Effects of external window form on residential building energy consumption

Transcription

1 Advanced Materials Research Online: ISSN: , Vols , pp doi:0.4028/ 203 Trans Tech Publications, Switzerland Effects of external window form on residential building energy consumption Zhao Chen,a, Li Bai,b, Feng Li 2,c Xincheng street 5088, Changchun city, Jilin province, China, Jilin Institute of Architecture and Engineering 2 Zhengyang street 4326, Changchun city, Jilin province, China, The second design and Research Institute of Jilin Province Architectural Design Group Co., Ltd. a chenzhao0703@63.com, b baili0308@63.com, c lifeng00@26.com Keywords: Windows Forms Building energy-saving Energy simulation Abstract. The author studies the factors on influencing energy consumption of three kinds of common forms of external window of the winter heating and summer cooling, according to the characteristics and influencing factors of living building external window of colding and heat load in severe cold areas, using the simulation software DeST-h to a certain residential building in Changchun City as an example. It analyses the effect of energy saving characteristics of different forms of windows and the influence on building energy consumption. It provides technical reference on rational design of the external window. Introduction The building energy consumption has rapid growth due to the development of the building industry and the improvement of people's living standard. Building energy conservation has important significance for China's energy-saving emission reduction work. The window energy consumption accounts for about 50% of the whole building energy consumption []. Therefore, the window is the key of building energy saving [2]. Many scholars conduct the research from changing the structure and performance of window glass, reducing energy consumption by decreasing the heat transfer coefficient of the form. The approach of this paper is different from the past, using DeST-h energy simulation software developed by Tsinghua University. An related article [3] specifically researched the accuracy of DeST-h models, arriving at the conclusion that accuracy of using DeST-h to simulate energy consumption of construction is completely qualified to be used in researches on construction. It analysis the factors of influencing energy consumption on winter heating and summer cooling of three kinds of common forms, ordinary windows, French windows and sun rooms. It also assesses energy-saving characteristics of different forms of windows and the effect on building energy consumption. Theory analysis. The basic structure of winter The basic consumption structure calculates according to the following formula Q = AK( tr to. w) a In the formula (), Q is the basic part of structure, W; () A is the envelope surface area of part,m 2 ; K is the heat transfer coefficient of envelope structure, W/(m 2 C); t R is the interior temperature of winter, C; t o. w is the exterior temperature of winter, C; a is the temperature difference correction coefficient of retaining structure. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-09/05/6,5:38:28)

2 620 Advances in Manufacturing Science and Engineering.2 The building cooling load in summer The building envelope is one of the main factors affecting the energy consumption of buildings. Cooling load through the building envelope heat gain is the main source of energy consumption of air conditioning system. Cooling load through the glass of the solar radiation heat gain accounts for a large part envelope heat gain. According to the " code for design of heating ventilation and air conditioning "(GBJ 9-87), the summer air-conditioning room design cooling load calculation should according to the unstable heat transfer calculation. 2 Mathematical model of external window heat transfer 2. The mathematical model of hourly heat transfer, The difference of window heat transfer temperature Heat transfer calculation of heat transfer bases on synchronization of windows because of the large heat transfer coefficient. The heat transfer of τ time is Q( ) = KF( tw tn) In the formula (2), ( τ) τ (2) Q is the heat transfer of windows, W; F is the size of the windows, m 2 ; t w is the hourly exterior temperature, C; t n is interior temperature, C; K is the heat transfer coefficient of windows, W/(m 2 K), K = / ( / α + R+ / α2) ; α, α2 is the heat transfer coefficient of internal and external wall surface; R is the thermal resistance of windows. 2, The hourly solar radiation heat gain of windows Assume that all of the radiation surface (including sky) and exterior temperature are the same according to the building material radiation associated with exterior air temperature observations. The radiation heat transfer is only refers to the sun and the sun scattering. Radiation heat gain calculations can be simplified. The solar radiation heat gain through windows associated with the towards of wndows, and changes with the s and specific time of day. I time solar heat gain calculates according to the following formula Q2 ( i,τ) = ( SSGD ( i) Xs() i + SSGd() i ) SC Xf F() i (3) In the formula (3), Q 2i,τ ( ) is i toward the time window radiation heat gain,w; SSG D () i is i toward the time direct heat gain, W/(m 2 ); SSG d ( i) is i toward the time scattering heat, W/(m 2 ); S C F ( i) is no shading transparent single (double) shading coefficient of glass windows, associated with the glass itself and the thickness of the air layer; F ( i) is the i toward the window area, m 2 ; X is the effective area coefficient of window; X s () i is the actual area ratio of sunlight irradiation. f 3, The penetration of the hourly heat Window air infiltration energy consumption not only related with construction and window frames and window sealing performance, but also associated with the volume of air flow through and the interior and exterior temperature. Wind penetration capacity calculates according to the following formula Q= 0.28C Ll( t t ) ρ (4) p n w w In the formula (4), Q is wind penetration capacity, W; Cp is air pressure ratio, kj/(kg C) ;L is the amount of the air into interior window aperture per meter, m 3 /(m h);l is seam length, m; t n is the interior temperature, C; t w is the exterior temperature, C; ρ w is the density of the exterior air, kg/ m Establishment of window heat balance equations Window heat balance equation including temperature nodes window inner, middle and outer glass heat balance equation. It shows in the following formula

