Window Shade Coefficient

[Cooch42]

I'm running a cooling load on a south exposed office area w/ all glass (1" tinted, low e w/ thermal break) walls. There is a 14' outside overhang. I'm using a current default shade coefficient of 0.811 in HAP. I believe I need to tweak this coefficient to reduce the grossly oversized load. Does anyone know the proper way to determine an accurate shading coefficient?

thanks

Nick

 

[GMcD]

You need to get the actual glass catalogue rated SHGC (Solar Heat Gain Coefficient) and use that, BUT, you have to do a solar angle check to see when the largest portion of the glass is actually exposed to direct sunlight during the warmest days of the year when you have the peak combined transmission load and solar gain load. Then the shaded portion of the glass gets the heat gain calculated with that exposures' "shaded" heat gain per SF factor, while the exposed to sunlight portion gets calculated with the full heat gain per SF factor. I am not that familiar with HAP to know if it has the ability to do solar shading on an hourly basis. You may have to hand-input the shaded vs unshaded portion of the glass areas to get a more accurate result.

 

[gepman]

The overhang and the shade coefficient are two different items. If you want to take into account the overhang go "shades" in the default library and build your shade there.

To model your window in HAP, click on the "detail" box which will allow you to build your window. If you know the window properties from the manufacturer then you can input the window properties directly into the shade coefficient. Most manufacturers give the SHGC (Solar Heat Gain Coefficient) which can be used to calculate the Shading Coefficient. I can't find the formula at the moment.