Revit MEP (Piping) cant design pipe, flow = 0

[richard_pasler]

Hello,

Im working on my bachelors thesis. I want to design some domestic water pipes. 

I have done my project. Everything well is connected, no errors. 

Problem is, that (in my opinion) fittings doesnt work. The flow flows from furnising item to closest fitting, than becomes 0l/s and pipe cant desing. System inspector is also not showing. Revit says to check the flows from furnishing items, but they are correct.

Anyone pls help? 

Thx. 

[RobDraw]

The fittings that come with Revit do work when the systems are built properly according to needs of Revit. Different systems cannot be connected and they need to be complete without open ends.

[iainsavage]

It is not the fitting which will usually be the cause of this, you just see the problem manifesting itself at the fitting.

The problem will be elsewhere in the system and it will not be "well connected" in a Revit sense.

Usually its a problem with the settings of the connectors on the plumbing fixtures or equipment, or too many open ends on the system.

I've solved several similar problems for people and you should be able to find other posts which might point you in the right direction.

If you want more assistance though you'll need to upload the model for investigation because there is no way to tell which part of the system is causing the issue without getting into the model.

[richard_pasler]

OK, thx, seems u know what to do 😄 Im uploading the model. 

[richard_pasler]

Yes, I know that. There are no open ends, but the connection between circulation and hot water can be a problem..

[RobDraw]

You're welcome. 

[iainsavage]

Straight off there are numerous warnings about flow direction mismatch so you need to examine the connectors on fixtures and equipment as I said.

I'll look into it further later on but you maybe want to have a go yourself (as a learning experience?)

[richard_pasler]

I already go through this mismatches, checked every family. Also with my uni collegue. And we cannot find the solution. But thx for the reply, I will go throw your posts and try to find a possible solution.

[iainsavage]

You've got a cross-connection between two systems here:

You can't have that.

You need to separate them or connect them via a piece of equipment (you can modify a tee family to act as a piece of mechanical equipment to pass flow from one system to the other).

Disconnecting this joint solves many of the flow mismatch errors but not all of them so I'll keep looking.

[richard_pasler]

Ok, very nice, I will try that, there will be also cross-connection between hot and circulation water. I have to repair that :D.

[RobDraw]

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@richard_pasler wrote:
the connection between circulation and hot water can be a problem..

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Why didn't you try fixing it before uploading the file?

[richard_pasler]

I didnt know about cross connections, but there were non open ends so nothing to fix.

[RobDraw]

I told you about it and you acknowledged it.

[iainsavage]

@richard_pasler I'm just getting back to you to see if you managed to sort out your flow problems or if you still need help with this?

I also thought I should point out to you that, although not related to your flow mismatch problems, your plumbing fixtures have the connectors set to Preset and have fixed flow values. That is unusual for plumbing systems and it is more usual to set the connectors to Fixture Unit and assign fixture unit values. In plumbing systems there is always diversity of use, you will never find every fixture discharging simultaneously at full flow, hence the use of fixture units or loading units which are calculated using probability theory.

If you don't use fixture units then once you've solved your flow mismatch problems and run a pipe sizing calculation you will get ridiculously large pipe size selections.

Be aware as well that Revit uses the International Plumbing Code method for fixture units and flow conversions.

[richard_pasler]

Oh, thanks. Yes, I still need help.
Yes, I know bout this. I preset flow values. My uni proffesor told me to set fixed unit values, so the revit can calucalate the flow :D. Before that, there were all 0l/s. I must try to read some of your fixed articles, meaby find a solution. Its quite hard, nobody knows revit - water pipework at my uni.

[RLY_15]

It's a good discourse to have with your professor - fixture unit summations for various types of equipment was based on research performed several decades ago looking at fixture flow rates and building use profiles. In the time since, we've dramatically reduced flow rates through fixtures like lavatories and water closets by various regional energy code mandates. I think IAPMO was taking measures to provide calculation methods intended to unify fixture unit calculations (high flow results) with present day fixture flow rates (low flow results).

A common occurrence would be in something like a small retail shop. By the book, the single unisex restroom and service sink might compute to ~15 GPM by the fixture flow method, even though you have a 0.25 GPM aerator on the faucet, a 1.28 gpf toilet bowl, and a seldomly used service sink at 2-5 GPM, the total of which would never reach 15 GPM even with all units at full flow.

[iainsavage]

Some of your plumbing fixture families had connectors set to Calculated. They should be Preset or Fixture Unit.

For the water heaters:-

• The cold water inlet connector should be set to Preset.
• The flow parameters should be Instance instead of Type.
• The flow parameter for the cold inlet should be made equal to the flow parameter for the hot water out connector by using a formula.
• By doing this the flow rate at the hot water connector is calculated from the connected plumbing fixtures and this rate is then passed to the cold water inlet pipe.

The hot water return (circulation) branches need to be disconnected from the hot water flow pipes, the resulting open ends need to be capped.

This loop below can't be allowed, the cold water system won't be able to analyse the parallel paths. You need to break the loop somewhere so that there is only one route to each fixture.

I think there are other similar cross-connections but I haven't tracked them down yet.

[richard_pasler]

I try to do what you write me before. Here is a result. @iainsavage  Brand new errors 😄 

Im adding the model also. Still doest calculating 😄 

[richard_pasler]

I try to do what you write me before. Here is a result. @iainsavage  Brand new errors 😄 

Im adding the model also. Still doesnt calculating 😄 

[iainsavage]

I'll take a look at your updated model later on (busy just now).

The new error that you are getting implies that you've actually fully disconnected part of the network which is not what I meant you to do.

For the part(s) which are in loops you break the loop in one location and cap off any open ends so that each plumbing fixture only has one unique route from system source to the fixture.