EGEE 102
Energy Conservation and Environmental Protection

Shading Devices


Before innovations in glass, films, and coatings in the past decade, a typical residential window with one or two layers of glazing allowed roughly 75 to 85 percent of the solar energy to enter a building, which has a negative impact on summertime comfort and cooling bills, especially in hot climates.

Instructions: Move your cursor over the numbers below to see the properties of a normal window.

Properties of a Normal Window

Click here to open a text description of the properties of a normal window activity

Listed below are the properties of a normal window

  • U-Factor = 1.11
  • SHGC = .86 (86% of solar heat gain transmitted, 14% blocked)
  • VT = 0.90 (90% of visible light transmitted, 10% blocked)

External Window Shading

External window shading devices such as awnings, roof overhangs, shutters, and solar screens, and internal shading devices such as curtains and blinds, can control the entry of solar heat. Although external window shading devices are about 50 percent more effective than internal devices at blocking solar heat, they do have some disadvantages.

External Window Shading

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External Window Shading

The list below describes different types of external window shading and their drawbacks

  1. Shutters, solar screens, curtains, and blinds make rooms dark
  2. Curtains and blinds also let in some of the undesirable heat
  3. External shading may create problems with the building's aesthetics
  4. External shading devices are sometimes expensive to build
  5. Roof overhangs that effectively shade east and west facing windows may be impractical to construct

Internal Shading Devices

The table below shows the percentages of the radiant energy that different types of internal shading devices transmit, reflect, or absorb.

Percent of Radiant Energy That Different Types of Internal Shading Devices Transmit, Reflect, or Absorb
Shade Type Transmitted energy (percent) Reflected energy (percent) Absorbed energy (percent
Roller Shades 25 percent 15 - 80 percent 20 - 65 percent
Vertical Blinds 0 percent 23 percent 77 percent
Venetian Blinds 5 percent 40 - 60 percent 35 - 55 percent