Solutions to the greenhouse effect of glass skylight

 Glass skylights are commonly used in modern buildings, but series problems happened when people enjoying the direct sunlight through the glass,for example: the high indoor temperature under the skylight, strong heat radiation, and the light irritates the eyes.This phenomenon of glass skylight is called greenhouse effect.

glass skylight project-Morn

What is the greenhouse effect?

Solar energy enters the room through the glass and cause the indoor temperature to rise, especially in summer, and the heat entering the room is not easy to naturally radiate through the building, which makes the indoor thermal comfort and light comfort deteriorates.

Even if the air temperature is suitable under the skylight, as long as there is sunlight, people still feel hot and uncomfortable, just like people standing outdoors under the sun.

Shopping malls with large scale glass skylight 2

Under the same indoor air temperature,the temperature felt by the human body under the building with ordinary windows and the skylight is very different,sometimes the overall air synthetic temperature under skylight can be 15℃ higher than windows.

Factors cause greenhouse effect?

large scale glass skylight with insulated glass

1. Solar shading coefficient:

The overall air synthetic temperature is directly proportional to the skylight solar shading coefficient.Better solar shading coefficient improve the thermal environment under the roof, and increase thermal comfort. It also helps reducing the cooling energy consumption in summer.

2. Solar radiation.

The overall air synthetic temperature is directly proportional to the solar radiation. In hot summer and cold winter areas the greenhouse effect under the skylight is extremely significant, and measures must be taken to solve it, otherwise the human body under the lighting roof feels overheated. In cold regions, there is also a period of strong solar radiation in summer.

 Measures to increase indoor comfort

laminated insulated glass applied in glass skylight

1. 
   

   Decrease skylight glass U value

Skylight glass are usually laminated insulated glass, laminated glass is inside to prevent glass fragments falls once glass broken.

In our previous posts,the glass thermal insulation performance (Glass U value) is affected by the glass installation angle.

learn more:How the glass U value been affected by the installation angle?

Firstly,skylight designers and architect should be aware of below conclusion:

In summer condition,glass U value is not affected by the installation angle,from 0° to 90°.

In cold winter conditions,glass U value decrease from 0° to 90°,take solarban 60 double silver low-E coating as example,glass U value decrease from 1.66 to 2.47,which helps reduce air heating costs.

Laminated insulated glass

 

Measures to reduce glass U value:

1. Using high performance double silver low-E andtriple silver low-E
2. Using argon filled insulated glass to replace the air inside glass.
3. Using warm edge spacer instead of traditional aluminium spacers to decrease glass edge thermal insulation.
4. Change double glazed units to triple insulated glass.

More details can be found here:

Insulated glass-feature,thermal performance&calculation tool

Extend:

Argon filled insulating glass VS warm edge spacer insulating glass

2. 
   

   Decrease glass Solar shading coefficient

Glass solar shading coefficient is related to the glass light transmittance,glass light reflectance,and the low e coating types.

High performance double silver low-E coatings and triple silver low e coatings transfer the sunlight into cold light,allow much less solar radiation through the glass.

Below tables shows the difference between single,double and triple silver low-E under same light transmittance.

Glass	LT %	SC	U value	Cooling load	AC Investment
6-12-6 Single Silver Low-E	67	0.65	1.96	2250.72KW	USD1,380,000
6-12-6 Double Silver Low-E	69	0.49	1.65	912.51KW	USD560,000
6-12-6 Triple Silver Low-E	67	0.38	1.65	525.93KW	USD323,000

For cold areas,customers can use high performance triple silver low-E coating for skylights projects.

Glass manufacturers also developed the right low e coatings suitable for glass skylight projects in hot areas.The features of this kind coating is medium light transmittance,high light reflectance and low solar coefficient compared with other coatings.

Glass Combination	LT %	LR(out) %	LR( in) %	U-Summer	U-Winter	SC	SHGC
6 MDE50D02+12A+6C	46	27	32	1.61	1.54	0.3	0.26
6MDE50D+12A+6C	47	27	36	1.63	1.57	0.37	0.32
6MDE48C+12A+6C	44	16	17	1.62	1.55	0.32	0.28

Other methods to decrease glass solar coefficient including body tinted glass,colorful PVB interlayer ,ceramic frit on glass surface,and even photovoltaic glass with opaque ceilings also works to help decrease glass SC value.

Colorful laminated glass for skylights

photovoltaic glass used on glass skylight

3. 
   

   Apply thermal insulation film on existing skylight projects

For already installed skylights,it’s impossible to change the existing glass combinations.Glass film is perfect option for customers to decrease glass solar coefficient,below pictures shows a project installing solar reflecting films ,after installation process,indoor temperature under the glass skylights decreased by 12-15 degree.

