Development and Characterization of Thermal Flow Sensors for Non-Invasive Measurements in HVAC Systems

Area of Science:

• Engineering
• Thermal Sciences
• Fluid Dynamics

Background:

• Traditional flow rate measurements in HVAC systems often employ ultrasonic techniques.
• Non-invasive methods are desirable to avoid disrupting fluid flow and system performance.
• Accurate flow rate monitoring is crucial for HVAC system efficiency and control.

Purpose of the Study:

• To investigate a novel non-invasive thermal flow transduction method for HVAC systems.
• To evaluate the feasibility and performance of thermal flow transduction as an alternative to ultrasonic methods.
• To develop a system capable of deriving mean volume flow rate from temperature differences.

Main Methods:

• Developed a thermal flow transduction system with two temperature sensors and a heater.
• Mounted sensors non-invasively on the outer surface of metal pipes.
• Utilized the temperature difference between sensors to infer fluid flow velocity.
• Conducted experimental characterizations of sensor prototypes, analyzing output, dynamic behavior, and noise density.
• Implemented error compensation for measurements across a wide range of fluid temperatures.

Main Results:

• Demonstrated the feasibility of non-invasive flow rate measurement using thermal transduction.
• Established a correlation between heater excess temperature and fluid flow velocity.
• Characterized sensor prototypes, including dynamic response and noise levels.
• Achieved error compensation for measurements across various fluid temperatures.
• Identified response time as a constraint for certain applications.

Conclusions:

• Non-invasive thermal flow transduction is a viable alternative for HVAC systems.
• The proposed method offers a way to measure flow rates without internal pipe disturbance.
• Further optimization is needed to address limitations in response time for dynamic applications.