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

Rapid development of glass structures

 As we mentioned in previous post:Glass panel design for skyscrapers glass facade,glass has 4 characteristics:Transparency,high strength,light weight and long durability.There’ll be no skyscraper without glass curtain walls.

Modern glass structure development was also been promoted by the glass production &processing technology,and new interlayers developed these years.

 

1. Glass production &processing technology.

 

In 2005, the 1^st piece low iron glass was produced in Jinjing group,.

In 2007,Jinjing group produced 7000*3660*19mm low iron float glass.

In May,2011, CSG produced the ultra long low iron glass 16000*3300mm,the glass was applied in Hongkong apple store.

Following that low iron glass Max size reached 18000*3660mm in China.

Clear float glass,from normal 4280/4580/4880*3300, to 13000*3300, 18000*3300, to now 18000*4580mm.

Matched glass processing equipment,including cutting,edging,tempering,laminating and insulating process equipment were also invented to fit the newest design idea.

ultra long glass tempering and laminating production

2. Structural interlayer development.

Laminated glass is used for structural glass projects.When designing with PVB laminated glass,glass bearing capability and strength is equal to the sum of the bearing capacity or rigidity of each piece of glass; when using SGP film, the equivalent thickness of the laminated glass can be the overall laminated glass thickness, so its bearing capacity and rigidity are greatly improved.

all glass curtain wall installation

Sample Project: All glass curtain wall

Facade panel:12+2.28SGP+12 Low-E+16A+12+2.28SGP+12 low iron tempered laminated insulated ,11780*1500mm.

Glass fin:12+2.28SGP+12+2.28SGP+12 low iron tempered laminated glass,11790*500mm.

Glass structure types:

Glass structures are commonly used for panels, including wall panels and load-bearing floors. In addition, when used in the main load-bearing structure, there are beams, columns and frames.

1. Glass beams:Glass beams are usually used as supporting structures for glass skylights.For safety reason, laminated glass must be used for the skylight panels and load-bearing beams.

The laminated glass panel can be supported either peripherally or point support.

Glass beams used in glass roofs

2. Glass Fins.

Modern glass fins are most widely used in point supported glass facade,especially when glass panels are ultra long and installed by top suspension support system.Multi layers laminated glass are used to increase the thickness of the glass, thereby increasing the width of the cross section of the glass fin.

stainless steel to connect glass fins

The upper and lower ends of the glass column are supported by hinges to withstand the dead weight, wind load and seismic force transmitted from the glass panel. The glass panel can be connected to the glass column by edge support or point support,Stainless steel plates can be used to connect several sections of glass columns into long columns.

all kinds of glass fins used in glass curtain wall

The large-area glass wall panels are supported by glass fins to form a transparent indoor space.

In 2015, the all-glass lobby of Hangzhou Zheshang Fortune Center created the world’s tallest glass fin record, with a glass column height of 28m. The glass column is divided into 3 sections, which are installed, positioned and connected on site. The glass column total thickness of 104.1mm. 5 pieces of 19mm ultra-white tempered glass and 4 layers 2.25mm SGP high-strength interlayer. The three sections of glass fins are connected on-site with stainless steel plates and stainless steel bolts.

hangzhou world record-28Meter height lobby

3. Oversized glass facade panels

Apple is the leader in applying oversized architectural glass panels on buildings,worldwide apple stores with glass boxes,glass structures used the world newest glass processing technology.

For thermal insulation consideration,the facade panels are always combine with high performance low-E coatings and been made into laminated insulated glass.

Hangzhou Apple store used 14500 height 3000 width glass panels

Hongkong Apple store used 18000 height 3000 width glass panels

4.Column-free glass wall

In 2015, Apple’s headquarters, which is shaped like a giant UFO was built in California, USA. The glass exterior wall adopts 14m X 3.3m ultra-large curved glass, toughened, insulating glass. The glass exterior wall is not supported by glass columns, and all the loads are borne by the glass panels alone.

Apple headquarter in USA

5.Glass Frames

Glass boxes is most seen in Apple stores,please check our previous post:Oversized laminated glass applied in Apple store to see the glass boxes,including the store in Fifth Avenus(New York), Round glass box (Shanghai).

All-glass buildings require a transparent glass frame. The beam and column are subject to great stress, so multi-layer toughened laminated glass should be used. Glass can be connected with stainless steel hardware,or structural sealants.

apple store in Shanghai-all glass structure

APPLE STORE

6.Glass stairs

In the glass building, the staircase naturally also adopts the glass structure. Laminated glass is used for the fence and pedals to ensure safety. The pedal is usually laminated with 3 pieces of glass, and the surface glass is usually anti-slip function to be realized with engraved surface.

Learn more:Modern Interior Glass Stairs & glass stair railings design

translucent anti slip glass stair in apple store

Conclusion：

Although glass has high strength, it is a brittle material after all, and the thin glass panels need careful strength and rigidity calculations when designing, and the lateral stability of the glass column should also be considered.

As a part of fast growing China glass processing industry,Morn would like to share what we know with every designers and architects,we also manufacture and supply structural glass to achieve your creative structural glass projects.

Download this article here:Rapid development of glass structures