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Contributor
9 . Preventive maintenance planning : Monitoring air flow during commissioning establishes a baseline for future reference . This data enables us to create a preventive maintenance plan , allowing regular checks on air flow to identify any changes or performance degradation over time .
10 . Client documentation and reports : Air flow measurements are vital for generating comprehensive commissioning reports for clients , building owners , and facility managers . These reports provide a detailed overview of the HVAC system ' s performance and serve as valuable records for future reference .
To achieve accurate air flow measurements , it ' s essential to use suitable instruments and proper techniques . Here are the most common air flow measurement instruments used in South Africa : 1 . Anemometers : These handheld devices measure air velocity in ducts . Vane anemometers , hot-wire anemometers , and thermal anemometers are the various types available . Vane anemometers use a rotating vane to measure velocity , while hot-wire and thermal anemometers utilise a heated element to gauge airspeed . These methods are non-intrusive and suitable for spot measurements .
2 . Pitot tubes : These instruments measure total pressure in the air flow . By comparing the total pressure with static pressure ( measured separately ), air velocity can be determined , which then allows us to calculate the air volume flow rate .
3 . Flow hoods ( capture hoods ): Flow hoods are designed to measure air volume flow rate at diffusers or grilles . Placed over the outlet , they capture and measure the airflow , commonly used for supply and exhaust air outlets .
4 . Orifice plates : Similar to Venturi meters ( see below ), orifice plates use a flat plate with a hole ( orifice ) that obstructs the airflow . The pressure drop across the orifice is measured to calculate the flow rate .
5 . Venturi meters : Based on the principle of fluid flow through a constricted pipe , Venturi meters measure the pressure differential across the constricted portion to determine the flow rate . They are often used for larger ducts and systems .
6 . Thermal dispersion flow meters : These meters use a heated element and temperature sensors to measure flow rate based on the cooling effect of moving air . The difference in temperature between the heated element and the ambient air is used to determine the flow rate .
7 . Ultrasonic flow meters : Ultrasonic flow meters use ultrasonic signals to measure airflow velocity inside the duct . By combining this with the duct ' s cross-sectional area , the volumetric flow rate can be calculated .
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RACA Journal I October 2023 www . refrigerationandaircon . co . za