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Building envelope design with the objective to ensure thermal, visual and acoustic comfort conditions
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Building and Environment 39 (2004) 281 – 287 www.elsevier.com/locate/buildenv
Building envelope design with the objective to ensure thermal, visual and acoustic comfort conditions G'ul Ko)clar Oral, Alpin K'oknel Yener∗ , Nurg'un Tamer Bayazit Faculty of Architecture, Istanbul Technical University, Taskisla, Taksim, 34439, Turkey Received 15 November 2002; received in revised form 28 May 2003; accepted 9 June 2003
Abstract To ensure conditions of thermal, visual and acoustic comfort in rooms with a minimum of energy consumption is of great importance for the health of the user and the energy conservation. One of the most important functions of the building envelope is, therefore, to control physical environmental factors such as heat, light and sound in order to realise de7ned comfort conditions for the user with a minimum of energy consumption. The objective of the present work was to develop an approach, which would allow the construction of a building envelope with optimal performance with respect to thermal, visual and acoustic comfort conditions thereby taking properties of the building envelope such as function, position, dimensions and orientation into account. ? 2003 Published by Elsevier Ltd. Keywords: Thermal comfort; Visual comfort; Acoustic comfort; Energy conservation; Envelope design
1. Introduction The building envelope may be de7ned as the totality of (building) elements made up of components which separate the indoor environment of the building from the outdoor environment. The building envelope is designed with respect to various determinants such as environmental, technological, socio-cultural, functional or aesthetic factors (Fig. 1). When only predominant physical environmental factors among the environmental factors, such as heat, light and sound, are taken into account, the outcome will be a solution depending on thermal, visual and acoustic parameters. The main functions of the building envelope with respect to physical environmental factors (heat, light, sound) are to ensure: • thermal comfort by controlling the in?uence of climatic elements, • visual comfort by controlling the natural light, and • acoustic comfort by reducing the noise to an acceptable level. ∗
Corresponding author. Tel.: +90-212-2931300/2160. E-mail addresses: [email protected], [email protected] (A.K. Yener). 0360-1323/$ - see front matter ? 2003 Published by Elsevier Ltd. doi:10.1016/S0360-1323(03)00141-0
To ensure permanence of a healthy environment for the user, and optimal performance in his activities, the conditions in the indoor environment must be adjusted as to ensure the desired thermal, visual and acoustic conditions, in other words, the conditions of thermal, visual and acoustic comfort. The thermal, visual and acoustic comfort conditions are, therefore, the basis on which to design the rooms and to evaluate their performance. Evaluation of the performance of a given design consists in comparing the achieved conditions with the comfort conditions. If the comfort conditions have not been achieved, the values of the relevant parameters are to be changed during the design process in order to ensure a built environment whose design aEords conditions ensuring thermal, visual and acoustic comfort of the user. In the light of the energy problem, another objective must be the reduction of energy consumption and energy expenses, to a minimum. This requires a design of the building envelope as an element of a passive system with optimal performance in its control of heat, light and sound. Such a design of the building envelope will result in an increased performance of its passive system which in turn will reduce the load of the active systems. The aim of the present work was to develop the sequential steps of an approach which may serve to produce a choice of solutions
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G.K. Oral et al. / Building and Environment 39 (2004) 281 – 287
Socioculture
Function
Heat BUILT ENVIRONMENT
Technology
Physical Environment
Light
Sound Economy
Fig. 1. Parameters with an in?uence on the design of the building envelope.
for the control of the main parameters with an in?uence on the design of building envelopes in order to achieve optimal conditions.
a room or an element. The main design parameters related to the built environment with an in?uence on the control of heat, light and sound, as well as energy conservation are given below.
2. Parameters with an inuence on the envelope design
2.2.1. Design parameters on the settlement unit scale
Envelope design, which aims at ensuring comfort conditions and energy conservation in the room, is possible with the determination of an appropriate set of values for the design parameters with an in?uence on the arti7cial environment as a function of the external conditions. The parameters with an in?uence on the envelope design will be separated for further consideration into two groups: parameters related to the external environment, and design parameters related to the built environment. The main parameters of each group are given below.
• • • •
2.1. Parameters related to the outdoor environment The parameters of this group of natural factors have a determining in?uence on the outdoor environment. They are beyond the control of the designer and must be considered with their given values. These parameters are: • • • • • •
Outdoor air temperature. Solar radiation. Outdoor humidity. Outdoor wind velocity. Outdoor illumination level. Outdoor sound level.
2.2. Design parameters related to the built environment The built environment is de7ned as designed and constructed by man, and can be considered under diEerent criteria of scale. The parameters attributed to this group may be considered on the basis of a settlement unit, a building,
Dimensions and orientation of external obstacles. Solar radiation re?ectivity of surrounding surfaces. Light re?ectivity of surrounding surfaces. Soil cover, and nature of the ground (plant cover and groups of trees).
