Physics-based HPWH Model
Find the design and control changes that raise your system COP, before you build a prototype or commit to a test program. The model resolves the full refrigeration cycle from physics, calibrates against a small amount of your own internal test data, then explores the design space you cannot reach by testing alone.
Built to raise your system COP
A higher COP is the goal that decides product cost, incentive certificate yield, and competitiveness. The hard part is knowing which change actually moves it: the compressor, the condenser geometry, the charge, the control law, or the interaction between them. AS/NZS 5125.1 performance testing only measures the design you have already built. Any change to the refrigeration cycle needs a fresh test, which is a slow and expensive way to improve a product.
This model works the other way around. It resolves the compressor, condenser, evaporator, expansion valve, and stratified tank from heat transfer and thermodynamic equations, so the effect of a design, control, or charge change on COP can be predicted before any hardware exists. We validate the model against a small amount of your own internal test data, then run it across the full design space to find where the COP gains are.
That replaces the slow retest cycle. 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. Exploring the options in simulation first, then testing the winner once, avoids most of that.
How the model works
We developed this model in-house, in Python, from the underlying physics. It is a completely new engine written for this purpose. It does not use TRNSYS or any other off-the-shelf simulation package. Each heat exchanger is solved cell by cell with local refrigerant properties and heat transfer, the compressor is characterised from its rated point and pressure-ratio behaviour, and the tank is modelled as a stratified column coupled to the wrap condenser. It captures behaviour specific to integral R290 microchannel units, including condenser-to-tank coupling and stratification, that general-purpose refrigeration software does not.
What you provide
Geometry
Tank, condenser, and evaporator dimensions
Compressor + charge
Rated point and refrigerant charge
Control law
Setpoint, superheat, and speed schedule
First-principles physics engine
Vapour-compression cycle solved against a stratified tank model
What the model predicts
COP and capacity
Across the full operating envelope
Tank stratification
Temperature profile through heat-up
Heat-up time
Time to reach setpoint at each ambient
A small set of parameters is identified from a minimal amount of your internal testing. That testing does not need to strictly follow a standard. By default it tends to follow the AS/NZS 5125.1 approach, which is more than enough, and the exact protocol is something we sort out at the start of the project. Once the model matches your unit, it runs across the full parameter space to find the design and control changes that raise COP.
Technology scope
The model is currently optimised for residential R290 integral microchannel heat pump water heaters. If your product uses a different refrigerant, condenser type, or configuration, get in touch. We can assess whether the model can be extended to cover your technology.
Informed by peer-reviewed research
- Corberán, Gonzálvez, Montes and Blasco (2001). ART: A Computer Code to Assist the Design of Refrigeration and A/C Equipment. Universitat Politècnica de València.
- Corberán, Fernández de Córdoba, Gonzálvez and Alías (2000). Semi-Explicit Method for Wall Temperature Linked Equations (SEWTLE): A General Finite Volume Technique for Complex Heat Exchangers.
- Shen, Nawaz, Baxter and Elatar (2018). Development and validation of a quasi-steady-state HPWH model with stratified tank and wrapped-tank condenser. International Journal of Refrigeration. DOI 10.1016/j.ijrefrig.2017.10.023.
Validated against real test data
The model was run blind against heat-up test data for a 260 L R290 integral heat pump water heater. Blind means the model never saw the unit's own test data. The compressor was characterised from its datasheet rated point and pressure-ratio physics, the heat exchangers from their geometry, and the refrigerant charge from the cycle. The figure compares the predicted heat-up against measurement for tank temperature, heating capacity, input power, COP, and tank stratification.
| Air temperature (dry / wet bulb) | Measured COP | Predicted COP | Measured vs predicted COP |
|---|---|---|---|
| 19 / 15°C | 5.14 | 5.21 | +1% |
| 32 / 22°C | 6.48 | 6.86 | +6% |
| 32.9 / 26°C | 7.12 | 7.19 | +1% |
| 8.5 / 7.3°C (frosting) | 3.98 | 4.55 | +14% |
COP is derived from the tank energy balance over the 15 to 55°C window. The 8.5°C case is a frosting condition, where wet and frost evaporator behaviour carries more uncertainty. The three warmer ambients are the clean benchmark, where predicted COP sits within 6% of measurement with no tuning to the unit's data.
What you can use it for
- COP and capacity diagnosis: identify which component limits efficiency in an existing design
- Design variant analysis: predict the effect of compressor sizing and heat exchanger geometry before tooling
- Control logic optimisation: test setpoint, expansion valve superheat, and compressor speed schedules against COP
- Refrigerant charge optimisation: find the active charge that suits a given system geometry
- New product pre-assessment: evaluate a proposed design before committing to a prototype or a lab booking
What we need to start
- Tank drawing
- Evaporator and compressor datasheets
- EEV control logic (setpoint, superheat, speed schedule)
- Refrigerant charge
- Internal test data (a standard heat-up test is enough)
Some items can be estimated where documents are incomplete. We confirm what is missing at the start of the project.
Apply the model to your product
Send us your model details and what you want to find out. We will tell you what we need and how the analysis would run.