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.

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