Duct static pressure simulation 6

[scottlsu]

I am currently working on a problem with a 20,000cfm VAV AHU. This has system powered terminal units (Carrier Moduline) which require 1" of static at the terminal unit in order to modulate. The problem is that there is not enough static pressure at most of the units for them to modulate. This is a roughly 30 year old setup, which I don't believe has ever had the ability to modulate.

I believe the fan was undersized to begin with. It was originally specified with a 20,000 @ 1.5" esp fan, which is currently in place. I am trying to specify a new fan which will provide 1" of static pressure at the furthest terminal. Can anyone assist me with a general approach to modeling this? If i am lacking .5" at the furthest terminal, I do not think it is as easy as adding .5" to the new fan specs, as i highly doubt this thing responds linearly.

I have tried using Revit MEP, however this does not allow you to simulate different static pressure conditions (it basically adds up all of the pressure drops to calculate ESP).

Please help!

 

[Waramanga]

thanks scottisu for sharing your problem with us. The reason I like this forum so much is because people bring their problems in their various shapes and sizes and often poorly defined (it is a forum after all!!!). The 'brain storming' I have witnessed on some problems here is brilliant on occasion. I dont think we regularly hit the mark or really solve someones problems directly via the forum (I agree that life is to complicated for that!!).

I can honestly say that some of you guys sitting at home with a beer and chewing on one of my badly defined, ill informed problems has really helped at times, so thanks. I hope to return the favour!

Also, I agree that it is very important to know when to call it quits and get a more senior engineer
involved, even if it blows your fee. It will likley be much cheaper than having your ass sued for the modifications that didnt work!! You need to weigh up risk versus reward. Your client will probably be impressed that you knew when to call in a higher power to solve the issue. No one thinks that a single engineer knows what the solution to every problem is!!!

cheers

 

[AnotherEllis]

I agree with Warmanga. I own my own firm, and usually have a pretty good idea of what's going on and what to do about it. But I'm not a 40+ year veteran and haven't seen everything.

For that reason I maintain relationships with other engineers and peers, esp. those I worked with in the past or went to school with. It's nice to have somebody to call and bounce ideas off of/ ask if they have seen the latest craziness, etc.

Sometimes "I don't know" is the right answer.

http://www.ellisconsultingengineers.com