Engine Room ventilation - Air out issue

[Ad Hoc]

Maybe I do not understand you all right....

Correct

Ok..what engines do you have in the ER..and do you have any generators too?

 

[Lucya]

Following my technical book a rectangular duct 0.7 m * 0.45 m has the same pressure loss as an round pipe of a diameter of 0.55 m (cross section areas are not the same, but the friction is). If the walls of the duct (leghth 2 m) are fair, there will be a pressure loss of 16 Pa = 16 N/m² . (A coarse surface would signifantly increase the pressure loss.) The grill resistance is to add. Is the grill horizontally oriented (rain in the ER)? If it is vertically oriented, the change of the direction of the airstream causes an additional resistance.

The grill is to be horizontally orientated.

 

[Heimfried]

I don't know anything about the intended fans, but just to give an example of a fan, which is able to deliver 19,650 m³/h (page 247 at the linked booklet): if you look at the graph it shows the nearly 20,000 m³/h are for "free discharge" (without any flow resistance). If the fan has to work against a pressure loss of e.g. 300 Pa, it delivers only 16,000 m³/h.

 

[Lucya]

Correct

Ok..what engines do you have in the ER..and do you have any generators too?

At least something I said is correct.

So, there are two diesel generators. each 65 kW

Edit: to be less confusional, it is a barge.

 

[Ad Hoc]

At least something I said is correct.

So, there are two diesel generators. each 65 kW.

Need make model number and tech data to get the spec's....since this give the heat rejection etc.

 

[Lucya]

Need make model number and tech data to get the spec's....since this give the heat rejection etc.

Scania Diesel Gen OL 621 C / HCM 534 C - 265 kW
(I missed "2" in post above regarding kWs)

 

[Heimfried]

[...]
My dilemma is not the required air for ER, my dilemma is whether the Outlet duct 0,3m2 x 2 PSC (0,6m2 SUM) are enough to exhaust around 6 m3/s of air?
Saying that the velocity in each duct must be 10 m/s to satisfy this requirement (there are two ducts of 0,3m2).
How can I check what air velocity will be in the duct without fan in Outlet duct (natural non-forced air out)..?
[...]

You will not achieve this exhaust rate in the outlet duct without using the pressure created by the intake fans. That means, if the ER door is open, the air takes a different path. May be, this would also be sufficient for required cooling - maybe not.

Assumed, the ER is closed, the 2 fans are able to deliver an intake of 11 m³/s against a pressure of say 300 Pa, then the 2 ducts will pass this flow rate to outside. But note that air velocities over (5 to) 7 m/s are tending to be noisy. Therefore in buildings they are unwanted. A ship is different, an ER is noisy too, but 20 m/s is a lot and pressure loss increases with air velocity.

 

[Lucya]

but 20 m/s is a lot and pressure loss increases with air velocity.

There are two ducts, so 2 x 0,3 m2 - resulting 10 m/s each? (Sum of Air-out cross section is 0,6 m2 - 6/0,6=10)... or I am doing it wrong, again?

 

[Ad Hoc]

Required E.R. airflow 40 m3/h ....

Well, according to those engine specs: https://www.scania.com/content/dam/...s/pdf/specs/power-gen/DC16_43A_500-550kVA.pdf

I get that you need roughly around 6.2m^3/sec or 370 m3/min

 

[Lucya]

Well, according to those engine specs: https://www.scania.com/content/dam/...s/pdf/specs/power-gen/DC16_43A_500-550kVA.pdf

I get that you need roughly around 6.2m^3/sec or 370 m3/min

40000 m3/h (around 11 m3/s), is the result I have for required ER airflow, since there are other equipment in the ER, not only generators.
Are the 0,3 x 2 PCS outlet ducts cross section resulting sum of 0,6 m2 sufficient to exhaust ER air of 6 m3/s (this value should maintain the ER temperature at max. delta T of 10C) without using the fan assistance (fan is only in the Air-in duct, pushing the air into ER)? And if yes, what is the calc which (theoretically) proves it?

 

[Ad Hoc]

Sorry Lucya

You're not reading correctly.

So...in order to ascertain if the numbers you have posted are correct - which could be the source of your dilemma in trying to calculate required air flow etc - what size and type of engines are in your ER..and what other, if any, sources of combustion too..such as gensets etc.

So...please list AL THE ITEM OF COMBUSTION..in the ER.....and you replied:

So, there are two diesel generators. each 65 kW

Just 2 gennies. But now you say:

40000 m3/h (around 11 m3/s), is the result I have for required ER airflow, since there are other equipment in the ER, not only generators....

I have asked what is in the ER...you said 2 gennies..now you say there is more.?????????????!!!!!!!!!!!!!!

Can't help you if you don't answer the questions.

 

[Lucya]

Yes, only two of generators which requires airflow for combustion + airflow for evacuation of heat emission from all of the ER equipment including gensets, exhaust pipes, other pipes in ER, electro cabinets incl. main switchboard, boiler for FW, pumps - of which I do not have at the moment asked data, only gensets).

The result was 11m3/s airflow needed, taking into account the needed airflow for combustion for gensets and needed airflow for evacuation of all equipment and pipes heat emission included other parameters (air density, specific heat capacity of air and temp difference).

But please, do not bother.
Thank you anyway, appreciate your efforts so far very much.

 

[Ad Hoc]

You are over thinking this, it is not a university exam question.

What sources of combustion do you have inside the ER..in TOTAL....for get pipes/cabinets etc.

You will have engines....yes???...if so..what size type and how many...do you have gensets...yes??..if so what size and how many.....any other major sources such as steering gear etc etc?

That's it.

You only need to focus on the major heat sources.

 

[Lucya]

I have edit my post before adding info that this is a barge, to make it less confusional, so only 2 gensets and already mentioned equipment/pipes are in ER. No propulsion.

 

[Ad Hoc]

...to make it less confusional,...

The skill of the engineer is to be factual no more no less and to have no ambiguity, and to comprehend the task at hand.

So, if ONLY 2 genset as noted, the required air is 6.8m3/s (if i use the stand by power heat) so call it 7.0m3/s.

This would give you something like:

With a pressure rise of no more than 250-300Pa.

So this gives you an ELTA fan of 800 model:

From this you can work the rest out, as Hiemfried notes. But this is for a pressurised ER and the air-in and air-out will be noisy. Thus to avoid the noise path you should cite the air-in and air-out away from the main structure and these should be insulated too.

Ideally, these fans should be controlled at 2 speeds so that in harbour (if noise control) or at cooler conditions the fan can be set at the lower speed to reduce noise and power consumption.