1. What is visible light transmittance?
The percentage of light intensity transmitted through glass within the visible spectrum (380 nm to 780 nm).
2. What is visible light reflectance?
The percentage of light intensity reflected by glass in the visible spectrum (380 nm to 780 nm).
3. What is solar transmittance?
The percentage of ultraviolet, visible, and near-infrared light energy transmitted through glass within the solar spectrum (300nm to 2500nm).
4. What is solar reflectance?
The percentage of ultraviolet, visible, and near-infrared light energy reflected by glass within the solar spectrum (300 nm to 2500 nm).
5. What is U value?
Under ASHRAE standard conditions, due to the heat transfer of glass and the temperature difference between indoor and outdoor, the air-to-air heat transfer is formed. Its imperial units are: British thermal units per square foot per hour per Fahrenheit. The metric unit is: watts per square meter per Kelvin. The lower the U value, the lower the heat transfer through the glass.
6. What is the condition of winter U value?
The outdoor air temperature is 0℉ (-18℃), the indoor air temperature is 70℉ (21℃), the outdoor air velocity is 15mph (24km/h), the indoor air is natural convection, and the sunlight intensity is 0BTU/h-ft2 (OW㎡ )(at night).
7. What are the conditions for summer U value?
The outdoor air temperature is 90℉ (-18℃), the indoor air temperature is 70℉ (21℃), the outdoor air velocity is 7.5mph (12km/h), the indoor air is natural convection, and the sunlight intensity is 248BTU/h-ft2 (OW /㎡ ) (daytime).
8. What is the shading factor?
Under the same conditions, the ratio of the heat transmitted by the solar radiation energy through the glass window to the heat transmitted through the 3mm transparent glass. The smaller the shading coefficient, the better the performance of blocking direct sunlight radiation.
9. What is relative heat gain?
The instantaneous total heating of solar energy passing through the glass window. These include solar radiation heating (shading coefficient) and conduction heating (U-value). The lower the relative heat increase, the better the performance. According to the ASHRAE standard, during the daytime in summer, the sunlight radiation intensity is 200BTU/h-ft2 (630W/㎡), and the outdoor and indoor temperature difference without sunshade is 14℉, then the relative heat increase = summer U Value × indoor and outdoor temperature difference + shading coefficient × solar radiation intensity, that is, relative heating increase = 14 × summer U value + 200 × shading coefficient [BTU/h-ft2] or, relative heating increase = 8 × summer U value + 630 × shading Coefficient [W/㎡].
10. What is thermal stress cracking?
Thermal stress cracks are produced from uneven temperatures in different parts of the glass. When the coated glass is exposed to direct sunlight, it mainly absorbs the infrared light and part of the visible light of the sun, which is converted into energy in the glass body, causing the glass body to form thermal expansion; while the glass part inside the aluminum frame structure cannot receive the same solar radiation, As a result, the glass is heated unevenly as a whole, and internal thermal stress is formed. The thermal expansion of the glass central region produces tensile stress in the edge region of the glass. This tensile stress exceeds the tensile strength of the edge region, which will cause the glass to break. The phenomenon of glass cracking due to thermal stress is that the cracks on the edge of the glass are neat and at right angles to the edge, the number of cracks is small, and the cracks in the middle of the glass are arc-shaped rather than straight.
11. What are the several aspects that affect thermal stress?
Building orientation, cold climate conditions, glass size and shape, HVAC installation location, window frame systems, indoor and outdoor shading, glass body absorption.
12. What is heat reflective glass?
Heat reflective glass is commonly referred to as coated glass, which is formed by coating metal film and metal oxide or nitride film on the glass surface, which is formed by reducing the shading coefficient Sc of the glass from 0.98 (6mm transparent glass) to 0.2~0.6 .
13. What are the characteristics of heat reflective glass?
Reduced UV transmission, multiple reflective shades, ideal visible light transmittance and reflectivity, high infrared heat ray reflectivity, low solar gain, ideal shading factor.
14. Application of single transparent glass?
It is mainly used in concealed observation windows, and coating on transparent glass or colored glass by vacuum magnetron sputtering equipment. The film surface must face the observed room where the light source is bright, and an appropriate illuminance ratio must be created to achieve the desired effect.
15. What is the wind load capacity?
That is, the ability to withstand uniform wind pressure. It is related to factors such as the size and thickness of the glass.
