Numerical Investigation on Thermal Behaviors of an Inclined Ventilated Roof

Manca, Oronzio; Mangiacapra, Antonio; Marino, Salvatore; Nardini, Sergio

doi:10.1115/esda2014-20391

Cited by 5 publications

(6 citation statements)

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“…Lastly, the structure is the element that holds permanent loads (the weight of the structure) and accidental overloads (weather elements) and resists to exceptional events (storms and earthquakes). The cooling effect of ventilation in the roof cavity is proved under real climatic condition and it is numerically verified testing geometrical parameters (air gap height, effect of the ridge, inclination of the slab) and thermal conditions [2][3][4]. Passive methods, like special roof systems in naturally ventilated residential buildings, are used to reduce the room cooling load in hot and humid climate [5,6].…”

Section: Introductionmentioning

confidence: 91%

Thermal behavior evaluation of ventilated roof under variable solar radiation

Bianco¹,

Diana²,

Manca³

et al. 2016

IJHT

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A ventilated roof has a good configuration for energy purposes, in order to respect the European Directive priority for building performance requirement to reduce energy consumption. In Mediterranean regions, with high level of solar radiation, the roof design should respect comfort and energy saving, considering that climatic conditions change depending on seasons and territories. This paper illustrates a numerical investigation on a prototypal ventilated roof for residential use, in order to evaluate its thermofluidodynamic behaviors as a function of the solar radiation applied on the top wall of the roof simulating summer and winter conditions. The roof is modeled as a single side and it is analyzed as twodimensional, in air flow, thanks to the commercial code Ansys-Fluent. Results are given in terms of temperature and pressure distributions, air velocity and temperature profiles along longitudinal and cross sections of the ventilated layer, in order to estimate the differences between the various conditions. Ventilated roof configuration results significant to reach optimal thermal and hygrometric conditions in summer and winter conditions.

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Section: Introductionmentioning

confidence: 91%

Thermal behavior evaluation of ventilated roof under variable solar radiation

Bianco¹,

Diana²,

Manca³

et al. 2016

IJHT

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“…(Banionis et al, 2012;Biwole et al, 2008;Černe & Medved, 2007;Givoni, 1969;Kośny et al, 2012) Separación entre las láminas de la cámara Incidencia en la fricción y en la velocidad del aire al interior de la cámara. (Chang et al, 2008;Ciampi et al, 2005;Dimoudi et al, 2006;Lee et al, 2009;Manca et al, 2014;May Tzuc et al, 2019) ACE, 18 (52) CC BY-ND 3.0 ES | UPC Barcelona, España | Variables de diseño de cubiertas ventiladas metálicas en el clima cálido húmedo | https://dx.doi.org/10.5821/ace.18.52.11811…”

Section: Variables Convección Radiación Conducciónunclassified

“…Variación del empuje del aire por flotabilidad térmica. (Biwole et al, 2008;Chang et al, 2008;Lee et al, 2009;Manca et al, 2014) Cambio en la incidencia de radiación reemitida por cubierta en el espacio interior. (Kabre, 2010) Orientación vientos dominantes Inducción de ventilación forzada por la cámara con impactos variables en el caudal de aire.…”

