How to calculate air flow from differential pressure
Precise airflow control keeps indoor environments comfortable, clean, and safe. Whether it is a hospital operating room, a semiconductor cleanroom, or a commercial HVAC system, reliable airflow measurement underpins system efficiency and environmental integrity. Yet airflow cannot be measured directly in many situations, especially when cleanliness or access limitations come into play.
That is where differential pressure measurements become invaluable. By using the pressure difference across a known restriction, engineers can accurately and consistently calculate air flow with a differential pressure sensor. For system designers, mastering differential pressure-based methods opens the door to smarter, more scalable ventilation control.
One particular setup, the dead-ended method, offers clear advantages for critical applications by protecting the sensor and maintaining measurement reliability.
Determining Air Flow Using Differential Pressure
When air flows through a duct or across a filter, it encounters resistance. This produces a pressure drop between the upstream and downstream sides of the restriction. That pressure difference, or differential pressure, can be used to calculate the rate at which air is moving.
The most commonly used formula is:
Q = C × A × √(2 × ΔP / ρ)
With this equation:
- Q is the volumetric airflow rate
- C is the discharge coefficient
- A is the cross-sectional area
- ΔP is the measured pressure difference
- ρ is the air density, adjusted for environmental conditions.
To apply this method, a differential pressure sensor is connected to pressure taps located upstream and downstream of the restriction. These taps send pressure readings to the sensor, which outputs a value that corresponds to the pressure drop. The output is then used to determine the airflow, either through onboard processing or external control systems.
Installing a differential pressure sensor with taps positioned across a flow restriction allows for accurate and continuous airflow monitoring. This approach is widely used in building management systems, pharmaceutical production, and industrial ventilation, where reliable measurement supports both operational control and environmental quality.
Introducing the Dead-Ended Method for Sensor Configuration
In systems demanding consistent performance with minimal maintenance, the way a sensor is integrated can make all the difference. The dead-ended method protects the differential pressure sensor from direct exposure to the airstream, resulting in increased measurement stability and longer device life.
What the Dead-Ended Method Is and How It Works
A dead-ended setup uses pressure tubing to connect two points in the airflow path to the sensor. One tap is placed upstream of the restriction, and another is positioned downstream of it. The air pressure is transmitted through sealed tubing, keeping the sensing elements isolated from contaminants and humidity.
Although physically separated from the airstream, the sensor receives accurate pressure readings and sends a signal, typically digital or analog, to the building automation system or local controller. The differential pressure value is then used to calculate the airflow with the same formula used in other configurations.
Why the Flow-Through Method Falls Short
Unlike the dead-ended approach, flow-through sensors are designed so that air passes directly through the sensor body. This means the sensing elements are constantly exposed to the same air being measured. While this may seem efficient in simple systems, it introduces reliability challenges over time.
Within environments that prioritize air purity and consistency, flow-through designs can quickly become problematic. Dust, moisture, and airborne chemicals may enter the sensor, causing drift, signal degradation, or sensor failure. Ongoing maintenance becomes a necessity, and accuracy is often compromised between servicing intervals. The dead-ended method eliminates most of these risks, offering a more reliable and maintenance-friendly alternative.
Benefits of Using the Dead-Ended Method
1. Protection from Environmental Contaminants
The sealed setup prevents airborne particles, moisture, and corrosive vapors from reaching the sensor’s internal components.
2. Improved Accuracy and Stability
Pressure readings remain stable and free from turbulence-related interference, supporting consistent differential pressure measurements over time.
3. Reduced Maintenance Requirements
Isolated components experience less wear, minimizing the need for recalibration or replacement.
4. Flexible Mounting Options
Sensors can be installed in protected, remote locations. Only the tubing connects to the airflow path.
5. High Reliability in Demanding Systems
Crucial infrastructure, including healthcare and pharmaceutical environments, benefits significantly from this method due to its resilience and long-term accuracy.
The HV Series from Superior Sensor Technology
Superior Sensor Technology’s HV Series is designed for environments that require accurate and stable airflow measurement across multiple pressure ranges. These differential pressure sensors are designed for use in HVAC systems, filtration control, and pressurization monitoring.
Features such as advanced digital filtering, temperature compensation, and signal amplification work together to deliver stable, noise-resistant performance. Combined with I2C and SPI communication interfaces, this design supports seamless integration into building automation platforms and industrial control systems. The result is a cohesive and reliable sensing solution that performs consistently across diverse and dynamic operating conditions.
Found in air handling systems, filtration modules, and pressure-sensitive zones, the HV Series differential pressure sensors provide uninterrupted, high-resolution data, resulting in smarter decisions and improved operational efficiency.
Strengthening Airflow Monitoring with Proven Sensor Design
Effective airflow measurement is built on accurate differential pressure sensing. By combining this measurement approach with the stability of the dead-ended method, Superior Sensor Technology’s HV Series enables precise, low-maintenance monitoring across a wide range of demanding environments. To learn how our HV Series differential pressure sensors can support your airflow control strategies, speak with our technical team today.
Quick downloads:
