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Insulating Glass

What is an insulating glass unit (IGU):

Insulating Glass Units (IGUs) are hermetically sealed combinations of two or more panes of glass separated by a dry airspace. IGUs improve the thermal performance of windows, thus significantly reducing heating and air-conditioning costs. IGUs also reduce interior condensation in cold climates, and increase comfort near windows, thus maximizing usable interior space.

The area between the glass panes, called a cavity, must be filled with dry air or gas. To ensure this dry environment, the spacer bars are filled with desiccant. A thin strip of butyl is applied on both sides of the spacer bar and it is then placed between the two glass pieces. The butyl serves as primary/interiror sealant and prevents gas exiting and moisture entering the cavity. A secondary/exterior sealant is then applied for mechanical strength. Silicone, polysulphide or polyurethane is usually used as a secondary sealant.

For a quality IGU, all materials must be mechanically strong, UV resistant, have a good moisture penetration protection and be stable in cold and hot conditions. Placing the primary sealant evenly without any interruptions, especially on the edges is vital for a quality production. If any of the above conditions is not met, there’s a risk of moisture penetration, which will result in the inside of the IGU becoming wet.

Gas penetration comparison table between primary and secondary sealants:
Lower value is better.

Materia	Application	Gas penetration value (l/mm²d)
Butyl	Primary sealant	0.01
Polysulphide	Secondary sealant	0.03
Polyurethane	Secondary sealant	0.3
Structural silicone	Secondary sealant	10

From the table above it becomes clear how important the primary sealant is for the gas penetration/leakage protection of the IGU. It is important that enough butyl (at least 4mm) is laid on each side of the spacer and that there are no interruptions, especially on the edges.

Equipment:

Having the right reliable equipment for IGU production ensures right planning and high quality product.

"Bul-It Glass” Ltd. owns two IGU production lines manufactured by one of the world’s leaders in the field – Lisec, Austria.

Technical specifications:

Maximum dimensions	2700 х 5000 mm
Minimal dimensions	200 х 300 mm
Maximum IGU thickness	60 mm
Maximum thickness of a single glass	15 mm
Argon gas filling	Yes, automatic up to 3500 mm and manual between 3500 mm and 5000 mm

IMPORTANT INFORMATION: DESIGN INSTRUCTIONS, MANUFACTURING, SAFETY, DURABILITY, STORAGE,INSTALLATION AND EXPLOITATION OF INSULATING GLASS.

How to choose the right IGU:

Nowadays there is a wide variety of glass types with different coatings and properties. This allows us to combine them differently into a double (single cavity) or tripple (double cavity) IGUs in order to achieve our goals when glazing. In order to choose the right structure it is important to prepare the anwers to the following questions:

What is the purpose of the building – living, commercial, office or other.
What are the climate conditions in the area of the building.
Which direction will the facade be facing – will it be facing the sun, are there strong winds in the area, etc.
Target savings for heating and cooling.
Design considerations such as color/tint of the glass.

USEFUL INFORMATION: IS THERE AN OPTIMAL GLAZING USING INSULATING GLASS UNITS?

Main IGU properties:

Light properties - by chooising tinted glass or glass with a special coating, different light properties can be achieved:

LT – light transmission, the percentage sun light that goes through the IGU.
LR – light reflection, the percentage of sun light that the outer glass reflects back and does not let into the room.
UVT – ultraviolet transmission, the percentage of UV light that goes throught the IGU.

Energy properties - by chooising tinted glass or glass with a special coating, different energy properties can be achieved:

ЕА – energy absorption, the percentage of energy/heat that the IGU absorbs in its mass.
ЕR – energy reflection, the percentage of energy/heat that the iGU reflects back and does not let into the room.
SF - solar factor, the percentage of energy/heat that enters the room.
U [W/m².K] - heat transfer coefficient. The smaller the value, the better heat insulation properties the IGU (or any other material) has.

Noise reduction properties:

Rw dB - noise cancellation coefficient in percent.
Tentative values:
- 25% for conventional glazing with single glass;
- 30% for IGU with a minimum of 20mm total thickness;
- 35% for IGU with a bigger thickness of 20mm.;
- 40-45% for tripple glazed IGU (two cavity IGU);
- over 50% for special structures, usually tripple glazed IGU with laminated glass;

Main functions of the insulating glass units:

Energy savings – keeping the heat inside the room during cold weather.

The energy saving effect of the IGUs are achieved by reducing the heat transfer through the unit. This can be done if multiple ways:

Chaning the width of the spacer (air/gas cavity).
Using inert gas (argon,krypton) to reduce natural convection inside the cavity.
Using Low-E glass with soft or hard coating.
Using tripple glazed (double cavity) IGUs with two Low-E glasses. This is the most effective method at the time.

