Window systems are important part of building facades.
Both functional and aesthetic aspects make windows indispensable parts of the building envelope. It consists of a window system, glass unit, joinery and solar control devices. Window systems are expected to meet many requirements. Window systems are required to have all the necessary features in terms of energy, physical behavior, user comfort needs, construction and usage process behavior. Windows must meet many requirements such as natural lighting, natural ventilation, visual comfort, thermal comfort, security, sound control. In today’s world where important problems such as global warming and climate changes are faced, one of the most important issues that concern us is energy conservation. Due to the fact that 93% of the energy resources we use today are “consumable energy”, it is important to find the most efficient way to use energy resources for heating-cooling in our buildings in terms of creating sustainable environments. At this point, windows play an important role in heat losses in buildings. During the design phase, windows should be designed and selected according to their thermal performance characteristics. It is seen that studies related to heat losses caused by windows are mostly focused on glass because of the area it covers and heat conduction occurs in the most transparent region. However, joinery is another important component affecting the thermal performance of the window system in terms of properties such as material, cross-section, thermal character and size.
In the design process, many factors should be considered when choosing the window type. In this period when energy is very important, the windows preferred in the building should meet the criteria regarding energy, user comfort, construction and usage process in the best way.
When these criteria are examined one by one, the expectations for the window system are;
Thermal control
Solar control
Daylight permeability
Air tightness
Voice control
Water and Humidity Control
Condensation Resistance
Visual Relationship and Privacy
Thermal comfort
Natural ventilation
Security
Aesthetic
Carrier
Lifetime
Maintenance
Sustainability
Low cost
Tempered Glasses
Tempered glasses, which are formed as a result of the rapid temperature change in the glass, are resistant to thermal stresses and impacts. When the glass breaks as a result of any impact, its internal tension causes the glass to break into small, round pieces. With this feature, it is suitable for use in window systems under the pressure of strong winds and severe heating-cooling, and especially in frameless systems. Tempered glasses are twice as durable as non-tempered Laminated Glass.
Laminated glasses are sandwich products formed by bonding clear glasses to each other using a polyvinyl butyral (PVB) interlayer with the help of heat and pressure. Laminated glasses are resistant against impacts. However, in case of breakage, the soft inner layer keeps the parts together and prevents them from falling apart, and human injuries are prevented. The PVB interlayer can be optionally colored or various prints can be created. In outdoor applications, it may be necessary to protect the edges of laminated glass with various insulating materials in order to prevent them from being affected by weather conditions and moisture and split into layers. Even small layer separations will compromise the strength of the glass.
Tinted Glasses
This type of glass has the ability to absorb sunlight in different proportions, depending on its color and thickness. They are used for solar control in the outer shell. Since a significant part of the absorbed radiation in single glass applications is given to the indoor environment, it may create discomfort in the indoor environment. In order to reduce the percentage of solar radiation absorbed by the glass and increase the thermal resistance of the glass, double glass with a gap is generally preferred. Colored glass that absorbs heat is used outside, colorless glass is used inside. Bronze, gray, green and blue tones are mostly preferred. Different colored glasses, heat transmittance value, reflectivity and other physical properties differ. The use of tinted glass reduces the glare caused by clear glass surfaces and the effect of excessive daylight. In other words, the daylight transmittance value (Tvis) decreases with the use of colored glass. The daylight transmission value is listed from highest to lowest for green, blue, bronze and gray colored glasses. Color darkening causes the natural lightening ability to decrease.
Reflective Glasses
Reflective glasses are glass type with high performance in terms of solar control. These coatings, which can be applied to colored or flat glass, are in the form of a thin metallic film layer at micron level. The thermal conductivity value of the coatings, which can be in metallic colors such as silver, gold, bronze, varies according to the thickness, reflectivity and the place where the coating is placed on the glass. Reflective glasses are perceived as a mirror with the effect of outdoor daylight during the day, and become dark but transparent by lighting the interior at night. Because of these features, it is generally preferred in office buildings that are less used at night. While reflective glasses reduce solar heat gain, they also prevent sunlight entry. This leads to the creation of interior spaces that are inadequate in terms of natural light, dark, and where visual comfort conditions cannot be achieved. While the sunlight reflected by buildings with such glasses is beneficial by illuminating dark streets and areas, in some cases it can be harmful due to the heat and glare problem it spreads to neighboring buildings, pedestrians and motorcyclists.
Low Diffusion Glasses (Low-e Coated Glasses)
Heat always moves from the hot surface to the cold surface by radiation on the glass surface. Very thin and transparent Low-e coatings placed on the inner surface of the glass prevent most of the heat transfer. Thus, the total heat flow value in the window system decreases. The most important features of Low-e glasses are that they reflect the long-wavelength heat radiation in the invisible area (infrared) and that they act like clear glass in the visible region and pass sunlight. While these glasses provide heat control thanks to their improved insulation values, the daylight permeability level is high due to their behavior like clear glass. In other words, in hot weather, it saves on cooling costs by bringing in less solar heat without sacrificing light, while in cold weather, it allows the warm air inside to be reflected back inside, maintaining the indoor temperature, reducing heat loss and saving on heating costs. There are three basic types of low-e in use today. The first are hard coated, high translucent low-e glasses. They are typically designed to reduce heat loss and provide solar gain. The second are soft coated types. These coatings allow some solar gain while reducing heat loss. The third type is spectrally selective less permeable coatings, also called solar low-e, which is a soft coating. These coatings are the low-e type that has the ability to reduce heat loss in winter and heat gain in summer. There is a selective permeable glass type suitable for the purpose for all climatic conditions and building types. It can be used in hot climate regions as well as in climatic regions where cold and hot live together.