Double Glazed Windows - Coursework Example

DOUBLE GLAZED WINDOWS COLLEGE PRESENTED TO Double Glazed Windows There is a growing trend where developers and consumers have becomemore sensitive regarding environmental issues around homes and other built environments. Sustainability in built environments usually requires that buildings attain energy efficiency continuously while at the same time reducing emission of pollutants to the environment. Sustainability is best achieved by emphasizing more on the use of natural forms of energy such as the solar energy instead of the conventional energy forms. The result is that buildings are fitted with high-quality systems that ensure efficiency and sustainability in the long term leading to the green building concept that has lately received much attention from consumers, developers and policy makers. Window glazing is one of the approaches to attain sustainability in built environments and especially in homes. Windows are essential as they allow lighting and fresh air in addition to facilitating a connection between the interior and outdoor environments. All the same, during summers, windows may lead to accumulation of heat in buildings, which increases room temperatures, or which may lead to heat loss in winters. Loss of heat during winters would require use of grid power, which increases costs and environmental pollution. As such, there is a need to develop energy efficient windows that facilitate comfort, reduce energy costs while still facilitating a cleaner and healthier environment around homes. Research has indicated that windows may lead to a loss of about 40% of heating energy during writers and a heat gain of about 87% during summers (Lyons & Hockings, 2013). Therefore, there is a need to enhance windows’ thermal performance in buildings to reduce energy costs and reduce greenhouse gases emitted by conventional energy forms besides having the windows perform their required roles in the best way possible. One of the versatile ways to ensure and improve thermal performance of windows is through double glazing of windows. Product Description Fig 1. A glazed window (Source: Lyons & Hockings, 2013) Glass is a product of silica, a component of sand among other components. Normal glass is applied in a variety of uses, which may include making of doors, windows, bottles, vision glass among other uses. When such glass is used for windows or doors, the thermal efficiency of the glass is not optimum as temperatures may rise or fall concerning the external weather conditions. Double glazing is a concept used to correct this inefficiency by ensuring glass windows perform efficiently. As such, double glazing is a concept used to prevent any energy loss while at the same time preventing the accumulation of heat in a house especially in summers. The concept of regulating temperatures at home is achieved through controlled energy transfer, mainly through windows and doors. Consequently, ensuring the efficiency of the windows and doors would lead to normalization of room temperatures away from the external temperatures. Considering that most parts of windows and doors are covered with glass, there is a need to ensure the glass does not transmit energy in preventing excessive heat loss or heat gains in buildings. The figure below shows how a double glazed glass works when illuminated by direct sunlight especially during the day. (Source: Lyons & Hockings, 2013) As seen from the figure above, in double glazing, a window consists of two sheets of glass, with a cavity in between the sheets, which is usually filled with an inert gas, commonly argon. In most cases, the glass sheets are 4mm thick and the gas cavity 16mm to 24mm wide (Lyons & Hockings, 2013). Inert gasses are preferred in double glazing considering their low thermal conductivity, which makes it possible to maintain room temperatures without any heat loss or gain. To ensure efficiency, the glass unit has to be sealed at the ends in ensuring the entire set up is air tight to prevent any loss of the inert gas or heat from the cavity. To achieve best results in double glazing, there is a need to consider a number of factors, all which have a direct bearing on the success of glazing and heat control in houses. One of the important aspects to consider is the type of glass used in the double glazed window. The best energy efficient glass to use in double glazing is the low emissivity, Low-E glass (Hafemeister, 2007). The glass contains a thin invisible layer of metal oxide on either side of the internal window panes. The thin oxide coating facilitates light to pass through while at the same time reducing cases of heat escaping from the room through the window. Glasses with high emissivity levels allow exchange of heat between the interior and exterior environments, which may lead to an increase or decrease in the room temperature levels. This may not achieve the required goal of ensuring energy efficiency in rooms. In addition, the space between the two glasses in double glazing plays an important role in ensuring the efficiency of glazed windows. The amount of inert gas used between the two sheets of glasses greatly determines the success of glazing; a thin gas film may have a higher emissivity compared to a larger gas film (Lyons & Hockings, 2013). Moreover, panel spacers are also important elements in designing the effectiveness of glazed window panels. Spacers are usually located around the edges of panels and are used to keep the two panels apart in creating the gas cavity. To ensure efficiency in double glazing, there is a need to use spacers with little or no metal elements (Historic Scotland, 2010). Metals have much higher emissivity rates compared to gasses. Consequently, the use of metals as spacers might lead to increased emissions of heat between the two planes, which may affect the effectiveness of the double glazed window. During the construction of double glazed windows, it is important to stress on the materials making the window, which would affect the efficiency of the window. For instance, windows made of PVC frames tend to last longer, and the frames are recycled at the end of the life cycle of the window compared to other frames. As such, PVC frames may offer better efficiency when used in double glazed windows compared to other forms of material frames (Center for Sustainable Energy, 2013). Wooden frames in making double glazed windows offer