2.2.2. Design parameters on the building scale • Orientation of the building. • Position of the building relative to the noise source. • Position of the building according to the other buildings and to the noise source. • Building form. 2.2.3. Design parameters on the room scale • • • •
Position of the room within the building. Dimensions of the room and its shape factor. Orientation of the room. Absorption coeKcient of the room for solar radiation entering through the transparent component . • Sound absorption coeKcients of the surfaces inside the room. • Total sound absorption coeKcient of the room. • Light re?ection coeKcients of the surfaces inside the room. 2.2.4. Design parameters on the element scale The design parameters related to be structural elements can be diEerentiated in two groups—as opaque and
G.K. Oral et al. / Building and Environment 39 (2004) 281 – 287
transparent components—and considered separately:
283
Outdoor Conditions
(a) Properties of the opaque components of the building envelope • • • • • • • • • • • • •
Determination of room properties
Thickness of the materials. Density of the materials. Speci7c heat of the materials. Heat conduction coeKcients of the materials. Light absorption and re?ection coeKcients of the surfaces. Sound transmission coeKcient. Porosity and roughness of the surface. Sound absorption coeKcient of the surface. Construction of the surface (?at, with interstices, ribbed). Single or multilayer structure. Depth of the cavity between the layers. Thickness and sound absorption of the insulating material used inside the cavity. Kind of connection between layers of diEerent materials, and their number.
Determination of comfort conditions
Building Envelope Alternatives
Calculation of the indoor thermal conditions NO Comfort conditions met? YES Calculation of the indoor accoustic conditions NO Comfort conditions met? YES
(b) Properties of the transparent components of the building envelope • • • • • • • • •
Dimensions of the transparent component. Number of layers of the glazing. Heat transmission coeKcient of the glazing. Absorption, re?ection and transmission coeKcient of the glazing for solar radiation. Transmission coeKcient of the glazing for diEuse sunlight. Transmission coeKcient of the glazing for direct sunlight. Transmission coeKcient of the glazing for sound. Type of frame used for the transparent component. Maintenance factor of the glazing.
3. Proposed approach The steps of an approach which serves the purpose of producing a choice of solutions, of how to optimally control the main parameters mentioned above with an in?uence on the design of the building envelope, are given in Fig. 2. The approach is explained below. 3.1. Determination of the values related to the outdoor environment For the design of an envelope satisfying the comfort conditions in the room, the 7rst step is to determine the values of the parameters related to the outdoor environment, which have been speci7ed in Section 2.1. These values for the local environmental conditions can be obtained from geographic, meteorological and topographical data, with due considera-
Calculation of the indoor visual conditions NO Comfort conditions met? YES Appropriate envelope alternatives determined
Fig. 2. Design process of the building envelope with respect to heat, sound and light.
tion of the data specifying the position of the building within a particular settlement. 3.2. Determination of the values related to the built environment The values related to the built environment can be determined after the design decisions regarding the diEerent scales mentioned above have been taken. Whether comfort conditions for the activities, for which the volumes are designed, can be achieved, depends on the correct decisions taken on the diEerent scales of the construction project. Comfort conditions for a user in a speci7c room can be de7ned as a state of physiologically minimal energy consumption, environmental harmony, maximisation of user performance, and psychological satisfaction with the environment [1]. The thermal, visual and acoustic comfort conditions to be ensured in the rooms are explained separately below.
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G.K. Oral et al. / Building and Environment 39 (2004) 281 – 287
3.3. Determination of the required indoor conditions of the room—(comfort conditions) Determination of the required comfort conditions in the room will be dealt with in three separate paragraphs dedicated to thermal, visual, and acoustic comfort conditions, respectively. 3.3.1. Determination of thermal comfort conditions The parameters which determine the thermal comfort conditions of the room are indoor air temperature, inner surface temperatures, indoor humidity and air ?ow within the room. In architectural and engineering projects, the thermal comfort conditions are explained quantitatively for the most part on the basis of graphical systems given in international standards. The ASHRAE Standard 55-81 determines the desired indoor thermal conditions (thermal comfort conditions) of a room with respect to the rooms function, the properties of the user, and the activity level for which the room will be used. Another standard with international validity de7ning thermal comfort conditions is the ISO Comfort Standard [2,3]. 3.3.2. Determination of acoustic comfort conditions The acoustic comfort conditions in built environments can be determined with the aid of performance and functional criteria. As a measure of annoying sound level, the noise criterion curves known as noise criteria-NC, noise reduction-NR, perceived noise criteria-PNC and balanced noise criteria-NCB may be used as basic values. These curves described the background noise as a function of acoustic comfort. With respect to the function and usage of a given room, they specify the highest acceptable noise limit within the room for the entire audible frequency range [4,5]. 3.3.3. Determination of visual comfort conditions It is possible to provide visual comfort conditions in rooms by ensuring certain values and limits for the illumination level, luminance and by taking the in?uence of colours into account. The illumination levels required to ensure comfort conditions are determined in international investigations, and are published in guidelines, standards and regulations. The required level changes as a function of the activities in the room in question [6,7]. In order to achieve visual comfort, it is necessary to control the in?uence of luminance, and to adjust the glare index values determined for rooms with diEerent functions. Certain decisions have to be taken during the building design process to ensure that the limits for these values are not exceeded. The light re?ection coeKcients of all surfaces in our environment, which act as secondary light sources, and their associated colours are of great importance. For the rooms, colours must be chosen which conform to the light re?ection coeKcients proposed for ceiling, walls and ?ooring as a function of the use of the room.
