| VISIBLE LIGHT TRANSMITTANCE,
within the visible spectrum (380 to 780 nanometers). the percent age of
light that is transmitted through the glass. |
| VISIBLE LIGHT REFLECTANCE,
within the visible spectrum (380 to 780 nanometers), the percent age of
light that is reflected from the glass. |
| SOLAR ENERGY REFLECTANCE.
Within the solar spectrum (380 to 2500 nanometers), the percent age of ultraviolet,
visible and near infrared energy that is transmitted through the glass. |
| SOLAR ENERGY TRANSMITTANCE,
within the solar spectrum (380 to 2500 nanometers), the percent age of ultraviolet,
visible and near infrared energy that is reflected from the glass. |
| U-VALUR, measure of air-to-air
heat transmission due to thermal conductance of glass and the deference
indoor and outdoor temperature under the ASHRAE standard. The unit is expressed
in English BTU/h/ft2/E°F or in metric W/m2/K. The lower the U-Value,
the less heat is transmitted through the glazing glass. |
| Winter U-Value is based on
0°F(-18°C) outdoor air temperature, 70°F(21'°C) indoor air
temperature, 15mph(24km/h) outdoor air velocity, natural convection of indoor
air and 0BTU/h/ft2(oW/m2) solar intensity (nighttime). |
| Summer U-Value is based on
90°F(32°C) outdoor air temperature, 75°F (24°C) indoor air
temperature, 7.5mph(12km/h) outdoor air velocity, natural convection of
indoor air and 248BTU/h/ft2 (783W/m2) solar intensity (daytime). |
| SHADING COEFFICIENT. The ratio
of solar heat gain through a glazing to the solar heat gain through a single
light of 3mm clear glass under the some set of conditions. The smaller the
number the better the window is at stopping the entry of solar heat radiation. |
| RELATIVE HEAT GAIN. The amount
of total instantaneous heat gain through a glazing taking into account the
effects of solar heat gain (Shading Coefficient) and conduction heat gain
(U-Value). The lower the value, the better the glazing is for reducing heat
gain. |
|
According to ASHRAE standard,
in summer daytime, solar Heat Gain Factor is 200BTU/h/ft2/°F (630W/m2)
and the outdoor air is 14°F Wanner than indoor air with no shading.
Relative Heat Gain = SummerU-Value (Outdoor minus indoor temperature)
+ Shading Coefficient * Solar Heat Gain Factor.
| RHG=Us*(14)+SC*(200)[BTU/h/ft2]
or RHG=Us*(8)+SC*(630)[W/m2] |
| 1W/m2=0.176BTU/h/ft2/0°F |
| 1W/m2=0.317BTU/h/ft2 |
| 1BTU/h/ft2°F=5.68W/m2/k |
| 1BTU/h/ft2=3.15W/m2 |
|