Morphological characterization of indigenous goats in the region of laghouat in algeria

peer reviewe

Natural convection heat transfer within multi-layer domes

Domes have become increasingly popular in modern building designs. Glazed domes are used to bring daylight and solar heat into the indoor space. For domes with multiple spaced layers of glazings, there is little information available on natural convection heat transfer within these layers. This information is required for the evaluation of the dome thermal performance (e.g., the U-factor). This paper presents a numerical study on heat transfer by laminar natural convection within multi-layer domes with uniform spacing heated from the outside. The flow and temperature fields within the domed enclosure were obtained using the control volume approach combined with the fully implicit scheme. Correlations for the heat transfer as a function of the dome shape and the gap spacing between the layers were developed under steady state conditions. The results showed that the convection heat transfer for fully hemispheric domes (half of spheres) may reach more than 13% higher than that for low profile domes (hemispherical caps) for small gap spacings (gap spacing-to-radius ratio. The critical gap spacing that yields the maximum heat transfer was quantified for each dome shape.Peer reviewed: YesNRC publication: Ye

Comparison between computed and field measured thermal parameters in an atrium building

This paper presents a comparison study between simulation and filed measurements of thermal parameters of an atrium building in Ottawa, Canada. The selected atrium was an enclosed three-storey building with a pyramidal skylight. Thc atrium was fully conditioned and has open corridors at each storey connecting it to adjacent spaces. The atrium space was used for circulation and reception while adjacent spaces are offices and meeting rooms. The atrium was monitored in June 1995 and in December 1995 to consider extreme conditions of the outdoor climate. The simulation results were obtained using ESP-r computer program. The comparison included those af predicted and measured solar radiation entering the atrium space at the rooftop, and predicted and measured indoor temperatures of the atrium floors. Results for the solar radiation showed good agreement between the measured and predicted values. When the mechanical system was turned off, the predicted temperatures were within + 2oC of the measured temperatures in winter. In summer, however, the predicted temperatures were 2-3oC higher than the measured temperatures.Peer reviewed: YesNRC publication: Ye

Transparent domed skylights: optical model for predicting transmittance, absorptance and reflectance

