A question about evapotranspiration and soil moisture Ratio in ecoroof results using EnergyPlus?

asked 2020-08-12 20:54:33 -0600

Majed
31 ●3

updated 2020-08-13 16:01:25 -0600

I want to ask about the process of calculating the Evapotranspiration in ecoroof. The amount of evapotranspiration in the simulation results is much higher than the rainfall amount, considering the irrigation was off in the simulation. Even when I removed the rainfall data we still have Evapotranspiration and moisture in the soil. I want to ask where this amount of water comes from without having rainfall and irrigation? is it absorbed from the surrounding humidity? Thanks in advance.

Comments

@Majed what simulation tool are you using? Please add a tag for the tool to your question so that others can provide better answers.

Aaron Boranian ( 2020-08-13 08:28:14 -0600 )edit

Just added a tag and modified the question. Thanks for your interest Aaron!

Majed ( 2020-08-13 16:02:59 -0600 )edit

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answered 2020-08-20 10:10:50 -0600

Aaron Boranian

14135 ●83 ●24 http://bigladdersoftware.com/

While the Input Output Reference explains the intent of the Green Roof object and its input fields, if you want to investigate these kinds of details related to calculations then you should review the Engineering Reference. Here, we can see that there is transpiration from the vegetation calculated separately from the transpiration from the soil. They both depend upon complex factors like stomatal resistance of vegetation, soil moisture content, vapor pressure difference between vegetation or soil and outside air, etc.

As this post mentions, EnergyPlus applies the Site:Precipitation object to green roofs -- the precipitation data in the EPW weather file is not used. Hopefully when you say that you "removed the rainfall data" you mean that you removed this object from your input file, since setting precipitation columns in the EPW weather file will not have an impact. You may want to add output variables for Green Roof Soil Near Surface Moisture Ratio and/or Green Roof Current Evapotranspiration Depth for further investigation.

You can also read this post for more information on the Green Roof object in EnergyPlus.