To ensure and verify the efficient airflow in the ducts and the optimum distribution (balance) of airflow in a heating, ventilation, and air conditioning (HVAC) system, a technician would use a balometer – a type of airflow meter. This tool/instrument measures several airflow parameters from diffusers and grilles. With this data, the HVAC technician can adjust the system’s airflow to achieve the desired temperatures and pressures in different areas and ensure that air is evenly distributed throughout a building for optimal comfort, efficiency, and performance.
Units for measuring volumetric airflow are cubic feet per minute (CFM) and standard cubic feet per minute (SCFM). Since the same volume of air can have different temperatures, pressure, and humidity, SCFM is standardized at 1 atmosphere pressure and 68°F temperature.
Balometer applications include HVAC commissioning, testing and balancing HVAC systems, troubleshooting HVAC systems, and clean room certification.
A balometer generally consists of an air collection or air flow hood, a flow measurement instrument, and a digital display. It measures the flow rate of air leaving or entering the ventilation outlet of an airflow system. Some balometers also measure the room’s atmospheric pressure as well as the temperature and relative humidity of the flowing air.
In addition to creating a healthy and energy-efficient environment and reducing energy bills, a balometer allows the HVAC technician to verify the HVAC system meets local codes, guidelines, and regulations for ventilation systems.
Balometer design
Some balometers use a differential pressure measurement system to measure an air stream’s velocity and flow rate. In addition to the air capture hood that could be 2 ft. x 2 ft. (610 mm x 610 mm), the instrument uses a measuring grid with many holes. When air flows through the grid, the pressure (measured compared to the atmospheric pressure) and temperature readings provide an average flow rate in SCFM over the entire measuring area.
Other tools/instruments/techniques for measuring air velocity/airflow include thermal anemometers, rotating vane anemometers, and digital micro-manometers. For example, air capture hoods that contain an anemometer convert a recorded air velocity into a volumetric measurement.
Some balometers have a detachable micromanometer that can be used with optional pitot tube and static pressure probes to make additional measurements. With the detachable micromanometer, the technician can also accurately measure pressure, velocity, and flow to ensure the system/installation meets industry standards.
Making the readings
The acceptable SCFM for supply reading and exhaust readings depends on different factors. To provide the required accuracy, the calibration standard and calibration date are typically listed on the calibration reading data sheet, which can include temperature, relative humidity, and barometric pressure readings. Some balometers include the capability to provide air changes per hour (ACPH) readings, which are also important to HVAC system installers.
Since a balometer can be used for certification purposes (including clean rooms), one of the aspects of choosing a balometer is a National Institute of Standards and Technology (NIST) traceable calibration certification.
References
Mastering Airflow: Achieving Perfect Air Balancing with a Balometer
Balometer – Designing Buildings
NT_DBM620-SmartKap_14-04-21_EN_1.pdf
TSI – Alnor Balometer Capture Hood EBT731
AABC Engineering Guide
Airflow meters (Balometers) | Sauermann Group
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