3 Advanced Materials Research Vols c dt ρ ( + q + q (5) P x = h t, a t ) + hr,, ( t, t) + h2,( t2 t) dτ dt2 c P 2 ρ 2 x2 = h ( t,2 t2 ) + h3,2 ( t3 t2) + q2 (6) dτ c dt ρ ( + q + q (7) 3 P3 3 x3 = h3 t3, a t3 ) + hr,3, ( t3, t3) + h2,3( t2 t3) dτ In the above three formulas, t, t 2, t 3 are the inner layer, the middle layer and the outer layer temperature of the glass, C; t,a, t 3,a are the adacent to the air temperature of t and t 3, C; q, q 2, q 3 are each layer of glass on the absorption of solar radiation heat gain, W/m 2 ; q, rad, q 3, rad are the radiant heat gain of t andt 3 W/m 2 ; h, h 3 are the heat transfer coefficient of inner and outer glass surface and air surface, W/(m 2 C); h i, is the integrated heat transfer coefficient between two adacent glass surface, W/(m 2 C); h r,,, h r,3, are the radiation heat transfer coefficient between the surface of the inner and outer environment and their corresponding, W/(m 2 C); t,, t 3, are the 3, rad temperature of the environment corresponding to the inner and the outer surface, C. 3 Building model Simulation is carried out according to a bedroom of a residential building in Changchun City. The method of comparative analysis is adopted using three forms of the bedroom of ordinary windows, French windows and sun rooms. External windows are used in heat transfer coefficient of K=2.5 W/ ( m 2 K ). The simulation parameters are set according to the design standard for energy efficiency of residential buildings in Jilin Province, local standards " ( energy 50% ) ". The external windows of common building called ordinary windows are shown in Figure. Under normal circumstances, the height of residential building window is about 500 mm, the width is 900 mm ~ 500 mm. It is shown that the bigger the width of the window, the larger the window area and building load. The window size is determined as 500 mm 500 mm in order to make the typical significance results. For the improvement of people's living standard after entering 80 age., some high-grade residential gradually uses French windows pursuing spacious visual effect,which has shown in Figure 2. The height of French windows is generally 300 mm ~ 600 mm accounting for the visual effects and structure. The dimensions of French windows in this paper is 800 mm 200 mm. In recent years sun rooms have been widely used in a number of high-grade residential and villa construction for more attention has been paid to lighting and ventilation function of residential buildings. The architectural schematic diagram is shown in Figure 3. Since three kinds of windows are glass, sun rooms size is 4900mm 200mm. Three kinds of window size and room size had shown in Table. All the window architecture is shown in Figure, Figure 2, Figure 3. Table Three forms of dimension Windows Forms windows Width (mm) windows Hight (mm) Height from the ground (mm) 3, rad windows Areas (m 2 ) Room areas (m 2 ) Ordinary windows French windows Sun rooms Using DeST to calculate the heat load and the cooling load of different sizes of various windows forms, the results are shown in Table 2. For more direct expression of the results, we put the energy consumption proportion of ordinary window as. Based on the results above, it can calculate the ratio