Installing solar reflective film on existing skylight projects

obviously decreased glass SC after installing films

4. Adding extra interior or exterior solar shading facilities.

The glass skylights can add external or internal shading facilities,for example outdoor fabric canopy,FSS roller awning,FCS awning,FTS awnings.Beside awnings, electrical aluminium louver systems also works to stop light transmit glass directly.

skylight external shading system-China Morn

The difference between internal shading and external shading system is：

External solar shading systems stop the direct solar radiation through the glass,the overall solar radiation through glass was minimized,but for structural reason,external shading systems price is higher.

Internal solar shading systems cannot decrease the heat through glass,but as the shadings color is light,the far radiation generated by the sunlight was decreased as well.

internal solar shading system for skylight

Both shading systems avoid the direct sunlight ,decrease the people apparent temperature.

Glass skylight brings light and sun energy into the room,architects and designers should take measures to minimize the negative high temperature caused by the direct sunlight through glass,and shading systems.

China Morn can helps manufacturing and supplying the right insulated glass based on your skylight project location,temperature and area,welcome contact us for your next skylight project.

Donwload this article here:Solutions to the greenhouse effect of glass skylight

20 FAQ about low emissivity glass-Glass Guidance

 

1. What’s the component of solar radiation?

The solar radiation include 3 parts: UV radiation (Wavelength range 0.01～0.38 microns),visible light (Wavelength range 0.38～0.75 microns),near infrared radiation(Wavelength range 0.75～3 microns).

2. 
   

   What’s the difference between near infrared radiation and far infrared radiation?

Near-infrared radiation comes directly from the sun, and its heat is not obvious, but it can be converted into heat after being absorbed by an object.Near infrared radiation cannot transmit the glass directly,it can be only been reflected or absorbed by the glass,after glass absorbing the near infrared radiation,glass temperature will increase and become a radiation source itself.

Far infrared is a result of solar energy conversion or artificial production,such as the stove,house appliance, human body,and the furniture that lighted by the sun.In summer,the exterior road,buildings are the main source of far infrared after lighted by the sun.

3. 
   

   What kind of thermal that are transferred through glass?

The energy that transferred through glass include direct solar radiation ,typical parameter to measure it is glass SC (Shading coefficient) and SHGC (Solar heat gain) .

The 2^nd part is convection conduction of heat transfer.It’s related to the infrared radiation. U value is the parameter to measure ,and measurement are W/m²K.

Transfer heat from a high-temperature object to a low-temperature object: heat conduction, heat convection, and thermal radiation.

4. 
   

   What’s glass SC ?

 

Glass SC is to measure the UV & visible light solar radiation transmitted the glass.

Glass SC is short for glass shading coefficient,which means Under the same conditions, the ratio of the solar radiant energy through the glass to the solar radiant energy through the 3mm transparent glass. The solar radiation energy through 3mm transparent glass is 630w/m2.

The higher SC value,the more solar radiation penetrated the glass to decrease heating costs in summer,it’s widely used in long winter areas.

The lower SC value,the better blocking effect of direct solar radiation and reduce the solar radiation energy entering the room,suitable for hot areas.

 

5. 
   

   What’s glass U value?

 

The heat energy transmitted through the glass due to convection conduction, includes the transmission of heat energy after the glass absorbs the heat energy and then radiates outward&inward. Therefore,lower emmissivity,the lower U value.

6. 
   

   What’s low e glass?

Low e glass is short for Low emissivity glass,is to have a multi layer coating composing metalic &chemical on glass surface to decrease the glass emissivity ratio from 0.84 to below 0.15,or even only 0.03.The typical emissivity of low e glass include single silver low-E,double silver low-E and triple silver low-E,which contains 1 layer, 2layer,and 3 layers silver coatings.Hard coated low e glass as relatively higher emissivity compared with the soft coated low e.

Hard coated low e VS Soft coated low e

Difference between Single silver low-E,double silver low e and triple silver low e

coating layer-single-double-triple silver lowe coating

7. 
   

   What’s the function of the low-E coating?

The feature of low e coating is thermal insulation.

The low emissivity coating can reflect the far infrared radiation directly,especially the silver layer inside the soft coated low-E coating can reflect 98% far infrared radiation like mirrors.

The coating has little capability absorbing the heat,which will control the glass surface temperature very well, the heat re-radiated out from the glass is little accordingly.

Despite controlling the infrared,the coating as a variety options with different visible light transmittance and SC value(0.2-0.7)  to control the ratio of direct solar energy transmitted through the glass,which can be selected by users both in hot and cold areas.

insulated glass-heat transfer-morn bm

 

8. 
   

   What’s the difference between solar reflective glass and low e glass?

 

Solar reflective glass reduces the shading coefficient of the glass and restricts the direct solar radiation from entering the room through the glass, thereby achieving the purpose of reducing air-conditioning costs and saving energy.

Low-E glass reduces the U value of the glass to restrict the far-infrared radiation from penetrating the glass,in addition, the shading coefficient has a large adjustment range, which can effectively control the direct solar radiation energy entering the room.

 

9. 
   

   What’s the mature coating types of low e glass?

 

There’re 2 kinds of low e glass,soft coated low e coating and hard coated low e coating.