Solar protection – reflecting the heat from the sun out of the room in the hot sunny days.

Clear glass and energy saving Low-E glass do not provide any solar protection. It is achieved by either retaining the sun energy inside the mass of the glass by using dark glass with a high EA value*, or by reflecting the sun energy/heat by using glass with a reflective/solar protecting coating. There is a direct correlation between solar protection (solar factor SF) and light transmission (LT) and achieving maximum comfort is a matter of finding the right balance between these two properties.

*Glass with property ЕА ≥ 60% must be tempered due to high risk of thermal stress. For glass with ЕА ≥ 40% it is highly recommended to have the edges arised.

VIDEO: What is Low-E glass. Source: glassed.vitroglazings.com

VIDEO: How does Low-E glass work. Source: glassed.vitroglazings.com

Noise protection/noise cancellation.

The coating and the color of the glass do not play any role in the noise cancellation properties of the glass. Noise protection is achieved by:

using laminated glass;
using tripple glazed (double cavity) IGUs;
using IGUs with different glass thickness (asymmetry);
using thicker glass in general;
increasing the width of the spacer (air/gas cavity);

Appearance and light transmission.

The appearance of the IGUs is determined by the color of the outer glass when looked from outside. Different colors/appearances are achieved by:

having tinted glass (when the mass of the glass is in a particular color/tint). The most common colors are green, blue, bronze (brown) and grey.
having coatings on the glass that can give a certain tone to the glass appearance.
having coatings on an alreay tinted glass.

Darker colors and coatings with stronger solar protection are inversely proportional to light transmission (LT), i.e. stronger solar protection darkens the room. The proportion between light transmission (LT) and solar factor (SF) determine the glass selective properties, or selective coefficient. The regular clear 4mm glass has the worst selective coeffiecient: 83% (LT) / 80% (SF) = 1.0375. A value of 2 and above is considered to be a very good selective coefficient. This is achieved by using 2 or 3 silver coatings, usually on low iron glass.

Safety and anti-burglary.

Safety in IGU can be achieved by using temepred and laminated glass. When temepred glass breaks, it falls apart into many small pieces that are not sharp and can not cut human skin. The worst injury that can happen to a person is a bruise or a scratch. The laminated glass remains in one place when broken. This makes it safer than temepred glass, albeit not stronger. Strength is actually the drawback of the lamniated glass in regards to temepred glass. Roghly, we can measure the strenght of the laminated glass to be equal to the strenght of monolithic glass with thickness about 60% of the total thickness of the laminated glass. In other words, we can say that the strength of a 10mm laminated glass (5+5) is about the same as the strenght of a single 6mm glass. In order to combine the best of both worlds it is best to use a combination of temepred and laminated glass in an IGU. A tempered glass can be placed outside the unit in order to withstand rought outside conditions, like strong winds, thermal load and deviations. A laminated glass can be placed inside the IGU in order to achieve the safety of the inhabitants.

The strength of the temepered glass alone is not enough to prevent burglary. It is susceptible to breakage by being hit with a sharp object. In order to achieve better burglarly protection it is advisable to use a combination of two or three laminated glasses in an IGU, where at least 4 layers of laminating foils are used between at least 3 glasses. Due to the tensile properties of the laminating foils it would take a really long time to bust through such a glass, even if one manages to break the glass panes. Oddly enough, in such cases it is important to install a better and stronger framing system, as regular frames might be easier to "unclip” if the IGU is hit hard enough.

"Warm edge” spacer - improved heat insulation around the perimeter of the IGU:

The spacer bar is the thermal bridge between the perimeter of the IGU and the environment. The standard aluminum spacer is a really good heat conductor, which makes it not the best choice if one is looking for maximum performance. By using "warm edge” spacer bars, usually made out of plastic of composit materials, we get a much better insulation around the perimeter of the IGU. This improves the combined performance of the glass and framing system by up to 10% and also prevents condensation appearing around the edges of the IGU. From an aesthetic point of view, the warm edge spacers are produced in many colors ( black, grey, brown, white and more). This makes this solution a nice improvement in interior design. "Bul-It Glass” partners with the swiss based manufacturer of warm edge spacers Swisspacer.

