DHW Heat Pump Validation Report · Test Matrix
DHW Heat Pump Test Matrix
Every parameter we varied, every gate we scored, every result we published — including the ones that fell outside band. Two stages, 28 in-scope scenarios, 19 PASS against EnergyPlus 26.1 on annual and monthly energy. All four exception classes are named and mechanism-characterised in the report.
A note on the downloadable case codes. The stages here are numbered sequentially, but the case codes inside the workbooks keep the prefixes they were run under — Stage 2’s files begin STAGE5_. Those strings are the identifiers of the EnergyPlus run directories the results came from, and renaming them would break the link between a published workbook and the run that produced it. We kept the traceable name over the tidy one.
Stage 1 — Steady-state single-tank shakedown
12 test cases, pass: 4/12
Reference engine: EnergyPlus 26.1.0 — WaterHeater:HeatPump:WrappedCondenser and :PumpedCondenser coupled to a 12-node WaterHeater:Stratified tank. Tank geometry, condenser span and control-sensor heights are taken verbatim from EnergyPlus's own shipped example files rather than fitted. EnergyPlus defines the thermal load; the two engines are then compared on heat-pump compressor electricity. Scored against ASHRAE Guideline 14-2023.
Parameters varied
| Parameter | Levels | Values |
|---|---|---|
| Condenser architecture | 2 | Wrapped-condenser residential, pumped-condenser stratified |
| Evaporator ambient temperature | 3 | 10 °C, 20 °C, 30 °C (constant) |
| Continuous draw rate | 2 | 0.003 L/s, 0.007 L/s — sized inside sustainable capacity so the resistance backup never fires |
| Storage volume | 1 | 0.189 m³ (50 gal), residential scale |
| Simulation period | 1 | 720 hours (30 days), constant ambient and constant draw |
Gates scored on every case
| Gate | Tolerance | Result |
|---|---|---|
| EnergyPlus reference integrity | 0 Severe, 0 Fatal; energy balance ≤ 1% of load | 12/12 — balance −0.05% to −0.30% |
| Total compressor electricity | ±5% (ASHRAE G14-2023) | 4/12 — wrapped 4/6, pumped 0/6 |
| Backup element quiescent | ≈ 0 kWh (proves draw is within capacity) | 12/12 — 0.00 kWh in every case |
| COP physical plausibility | COP 2–6, rising with ambient | 12/12 — wrapped 3.90→6.30, pumped 2.97→4.73 |
Stage 2 — Annual realistic building load, four climates
16 test cases, pass: 15/16
Reference engine: EnergyPlus 26.1.0 — WaterHeater:HeatPump:* + WaterHeater:Stratified, driven by the DOE / ASHRAE 90.1-2019 Large Hotel prototype's own SWHSys1 use-side heat delivery. The prototype is run as shipped, so the DHW draw is an authority's rather than an assumption. Wet-bulb evaporator inlet cross-checked against EnergyPlus's own System Node Wetbulb Temperature to within 0.024 K over 8,760 hours. Scored against ASHRAE Guideline 14-2023.
Parameters varied
| Parameter | Levels | Values |
|---|---|---|
| Condenser architecture | 2 | Wrapped-condenser, pumped-condenser |
| Climate | 4 | Chicago 5A (cold), San Francisco 3C (mild marine), Tampa 2A (hot humid), Golden CO (semi-arid, −24.6 °C winter) |
| Evaporator ambient source | 2 | Indoor mechanical room (constant ~20 °C), outdoor (weather-file driven) |
| Equipment bank | 1 | 4 × 20 kW modules with 3.0 m³ storage, sized from the measured load against the element-trip threshold |
| Annual DHW load | 4 | 161–219 MWh/yr, load factor ≈ 0.43 (≈ 55 L per room per day across ~200 rooms) |
| Simulation period | 1 | 8,760 hours (full year), real weather |
Gates scored on every case
| Gate | Tolerance | Result |
|---|---|---|
| Annual compressor electricity | ±5% (ASHRAE G14-2023 annual sum) | 15/16 — spanning −2.14% to +3.79% |
| Monthly NMBE | ±5% (ASHRAE G14-2023 monthly) | 16/16 |
| Monthly CV(RMSE) | ≤ 15% (ASHRAE G14-2023 monthly) | 16/16 — spanning 1.75% to 9.49% |
| EnergyPlus reference integrity | 0 Severe, 0 Fatal; balance ≤ 1% of load | 16/16 — balance −0.02% to −0.04% |
| Cold-ambient lockout | reported vs EnergyPlus, not gated | Lockout hours match exactly (598 h, Golden outdoor) |
| Peak hourly demand | ±10% — REPORTED, NOT GATED | 14/16 — 2 mild-climate indoor misses |
| Timestep-sensitivity control | flat part-load curve must show ≈0% shift | Confirmed 16/16 — wrapped +0.19%, pumped −6.21% |
Timestep-sensitivity control test
A falsifiable prediction, tested on all 16 Stage-2 scenarios. For a single-speed compressor the part-load ratio is its fractional on-time, and the part-load efficiency curve penalises low part-load. That penalty is evaluated at the simulation timestep, so a coarser timestep averages the on-time into a lower part-load ratio and charges a larger penalty. The wrapped-condenser archetype carries a flatpart-load curve and therefore cannot be timestep-sensitive; the pumped-condenser archetype carries a sloped one and must shift. Every scenario was re-run at EnergyPlus’s own 15-minute timestep to test it.
| Archetype | Part-load curve | Mean shift 60 → 15 min | Range | n |
|---|---|---|---|---|
| Wrapped condenser | flat (1.0, 0, 0) | +0.19% | +0.10% … +0.28% | 8 |
| Pumped condenser | sloped (0.75, 0.25, 0) | −6.21% | −8.13% … −3.90% | 8 |
The two families do not overlap at any point, and there is no counter-example. One consequence is reported because it bears on how the result should be read: the finer timestep does not produce a clean sweep. At 15 minutes the score is also 15 of 16, but a differentscenario falls outside band. Moving to the finer timestep is therefore a re-calibration of the part-load treatment rather than a correction, which is why it has not been adopted as a fix. The practical figure for a user is that pumped-condenser annual energy carries a timestep sensitivity of roughly 6–8%, and wrapped-condenser carries none.