Hard coated low e glass is manufactured on a float glass production line. This type of glass has a single variety, poor heat reflection performance. Its only advantage is that it can be used as monolithic glass or been laminated.

Soft coated low e glass is manufactured by the vacuum magnetron sputtering process .It has a variety of colors, excellent heat reflection performance, and obvious energy-saving characteristics. The disadvantage is that it must be made into insulated glass,or the coating will be oxidized once exposed in the air.

 

10. 
    

    Does low e glass wok at night?

 

Yes,low e glass work anytime.No matter what kind of far infrared,whether it’s caused by the solar,or artificial far infrared,it can always reflect the infrared heat.

 

11. 
    

    How does low e coating works in summer and winter?

 

In winter, the indoor temperature is higher than outdoors, and the far-infrared heat radiation mainly comes from indoors. Low-E glass can reflect it back indoors to keep indoor heat from escaping.

In summer, the outdoor temperature is higher than indoors, Low-E glass can reflect the exterior heat out to prevent heat from entering the room. For outdoor solar radiation, Low-E glass with low shading coefficient can be selected to restrict its entry into the room, thereby reducing cooling costs.

12. 
    

    Low-E coating on surface #2 or surface #3?

Insulating glass has 4 surfaces, the number from outdoor to indoor is 1#, 2#, 3#, 4# surface.

In areas where the heating demand exceeds the cooling demand , the Low-E film layer should be on surface #3.  Conversely, in areas where cooling demand exceeds heating demand (southern areas), the Low-E film should be on the 2nd surface.

Low e coating position-Surface #2 VS Surface #3

low e coated glass -morn-china-manufacturer-morn

13. 
    

    What’s the function of argon filled in insulated glass?

 

Argon is an inert gas, and its heat transfer performance is worse than air. Therefore, argon filled insulated glass will have better thermal insulation,lower U value, argon also protect the Low-E film.

 

14. 
    

    How much Uv the low-e coating can block?

 

Ultraviolet is short-wave radiation, invisible to the naked eye, it accounts for about 2% of the total solar radiation. Ultraviolet rays can kill bacteria, but long-term exposure can burn human skin and eyes, and also cause furniture and clothing to fade.

 

Low-E glass can reduce ultraviolet rays by 25%. compared with clear glass, It cannot completely avoid furniture fading, but it can slow down the fading.

 

15. 
    

    Do shades, trees and awnings affect the performance of Low-E glass?

 

These objects can restrict the heat and light entering the room through the glass window, that is, block part of the solar energy from passing through, but it does not affect the performance of Low-E glass.

insulated glass with frosted glass effect-MORN -CHINA

16. 
    

    Is the windows&glass installation angle affect the glass U value?

Yes,the glass U value and shading coefficient are not affected by the installation angle,while in winter,the glass U value increase significantly with the angle from 90degress to 0 degrees.So for glass roofs,skylights,please select a low e coating with better U value.

How the glass U value been affected by the installation angle?

The double glazed unit used in glass skylight should be toughened glass or heat strengthened glass.The inner pane may be toughened or laminated GLASS.

17. 
    

    What’s the effect combing the low e coating with body tinted glass?

 

There’re 3 kinds of combinations:

Coating directly on body tinted glass, clear low e glass + body tinted insulated glass, laminate body tinted glass with clear low e coated glass.

Tinted glass can further reduce the shading coefficient,thereby restricting more direct solar radiation from entering the room. Therefore, the combined effect of these three methods is very good, and it is more suitable for use in tropical regions. Combining with colored glass can also greatly increase its decorative effect.

But do pay attention that coating on tinted glass price is higher ,also contains many advantages and disadvantages.

glass curtain wall with tinted glass insulated glass-morn-china

18. 
    

    What’s the lifetime of low e coating?

Hard coated low e glass lifetime is same as the glass lifetime.

Soft coated low-E glass,after unpack the glass package,it’s suggested to make into insulated glass asap,or the coating will be damaged or oxidized within 30 days or even shorter time.

Once been made into insulated glass,the coating lifetime is same as the glass sealing time.

 

19. 
    

    Where can we buy high performance low e coated glass?

Hard coated low-E manufacturers in China include AGC, Jinjing, SYP,Kibing.

Hard coated low e options in China

As Soft coated low-E must be made into insulated glass,it’s suggested to purchase finished insulated glass with high performance low e coating directly,Morn glass is your turnkey coated glass supplier,our products include single,double and triple silver low e insulated glass,click below link to check our coated glass performance data:

W1.1 and W1.16 low E coating for greenhouse /conservatory

Morn-Coated glass performance data

Morn-Triple silver low-E glass performance data

triple silver low-E coated glass-solarban 70XL-CHINA

20. What’s low e coated glass price?

The glass price varies based on different project requirement,generally the glass combination,glass size,materials used in the insulated glass ,and many other factors-glass packing,broken&replacement,shipping costs affect the final insulated glass price.

 

Need more help? Contact us through marketing@cnmorn.com, our glass expert are ready to serve you.

Download this article here:20 FAQ about low emissivity glass-Glass Guidance