A NOOBIE on the loose!

Hi,

I'm a noob mechanical engineer fresh from the academics. Just recently (well about a year now I guess) I have formally started work on a construction company. I have been tasked to do a bit of "hard work" :Din the commissioning of several key systems on one project.

Dealing with fans, I have submitted some fan selections for approval to the designers, unfortunately it came back with a comment asking for a pressure drop calculations. Now the gist is... i know only this as a subject problem in completing the Ref&aircon course in my college, I havent really dealt with it much untill i got myself in this kind of work. (I was planning to go on automotive line of work).

Treat me as a 5 year old if you may, what i need is just a step by step guide to do this. I have the chart tabulation for the fans, design of duct (Its actually a series of roof exhaust fans with a duct riser serving 8 floors), the fan curves and the technical background in my mind.... is this enough? HELP ME PLEASE!!!

---- oh another thing,

I want to learn duct design and closed circuit chilled water system piping design and equipment selection, theres this "DISC DUCTULATOR" (Japan origin) that I saw my design manager uses.... you know any information about this things?

Currently im on schedule for a course in Duct design and Refrigeration system seminars, however, that will happen about 3 months from now as i complete my administrative course. So just now please help me with the one above.... please....

thanks.... like I said... I'm a newbie on the loose, and i only have my d*ck to go with it....

Thanks

If you want a ductulator try here...
http://www.bookmarki.com/Trane-Ductu.../traneduct.htm

or better still, maybe a free one...
http://www.crownproductsco.com/freeductulator.htm

Hi and welcome to the forum.
I can recommend the 'Cook Book "as posted by Brian_Uk years ago, a site search may find it for you.

I have a ductulator from Trane. It was old and grubby when I got it 'bout 15 years ago, but quicker than any computer program

m/s on one side and fpm on the other.

I have an excel duct sizing sheet somewhere.

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Originally Posted by RSTC

I have a ductulator from Trane. It was old and grubby when I got it 'bout 15 years ago, but quicker than any computer program

m/s on one side and fpm on the other.

I have an excel duct sizing sheet somewhere.

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Yep, that's what I think also. I cant carry my notebook all the time inside the job site, It was suggested to me by a peer to go and buy one so that I can easily make on-site adjustments to the installations as I go around to do inspection. However, Its quite a problem for me to buy one since I don't know where I can find one here in Vietnam.

OT:
While here, there's one question i would like to ask, on an installed exhaust system, what happens if the total duct pressure loss is higher than the fan static pressure?
In the absence of exhaust flow requirement (grille & duct airflow req) for the system, I only have the Fan data and the duct size, how should I start calculating for the pressure losses to check if the Fan will perform well?

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Originally Posted by ewokxz

While here, there's one question i would like to ask, on an installed exhaust system, what happens if the total duct pressure loss is higher than the fan static pressure?

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The fan will stall - air flow drop off and motor over heat

Quote:

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In the absence of exhaust flow requirement (grille & duct airflow req) for the system, I only have the Fan data and the duct size, how should I start calculating for the pressure losses to check if the Fan will perform well?

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If you have the fan curve, you can measure the air volume in the duct and plot it on the fan curve, which will allow you to read the ESP.

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Originally Posted by Magoo

Hi and welcome to the forum.
I can recommend the 'Cook Book "as posted by Brian_Uk years ago, a site search may find it for you.

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Coo, that's an old one Magoo, mind you it's still available and for iphones a as well now.

http://www.lorencook.com/about/destools.htm

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Originally Posted by frank

If you have the fan curve, you can measure the air volume in the duct and plot it on the fan curve, which will allow you to read the ESP.

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Meaning I have to take actual air flow reading? If for example I have yet to take the actual flow data, how can I do it on paper? Will I assume a volume flow required for each inlet extract locations (grilles) and go up from there or should I start from the fan using the max fan capacity then move down to the end points of the duct line?

For the duct shaft riser, any condition I need to consider that will differ from the horizontal exhaust ducting?

