Influence of Fenestration dimension on energy consumption

A generally accepted way of energy efficient building fenestration has been to have small windows facing north and large windows to the south. This is to minimize losses on the north side while gaining as much solar heat as possible on the south. But there are other factors which affect the area of windows in all buildings sides which should to be studied and then define optimum window size. Over the past decade, many studies has been conducted to estimate the energy-saving potential of windows for various climates. Furthermore, using computational analysis the optimum window size and type for minimizing building energy consumption have also been explored. All the researches have proven that considerable energy can be conserved when windows are designed properly. (Ko 2009)

Iqbal and Al-Homoud conducted an evaluation of various energy conversation measures by using the Visual DOE-4 energy simulation program. For one of the energy conservation methods, a 7% reduction in energy consumption was achieved in summer by using an efficient glazing system. It is recommended that low-e double-glazed windows be employed for energy efficiency, particularly in large, double-glazed buildings in hot climates. They concluded that using more energy-efficient windows (high R-value and low-e) can be beneficial for reducing energy consumption and improving indoor comfort levels. (Iqbal and Al-Homoud 2007)

Mehlica et al. analyzed how to minimize heating and cooling loads by means of optimum window size and building aspect ratio. Based on a computer simulation in five different climate regions in Turkey, it was concluded that a window size of 25%

facing the south was the optimum for hot climates. (Inanici and Demirbilek 2000)

Mari-Louise Persson et al. investigated how decreasing the window size facing south and increasing the window size facing north in low energy houses would influence the energy consumption. The results show that the size of the energy efficient windows does not have a major influence on the heating demand in the winter, but is relevant for the cooling need in the summer. This indicates that instead of the traditional way of building passive houses it is possible to enlarge the window area facing north and get better lighting conditions. To decrease the risk of excessive temperatures or energy needed for cooling, there is an optimal window size facing south that is smaller than the original size of the investigated buildings. (Persson, Roos et al. 2006)

K. Hassouneh and others, conducted an evaluation of Influence of windows on the energy balance of apartment buildings in Amman. It has been found that choosing a larger area facing south, east and west can save more energy and decrease heating

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costs in winter using certain types of glazing, while decreasing the glazing area facing north can save money and energy. However, it has been found that the energy can be saved in the north direction if certain types of glazing has been used. In the apartment building, it is found that certain combination of glazing is energy efficient than others.

This combination consists of using large area of certain types of glass in the east, west and south direction, and certain types of glass in the north direction or reducing glazing area as possible in the north direction. (Hassouneh, Alshboul et al. 2010)

Carlos E. Ochoa et al. have done a consideration on design optimization criteria for windows providing low energy consumption and high visual comfort. The results were classified using a graphical optimization method, obtaining a solution space satisfying both energy and visual requirements. Most project expectations can be met within the range of sizes. However, unprotected windows barely meet acceptance criteria, needing additional control devices. Applying various related criteria with adequate values increases the diversity of acceptable solutions but too many limits it.

Clear objectives and acceptance ranges have to be conceptualized in order to translate them into decisions. (Ochoa, Aries et al. 2012)

Vesna ˇZegarac Leskovar et al. has done a research on the approach in architectural design of energy-efficient timber buildings with a focus on the optimal glazing size in the south-oriented facade. A parametric analysis is performed on the variation of the glazing-to-wall area ratio (AGAW) from 0% to 80% for six different exterior wall elements with different thermal properties. Modifications are performed for the main cardinal directions, while a detailed analysis is carried out only for the south facade. It is evident from the results that the increase of the south-oriented glazing surfaces installed in the single-panel wall elements with higher U-values acts positively on the sum total of energy demand for heating and cooling. The research

Fig. 11: Influence of daylight on heating, cooling and artificial lighting systems

(Ochoa, Aries et al.

2012)

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main objective was to demonstrate an approach which could be used by architects to define the optimal glazing surface for a specific direction in order to obtain the optimal model of an energy-efficient house, depending on a single independent variable (Uwall-value). But the results showed that it is difficult to establish what a realistic optimal model is since most of the buildings are unique and trends also vary over time.

However, by applying the research presented approach to each individual timber-frame house, the optimal glazing surface is determinable with reference to the lowest energy demand for heating and cooling. Such application would still allow the houses to keep their uniqueness. (Leskovar and Premrov 2012)

John A. Tinker et al. studied an Ideal Window Area concept for energy efficient integration of daylight and artificial light in buildings. He presents a methodology to predict the potential for energy savings on lighting using an Ideal Window Area concept when there is effective daylight integration with the artificial lighting system.

The energy analysis work was performed using the Visual DOE program for the climatic conditions of Leeds, in the UK, and Florianopolis, in Brazil. Following this, the potential for lighting energy savings was assessed for each room using a method based on Daylight Factors. It was observed that the potential for energy savings on lighting in Leeds ranged from 10.8% to 44.0% over all room sizes and room ratios for an external illuminate of 5000 lux; and in Florianopolis, the potential ranged between 20.6% and 86.2% for an external illuminate of 10000 lux. (Ghisi and Tinker 2005)

Andrea Gasparella et al. has done an analysis and modeling of window and glazing systems energy performance for a well-insulated residential building. This work evaluates the impact of different kinds of glazing systems (two double and two triple glazing), window size (from 16% to 41% of window to floor area ratio), orientation of the main windowed facade and internal gains on winter and summer energy need and peak loads of a well-insulated residential building. The climatic data of four localities of central and southern Europe have been considered: Paris, Milan, Nice and Rome. A statistical analysis has been performed on the results in order to identify the most influencing parameters. It is possible to summarize the results as follows:

