Abstract
In this study, an in-duct ultrasonic airflow measurement device has been designed, developed and tested. The airflow measurement results for a small range of airflow velocities and temperatures show that the accuracy was better than 3.5% root mean square (RMS) when it was tested within a round or square duct compared to the in-line Venturi tube airflow meter used for reference. This proof of concept device has provided evidence that with further development it could be a low-cost alternative to pressure differential devices such as the orifice plate airflow meter for monitoring energy efficiency performance and reliability of ventilation systems. The design uses a number of techniques and design choices to provide solutions to lower the implementation cost of the device compared to traditional airflow meters. The design choices that were found to work well are the single sided transducer arrangement for a “V” shaped reflective path and the use of square wave transmitter pulses ending with the necessary 180° phase changed pulse train to suppress transducer ringing. The device is also designed so that it does not have to rely on high-speed analogue to digital converters (ADC) and intensive digital signal processing, so could be implemented using voltage comparators and low-cost microcontrollers.
Highlights
Ventilation and air conditioning (HVAC) systems are difficult and costly to monitor for energy efficiency performance and reliability
In the 250 mm diameter circular duct, the range of airflow velocities produced was limited by the output of the inlet fan to between 2 m/s and
In both configurations the root mean square (RMS) percentage error was less than 3% with a linear response as shown by the high R2 values for the straight line fit across the range of air velocities tested
Summary
Ventilation and air conditioning (HVAC) systems are difficult and costly to monitor for energy efficiency performance and reliability. According to Yu et al [1] they are fragile, expensive and create an additional pressure loss, and their sensitivity is reduced with the reduction in airflow velocity As buildings evolve, they will require higher levels of insulation and air tightness which will require ventilation systems to provide the minimum number of air changes and reduced energy usage by recovering heat from the air before it is expelled. They will require higher levels of insulation and air tightness which will require ventilation systems to provide the minimum number of air changes and reduced energy usage by recovering heat from the air before it is expelled This will necessitate the need for monitoring of the operating performance of these systems so that air quality or building energy efficiency is not detrimentally affected [2,3]. The monitoring of airflow rates can indicate problems in the design, installation and operation of a HVAC system [2,3,4]
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