Abstract
This paper presents the reasonability of using an increased proportion of glazing surfaces in prefabricated timber-frame buildings with a special focus on energy efficiency by using an enlarged glazing area in the south façade. The research is based on a case study of a two-storey house built in a prefabricated timber- frame structural system taking the climate data for Ljubljana into consideration. Parametric analysis is performed on the variation of an increased proportion of the glazing surface's impact in the south side of the building according to the total surface of the south façade (AGAW) as a basic variable. The analysis was carried out on different exterior wall elements having different thermal properties, while the rest of the parameters, such as the ground plan of the model as well as the active systems, roof and floor slab assemblies, climate condition, etc. remain constant. The basic theoretical contribution of the presented research is the transformation of a complex energy related problem to only one single independent variable (U -value) wall which becomes the only variable parameter to determine the optimal glazing area size value (AGAW ) for opt all contemporary prefabricated timber construction systems. Keywords: timber; energy efficiency; glazing; modeling 1. Introduction friendly, but also due to the extremely positive feelings T he pre se nt t i m e s, c ha ra c t e ri z e d by spe c i fi c that homeowners have when living in such houses. circumstances in the sphere of climate change, witness Additionally the use of glazing surfaces in timber an intensive focus of the sciences of civil engineering structures is becoming an important issue of energy- efficient construction. Over a number of years of and architecture in searching for ecological solutions development, glazing manufacturers have improved and construction methods that would allow for greater their products' thermal-insulation and strength energy efficiency and, consequently, for a reduced properties as well as their coefficient of permeability environmental burden. The brick and concrete of total solar radiation energy and thus enabled the use industry is responsible for about 10% of global CO of large glazing surfaces, primarily south-oriented, emissions into the environment whereas wood helps not only to illuminate indoor areas but also to ensure the environment by absorbing and storing CO while it solar heating. It follows that timber construction along grows. Being a natural raw material, timber represents with the use of suitable and correctly oriented glazing one of the best choices for energy efficient construction surfaces represents a great potential in residential since it also functions as a material with good and public building construction. Many studies have thermal properties if compared to other construction been performed since then focusing on the research materials, has good mechanical properties and ensures of specific parameters that influence the energy a comfortable indoor living climate. Respecting all performance of buildings. these facts the energy-efficient properties of timber- The research of general methods for estimating the frame buildings are, in comparison with other types total area of the exposed surface of domestic buildings of building, constructed with concrete, brick or steel, by authors Steadman and Brown (1987) was performed excellent but not only because well-insulated buildings on the basis of an empirical study of a house plan from use less energy for heating, which is environmentally the city of Cambridge. Among a range of researched parameters, such as the relationship between the wall *Contact Author: Miroslav Premrov, Facul ty of Civil area and floor area, built form etc., the glazing areas Engineering, University of Maribor, Smetanova ul. 17, are examined from the viewpoint of heat loss. Interest SI-2000 Maribor, Slovenia is focused principally on south-oriented glazing. Tel: +386-2-2294300 Fax: +386-2-2524179 Among comparable latter studies a parametric study E-mail: miroslav.premrov@uni-mb.si of heating and cooling demand was performed by ( Received April 12, 2011 ; accepted January 23, 2012 ) Bülow-Hübe (2001) in order to determine the optimal Journal of Asian Architecture and Building Engineering/May 2012/78 71 design for office windows for the Swedish climate. The timber construction systems. study is based on a single-person office model with The first part of the paper presents the principal windows in the south facade. It includes many variable timber structural systems as well as the main parameters, such as glazing size, type and