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OpenStudio: should you add adiabatic pipes and bypass branches manually?

asked 2015-09-18 08:49:39 -0500

I noticed that OpenStudio tends to add automatically some adiabatic pipes in the plant loops even if you didn't put any, including:

  • A Supply outlet pipe
  • A Demand inlet pipe
  • A Demand bypass pipe
  • A Demand outlet pipe

Why is it adding a bypass only to the demand and not the supply?

It seems that OpenStudio checks whether you have included the inlet/outlet pipes and doesn't add them if there are already there. But it seems that it will always add a demand pipe, even if you do have one. Why?

Should/can you manually create the pipes?

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answered 2015-09-18 09:21:54 -0500

OpenStudio's behavior is based on a mix of superstition and (perhaps outdated) guidance that E+ has fewer convergence errors if there is a demand bypass pipe, even if that bypass has no flow or negligible flow moving through it. I admit I don't have data handy to back this up though. I am more than happy to reconsider this behavior if we have some evidence to motivate a change. I have always been a little reluctant to insert magic stuff into the topology like this, but I think this is fairly unobtrusive. It doesn't muck with nodes surrounding components you put in your model and it has been in there for a long time. Maybe if we make a change we should just beef up the logic to not add the demand bypass pipe if there is already one there.

As for the inlet and outlet pipes, the deal is that the way E+ input syntax is structured, there are necessarily "Branch" objects before and after the splitter mixer pairs, and branches necessarily have at least one component on them or the input syntax is not valid. In the OS -> E+ translator software, we are checking to make sure there is at least one component on the inlet/outlet branches and adding a pipe if nothing else is there to keep the simulation from failing for a trivial reason.

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Github issue here showing that I agree with you that "we should just beef up the logic to not add the demand bypass pipe if there is already one there"

Julien Marrec's avatar Julien Marrec  ( 2015-09-18 09:25:33 -0500 )edit

If you look at the Plant Application Guide, they say you should have a bypass on both supply and demand sides (equivalent to a common pipe splitting the loop into two half loops)

Julien Marrec's avatar Julien Marrec  ( 2015-09-18 10:41:42 -0500 )edit

Plant Application Guide: "Operating/active components (except pumps) should be bypassed by adding a bypass branch parallel to the branch containing the active component."

Julien Marrec's avatar Julien Marrec  ( 2015-09-18 10:45:17 -0500 )edit

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Asked: 2015-09-18 08:49:39 -0500

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Last updated: Sep 18 '15