MEPS Simulation
Before you ship a unit to a lab, know your test result, your certificate yield, and where you sit against the market. We simulate the AS/NZS 5125.1 Appendix H procedure on a validated heat pump water heater model, report the same quantities the lab would, and show you the control-setting change that fixes a fail before you book the test.
Why model Appendix H before you test
Standards Australia has published AS/NZS 5125.1:2014 Amd 1, which introduces the Appendix H test method for air source heat pump water heaters. This is the method expected to underpin minimum energy performance standards (MEPS) under the GEMS framework. COP is the regulatory output: once GEMS is confirmed, the MEPS pass or fail is set against the Appendix H COP. The Decision Regulation Impact Statement has signalled a level equivalent to 60% energy savings under AS/NZS 4234, though that figure is not confirmed until the legislation is finalised.
The detail that catches manufacturers out is the delivery temperature. Appendix H requires delivered hot water at or above 50°C. AS/NZS 4234 simulation uses 45°C. A product optimised around the 45°C threshold, with a lower set point, narrow deadband, or smaller storage volume, can show reduced deliverable volume and a different COP under Appendix H. Physical testing is an expensive place to discover that. A laboratory retest at a Chinese facility runs into the tens of thousands of dollars once shipping and scheduling are counted, and adds months to a product timeline.
Simulating Appendix H first answers the questions that decide the test outcome while there is still time to act on them. It tells you where the COP sits relative to the likely MEPS level, whether the deliverable volume holds at 50°C, and which control or design change moves the result. You then book the laboratory once, for the configuration most likely to pass.
What the simulation gives you
We reproduce the Appendix H test sequence on a simulation of your unit, then report the quantities the standard measures: COP, maximum deliverable heated water volume, reheat time, recharge rate, and energy consumption. The COP is checked against the proposed MEPS threshold so you see the margin directly. The simulation runs on our in-house first-principles heat pump water heater model, validated against real test data, so the predicted behaviour reflects the physics of your specific configuration rather than a generic curve.
What you provide
Product configuration
Tank volume, set point, deadband, boost logic
Performance data
AS/NZS 5125.1 test results or component data
Control law
Compressor restart and recovery strategy
Appendix H protocol simulation
Test sequence reproduced on a validated HPWH model
What you get back
COP vs MEPS threshold
Margin to the proposed GEMS level
Deliverable volume above 50°C
Hot water available at the Appendix H threshold
Reheat time and recharge rate
Recovery after draw-off, as reported to GEMS
Where GEMS MEPS stands
Appendix H is published, but MEPS is not yet active. The compliance date, the final MEPS COP level, and the registration requirements are confirmed through GEMS legislation, which is still to come. We model against the published Appendix H method and update the assessment as the GEMS requirements firm up.
See the simulation, not just a lookup table
What the report tells you — 1 of 5
Your likely MEPS test result
The headline deliverables the lab would report, for a representative 320 L integral R290 heat pump water heater: COP, deliverable volume, recharge time and rated load size across the Hot, Average and Cold conditions.
| Deliverable | Hot | Avg | Cold |
|---|---|---|---|
| Max delivery V50 (L) | 316.4 | 317.7 | 317.9 |
| Max delivery V_del (L) | 260.3 | 261.3 | 261.3 |
| Recharge time t_RH_adj (min) | 317.7 | 344.0 | 565.3 |
| Rated 24-hr load size | 9 | 4 | 4 |
| 24-hr load L_cycle (MJ) | 85.0 | 38.0 | 38.0 |
| 24-hr COP_cycle | 3.646 | 3.032 | 1.952 |
What the report tells you — 2 of 5
How much headroom you have at the lab
Set point and dead-band cost nothing to change before the lab test, and they directly affect how much headroom you carry above the Appendix H 50°C delivery floor. We sweep the grid and compare your as-declared setting against a conservative option and the setting we'd recommend for the widest safety margin.
| Scenario | SP / DB | Margin | STC Z3 | VEEC |
|---|---|---|---|---|
| As declared | 60°C / 10K | +1.2 K | 31 | 9 |
| Conservative 60/8 | 60°C / 8K | +1.2 K | 31 | 9 |
| RecommendedWider margin | 60°C / 12K | +3.0 K | 31 | 9 |
Margin is the worst-condition delivery temperature above the 50°C Appendix H floor. STC (zone 3) and VEEC (1D metro) are shown for reference alongside the margin, not as the target: in this example the recommended setting carries the identical certificate outcome to the as-declared setting — the change is about test-result reliability, not certificate value. Lock the chosen settings before the unit ships — the tested configuration is the registered configuration.