4 622 Advances in Manufacturing Science and Engineering of energy consumption of the other two forms window of the thermal and cooling load. The result are shown in Table3. Figure Ordinary windows Figure 2 French windows Figures 3 Sun rooms Table 2 Energy consumption in cooling and thermal load of three forms Windows Forms heat load quota of the year cooling load quota of the year heat load of the heating cooling load of air-conditioning Ordinary windows French windows Sun rooms Windows Forms Table 3 Energy consumption ratio table of three forms heat load quota of the year cooling load quota of the year heat load of the heating cooling load of air-conditioning Ordinary windows French windows(compared with ordinary windows) Sun rooms(compared with ordinary windows) sun rooms (compared with French windows) Analysis of calculation results 4. Analysis of thermal load, heat load quota of the year heat load quota of the year is the main basis for heating design and determinants of initial investment. The relative proportion of maximum heat load quota of the year is shown in Table 3. If ordinary windows data is, French windows is.04 times larger than ordinary windows, sun rooms is.3 times bigger than ordinary windows. According to current engineering practice, the initial investment of heating system is commonly in 30 yuan / m 2 and 80 yuan / m 2[4]. It is generally considered that heating design load of French windows is much higher than ordinary windows, sun rooms design load is even more higher. The simulation result is different from the imagination, which is more scientific and practical.

5 Advanced Materials Research Vols Further research is carried out to see that increased heat load of the sun rooms and is not proportional to area increase of the window. The data of ordinary windows and French windows have been changed to simulation to the same room. The result has shown that width of ordinary windows changes from.5m to 2.4m,but maximum heat load quota only increases from W /m 2 to W /m 2 in the case of window height is.6m. In the same room, when ordinary windows change French windows in the case of window height is 2.m, maximum heat load quota only increases from 60.68W /m 2 to 62.09W /m 2.From the above results, it s shown that design load value does not change much increased window area. The bigger the area of the windows, the larger the heat transfer coefficient. At the same time, indoor solar heat gain also increases during the day, so indoor heat load reduced. It used to be avoid larger windows for saving the initial investment. This account is not necessary according to the calculation. The reason of large energy consumption is that the air infiltration rate is higher than the design value, not for the windows forms. Ultimately the problem is form, material and quality of the proect. Therefore, French windows can be widely used in practical engineering, and sun rooms are acceptable as an emerging form ust from the design index point. 2, heat load of the heating heat load of the heating are the superposition of thermal heating cumulative hourly quarter. The simulation results shown that the average heat load of the heating of French windows is 0.83 times smaller than that of ordinary windows. Sun rooms is 2.4 times bigger than ordinary windows. First of all,all the selected windows are in the south side of building room. The solar radiation of south external windows in winter are greater than that of the heat loss.from the perspective of the most heat gain in winter, heat radiation absorbed from south wall should be as large as possible and greater than heat loss of the outward to compensating the building load. The window area selected in design should be as large as possible, in order to meet the requirements of indoor temperature. Because the solar radiation of French windows are larger than that of ordinary windows, average heat load of the heating of French windows are smaller than that of ordinary windows. Further more, the curtains as insulation measures can effectively avoid the penetration of the wind window reducing the heat load in severe cold area. It costs high energy to sun rooms meeting requirements for comfort and beauty of people through comparative study of Table 3. In the case of heat charge, operating cost of heating system not only within the human capacity, but also to meet the principle of energy conservation. The energy consumption of sun rooms are 2.4 times greater than that of ordinary windows in high-grade residential and villa. It can be found through the above analysis that choice of sun rooms should be cautious considered during the energy ratio of the heating system design. 4.2 Analysis of cooling load, cooling load quota of the year cooling load quota of the year is the main basis for air-conditioning design. As it shown in Table 3, maximum cooling load quota of the year of French windows is 2.36 times bigger than that of ordinary windows. Sun rooms is 2.68 times bigger than ordinary windows. Because of Changchun City is located in the severe cold area which has short air-conditioning, cold load is much smaller than heat load. Although it shown in results that the maximum cooling load quota of the year and the initial investment of French windows are the largest in three forms of windows. Air conditioning initial investment is acceptable because of rarely operating the air-conditioning during the severe cold area. Generally speaking, considering from the maximum cooling load quota of the year, the initial investment of French windows are as similar as that of ordinary windows. 2, cooling load of the air-conditioning cooling load of the air-conditioning are the superposition of cooling consumption cumulative hourly quarter. As it shown in Table 3, French windows is.63 times bigger than that of ordinary windows. The sun room is 4.46 times bigger than ordinary windows.

