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Precipitation output is not equal input

asked 2016-10-25 23:07:57 -0500

Jahe's avatar

updated 2017-05-04 06:13:20 -0500

I try to simulate a green roof with EnergyPlus with my own meteorological data. I read my precipitation [m per hour] data from a text file (tab separated columns, decimal separator is a point) via the object schedule:file. I get no errors but the precipitation output values do not correspond well to my input values. The timesteps with precipitation are mostly correct (but not always) and the output values are much higher but there is no constant factor (but the majority is a factor of 29.5 higher than the input)...Exactly the same happens when I try to use the irrigation schedule. I would be very happy if anyone could give me a hint what's going wrong here (I tried EP versions 8.1 and 8.6).

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answered 2016-10-26 08:31:29 -0500

Archmage's avatar

It sounds like you are using the Site:Precipitation object. Have you set both the Design Level for Total Annual Precipitation and Average Total Annual Precipitation to the same value? The way it works is a little tricky but intended to be able to scale the rainfall pattern up or down to model wetter or drier years by just changing one number in the Design Level.

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Thank you for your fast reply. Yes, I use the Site:Precipitation object. First I had following inputs: Model: ScheduleAndDesignLevel, Design Level: 0.437 (my annual sum), Schedule Name: my schedule name, Average annual sum: 0.437. The output cumulative sum was 24.6 higher than my input, so I divided now 0.437/24.6 = 0.018 which I use as new input for the Design Level. I now get the correct annual sum as output but the rainfall pattern is totally wrong: in the first half of the year it is much less and in the second much higher than my data values. Any help with that?

Jahe's avatar Jahe  ( 2016-10-26 12:34:10 -0500 )edit

To rephrase my question: is it possible that EnergyPlus just uses my precipitation data as they are without modulating the data somehow?

Jahe's avatar Jahe  ( 2016-10-26 14:16:12 -0500 )edit

Interesting to note is that the modelled moisture ratio of the substrate corresponds quite well with my measurements, when I don't lower the value of the design level input (and badly when I do so). Might something be wrong with the precipitation reporting?

Jahe's avatar Jahe  ( 2016-10-26 18:07:59 -0500 )edit

The Average Total Annual Precipitation should equal the sum of the schedule. You can report an output variable called Schedule Value to check the values of your schedule pattern.

Archmage's avatar Archmage  ( 2016-10-26 18:51:41 -0500 )edit

I have correct values now (schedule values = input values). The Environment:Green roof cumulative precipitation depth are still not correct, but I am now very sure that the rest is working correctly. Thank you for your help!

Jahe's avatar Jahe  ( 2016-10-26 22:07:10 -0500 )edit

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Asked: 2016-10-25 23:07:57 -0500

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Last updated: Oct 26 '16