
  • Measure: command vs position/step count (if available), coil drive status, response time trend.
  • Pass: position changes are observable; faults are latched with event snapshots.
  • Fail signals: command issued but no movement evidence; frequent coil faults without current proof.
B4Pump interface validation
  • Measure: Pump_RPM tach capture; Flow response; ΔP/pressure trend (if available).
  • Pass: RPM ↑ leads to Flow ↑ and ΔP trend coherence; pulse-loss counter remains low.
  • Fail signals: RPM present but Flow≈0; ΔP noise spikes; tach dropout under EMI events.

Loop tests (prove ΔT/flow/mixing stability and transitions)

  • ΔT step response: apply mixing valve step or capacity step → validate Tsupply/Treturn alignment, ΔT lag, and noise floor.
  • Flow sweep: sweep Pump_RPM across range → verify Flow and ΔP coherence; identify air lock/clog patterns.
  • Mixing stability: hold supply target → evaluate overshoot, oscillation, valve activity rate, and settle time.
  • Freeze/defrost transitions: enter/exit transitions → ensure actions match protection matrix and logs include mode/state bits.

Metering tests (protect COP credibility)

  • Known operating points: compare electrical-in trend vs thermal-out trend at several stable points (avoid chasing absolute COP only).
  • Offset checks: verify ΔT offset and Flow scaling; confirm “COP confidence” downgrades when sensors become unreliable.
  • Sanity cases: introduce pulse loss or ΔT lag → confirm COP is flagged low-confidence rather than reported as a clean number.

Remote diagnostics tests (fault injection → log completeness verification)

  • Inject no-flow: force Flow≈0 with RPM present → event must include Flow, Pump_RPM, ΔP (if), ΔT, counters.
  • Inject over-temp: exceed Tsupply threshold → event must include Tsupply/Treturn, Mixing_Pos, mode/state, action taken.
  • Inject DC link sag: reduce Vdc margin → event must include Vdc, Iphase, compressor speed, trip class UVLO/OVP.
  • Inject comm errors: raise CRC/timeouts → logs must prove comm failure vs missing data generation (sequence gaps).

Deliverable: staged checklist + acceptance metrics (pass/fail signals)

Stage Step (what to do) Stimulus Measure (proof signals) Pass/Fail metric If fail, first suspect
Bench Rail & reset integrity Power cycle + load step Vdc + LV rails + reset_reason + reboot_count Pass: no reset loops; rail dips do not align with false trips Supervisor thresholds / wiring / ground reference / sampling window
Bench Current sense calibration Known current points + trip-edge capture Iphase offset/gain + Vdc + driver fault pin Pass: stable offset; peaks captured without clipping; consistent correlation Shunt amp bandwidth / ADC range / anti-alias filter / layout coupling
Loop ΔT step response Mixing valve step or capacity step Tsupply/Treturn time series + ΔT lag/noise Pass: bounded lag; no sign flips; noise within target Sensor placement/insulation / filtering too heavy / sampling misalignment
Loop Flow sweep coherence Pump_RPM sweep Flow + Pump_RPM + ΔP trend + pulse_loss_count Pass: RPM↔Flow↔ΔP coherence; low pulse loss Air lock / clog / wrong pump curve / flow sensor dropout
Field Freeze/defrost transitions Transition entry/exit scenarios Mode/Defrost/Frost bits + actions + snapshots Pass: correct action sequence; logs complete and ordered (sequence_id) State machine gaps / missing log triggers / hysteresis too small
Any Fault injection log completeness No-flow / over-temp / Vdc sag / comm CRC Fault code + trip class + snapshot bundle + counters Pass: evidence fields present; counters increment; sequence continuity Schema missing fields / snapshot trigger missing / buffer overwrite policy

Concrete MPN examples (controller-relevant blocks used by this test plan)

The following part numbers are reference examples for selection and validation; equivalents are acceptable when key specs match. Choices depend on voltage class, isolation needs, and the targeted compressor/pump power level.