Daylighting and thermal loads are very important design issues for skylight design, especially in large spaces such as atria. However, the trade-off between daylighting and thermal performance of skylights hasbeen difficult to solve, due to a lack of daylighting and thermal design tools. A mathematical model was developed to predict the visible/solar transmittance, absorptance and reflectance of multi-glazed domedskylights for both direct and diffuse radiation. The model is based on tracking the beam and diffuse radiation transmission through the dome surface. Since all building-energy simulation and fenestration-rating toolsare limited to planar skylights, the model was translated into a simple method where domed skylights were substituted by optically equivalent planar skylights. The results showed that domed skylights yield slightlylower visible/solar transmittance at low sun zenith angles and substantially higher visible/solar transmittance at high sun zenith angles, or near the horizon than planar skylights having the same aperture. Absorptance ofdomed skylights is higher than that of planar skylights, particularly at high sun zenith angles, or near the horizon. The model was also compared to the IESNA transmittance calculation procedure for domed skylights and to the Wilkinson model. IESNA transmittance calculation procedure overestimates by 19% the transmittance of a dome at low sun zenith angles and significantly underestimates the transmittance of a dome at high sun zenith angles, or near the horizon. However, the Wilkinson model significantly underestimates the transmittance of a dome for both low or high sun zenith angles.L'\ue9clairage naturel et les charges thermiques sont des \ue9l\ue9ments tr\ue8s importants de la conception des puits de lumi\ue8re, en particulier dans les grands espaces tels que les atriums. Il a toutefois \ue9t\ue9 difficile d'en arriver \ue0 un compromis entre l'\ue9clairage naturel et la performance thermique des puits de lumi\ue8re en raison de l'absence d'outils de conception d'\ue9clairage naturel et de conception thermique. On a d\ue9velopp\ue9 un mod\ue8le math\ue9matique de pr\ue9vision des coefficients de transmission, d'absorption et de r\ue9flexion du rayonnement solaire/visible des coupoles d'\ue9clairage \ue0 vitres multiples, tant dans le cas d'un rayonnement direct que dans celui d'un rayonnement diffus. Le mod\ue8le est fond\ue9 sur le suivi du faisceau et de la transmission du rayonnement diffus \ue0 travers la surface de la coupole. Comme tous les syst\ue8mes de simulation \ue9nerg\ue9tique de b\ue2timent ou d'\ue9valuation de fen\ueatrage sont restreints aux puits de lumi\ue8re plans, on a converti le mod\ue8le en une m\ue9thode simple dans laquelle les coupoles d'\ue9clairage \ue9taient remplac\ue9es par des puits de lumi\ue8re plans et \ue9quivalents sur le plan optique. Les r\ue9sultats ont d\ue9montr\ue9 que les coupoles d'\ue9clairage ont un coefficient de transmission du rayonnement solaire/visible l\ue9g\ue8rement plus faible lorsque l'angle z\ue9nithal du soleil est faible, et substantiellement plus \ue9lev\ue9 lorsque l'angle z\ue9nithal est \ue9lev\ue9, ou que le soleil est pr\ue8s de l'horizon, que celui des puits de lumi\ue8re plans ayant la m\ueame ouverture. Le coefficient d'absorption des coupoles d'\ue9clairage est plus \ue9lev\ue9 que celui des puits de lumi\ue8re plans, particuli\ue8rement lorsque l'angle z\ue9nithal du soleil est \ue9lev\ue9 ou que l'astre est pr\ue8s de l'horizon. On a \ue9galement compar\ue9 le mod\ue8le \ue0 la m\ue9thode de calcul du coefficient de transmission utilis\ue9e par l'IESNA pour les coupoles d'\ue9clairage, de m\ueame qu'au mod\ue8le Wilkinson. La m\ue9thode de calcul de l'IESNA surestime de 19 % le coefficient de transmission d'une coupole lorsque l'angle z\ue9nithal du soleil est faible et le sous-estime de fa\ue7on significative lorsque l'angle z\ue9nithal du soleil est \ue9lev\ue9 ou que l'astre est pr\ue8s de l'horizon. Cependant, le mod\ue8le Wilkinson sous-estime de fa\ue7on importante le coefficient en question, que l'angle z\ue9nithal du soleil soit faible ou \ue9lev\ue9.Peer reviewed: YesNRC publication: Ye

Daylight availability in top-lit atria: prediction of skylight transmittance and daylight factor