orientation, preferences regarding low-energy construction. Some daylight utilisation, internal load, ventilation rate, wall basic energy-efficient house design requirements are insulation and climate. Another Swedish study was presented in Chapter 2. The second part, starting with performed by Persson et al (2006a) for 20 low-energy Chapter 3, focuses on the reasonability of using an terraced houses built in 2001 outside Gothenburg. The increased proportion of glazing surfaces performed analysed houses are oriented with the large window on a parametric analysis on a two-storey timber-frame area facing south and the building construction is more house. Based on the parametric analysis Chapter 4 air tight and more insulated than traditional houses in presents the generalisation of the problem related to Sweden. The variable parameters of this research are the energy demand dependence as well as the optimal the orientation, U-values of the construction elements glazing area size dependence on one single variable, and different triple glazed window combinations. It the U –value, which becomes the only variable wall is shown that less energy is needed for heating if the parameter for all contemporary prefabricated timber houses are placed with the large window area facing construction systems, independently of the type of south. Orienting the windows to the west or east does construction system. Calculations do not consider not noticeably influence the energy balance. Next, various active systems' impacts (heat recovery many findings are stated in the dissertation of Persson ventilation, solar collectors, PV panels, heat pumps, (2006b) which are in some respects comparable to the etc.). The comparative analysis results can nevertheless authors' research. According to Pagliano et al. (2007) serve as a good frame of reference for civil engineers the optimum glazing surface for mild winters is equal and architects in an approximate estimation of energy to 30% of the total surface of the building. In locations demands accompanying the different positioning and with more severe winters this optimum does not exist proportion of glazing surfaces while using various but a glazing surface of between 15% and 30% of the pre fa bri c a t e d t i m be r-fra m e wa l l e l e m ents. It i s total surface is recommended. important to stress that the presented analysis is limited Among the existing studies many of them are to timber construction only, therefore a specific thermal provided for non-European climates. Bouden (2007) capacity of lightweight timber structures is considered investigated whether glass curtain walls are appropriate in all calculations. for the Tunisian climate. The influence of windows on the energy balance of apartment buildings in Amman, 2. Energy Efficiency of Timber-Frame Buildings Jordan, is analysed in a study performed by Hassouneh 2.1 Timber-frame construction system et al. (2010). In general all of the presented studies deal Timber is commonly associated with lightweight mainly with the influence of variable parameters on construction although it is ubiquitous as a building the energy performance of buildings of different types material. Timber construction is an important part (residential, offices, public) and mainly of massive of the infrastructure in a number of areas around the construction systems. From the existing research the world. Brand new and improved features, having authors can summarize that the process of defining been introduced in the early 80's of the last century, the optimal residential building is very complex, and brought about the expansion of timber-frame buildings is influenced by the specific basic parameters listed all over the world. The most important are the below: following introduced changes: transition from on-site - location of the building and climate data for the construction to prefabrication in a factory; transition specific location, from elementary measures to modular building and - orientation of the building, development from a single-panel to a macro-panel - properties of installed materials, such as timber, wall prefabricated panel system. All of these greatly glass, insulation, boards etc., improve the speed of building. Respecting all these - building design (form, ground plan, composition facts the energy-efficient properties of timber-frame of the building envelope, window size and buildings are, in comparison with other types of arrangement in the façade), buildings (brick, concrete, steel) excellent, but not only - selection of active systems. because well insulated buildings use less energy for One of the general critical