much lower environmental impact though wooden frames would require constant maintenance, which may be an added cost (Lyons & Hockings, 2013). As such, wooden frames are usually applied in areas that require conservation and especially in repairs where the original windows were made of timber frames. Another versatile material suitable for making double glazing windows is the aluminum or steel frames. These are slimmer and long-lasting frames, which may be recycled after the service life of the window. Therefore, this frame ensures sustainability and versatility when constructing double glazed windows. Lastly, composite frames in window glazing offer better versatility concerning application in different weather conditions. Composite frames are made of a thin timber frame covered with plastic or aluminum coating. The fact that the frame is waterproof reduces the need to maintain such windows, which ensures sustainability, efficiency and better performance at lower costs. Manufacturing of double glazed windows There are wide varieties of glazing glasses in the market. Consequently, there are a number of critical factors to consider in ensuring the success of window glazing and attaining sustainability. Importantly, there exist different products in the market, all which solve a specific need. For instance, some glazing glass may be manufactured to control daytime lighting, to ensure security or to control noise pollution (Dalal, Naylor & Roeleveld, 2009). As such, there is a need to select the right materials that offer the right utility as required. Consequently, different types of glasses offer varying properties that determine the quality of the end product. For instance, using glazed windows to reduce the amount of sunlight or solar radiation of light in homes especially during days may affect the amount of daylight that enters a building. In other words, the amount of light transmitted into the building through glazing depends on the rate of visible light transmittance (VLT) (Lyons and Hockings, 2013) of the window. This would imply that having a material for double glazing with low light transmittance would lead to dark rooms, which would necessitate lighting of the house even during the day time. Such daytime lighting may translate to higher costs of energy and more pollution as the demand for conventional energy would increase. Such a factor would suggest that any glass used has to have a high light transmittance value to ensure the efficiency of glazing is achieved. Consequently, there are a number of glass types available for glazing, with each glass type offering different results during the glazing process. Toned glass. In some cases, during the glass manufacturing process, manufacturers do add some colors to the glazing glass. The result is that different colors offer different solar heat gain coefficients (SHGC) and visible transmittance of the window, VLT (Hafemeister, 2007). However, this color does not affect the conductivity of the glass. However, heavy toning of the glazing glass with colors may only allow in the room visible wavelengths while blocking any near –infrared wavelengths. This result would be lowered solar heat gain coefficient while maintaining the visible transmittance of the window (Lyons and Hockings, 2013). As such, the double glazed windows do maintain room temperatures as much as possible while allowing clear visibility considering the transmittance of the window is not affected. Another class of glass used in double window glazing is the low emissivity glass or Low-E glass. The low-E or the high transmission glass contains a coating that facilitates the passage of sun’s daylight into the house while at the same time limiting the infra-red heat that may escape through the windows (Lyons and Hockings, 2013). On the other hand, the Low-E glass contains a special coating that limits the amount of solar heat while ensuring better levels of visible light transmission. As such, Low-E coated glass makes it possible to have glass walls in living rooms. Another commonly used type of glass in double glazing is the laminated glass. A laminated glass contains a plastic layer that offers the glass improved impact resistance. The lamination ensures the glass does not break to form shreds that may endanger users (Center for Sustainable Energy, 2013). Consequently, these types of glasses are applicable in bathrooms, doors, staircase ways and in other areas that have a high likelihood of human impact Essentially effective double glazing requires the following tips in manufacturing of the windows in addition to their maintenance to achieve the best results and enhance efficiency. One, the frame of the window has to be thermally broken or have to be made from PVC, wood or any other suitable insulating material. Ideally, insulation materials have a lower likelihood of attracting condensation and tend to lose much less heat compared to windows made of aluminum frames (Lyons and Hockings, 2013). The limiting factor with aluminum frame is that they tend to attract condensation especially during winters, a problem common even with double glazed windows. Statistics indicate that PVC or wooden frames may reduce heat by about 40% compared to thermally broken aluminum, which has an efficiency of about 20% (Center for Sustainable Energy, 2013). Therefore, the best insulation materials tend to offer the best results in manufacturing of double glazed windows compared to the use of aluminum. Table 1. Comparing performance of different glazed windows Window type Uw SHGCw TVw Single glazed aluminum window 3mm clear glass 6.9 0.77 0.80 PVC/ Timber single glazed window 3mm clear glass 5.5 0.69 0.72 Double glazed Aluminum window 3mm clear glass 6mm air gap, 3mm glass 4.2 0.69 0.72 Double glazed PVC/timber window 3mm clear glass 6mm air gap, 3mm glass 3.0 0.61 0.65 (Source: Lyons and Hockings, 2013) Where Uw- amount of heat through a glazed window SHGCw- solar heat gain coefficient TVw- visible transmittance of the glazed window As the table above indicates, a double glazed window using PVC or timbers, which have lower conductivity offers the efficiency levels in buildings. Though the window has relatively lower visible transmittance compared to the other options, the window performs better in all other aspects compared to the other windows. For instance, the window reduces any gain or loss of heat from the room, maintaining room temperatures as