Double Glazed Windows - Term Paper Example

Environmentally Sustainable Design Name: Course: Instructor: Institution: Date of Submission: Executive Summary Double Glazing is the process of window insulation that helps in energy saving. Double glazed windows are the kind of windows that retain heat when necessary and avoid heat retention depending on the season. Double glazed windows are determined through the materials used to develop them that ensure they perform as expected. The double glazed windows performance is considered high since they can increase the warmth in the internal area of the building. The double glazed windows also improve performance through reducing outside noise to the inner building, and improve energy efficiency. The development of the windows goes through specific considerations that must be adhered such as spacing between the glasses used, the gas used to ensure the airtightness that leads to the improved performance of the double gazed windows. Introduction Double-glazing, is the process where a window undergoes the glazing process, where the windows have two glass panes. The calculations provided below show the need for implementing the right inches and gas between the windows to ensure they perform as required. Double glazed windows are airtight, which guarantee the loss of condensation between the window pane or glasses used. Double glazing is an environmentally suitable design, since it is effective in saving energy and friendly to the environment since they reduce GHG emissions. The effectiveness of the double glazing windows is presented below, which shows the superiority of the windows. The paper will then demonstrate the process of designing and implementing the double glazed windows, and how calculations are used to ensure the effective development of the windows. Effectiveness of Double Glazing Double-glazing is identified as the best window insulation method for saving energy, which can reduce energy consumption in buildings (Urbikain & Sala, 2012). It is a glass with the high capability of saving and retaining heat compared to other glasses such as the single-glazed windows. The windows are efficient for splitting the heat loss through the windows, they improve the thermal comfort of the homes or organizations that have installed them, reduce the external noise and eliminate the condensation that forms during cold weather. Some characteristics of double glazing windows play a significant role in influencing the performance of the windows. For instance, the double glazed windows made from materials such as wood or uPVC do not draw condensation neither can they retain heat. Those with cracked aluminium frames also cut heat retention with about 20% while associated to uPVC, which promotes a heat loss of 40% of the total heat collected. Thus, the thermal frame of the window must not be broken to guarantee a 100% retention of the heat collected, and the material used must be considered. Additionally, the emissivity of the glass is of high importance. The low glass emissivity allows heat and light in then redirects the heat fleeing back to the room. Thus, it warranties that about 20% of the total heat retained is lost. Using multiple coatings of seals is also a process of keeping draughts, noise and moisture out of room. The material used for spacing should be made of plastic or stainless steel, which are effective in minimizing the heat loss (EECA, 2016). The effectiveness of tinting double-glazed windows Figure 1 shows a schematic diagram of a double glazed window. In our analysis of heat flow double glazed windows with an area A m2 we expressed the heat transfer from the outside environment to the interior of a building as 𝑄 /𝐴 = 𝜏1𝜏2𝐼 + ℎ𝑖 (𝑇𝑔,2 – 𝑇𝑖) W/m2 According to the equation above, heat flows directly, through the panes where 𝜏1 represents the transmittance of heat from the outer pane, and 𝜏2 is the transmittance of heat from the inner pane. hi W / (m2.oC) presents the co-efficient of heat transfer from the inner pane to the building. Based on the equation above, the heat transfer process through the double glazed windows is dependent on many factors where one includes the transmittance of heat through the window. The equation presents solar irradiance as 1 W/m2. The temperature from the outer surface of an environment and the interior temperatures have high differences, which leads to the need of the double glazing windows. High thermal resistance is the important factor for the glasses to retain heat dependent on the climate. Heat retention of a double glazed window is determined by the transmitted energy, reflected and absorbed energy as well. The equation presents this process effectively where heat transmission is presented as 𝜏1𝜏2𝐼 while the energy absorbed is presented as ℎ𝑖 (𝑇𝑔,2 – 𝑇𝑖). Therefore, the energy transmission of the window is balanced through retention and energy collected by the window. Therefore, double glazing is effective in offering thermal comfort since its installation must consider the external and internal temperatures to attain the equilibrium temperature for the implementation (Astralian Government, 2016). Designing and Installation of Double-Glazed Windows Windows consist of structural frames, glass panes, sealants and