Atrium and skylight shapes are important architectural design elements. Atrium and skylight shapes influence daylight availability within the space and, therefore, lighting energy consumption. There is a lack of prediction models for skylight transmittance and daylight availability in atriums. A new concept was developed to predict the diffuse transmittance of skylights. A skylight shape is converted into a representative shape through a shape parameter. Generic formulae for the skylight diffuse transmittance were developed under different sky conditions. A zonal model combined with the flux transfer method was developed to predict daylight availability in top-lit atriums through the prediction of the average Daylight Factor at the atrium floor and ceiling (non-glazed portion of the roof), and the local DF normal to walls. The developed DF model was compared with currently available models derived from theory and experiments under artificial skies. The results showed that the computed diffuse transmittance for translucent skylights under real pertly-cloudy or clear skies may reach up to 33% in summer and 56% in winter higher than that under CIE overcast skies. The developed zonal model yielded very close results to the models based on the finite-element method. However, models based on physical scale measurements lack general consensus among themselves, and may produce average DF values at floor level up to 45% higher than those produced by the zonal model. Physical scale models may also yield local DF values normal to walls up to 50% lower than those predicted by the zonal model.La forme d'un atrium ou d'un puits de lumi\ue8re est un \ue9l\ue9ment important de la conception architecturale. Elle influence la disponibilit\ue9 de la lumi\ue8re naturelle dans le local et, donc, la consommation d'\ue9nergie li\ue9e \ue0 l'\ue9clairage. On manque de mod\ue8les servant \ue0 pr\ue9voir la transmittance des puits de lumi\ue8re et la disponibilit\ue9 de la lumi\ue8re naturelle dans les atriums. On a mis au point un nouveau concept servant \ue0 pr\ue9voir la transmittance diffuse des puits de lumi\ue8re. Pour ce faire, on convertit une forme de puits de lumi\ue8re en une forme repr\ue9sentative au moyen d'un param\ue8tre de forme. On a \ue9labor\ue9 des formules g\ue9n\ue9riques servant \ue0 calculer la transmittance diffuse d'un puits de lumi\ue8re selon diff\ue9rents \ue9tats du ciel. On a mis au point un mod\ue8le zonal qui, alli\ue9 \ue0 la m\ue9thode de transfert de flux, permet de pr\ue9voir la quantit\ue9 de lumi\ue8re naturelle disponible dans un atrium \ue9clair\ue9 par dessus, gr\ue2ce \ue0 la pr\ue9vision du coefficient d'\ue9clairage diurne (c. \ue9. d.) au niveau du plancher et du plafond de l'atrium (partie non vitr\ue9e du toit), et du c. \ue9. d. local perpendiculairement aux murs. On a compar\ue9 le mod\ue8le de c. \ue9. d. mis au point avec les mod\ue8les actuellement disponibles, qui sont d\ue9riv\ue9s de la th\ue9orie et d'exp\ue9riences conduites sous des ciels artificiels. Les r\ue9sultats obtenus ont d\ue9montr\ue9 que la transmittance diffuse d'un puits de lumi\ue8re translucide calcul\ue9e sous un ciel partiellement nuageux ou clair peut \ueatre jusqu'\ue0 33 % plus \ue9lev\ue9e l'\ue9t\ue9 et 56 % plus \ue9lev\ue9e l'hiver que celle sous un ciel couvert selon les crit\ue8res de la CIE. Le mod\ue8le zonal mis au point a donn\ue9 des r\ue9sultats tr\ue8s proches de ceux obtenus \ue0 l'aide des mod\ue8les fond\ue9s sur la m\ue9thode des \ue9l\ue9ments finis. Cependant, les mod\ue8les fond\ue9s sur des mesures \ue0 \ue9chelle physique n'ont pu parvenir \ue0 un consensus et les valeurs de c. \ue9. d. moyennes obtenues au niveau du sol \ue0 l'aide de ces mod\ue8les peuvent \ueatre jusqu'\ue0 45 % plus \ue9lev\ue9es que celles produites par le mod\ue8le zonal. Les mod\ue8les \ue0 \ue9chelle physique peuvent \ue9galement donner des valeurs de c. \ue9. d. locales perpendiculairement aux murs qui sont jusqu'\ue0 50 % plus basses que celles pr\ue9dites par le mod\ue8le zonal.Peer reviewed: YesNRC publication: Ye

Prediction model of optical characteristics for domed skylights under standard and real sky conditions

