ABD SS6 - Hydraulic calculations

Question

Hello, 
 I have an issue with hydraulic calculation which are made for ventilation installation. 
 What I need is to calculate a pressure loss on a ductwork to fit a correct fan or ahu. For those who are not a sanitary engineers i explain that for that calculation I have to total linear loss which depands on duct's roughness and lenght and local losses which are couses by changing duct direcion, dimensions etc. 
 ABD has a tool called Duct System Sizing Dialogs but what I find is that it calculate only a linear losses and not even for duct's size which I drawn in a model but for duct's size which is set on settings>limit duct velocity. And here my question: 
 - can ABD callculate also local losses causes by elbows, transitions etc? 
 - can I set Duct System Sizing tool to make a calculation for a duct's size which I drawn on a model? 
 - can I export that calculation to an exel file? 
 It seems that without program's abilty to make that simple calculations I will have to find out another program to make it. Does anyone know a program which is working with aecosim and can make those calculations?

Marc Thomas · Accepted Answer

I am not a mechanical engineer, but my understanding of the Duct Sizing Utility is that it does take into account the pressure losses caused by all elements in the system it " uses a combination of the accepted algorithms to size duct based on the constant velocity and equal friction methods prescribed by industry standards such as ASHRAE and CIBSE. This workflow consists of allowing you to first route duct systems in a single line exercise to create a complete HVAC system, size the fan requirements and duct sizes and rebuild the system as calculated." 
 The workflow is described in the help documentation, there is a lot of detail on how the Duct Sizer works. Also take a look at the training sessions AECOsim Building Designer Mechanical - HVAC Design .

dominic SEAH · Answer

Tomasz,

I think that you will have better luck if you post in the Building Performance forum.

communities.bentley.com/.../113905

Apparently, Hevacomp has something called Netsys that sounds like what you are looking for.

stan.white · Answer

I don't know if the leading manufactures of duct sizing programs will recognize the file format that AECOsim generates. It has been a while since I used the Carrier and Trane duct sizing programs, maybe now their programs do read DGN /DWG.

stan.white · Answer

Is it your intention to achieve balance via your calculations? Or are you just trying to blow air and pressure through existing geometry, and spit out the numbers? 
 
Our sizing utility is “equal friction method” to attempt to balance flow. 
So... if existing geometry (think exaggerated) were to be loaded into the Duct Sizing Utility, AND... All the ducts were then locked in Sizes to the existing geometry... You would get calculated losses per component...BUT… you are making all the assumptions of actual flow at the ends, when in fact, all the air could be blowing out of the nearest hole, if that is true, So the answer is “no”. A sizing utility attempts to achieve desired flow at the outlets. Only then, can pressure losses be predicted. 
 
This is an applied science called Computational Fluid Dynamics, which attempts to predict flow and pressure losses on existing geometry. So the short answers is, if you are not “balancing” to predict flow, your pressure losses are not accurate. That’s not a limitation of the software, it’s a scientific statement of the method employed.

ABD SS6 - Hydraulic calculations

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