Block Why it is needed in H2-11/H2-12 Concrete MPN examples (non-exhaustive)
Motor-control MCU PWM/timers + ADC capture windows + fault pins + logging orchestration ST STM32G4 series · TI C2000 F2837x series · Microchip SAM E70 series
3-phase gate driver Inverter trip proof (fault pins) and deterministic shut-down behavior TI DRV8323 · Infineon 6EDL04I06NT · onsemi NCV7725 (driver class reference)
Shunt current sense amplifier Accurate Iphase evidence near trip edges; avoids false OCP claims TI INA240 · ADI AD8418A · TI INA181
Hall current sensor IC/module Galvanic isolation option and robust current trending for diagnostics Allegro ACS758 · Allegro ACS70331 · LEM HO series (module family)
Energy metering (AC input) Electrical-in credibility for COP confidence and commissioning reports ADI ADE9153A · TI AMC3302 (isolated modulator class) · Renesas RAA211x (metering class reference)
RTD/temperature interface ΔT trust: stable excitation + linearization + diagnostics flags ADI MAX31865 · TI ADS124S08 (precision ADC) · ADI ADT7310 (temp sensor option)
Pressure / ΔP analog front-end Hydronic restriction/air patterns: ΔP trend evidence without excessive lag TI INA826 (in-amp class) · ADI AD8421 · TI OPA333 (low-drift op-amp)
EEV / stepper driver Command→movement evidence; fault reporting for actuator isolation TI DRV8846 · ST L6470 · Allegro A4988 (stepper class reference)
Solenoid / coil driver Reversing valve / solenoid actuation with open/short detection options TI DRV103 · Infineon BTS500xx (smart high-side family) · ST VNQ/VN5E families
RS-485 transceiver Remote diagnostics reliability evidence (CRC/timeouts) depends on robust PHY TI THVD1450 · Analog Devices LTC2862 · Maxim/ADI MAX13487E
Ethernet PHY Link up/down evidence and stable field connectivity Microchip LAN8720A · TI DP83825I · Microchip KSZ8081
Supervisor / watchdog Proves resets and prevents silent lock-ups that erase evidence TI TPS3823 · Maxim/ADI MAX706 · Microchip MCP131
Log memory (NVM) Preserves trip-edge snapshots for field root-cause Fujitsu MB85RS64V (FRAM) · Cypress/Infineon S25FL (SPI NOR family) · Microchip 25AA1024 (EEPROM class)
Validation & Commissioning — Bench → Loop → Field Repeatable checklist + acceptance metrics + log completeness Bench rails · sensing · actuators Loop ΔT · flow · mixing stability Field transitions · robustness · logs Vdc + rails + reset_reason Iphase calibration + trip-edge Valve & pump actuation proof Pass/Fail no resets · coherent signals ΔT step response (lag/noise) Flow sweep (RPM↔Flow↔ΔP) Mixing stability (overshoot) Pass/Fail bounded oscillation · coherence Freeze/defrost transitions Metering sanity cases Fault injection → log completeness Pass/Fail snapshot fields + sequence_id OK ICNavigator
Figure F11. Staged validation pipeline with pass/fail metrics and remote-log completeness checks.
Cite this figure Figure ID: F11 · ICNavigator

H2-12 — Field debug playbook (symptom → evidence → isolate → first fix)

Fast field value comes from forcing each symptom into an evidence chain: first 2 measurements → discriminator → first fix. Each item also lists the minimal must-log fields required for remote reproduction.

Rules for evidence-driven debugging

  • Start with delivery evidence: Flow + ΔT outrank comfort impressions.
  • Separate delivery vs capacity: Pump_RPM/ΔP coherence distinguishes circulation faults from compressor-side faults.
  • Demand logs before conclusions: if snapshots are missing, treat it as an observability fault and fix logging first.

S1 “Supply temp looks OK, rooms still cold”

First 2 measurements: Flow + ΔT (Tsupply − Treturn).

Discriminator: Flow present but ΔT very small → mixing over-dilution / too much flow / ΔT lag; Flow weak or pulse-loss → delivery failure (air lock, clog, closed valve).

First fix: verify RPM↔Flow↔ΔP coherence; purge air / confirm valve open state; reduce filter lag on temp chain if ΔT shows unrealistic phase shift.

Must-log: Tsupply/Treturn/ΔT, Flow, Pump_RPM, ΔP/pressure(if), Mixing_Pos, validity_flags.

S2 “Short-cycling (frequent on/off)”

First 2 measurements: ΔT trend + compressor speed (or run-time window).

Discriminator: ΔT near zero with high flow → capacity not transferring to slab (mixing/flow mismatch); ΔT oscillates with large lag → temp sensing/filtering causing control instability.

First fix: run ΔT sanity checks (sign stability, lag window); tune mixing control hysteresis/hold time; adjust pump command to keep ΔT in a stable band.

