Connect the controller like a real device
Expose live Modbus values over TCP or RTU so the external application can connect immediately.
HVAC Compressor Control Test Platform
Test external compressor controls before site commissioning.
ModbusSim is a Windows desktop application that simulates TT and VT compressor behavior over Modbus TCP or RTU. Connect an external controller, run realistic compressor responses built from field logs and engineer-estimated curves, monitor how the control system performs, and export evidence from the session.
Use it for first connection checks, realistic behavior testing, machine log replay, and control-quality review.
Modbus TCP and RTU
TT and VT compressor families
Behavior model, replay, calculated mode
Monitoring and report export
Why HVAC Engineers Use It
It answers the controller-testing question that generic Modbus tools do not.
A generic Modbus tool can prove that a register map exists. It does not tell you whether an external control system starts, loads, unloads, protects, faults, and resets a compressor system correctly.
Test realistic compressor response
Use field-log evidence and engineer-estimated curves instead of relying on one narrow formula or one narrow recording.
Keep engineering evidence
Monitor transitions, warnings, faults, and recovery, then export the session for review.
Workflow
How the workflow works
The application should feel like an engineering test workflow, not like a register editor.
1
Connect the external controller
Set the compressor type, live system layout, and Modbus connection so the external application can talk to the simulator as if it were the target system.
2
Build or restore the behavior model
Use field logs where real data exists and complete the missing ranges with engineer-estimated curves where the logs do not cover startup, shutdown, fault, or wider capacity behavior.
3
Run the scenario
Start the external controller and apply the test demand or event. Check how the simulated compressor moves through startup, running, unloading, warning, fault, and reset conditions.
4
Monitor and document the result
Use the Control Quality Monitor to compare command and response, capture timing and state changes, and export a report when the run should be kept as engineering evidence.
Product Screenshots
Show the real application surfaces used in the workflow.
These screens show the main surfaces used during controller connection, behavior setup, monitoring, and report preparation.
Live system dashboard
Live compressor state, demand, RPM, pressure, power, and connection status.
Behavior setup
Compressor behavior model setup with editable engineering inputs.
Control Quality Monitor
Monitor view for command, response, trends, and report evidence.
Modes
Choose the right mode for the job
The product includes three main user-facing modes because HVAC testing needs more than one kind of realism.
Compressor Behavior Model
Use this as the main engineering mode. It combines field-log evidence with engineer-estimated completion so the simulated compressor can answer the controller across a wider operating range than a single recorded log.
Machine Log Replay
Replay one recorded machine log exactly. Use it when you want to compare the simulator against a known event, confirm that a captured sequence can be reproduced, or run a regression check against a reference recording.
Basic Calculated Model
Use this for first communication checks and coarse troubleshooting when the behavior model is not ready yet. It is useful for getting a controller connected quickly, but it should not be treated as the final realism target.
An off or hold state can also be used when values need to stay fixed, but the three modes above are the main testing paths.
Behavior Model
Field logs where available. Engineer curves where needed.
Real projects rarely include complete logs for every startup profile, capacity point, warning threshold, fault event, or power-loss condition. A useful simulator cannot stop where the field log stops.
The behavior model uses real machine data where it exists and lets the engineer complete the uncovered ranges with estimated curves where it does not. That makes the simulator practical for real controller testing instead of limiting it to one narrow replay.
- Anchor the model with field evidence where the machine was actually observed.
- Complete missing startup, running, stopping, warning, and fault ranges with engineer-estimated points.
- Tune one scenario at a time and retest immediately.
- Keep the model focused on believable compressor behavior, not just mathematical output.
Best practical model: field-log evidence plus engineer-estimated completion.
Approved behavior setup screenshot from assets/img/screenshots/behavior-setup.png.
Control Quality Monitor
The evidence view of the application. Use it to judge what the controller requested, what the simulated compressor answered, when warnings or faults appeared, and whether recovery happened correctly.
Trend engineering points
Compare multiple compressors
Keep preset traces active
Capture timing and faults
Export report
PASS
WATCH
FAIL
Monitoring And Reporting
See what the controller requested and how the compressor answered.
A good report should let another engineer understand what was tested, what conditions were applied, and whether the result was pass, watch, or fail.
- Trend the active engineering points during the run.
- Compare multiple compressors in one scenario.
- Capture timing, limits, warnings, faults, and reset behavior.
- Export the run as a report when the result should be kept.
Next Step
Move from product understanding to action.
Documentation gets the engineer started. Pricing explains the license path. Download and support complete the installation and trial workflow.