Section: Inclinaciónunclassified

Variables de diseño de cubiertas ventiladas metálicas en el clima cálido húmedo

Ruiz¹,

Pages-Ramon²,

Isalgué³

et al. 2023

ACE: Architecture, City and Environment

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La construcció amb cobertes de làmina metàl·lica autoportant està molt estesa entre la població amb baixos recursos econòmics i tecnològics a causa del seu reduït cost i facilitat d’instal·lació. En latituds amb alta radiació solar directa i difusa, el comportament tèrmic és molt desfavorable a causa de la seva alta transmitància. Crear una coberta de doble fulla amb possibilitat de ventilació pot significar una millora de les condicions de confort interiors. En aquest estudi es defineixen 3 variables de disseny de cobertes ventilades metàl·liques per avaluar-ne el comportament davant la transferència de calor en un clima càlid humit. Les variables estudiades són la separació de les fulles, la inclinació de la coberta i la reflectància de l’acabat superficial exterior. Amb l’objectiu de comparar el comportament tèrmic de les cobertes ventilades, es van mesurar les temperatures superficials i de l’aire en diferents condicions al llarg de 5 mesos, per a això, es van fabricar quatre prototips, un amb coberta simple i tres amb cobertes ventilades, amb la possibilitat de modificar-ne les variables de disseny. Aquestes modificacions van permetre identificar els rangs de configuració que van presentar menors increments de temperatura respecte a la coberta simple de referència. Els resultats obtinguts mostren que una alta reflectivitat del full exterior, una separació més gran de les fulles i un augment de la inclinació de la coberta són factors que permeten disminuir el sobreescalfament per coberta, sent el nivell de reflectància de l'acabat superficial del full exterior el paràmetre amb més impacte. In hot-humid climates, construction of self-supporting metal sheet roofing is widespread among population with low economic and technological resources due to its low cost and ease of installation. In latitudes close to the equator. with high direct and diffuse solar radiation, thermal behavior of metal roofing is very unfavorable because of its high transmittance and the amount of radiation received by the horizontal plane. Duplicating the metal sheet by creating a double sheet roof with the possibility of ventilation can mean an improvement in interior comfort conditions. In this study, 3 design variables of ventilated metal roofs are defined to evaluate their heat transfer behavior in a hot-humid climate. The studied variables are: distance between the metal sheets, roof inclination and reflectance of exterior surface finish. In order to compare the thermal behavior of the ventilated roofs, surface and air temperatures were measured under different conditions over a 5-months period. Hence, four modules were manufactured, one with a single metal sheet roof and three with ventilated cavities, all of them with the possibility of changing the design variables. These modifications allowed to identify the configuration ranges that presented lower temperature records compared with a simple metal sheet roof. Results showed that a high reflectance level of the external foil, a greater distance between the metal sheets and a pronounced roof inclination, are factors that allow reducing roof overheating, in which surface reflectance level of the external sheet was the parameter with the greatest cooling impact. La construcción con cubiertas de lámina metálica auto portante está muy extendida entre la población con bajos recursos económicos y tecnológicos debido a su reducido costo y facilidad de instalación. En latitudes con alta radiación solar directa y difusa, su comportamiento térmico es muy desfavorable debido a su alta transmitancia. Crear una cubierta de doble hoja con posibilidad de ventilación puede significar una mejora de las condiciones de confort interiores. En este estudio se definen 3 variables de diseño de cubiertas ventiladas metálicas para evaluar su comportamiento ante la transferencia de calor en un clima cálido húmedo. Las variables estudiadas son: la separación de las hojas, la inclinación de la cubierta y la reflectancia del acabado superficial exterior. Con el objetivo de comparar el comportamiento térmico de las cubiertas ventiladas, se midieron las temperaturas superficiales y del aire en distintas condiciones a lo largo de 5 meses, para lo cual, se fabricaron cuatro prototipos, uno de ellos con cubierta simple y tres con cubiertas ventiladas, con la posibilidad de modificar sus variables de diseño. Dichas modificaciones permitieron identificar los rangos de configuración que presentaron menores incrementos de temperatura con respecto a la cubierta simple de referencia. Los resultados obtenidos muestran que una alta reflectividad de la hoja exterior, una mayor separación de las hojas y un aumento de la inclinación de la cubierta son factores que permiten disminuir el sobrecalentamiento por cubierta, siendo el nivel de reflectancia del acabado superficial de la hoja exterior el parámetro con mayor impacto.

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“…Studies have been performed on the air flow rate in air cavities considering wind as a driving force (Gullbrekken, 2018). Thermal buoyancy has also been studied, but mostly from the perspective of heat removal in hotter climates (Biwole et al, 2008;Bunnag et al, 2004;Chami and Zoughaib, 2010;DeWith et al, 2009;Lee et al, 2009;Li et al, 2016;Manca et al, 2014;Susanti et al, 2008). An experimental study on the ventilation of wall air cavities from a moisture perspective was performed by Vanpachtenbeke et al (2017).…”

Section: Introductionmentioning

confidence: 99%

Model of thermal buoyancy in cavity-ventilated roof constructions

Säwén

Stockhaus

Hagentoft

et al. 2021

Journal of Building Physics

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Timber roof constructions are commonly ventilated through an air cavity beneath the roof sheathing in order to remove heat and moisture from the construction. The driving forces for this ventilation are wind pressure and thermal buoyancy. The wind driven ventilation has been studied extensively, while models for predicting buoyant flow are less developed. In the present study, a novel analytical model is presented to predict the air flow caused by thermal buoyancy in a ventilated roof construction. The model provides means to calculate the cavity Rayleigh number for the roof construction, which is then correlated with the air flow rate. The model predictions are compared to the results of an experimental and a numerical study examining the effect of different cavity designs and inclinations on the air flow rate in a ventilated roof subjected to varying heat loads. Over 80 different test set-ups, the analytical model was found to replicate both experimental and numerical results within an acceptable margin. The effect of an increased total roof height, air cavity height and solar heat load for a given construction is an increased air flow rate through the air cavity. On average, the analytical model predicts a 3% higher air flow rate than found in the numerical study, and a 20% lower air flow rate than found in the experimental study, for comparable test set-ups. The model provided can be used to predict the air flow rate in cavities of varying design, and to quantify the impact of suggested roof design changes. The result can be used as a basis for estimating the moisture safety of a roof construction.

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Numerical Investigation on Thermal Behaviors of an Inclined Ventilated Roof

Cited by 5 publications

References 0 publications

Thermal behavior evaluation of ventilated roof under variable solar radiation

Thermal behavior evaluation of ventilated roof under variable solar radiation

Variables de diseño de cubiertas ventiladas metálicas en el clima cálido húmedo

Model of thermal buoyancy in cavity-ventilated roof constructions

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