remarks of the authors heating, which is environmentally friendly, but also regarding existing studies on the impact of windows on due to the extremely positive feelings of homeowners heating and cooling demand was that most of them are when living in such houses. There are two main and just calculations for a single building. In the authors' competitive prefabricated structural systems mostly research an attempt for a more systematic analysis used in residential timber buildings: a timber-frame has been made, with the model of a building of their system and a massive panel system. In this research base-case study being performed in many variations of the authors' attention is focused on the timber-frame 72 JAABE vol.11 no.1 May 2012 Vesna Žegarac Leskovar construction system. The behaviour of the massive m, containing all protection and insulation layers as panel system is very similar to the timber-frame, some well as window and door openings, are completely comparison of the calculated results can be found in produced in a factory, Kozem Šilih and Premrov (2010). Žegarac and Premrov (2010). 2.2 Basic requirements of energy-efficient house Prefabricated single-panel timber-frame walls as design main vertical bearing capacity elements, of usually The definition of an energy efficient house design typical dimensions with a width b = 1250 mm and a is related to the specific design approach comprising height h = 2500 – 2600 mm, are composed of a timber exactly defined parameters which infl uence t he frame and sheets of board-material fixed by mechanical energy balance of buildings. The basic aim of energy- fasteners to both sides of the timber frame (Fig.1.). efficient house design is to take advantage of as many renewable energy sources and of climatic conditions in combination with low energy technology as possible in order to reduce the need for conventional building technology which is inefficient or consumes a lot of fossil fuel energy. Parallel to a reduced demand for a fossil fuel to heat the building, the CO emissions are reduced as well. There exist few classifications of energy-efficient houses that differ from each other minimally regarding energy demand. As an example a low-energy house is a house with an annual requirement for a space heating energy demand of less than 50 kWh/m a, however the requirements differ from one country to another, while for a passive house this requirement is strictly defined with the value being lower than 15 kWh/m a in all countries. According to the Slovene legislative framework, the system of ener gy performance Fig.1. Composition of a Single-Panel Timber-Frame Wall Element certification is defined in rules on the methodology There are many types of panel sheet products of c onstruct ion a nd i ssua nc e of bui ldi ng e nergy available which may have some structural capacity certificates (2010). On the basis of these rules, the such as wood-based materials (plywood, oriented classification of energy-efficient houses in classes A1, strand board, hardboard, particleboard, etc.) or fibre- A2, B1, B2 and C, related to annual heating demand, is plaster boards (FPB), originally started in Germany defined. and recently the most frequently used type of boards In an energy-efficient hous e the s pecified low in Central Europe, Premrov and Kuhta (2009). energy demand can be achieved by well-considered The sheathing boards on both sides of the wall can design that includes a proper selection of building b e c o v e r e d wi t h a 1 2 . 5 m m g y p su m - c a r d b o a r d . materials, excellent envelope insulation, good air Development from an old single-panel to a new macro- tightness, thermally efficient glazing, a compact form panel wall system (Fig.2.) in the middle of the 90's of the building, construction without thermal bridges of the last century also greatly increased the speed of and passive solar design which is preconditioned by building. appropriate southern orientation with well-designed shading. On the other hand the optimal selection of active technical systems which include heat recovery ventilation, heating systems with ground source heat pumps, solar panels, lightning with low energy lamps and more, are required for achieving the best performance of an energy-efficient house and an appropriate quality of living. Lately, the option of embedding more glass surfaces into a building is becoming very popular due to energy efficiency. An appropriate size and orientation of such enlarged glazing areas in timber-frame structures is therefore very important from the viewpoint of the optimal energy-efficient design of buildings. Fig.2. Composition