spacers (Barnes & Fulford, 2011). The design of double glazed windows is dependent on the type of glass used, frames, and coatings through efficient fine-tuning of the window. The performance of the window is influenced by many factors such as the gas between the windows, emissivity of the glazing, number of panes used, material used to create the space, and the material of the material (Ander & FAIA, 2014). When designing the windows, specification of the window and the glazing system is important as it influences the efficiency of the window to save energy and provide comfort to those using them. Designing the double-glazed is highly dependent on the problem or need one has to solve. Some of the characteristics the designers consider is whether the design of the window is to handle the problem of heat loss or gain. Other factors to consider include the visual requirements such as the windows should ensure privacy of the owner is protected view and glare. Shading and sun control should also be considered including thermal comfort, controlling the condensation, ultra violet and acoustic control, color effects, daylighting and other energy requirements. Designing the Windows First, one specifies characteristics such as the U-Value of the window, the solar heat co-efficient of gaining heat and other shading co-efficient. The transmittance of the window must also be specified. Based on the equation above, the efficiency of the window was achieved with an indication of the coefficients and transmittances. The equation also presents that the designer may specify the color of tinting or coatings if needed. The U-value throughout the design stipulates the flow of heat over either radiation, conduction or convention based on temperature differences in the outside and inside environments. The equation provided above gives the transmittances of both inside and outside of the environment, the window is to be installed. On the stipulation the u-value used is high, the higher the transference of heat leading to a high heat loss during winter. When using aluminum materials for the frame of the windows, the u-factors may range from a 1.3 Bitus/hr/ft2.of, which is high for a single- glazed window, and consequently, low for a double glazed window. The coefficient of the solar heat, demonstrates the energy of the sun that strikes the window is transmitted to the window in form of heat. With an increase in the gain of solar heat coefficient, the heat retention through a window grows. The ratio of the solar coefficients ranges from 0-1 where 0 stipulates that none of the heat striking the window is retained as heat while 1 means all the energy of the sun striking the window is retained as heat. Thus, with a 0.5 coefficient, half of all energy striking the window from the sun is retained into the window. However, in the designing process, windows that have a high air conditioning loads, low coefficients are preferred. The shading coefficient is perceived as the ratio of heat gain through any given glazing when likened to a clear window of 1/8 inches of the pane. The transmittance in the equation was provided for both the outside and inside environments surrounding the window. The importance of these transmittances is that they provide the visible solar spectrum transmitted through a glass from inside or outside of the window. It is important to consider factors such as fritting, gas fills, switchable optics, and retrofit films. Fritting during the designing of the window considers the coatings of the window materials. They may derive from frits or ceramics. Gas fills refers to the gases injected between glass panes that assist in reducing the convective and conductive processes of heat transfer. Switchable optics refer to the glazing’s that alter optical properties by using temperature, light or voltages. Thus, when used in double-glazing, they assist to ensure the widows retain more heat. Practical Design of the Double Glazed Windows To design the windows, the above specifications and requirements must be considered. You need to have to glass panes equal sizes in all dimensions with a minor gap between them. The space between the glass panes is then filled with gas. However, the designer must choose the glass panes for double-glazing with the lowest emissivity also identified as the low-e glass. The glass with a low emissivity has an unseen metallic layer of different benefits. Some low emissivity glasses have a high solar gain, which can be highly beneficial in areas where the summers are cold, or winters. The window with a high solar gain help reduce heat loss and increase the heat retention providing comfort to the users of the panes. Others with low moderate solar gain assist in protecting interiors of building from the ultraviolet rays. Those with a low solar gain offer an improved protection from the ultraviolet rays. The gas space is important for blocking the heat transfer from the window to the environment. Argon is the gas used primarily because of it is denser than air. The panes should be completely sealed to perform as expected. Thus, the materials used for the sealing should be strong and withstand any weather since they will be exposed to high temperatures of direct heat from the sun among other weathers (Wang & Wang, 2014). The frame requires materials such as aluminum among others, which must be compatible with the sealant material used. These considerations are important since they help avoiding bridges in the entire window installation that may affect the transfer of heat from the glass to the environment. The materials used such as spacers, frames, sealants and gas are the materials that determine the heat bridge is avoided during the installation process. Installation of Double-Glazing Windows During the first stage of installation, one must consider the sealant material to be used, to determine the material of the frame. Installing the double glazed windows is expensive, and costly to maintain. The installation begins with the development of a risk assessment to ensure the protective equipment needed by the installers are available as well as to ensure the equipment in the buildings do not get damaged. Let us assume the window is using either timber or aluminum material for the frames (FENSA, 2014). To install the windows, they get fixed to the appropriate space using screws, or any other option that seems best. The fixing brackets are provided using the angle grinders. The dimensions of the windows during the installing should be secured as follows depending on the frame material. However, the dimensions are dependent on the size of the window been installed. The installation packers of the fixing positions of the windows should be used to prevent the frame distortion. Thus, the materials used shoud be resistant to corrosion, rotting and compression as well. When finishing, the trims help to neaten the area between the window for improved view. The position of the frame should be positioned in a space where it reduces the amount of poor performance of the window It ensures that the after the installation, it operates effectively while bridging the DPC. Calculating the temperature of the inner pane of glass Calculating the energy performance of a window, the characteristics of the window as environmental variables must be considered. The design of the window is important in ensuring conservation of energy, which is attained by calculating the heat transfers through the window, including the inner pane. To calculate the temperature of the inner pane of a glass the formula below is used. Tg2 represents the temperature of the inner pane of the glass a1= - alpha1*I-ho*To; b1= ho + k/d; c1= - k/d; a2= - alpha2*I*tau1-hi*Ti; b2 = - k/d; c2= hi + k/d; Tg2 = (a2 / b2 – a1 / b1) / (c1 / b1 – c2 / b2) Tg2 = The temperature of the inner pane of the glass Where: alpha1 = the absorption of the outer pane of the glass I = the intensity of solar radiation striking the window ho = the external heat transfer coefficient To = temperature of external environment k = Thermal conductivity of gas in inter-pane cavity d = Thickness of inter-pane cavity alpha2 = Absorption of inner pane tau1 =Transmittance of outer pane hi= the internal heat transfer coefficient Ti = is the temperature of the internal environment. Therefore, the temperature of the inner glass pane of a window is calculated by first attaining some characteristics of the window, and the internal and external environments. For instance, to get the temperature of the inner pane of the glass one must have the absorption rate of the outer and inner panes of the glass. The external and internal temperatures of the environment, internal and external heat coefficients are also used. The intensity of the sun energy that strikes the window must be used. The transmittance of the outer and inner panes of the glass, include the thickness and thermal conductivity of the inner pane cavity as provided above. Heat Flow through Double Glazed Window Calculating temperature of inner pane of glass a1= - alpha1*I-ho*To; a1 = - 0.04 * 810 – 17 * 39 a1 = - 32.4 – 663 a1 = - 695.4 b1= ho + k/d; b1 = 17 + 0.024 / 0.01 b1 =17 + 2.4 b1 = 19.4 c1= - k/d; c1 = - 0.024 / 0.01 c1 = - 2.4 a2= - alpha2*I*tau1-hi*Ti; a2 = - 0.04 * 810 * 0.87 – 6 * 21 a2 = - 28.19 – 126 a2 = - 154.9 b2 = - k/d; b2 = - 0.024 / 0.01 b2 = -2.4 c2= hi + k/d; c2 = 6 + 0.024 / 0.01 c2 = 6 + 2.4 c2 = 8.4 Thus, the temperature of the inner pane of the glass Tg2 = (a2 / b2 – a1 / b1) / (c1 / b1 – c2 / b2) Tg2 = (-154.9 / - 2.4 - -695.4 / 19.4) – (-2.4 / 19.4 – 8.4 / -2.4) Tg2 = (64.5417 - - 35.8454) – (- 0.1237 - -3.5) Tg2 = 100.3871 – 3.6237 Tg2 = 96.7634 Heat flow through the double glazed window – W/m^2 Qbya = tau1 * tau2 * I + hi (Tg2 –Ti) = 0.87 * 0.87 * 810 + 6 (96.7634 – 21) = 0.87 * 0.87 * 810 + 6 (75.7634) = 0.87 * 0.87 * 810 + 454.5804 = 613.089 + 454.5804 Qbya = 1,067.6694 Overall heat transfer co-efficient U = 1 / (1 / ho + 1 / hi + d / k) U = 810 / (810 / 17 + 810 / 6 + 0.01 / 0.024) U = 810 / (47.6470 + 135 + 0.4167) U = 810 / 183.0637 U = 4.4247 Heat Flow through the glazing – W/m^2 – Calculated using the equation Qbya_neat = tau1 * tau2 * 1 + U * (To – Ti) + U * (alpha1 + alpha 2 * tau1) ho + (d / k) * alpha2 * tau1) * 1 Qbya_neat = 0.87 * 0.87 * 810 + 4.4247 * (39 – 21) + 4.4247 * (0.04 + 0.04 * 0.87) 17 + (0.01 / 0.024) * 0.04 * 0.87) * 810 Qbya_neat = 0.87 * 0.87 * 810 + 4.4247 * 18 + 4.4247 * 7.3916 + 0.4167) * 0.04 * 0.87) * 810 Qbya_neat = (0.87 * 0.87 * 810) + (4.4247 * 18) + (4.4247 * 7.3916) + 11.745 Qbya_neat = 613.089 + 79.6446 + 32.7056 + 11.745 Qbya_neat = 737.1842 Heat Flow through the double Glazed window Q = A * Qbya Q = 4.0 * 1,067.6694 Q = 4.270.6776 Double-Glazing During the Night The performance of the window during the night is dependent on the heat retained during the day. The double glazing window helps in ensuring heat loss is managed by saving energy. During the night, there is no sunlight for heat flow through the building. Heat flow is the process of double glazing during the night where heat is transmitted to the interior of the building at a certain rate. Thus, the double glazing window during a cold season ensures the interior building is warm, which reduces the need for other energy techniques to guarantee energy efficiency. In other areas, the windows also ensure that draught is managed, since the heat striking the window to the interior of the building is managed. That is; it reduces condensation by increasing the efficiency of energy through the build-up of energy inside the windows. Argon gas is the gas used in the space between the glasses, among others such as sulphur. The benefit of using the gas is that it creates the barrier between the windows, which effectively assists in creating a barrier that blocks heat from getting back to the environment. Double glazing windows are the most efficient windows that promote environmental sustainability. Though the installation of these windows is expensive since the cost of windows (double glazed windows) is high, including the cost of maintaining and replacing the windows. Investing in energy efficient windows will support environmental sustainability through reducing the bills that organizations, building have since the double glazed windows promote solar cooling, and heating. The double glazed windows have numerous benefits to their users such as reducing solar heat gain, and loss depending on the external climate of the user. In areas where the users have a cold seasons, the glasses help retain heat, while in areas where there is a hot climates, the windows effectively reduce the heat retention process. The windows also block the UV lights among others as provided above. Once the windows are installed, they have a long life cycle of about 40 years, showing the maintenance costs are low. However, when they are cracked inside or the sealants are not compatible with the frame materials, they have complications such as not performing as expected, and replacing the windows is expensive among other challenges of the models of the double glazed windows missing in the market among other benefits. Double glazing windows are beneficial since they are effective in energy efficiency through the sunshine, wind, humidity, and temperature of the environment. The designer must consider the need of the user by considering the external climate conditions in the user’s environment, design of the building, materials used in the building and other factors that determine effective performance of the windows among other glazing systems thermal properties. It cuts the heat loss of buildings by half or more depending on the design of the window installed. Environmentally, it supports sustainability since it may be used in handling the current climate change issue, which are influenced by energy consumption. Conclusion Double-glazing is expensive to install but worth the cost due to the benefits, it offers the users and the environmental benefit attained. The process of double glazing is beneficial as a sustainable design since the energy retained by the windows can be used for cooling, heating and lighting, which increases the appearance of the indoor environment where the windows are used. As presented above, the right calculations for every part are important since they help by increasing the performance of the windows. This technology has increased energy saving, which in turn makes it an environmental suitable design. References Ander, D. G. & FAIA, 2014. Windows and Glazing: WBDG. National Institute of Building Sciences. [Online] Available at: https://www.wbdg.org/resources/windows.php [Accessed 22 10 2016]. Astralian Government, 2016. Glazing. [Online] Available at: http://www.yourhome.gov.au/passive-design/glazing [Accessed 21 10 2016]. Barnes, B. & Fulford, R. G., 2011. Mathematical Modelling with Case Studies: A Differential Equations Approach using Maple and MATLAB, Second Edition. 2 ed. New York: CRC Press. EECA, 2016. EECA Energywise; THE POWER TO CHOOSE. [Online] Available at: https://www.energywise.govt.nz/at-home/windows/double-glazing/ [Accessed 21 10 2016]. FENSA, 2014. Guide for Compliance with Building Regulations in England and Wales for Replacement Doors and Windows in Dwellings. FENSA. https://www.modernupvcwindows.co.uk/brochures/fensa-guide---2014.pdf, Volume 3, pp. 1-46. Urbikain, K. & Sala, M. J., 2012. Heat Transfer through a Double-Glazed Unit with an Internal Louvered Blind: Determination of the Thermal Transmittance using a Biquadratic Equation. International Journal of Heat and Mass Transfer, Volume 55, pp. 1226 -1235. Wang, T.-P. & Wang, L., 2014. A Steady Heat Transfer Model of Hollow Double Glazing Under Entire Wave Length Heat Radiation. Energy and Buildings, Volume 81, pp. 72-83 Read More