Comparison table with parameters, suggested applications and sample IGU structures:

Structure	Light properties			Heat properties			U-coeff.		Noise properties		Additional information
	[%]			[%]			[W/m².K]		Rw	noise
	LT	LR	UVТ	EA	ЕR	SF	Air	Argon 90%	dB	reduction [%]
4 clear – 16 – 4 clear	83	15	-	9	14	80	2.7	2.6	31	-	Base IGU, no advantages.
6 clear – 16 – 4 clear	82	15	-	12	13	78	2.7	2.6	35	-	-
6 clear – 16 – 6 clear	81	15	-	14	13	78	2.7	2.6	33	-	-
4 green – 16 – 4 clear	71	12	-	44	8	53	2.7	2.6	31	-	-
6 green – 16 – 4 clear	66	11	-	54	7	45	2.7	2.6	35	-	-
6 green – 16 – 6 clear	65	11	-	55	7	45	2.7	2.6	33	-	-
4 clear – 16 – 4 Low-E	82	11	-	15	27	65	1.4	1.1	31	-	-
6 clear – 16 – 4 Low-E	81	11	-	18	26	64	1.4	1.1	35	-	-
6 clear – 16 – 6 Low-E	80	11	-	19	26	63	1.4	1.1	33	-	-
4 green – 16 – 4 Low-E	69	10	-	51	11	44	1.4	1.1	31	-	-
6 green – 16 – 4 Low-E	64	9	-	60	8	38	1.4	1.1	35	-	-
6 green – 16 – 6 Low-E	63	9	-	60	8	38	1.4	1.1	33	-	-
4 four season– 16 – 4 clear	61	22	-	24	38	40	1.3	1.0	31	-	-
6 four season– 16 – 4 clear	60	22	-	27	36	39	1.3	1.0	35	-	-
6 four season– 16 – 6 clear	60	22	-	28	36	39	1.3	1.0	33	-	-
4 clear– 16 – 4 clear– 16 – 4 clear	76	21	-	13	19	73	1.8	1.7	32	-	-
4 clear– 16 – 4 clear– 16 – 4 Low-E	75	18	-	20	29	60	1.1	0.9	32	-	-
4 Low-E – 16 – 4 clear– 16 – 4 Low-E	73	14	-	25	30	53	0.8	0.6	32	-	-
4 four season– 16 – 4 clear– 16 – 4 clear	56	25	-	27	39	37	1.0	0.8	32	-	-
4 four season– 16 – 4 clear– 16 – 4 Low-E	55	24	-	30	39	36	0.7	0.5	32	-	-
6 clear – 16 – 4 clear– 16 – 4 clear	75	20	-	15	18	71	1.8	1.7	36	-	-
6 clear – 16 – 4 clear– 16 – 4 Low-E	74	17	-	22	27	58	1.1	0.9	36	-	-
6 Low-E – 16 – 4 clear– 16 – 4 Low-E	73	14	-	28	28	52	0.7	0.6	36	-	-
6 four season– 16 – 4 clear– 16 – 4 clear	56	25	-	29	37	37	1.0	0.8	36	-	-
6 four season– 16 – 4 clear– 16 – 4 Low-E	55	23	-	33	37	35	0.7	0.5	36	-	-
6 clear– 16 – 4 clear– 16 – 6 clear	75	20	-	17	18	71	1.8	1.7	37	-	-
6 clear– 16 – 4 clear– 16 – 6 Low-E	74	17	-	23	27	58	1.1	0.9	37	-	-
6 Low-E – 16 – 4 clear– 16 – 6 Low-E	73	14	-	28	28	52	0.7	0.6	37	-	-
6 four season– 16 – 4 clear– 16 – 6 clear	56	25	-	30	37	37	1.0	0.8	37	-	-
6 four season– 16 – 4 clear– 16 – 6 Low-E	54	23	-	33	37	35	0.7	0.5	37	-	-
6 Cool Lite SKN176 – 16 – 6 clear	70	13	-	28	37	37	1.3	1.0	33	-	-
6 Cool Lite SKN176 – 16 – 4 clear– 4 Low-E	63	15	-	31	38	35	0.7	0.5	36	-	-
4 clear– 16 – 4.4.1 clear laminated	81	15	-	17	13	77	2.7	2.6	35	-	-
4 clear– 16 – 4.4.2 clear laminated	81	15	-	19	13	77	2.7	2.6	37	-	-
4 four season– 16 – 4.4.1 clear laminated	60	22	-	27	38	39	1.3	1.0	35	-	-
4 four season– 16 – 4.4.2 clear laminated	60	22	-	27	38	39	1.3	1.0	37	-	-
4.4.1 clear laminated– 16 – 4 Low-E	80	11	-	25	22	59	1.3	1.1	35	-	-
4.4.2 clear laminated– 16 – 4 Low-E	80	11	-	27	21	59	1.3	1.1	37	-	-
4 clear– 16 – 4.4.1 Low-E laminated	80	11	-	20	27	64	1.3	1.1	35	-	-
4 clear– 16 – 4.4.2 Low-E laminated	80	11	-	21	27	64	1.3	1.1	37	-	-
6 clear– 16 – 4.4.1 Low-E laminated	80	11	-	23	26	63	1.3	1.1	38	-	-
6 clear– 16 – 4.4.2 Low-E laminated	80	11	-	23	26	63	1.3	1.1	39	-	-

USEFUL INFORMATION: DOES OPTIMAL GLAZING STRUCTURE EXISTS?