16. What is the control range of the crushing rate?
Theoretically, it should be controlled within 3% (deductible broken rate). Due to market changes, it is no longer possible to achieve.
17. How many types of substrates (original glass) are there?
The answer given by the editor: transparent glass, tinted glass, tinted glass is often used: F green, H green, Chinese green, lake blue, American blue-green, Belgian blue-green.
18. What are the spectral bands of solar radiation, visible light, ultraviolet light, and infrared light?
Solar radiation: 230-4000 nm wavelength
Visible light: 380-780 nm wavelength
Ultraviolet light: 10-400 nm wavelength
Infrared light: 750-2500 nm wavelength
19. What is the energy ratio of solar radiation, visible light, ultraviolet light, and infrared light to the total solar radiation energy?
Solar radiation: 98%, visible light: 42.5%, ultraviolet light: 13.8%, infrared light: 3.1%. The percentage of light intensity transmitted through glass within the visible spectrum (380 nm to 780 nm).
LOW-E glass articles
20. What are the main composite products of glass?
There are mainly tempered, semi-tempered, interlayer, hollow, coating, and their different combinations. For example, toughened coated insulating glass, coated laminated insulating glass, etc.
21. What is the shading coefficient Sc, and which part of the heat transfer does it reflect?
Shading coefficient Sc: Under the same conditions, the ratio of the solar radiant energy passing through the glass to the solar radiant energy passing through the 3mm glass. The solar radiation energy through 3mm transparent glass is 630w/㎡. Sun shading coefficient Sc = direct solar radiation energy ÷ 630 w/㎡ direct solar radiation energy = 630 w/㎡ × Sc. The shading coefficient reflects the heat transfer of direct solar radiation through the glass.
22. Is the shading coefficient Sc high or low?
Glasses with different shading coefficients are suitable for regions with different climates. The shading coefficient is high, and the solar radiation entering the room through the glass window is more, thereby reducing the heating cost in winter. This kind of glass is suitable for use in northern regions with long winters. The shading coefficient is low, and the blocking effect on direct solar radiation is good, which can reduce the direct solar radiation energy entering the room. This kind of glass is suitable for use in southern regions with long summers.
23. What is U value? What part of the heat transfer does it reflect?
The U value reflects: the heat energy transmitted through the glass due to convection conduction, including the heat energy absorbed by the glass and then radiated outward. Therefore, the emissivity E of the glass is low, and the U value is correspondingly low. Convective conduction heat energy = U value × (T outdoor – T indoor) T outdoor and T indoor are the indoor and outdoor temperatures respectively.
24. How many parts constitute the total heat energy transmitted through the glass? How to express?
There are two parts: direct solar radiation heat transfer and convective conduction heat transfer. Expressed by formula: O total = 630 × Sc + U × (T outdoor – T indoor)
25. What are the components of solar radiation?
It consists of three parts: ultraviolet radiation, with a wavelength range of 0.01 to 0.4 microns.
Visible light with a wavelength range of 0.4 to 0.76 microns.
Near-infrared radiation, wavelength range 0.76 ~ 3 microns
26. Does the far-infrared thermal radiation come directly from the sun?
Far-infrared thermal radiation comes indirectly from the sun, and this part of the energy is thermal energy, which is radiated by the sun when it is irradiated on the object and then absorbed by the object, and its wavelength range is distributed in the range of 3-40 microns. In summer, the far-infrared heat radiation emitted by outdoor roads and buildings under sunlight is one of the main heat sources from outside.
27. Is there any far-infrared heat radiation indoors?
Yes, indoor far-infrared heat radiation comes from heating, household appliances, furniture exposed to sunlight, stoves and human bodies, and is the main heat source from indoors in winter.
28. How does far-infrared thermal radiation pass through glass?
Far-infrared thermal radiation cannot directly pass through ordinary glass, but can only be absorbed or reflected by glass. After the glass absorbs this part of energy, the temperature will rise, and lose this part of energy through convection conduction with the air and heat radiation to both sides. Therefore, this part of energy finally passes through the glass, but it is absorbed first and then absorbed. transmitted through radiation.
29. How to distinguish far-infrared thermal radiation and near-infrared radiation?
Near-infrared radiation comes directly from the sun, and its thermal sensation is not obvious, but it can be converted into heat after being absorbed by objects. Far-infrared thermal radiation, as a result of solar energy conversion or as a result of human production, is itself heat. Observing the sunlit road in summer, you can see waves of thermal radiation rising from the ground (that is, solar energy is being converted into thermal radiation). In winter, close to the heater, you can directly feel the heat radiation.