Heat retention of a double glazed window is determined by the transmitted energy, reflected and absorbed energy as well. The equation presents this process effectively where heat transmission is presented as 𝜏1𝜏2𝐼 while the energy absorbed is presented as ℎ𝑖 (𝑇𝑔,2 – 𝑇𝑖). Therefore, the energy transmission of the window is balanced through retention and energy collected by the window. Therefore, double glazing is effective in offering thermal comfort since its installation must consider the external and internal temperatures to attain the equilibrium temperature for the implementation (Astralian Government, 2016).

Designing and Installation of Double-Glazed Windows Windows consist of structural frames, glass panes, sealants and spacers (Barnes & Fulford, 2011). The design of double glazed windows is dependent on the type of glass used, frames, and coatings through efficient fine-tuning of the window. The performance of the window is influenced by many factors such as the gas between the windows, emissivity of the glazing, number of panes used, material used to create the space, and the material of the material (Ander & FAIA, 2014).

When designing the windows, specification of the window and the glazing system is important as it influences the efficiency of the window to save energy and provide comfort to those using them. Designing the double-glazed is highly dependent on the problem or need one has to solve. Some of the characteristics the designers consider is whether the design of the window is to handle the problem of heat loss or gain. Other factors to consider include the visual requirements such as the windows should ensure privacy of the owner is protected view and glare.

Shading and sun control should also be considered including thermal comfort, controlling the condensation, ultra violet and acoustic control, color effects, daylighting and other energy requirements. Designing the Windows First, one specifies characteristics such as the U-Value of the window, the solar heat co-efficient of gaining heat and other shading co-efficient. The transmittance of the window must also be specified. Based on the equation above, the efficiency of the window was achieved with an indication of the coefficients and transmittances.

The equation also presents that the designer may specify the color of tinting or coatings if needed. The U-value throughout the design stipulates the flow of heat over either radiation, conduction or convention based on temperature differences in the outside and inside environments. The equation provided above gives the transmittances of both inside and outside of the environment, the window is to be installed. On the stipulation the u-value used is high, the higher the transference of heat leading to a high heat loss during winter.

When using aluminum materials for the frame of the windows, the u-factors may range from a 1.3 Bitus/hr/ft2.of, which is high for a single- glazed window, and consequently, low for a double glazed window. The coefficient of the solar heat, demonstrates the energy of the sun that strikes the window is transmitted to the window in form of heat. With an increase in the gain of solar heat coefficient, the heat retention through a window grows. The ratio of the solar coefficients ranges from 0-1 where 0 stipulates that none of the heat striking the window is retained as heat while 1 means all the energy of the sun striking the window is retained as heat.

Thus, with a 0.5 coefficient, half of all energy striking the window from the sun is retained into the window. However, in the designing process, windows that have a high air conditioning loads, low coefficients are preferred. The shading coefficient is perceived as the ratio of heat gain through any given glazing when likened to a clear window of 1/8 inches of the pane. The transmittance in the equation was provided for both the outside and inside environments surrounding the window. The importance of these transmittances is that they provide the visible solar spectrum transmitted through a glass from inside or outside of the window.

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