An open-source, high-precision instrument designed for measuring air flow in residential ventilation systems (HRV/MVHR). By using active zero-pressure compensation, this device eliminates its own pneumatic resistance, providing "invisible" measurements that do not disturb the ventilation system's balance.
Traditional flow hoods create backpressure, leading to underestimated flow readings. This device uses a secondary SDP800-500PA differential pressure sensor to monitor the pressure inside the hood. An integrated Arctic S8038-10K fan is controlled via a PID loop to maintain exactly
The ESP32-WROOM utilizes two independent I2C buses to ensure high-speed data acquisition without bus collisions between identical sensors.
| Component | Function | ESP32 GPIO | Notes |
|---|---|---|---|
| I2C Bus 0 | Data / Clock | 21 / 22 | BME280, OLED, SDP800 (Venturi) |
| I2C Bus 1 | Data / Clock | 25 / 26 | SDP800 (Zero-Pressure Sensor) |
| Encoder | CLK / DT / SW | 2, 4, 15 | Menu & Calibration |
| PWM Fan | Speed Control | 27 | 25kHz PWM signal |
The 1.3" OLED (SH1106) provides a high-density data overview using a context-aware interface.
- Short Press: Opens the Quick-Profile Menu to switch between calibrated profiles (Axial/Radial - Supply/Extract).
- Long Press (>2s): Enters the System Menu (Back, Tune Zero-Comp, Tune Flow, Tune PID).
The screen is optimized for the SH110X library using textsize 1 and textsize 2.
| Position | Content | Example |
|---|---|---|
| Top Left | Active Setpoint | Set: 1.25 Pa |
| Top Right | Profile Name | RAD-SUPPLY |
| Center | Flow Rate | 125.4 m3/h |
| Row 3 | Hood P / Temp | P: 0.1 Pa / 21.2 C |
| Bottom | Baro / Hum | 1014 hPa / 42 % |
The device uses a "Live-Trim" methodology. Settings are automatically saved to the active profile in the NVS Flash memory (Preferences.h).
- Tune Zero-Comp: Adjust the setpoint (range -25 to +25 Pa) while connected to the test bench to compensate for air impingement (common in radial valves).
- Tune Flow: Rotate the encoder to align the meter's flow reading with the reference Test Bench.
- Tune PID: Select P, I, or D using inverse video highlighting. Adjust parameters in real-time and observe fan stability immediately.
Precision is maintained by calculating the density of moist air using the Magnus-Tetens approximation:
Calculated based on the pressure differential across the Venturi throat:
Where Beta (
- Material: PETG (0.2mm layer height) for structural integrity and heat resistance.
- Venturi Tube: Printed in three sections (Inlet, Throat, Outlet) and bonded with epoxy resin.
- Direct Drive: Highly recommended to minimize stringing in PETG parts.
- Dual Piezometric Rings: The final Venturi design features integrated pressure rings at both the inlet and the throat. Each ring averages the static pressure from multiple points to ensure high accuracy.
- Flow Hood Sensing: The flow hood utilizes a 12-port averaging ring (2.5mm ports) to provide a stable signal for the zero-pressure logic.
- Reversible Adapters: Custom adapters allow the flow hood to be mounted on either side of the core assembly. This allows switching between supply and extract measurements while maintaining optimal aerodynamic orientation for the fan and Venturi.
This project is licensed under the MIT License.