30. What is LOW-E glass?
LOW-E glass is low-emissivity glass, which is formed by coating the glass surface and reducing the emissivity E of the glass from 0.84 to below 0.15.
31. What are the characteristics of LOW-E glass?
High infrared reflectivity, can directly reflect far infrared heat radiation.
The surface emissivity E is low, and the ability to absorb external energy is small, so the heat energy radiated is less.
The shading coefficient Sc has a wide range, and the amount of solar energy transmitted can be controlled according to the needs to meet the needs of different regions.
32. Why can the LOW-E coating reflect heat?
The LOW-E coating is coated with a silver layer, which can reflect more than 98% of far-infrared heat radiation, thus directly reflecting heat like a mirror reflecting light. The shading coefficient Sc of LOW-E can be from 0.2 to 0.7, so that the direct solar radiation energy entering the room can be adjusted according to the needs.
33. What is the functional difference between LOW-E glass and heat reflective glass?
Heat-reflecting glass is to reduce the shading coefficient of the glass and limit the direct solar radiation to enter the room through the glass, so as to reduce the cost of air conditioning and save energy. LOW-E glass is to reduce the U value of the glass and limit the far-infrared heat radiation to pass through the glass, so as to achieve the purpose of reducing the heat energy of convection and conduction through the glass. At the same time, the shading coefficient Sc of LOW-E glass has a large adjustment range, which can effectively control the direct solar radiation energy entering the room.
34. What are the main types of mature coated glass technology?
There are two main types: online coating, vacuum magnetron sputtering coating (also known as offline coating). On-line coated glass is manufactured on a float glass production line, which has a single variety, poor heat reflectivity, and low manufacturing cost. Its only advantage is that it can be hot-bent. The coated glass manufactured by the vacuum magnetron sputtering process has a variety of varieties, excellent heat reflection performance, and obvious energy-saving characteristics. Its disadvantage is that it cannot be processed by hot bending.
35. Can LOW-E glass be used as a single piece?
The LOW-E glass manufactured by the vacuum magnetron sputtering process cannot be used as a single piece, but can only be used as synthetic insulating glass or laminated glass. But its emissivity E is far lower than 0.15, and can be as low as below 0.01.
The LOW-E glass manufactured by the online coating process can be used in a single piece, but its emissivity E=0.28, strictly speaking, it can no longer be called LOW-E glass (scientifically, an object with an emissivity E≤0.15 is called low-emissivity object).
Low-E glass is most effective in the similar closed space formed in the sealed insulating glass, because this closed space eliminates the air flow on the low-e surface, so that the low-e glass can work better.
36. Is the performance of LOW-E glass the same?
From a technical point of view, all Low-E glass handles the spectral curve in the same way, but not all perform in the same way. The Low-E glass produced by Yaopi Company is not only suitable for use in the cold regions of the north, but also suitable for use in the warm and tropical regions of the south due to its different properties.
37. Which type of LOW-E glass is suitable for the northern cold regions?
The answer given by the editor: The CES series LOW-E glass produced by CSG is suitable for the northern region. It has a low U value, and at night, it prevents the far-infrared heat radiation in the room from leaking to the outside by limiting the heat transfer by convection and conduction. It has a high shading coefficient, so it can allow more direct solar radiation to enter the room during the day. At this time, there is no far-infrared heat radiation in the cold outdoors, and the far-infrared heat radiation in the room is limited indoors, thus playing the role of solar energy. The effect that can enter but cannot exit.
38. Which LOW-E glass is suitable for the southern temperate zone?
The answer given by the editor: CEB series LOW-E glass produced by CSG Group is suitable for the southern region. It has a low shading coefficient, which can limit the direct solar radiant energy from entering the room during the day. In these areas, the far-infrared heat radiation from outdoors is much greater than that from indoors no matter day or night. His low U value makes it possible to block these heat energy outside, thereby limiting both solar energy and outdoor heat energy from entering the room.
39. Do all LOW-E glass look the same?
My answer: different! The LOW-E of the CES series looks highly transparent, with a transmittance of over 60% and a light color. The LOW-E of the CEB series seems to have low transparency, the transmittance is below 55%, and the color is relatively dark.
40. Does LOW-E glass still work at night?
yes! LOW-E glass works day and night. In winter, heat (far-infrared heat radiation) will be reflected back to the room day and night, because the heat generated by heating or converted from solar energy exists in the form of far-infrared heat radiation.
