TemperingValve over cooling water

asked 2016-12-02 12:08:31 -0500

jugonzal07
659 ●1 ●11

updated 2016-12-08 16:02:16 -0500

Hi all,

Long story short, I have a tempering valve that is meant to lower the temperature from a storage tank down to 60 C if the storage tank temperature is too high (storage tank connected to solar collectors). However, when looking at the output data I've found the tempering valve over cools the water from the storage tank (e.g. 67 C water down to 48 C). If only cooled to 60 C, the instantaneous water heater wouldn't need to add any energy.

Here is a picture of my setup with labels:

image description

I was surprised to see the tankless water heater doing as much work as it was and decided to take a look at the hourly data and found many cases where the storage water was > 60 C but the tankless water heater was still heating water. As stated before, it looks like the tempering valve is overdoing it when bringing in cool water. It will nearly always bring the temperature down below 60C. I labeled all the tempering valve nodes in blue to help show what I set the tempering valve parameters to.

Any advice would be greatly appreciated!

EDIT: My colleague suggested a setup similar to this:

image description

[UPDATE: 12/8/16] - As you'd imagine, having a supply component on the demand side causes a few issues. The hourly energy data [i.e., the data I got out of out.csv] looks great and seems to correct issues with overcooling-- however, my manual energy calculations do not match with openstudio's reports.

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answered 2016-12-05 15:37:44 -0500

Kyle Benne
6027 ●4 ●9 https://www.openstudio.net/

The node configuration you have labeled as "Stream 2 Source Node", "Temperature Setpoint Node", and "Pump Outlet Node" are the OpenStudio defaults. If you leave those input fields blank in the TemperingValve object, as you might have, your idf file will automatically be created with settings like you have illustrated.

You could try overriding the OpenStudio defaults since they were not anticipating a component between the plant mixer and the outlet node. I'm not confident it is the source of your error, but consider adding a setpoint manager to the node immediately after the mixer and then setting the tempering valve's Temperature Setpoint Node field to the node immediately after the mixer. You do this by clicking on the tempering valve icon and then selecting the node name from the drop down menu.

By the way the logic for the OpenStudio default setting is located here in the source code if you would like to inspect it. If you have left empty settings then this logic will fire when OpenStudio creates the idf file.

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Thanks Kyle,

Unfortunately I had issues with placing a setpoint manager before the tankless water heater (before attempting to move the tankless water heater over to the demand size). If I tried that setup, my OS would simply crash and close out. My colleague had similar results. That said, the code you linked was enlightening-- thank you. At the moment I have code manually adding those nodes, but it's good to know that default options exist.

Take a look at my edit above to see my current attempt at fixing this issue. If anything looks suspect, please don't hesitate to let me know.