Engine Room Ventilation

I’d like to elicit opinions on engine room ventilation fans for diesel inboards. These fans are to cool the engine room space, not combustion air, with the engines off. Should they blow air in, blow air out, or one in and one out???? What’s the best way based on your experience?

 

I seem to remember something about fan efficiencies being greater when used to pull air out of a cavity, as opposed to pushing it in. If you find that you're creating a vacuum in the space, then you need a make up fan (one in one out)

 

If you apply negative pressure to the space (draw air out) gases and heat will not get into the living spaces, but will be forced to vent to the outside through ducting. If the space is pressurized then the living spaces, bilge and every corner of the boat will get this air pushed into anything with less pressure.

In a perfect world these spaces would only vent out of the boat, but in reality, engine space air leaks out through the ceilings, bilge access hatches, cabinets, etc.

I use fans to depressurize the engine space, if there is leakage it will draw air in from those areas I don't want air leaking into.

 

I would draw the air out of the room you want to vent, that's most common in most applications. I read somewhere that if you have an (BIG)engine with the air intake in the engine room you should be carefull that the engine does not the stop the venting blower to turn (burn) as the engine is consumeing much air during operation. So it should be turned off?

Greetings,

Daniel Peeters

 

Engines off

We're talking about the condition of cooling the engine space after they have been shut off and are sitting there still hot.

 

Is there any issue with creating a vacuum in an engine room? I mean hatches and doors could either pop open or be impossible to open once closed. You'd have to shut the fan off to get in and out of some spaces, wouldn't you?.

 

dereksireci,

I would use just one fan on the ventilation outlet (so, blowing out). You'd get the lower pressure in the engine room, so no fumes going to the accommodation (nice comment, PAR). From outside fresh air comming in, and no risk of getting a real vacuum.

 

Air outlet up high in engine space, natural convection plus fan assist draws hot air out; air intake ducted to opposite side of engine room down low, no fan assist, convection or fan vacuum draws cool air in, duct outlet placement allows air to wash over hot engine on its way to outlet. Air inlet should be about twice the cross-sectional area of the air outlet (rule of thumb, for precise sizing do combustion air intake and thermal exchange calcs) to provide adequate flow for both combustion and ventilation air supply.

 

Now, that is what I meant! Thanks, mmd.

 

You might be able to find a solution here: JEC Marine who supply DC brushless marine engine room fans. www.jecmarine.com

 

One vent in, one vent out. Opposites sides of boat. Engines do not need ventilation as such. They have their own ventilation needs But when they are on they suck alot. But humans sweat alot in a engine room, and carbon does kill them. I hope this answers your question... yes you can have an exhaust leak...

 

I agree with most here. Blowers should exhaust air from the engine room, but since diesels use a lot of air, there also needs to be air inlets. You won't create a vacuum, but will lower the pressure in the engine room, which prevents exhaust fumes and CO from getting into accommodation spaces. Remember the old trick of opening a hatch while the engine is running? If the engine speeds up, it is not getting enough air. There is nothing wrong with running the blower while the engine is running. Running it after the engine shuts down will help cool things down. But I have seen very few people actually do that.

 

BTW, Big diesel engines need lots of air... lots.. When I did the numbers and I forgot the CFM, they needed 2 vents 24 inchs long and 8 inchs wide. If I was to close these up they might suck parts of the boat closer to the engines.

 

http://www.proboat.com/2015/06/venting-the-engineroom/