41. How does LOW-E glass work in summer and winter?
●In winter, the indoor temperature is higher than that of the outdoors, and the far-infrared heat radiation mainly comes from the indoors. The LOW-E glass can reflect it back to the indoors so as to keep the indoor heat from leaking out. For part of the solar radiation from the outside, LOW-E glass can still allow it to enter the room, and this part of energy is absorbed by indoor objects and then converted into far-infrared heat radiation and left indoors.
●In summer, the outdoor temperature is higher than the indoor temperature, and the far-infrared heat radiation mainly comes from outside the city. Low-e glass can reflect it to prevent heat from entering the room. For solar radiation from the outside, LOW-E glass with a low shading coefficient can be selected to limit its entry into the room, thereby reducing quality costs (air conditioning costs).
42. How to estimate the electricity cost saved by LOW-E glass?
The answer given by the editor: See the calculation in “Evaluation of Energy-saving Characteristics of Low-E Glass” for details.
43.Which surface of the insulating glass is the most suitable for the LOW-E coating?
The answer given by the editor: Insulating glass has 4 surfaces, which are 1#, 2#, 3#, and 4# surfaces from the outside to the city. In areas where the heating demand exceeds the cold demand (northern area), the LOW-E film layer is known as the 3# surface. Conversely, in areas where the cooling demand exceeds the heating demand (south area), the LOW-E film layer should be located on the 2# surface.
44. What is the role of filling argon in insulating glass?
Argon is an inert gas, its thermal conductivity is worse than that of air, so filling it into the insulating glass can reduce the U value of the insulating glass and increase the heat insulation of the insulating glass. For Low-E insulating glass, argon also has the effect of protecting the Low-E film layer.
45. What are the side effects of ultraviolet rays?
Ultraviolet radiation is short-wave radiation, invisible to the naked eye, and it accounts for about 2% of the total energy of solar radiation. Ultraviolet rays can kill bacteria, but prolonged exposure can burn human skin and eyes, as well as fade furniture and clothing.
46. How much ultraviolet light can LOW-E glass attenuate?
Compared with ordinary single-piece transparent glass, LOW-E glass can reduce ultraviolet rays by 25%. Compared with heat-reflective coated glass, LOW-E glass can reduce ultraviolet rays by 14%. Low-E glass cannot completely prevent furniture fading, but it can slow down fading.
47. How does LOW-E glass affect indoor plants?
There is no adverse effect on most different plants. For the impact on special rare plants, please consult relevant flower experts.
48. Do sunshades, trees and awnings affect the performance of LOW-E glass?
These objects can limit the heat and light entering the room through the glass window, that is, block the penetration of solar energy, but do not affect the performance of LOW-E glass.
49. In which direction is it best to install LOW-E glass?
In winter, no matter which direction the LOW-E glass faces, it will not affect its performance, because it mainly emits indoor heat. However, the effect of installing facing north is the best. After all, LOW-E glass prevents indoor heat loss and also limits solar radiation to some extent.
In summer, LOW-E mainly reflects outdoor heat, so it is suitable for installation in any direction, but the best effect is installed in the east, west, and south directions, so it can also reduce the penetration of solar energy.
50. How long does the LOW-E coating last?
The duration of its coating layer is the same as the duration of the sealing of the insulating glass space layer.
51. What is the effect of combining LOW-E glass with tinted glass?
There are three combinations: coating LOW-E film on tinted glass, synthesizing hollow glass with tinted glass, and synthesizing laminated glass with tinted glass. Tinted glass can further reduce the shading factor of combined glass products, thereby restricting more direct solar radiation from entering the interior. Therefore, the combined use of these three methods works well, and is more suitable for use in the southern temperate tropics. Combining with tinted glass can also greatly increase its decorative effect.
52. How to judge whether there is LOW-E glass on the insulating glass?
It can be monitored and judged according to the following steps:
A. Observe the four images presented in the glass (in other words, there are 4 flames and 4 objects).
B. Put the match or bright object in front of the window (whether you are in the city or outside), if it is LOW-E glass, the color of one image is different from the other three images, if the color of the four images is the same, it can be determined LOW-E glass is not installed.
53. Does the user need to do anything to maintain LOW-E glass products?
unnecessary! Because the LOW-E film is sealed in the middle of the insulating glass or laminated glass, no maintenance is required, only the surface of the glass needs to be maintained.