U-factors Projected X/Y Direction

[K Chan]

Hello!

What is the explanation/reasoning of the different options for the directional selection via drop downs in the U-factors window?

The default when I select to show U-factors is "Projected In Glass Plane"; however, how does "Projected X Direction" or "Projected Y Direction" correspond to the detail?

Please see attached for a plan detail (rotated). The "Projected in Glass Plane" is U-value 3.2411 as is the "Projected Y". However, the "Projected X" is U-value 1.5582. The section type is selected as Jamb and the gravit arrow goes into the page, as intended and anticipated.

It seems that any U value for the assembly should be "Projected in Glass Plane". As this is not a corner or skylight to wall transition condition, I'm not sure that the "Projected X/Y" or "Custom Length" options come into play (per simulation manual NFRC 100-2014).

Any insight would be appreciated. Thanks!

[yal...@gmail.com]

Hi.

X axis is horizontal and Y axis is the vertical and the projected length is measured as a projection perpendicular to the axis. You'll see this relationship by the length dimension in the other outputs.

U value of frames is simply an averaging of heat flux at the defined frame u-factor tag to a flat plane that can be used in area average calculations.

Here for example the length in the projected Y and glass plane is the sightline of the frame 3" and the projected X is the depth of the frame 6.24016". If you factor the u-value 3.2411 * 3" / 6.24016" = 1.5582.

Uframe = Qframe / deltaT / L where Qframe= heat flow at frame boundary, deltaT= temperature difference in/out, L = projected frame dimension (ISO 15099 Equation 11).

When you insert glazing Therm automatically gives the u-values in the glass plane however you can change them if you need depending on the condition. It gives you more options and flexibility if you are looking at spandrels, solid walls, etc. or assemblies with no glazing.

Yalin