Must-log: Tsupply/Treturn/ΔT, Flow, Pump_RPM, Mixing_Pos, Compressor_Speed, mode_state.

S3 “Compressor trips on cold days”

First 2 measurements: Vdc sag + Iphase peak (trip-edge window).

Discriminator: trips coincide with defrost transitions/state changes → transient management; Vdc sag without state transition → power margin/UVLO thresholds; Iphase spikes with stable Vdc → current-sense/driver behavior.

First fix: enforce trip-edge snapshot capture (Vdc, Iphase, driver fault); adjust ramp limits during transitions; validate UVLO/OCP thresholds against real waveforms.

Must-log: Vdc, Iphase, Compressor_Speed, fault_code, trip_class, mode/defrost state, sequence_id, trip counters.

S4 “Frequent defrost / heat drops”

First 2 measurements: frost/defrost state evidence + valve position (EEV/Mixing where available).

Discriminator: defrost triggered without matching frost evidence → sensor/threshold issue; defrost triggered with evidence but delivery collapses → hydronic side not buffered (flow/mixing response).

First fix: log defrost entry/exit snapshots; verify transitions do not override pump/mixing into no-delivery; adjust state gating so COP and comfort are not computed across mixed modes.

Must-log: frost_state, defrost_state, Tsupply/Treturn/ΔT, Flow, Pump_RPM, valve positions, counters.

S5 “COP looks great/bad but feels wrong”

First 2 measurements: COP confidence inputs: (ΔT validity + Flow validity) plus state bits (defrost/freeze-protect).

Discriminator: ΔT or Flow invalid / pulse-loss present → COP is not trustworthy; state mixing (defrost windows included) → COP polluted.

First fix: enforce COP confidence gating (High/Medium/Low); fix ΔT placement/insulation and flow measurement coherence before interpreting COP.

Must-log: ΔT, Flow, validity_flags, mode/defrost state, electrical-in boundary marker (AC vs DC link if used).

S6 “Remote faults but no actionable data”

First 2 measurements: snapshot bundle completeness + sequence_id continuity.

Discriminator: missing fields with continuous sequence → schema gap; sequence gaps + CRC/timeouts rising → communication loss; continuous comm but no new events → event trigger missing.

First fix: implement minimum viable log schema: fault_code + trip_class + snapshot_id + counters; add triggers at trip edges and state transitions; protect ring buffer from overwrite of critical events.

Must-log: fault_code, trip_class, snapshot fields, sequence_id, comm_crc_err/timeout/retry counters.

S7 “Supply temperature oscillates; valve ‘hunts’”

First 2 measurements: Tsupply trend + Mixing_Pos activity rate.

Discriminator: Tsupply oscillation with slow ΔT sensors → measurement lag; oscillation with stable sensors → loop gain/hysteresis/hold-time mismatch.

First fix: reduce excessive filtering delay; add minimum hold time on valve moves; validate ΔT sampling alignment to prevent control chasing stale data.

Must-log: Tsupply/Treturn/ΔT, Mixing_Pos, Flow, Pump_RPM, validity flags.

S8 “Pump runs, but heat delivery collapses intermittently”

First 2 measurements: Pump_RPM + Flow (plus ΔP if available).

Discriminator: RPM steady but Flow drops with ΔP spikes → air/cavitation; RPM steady but Flow drops with ΔP rising trend → clog/filter restriction; Flow signal drops while ΔP/RPM coherent → flow sensor dropout.

First fix: purge air and verify filter/strainer; use coherence checks to isolate sensor failure; add pulse-loss counter thresholds to trigger “no-flow” protection with evidence snapshots.

Must-log: Flow, Pump_RPM, ΔP/pressure(if), pulse_loss_count, ΔT trend, event timestamps.

Field Debug — Symptom → Evidence → Isolate → First Fix Radiant-specific: delivery coherence dominates early decisions Symptoms Cold rooms, supply OK Short-cycling Trips on cold days Frequent defrost / heat drops COP feels wrong Remote faults, no data Evidence nodes ΔT + Flow (delivery proof) Pump_RPM + ΔP coherence Vdc + Iphase (trip-edge) State bits (defrost/freeze) Validity + counters Log completeness + sequence_id Isolate → First fix Delivery issue purge / verify valves / adjust pump Capacity / trip capture Vdc/I edge / tune ramps Sensor / lag placement / insulation / filtering Observability gap fix schema / triggers / buffer policy ICNavigator
Figure F12. Field decision map: symptoms route into delivery/capacity/sensor/observability branches using minimal proof signals.
Cite this figure Figure ID: F12 · ICNavigator

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H2-13 — FAQs (evidence-anchored, controller-local)

Each answer lands back on measurable signals: ΔT, Flow/ΔP, drives (Vdc/Iphase), metering boundary, and log completeness. No thermostat UX, no zoning/TRVs, no cloud platform design.

