Engine Room Blowers
When To Consider Active Ventilation
A diesel engine will draw in as much air as it needs; however, the harder it has to work the less efficiently the engine is working – wasting fuel, limiting rpm, increasing carbon build-up and causing extra engine wear.
If the engine room is closed up tightly, to minimize noise, then a system of active ventilation may be necessary.
Adequate air flow to the engine room is even more important in tropical conditions. A good ventilation system should maintain the engine room temperature within 16°C (30°F) of the ambient outside temperature (e. g. a maximum engine room temperature of 41°C (105°F) in 25°C (77°F) weather.
From page 80 Marine Diesel Basics 1
Two Types of Blowers
Active ventilation uses blowers to increase inflow and, in a well-designed system, outflow.
Only fans rated for continuous duty should be installed for engine room ventilation; these are typically “squirrel cage” fans (axial fans).
Inline bilge blowers, though often used for engine room ventilation, are designed to run for short periods to vent fumes and vapours (e. g. gasoline, propane, hydrogen). They are not intended for continuous duty and typically have a service life of only 300 – 350 hours.
This table is a theoretical comparison of active and passive ventilation. Actual performance will depend on the specific installation, (e. g. length & bends in ducting).