3.4. Determination of the building envelope alternatives The envelope of the room is constructed of transparent and opaque components. For this reason, the properties of these components have been treated separately in this step of the procedure. The choice of transparent components is rather limited, therefore, the determination of the kind and properties of these components should be a priority in the envelope design process. 3.4.1. Determination of the transparent component properties The transparent component of the envelope has certain objectives, like maximisation of the daylight entrance, controlling the direct sunlight, minimising the heat gain during overheated period, providing glare control and view to the outdoor environment. These objectives are sometimes contradictory and their importance depends on parameters like, region, latitude, season, function and occupation time. This complexity requires a speci7c solution for each project. Window dimensions are generally given as transparency ratio, which equals to the ratio between the window area and the window wall area. The lower limit of the transparency ratio is to be accepted as 20% in order to satisfy the psychological human needs and visual communication with the surrounding environment [8]. The upper limit of this value depends on aspects such as heat conservation and noise control, as well as on structural properties of the room, its function and the arrangement of the settlement. The glazing type to be used for the windows is determined with respect to its transmission, absorption and re?ection for heat, light and sound, as well as aspects such as function, aesthetic impression and price, among others. Since the window frames are manufactured from diEerent materials with diEerent thicknesses, their speci7c construction has an in?uence on heat loss or conservation, on the amount of daylight and the noise level. With a market research of the available products with respect to their heat, light and sound transmission values, their thickness, structural properties, functionality, aesthetic appeal and price, a choice of appropriate windows can be determined. 3.4.2. Determination of the opaque component properties As a main determinant of the transmission of the physical factors, in order to design an opaque component alternative, decisions are taken with respect to. (a) the surface properties of the opaque elements (sound absorption coeKcient, construction, solar radiation absorption coeKcient, etc.), (b) the cross-section properties of the opaque elements (single or multiple layer, total mass, heat conduction coeKcients of the materials, etc.),
G.K. Oral et al. / Building and Environment 39 (2004) 281 – 287
285
(c) the properties of the diEerent components (door and window area, density, number of layers, total heat conduction coeKcient of the component, etc.), (d) the total weight of the opaque element, (e) the total stiEness factor of the opaque element.
The values for the indoor air and inner surface temperatures based on the approved choices are then to be compared with the values speci7ed in comfort standards. On the basis of this comparison appropriate choices with respect to thermal comfort will then be determined.
The optimal values of these parameters are the qualitative and quantitative framework for the building envelope design which ensures the comfort conditions with respect to heat, light and sound control, as well as the highest performance of the system as speci7ed in Section 3.3.
3.5.2. Calculation of the indoor acoustic conditions The opaque component is the most important element of the building envelope, which controls the penetration of physical environmental factors inside the building through walls or slabs. Most opaque components usually consist of several layers of diEerent material or an assemblage of two or more panels with diEerent transmission coeKcients. The sound transmission property of a panel is given by a quantity referred to as transmission loss—TL or sound reduction—R which de7nes as the loss in sound pressure levels occurs as the sound passes through the panel. The noise reduction— NR, between two space is primarily a function of the reduction of the panel which separates the noisy space from the critically sensitive space, the total area of the panel and the amount of the sound absorption present in the receiving room. The smaller the area of the panel and the greater the absorption in the receiving room, the greater the noise reduction [9]. For this reason, in order to determine the indoor acoustic conditions, the values of the noise reduction (sound level establishing inside the room) which are required for the envelope (NR req ), must be calculated with respect to the outdoor noise level in?uencing the envelope, the acceptable noise criteria levels to be ensured inside the room and the total sound absorption properties of the internal surfaces of the room. In order to determine whether the envelope has the required properties, the values for the actual sound reduction (Ract ) of the envelope must be calculated after
3.5. Calculation of the indoor conditions in the room and evaluation of the alternatives The indoor conditions of the room, which will be realised with the proposed alternatives, are calculated separately for the thermal, acoustic and visual conditions. 3.5.1. Calculation of the indoor thermal conditions The most important climatic elements, which determine heating energy conservation and the thermal comfort of the room, are the indoor air temperature and the inner surface temperatures (mean radiant temperatures). As long as the indoor air temperature and the inner surface temperatures stay within de7ned limits, the related humidity value and the indoor air ?ow are parameters with a secondary in?uence on the thermal comfort. Therefore, in order to evaluate whether the thermal comfort conditions have been achieved in the room, the indoor air and inner surface temperatures must be calculated with respect to the position, dimensions and the shape factor of the room, as well as its orientation, and the properties of the chosen transparent and opaque components (Fig. 3).
Regional climatic data
Determination of the room properties
Determination of the transparent component properties
Determination of the opaque component properties
Determination of the calculation period (the design day)
Calculations . Solar radiation on building service . Sol-air temperatures affecting outer surface of building . Heat loss and gain through opaque and transparent components . Inner surface temperatures (mean radiant temperature) . Indoor air temperatures
Determination of mean radiant temperature and indoor air temperature
Fig. 3. Calculation of the indoor thermal conditions caused by the proposed alternative.
286
G.K. Oral et al. / Building and Environment 39 (2004) 281 – 287 Determination of the calculation time of the day
Determination of the room properties
Outdoor noise level
Determination of the transparent component properties
Calculations . Sound transmission coefficient of transparent and opaque component . Average sound transmission coefficient of building envelope . Total sound absorptivity of the room . Total sound transmission loss value of building envelope
Determination of the opaque component properties
Determination of the noise reduction availability of the proposed envelope
Fig. 4. Calculation of the indoor sound levels caused by the proposed alternative.