of a Macro-Panel Timber-Frame Wall Element Because all elements in timber-frame walls are 3. Numerical Study prefabricated, the erection of such a building is very In this chapter the parametric numerical case study fast. The wall elements in a total length up to 12.5 of a two-storey house and its parametric analysis of an JAABE vol.11 no.1 May 2012 Vesna Žegarac Leskovar 73 increased-proportion-of-the-glazing-surfaces impact on glazing configuration with a g-value of 52% and U energy demand for heating and cooling is presented. = 0.51 W/m K assures a high level of heat insulation 3.1 Simulation model and light transmission, Gustavsen et al. (2007). The Description of the base case study model: window frame U-value is U = 0.73 W/m K, while the The external horizontal dimensions are 11.66 m x frame width is 0.114 m. The glazing-to-wall area ratio 8.54 m for the ground floor and 11.66 m x 9.79 m for (AGAW) of the south-oriented façade is 27.6%, while the upper floor. The total heated floor area is 168 m . the AGAW values of the rest of the cardinal directions The ground plan of the considered base-case study are 8.9% in the north, 10.5% in the east and 8.5% in model is presented in detail in Žegarac Leskovar and the west façades. Premrov (2011). A three-dimensional model of the Climate and orientation: house is shown in Fig.3. The house is located in Ljubljana and oriented with the longer side with the large glazed area facing south. The city of Ljubljana is located at an altitude of 298 m, latitude of 46°03' and longitude of 14°31' east. Considered climate data from ARSO (2010) given by months are presented in Table 1. Shading: The house is constructed with a south-oriented extended overhang above the ground floor (see Fig.3.), which blocks the direct solar radiation from entering the ground floor windows to the south during the Fig.3. Three-Dimensional Model of the House summer, while allowing it to enter in winter when Construction: the angle of incidence of the sun is lower. The rest of The exterior walls are constructed using a timber- the windows on the upper floor and those of the east, frame macro-panel system. The exterior wall U-value west and north-oriented walls are shaded with external of the base case is 0.137 W/m K. Owing to the shading devices. The authors selected the temporary characteristics of the exterior wall the base case shading reduction factor z=50% for glazing areas in all model was labelled as TF 2 with the timber class C22 four façades. according to EN 338 (2003). The U-values of the other Internal gains and HVAC: 2 2 external construction elements are 0.135 W/m K for A value of 2.1W/m for internal heat gains from the floor slab, 0.135 W/m K for the flat roof and 0.130 electric appliances and body heat was used in the W/m K for the south-oriented overhang construction PHPP (internal heat sources) calculation. The house above the ground floor area. is equipped with a central heat recovery unit. The Glazing: efficiency of the selected unit which is placed within A window glazing (Unitop 0.51 – 52 – UNIGLAS) the thermal envelope is specified with values of 82% with three layers of glass, two low-emissive coatings for heat recovery efficiency and 0.41 Wh/m for and krypton in the cavities for a normal configuration electrical efficiency. The average air change rate is -1 of 4E-12-4-12-E4, each cavity being 12 mm thick, set to a minimum recommended value of 0.30 h . To with 4 mm thick glass panes, was installed. The prevent overheating in the summer period the summer Table 1. Climate Data for Ljubljana (ARSO, 2010) JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC YEAR Average temperature -1.1 1.4 5.4 9.9 14.6 17.8 19.9 19.1 15.5 10.4 4.6 0.0 9.8 Nr. of days with lowest 23.7 18.2 11.5 2.1 0.1 0.0 0.0 0.0 0.0 2.0 10.5 21.3 89.6 temperature <= 0.0 °C Nr. of days with highest 0.0 0.0 0.0 0.6 4.7 12.2 19.6 16.9 6.3 0.3 0.0 0.0 60.6 temperature >= 25 °C Absolute highest temperature 14.8 18.9 24.6 29.3 31.1 34.7 37.1 36.5 31.5 26.9 21.9 16.7 37.1 Average relative humidity at 7 91.1 89.5 89.5 86.9 85.9 86.2 87.0 91.8 95.1 94.4 92.6 91.3 90.2 am (%) Average relative humidity at 2 78.1 66.9 57.9 52.9 51.9 54.5 51.6 53.9 59.0 64.3 75.2 81.2 62.4 pm (%) Average duration of solar 47 85 128 162 210 221 260 230 164 116 56 37 1712 radiation (h) Nr. of clear days 1.8 2.8 3.4 3.1 2.8 2.9 5.1 4.5 1.7 2.0 1.3 1.0 32.5 (cloudiness < 2/10) Nr. of cloudy days (cloudiness 18.1 13.7 13.2 11.2 9.1 8.5 5.8 5.9 7.9 11.6 17.4 19.9 142.2 > 8/10) Nr. of days with fog 15.3 10.2 6.8 4.2 4.9 5.1 6.1 9.8 15.2 15.4 12.8 15.2 120.8 74 JAABE vol.11 no.1 May 2012 Vesna Žegarac Leskovar