Sensing Flow in Heating & Ventilation Systems

Welcome to “The Pressure to be Perfect” blog from AdVanced Sensor that discusses pressure measurements that are made every second of our lives and without our knowledge. This blogs discuss the many applications and industries that use pressure sensors to measure flow, force, and pressure.

Take this common circumstance. In my building, the thermostat that controls the heating and cooling is located in my office. While I try to set the temperature that satisfies all my fellow colleagues; I am rarely successful, no matter the setting, I cannot keep everyone comfortable. The perfect pressure solution is the VAV (variable air volume) sensor.

Here are some details. At left is a simple diagram showing a roof top air handling system with ventilation outlets in specific rooms. Within each air outlets is a variable air volume control box. The control box connects with common air ducting and manages the air flow into each room. Consisting of a damper, electronics, and a sensor these systems can measure and adjust the air flow by modulating the air damper position creating a comfortable environment for the occupant.

There are essentially two methods to measuring the air flow. The most common method uses a differential pressure sensor (∆P) that measures flow across a restriction. The pressure is directly proportional to the flow rate; higher flow rates results in higher pressures generated. This method generally uses ceramic capacitive technology or MEMS capacitive technologies. The competing method measures flow rate directly using a thermo-anemometer technique. In this case, the silicon diaphragm is heated to a constant temperature and as laminar air flow passes over reducing its temperature, the amount of current required to keep the temperature stable can be correlated to air flow.

What do you think?

So much going on inside my office. Drop me a line if you have a questionon measuring pressure. Or just let me know about your common acquaintances’ with pressure. I will address it in an upcoming blog.

John Brown, Business Development AV Sensors (business.development@avsensors.com)

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