FAQ 01 Why is ΔT sometimes “negative” for a few minutes—sensor placement or mixing valve behavior?
First 2 measurements: raw Tsupply/Treturn traces + Mixing_Pos (or mixing command). Discriminator: if ΔT sign flips coincide with mixing moves or mode transitions, it is usually mixing/recirculation behavior; if sign flips occur with no valve activity and temps look noisy or phase-shifted, it is usually sensor contact/insulation or sampling alignment. First fix: reduce temperature chain lag, improve pipe coupling, and time-align samples used for ΔT.
Read more: H2-4 ΔT capture H2-3 Control loops
FAQ 02 Radiant loop warms slowly: check flow first or compressor capacity first—what proves it?
First 2 measurements: Flow + ΔT (Tsupply−Treturn). Discriminator: low/unstable Flow, high pulse-loss, or incoherent RPM↔Flow trends prove a delivery problem; stable Flow with persistently tiny ΔT points to mixing dilution, sensor lag, or capacity not reaching the hydronic side. First fix: restore circulation coherence (purge air, check restrictions, verify valve open state) before tuning compressor or mixing targets.
Read more: H2-5 Flow & pressure H2-3 Control loops
FAQ 03 COP estimate jumps wildly: which two signals are usually lying?
First 2 measurements: ΔT validity (noise/lag) + Flow validity (pulse_loss_count / coherence). Discriminator: COP is unreliable when either ΔT is phase-lagged/unstable or Flow is inferred incorrectly or dropping pulses; COP also becomes meaningless if defrost/freeze-protect windows are included without gating. First fix: enforce COP confidence levels (High/Medium/Low) and exclude mixed-mode intervals; repair ΔT placement and Flow coherence before interpreting COP numbers.
Read more: H2-7 Metering & COP H2-4 ΔT capture
FAQ 04 Short-cycling: is it ΔT control instability or a minimum compressor speed limit?
First 2 measurements: ΔT trend + Compressor_Speed (or run-time window). Discriminator: if compressor speed repeatedly clamps at its minimum while ΔT remains small, the system may be hitting a capacity floor for the current hydronic demand; if Mixing_Pos activity is high and ΔT oscillates with strong lag/noise, instability is usually driven by sensing/filtering and loop gains. First fix: stabilize ΔT sensing and mixing control hold-time before changing compressor limits.
Read more: H2-3 Control loops H2-4 ΔT capture H2-6 Drives & trips
FAQ 05 Pump running but no heat delivered: air lock vs clogged filter—what evidence separates them?
First 2 measurements: Pump_RPM + Flow (add ΔP if available). Discriminator: air/cavitation often shows intermittent Flow collapse with noisy ΔP spikes while RPM is stable; a clogged strainer/filter more often shows persistently low Flow with a rising ΔP trend as RPM increases. First fix: purge air and verify venting first; if ΔP continues to rise with stable RPM, inspect restrictions and confirm the pump curve matches the loop.
Read more: H2-5 Flow & pressure
FAQ 06 Mixing valve keeps hunting: is it sensor lag, wrong PID, or actuator deadband?
First 2 measurements: Tsupply response timing + Mixing_Pos activity rate. Discriminator: if valve moves but Tsupply responds late or inconsistently, sensor lag/filter delay is dominant; if Tsupply responds promptly but overshoots and oscillates, loop gains/hold-time are likely wrong; if commands change but position evidence does not, actuator deadband/sticking or driver faults dominate. First fix: fix measurement delay first, then tune hold-time/hysteresis, then verify actuator motion evidence.
Read more: H2-3 Control loops H2-4 ΔT capture
FAQ 07 Compressor trips only during defrost transitions: what snapshot must be logged?
First 2 measurements: trip-edge Vdc + Iphase peak captured in the same window. Discriminator: Vdc sag preceding the fault points to supply margin/UVLO; Iphase spikes with stable Vdc points to transient current events or current-sense/driver behavior; driver fault pins provide the decisive classification. First fix: enforce a minimum snapshot bundle at every defrost entry/exit and trip edge: Vdc, Iphase, Compressor_Speed, driver_fault, defrost_state, trip_class.
Read more: H2-8 Remote diagnostics logs H2-6 Drives & trip evidence
FAQ 08 Supply temperature is capped for floor safety: how to prove it’s protection logic, not capacity loss?