Outdoor illumination level Outdoor obstructions Outdoor ground material
Determination of the room properties
Determination of the transparent component properties
Determination of the reference points for calculation related to the type of the activity
Calculations . Daylight availability . Daylight glare index
Determination of the daylight availability of the room with proposed envelope
Determination of the day of the year and time of the day for calculation related to the occupation time of the room
Fig. 5. Calculation of the indoor illumination level caused by the proposed alternative.
the sound reduction values and their related sound transmission coeKcients have been determined separately for the opaque and the transparent components of the envelope, separating the noisy area from the receiver room (Fig. 4). Comparison of the actual noise reduction (Ract ) with the required sound reduction values (NR req ) aEords the choices which are appropriate with respect to acoustic comfort, that is, all values Ract satisfying the condition Ract ¿ NR req . 3.5.3. Calculation of the indoor visual conditions Depending on the geographic and atmospheric properties of the region where the building is located, diEerent values for the outdoor illumination level will be found. The values of the illumination level establishing inside the room must be calculated taking properties such as orientation and dimensions of the room, window design and light re?ection coeKcients of the internal surfaces into account. The
main determining parameters in this calculation are the dimensions and light transmission properties of the transparent component. Daylight glare problems should be analysed, especially in sidelighting concepts, which allow direct sunlight into the rooms and provide a direct view of the sky simultaneously with the work surface (Fig. 5). The calculated indoor levels of illumination are then compared with the required levels of illumination to meet comfort conditions with respect to the function of the room in order to select the appropriate choices among the available range of alternatives. 3.6. Evaluation The evaluation process comprises a comparison of the calculated thermal, visual and acoustic indoor conditions, which are results of the considered alternatives from which
G.K. Oral et al. / Building and Environment 39 (2004) 281 – 287
to build the room envelope, with the required indoor conditions (comfort conditions). As a result of this comparison of the alternatives of combinations of transparent and opaque components among the range of choices, those which ensure thermal and acoustic comfort conditions are determined and can then be used as basis for those combinations which meet the visual comfort conditions. Among the remaining combinations an appropriate choice for the envelope is then made. If the evaluation leads to the conclusion that none of the envelope choices taken into consideration satis7es the desired indoor conditions, a decision must be taken on which parameters, with an in?uence on the built environment, are to be changed in order to ensure the comfort conditions in the indoor environment. This process is to be repeated until a suitable set of parameters are found. 4. Conclusion In the present work, the individual steps of an approach have been explained, which may be used in the design of building envelopes with optimal performance in ensuring thermal, visual and acoustic comfort conditions, as well as energy conservation. The evaluation of the diEerent envelope alternatives for appropriate choices is based on the criterion of “ensuring thermal, visual and acoustic comfort conditions”. In this paper the evaluation process is considered as a sub-process of the design procedure, which oEers the opportunity to evaluate a project before the actual construction process is initiated. Such an evaluation is important with respect to ensuring thermal, visual and acoustic comfort conditions of the arti7cial environment at the 7nal stage of the project, as well as the determination of the optimal values for the design parameters. If the evaluation process yields the result that the envelope surrounding the volume ensures the required indoor conditions, in other words, shows the required performance, the 7nal project may then be concluded and the application stage initiated.
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The optimisation of the performance of the building envelope controlling heat, light and sound should be achieved if standards and regulations are put into force, which take account of all aspects of the problem. Standards and regulations, which can be considered as inputs of the project should be improved to optimise the building envelope in order to provide the comfort conditions. With the aid of the proposed approach, an optimisation of physical environmental parameters with the aim of ensuring comfort conditions for the user, as well as the determination of envelope alternatives ensuring minimal energy consumption will be possible. If the building industry would follow such an approach, users would be ensured of comfort conditions in their indoor environment and energy consumption would be economised. With such an approach, the current negative 7nancial effect associated with the creation of comfort conditions in buildings on both the individual user and the national economy would be removed, and comfort conditions could be achieved with minimal cost with the right decisions taken as early as at the design stage. References [1] Berk'oz E, K'uc) u' kdo u M, et al. Energy eKcient housing and settlement ' TAK, NTAG 201, 1995 [in Turkish]. design. TUB [2] ASHRAE STANDARD 55-81. Thermal comfort conditions for human occupancy. Atlanta: American Society of Heating Refrigerating and Air Conditioning Engineers; 1981. [3] ISO Standard 7730. Moderate thermal environments. International Organization for Standardisation, 1983. [4] Beranek L. Balanced Noise-Criterion (NCB) curves. Journal of the Acoustical Society of America 1989;86(2):650–64. [5] Kurra S. Environmental noise control in built and environmental design: an example of Istanbul. ITU Faculty of Architecture; 1982 [in Turkish]. [6] CIE, Anon. CIE Publication, No. 29.2, Guide on interior lighting, 1986. [7] CIBSE, Code for interior lighting, 1994. [8] Lynes JA, Crisp VHC. A model of daylight availability for daylighting design. BRE, Dep. of. Env. PD143/79, BRS, Garston, 1979. [9] Mehta A, Johnson J, Rocafort J. Architectural acoustic, principle and design. Englewood CliEs, NJ: Prentice-Hall; 1999.
