Incidence angle in EnergyPlus

asked 8 years ago

it
123 ●4

updated 8 years ago

__AmirRoth__

4446 ●5 ●17 http://bleedinggreenna...

I am wondering how EnergyPlus takes incidence angle into account when it calculate solar radiation transmittance from outdoor to indoor. I would believe that there is a different solar heat gain coefficient when solar radiation strikes a glazing pane at noon and afternoon. SHGC in noon could be higher than one in afternoon. Because WINDOW developed by LNBL can show this phenomenon, EnergyPlus could consider SHGC varied in time. Is there information about a calculation method for incidence angle ? In addition, is a calculation method able to consider incidence angle for both a transparent glazing and a translucent glazing?

Your comments are appreciated.

Regards, IT

answered 8 years ago

Archmage

7205 ●3 ●11

SHGC is a specific metric for window performance, but it is not something that EnergyPlus ever uses directly during a simulation. EnergyPlus will report out a value for center-of-glass SHGC based on the window description, but that is for a special case used for standard reporting with direct normal incidence and fixed thermal boundary conditions. As you say, a real time SHGC, were such a report available, would vary over time with incidence angle as well as the thermal conditions surrounding the window. EnergyPlus already does take this into account.

There is a section in the Engineering Reference called Calculation of Angular Properties that describes how angle of incidence is handled for window performance.

The WindowMaterial:SimpleGlazingSystem has an SHGC input, but it is used by a model that then constructs a more detailed representation of the window, with a different angular model (see table Normalized Transmittance Correlations for Angular Performance), and it would also have a time-varying "SHGC."