Solar Radiation Energy97% of the energy is concentrated within the 0.3-2.5 um wavelength range, with this portion originating from outdoors; below 100°C, the radiant energy of objects is focused in the longer wavelengths above 2.5 um, primarily from indoor sources.
If the room's window serves as the boundary... During the winter, we want to allow radiant energy from the outdoors to enter in high-latitude regions, while preventing indoor radiant energy from escaping. If we define the boundary by the wavelength of radiation, the dividing point between indoor and outdoor radiant energy is atAt the 2.5um wavelength, selecting a room window with certain functionality becomes crucial.
A standard 3mm thick transparent glass allows for an 87% transmission rate of solar radiation energy, with most of the outdoor radiation passing through during the day. However, at night or during rainy weather, 89% of the heat radiation energy from indoor objects is absorbed, causing the glass temperature to rise. Subsequently, the glass dissipates its heat through radiation to the indoor and outdoor environments and by convection, rendering it ineffective in blocking indoor heat from escaping to the outside.
Low-E insulating glass has a transmission rate of over 60% for solar radiation between 0.3-2.5 micrometers. During the day, most of the outdoor radiant energy can pass through, but at night or on rainy days, approximately 50% or more of the indoor objects' thermal radiation is reflected back into the room. Only less than 15% of the thermal radiation is absorbed and then dissipated through re-radiation and convection. Therefore, it effectively prevents indoor heat from escaping outdoors. This characteristic of Low-E glass allows it to control the unidirectional flow of thermal energy to the outside.
Sunlight's short waves pass through window glass and照射 onto indoor items. These items, heated, will then re-radiate as long waves. These long waves are"Low-E" window glass blocks heat from escaping back into the room. In fact, the re-radiation through the glass is reduced to 85%, improving the insulating performance of the glass.