Risk of breakage after installation and prevention methods:

IMPORTANT INFORMATION: DESIGN INSTRUCTIONS, MANUFACTURING, SAFETY, DURABILITY, STORAGE,INSTALLATION AND EXPLOITATION OF INSULATING GLASS.

IMPORTANT INFORMATION: REASONS AND CHARACTERISTICS OF GLASS BREAKAGE.

Type of breakage	Reason	Prevention
	Точков удар с остър предмет или твърд предмет, попаднал между стъклата.	Добра сепарация и по-внимателно складиране и манипулиране на стъклата.
	Точков удар с остър предмет или твърд предмет, попаднал между стъклата при температурно заздравено стъкло.	Добра сепарация и по-внимателно складиране и манипулиране на стъклата.
	Прекомерно механично натоварване на стъклото (силен вятър, подпиране с тяло или друг тежък предмет) при стъклопакет, който вече е термично натоварен (загрят от слънцето).	Обработка на ръба на стъклата. Закаляване на външното стъкло.
	Счупване поради термично натоварване.	Избор на стъкла с по-ниска абсорбция на енергия. Обработка на ръба на стъклата. Закаляване на външното стъкло.
	Продължително неравномерно механично натоварване.	Обработка на ръба на стъклата. Закаляване на стъклата.
	Твърде голямо напрежение от температурно разширение на газа в стъклопакета поради разлика в температурата на производство и инсталация или надморска височина.	Обработка на ръба на стъклата. Закаляване на стъклата.
	Счупване поради осукване на стъклото или допир в твърд предмет поради разместване на конструкцията или температурно разширение.	Премахване на конфликтни точки с твърди предмети. Увеличаване на дебелината на стъклата. Обработка на ръба на стъклата. Закаляване на стъклата.
	Счупване поради точково механично натоварване, причинено от твърде голяма тежест на стъклата и неправилно манипулиране.	Правилен подбор на дебелина на стъклата и правилно манипулиране със стъклата.
	Счупване поради точков удар в ръба, най-често от удар или грешката при монтаж.	Правилно боравене със стъклата.
	Счупване поради натоварване на ръба на стъклата или престягане при укрепване.	Правилно боравене и укрепване на стъклата.
	Счупване поради разлика в температурата на центъра и периметъра на стъклото.	Обработка на ръба на стъклата. Закаляване на стъклата.
	Засенчване отвън или наличието на обемисти предмети в непосредствена близост до стъклената повърхност отвътре. Външни условия за такива счупвания създават: козирки, дървета, сгради или други обекти причиняващи частично засенчване на стъклените повърхности. Вътрешни фактори могат да бъдат: мебели, части от строителната конструкция, щори и др. разположени в непосредствена близост до стъклената повърхност възпрепятстващи добрата вентилация и охлаждане.	При възможност да се махне причината, която създава засенчването (скеле, мебел, рекламни материали). Избор на стъкла с по-ниска абсорбция на енергия. Обработка на ръба на стъклата. Закаляване на външното стъкло.

VIDEO: Risk from breakage due to thermal stress. Source: glassed.vitroglazings.com

Size of the IG units and recommended thickness of the glass and spacers:
(all dimensions are in millimeters)

Glass thickness monolithic/laminated	Max width not tempered/tempered*	Max height not tempered/tempered*	Min. spacer width	Max size when square not tempered/tempered*	Max sides ratio
4 / 3.3.1 / 3.3.2	2200 / 2800	1300 / 1800	8 up to 2 m² 10 up to 3 m² 12 up to 4 m² 14 up to 5 m² 16 over 5 m²	1300 / 1800	1:4
5 / 4.4.1 / 4.4.2	2800 / 3400	1700 / 2400		1300 / 2000	1:6
6 / 5.5.1 / 5.5.2	3500 / 4000	2000 / 2400 **		2000 / 2400	1:8
8 / 6.6.1 / 6.6.2	4000 / 4800	2500 / 2400 **		2500 / 2400 **	1:10
10 / 8.8.1 / 8.8.2	4500 / 4800 **	2700 / 2400 **		2700 / 2400 **	1:10
12	5000 / 4800 **	2700 / 2400 **		2700 / 2400 **	1:10

^* - tempered ot heat strengthened monolithic glass

^** - limited by the maximum temperening dimensions