Solar Heat Gain & Heat Loss

Daylight costs nothing, and adds considerably less heat to a space than the equivalent amount of illumination from electric lights.

Solar Heat Gain

Skylight save energy by providing adequate daylight illumination in buildings so that electric lights can be turned off when they are not needed.By reducing the amount of heat contributed to a building by electric lighting, skylight can also significantly reduce the need for cooling.

Solar Heat Gain Coefficient (SHGC) measures how much heat from the sun is blocked and is expressed as a number between 0 and 1. The lower the SHGC, the more a product is blocking solar heat gain.In hot Southern climates, a lower SGHC is particularly important during the summer cooling season.
In Northern climates, a higher SGHC may be desired to lessen the cost of heating during the cold winter months .

Heat Loss

Skylight can potentially also increase heating loads by allowing more heat to escape through the roof and increase cooling loads by letting more of the sun’s heat enter a building. The optimum balance of light and cooling savings versus increased needs for heating or cooling is a function of the building design, the building operation, and the local climate conditions.
When discussing U-value, we are mainly concerned with the heat losses in winter, because for most parts of the country, the difference between outside winter temperatures and normal inside temperatures are so much greater than those in the summer. Considering U-value only to estimate summer thermal transmittance will overestimate this component of heat gain because in the summer, the stratified air rises and is trapped in the light well. This stratified air acts like a blanket, insulating somewhat against heat transfer.

The Potential Energy Savings are Substantial

For example, the potential savings for a few typical buildings in the Los Angeles area were calculated using 1998 energy costs, weather conditions from the San Bernardino Valley, and many default assumptions. An average grocery store might save about $16,000 per year in operating costs, or $0.32 per square foot with the use of an appropriately sized skylighting system. A typical elementary school might save about $7,500 per year in operating costs, or $0.23 per square foot. An industrial processing and distribution center might save about $0.12 per square foot.
These numbers vary considerably, based on building design, operation, climate location, and energy costs. Given these variables, the value of savings from skylighting might reasonably be expected to vary from a high of about $0.75 per square foot for air-conditioned buildings with intensive lighting use, and a low of $0.05 per square foot for unconditioned buildings with low lighting requirements (for 1998 energy prices).

Energy Savings

CPI Daylighting Product Data Sheets

  • QUADWALL® U Values
    Quadwall U-factor rating per NFRC
    Colors, Solar & Thermal Performance (VT, SHGC, U-Factor)
  • Solaquad Performance Data
    The position of the SolaBlades® in relation to the sun determines the amount of sunlight and heat gain transmitted through the panel.
  • Pentaglas12
    Translucent Panel Colors, Solar & Thermal Performance (VT, SHGC, U-Factor)
  • Pentaglas16
    Translucent Panel Colors, Solar & Thermal Performance (VT, SHGC, U-Factor)


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