Building and Environment 39 (2004) 281 – 287 www.elsevier.com/locate/buildenv
Building envelope design with the objective to ensure thermal, visual and acoustic comfort conditions G'ul Ko)clar Oral, Alpin K'oknel Yener∗ , Nurg'un Tamer Bayazit Faculty of Architecture, Istanbul Technical University, Taskisla, Taksim, 34439, Turkey Received 15 November 2002; received in revised form 28 May 2003; accepted 9 June 2003
Abstract To ensure conditions of thermal, visual and acoustic comfort in rooms with a minimum of energy consumption is of great importance for the health of the user and the energy conservation. One of the most important functions of the building envelope is, therefore, to control physical environmental factors such as heat, light and sound in order to realise de7ned comfort conditions for the user with a minimum of energy consumption. The objective of the present work was to develop an approach, which would allow the construction of a building envelope with optimal performance with respect to thermal, visual and acoustic comfort conditions thereby taking properties of the building envelope such as function, position, dimensions and orientation into account. ? 2003 Published by Elsevier Ltd. Keywords: Thermal comfort; Visual comfort; Acoustic comfort; Energy conservation; Envelope design
1. Introduction The building envelope may be de7ned as the totality of (building) elements made up of components which separate the indoor environment of the building from the outdoor environment. The building envelope is designed with respect to various determinants such as environmental, technological, socio-cultural, functional or aesthetic factors (Fig. 1). When only predominant physical environmental factors among the environmental factors, such as heat, light and sound, are taken into account, the outcome will be a solution depending on thermal, visual and acoustic parameters. The main functions of the building envelope with respect to physical environmental factors (heat, light, sound) are to ensure: • thermal comfort by controlling the in?uence of climatic elements, • visual comfort by controlling the natural light, and • acoustic comfort by reducing the noise to an acceptable level. ∗
Corresponding author. Tel.: +90-212-2931300/2160. E-mail addresses: [email protected], [email protected] (A.K. Yener). 0360-1323/$ - see front matter ? 2003 Published by Elsevier Ltd. doi:10.1016/S0360-1323(03)00141-0
To ensure permanence of a healthy environment for the user, and optimal performance in his activities, the conditions in the indoor environment must be adjusted as to ensure the desired thermal, visual and acoustic conditions, in other words, the conditions of thermal, visual and acoustic comfort. The thermal, visual and acoustic comfort conditions are, therefore, the basis on which to design the rooms and to evaluate their performance. Evaluation of the performance of a given design consists in comparing the achieved conditions with the comfort conditions. If the comfort conditions have not been achieved, the values of the relevant parameters are to be changed during the design process in order to ensure a built environment whose design aEords conditions ensuring thermal, visual and acoustic comfort of the user. In the light of the energy problem, another objective must be the reduction of energy consumption and energy expenses, to a minimum. This requires a design of the building envelope as an element of a passive system with optimal performance in its control of heat, light and sound. Such a design of the building envelope will result in an increased performance of its passive system which in turn will reduce the load of the active systems. The aim of the present work was to develop the sequential steps of an approach which may serve to produce a choice of solutions
282
G.K. Oral et al. / Building and Environment 39 (2004) 281 – 287
Socioculture
Function
Heat BUILT ENVIRONMENT
Technology
Physical Environment
Light
Sound Economy
Fig. 1. Parameters with an in?uence on the design of the building envelope.
for the control of the main parameters with an in?uence on the design of building envelopes in order to achieve optimal conditions.
a room or an element. The main design parameters related to the built environment with an in?uence on the control of heat, light and sound, as well as energy conservation are given below.
2. Parameters with an inuence on the envelope design
2.2.1. Design parameters on the settlement unit scale
Envelope design, which aims at ensuring comfort conditions and energy conservation in the room, is possible with the determination of an appropriate set of values for the design parameters with an in?uence on the arti7cial environment as a function of the external conditions. The parameters with an in?uence on the envelope design will be separated for further consideration into two groups: parameters related to the external environment, and design parameters related to the built environment. The main parameters of each group are given below.
• • • •
2.1. Parameters related to the outdoor environment The parameters of this group of natural factors have a determining in?uence on the outdoor environment. They are beyond the control of the designer and must be considered with their given values. These parameters are: • • • • • •
Outdoor air temperature. Solar radiation. Outdoor humidity. Outdoor wind velocity. Outdoor illumination level. Outdoor sound level.
2.2. Design parameters related to the built environment The built environment is de7ned as designed and constructed by man, and can be considered under diEerent criteria of scale. The parameters attributed to this group may be considered on the basis of a settlement unit, a building,
Dimensions and orientation of external obstacles. Solar radiation re?ectivity of surrounding surfaces. Light re?ectivity of surrounding surfaces. Soil cover, and nature of the ground (plant cover and groups of trees).
