Consideration of shading factors

 Product(s):Hevacomp Mechanical Designer
 Version(s):V8i (N/A)


The PartL 2013 calculation utilises a number of methods for considering shading factors.


In terms of shading for PartL there are three considerations:

  1. Overhangs
  2. External shading devices/fins
  3. Internal blinds

Overhangs and fins

This information can be entered under the "Misc." page in PartL, on the "Additional surface data" tab.

 Once a Window is selected, the Glazing data input becomes active. Please note that, as described in our Glazing Data wiki, the Shading position will depend on the Blind type selecting for that glazing type, within the Glazing Data menu:

 Transmission Factor

A Transmission Factor can be applied to windows to allow overhangs and fins to be considered. This method is taken from the iSBEM manual. Note that Transmission Factor is analogous with Correction Factor in Part L 2010

75.6 Transmission correction factors
The transmission correction factor for windows can be calculated from:

TS = Fo Ff


Fo is the partial shading correction factor for overhangs

Ff is the partial shading correction factor for fins

A transmission factor of 1 refers to 100% of light transmitted; i.e. no shading from fins or overhangs

Shading from overhangs and fins

Shading from overhangs and fins depends on the overhang or fin angle, latitude, orientation and local climate. Seasonal shading correction factors for typical climates are given in Tables 10 and 11. The effect of shading from the horizon - ground, trees, other buildings - is not considered by the SBEM calculation engine.

 Figure 43: Shading from overhangs and fins

For the purpose of this calcualtion, the angles alpha and beta (dashed lines) are taken between
the plane of the window and overhand of fin shadow at mid window.

Table 10: Partial shading correction for overhang, Fo Table 11: Partial shading correction for overhang, Ff

Projection Ratio

This is the 'developed area to projected area' ratio for the window or rooflight. The developed area is the total area of glass plus the frame, and the projected area is the area of the opening in the wall/roof. For domed or conical rooflights this ratio can be larger than 1. For typical windows and flat rooflights, the ratio would be 1.

This figure cannot be less than 1. The default figure for windows is 1, and for rooflights is 1.3

Frame Factor

Frame Factor is the ratio of the window or rooflight are which is occupied by the frame to the total window or rooflight area. The default value is 0.1 for a window (10% of the total area is frame, 90% is glazing) and 0.3 for a rooflight (30% of the total area is frame, 70% is glazing). This ratio must be between 0 and 1.

Internal Blinds

At this stage the SBEM calculation engine does not support internal blinds

From iSBEM users guide:

"SBEM currently does not model the re-radiation effects of blinds where
solar gain entered the space before it is modulated by the shading device"