What the report tells you — 3 of 5
Where you sit against the market
Your simulated result benchmarked against the anonymised field of 500+ residential heat pump water heaters EnergyAE has modelled. No competitor identities, ever — percentile position only.
| Metric | Hot | Avg | Cold |
|---|---|---|---|
| 24-hr cycle COPhigher better | 41st percentile | 32nd percentile | 52nd percentile |
| Max delivery volume (L)higher better | 93rd percentile | 93rd percentile | 94th percentile |
| Recharge timelower better | 9th percentile | 11th percentile | 10th percentile |
The percentile is the share of the field this model outperforms on that metric and condition: the 90th percentile beats 90% of the field.
What the report tells you — 4 of 5
What it means in certificates
Provisional STC, VEEC and ESC counts from the AS/NZS 4234:2021 annual runs at the report's control settings, with an indicative reference-price value, shown here purely as reference information. A dwelling earns under one scheme and one scenario, not a sum of these rows.
| Certificate | Declared | Recommended |
|---|---|---|
| STC (SRES, national) — zone 3 | 31$1,223 | 31$1,223 |
| STC (SRES, national) — zone 4 | 34$1,341 | 34$1,341 |
| STC (SRES, national) — zone 5 | 33$1,302 | 33$1,302 |
| VEEC 1D metro (Vic zone 4) | 9$749 | 9$749 |
| ESC D17 metro (NSW zone 3) | 28$815 | 28$815 |
The recommended setting from the previous section produces the same certificate outcome as declared — the wider margin comes at no certificate cost. Reference prices: STC $39.45, VEEC $83.25, ESC $29.1 (as at 2026-07-07). Certificate spot prices move — confirm current market pricing before any commercial decision. A dwelling earns under one scheme and one scenario, not a sum of these rows.
What the report tells you — 5 of 5
Which design change moves the needle
Genuine performance and efficiency improvements — a better COP, lower tank heat loss, lower standby draw — re-simulated (not scaled) from the as-declared settings, and how each shows up in the annual energy savings and compliance figures.
| Design change | Δ savings | Δ STC Z3 | Δ VEEC |
|---|---|---|---|
| COP +5% | +1.0 pp | +1 | +1 |
| Tank heat loss -10% | +0.4 pp | +1 | 0 |
| Standby power -20% | +0.0 pp | 0 | 0 |
Sensitivities, not engineering advice: whether a change is reachable depends on the design (compressor, refrigerant charge, insulation spec), and any change must be re-tested and re-modelled.
Appendix H is not AS/NZS 4234
The two test regimes pull in different directions, and a setting that maximises one can cost the other. If you change control settings for Appendix H, the same logic must be reflected in your CER, VEU, and ESS submissions: a product should not be tested for MEPS using one configuration while being registered for incentive schemes under another. Modelling both together keeps the declarations consistent and avoids a later re-submission.
| Aspect | AS/NZS 4234 simulation | AS/NZS 5125.1 Appendix H |
|---|---|---|
| Minimum useful delivery temperature | 45°C | 50°C |
| Primary regulatory output | Annual energy savings | COP |
| What it drives | STC and VEEC certificate yield | GEMS MEPS pass or fail |
| Also reported | Not applicable | Deliverable volume, reheat time, recharge rate |
The same first-principles engine powers our Physics-based HPWH Model, where you can see how the predictions were validated blind against measured heat-up data, with COP agreeing to within 1% on the clean benchmark ambients.
For a walkthrough of how the Appendix H test procedure works, including the tank stratification behaviour behind these results, see our guide: Understanding AS/NZS 5125.1 Amendment 1 Appendix H for MEPS Testing.
What you can use it for
- Quantify the margin to the MEPS COP threshold before you book a laboratory
- Test whether control settings tuned around the 45°C AS/NZS 4234 threshold still hold up at the 50°C Appendix H threshold
- Identify likely failure modes (low deliverable volume, slow recovery) and the control or design change that fixes them
- Keep the Appendix H test configuration aligned with the control logic declared to CER, VEU, and ESS
- Screen a product range to decide which models need attention before GEMS registration
What we need to start
- Tank drawing and storage volume
- Control logic: set point, deadband, compressor restart, boost element behaviour
- An AS/NZS 5125.1 test report if available, or component datasheets
- The intended Appendix H test configuration
- Any existing AS/NZS 4234 modelling or scheme submission for the product
Some items can be estimated where documents are incomplete. We confirm what is missing at the start of the project.
Request a MEPS Pre-Appraisal
For a product we have already modelled to AS/NZS 4234, the Pre-Appraisal is a fixed-price report. Tell us the product and how many models, and we prepare a formal Xero quotation for you to approve. There is no online payment.
The fixed price assumes we have already modelled each unit to AS/NZS 4234. If a unit has not been modelled yet, we quote the AS/NZS 4234 modelling separately. Tell us in the notes and we will confirm.
Pre-assess your product against Appendix H
Send us your model details and tell us whether you already have AS/NZS 5125.1 test data. We will tell you what we need and how the assessment would run.