2.2.2. Design parameters on the building scale • Orientation of the building. • Position of the building relative to the noise source. • Position of the building according to the other buildings and to the noise source. • Building form. 2.2.3. Design parameters on the room scale • • • •
Position of the room within the building. Dimensions of the room and its shape factor. Orientation of the room. Absorption coeKcient of the room for solar radiation entering through the transparent component . • Sound absorption coeKcients of the surfaces inside the room. • Total sound absorption coeKcient of the room. • Light re?ection coeKcients of the surfaces inside the room. 2.2.4. Design parameters on the element scale The design parameters related to be structural elements can be diEerentiated in two groups—as opaque and
G.K. Oral et al. / Building and Environment 39 (2004) 281 – 287
transparent components—and considered separately:
283
Outdoor Conditions
(a) Properties of the opaque components of the building envelope • • • • • • • • • • • • •
Determination of room properties
Thickness of the materials. Density of the materials. Speci7c heat of the materials. Heat conduction coeKcients of the materials. Light absorption and re?ection coeKcients of the surfaces. Sound transmission coeKcient. Porosity and roughness of the surface. Sound absorption coeKcient of the surface. Construction of the surface (?at, with interstices, ribbed). Single or multilayer structure. Depth of the cavity between the layers. Thickness and sound absorption of the insulating material used inside the cavity. Kind of connection between layers of diEerent materials, and their number.
Determination of comfort conditions
Building Envelope Alternatives
Calculation of the indoor thermal conditions NO Comfort conditions met? YES Calculation of the indoor accoustic conditions NO Comfort conditions met? YES
(b) Properties of the transparent components of the building envelope • • • • • • • • •
Dimensions of the transparent component. Number of layers of the glazing. Heat transmission coeKcient of the glazing. Absorption, re?ection and transmission coeKcient of the glazing for solar radiation. Transmission coeKcient of the glazing for diEuse sunlight. Transmission coeKcient of the glazing for direct sunlight. Transmission coeKcient of the glazing for sound. Type of frame used for the transparent component. Maintenance factor of the glazing.
3. Proposed approach The steps of an approach which serves the purpose of producing a choice of solutions, of how to optimally control the main parameters mentioned above with an in?uence on the design of the building envelope, are given in Fig. 2. The approach is explained below. 3.1. Determination of the values related to the outdoor environment For the design of an envelope satisfying the comfort conditions in the room, the 7rst step is to determine the values of the parameters related to the outdoor environment, which have been speci7ed in Section 2.1. These values for the local environmental conditions can be obtained from geographic, meteorological and topographical data, with due considera-
Calculation of the indoor visual conditions NO Comfort conditions met? YES Appropriate envelope alternatives determined
Fig. 2. Design process of the building envelope with respect to heat, sound and light.
tion of the data specifying the position of the building within a particular settlement. 3.2. Determination of the values related to the built environment The values related to the built environment can be determined after the design decisions regarding the diEerent scales mentioned above have been taken. Whether comfort conditions for the activities, for which the volumes are designed, can be achieved, depends on the correct decisions taken on the diEerent scales of the construction project. Comfort conditions for a user in a speci7c room can be de7ned as a state of physiologically minimal energy consumption, environmental harmony, maximisation of user performance, and psychological satisfaction with the environment [1]. The thermal, visual and acoustic comfort conditions to be ensured in the rooms are explained separately below.
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G.K. Oral et al. / Building and Environment 39 (2004) 281 – 287
3.3. Determination of the required indoor conditions of the room—(comfort conditions) Determination of the required comfort conditions in the room will be dealt with in three separate paragraphs dedicated to thermal, visual, and acoustic comfort conditions, respectively. 3.3.1. Determination of thermal comfort conditions The parameters which determine the thermal comfort conditions of the room are indoor air temperature, inner surface temperatures, indoor humidity and air ?ow within the room. In architectural and engineering projects, the thermal comfort conditions are explained quantitatively for the most part on the basis of graphical systems given in international standards. The ASHRAE Standard 55-81 determines the desired indoor thermal conditions (thermal comfort conditions) of a room with respect to the rooms function, the properties of the user, and the activity level for which the room will be used. Another standard with international validity de7ning thermal comfort conditions is the ISO Comfort Standard [2,3]. 3.3.2. Determination of acoustic comfort conditions The acoustic comfort conditions in built environments can be determined with the aid of performance and functional criteria. As a measure of annoying sound level, the noise criterion curves known as noise criteria-NC, noise reduction-NR, perceived noise criteria-PNC and balanced noise criteria-NCB may be used as basic values. These curves described the background noise as a function of acoustic comfort. With respect to the function and usage of a given room, they specify the highest acceptable noise limit within the room for the entire audible frequency range [4,5]. 3.3.3. Determination of visual comfort conditions It is possible to provide visual comfort conditions in rooms by ensuring certain values and limits for the illumination level, luminance and by taking the in?uence of colours into account. The illumination levels required to ensure comfort conditions are determined in international investigations, and are published in guidelines, standards and regulations. The required level changes as a function of the activities in the room in question [6,7]. In order to achieve visual comfort, it is necessary to control the in?uence of luminance, and to adjust the glare index values determined for rooms with diEerent functions. Certain decisions have to be taken during the building design process to ensure that the limits for these values are not exceeded. The light re?ection coeKcients of all surfaces in our environment, which act as secondary light sources, and their associated colours are of great importance. For the rooms, colours must be chosen which conform to the light re?ection coeKcients proposed for ceiling, walls and ?ooring as a function of the use of the room.
