## Window Energy Efficiency: Solar Heat Gain and Visible Transmittance

2018-08-22T11:55:28-07:00

Conduction and Radiation of Thermal Energy In my last blog post, I wrote about the conduction and radiation of thermal energy through windows and the thermal transmittance value, called the U-Factor, that characterizes that heat transfer.  The U-factor is useful in evaluating window performance and making wise decisions when specifying components for a building, but it is only one piece of the puzzle.  The National Fenestration Research Council (NFRC) mandates a second value alongside U-factor in its certification process, called the Solar Heat Gain Coefficient (SHGC).  SHGC represents the ability of a window to resist heat gain from radiation, like the sunlight in Figure 1.  This is obviously a challenge, given that the entire point [...]

Window Energy Efficiency: Solar Heat Gain and Visible Transmittance 2018-08-22T11:55:28-07:00

## Window Energy Efficiency: Thermal Transmittance

2018-08-22T11:46:58-07:00

Figure 1: Windows catching sunlight By Magda S [FreeImages.com Content License] In our last blog post, I wrote about the thermal resistance (R-value) and transmittance (U-factor) of insulation and windows.  The R-value represents how well a material prevents heat transfer through its thickness, and U-factor is its inverse, representing how much heat a material will conduct through.  These values are fairly simple to calculate for most building materials materials like the bricks and panels in Figure 1, as they primarily experience only conductive heat transfer.  Windows are a more challenging proposition, however, since the heat transfer through them includes radiation across the entire spectrum, not just the visible light we see and the infrared we feel.  In [...]

Window Energy Efficiency: Thermal Transmittance 2018-08-22T11:46:58-07:00

## Energy Efficiency in Building Materials, Insulation and Windows

2018-04-04T09:48:28-07:00

Figure 1: FLIR image of two houses showing energy loss. Colors towards red on the scale indicate warmer surfaces and more energy loss. The basic principle behind thermal insulation is simple to understand.  The harder it is for heat to travel through a material, the better insulator that material will make.  In this blog, I’m going to take a look at how that effectiveness is quantified, after a brief review of the three methods of heat transfer.  The building and construction industry use a ratio called the R-factor to indicate how well a building material can insulate a space.  Also called the thermal insulance or thermal resistance, a higher R-value indicates a more effective insulator. Heat Transfer Methods There are [...]

Energy Efficiency in Building Materials, Insulation and Windows 2018-04-04T09:48:28-07:00