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Time lag and decrement factor

asked 2022-05-29 20:53:33 -0600

Houri's avatar

updated 2022-07-10 13:32:40 -0600

Can I measure the time lag and decrement factors of different wall constructions? I am using EnergyPlus and OpenStudio.

Update: Thank you for your answer. I used the "Add output variable" measure to OS measures and ran the simulation, but opening the OS results report, There is no data available for Surface temp when I look into "openstudio Results" Report. Couldn't figure out what is the mistake in data input request. C:\fakepath\Surface outside air temp.JPGHere is the link to my OS simulation file.

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@Houri what simulation tool are you using? Please mention it in the title or body of your post, as well as add a tag so that others can provide better help.

Aaron Boranian's avatar Aaron Boranian  ( 2022-05-30 11:06:00 -0600 )edit

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answered 2022-05-30 16:57:20 -0600

Time lag (the time between the max outside face temperature and max inside face temperature) and decrement factor (ratio of max inside face temperature to max outside face temperature) are not standard output variables that EnergyPlus or OpenStudio can generate. You can read more about these thermal mass properties in a blog post here.

These thermal mass properties change each day (or whatever period you want to measure these max temperatures for). Here is the process I would recommend:

  1. Add Output:Variable objects to your model that will generate results for Surface Outside Face Temperature and Surface Inside Face Temperature for the surfaces you want to calculate time lag and decrement factors for.
  2. Use Microsoft Excel to find the max of each of these variables for each surface for a day (or whatever period you want to use), then calculate the time lag and decrement factor for that period from these max temperatures.

There are alternatives to Microsoft Excel:

These alternatives to Microsoft Excel are more complex, but will make this process MUCH faster if you need to review the time lag and decrement factor across multiple models or iterations of the same model.

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Thank you @aaron. It was helpful. Where can I find the generated results?

Houri's avatar Houri  ( 2022-06-02 05:24:20 -0600 )edit

@Houri you can read OS App docs for Requesting Output Variables and Using Data Viewer (DView) to plot those results. This post also has LOTS of options to generate CSV from these output variables.

Aaron Boranian's avatar Aaron Boranian  ( 2022-06-02 08:45:01 -0600 )edit

@Houri for an example of how to request output variables and analyze time-series outputs in DView, you should watch this video. Accessing DView from the OS App is shown at the 5:45 mark.

Aaron Boranian's avatar Aaron Boranian  ( 2022-06-13 09:15:51 -0600 )edit

@aaron Thank you. Your comments were really helpful and I've got answer to my question.

Houri's avatar Houri  ( 2022-07-18 21:32:23 -0600 )edit

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Asked: 2022-05-29 20:53:33 -0600

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Last updated: Jul 10 '22