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precipitation: EPW vs Site:Precipitation

asked 2018-07-31 05:54:23 -0500

Gio gravatar image

Hi, I'm using EnergyPlus.

My question is straightforward: between EPW and the object Site:Precipitation data, which one has the priority? Does the Site:Precipitation object overwrite the EPW data?

Thank you

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answered 2018-07-31 12:35:59 -0500

updated 2018-07-31 12:36:52 -0500

Site:Precipitation is used by WaterUse:RainCollector and Material:RoofVegetation (EcoRoof). It can be reported using Output:Variable "Site Precipitation Rate" and "Site Precipitation Depth" (system timestep).

The liquid precipitation data in the epw file are not used. If there are values there, they can be reported using Output:Variable "Site Precipitation Depth" (zone timestep), but none of the simulation models use it. (Yes, it's the same variable name as above, but this one is keynamed "Environment" and the one above is named "Site:Precipitation".)

Related, but different, the epw file rain flags (is it raining now?) are used by default to alter boundary conditions for the surface outside heat balance, GroundHeatExchanger:Pond, and GroundHeatExchanger:Surface. The epw rain flags can be disabled in the RunPeriod object. Note that rain amounts specified in Site:Precipitation do not impact the rain flag status.

Reference issue #4714.

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I need it for the green roof. That's clear, thanks

Gio gravatar image Gio  ( 2018-07-31 15:00:00 -0500 )edit

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Asked: 2018-07-31 05:54:23 -0500

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Last updated: Jul 31 '18