First 2 measurements: protection state bit + Mixing_Pos clamp behavior. Discriminator: if a floor-safety/over-temp trigger is active and mixing action is clamped (or pump strategy changes), the cap is intentional; if no protection state is active, the same temperature ceiling usually indicates limited delivery (Flow/ΔT) or capacity constraints. First fix: log trigger→action mapping (state, thresholds, clamp commands) and separate protected intervals from normal control when evaluating performance.
Read more: H2-9 Protection logic H2-3 Control loops
FAQ 09 Flow sensor reads OK but ΔP suggests otherwise: which one to trust, how to validate fast?
First 2 measurements: RPM sweep coherence + pulse_loss_count. Discriminator: if Pump_RPM changes and ΔP trends accordingly while Flow stays flat, the Flow chain is likely wrong (dropouts, scaling, installation); if Flow changes with RPM but ΔP does not respond, the ΔP tapping/conditioning may be wrong or too filtered. First fix: use a short RPM sweep to establish a coherence baseline, then lock the “trusted” signal and flag the other as low-confidence until corrected.
Read more: H2-5 Flow & pressure
FAQ 10 Electrical input metering disagrees with the utility meter: where is the measurement boundary wrong?
First 2 measurements: metering location (AC line vs DC link) + included loads list (compressor inverter, pump, valves, auxiliaries). Discriminator: DC-link metering misses upstream PFC losses and often excludes auxiliary loads; AC-line metering includes everything, including standby and defrost-related loads. First fix: label the boundary explicitly in logs and reports, then compare only equivalent windows; apply calibration at known steady operating points.
Read more: H2-7 Metering boundary
FAQ 11 Remote diagnostics says “EEV fault”: how to distinguish driver fault vs mechanical sticking remotely?
First 2 measurements: driver fault flags (open/short/overcurrent) + command-to-response evidence (step count/position or indirect thermal response). Discriminator: if fault flags assert or coil current evidence is abnormal, the driver/wiring side dominates; if no driver faults exist but commanded moves produce no expected system response over a reasonable window, mechanical sticking or valve-side issues dominate. First fix: log both the actuator command and the driver health snapshot at every “EEV fault” event.
Read more: H2-8 Remote diagnostics logs H2-6 Actuator drives
FAQ 12 After a power outage, the system behaves unstable for 10 minutes: which states must be restored/logged?
First 2 measurements: reset_reason + restored state set (mode_state, defrost_state, Mixing_Pos/EEV position, filter/Integrator reset flags). Discriminator: instability with missing/incorrect restored states indicates control restarting from a wrong initial condition; repeated resets or brownouts indicate rail/Vdc margin issues and incomplete logging due to reboots. First fix: persist a minimal “resume state” and record a boot snapshot (states + counters) so the first 10 minutes can be explained, not guessed.
Read more: H2-8 Logging schema H2-3 Control state

Notes: Answers intentionally reference controller-visible evidence only. If a signal is not available (e.g., ΔP), substitute the nearest coherence proof (RPM↔Flow↔ΔT) and log the confidence downgrade.

FAQ Evidence Map — What to Trust First ΔT · Flow/ΔP · Drives · Metering boundary · Logs Common questions ΔT sign flip / negative Slow warm-up / cold rooms Short-cycling Trips in transitions COP mismatch / jumps Remote “fault” no proof Evidence nodes ΔT (Tsupply − Treturn) Flow + pulse-loss ΔP / pressure trend Pump_RPM + Mixing_Pos Vdc + Iphase (trip-edge) Metering boundary + state bits Logs: snapshot + sequence_id Fast outcome Delivery vs capacity coherence separates branches Control stability lag + hunting proof Trip classification Vdc vs Iphase vs driver fault COP credibility boundary + state gating Remote actionable logs schema + triggers + continuity ICNavigator
Figure F13. FAQ evidence map: which signals to check first to keep answers controller-local and proof-driven.
Cite this figure Figure ID: F13 · ICNavigator
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