ventilation for cooling through manual window night Description of the software and calculation method: ventilation with a corresponding air change rate of The PHPP 2007 programme (Feist, 2007) was -1 0.20 h was planned. Furthermore additional summer used to perform calculations of energy demand. The operation of the heat recovery ventilation system software was found to be able to describe the thermal was planned as well. No other cooling devices were building characteristics of passive houses surprisingly installed. The interior temperatures were designed to a accurately, although it can be used also for low-energy T of 20°C and T of 25°C. No solar collectors were house design. The calculation method of the parametric min max installed. case study process is presented graphically in Fig.6. Parameters varied: The influence on the energy demand of the following factors was studied: a.) The glazing size in four different cardinal directions; south, north, east and west. b.) Modifications of the glazing area size were performed in the range of AGAW from 0% to nearly 80%, and made step by step through adding window elements to the totally unglazed facade, as shown in Fig.4. Fig.6. Case Study Calculation Method 3.2 Results and discussion T h e c o m p a ri so n o f a nn u a l e n e rg y d e m a n d f o r heating (Q ) and cooling (Q ) as a function of the h k glazing area size for different cardinal directions of the TF 2 construction system is presented in Fig.7. a.) b.) Fig.4. South-Oriented Façade of the Base-Case Model with Schemes of the Glazing Area Size Modification c.) Modifications of the glazing area size were performed separately for each cardinal direction, for three timber-frame macro-panel systems: TF 1 with U=0.164 W/m K, TF 2 with U=0.137 W/ 2 2 m K and TF 3 with U=0.102 W/m K. Additional modifications of AGAW were made only for the south-oriented glazing areas for three classical Fig.7. Energy Demand for a.) Heating (Q ) and b.) Cooling (Q ) h k single-panel systems with higher U-values: in TF 2 System as a Function of AGAW TFCL 1 (U=0.70 W/m K), TFCL 2 (U=0.47 2 2 W/m K) and TFCL 3 (U=0.30 W/m K). The It is found that the largest influence of increasing the composition of the treated construction systems glazing area size is evident for the south orientation is shown in Fig.5. (Fig.7.a), where Q decreases almost linearly with a growing AGAW and the heat gains at AGAW=0.79 add up to almost 13 kWh/m a or for about 50% of the Q value at AGAW=0. The increase of Q for almost h h 6 kWh/m a or 29% related to the energy demand for heating at the starting-point shows that the influence of changing the glazing area facing north is less expressive than that of its southern counterpart. East TF CL 2 TF 1 TF 2 TF 3 and west orientations show quite similar behaviour. Fig.5. Cross-Sections of the Analysed Exterior Wall Elements To explain the positive influence of enlarged AGAW JAABE vol.11 no.1 May 2012 Vesna Žegarac Leskovar 75 for the south façade it is necessary to present solar the main point of the authors' special interest, will be gains and transmission losses effected by using an additionally analysed and compared for all construction appropriate size of glazing. Therefore, the results systems. The most interesting point is the comparison for the value of AGAW = 0.41, which is the optimal of the Q +Q demand for different construction systems h k glazing area size for the TF 2 system (see Table 2.), are (TF 1 – TF 3), which is presented in Fig.9. graphically presented in Fig.8. Fig.9. Comparison of Sum Total of Energy Demand for Heating and Cooling as a Function of AGAW for Southern Orientation of Selected TF Construction Systems (TF 1 – TF 3) The results for sum total energy demand show an Fig.8. Solar Gains and Transmission Losses by AGAW = 0.41 interesting appearance related to the optimal point with It is evident that the solar gains are in this case the lowest Q +Q demand, which is clearly evident in h k higher (QS=24.4 kWh/m a) than the transmission the TF 3 construction system appearing at the range of losses through the same windows (QT=-17.4 kWh/ AGAW≈0.34-0.38, quite evident in the TF 2 system m a) and therefore, the influence of the glazing in the at AGAW≈0.41 and less evident in the TF 1 system south façade is positive. at AGAW≈0.42–0.50. The authors assume that the A comparison of the cooling demand behaviour optimal share of glazing surface in south-oriented patterns presented in Fig.7.b shows the lowest Q exterior walls depends on the thermal transmittance for the north orientation, while the west and east of the exterior wall. The optimal share of the glazing