6 624 Advances in Manufacturing Science and Engineering In summer, the difference between interior and exterior temperature is small in air conditioning room, so as the heat transfer. It is mainly consider that how to reduce the solar heat gain from the window into the interior. Because solar heat gain are only existed in the south window in severe cold area in summer,the heat gain of external windows radiation are bigger than that of the temperature difference, which accounted for about 2/3 in the whole heat gain of external windows. Therefore, the larger the window area is, the more radiant heat gain have. The simulation results shown that radiant heat gain of sun rooms are the biggest. The interior temperature can be adusted by natural ventilation for cool climate in summer morning and night. Air conditioning is not required 24 hours of operation. People are more willing to accept the natural ventilation to reduce interior temperature. According to the author's survey, the runtime numbers of air conditioning system in residential building each summer is not exceeding 300 hours, which is equivalent to a dozen days in annual operation. The proportion of cooling cumulative energy accounted for the total building energy consumption is very small. So for the high-grade residential areas, energy consumption of the sun rooms is four times than that of energy consumption of ordinary windows which can be accepted. The simulation results shown that consumption of French windows is only.64 times bigger than that of the ordinary windows, which with the level of comfort and vision of sun rooms. As a result, French windows should be widely used in practical engineering.sun rooms should be used selectively in the high-grade areas. 5 Conclusion () Three forms of design load have little difference in the kinds of materials and construction quality satisfied the design conditions. Saving the initial investment of heating is not necessary. Comparing of operating cost of heating, French windows have moderate energy consumption which can be used in large areas. For the high-grade residential areas, energy consumption of sun rooms is several times than that of energy consumption of ordinary windows which can be accepted. But whether the widespread use of sun rooms or not for design should also be considered carefully. (2) The big design cooling load and initial investment are acceptable for French windows and sun rooms because of rarely operating the air-conditioning during the severe cold area. Operating costs of high energy consumption in a short time can be tolerated in the high-grade areas, enoying the bright and spacious sun rooms. The proportion of cooling consumption accounted for the total building energy consumption is very small. But French windows should be selected for the form design of general sense (3) Calculation and comparison of energy consumption in residential buildings are relatively intuitive and convenient using dynamic simulation software DeST-h. This paper has guiding function on the forms of windows in residential buildings in severe cold area. Acknowledgements This work was financially supported by the Youth Development Fund for science and technology proect of Jilin architectural and Civil Engineering Institute and the Jilin provincial Department of "Twelve-Five" research, science and technology Proect. References [] Zhaoian Li, Yi Jiang: Analysis and Thinking of Energy Consumption in the Building of our Country, Journal of Architecture.Vol. 7 (20), p [2] Qian Wang, Yingwei Zhang: Principle and Application of Energy-saving Low-E coated Glass, Energy-saving technology. Vol. 5 (20), p [3] Xiaoliang Zhang: Stimulation Software for Environment Design of Construction DeST, Heating Ventilation and Air Conditioning, Vol. 9(2004), p [4] Overall Plan for Changchun City ( ).

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