Just in, I just found out that the system design is for the "CORRIDOR SMOKE EXTRACT" system. Any literature that can guide me thru this?

Can I remind everyone that this is a welcome forum only :)

Any tech questions should be addressed in the correct forum.

Thread Moved

Feast your eyes on this and this
and this one is a corker

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Originally Posted by WebRam

Can I remind everyone that this is a welcome forum only :)

Any tech questions should be addressed in the correct forum.

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Thank You Sir, :)

Quote:

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Originally Posted by frank

Feast your eyes on this and this
and this one is a corker

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Hoa!... many thanks Sir Frank....

In normal practice... standard and code aside, how much flow or air velocity is required for a smoke exhaust grille? And what type of grille can be used? Another thing is, do I still need to have a VCD on the grille side for this kind of smoke extract system?

P.S.
I Googled this item... called the AeroDuct xls program from ThermExcel. Anybody has a copy they can share? :D

http://www.thermexcel.com/english/program/duct.htm

Quote:

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Originally Posted by ewokxz

In normal practice... standard and code aside, how much flow or air velocity is required for a smoke exhaust grille? And what type of grille can be used? Another thing is, do I still need to have a VCD on the grille side for this kind of smoke extract system?

P.S.
I Googled this item... called the AeroDuct xls program from ThermExcel. Anybody has a copy they can share? :D

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The grille velocity will depend on your airflow rate and the grille free area. You will want the minimum resistance for the fan so size the grille accordingly.

The grille type may be decided by the decor of the surrounding area.

A VCD is only required if it needed for balancing purposes.

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Originally Posted by Brian_UK

The grille velocity will depend on your airflow rate and the grille free area. You will want the minimum resistance for the fan so size the grille accordingly.

The grille type may be decided by the decor of the surrounding area.

A VCD is only required if it needed for balancing purposes.

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OT:
I was a bit on the off-side here when I asked about this thing... I was relying too much on intuition just to short-cut this thing.... anyways... thanks for the wake-up.

I have to ask this in return tho.
I used the ASHRAE Duct Fitting database to cross check my calculation, however, there is a value I get that is like this for the following parameters,

-->
for an EXHAUST Duct TEE Junction at the Riser (600 x 500 @1915 lps), using a 45° entry branch (500 x 175 - @383 lps) I'm getting a -94Pa branch pressure loss (@4.4 m/s) and a +7Pa main duct loss (@6.4m/s). What does a negative value denotes?

Several questions also

1. When do you get an "overflow" condition in the ducting system?
2. If in my calculation, the value for the Pressure loss becomes negative (e.g. -54 Pa)... what does it give me? do I add it to the rest of the positive Pressure loss values?

I'm not a duct designer but have often referred to the best book I know on the subject - Woods Practical Guide to Fan Engineering.
http://www.mrv.com.tr/teknik/mrv11.pdf

There is a paragraph 6.5.13, page 87 which describes your phenomenon and confirms there being a 'transfer of energy' to the main duct.

It's a long read but worth checking back on from time to time. :)

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Originally Posted by Brian_UK

I'm not a duct designer but have often referred to the best book I know on the subject - Woods Practical Guide to Fan Engineering.
http://www.mrv.com.tr/teknik/mrv11.pdf

There is a paragraph 6.5.13, page 87 which describes your phenomenon and confirms there being a 'transfer of energy' to the main duct.

It's a long read but worth checking back on from time to time. :)

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Thanks a bunch sir Brian,
Actually, its quite a dilemma for me also. As a mechanical Engineer who's just starting to venture out in refrigeration and general HVAC, I found its like a different world out here. I have the "theories" that goes with the academics but putting things from paper to actual condition is a pain in the *ss.

Right now I just realized (to answer my own question back) that the negative data denotes a backward flow, meaning instead of branch to main, the air flow goes back to the branch, theoretically that is, same goes for the "overflow" thing. Makes me think air is never an absolute science to begin with.

Thank you so much for the help guys. I managed to go around my problem with the help.