01Lower flow changes temperature rise and cooling
At the same heater power, lower air mass flow increases the theoretical temperature rise. In practice, the controller may reduce output, but local temperature can still rise if sensor placement, response time or stage switching is unsuitable.
A nonuniform flow profile can leave some element surfaces with much lower local velocity than the average. One outlet sensor may not detect a local hot region.
02Check likely causes in sequence
- Clogged filters, partly closed dampers or blocked ductwork
- Fan rotation, speed or operating point differs from design
- Duct leakage or upstream elbows distort the flow profile
- Heater pressure drop exceeds available fan margin
- Airflow sensor location, range or calibration is unsuitable
Check fan operation and system resistance, then measure velocity or flow across the heater face. If a pressure or airflow switch is installed, inspect its setpoint, impulse lines and signal state.
03Interlocks should cover startup and operation
A common design includes fan status and proven airflow in the heater permissive, with airflow monitoring during operation. Whether low flow causes an immediate trip, a particular reset method or a delay depends on thermal inertia, process needs and the risk review.
An independent high-limit device can provide another layer of protection, but does not replace airflow interlocking. Place sensors to represent the relevant risk area and check their operation and calibration periodically.
04Keep comparable commissioning data
Record fan speed, filter condition, damper position, airflow, inlet/outlet temperatures, current and heater output. Verify normal flow, minimum allowed flow and interlock action so displayed values match the actual system.
If there is an unusual odor, discoloration or abnormal temperature rise, stop heating under the site procedure and investigate. Authorized personnel should confirm repairs and protection tests before restart.