orientations show almost equivalent behaviour which is area in walls with extremely low U-values is smaller similar to the behaviour for the south orientation. From than that of walls with higher U-values. It is interesting the presented data it is evident that an increase in the to compare the results with a study performed by size of the glazing surfaces in all of the main cardinal Inanici and Demirbilek (2000) who analysed variations directions has a relatively negative influence on the of the window-to-wall ratio from 25 to 90% for energy demand for cooling. The presented analyses different types of climate in Turkey. The results for the generally accord well with the results of parametric apartment units showed that when increasing the south study research on the effect of glazing type and size facing window area the total energy load decreased for on annual heating and cooling demand for Swedish cool climates and increased for the warm climates. The timber-frame offices, Bülow-Hübe (2001) and low- optimum size in hot climates was 25% of the facade energy houses, Persson (2006a) and Persson (2006b), area (AGAW=0.25), which is lower as in the authors' taking into account of course differences in climate, as case. well as with some statements from design guidelines For purposes of comparison as well as for support in for comfortable low-energy homes considering the setting up the basic principle of the glazing surface's climate in Milan, Pagliano et al. (2007). Furthermore, impact on energy behaviour patterns, an analysis of the the obtained results show a relatively good coincidence classic single-panel prefabricated wall elements (Fig.1.) with the values for energy demand related to the was carried out, but only for the south orientation. The different glazing area sizes with different glazing types TFCL 2 with U =0.47 W/m K, as well as the two wall for the case study in Amman, Hassouneh et al. (2010), additional fictive wall elements TFCL 1 with U =0.70 wall 2 2 taking into account some differences in external air W/m K and TFCL 3 with U =0.30 W/m K were wall temperature and duration of solar radiation considered analyzed. The analyses of the sum total of heating and in the calculations. cooling demand presented in Fig.10. seem to be the The behaviour of energy demand patterns of the most interesting. TF 1, TF 2 and TF 3 systems for the west and east It is evident from the presented results that at higher directions are very similar, so that the patterns for the U-values of exterior wall elements the functional northern orientation show only the increase in energy optimum (lowest Q +Q value) disappears, the Q +Q h k h k demand. No noticeable decrease in energy demand, function curve passes from parabolic dependence in neither for Q or Q , appears for these orientations construction systems with extremely low U -values h k wall (N, W, E), therefore only the south direction, which is (TF 2 and TF 3) to linear dependence in construction 76 JAABE vol.11 no.1 May 2012 Vesna Žegarac Leskovar It is important for further approaches that in this case the results presented are almost equal for both construction systems. There are, however, some negligible differences evident at higher AGAW values, caused by a different thickness of wall elements which affects the fact that both systems have different total sizes of external wall area. Additionally, the authors also analysed three different massive panel systems (type KLH 1, KLH 2 and KLH 3) with different U - wall values. The complete analysis with the calculated results for energy demand for heating and cooling is Fig.10. Comparison of Energy Demand for Heating and Cooling as a Function of AGAW for the Southern Orientation of Selected presented in Žegarac Leskovar and Premrov (2011). TF Construction Systems The calculated results for optimal AGAW values of all analysed types of external wall elements are presented systems with high U -values (TFCL 1 – TFCL 3). wall in Table 2. The inclination of a function line presenting TFCL systems depends on the U -value. wall Table 2. Optimal Values of AGAW in a South Oriented External Wall Element for Selected Timber Construction Systems 4. Generalisation of the Problem on One Single Const ruc t . U AGAW wall optim. AGAW 2 optim. Independent Variable (U -value) system [W/m K] adjusted wall The main aim and scientific contribution of the TF 1 0.164 0.42 – 0.50 0.47 TF 2 0.137 0.41 0.41 pre se nt ed st udy i s i n de ve l opi ng a n i nnova t i ve TF 3 0.102 0.34 – 0.38 0.37 theoretical approach applicable for the architectural KLH 1 0.181 0.52 – 0.54 0.53 design of an optimal energy-efficient prefabricated