This paper presents analytical models developed to predict the overall optical characteristics of domed skylights under direct and diffuse light subject to different sky conditions. The specific objectives were to: 1) predict the overall optical characteristics (transmittance, absorptance and reflectance) of domed skylights under direct beam and diffuse light; and 2) compare the overall optical characteristics under standard sky (luminance-based) conditions with those under real (illuminance-based) sky conditions. The models are based on a ray-tracing technique, and can handle domed skylights of different shapes with transparent or translucent glazing.Ce document pr\ue9sente des mod\ue8les analytiques que l'on a mis au point dans le but de pr\ue9dire les caract\ue9ristiques optiques globales de lanterneaux \ue0 d\uf4me sous lumi\ue8re directe et lumi\ue8re diffuse, suivant diverses conditions de ciel. Les objectifs sp\ue9cifique \ue9taient : 1) la pr\ue9diction des caract\ue9ristiques optiques globales (transmittance, coefficient d'absorption et facteur de r\ue9flexion) des lanterneaux \ue0 d\uf4me sous faisceau de lumi\ue8re directe et lumi\ue8re diffuse; et 2) la comparaison des caract\ue9ristiques optiques globales en conditions de ciel standard (fond\ue9es sur la luminance) avec celles en conditions de ciel dites r\ue9elles (fond\ue9es sur l'\ue9clairement). Les mod\ue8les s'appuient sur une technique de lancer de rayon et admettent des lanterneaux \ue0 d\uf4me de diff\ue9rentes formes, avec vitrage transparent ou translucide.Peer reviewed: YesNRC publication: Ye

Predicting optical and thermal characteristics of transparent single-glazed domed skylights

Optical and thermal characteristics of domed skylights are important to solve the trade-off between daylighting and thermal design. However, there is a lack of daylighting and thermal design tools for domed skylights. Optical and thermal characteristics of transparent single-glazed hemispherical domed skylights under sun and sky light are evaluated based on an optical model for domed skylights. The optical model is based on tracking the beam and diffuse radiation transmission through the dome surface. A simple method is proposed to replace single-glazed hemispherical domed skylights by optically and thermally equivalent single-glazed planar skylights to accommodate limitations of energy computer programs. Under sunlight, single-glazed hemispherical domed skylights yield slightly lower equivalent solar transmittance and solar heat gain coefficient (SHGC) at near normal zenith angles than those of single-glazed planar skylights. However, single-glazed hemispherical domed skylights yield substantially higher equivalent solar transmittance and SHGC at high zenith angles and around the horizon. Under isotropic skylight, single-glazed hemispherical domed skylights yield slightly lower equivalent solar transmittance and SHGC than those of single-glazed planar skylights. Daily solar heat gains of single-glazed hemispherical domed skylights are higher than those of single-glazed horizontal planar skylights in both winter and summer season. In summer, the solar heat gain of single-glazed hemispherical domed skylights can reach 3% to 9% higher than those of horizontal single-glazed planar skylights for latitudes varying between 0o and 55o (north/south). In winter, however, the solar heat gains of single-glazed hemispherical domed skylights increase significantly with the increase of the site latitude, and can reach 232% higher than those of horizontal single-glazed planar skylights, particularly for high latitude countries.Les caract\ue9ristiques optiques et thermiques des coupoles d'\ue9clairage jouent un r\uf4le important dans la d\ue9termination du compromis entre l'\ue9clairage naturel et la protection thermique. On manque cependant d'outils de conception de l'\ue9clairage naturel et de conception thermique pour les coupoles d'\ue9clairage. Les caract\ue9ristiques optiques et thermiques des coupoles d'\ue9clairage h\ue9misph\ue9riques \ue0 vitrage simple transparent sous la lumi\ue8re du soleil ou du ciel sont \ue9valu\ue9es en fonction d'un mod\ue8le optique de coupole. Celui-ci est fond\ue9 sur le suivi de la transmission du faisceau et du rayonnement diffus \ue0 travers la surface de la coupole. On propose une m\ue9thode simple qui consiste \ue0 remplacer les coupoles d'\ue9clairage h\ue9misph\ue9riques \ue0 vitrage simple par des puits de lumi\ue8re plans \ue0 vitrage simple optiquement et thermiquement \ue9quivalents, ce qui permet de tenir compte des limitations des programmes informatiques relatifs \ue0 l'\ue9nergie. Sous la lumi\ue8re solaire et lorsque l'angle z\ue9nithal du soleil est presque un angle droit, une coupole d'\ue9clairage h\ue9misph\ue9rique \ue0 vitrage simple a un coefficient \ue9quivalent de transmission du rayonnement solaire et d'apport par rayonnement solaire l\ue9g\ue8rement plus faible que celui d'un puits de lumi\ue8re plan \ue0 vitrage simple. Le coefficient en question est toutefois substantiellement plus \ue9lev\ue9 lorsque l'angle z\ue9nithal du soleil est \ue9lev\ue9 ou que celui-ci se trouve pr\ue8s de l'horizon. Sous la lumi\ue8re du ciel isotropique, le coefficient \ue9quivalent de transmission du rayonnement solaire et d'apport par rayonnement solaire d'une coupole d'\ue9clairage h\ue9misph\ue9rique \ue0 vitrage simple est l\ue9g\ue8rement plus faible que celui d'un puits de lumi\ue8re plan \ue0 vitrage simple. L'apport par rayonnement solaire quotidien d'une coupole d'\ue9clairage h\ue9misph\ue9rique \ue0 vitrage simple est plus \ue9lev\ue9 que celui d'un puits de lumi\ue8re plan \ue0 vitrage simple horizontal, aussi bien l'hiver que l'\ue9t\ue9. En \ue9t\ue9, l'apport par rayonnement solaire d'une coupole d'\ue9clairage h\ue9misph\ue9rique \ue0 vitrage simple peut \ueatre de 3 \ue0 9 % plus \ue9lev\ue9 que celui d'un puits de lumi\ue8re plan \ue0 vitrage simple horizontal dans le cas des latitudes variant entre 0 \uba et 55 \uba (nord/sud). En hiver toutefois, l'apport par rayonnement solaire d'une coupole d'\ue9clairage h\ue9misph\ue9rique \ue0 vitrage simple augmente de fa\ue7on importante avec la latitude et peut \ueatre jusqu'\ue0 232 % plus \ue9lev\ue9 que celui d'un puits de lumi\ue8re plan \ue0 vitrage simple horizontal, particuli\ue8rement dans les pays des hautes latitudes.Peer reviewed: YesNRC publication: Ye

