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Error when using Tempering Valve

asked 2015-12-09 14:49:55 -0500

RChidwick gravatar image

updated 2015-12-09 17:27:52 -0500

Hello community,

I am trying to create a plant loop with a boiler and a mixed water heater (acting as a HW storage tank) on the supply side and a low temperature radiant variable flow heating coil on the demand side. I asked a question a little while ago about how to do this (here) and got some great help. A suggestion was to use a tempering valve on the supply side to determine where the hot water should come from when there is demand by the radiant floor. I have played around with the tempering valve but keep getting errors.

I am currently getting this error: * Severe * TemperingValve object needs to be on an ACTIVE branch

Here is a picture of my plant loop. image description

Node 9 is the outlet of the boiler. Node 4 is the plant loop setpoint node (setpoint manager at the right of the picture). Node 13 is the outlet of the pump

I have tried putting the valve on each branch of the supply side, before and after the boiler or hot water tank. I have posted a comment about this in another question I asked, but I thought it would be better to ask a new question where I can provide more information about what I have tried.

Thank you

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answered 2015-12-10 09:35:47 -0500

updated 2015-12-10 09:37:40 -0500

OpenStudio is tested in the configuration described in the EnergyPlus documentation. In this configuration the tempering valve is alone on a branch and in parallel to some other heating component. The idea being that the tempering valve will draw some amount of unheated water around the heating component to temper the final outlet condition.

Your situation is a little different since you have the tempering value in series to the hot water tank. I don't entirely understand what it is trying to accomplish, but I am surprised it causes your simulation to fail. The inputs to the tempering valve look right to me. In particular your node inputs. Note that if you leave these blank OpenStudio will take a best guess at what they should be when it creates the idf file. This defaulting is however based on the configuration described in the E+ documentation, and if you specifically set particular nodes as you have, then OpenStudio will respect them.

With respect to the actual error that E+ is giving you about the tempering valve on an active branch, that is surprising to me given that OpenStudio is known to work when the tempering valve is alone on the branch. The OpenStudio Model does not expose the branch object or its active/passive input field, because generally this input is confusing to users, and because OpenStudio can typically interpret the correct choice when making the idf file. For testing purposes you could modify the idf file so that the tempering valve branch is set to active. If that works then report back and we can codify this into OpenStudio and in the mean time you can use an EnergyPlus Measure in your workflow. I would be willing to help you write the Measure if you need some guidance.

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Thank you for your reply. I misunderstood the purpose of the tempering valve, but once I read it's description and purpose I realised that hydronic loop above was not the best solution to my problem.

I did try your suggested solution of editing the IDF file and setting the tempering valve branch to active, but the simulation still failed. I also tried setting all the branches to active, but it still failed. But like I said, I have since changed my approach to modelling the thermal energy storage.

Once again thank you for your help.

RChidwick gravatar image RChidwick  ( 2016-01-14 14:07:52 -0500 )edit

"The TemperingValve is an Active component and the other path should have only Passive components. Only two paths in the splitter/mixer can be used; bypasses are not allowed. No other Connector:Splitter and Connector:Mixer pair can be used on the supply side of the plant loop."

It seems like the TemperingValve should be on its own branch, and @Kyle Benne, if OpenStudio is automatically creating a bypass branch, that could explain it too

Julien Marrec gravatar image Julien Marrec  ( 2016-05-31 04:27:17 -0500 )edit

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Asked: 2015-12-09 14:49:55 -0500

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Last updated: Dec 10 '15