Reflectance of Shading Surfaces in EnergyPlus

energyplus
shading

#1

Hi everybody,

I am running energy simulations with Honeybee/energyPlus.I would like to be able to account for the influence of the urban context on one building’s heating/cooling loads.

The solar masks aspects are ok. I have a brep for the urban context that I input in the “Honeybee EP Context Surfaces” component.

But I don’t find the way to input albedo/reflectance values for the urban context. I have tried to input a RADMaterial in the “Honeybee EP Context Surfaces” component. But my simulation results do not change when I change the reflectance of the RADMaterial.

Many thanks in advance for your help!


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#2

Marc,

The E+context doesn’t take into account the properties of the surroundings. Rather it relates to the context as shading objects, i.e. blocking the sun.

-A.


#3

Hi Marc,

RADMaterial will only and only be used when the file is getting exported to Radiance. This is normal that it’s not changing the results.

EnergyPlus shading objects don’t have a field for reflectance and use .2 as default. You can use ShadingProperty:Reflectance to change the default value. We don’t support this in Honeybee interface right now but you can create the objects and add them to your energy model using additionalStrings_ input.

I put a simple example together were I change the reflection for shading surfaces to .5 for unglazed part of shading and portion and .7 for glazed part. I also set the percentage of glazing to 50% of the surface area.

I didn’t put any input checks. Make sure to read the documentation to put valid input values for energyplus otherwise the energyplus simulation will fail. I also assumed that all the shading surfaces (context) will be planar surfaces.

Keep in mind that it will only effect the results if you are using one of the solar distributions with reflections. Honeybee is using FullInteriorAndExteriorWithReflections by default so you should be fine if you’re using the default settings.

Hope it helps,

Mostapha

shadingReflectance.gh (493 KB)


#4

Hmmmm,

I learned something new today!!

Always related to the shading objects as they are all under the same conditions.

Thanks,

-A.


#5

Excellent!

Thanks Mostapha, this can come in handy :slight_smile:


#6

Hi Abraham and Theodore, Now that you both seem to be interested do you think that we should add this to Honeybee shading objects as a default option?


#7

Hi Mostapha,

I do. Do you mean implementing the material properties into the HB_HB_EPContextSrf?

It is important to keep the EPTransSchedule_ input. I’m not sure if there is a chance of conflict between both possibilities …?

Thanks,

-A.


#8

Interestingly enough EnergyPlus doesn’t change reflectance based on transmittance schedule! It stays the same regardless. That’s one of the reasons that I was initially so skeptical about implementing it into Honeybee. It can get people pretty confused.

Note that a shadowing transmittance schedule (ref: Shading Surfaces, Field: Transmittance Schedule Name) can be used with a reflective shading surface. However, EnergyPlus assumes that the reflectance properties of the shading surface are constant even if the transmittance varies


#9

So it is worth to implement, i think.

Thanks,

-A.


#10

Hi Mostapha,

Thanks a lot for your help!

As I am no expert in e+ your example was really useful!

Marc


#11

Hi Mostapha,

is it possible to insert (by an Honeybee tool) the “ShadingProperty:Reflectance” to associate with the “Shading:Building:Detailed” geometry? I would use this parameter in order to set all the reflectance properties of the possible external shadings (louvres, fix shadings etc…).

If i use the RADmat, does it take into account the Radiance material properties in the E+ calculation? If yes, where is the shading material in the .idf file?

Thanks a lot!

Nic


#12

I know it’s kind of an old post but I was wondering if this option is implemented yet? Also, I can’t download Mostapha’s Grasshopper definition, can someone please re-upload it.


#13

@mostapha I was able to get the file from the old discussion board. I tested your script in a simple office room and a large glazed surface across the room. I tested different reflectance values and WWR ratios, I initially anticipated to see some changes in cooling loads due to solar heat gain from the sunlight bounced off the glazed surface (glazed surface is facing south, location is Houston) but didn’t see any changes in heating/cooling loads. Any ideas? If the script isn’t valid anymore, any other way I can account for the solar reflectance of my shading surfaces for EP analysis. Here is my simple room file Ref_shading_E_Rev5.gh (557.5 KB)


#14

@mostapha I just retried the script using the EP component instead of the Openstudio one and I noticed a difference in the cooling and heating loads! Very strange!


#15

@RaniaLabib if you really want to precisely test the reflections (specular) from glass (contexts), you probable need to model those glass surfaces as context zones’ window. Context here I mean the regular zone instead of shading. Construction for the glass will be: SHGC and VT = 1- reflectance.
ps: I found the reflectance setting in EP shading obj doesn’t work well with specular reflection.

Here I am testing the exterior surface temperature:



#16

@MingboPeng, I finally am able to start testing this. When you say Context zone window, does this mean I model the reflective surface as a window of a zone and connect it directly to the HB zones input in my run_OS_simulation component?