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pv shading effect on thermal loads using Openstudio

asked 2016-11-19 03:06:31 -0500

shahin1992 gravatar image

updated 2017-05-04 06:58:19 -0500

i added pv to my Openstudio model, i did get the extra generated energy in my simulation results yet there was no change to the thermal loads which i think is weird since the material is different, the conductivity shall be different too thus the thermal loads must change? any idea what went wrong! Model pic Osm Model i know there has been another question on using Pv in energyplus Pv shading effect on energyplus i also tried to use a pv layer unattached to the roof in case if that was the problem as you can see here but thermal loads increased by around 16% which i don't understand because loads are supposed to decrease since shading effect should be helping in reducing cooling loads.

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answered 2016-11-20 12:49:54 -0500

1) The OS:Generator:Photovoltaic object in your osm looks like this:

{94b0d33a-5d67-43d5-81f1-d43d8c01601e}, !- Handle
Generator Photovoltaic 2,               !- Name
{025d69f9-56d2-4b82-bdc2-f5e3cc2cded4}, !- Surface Name
{992a551d-7ee1-4dcf-98ef-a349d6248401}; !- Module Performance Name

which compared to the documentation for that equivalent EnergyPlus object is missing the last three fields, including Heat Transfer Integration Mode, which (I think) effects how the PV system interacts with the building surface heat transfer. If you look at the translated idf (out.idf) you'll see that the object has been translated as:

Generator Photovoltaic 1,               !- Name
Surface 24,                             !- Surface Name
PhotovoltaicPerformance:Simple,         !- Photovoltaic Performance Object Type
Photovoltaic Performance Simple 1,      !- Module Performance Name
Decoupled,                              !- Heat Transfer Integration Mode
1,                                      !- Number of Modules in Parallel {dimensionless}
1;                                      !- Number of Modules in Series {dimensionless}

So the temperature calculation of the PV array is decoupled from the heat transfer surfaces, which probably explains why you aren't seeing a difference.

I'm not sure why OpenStudio is creating an incomplete object, perhaps @macumber or @Julien Marrec can provide input. The methods to assign those fields work, so until the problem is resolved within OpenStudio you could edit the plugin script used to create the PV system. For example, inserting


at line 120 of C:\Program Files\OpenStudio 1.13.0\Ruby\openstudio\sketchup_plugin\user_scripts\Alter or Add Model Elements\Add_Photovoltaics.rb and using the edited script to re-generate the PV system, the relevant field should be created and set in the object.

2) Not sure how you modeled a 'pv layer unattached to the roof', but I suspect you may have added a second roof heat transfer surface, instead of creating a shading surface and assigning the PV system to that. When I add a shading surface above the roof of your model the peak cooling load is reduced.

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i changed the file by adding the line you told me about to line number 20 in the ruby file and created the pv model again using the new file but yet i got no changes. i used fortran to read the file and i added the line as you can see in the attached picture here what did i do wrong ?

shahin1992 gravatar image shahin1992  ( 2016-11-21 08:05:12 -0500 )edit

Strange, that's a different location in the file than I meant. Try adding the line right after

panel = OpenStudio::Model::GeneratorPhotovoltaic::simple(model)

After you save the file you'll also have to either restart sketchup or do Extensions > OpenStudio User Scripts > Load User Scripts to reload the changed script.

Eric Ringold gravatar image Eric Ringold  ( 2016-11-21 08:34:23 -0500 )edit

@shahin1992: It seems that the PhotovoltaicPerformance:Simple model will not do anything with the Heat Transfer Integration Mode input (see Julien's comments here.)

Eric Ringold gravatar image Eric Ringold  ( 2016-11-21 14:51:58 -0500 )edit

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Asked: 2016-11-19 03:06:31 -0500

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Last updated: Nov 20 '16