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# Surface Inside Face Solar Radiation Heat Gain Rate vs SurfaceProperty:SolarIncidentInside

Dear Everyone,

I am trying to simulate extremely complex environments using EnergyPlus and Radiance. Since I am used to use Radiance, my apporach is to

1. Calculate Solar irradiance over walls
2. Create a Schedule for EnergyPlus that will be read using the SurfaceProperty:SolarIncidentInside.

However, I am having some trouble reading the documentation. Even though its name is SolarIncidentInside, then the documentation basically says the schedule will replace the absorbed solar radiation... the units are W/m2. All cool for now.

However, when I try to report it using the Output:Variable,*,Surface Inside Face Solar Radiation Heat Gain Rate per Area,hourly;, I do not get the same value as in the Schedule... and they do not even match the values multiplied by the surface absorbtance.

Can anyone please explain this discrepancy to me?

Kind regards,

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From the source code (SolarShading.cc, line 6758)

AbsIntSurf = Construct( Surface( SurfNum ).Construction ).InsideAbsorpSolar;
//SolarIntoZone = GetCurrentScheduleValue(SurfIncSolSSG(iSSG)%SchedPtr) * Surface(SurfNum)%Area
SolarIntoZone = GetCurrentScheduleValue( SurfIncSolSSG( iSSG ).SchedPtr );
AISurf( SurfNum ) = SolarIntoZone * AbsIntSurf;


Schedule value gets multiplied by the solar absorptance of the inside material of the construction. If the solar absorptance of the inside material is set to 1, as shown below, it should fix the above issue.

  Construction,
Room Ceiling,            !- Name
Plywood - 3/8 in,        !- Outside Layer
2x6 Wood Stud R19,       !- Layer 2
Gypsum board - 5/8 in;   !- Layer 3

Material,
Gypsum board - 5/8 in,   !- Name
Smooth,                  !- Roughness
0.015875,                !- Thickness {m}
0.17,                    !- Conductivity {W/m-K}
800,                     !- Density {kg/m3}
1090,                    !- Specific Heat {J/kg-K}
0.9,                     !- Thermal Absorptance
1.0,                     !- Solar Absorptance
0.3;                     !- Visible Absorptance

more

Thanks very much, Chandan. That was very very helpful.... The reported values and the schedule still do not match, though.

I read somewhere that the scheduled values are used to "propagate" Radiation within the room. Is that so? That is... Solar radiation arrives to the surfaces, and then EnergyPlus calculates the solar radiation that would end up in all other surfaces due to intereflections.

( 2016-03-03 06:04:23 -0500 )edit
1

If that doesn't fix the issue, the only other thing can recommend is to report Surface Inside Face Lights Radiation Heat Gain Rate per Area and see if it has non-zero values. That would probably explain the difference. I never had to use this object. Hopefully others can shed some more light into it.

( 2016-03-03 19:56:49 -0500 )edit