A Numerical method for the treatment of discontinuous thermal conductivity in phase change problems

Peer reviewed: YesNRC publication: Ye

Development of analysis software for the optical characteristics and daylighting performance of conventional and tubular skylights

This paper presents the development of analysis software for the optical characteristics and daylighting performance of conventional and tubular skylights. It focuses on the software structure, inputs, outputs and analysis modules. It provides preliminary results from the prediction models for the beam transmittance of barrel vault skylights, diffuse transmittance of domed skylights under different sky conditions, and average Daylight Factor on internal room surfaces. The work included the development of prediction models for optical and daylighting performance of different skylight shapes, experimental and analytical validation of the prediction models, and software design.Ce document pr\ue9sente le d\ue9veloppement d'un logiciel d'analyse des caract\ue9ristiques optiques et de la performance de l'\ue9clairage naturel des lanterneaux de type classique et des lanterneaux tubulaires. Les travaux portent essentiellement sur la structure du logiciel, les entr\ue9es, les sorties et les modules d'analyse. On y pr\ue9sente par ailleurs les r\ue9sultats pr\ue9liminaires des mod\ue8les de pr\ue9diction du facteur de transmission de faisceau des lanterneaux en vo\ufbte d'ar\ueate, du facteur de transmission diffuse des lanterneaux \ue0 d\uf4me sous diverses conditions de ciel, ainsi que le coefficient d'\ue9clairage diurne moyen sur les surfaces internes de la pi\ue8ce. Sont comprises dans ces travaux l'\ue9laboration de mod\ue8les de pr\ue9diction des performances optiques et d'\ue9clairage naturel de lanterneaux de diff\ue9rentes formes, la validation exp\ue9rimentale et analytique des mod\ue8les de pr\ue9diction, ainsi que la conception du logiciel.Peer reviewed: YesNRC publication: Ye