3.4. Determination of the building envelope alternatives The envelope of the room is constructed of transparent and opaque components. For this reason, the properties of these components have been treated separately in this step of the procedure. The choice of transparent components is rather limited, therefore, the determination of the kind and properties of these components should be a priority in the envelope design process. 3.4.1. Determination of the transparent component properties The transparent component of the envelope has certain objectives, like maximisation of the daylight entrance, controlling the direct sunlight, minimising the heat gain during overheated period, providing glare control and view to the outdoor environment. These objectives are sometimes contradictory and their importance depends on parameters like, region, latitude, season, function and occupation time. This complexity requires a speci7c solution for each project. Window dimensions are generally given as transparency ratio, which equals to the ratio between the window area and the window wall area. The lower limit of the transparency ratio is to be accepted as 20% in order to satisfy the psychological human needs and visual communication with the surrounding environment [8]. The upper limit of this value depends on aspects such as heat conservation and noise control, as well as on structural properties of the room, its function and the arrangement of the settlement. The glazing type to be used for the windows is determined with respect to its transmission, absorption and re?ection for heat, light and sound, as well as aspects such as function, aesthetic impression and price, among others. Since the window frames are manufactured from diEerent materials with diEerent thicknesses, their speci7c construction has an in?uence on heat loss or conservation, on the amount of daylight and the noise level. With a market research of the available products with respect to their heat, light and sound transmission values, their thickness, structural properties, functionality, aesthetic appeal and price, a choice of appropriate windows can be determined. 3.4.2. Determination of the opaque component properties As a main determinant of the transmission of the physical factors, in order to design an opaque component alternative, decisions are taken with respect to. (a) the surface properties of the opaque elements (sound absorption coeKcient, construction, solar radiation absorption coeKcient, etc.), (b) the cross-section properties of the opaque elements (single or multiple layer, total mass, heat conduction coeKcients of the materials, etc.),
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(c) the properties of the diEerent components (door and window area, density, number of layers, total heat conduction coeKcient of the component, etc.), (d) the total weight of the opaque element, (e) the total stiEness factor of the opaque element.
The values for the indoor air and inner surface temperatures based on the approved choices are then to be compared with the values speci7ed in comfort standards. On the basis of this comparison appropriate choices with respect to thermal comfort will then be determined.
The optimal values of these parameters are the qualitative and quantitative framework for the building envelope design which ensures the comfort conditions with respect to heat, light and sound control, as well as the highest performance of the system as speci7ed in Section 3.3.
3.5.2. Calculation of the indoor acoustic conditions The opaque component is the most important element of the building envelope, which controls the penetration of physical environmental factors inside the building through walls or slabs. Most opaque components usually consist of several layers of diEerent material or an assemblage of two or more panels with diEerent transmission coeKcients. The sound transmission property of a panel is given by a quantity referred to as transmission loss—TL or sound reduction—R which de7nes as the loss in sound pressure levels occurs as the sound passes through the panel. The noise reduction— NR, between two space is primarily a function of the reduction of the panel which separates the noisy space from the critically sensitive space, the total area of the panel and the amount of the sound absorption present in the receiving room. The smaller the area of the panel and the greater the absorption in the receiving room, the greater the noise reduction [9]. For this reason, in order to determine the indoor acoustic conditions, the values of the noise reduction (sound level establishing inside the room) which are required for the envelope (NR req ), must be calculated with respect to the outdoor noise level in?uencing the envelope, the acceptable noise criteria levels to be ensured inside the room and the total sound absorption properties of the internal surfaces of the room. In order to determine whether the envelope has the required properties, the values for the actual sound reduction (Ract ) of the envelope must be calculated after
3.5. Calculation of the indoor conditions in the room and evaluation of the alternatives The indoor conditions of the room, which will be realised with the proposed alternatives, are calculated separately for the thermal, acoustic and visual conditions. 3.5.1. Calculation of the indoor thermal conditions The most important climatic elements, which determine heating energy conservation and the thermal comfort of the room, are the indoor air temperature and the inner surface temperatures (mean radiant temperatures). As long as the indoor air temperature and the inner surface temperatures stay within de7ned limits, the related humidity value and the indoor air ?ow are parameters with a secondary in?uence on the thermal comfort. Therefore, in order to evaluate whether the thermal comfort conditions have been achieved in the room, the indoor air and inner surface temperatures must be calculated with respect to the position, dimensions and the shape factor of the room, as well as its orientation, and the properties of the chosen transparent and opaque components (Fig. 3).
Regional climatic data
Determination of the room properties
Determination of the transparent component properties
Determination of the opaque component properties
Determination of the calculation period (the design day)
Calculations . Solar radiation on building service . Sol-air temperatures affecting outer surface of building . Heat loss and gain through opaque and transparent components . Inner surface temperatures (mean radiant temperature) . Indoor air temperatures
Determination of mean radiant temperature and indoor air temperature
Fig. 3. Calculation of the indoor thermal conditions caused by the proposed alternative.
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G.K. Oral et al. / Building and Environment 39 (2004) 281 – 287 Determination of the calculation time of the day
Determination of the room properties
Outdoor noise level
Determination of the transparent component properties
Calculations . Sound transmission coefficient of transparent and opaque component . Average sound transmission coefficient of building envelope . Total sound absorptivity of the room . Total sound transmission loss value of building envelope
Determination of the opaque component properties
Determination of the noise reduction availability of the proposed envelope
Fig. 4. Calculation of the indoor sound levels caused by the proposed alternative.
