Connector Flow Configuration: Preset vs. Calculated vs. System

[dbillion]

Greetings,
If creating content to build a system, I'm assuming that I should set the Diffusers' duct connection Flow Configuration to Preset, right? That way I can set the airflow at the diffusers. Am I right so far?

At the fan, do I make the Connection Flow Connection Calculated or System? Why? What is the difference? There is no definition or explanation in any of the tutorals.

Regards,

Dave

[jason.martin]

Preset is appropriate for the air terminals.
System or Calculated may be appropriate for the fan's. It depends a bit... If you are actually creating systems, then in "most cases" either would potentially work. If you are not creating systems, then setting the fan to "system" would mean that the fans would take on the flow of the default systems, and it would be wrong. Setting it to calculated means that it actually reads the value of the duct that connects to the connector and sets the flow based on that duct (or fitting). Setting it to system means that it reads the flow from the system that it is assigned to. This can create conflicts where the flow on the duct is different than the flow of the system itself.
hth
jason

[dbillion]

Most of that makes sense to me and I'll set the fans to Calculated. I figured the Terminals should be set to Preset.
Thanks for the input.
Just wondering, under what circumstance would a duct's flow differ from the system?
That's got me a little puzzled.

Dave

[jason.martin]

For air systems, I actually can't think of a case where the system flow shouldn't match the flow on the connector of a duct (but I also haven't thought about it very much).
For piping systems is is much more common to have situations like "parallel" pumps where the flow on a pump may be a percentage of the system flow, rather than the flow on the pipe connecting to it.
It is for these types of parallel systems that the system flow parameter was introduced. Duct was simply updated to match what was done for piping.
hth
jason

[KMAeng]

Check out this Autodesk University class on connectors. The handout helped me a bunch, especially with the "System" setting.

http://au.autodesk.com/?nd=class&session_id=3212

Download the class handout under "Class materials" or try this link

http://au.autodesk.com/?nd=material&session_material_id=1495

[dbillion]

Hey,
Thanks for all the input. Things are much clearer!

Dave

[KyleB_Autodesk]

Dave,
You'll probably find the videos I made on Inside the System helpful to illustrate the Flow Configuration settings. Check them out:

Part 1

Part 2

Cheers,
Kyle B
Product Manager
BIM Simulation & Emerging Technologies

[cgpowell]

Kyle/ Jason,

This is an old thread but the comment about the intended use for system flow config. connectors made me wonder if there is any guidence on best practice  or intended use for connectors in the mechanical, electrical & public health systems.

I havent found any and now knowing when system flow configeration could be use will be very useful as Systems are now becoming more & more important. Most examples seem to be on mechanical pipework, with little on drainage & vent systems

Thanks,

Chris Powell

[Iev60047]

@KyleB_Autodesk , those links you posted work, but it appears that the videos are no longer available. Is this a personal issue, or are other people able to access this resource? Thanks in advance!

and @KMAeng the links you posted are now dead. Do you happen to have those resources still, or does anyone know of an equivalent resource/document?

Edit: Dead link request.

[iainsavage]

@Iev60047 That link that I posted to the Getting into the Flow document should help you to understand connectors.

Here it is again.

https://thebuildingcoder.typepad.com/files/me204-3_connectors_in_revit_mep_content.pdf

Preset would usually be for terminal devices such as air terminals, radiators etc. You would preset the flow value at the terminal either by typing it into a parameter or as the result of a formula.

Calculated would usually be used for source equipment such as boilers, chillers, etc. The totalised flow from all connected terminals would be calculated and passed into the equipment. Calculated can also be used for in-line equipment such as pumps, fans, balancing valves/dampers etc.

System is used in the same way as Calculated but when there are parallel pieces of equipment which each share a proportion of the total flow. When System is chosen a flow factor parameter appears and this is used to allocate flow proportion to each device e.g. two boilers in parallel would each have a flow factor of 0.5.

For equipment such as a water heater you might used Calculated on the hot supply connector then pass that value, via parameters, to a Preset connector on the cold water connection which will then in turn pass this value to a Calculated connector at the cold water tank.