- The use of large glazings enhances winter performance but worsens slightly the peak of winter loads (the adoption of shutters for night hours could limit this problem);

- There is an improved effect for the south orientation, which is the best performing in winter;

- In winter, the use of windows with low thermal transmittance is useful if accompanied by high solar transmittance;

- However higher solar transmittance considerably worsens summer performance;

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- Selective shading systems should be installed to improve summer performance without affecting the winter one. (Gasparella, Pernigotto et al. 2011)

Samar Jaber et al. in his study of thermal and economic windows design for different climate zones showed that heating load is highly sensitive to windows size and type as compared with cooling load. Also, he showed that with a well-optimized glazed window energy saving can be reached up to 21%, 20% and 24% for Amman, Aqaba and Berlin, respectively.(Jaber and Ajib 2011)

He in his next study, discussed assessment of best orientation of the building, windows size, thermal insulation thickness from energetic, economic and environmental point of view for typical residential building located in Mediterranean region. The results showed that about 27.59% of annual energy consumption can be saved by choosing best orientation, optimum size of windows and shading device, and optimum insulation thickness. (Jaber and Ajib 2011)

Sharifah Nor Fairuz et al. has researched the performance of daylight through various type of fenestration in residential buildings in Malaysia. The analysis has done for casement window and louver window with clear glass, obscure glass or tinted glass which are commonly used as residential fenestration in Malaysia, and the VT, SHGC and U-value for most efficient visual comfort and daylight illumination have been presented. (Husin and Harith 2012)

A. Laouadi et al. investigated developing skylight design tools for thermal and energy performance of atriums in cold climates. Design tools were developed to quantify the impact of the design alternatives on the performance outputs. The design tools were cast into two-dimensional linear relationships with the glazing U-value and SHGC ratios as independent parameters. The results for enclosed atriums showed that the annual cooling energy ratio increased at a rate of 1.196 per unit of SHGC ratio and decreased at a rate of 0.382 per unit of U-value ratio. However, the annual heating energy ratio increased at a rate of 1.954 per unit of U-value ratio and decreased at a rate of 1.081 per unit of SHGC ratio. Similar trends were also found for the three-sided and linear atriums. Pyramidal/pitched skylights increased the solar heat gain ratio by up to 25% in the heating season compared to flat skylights. The effect of the skylight shape on the annual cooling and heating energy may be positive or negative, depending on the glazing U-value and SHGC ratios and the atrium type. Atriums open to their adjacent spaces reduced the annual cooling energy ratio by up to 76%

compared to closed atrium spaces. However, open atrium spaces increased the annual heating energy ratio by up to 19%. (Laouadi, Atif et al. 2002)

Hee in his research ‘The role of window glazing on daylighting and energy saving’, says the qualities and performances of glazing are proportional to the costs. It

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is wise to perform techno-economics evaluation to obtain the suitable glazing for a building. Due to the higher costs of dynamic glazing, it is more suitable to be installed in the building, which needed high performance in term of daylighting and energy saving such as commercial buildings. (Hee, Alghoul et al. 2015)

Tsikaloudaki in the paper “The energy performance of windows in Mediterranean regions”, found that for the cooling mode the energy performance of windows in warm climates is influenced significantly by their thermophysical properties. More specifically, the impact of solar transmittance is significant and its optimal selection can contribute in minimizing the energy consumption, especially in environments with controlled ventilation, such as offices. On the contrary, advanced fenestration products with low thermal transmittance seem to behave unfavorably, since their extremely low thermal transmittance prohibits the dissipation of heat toward the ambient environment and results ultimately in higher cooling energy loads.

(Tsikaloudaki, Laskos et al. 2015)

Pyeongchan Ihm in a study of Impact of window selection on the energy performance of residential buildings in South Korea, carried out detailed energy simulation analyses coupled with economical and environmental assessments to assess the thermal, economical, and environmental impacts of glazing thermal characteristics as well as window sizes associated with housing units in various representative climates within South Korea. The results of the analyses have clearly indicated that selecting glazing with low solar heat gain coefficient is highly beneficial especially for large windows and for mild climates. In particular, it is found that using any double-pane low-e glazing would provide better performance for windows in residential buildings than the clear double-pane glazing, currently required by the Korean building energy code. (Ihm, Park et al. 2012)

Farshad Nasrollahi in his research on climate and energy responsive housing in continental climates of Iran has provided these instructions for windows as the results:

-If the building has the same triple glazed window ratio in all orientations with external blinds, the optimal window ratio (in all orientations) is 40%, but with internal shading devices or with no shading devices, the most efficient window ratio is 30%.

-In a building with the same double-glazed window ratio in all orientations and external blinds, the optimal window ratio (in all orientations) is 30%.

-In the case of using triple glazed windows with external shading devices in only an east, west or south orientation, an increase in window area reduces the building’s total energy demand. This is most effective for south-facing windows. Therefore, if a building can have windows in only one of the above-mentioned orientations, from the

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viewpoint of energy efficiency it is best to maximize this window area. North-facing windows increase both heating and cooling energy consumption under all conditions and thus must be minimized.

- Increasing the number of south-facing windows to 100%

- Decreasing the north-facing windows (in all conditions) to 0%

- Decreasing the east and west-facing windows to 0% for buildings with a large area of south-facing windows

- Increasing the east and west-facing windows up to 100% for buildings with no south-facing windows (Nasrollahi 2009)

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