An airflow capture hood measures the air passing through a terminal by enclosing its discharge or intake. The result depends on hood fit, flow direction, measurement range and the influence of the hood on the terminal. It is different from taking a single air-velocity reading in front of a grille.
First, establish a complete capture
Choose a hood size and shape that enclose the terminal and can seal against the surrounding surface. Check nearby lights, wall edges and ceiling features that can prevent proper placement. A partly covered diffuser allows bypass flow and cannot be treated as a complete terminal measurement.
Consider handling at the actual height. Hood weight, clearances and access equipment influence whether the operator can hold it consistently without distorting the opening or damaging the ceiling.
Then, assess measurement influence
Placing a hood over a terminal can add resistance and change the flow being measured. TSI's capture-hood information describes backpressure compensation among its measurement features. Such compensation is equipment- and procedure-specific; it should not be assumed for every hood.
Swirl, uneven velocity distribution and low flow can also affect applicability. Follow the selected instrument's method and limits, including any required accessories. If the terminal geometry is unsuitable, the balancing engineer may need an alternative measurement approach.
Finally, preserve the operating context
Record supply or extract direction, terminal identification, system operating state and the selected instrument settings. A building with variable air volume needs a defined test condition before readings can be compared with design values. Changes to neighbouring branches can influence a terminal after it was measured.
Keep calibration and functional checks current, and review unusual readings before adjusting dampers. A capture hood measures terminal airflow; it does not directly establish filter integrity, room particle class or every aspect of ventilation performance.
For airflow capture hoods, send shengtongjh the terminal dimensions, expected flows, directions and access conditions to select a practical measurement kit.