Outdoor illumination level Outdoor obstructions Outdoor ground material
Determination of the room properties
Determination of the transparent component properties
Determination of the reference points for calculation related to the type of the activity
Calculations . Daylight availability . Daylight glare index
Determination of the daylight availability of the room with proposed envelope
Determination of the day of the year and time of the day for calculation related to the occupation time of the room
Fig. 5. Calculation of the indoor illumination level caused by the proposed alternative.
the sound reduction values and their related sound transmission coeKcients have been determined separately for the opaque and the transparent components of the envelope, separating the noisy area from the receiver room (Fig. 4). Comparison of the actual noise reduction (Ract ) with the required sound reduction values (NR req ) aEords the choices which are appropriate with respect to acoustic comfort, that is, all values Ract satisfying the condition Ract ¿ NR req . 3.5.3. Calculation of the indoor visual conditions Depending on the geographic and atmospheric properties of the region where the building is located, diEerent values for the outdoor illumination level will be found. The values of the illumination level establishing inside the room must be calculated taking properties such as orientation and dimensions of the room, window design and light re?ection coeKcients of the internal surfaces into account. The
main determining parameters in this calculation are the dimensions and light transmission properties of the transparent component. Daylight glare problems should be analysed, especially in sidelighting concepts, which allow direct sunlight into the rooms and provide a direct view of the sky simultaneously with the work surface (Fig. 5). The calculated indoor levels of illumination are then compared with the required levels of illumination to meet comfort conditions with respect to the function of the room in order to select the appropriate choices among the available range of alternatives. 3.6. Evaluation The evaluation process comprises a comparison of the calculated thermal, visual and acoustic indoor conditions, which are results of the considered alternatives from which
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to build the room envelope, with the required indoor conditions (comfort conditions). As a result of this comparison of the alternatives of combinations of transparent and opaque components among the range of choices, those which ensure thermal and acoustic comfort conditions are determined and can then be used as basis for those combinations which meet the visual comfort conditions. Among the remaining combinations an appropriate choice for the envelope is then made. If the evaluation leads to the conclusion that none of the envelope choices taken into consideration satis7es the desired indoor conditions, a decision must be taken on which parameters, with an in?uence on the built environment, are to be changed in order to ensure the comfort conditions in the indoor environment. This process is to be repeated until a suitable set of parameters are found. 4. Conclusion In the present work, the individual steps of an approach have been explained, which may be used in the design of building envelopes with optimal performance in ensuring thermal, visual and acoustic comfort conditions, as well as energy conservation. The evaluation of the diEerent envelope alternatives for appropriate choices is based on the criterion of “ensuring thermal, visual and acoustic comfort conditions”. In this paper the evaluation process is considered as a sub-process of the design procedure, which oEers the opportunity to evaluate a project before the actual construction process is initiated. Such an evaluation is important with respect to ensuring thermal, visual and acoustic comfort conditions of the arti7cial environment at the 7nal stage of the project, as well as the determination of the optimal values for the design parameters. If the evaluation process yields the result that the envelope surrounding the volume ensures the required indoor conditions, in other words, shows the required performance, the 7nal project may then be concluded and the application stage initiated.
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The optimisation of the performance of the building envelope controlling heat, light and sound should be achieved if standards and regulations are put into force, which take account of all aspects of the problem. Standards and regulations, which can be considered as inputs of the project should be improved to optimise the building envelope in order to provide the comfort conditions. With the aid of the proposed approach, an optimisation of physical environmental parameters with the aim of ensuring comfort conditions for the user, as well as the determination of envelope alternatives ensuring minimal energy consumption will be possible. If the building industry would follow such an approach, users would be ensured of comfort conditions in their indoor environment and energy consumption would be economised. With such an approach, the current negative 7nancial effect associated with the creation of comfort conditions in buildings on both the individual user and the national economy would be removed, and comfort conditions could be achieved with minimal cost with the right decisions taken as early as at the design stage. References [1] Berk'oz E, K'uc) u' kdo u M, et al. Energy eKcient housing and settlement ' TAK, NTAG 201, 1995 [in Turkish]. design. TUB [2] ASHRAE STANDARD 55-81. Thermal comfort conditions for human occupancy. Atlanta: American Society of Heating Refrigerating and Air Conditioning Engineers; 1981. [3] ISO Standard 7730. Moderate thermal environments. International Organization for Standardisation, 1983. [4] Beranek L. Balanced Noise-Criterion (NCB) curves. Journal of the Acoustical Society of America 1989;86(2):650–64. [5] Kurra S. Environmental noise control in built and environmental design: an example of Istanbul. ITU Faculty of Architecture; 1982 [in Turkish]. [6] CIE, Anon. CIE Publication, No. 29.2, Guide on interior lighting, 1986. [7] CIBSE, Code for interior lighting, 1994. [8] Lynes JA, Crisp VHC. A model of daylight availability for daylighting design. BRE, Dep. of. Env. PD143/79, BRS, Garston, 1979. [9] Mehta A, Johnson J, Rocafort J. Architectural acoustic, principle and design. Englewood CliEs, NJ: Prentice-Hall; 1999.