SolarTransmittance vs. Solar Heat Gain Coefficient for EP material

grasshopper honeybee-legacy
1

Hi all,

I have a question about the “solarTransmittance” input in the “EPGlassMAT” component from HB.
In the software DesignBuilder, for a window, there is a differentiation of the Solar transmittance (fraction of solar radiation entering the room at normal incidence, through the glass) and the Solar Heat Gain Coefficient, which is the fraction of solar radiation entering the room PLUS the heat gain from the glass itself (that comes from the solar absorbtion of the glass). The SHGC is calculated for specific temperature and solar conditions.

My question is this : in HB, does the solarTransmittance refer simply to the fraction of solar radiation entering the room at normal incidence, through the glass of the it refer to the SHGC ?

Regards,

Vincent

2

Hi @Vincent,

Both software are using EnergyPlus under the hood so you can refer to EnergyPlus documentation to see the description for each object. See this link for your specific case.

https://bigladdersoftware.com/epx/docs/8-1/input-output-reference/page-010.html#windowmaterialglazing

and solar transmittance field:

https://bigladdersoftware.com/epx/docs/8-1/input-output-reference/page-010.html#field-solar-transmittance-at-normal-incidence

3

Hi @mostapha , thanks for your answer.

Can you confirm me that the “SolarTransmittance” input in “EPGlassMAT” component in HB becomes “Solar Transmittance at Normal Incidence” of EnergyPlus ?

If so, that means EnergyPlus might convert it to a slightly different solar transmittance ratio if we have specified for example the thickness.

Regards,

Vincent

PS : LadyBug tools are pretty amazing tools overall, well done for all the work you guys are doing !

4

Hi everyone,
I am trying to determine Solar Heat Gain through my custom window for every time step of specific period. (I am conducting an experiment with sensors installed and I need the data to compare the results I am getting)
I suppose I am half way through, I finally could generate excel file for every hour for direct and diffuse solar incident that enters the window. However, I cannot seem to find any components to calculate the absorbed solar radiation by the window for every specific timesteps (as I need that value to get my total solar heat gain through the window). I was wondering if anyone can guide me through this.
SOLAR HEAT GAIN COEFFICIENT OF BIPV WINDOW.gh (140.3 KB)
I also am comparing the results I am getting from HB for solar irradiance and from LB, there is less radiation using LB? I am a bit confused and was wondering if I am doing something wrong.
Thank you in advance,
Sara

5

Hi @Saraesk,

I’m working on a similar topic. Did you answered your question ?
I suppose only direct + diffuse sun hits the window.

THEN, part of this incident flux is absorbed by the windows, and some of the absorbed heat is reemitted inwards. Does that makes sens ?

Also maybe consider this thread : Comparing Radiation behind Different Glass - #10 by chris