Professional Q&A

Visible light transmission ratio at normal incidence. Its wavelength is from 380um to 780um, accounting for 43% of the heat source of thermal radiation, so the transmittance of visible light can be appropriately controlled. That is to say, if the area of ​​​​the glass is large enough, there is no need to make the visible light transmittance ratio too high. On the one hand, it can reduce the heat source, and on the other hand, it can make the eyes more comfortable. The sun is over Chiayi on June 21 (summer solstice) every year in Taiwan. At this time, it is the area with the strongest sunlight in the world. On sunny days, the illumination is as high as ten There are more than 10,000 LUX, but the indoor illumination does not need to be too high. The illumination we need for reading is only 3,000 LUX! Too much light coming in will cause too much heat, causing the air conditioner to consume more electricity. The sun has visible light and invisible light. Visible light is the light that can be observed by the naked eye, and invisible light is ultraviolet and infrared light. Therefore, we cannot learn how cold regions such as Europe, the United States, and Japan respond to the sun. They do not need insulation when they are cold, but need to keep warm.

The ratio of direct vertical incidence of ultraviolet rays, Ultraviolet (UV) Trasmittace transmittance (tuv%), ultraviolet light is invisible light waves, short-wave radiation energy from the sun, the wavelength range is 200nm to 380nm, it is the most damaging part of sunlight The light waves are divided into UV-A, UV-B, and UV-C. The shorter the light wave, the more lethal it is. However, UV-C (wavelength range is 280nm to 320nm) is almost consumed when it enters the earth’s atmosphere, that is, There is no UV-C on the surface of the earth. The sterilization of dishwashers and washing machines is UV-C. UV-B (V) can cause damage to the retina, while UV-A (wavelength range is 320nm to 380nm) can cause stains on the skin. And skin lesions. Check on Wikipedia or GOOGE, etc. The real wavelength of ultraviolet rays is 400um! Especially this wavelength is short-wave blue light, which is the most harmful to the eyes!

The ratio of direct vertical incidence of infrared rays, infrared (IR) Transmittance Transmittance (Tir%) Infrared light is an invisible light wave, which is the longer wave radiation energy from the sun. The long range is 780nm to 2500nm. It is the thermal sensation in sunlight. Higher light waves are also the main heat source, accounting for 54% of the heat sources. The most important thing for heat insulation is to isolate the heat source in this band. However, the heat source in this band can be divided into two types: absorbed heat and reflected heat. If it is absorbed If it gets hot, secondary radiant heat will be generated, so reflecting infrared heat is the best way to insulate. No matter what, even visible light is also a heat source. When the heat on the glass is absorbed, the re-radiation ratio of the glass becomes very important. Therefore, the process of heat insulation is to first block the direct heat of the sun, that is, first Low R(Low Radiation), and then Low E (Low Emissivity). Low E is to reduce the re-radiation of heat on the glass. In tropical areas, less heat on the glass enters the room (that is, Low faces the room, so that the re-radiation heat of the glass is as low as possible. Emitting outward, the inward side is the Low side)

Gri refers to the light reflectivity of the exterior glass. The reflectivity or light reflectance (pv%out) is the percentage of visible light at normal incidence that is directly reflected by the outdoor glass.

Absorption rate (e%) of glass (solar energy, light or ultraviolet light). If light does not penetrate, it will be reflected or absorbed. Yield = 100% transmittance, reflectivity.

SHGC is the solar radiation acquisition rate of the full light wave, that is, the total penetration rate of direct radiation and secondary re-radiation of UV+VLT+IR, which does not include the heat source of thermal conduction (ηi) but includes the re-radiation heat source of material absorption. Also called (etai value).

The SC value is called the shielding coefficient or blackbody radiance in Taiwanese academic circles, while in mainland China it is more directly called the solar shielding rate (more understandable). When teaching the SC value, the author uses the “total radiance penetrated through glass”, which is the sun’s What passes through the glass is the total light wave solar radiation acquisition rate, that is, the total thermal transmittance of direct and secondary re-radiation of UV, VLT, and IR. The difference from SHGC refers to the total radiation transmittance of the glass. The solar transmittance is 0.87, so SHGC/0.87 is the SC value. The SC value of 5mm transparent glass (the total radiation rate of sunlight penetrating through the glass) is 0.97, which means the total thermal radiation transmittance of 5mm glass is 97%.

U value refers to thermal conductivity. The thermal insulation conductivity of a material is measured by the thermal resistance R value. The R value is the reciprocal of the U value of thermal conductivity. There are three ways of heat transfer: thermal conduction, thermal radiation and thermal convection. The heat conduction refers to the U value.

The E-value (Emissivity), which the great scientist Max Planck won the Noel Prize in 1918, is called the blackbody emissivity in the academic world, because it doesn’t really make people understand what a blackbody is? So I will use the “thermal re-emissivity of the material” 』The explanation is relatively simple and easy to understand, that is, how the re-radiation rate of the glass is reduced after the glass absorbs heat. It is usually described as Low, where E refers to Emissivity.

Relative Heat Gain (RHG) refers to the total amount of heat penetration, not the rate! The metric unit is W/m2, not %! RHG refers to the total transmission amount of heat sources of both “radiant heat” and “conduction heat” from the sun. The radiation is the total primary and secondary radiation and also includes the black body radiance. The formula is RHG=(Scx630)+(Ux7.8) where 7.8 refers to the annual average temperature difference between indoor and outdoor in Taiwan. 630 is a constant determined by scientists.

Sound Transmission Class (STC) refers to the sound insulation of glass, measured in decibels. It is worth mentioning that generally speaking, people think that hollow glass is more sound-insulating than laminated glass, but in fact this is not the case. With 5+5 gluing The STC of glass is 35 decibels, but the STC of 5+12A+5 insulating glass is 30 decibels. Each decibel means that the volume exceeds double, and the standard setting of 0 points is based on what people with normal hearing can hear. determined by the smallest sound. Each 10-point increase equals a 10-fold increase in intensity.

When comparing the efficiency of light, the higher the visible light, the higher the relative SHGC. On the contrary, we hope that the lower the SHGC, the more visible light can be retained. Does infrared ultraviolet rays absorb heat or reflect heat? What is the re-emissivity after absorbing heat? It is the main factor that becomes the level of SHGC. LSG (visible light transmittance)/(SHGC), the higher the data, the better.

It refers to the low re-radiation of glass heat (note! It is not the low direct heat radiation of solar heat). Re-radiation is also called secondary radiation.

It refers to low direct solar radiation (meaning that the transmittance of direct solar radiation is very small). Direct solar radiation is also called primary radiation.

It is emphasized that the direct radiation of the sun is first reduced, because the radiant heat from the sun is absorbed, the glass heats up, and the hot glass will produce secondary radiation, so Low E glass (low re-radiation of self-heating) is used to re-radiate the heat to The indoor part is effectively reduced, which is Low R/E. Therefore, the Low R glass must absorb heat first and then Low E to be effective.