Pitfalls #1 – Gas temperature at start-up
Gas temperature at start-up: why it distorts fan selection
“But we provided the correct operating conditions…”
This is a sentence we hear frequently after a difficult commissioning.
On paper, everything looked right: the fan was selected for the nominal operating conditions. Yet at start-up, the motor trips or the absorbed current exceeds the limits.
In most cases, the root cause is the same: transient operating conditions, and especially gas temperature at start-up, were not considered.
The classic pitfall: focusing only on steady-state operation
Most fan inquiries include:
- airflow,
- pressure losses,
- nominal gas temperature.
That makes sense — but it is often incomplete.
In many industrial processes, the fan does not start under nominal conditions.
At start-up, the gas is usually:
- colder,
- and therefore denser.
This difference has a direct impact on fan behavior.
Why a lower temperature matters
At constant speed, higher gas density results in:
- higher developed pressure,
- higher absorbed power,
- and therefore a real risk of motor overload.
A fan that is perfectly suited for nominal operation may become electrically out of limits at start-up, simply because the actual gas temperature was overlooked.
👉 The gas temperature at start-up, and more broadly transient operating conditions, are not a detail.
The supplier’s role… and the importance of context
A good supplier will be able to guide you through this reasoning and challenge the data.
But this is only possible if the initial request provides enough context.
A selection based solely on nominal conditions limits the ability to:
- anticipate critical phases,
- secure start-up,
- recommend the right solutions (VSD, start-up strategy, motor margins).
The quality of the selection directly depends on the quality of the information shared.
Key takeaway
Most start-up issues are not caused by a “bad fan”,
but by a selection based on an incomplete operating scenario.
In this Pitfalls in Selecting Fans series, we will continue sharing these real-life lessons from the field.