Generator Ventilation and Airflow Basics

In Short

Generator ventilation is the airflow that supplies the engine with combustion air and carries the heat of the set away. If enough air does not arrive, the room or enclosure heats up, the engine loses output and eventually shuts down, so the size and position of the openings matter as much as the generator itself.

A diesel generator is an air machine as much as a fuel machine. The engine breathes some of it for combustion; the rest carries away the heat of the radiator, the engine surface, the alternator and the exhaust pipe. If that air does not arrive, the room or the enclosure heats up, the engine loses output and finally shuts down on high coolant temperature. This guide explains the airflow of a generator installation and why the openings matter.

How Much Air, and Where It Goes

The radiator fan sets the flow on a set with a mounted radiator: the engine maker's data sheet gives the airflow of the fan and the restriction the fan can work against. The air enters the room through the inlet opening, passes the alternator and the engine, is drawn through the radiator and leaves through the outlet opening or a duct. On a set with a remote radiator the room needs its own ventilation fans for the heat the engine and alternator give off into the room.

The combustion air is taken from the room through the engine's own filter, or from outside through a duct on dusty sites. The room air temperature at the engine inlet matters: engine makers reduce the output when the intake air is hot, and an enclosure that runs hotter than the outside costs power.

Openings, Louvres, Hoods and Silencers

Everything in the air path - the inlet louvre, the bird screen, the attenuator, the room itself, the outlet duct, the outlet louvre or hood - adds resistance, and the radiator fan can only push against so much. If the total is too high, the airflow falls below the engine maker's figure and the radiator cannot do its job. AXON checks the whole path for each project.

Acoustic installations put silencers in both openings, and the silencers that reach the sound level also add resistance that the fan must overcome; the two are planned together. Weather louvres keep rain out, hoods turn the opening away from the wind, and bird and insect screens must not become the restriction.

Hot Climates, Altitude and Recirculation

In a very hot climate the air that enters is already hot, so the rise in the room must be kept small: every degree the enclosure runs hotter than the outside is a degree lost at the radiator. Inlets go on the shaded side, the roof is insulated, and the air path is kept short. At altitude the air is thinner, the fan moves less of it and the engine maker reduces the output, so the site height has to be stated.

The usual mistake is recirculation: the hot outlet air finds its way back to the inlet, around a corner, over a roof or between two enclosures standing too close. The inlet temperature creeps up, the set derates on a hot day, and nobody sees why. Outlet and inlet are placed on different sides, the outlet is directed upwards or away, and enclosures in a row are spaced or their outlets aligned so that one does not feed the next. AXON plans the ventilation of its enclosures and containers with the air path, the silencers and the site together, and builds the air inlet hoods, louvres and outlet chimneys that go with it.

In short

The radiator fan airflow and its allowed restriction come from the engine maker
Every part of the air path adds resistance, and the fan can only push against so much
Silencers bring the sound level and the resistance together
A hot room costs engine output; hot climates need short, shaded air paths
Recirculation of hot outlet air is the common fault; placement and direction prevent it
AXON designs the ventilation of its enclosures and builds the hoods, louvres and chimneys

What to send with an enquiry

Generator set model and the engine maker's airflow and restriction data
Site ambient temperature, altitude and prevailing wind
Sound limit and the distance it applies to
Room or enclosure dimensions and where the openings can be
Dust conditions and whether combustion air must come from outside
Neighbouring units and obstacles near the openings

Send an enquiry Send us files

Questions we are often asked

How much air does a generator need?

The engine data sheet states it: the radiator fan airflow plus the combustion air. Large sets move a great deal of air, and the exact figure is per model.

Can the inlet and the outlet be on the same wall?

Only with care: the hot outlet air must not reach the inlet. Different walls or a directed outlet are safer; where the same wall is unavoidable the outlet is ducted up and away.

What temperature should the room run at?

As close to the outside temperature as the design allows. The engine maker's data for intake air shows what each degree of rise costs in output.

Do silencers reduce the airflow?

They add resistance, and if the fan cannot overcome it the airflow falls. The silencers are chosen with the fan in mind; where that does not work, ventilation fans are added.

What about a remote radiator?

The radiator duty leaves the room, and the room only needs the heat given off by the engine and the alternator ventilated, by dedicated fans. The combustion air still comes in.