constant as possible despite external weather, as indicated by Uw. In addition, the window limits the possibility of heat from the sun directly passing to the room as indicated by SHGCw. As such, a double glazed window using timber or PVC frames offers the best option for maintaining room temperatures when used in buildings. Another critical factor to consider in the manufacturing of double glazed windows is that glasses that offer the lowest emissivity offer the best efficiency in the use of these windows. Low-emissivity glass tends to pass light and heat into the room but prevents heat from escaping from the room, thereby achieving and maintaining better room temperatures especially during winters. A Low-E glass may reduce heat loss from rooms by an efficiency of 20% to 30% compared to a double glazed window that does not apply the low-E materials (Lyons and Hockings, 2013). In addition, there is a need to stress the use of a good number of seals that keep away moisture, noise, and drafts. This also requires proper sealing of the joints between the glazed glass and the frame. Again, proper sealing requires the use of spacers with low emissivity, which might imply that spacers made of steel or plastic would perform much better compared to those made of aluminum while separating the glass panes. The former are better in preventing heat loss and preventing cases of condensation compared to the use of aluminum spacers (Dalal, Naylor & Roeleveld, 2009). Compared to the use of air in the cavity between the glass layers in double glazing, inert gasses perform much better due to their superior insulation capabilities. Inert gasses have the ability to reduce heat loss by 3% to 9% better compared to the use of air, which makes inert gasses more preferable in double glazing compared the use of air. Currently, building regulations in England and Wales require new windows to meet certain standards with respect to sustainability and efficiency. Any new window in England and Wales must have a Windows Energy Rating (WER), and a band to indicate this rating with a U-value of 1.6 in Scotland, England and wales. In Northern Ireland, any new window has at least to have a WER band E or a U value 2.0 or either a center plane of U value 1.2 (Lyons and Hockings, 2013). People living in conservation areas rated ‘article four’ or those living in listed buildings have to do with additional regulations in addition to the WER rating. In this case, article four limits any rights of the tenant from making any alteration or development to the building before replacing such windows where a need may arise. Benefits of Double Glazing Windows All the same, there are a number of benefits that developers, tenants, and other related parties may derive from the use of double glazed windows in homes. The major benefit accrued with the use of these windows is lowered energy bills per year. A building fitted with efficient double glazing windows could save about 135 pounds annually in terms of energy bills (Lyons and Hockings, 2013). The amount is a great saving not only in terms of money but also in reducing pollution from conventional energy sources. In other words, efficient use of double glazed windows leads to reduced carbon footprint, a major concern contributing to global warming. Double glazing is not only energy efficient but also leads to sustainability in achieving green. Efficient double glazed windows make homes more comfortable by reducing the heat lost through windows while at the same time reducing draughts in homes. As such, the windows do regulate room temperatures to facilitate comfort in homes notwithstanding the type of weather. In addition to maintaining favorable room temperatures, double glazed windows have an added advantage of filtering external noise, making homes peaceful and quiet for relaxation. Double glazed windows also do reduce the condensation that accumulates on the inside of windows at homes. Therefore, there are major benefits of designing and installing double glazed windows in homes besides the control of room temperatures in extreme weather conditions. Essentially, the lifetime of a double glazed window is about 20 years. The gas inside the glass planes cavity usually evaporates at the rate of 0.5 to 1% annually, making the thermal performance of the windows to weaken considerably when 25% of the gas has evaporated (Center for Sustainable Energy, 2013). In such cases, there is a need to replace the window or better undertake a secondary glazing operation to ensure efficiency of the glazed windows. In summarizing, as the cost of energy increases and as people are sensitized to live sustainably, double window glazing has emerged one of the best ways to meet this end. Double glazed windows are highly energy-efficient; they minimize noise besides permitting light through in connecting the inside with the outside of the room. The windows ability to control and maintain room temperatures makes it ideal especially for extreme weather conditions in summers and winters. As a result, in choosing double glazed windows, there is a need to consider the space between the glass panels for optimal thermal performance and ensure the use of inert gas such as argon in the cavity, which have low conductivity coefficients. In addition, there is a need to ensure the window is made of Low-E glass, which performs excellently in reducing the amount of heat escaping from a room. However, double glazed windows, due to the above inherent features do cost relatively longer than single glazed or normal windows, though the windows have a high cost-benefit advantage. List of References Center for Sustainable Energy. 2013. Energy Efficient Glazing. Available at http://www.cse.org.uk/advice/advice-and-support/energy-efficient-glazing-double-glazing [Accessed 5 March 2015]. Dalal, R., Naylor, D & Roeleveld, D. 2009. A CFD study of convection in a double glazed window with an enclosed pleated blind. Energy and Buildings, 41 1256–1262 Hafemeister , D. 2007. Physics of Societal Issues: Calculations on National Security, Environment and energy. San Luis, CA: Springer Science. Historic Scotland 2010. Windows managing change in the historic environment. Edinburgh: Longmore House. Lyons P. & Hockings B. 2013. Your Home: Australia’s guide to environmentally sustainable homes. Australia government. Available at http://www.yourhome.gov.au/passive-design/glazing [Accessed 5 March 2015]. Read More