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Thread: Duct Static Pressure Calculation in Revit... is anyone using this?

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    Duct Static Pressure Calculation in Revit... is anyone using this?

    I've known that this was a thing for years, but I always considered it to be one of the many MEP features that "wasn't ready for Prime Time" (like MEP's abysmal Heating and Cooling Load function.)

    But recently, I started tinkering with small duct systems on a project of mine and discovered that I was actually getting reliable data. I had to make a few changes to some of our standard duct fitting families, but it seems to be working! At some point (2016 maybe?) Revit started automatically assigning the correct ASHRAE Loss Coefficient Table data for duct fittings, which makes all the difference. I've checked the Revit SP values against my hand-calculated results and they're within 5% of each other.

    So, has anyone else been doing their Duct Static Pressure Loss calculations in Revit?

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    Yes we are doing all duct calculations & sizing in revit, the main problem we found was 90 bends did not have the correct table & we could not find out why so we just rote a small tool that changed them all with one click.

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    Quote Originally Posted by Chris.kershaw View Post
    We could not find out why so we just rote a small tool that changed them all with one click.
    Could you elaborate on how you made this change? I've tried and couldn't find a way to do it.

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    when you select a fitting you can edit the loss method settings and change the associated Ashrae table but you can only do this one at a time we wrote a small routine that dose the whole model for you in one click

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    Personally I find it really bizzare that the loss method and table settings are all INSTANCE parameters... If you could set it in the Type or in the family with formulas there would be no need for extra programs.

    Another reason why the pipe and duct pressure calcs dont get used so much here in europe is that there are sometimes differences between the ASHRAE methods and local standards. However, if you are interested in programming you can make your own calcs for any of the pipes/ducts/fittings/system types.
    The Building Coder: User MEP Calculation Sample

    Ive just started playing around with this, but cant find any examples newer than 2013....

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    You have to have it as an instance how would you manage bends as they are one family with many different angles

    We have done lots of testing and Revit is closer to manual calculations than some of the popular stand alone design packages that have been used for a long time in the UK and the new ones

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    Quote Originally Posted by Chris.kershaw View Post
    You have to have it as an instance how would you manage bends as they are one family with many different angles

    We have done lots of testing and Revit is closer to manual calculations than some of the popular stand alone design packages that have been used for a long time in the UK and the new ones
    Does it u

    it use proper tables? as ashrae is not UK stanadard is it?
    Last edited by nick_h; January 28th, 2017 at 09:36 AM.

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    I was hung up about that too at first but i don't believe there is any law saying you cant use ashrea tables in the uk, as i said we tested against manual calcs and the were very similar

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    Quote Originally Posted by Chris.kershaw View Post
    I was hung up about that too at first but i don't believe there is any law saying you cant use ashrea tables in the uk, as i said we tested against manual calcs and the were very similar
    I did give it a quick go the other day and sized some duct and the engineered passed it.

    What your normally workflow for designing ductwork in revit. Setting the airflow (preset parameter) to all the air terminals routing duct and click duct size and going from there, or is there other ways.


    Sent from my iPhone using Tapatalk

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    You can do that, i usual sit down with the designer at the start go through the basics for the job like where the risers are where we think the mains runs will go and whats accepable velocity in diffrent areas. Then i would start drawing like you say putting flows on grilles belmouths i dont use the sizing tool i just check it manualy as im going as ill be thinking about coord as well so i might be aware of an area with pipe crossing so ill make the duck flatter. Once ive dont a floor ill give it to the design as a colour fill drawing with velocitys and tags with flows as well as the pressure drop export. Depending on the designer they will either go into revit them self and tweek a few things or sit down with me and tell me what to change.

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