SOLAR CONTROL GLASS

Sun equals radiation. Depending on its altitude and time of year, the sun can release vast quantities of energy. Thus, for example, the insolation of solar energy on a summer's day around noon on a horizontal surface can amount to approximately 800 W/m2.

Large-area glazing has become the obvious choice in modern buildings, but in the summer months, the unwelcome heating up of rooms can be a problem. Solar control insulating Glass helps here: it lets the daylight through but reduces the amount of incident solar energy.

The g value, the light transmission, and the visual appearance can be influenced by factors such as the coating material, the coating thickness, and the color of the Glass. Despite low energy transmittance, every solar control coating is optimized to maintain high light transmission.

Low-emissivity coated Glass can be used to control longwave infrared radiation.

The benefits of solar control glass

• Reduction in solar energy transmittance
• Adequate protection against unwanted room heating
• Reduction in the cooling and heating energy demand in summer
• In combination with an excellent thermal insulation coating, low energy consumption in winter
• Greater comfort and a pleasant temperature level
• High light transmission, for optimum utilization of natural daylight
• Depending on the architecture, neutral or colorfully brilliant appearance
• Combinable with solar control and safety functions

To temper or not to temper?

Solar control glass absorbs more heat than regular float glass or thermal insulation glass. Partial shading can cause the pane surface to heat up to different degrees. If the temperature difference is too significant, the pane will fracture. Thermal tempering is used to increase the temperature change resistance to such an extent as to virtually rule out the risk of breakage due to thermal influences. The radiation absorptance can be used as a guideline for whether thermal tempering of the coated pane is necessary or not. If it is more than 50 %, tempering is usually required.

Solar Control Glass

Performance

KEY PERFORMANCE FACTORS

Light transmission/light transmittance (LT)

The light transmittance of glazing denotes the percentage of solar radiation in the visible light range (380 – 780 nm) transmitted from the outside to the inside.

Light absorption/light absorptance (LA)

The light absorptance denotes the proportion of solar radiation in the visible range (380 – 780 nm) absorbed by the glazing. Light absorption is a less common characteristic quantity.

Light reflection/light reflectance (LR)

The light reflectance denotes the percentage of solar radiation in the visible light range (380 – 780 nm), which is reflected outwards.

Total energy and Glass

Radiation transmission/radiation transmittance (RT)

The radiation transmittance, also known as energy transmittance, denotes the proportion of radiation in the total solar spectrum allowed to pass through by the glazing.

Radiation absorption/radiation absorptance (RA)

The radiation absorptance, or energy absorptance, denotes the proportion of radiation in the entire solar spectrum absorbed by the glazing.

Radiation reflection/radiation reflectance (RR)

The radiation reflectance, or energy reflectance, of glazing, denotes the proportion of radiation in the total solar spectrum that is reflected directly outwards by the glazing.

Total energy transmission/ total energy transmittance (g value)

The total energy transmittance is an essential characteristic quantity for glazing, aside from the U value. It indicates how much of the outer-impinging solar energy ultimately passes into the room interior. For optimum passive solar energy utilization, the g value should be as high as possible, and for optimum solar control effect, as low as possible.

Shading coefficient

The shading coefficient is a characteristic quantity derived from the g value, with two different derivations: traditional Shading coefficient = g value: 0.80 (standard in Germany) and Shading coefficient = g value: 0.87 (expected in the UK and the USA). The purpose of the shading coefficient is to compare the shading effect of glazing with the shading effect of conventional uncoated double insulation glazing (g value = 0.80) or of single glazing with 6 mm thick float glass (g value = 0.87). Relevant directives and guidelines for calculating cooling loads frequently require not the g value but the shading coefficient. To avoid misunderstandings, it is advisable in each case when specifying shading coefficients to define the basis for calculation exactly!

General color rendering index (Ra)

The general color rendering index measures the change in the light (or its influence on the rendering of colors, where eight different standardized shades are assessed) by a piece of glazing.

The higher the color rendering index, the fewer colors the glazing alters. A rendering index of 95 – 100 means minor color changes, while an index of 90 – 95 means minor color changes. The color rendering index can be an essential decision-making criterion, particularly in the case of museums, galleries, and craft and industrial activities where colors play a significant role.

The higher this value, the less the color is altered when looking through the glazing.

The U value

The heat transfer coefficient (U value) is the unit of measure for determining the heat loss of a component. The U value specifies the amount of heat that passes per unit of time through 1 m2 of an element with a temperature difference of 1 K. The lower the U value, the lower the heat losses to the outside and the lower the energy consumption.

The U value (according to the test standard EN 673 Ug) is probably an essential characteristic of insulating Glass. The Ug value can be determined using certified calculation methods for each insulating glass structure. The Ug value applies to the so-called undisturbed area, i.e., without the influence of the edge area (in which the heat flow is much greater). The edge seal is, therefore, of no importance to the Ug value. Only when the U value has been determined for the whole window (glass incl. window frame) does the Uw value (w = window) have a bearing.

Energy or heat transfer inside the insulating Glass occurs in three ways: through the individual glass panes and the gas or air fillings in the cavities. Convection is through the flow of the gas or air fillings in the cavities. Radiation, through the glass surface's heat radiation (longwave infrared radiation). Heat radiation makes up the most significant share (approx. 2/3) of the heat loss.

Areas of application for DOUBLE OR TRIPLE SILVER COATINGS

• Wherever reasonable solar control, together with plenty of daylight, is wanted.
• For new buildings and renovations
• For residential, office, and public buildings.
• For commercial and industrial buildings.
• In large-area glass facades.

Storage of coated insulating Glass

The insulating Glass should never be exposed to direct sunlight or partial shading, particularly in the summer months. This makes it highly prone to thermal fracture.