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Generator Room Ventilation Application and Installation

Sizing Considerations

Ventilation Fans 


Except for special applications, natural draft ventilation is too bulky for practical consideration. Adequate quantities of fresh air are best supplied by powered (fan-assisted) ventilation systems. 


Generators in generator room
(photo credit: Caterpillar )



Fan Types 


The following types of ventilation fans are typically used. 

• Vane-axial 
• Tube-axial 
• Propeller 
• Centrifugal (squirrel cage blowers) 

The selection of fan type is usually determined by ventilation air volume, pressure requirements and space limitations within the engine room. The fans have various qualities that make them better suited to certain applications. 

Fan Location 


Fans are most effective when they withdraw ventilation air from the engine room and exhaust the hot air to the atmosphere. However, ideal engine room ventilation systems will utilize both supply and exhaust fans. This will allow the system designer the maximum amount of control over ventilation air distribution. The fan motors should be mounted outside the direct flow of hot ventilating air for longest motor life. The design of centrifugal fans (squirrel cage blowers) is ideal in this regard, but their size, relative to the vane-axial or tube-axial fans, sometimes puts them at a disadvantage.

Fan Sizing 



Fan sizing involves much more than just selecting a fan that will deliver the airflow volume needed to meet the cooling air and combustion air requirements. It requires a basic understanding of fan performance characteristics and ventilation system design parameters. 

Similar to a centrifugal pump, a fan operates along a specific fan curve that relates a fan’s volume flow rate (m3 /min or cfm) to pressure rise (mm H2O or in. H2O) at a constant fan speed. Therefore, fan selection not only requires that the volume flow rate be known, but also that the ventilation distribution system be known in order to estimate the system pressure rise. This information allows the optimum fan to be selected from a set of manufacturers’ fan curves or tables. 


Exhaust Fans 


Ventilation air exhaust systems should be designed to maintain a slight positive or negative pressure in the engine room, depending on the specific application. Positive pressure should normally not exceed .050 kPa or (0.2 in. H2O). 


This positive pressure provides the following advantages.


• It prevents the ingress of dust and dirt, which is especially beneficial for those applications involving engines that draw their combustion air from the engine room. 

• It creates an out draft to expel heat and odor from the engine room. Some applications, such as a marine application where the engine room is adjacent to living quarters, require that a slight negative pressure be maintained in the engine room. This negative pressure should not normally exceed 0.127kPa (0.5 in. H2O). 


The excess exhaust ventilation provides the following advantages. 


• It compensates for the thermal expansion of incoming air. 
• It creates an in draft to confine heat and odour to the engine room. 


Two Speed Fan Motors 


Operation in extreme cold weather may require reducing ventilation airflow to avoid uncomfortably cold working conditions in the engine room. This can be easily done by providing ventilation fans with two speed (100% and 50% or 67% speeds) motors.




This article was extracted from "Engine Room Ventilation, Application and Installation Guide" by Caterpillar, the full guide can be downloaded below.




Download the Free Guide Here








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