KLH 2 0.148 0.41 – 0.46 0.43 timber house. In this way it is important to transform KLH 3 0.124 0.38 – 0.40 0.39 this complex energy related problem, dependent on systems ≥ 0.193 ≈ 0.80 0.80 the structural system, to only one single independent variable (U -value) which becomes the only variable wall Based on the presented results in Table 2. it is parameter to determine the optimal glazing area size now possible to analyse the relationship between the value (AGAW ) for all contemporary prefabricated opt optimal glazing size in south-oriented external wall timber construction systems. elements (AGAW ) related to Q +Q energy demand opt h k To set up the basic theory of the research on one and the thermal transmittance of the wall element single independent variable it is first necessary to (U ). The data presented in Fig.12. show the values wall observe and compare the energy demand behaviour of AGAW, at which the sum total of heating and for both, for the new macro-panel wall elements as cooling demand reaches the lowest value, dependant well as for the classic wall elements with single- on the U-value of the selected external wall element panel construction, where the thermal transmittance of as the only independent variable. It is evident that the the selected wall elements is fictively set at an equal optimum or the convergence of the function curves for value. In Fig.10. the authors present a comparison AGAW appear only in systems with a U -value ≤ opt wall of the energy demand Q +Q for TF 3 and TFCL 2a h k 0.193 W/m K. construction systems, where wall elements with an As the U -value is higher, the optimal share of wall equal U -value = 0.137 W/m K are analysed. The wall south oriented glazing size is also higher. Reaching U -value for TFCL 2a system is obtained by adding a wall the limiting U -value = 0.193 W/m K, the values wall fictive mineral wool insulation with a thickness of 220 for an optimal AGAW converge towards the maximal mm and λ = 0.04 W/mK to the single-panel TFCL 2 glazing surface. For the analysed construction systems wall element composition. Fig.11. Comparison of Energy Demand as a F unction of Fig.12. Optimal Values of AGAW in a South Oriented AGAW for Southern Orientation of Selected TF 3 and TFCL 2a External Wall Element as a Function of U -value for Timber wall Construction Systems with a Unique U -value=0.102 W/m K wall Construction Systems JAABE vol.11 no.1 May 2012 Vesna Žegarac Leskovar 77 2 with an U -value > 0.193 W/m K no optimum or References wall 1) ARSO (2010) Climate conditions in Slovenia, http://meteo. convergence for AGAW appears. 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Energy and Buildings oriented external walls improves the energy efficiency 38, pp.181-188. of the building. 13) Persson, ML., (2006b) Windows of Opportunities, The Glazed However, due to the relatively high price of such Area and its Impact on the Energy Balance of Buildings. PhD special three-layer glazing type, this might not be the Thesis, Uppsala Universitet. 14) Premrov, M. and Kuhta, M., (2009) Influence of Fasteners optimal solution from an economic point of view. Disposition on Behaviour of Timber-Framed Walls with Single In this way it is important to transform the energy Fibre-Plaster Sheathing Boards. Construction and Building problem on one single independent variable, the U - wall Materials 23 (7), pp.2688-2693. value, to generalize the theoretical findings, based on 15) Steadman, P. and Brown F. (1987) Estimating the exposed surface an analysis of the authors' base case study, to be valid area of the domestic stock, Energy and urban built form, 113-131, University of Cambridge. for the whole timber construction, regardless of the 16) Žegarac Leskovar, V. and Premrov, M. (2011) Impact of the construction system. According to the results presented proportion of glazing surface in south facade on energy efficiency in Fig.12., the determined function for the optimal of prefabricated timber buildings. Les Wood 63 (3), pp.56-65. south oriented glazing size (AGAW ) offers us the opt opportunity to select the optimal way of renovation with a possible combination of improving the thermal properties of the external walls with the installation of an additional layer of insulation (decreasing U-wall value) and the installation of the optimal glazing size in the south-oriented façade, which is in the case of a lower U -value noticeably lower. wall 78 JAABE vol.11 no.1 May 2012 Vesna Žegarac Leskovar
Journal
Journal of Asian Architecture and Building Engineering
– Taylor & Francis
Published: May 1, 2012
Keywords: timber; energy efficiency; glazing; modeling
