Impact of Heat Reflective Coatings on Heat Flows Through the Ventilated Roof With Steel Coatings

Banionis, Karolis; Monstvilas, Edmundas; Stankevičius, Vytautas; Bliūdžius, Raimondas; Miškinis, Kęstutis

doi:10.3846/13923730.2012.700943

Cited by 6 publications

(6 citation statements)

References 10 publications

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“…(Givoni, 1969;Rawat & Singh, 2022;Synnefa et al, 2012) Emisividad Variación de la reemisión de calor al interior del espacio. (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

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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Section: Variables Convección Radiación Conducciónunclassified

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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“…Meanwhile, the rate of entry of solar heat is the largest contributor to indoor heat and needs to be conditioned so as not to disturb thermal comfort, this needs to be considered, especially from the side of the building roof (Leonardus Murialdo Fransiskus Purwanto 2019). The choice of building materials, roof covering color, roof construction, ceiling covering and dampening efforts need to be carefully considered so that the building becomes more comfortable and shadier (Banionis et al 2012;Ashhar and Lim 2020).…”

Section: Introductionmentioning

confidence: 99%

Heat transfer on residential roofs with the HT-Flux software

Purwanto

2023

ARTEKS J. Tek. Arsit.

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Buildings in Indonesia, which has a humid tropical climate, receive direct exposure to sunlight on the roof. The influence of this heat will directly affect the space under the roof and will increase the temperature significantly. Heat transfer is often not taken into account carefully in building physics calculations, even though increasing temperature will affect energy consumption. This research was carried out to determine the distribution of heat and how to prevent the entry of solar heat through the HT-Flux software. The aim of this research is to analyze heat transfer patterns and prevention efforts in buildings. The research method used is an experimental method, where roof construction patterns are tested, to obtain the right roof construction in tropical areas. The result of this research is to obtain damping on the roof by testing it with HT-Flux software.

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“…Li [2016] studied that the effect of the ventilated layer of the roof was strong on the themperature delay of the roof, but it was weak on the delay time. Banionis [2012] showed that installing radiant barriers with low emissivity coefficient into the roof construction reduced the additional radiative heat flow caused by the interior surface of the roofs coating into the building. This paper illustrates a numerical investigation on a prototypal ventilated roof for residential use, under summer and winter conditions.…”

Section: Introductionmentioning

confidence: 99%

Radiation Effect on Transient Natural Convection in Ventilated Roofs

Bianco

Diana

Manca

et al. 2017

Proceedings of CHT-17 ICHMT International Symposium on Advances in Computational Heat Transfer May 28-June 1, 2017, Napoli, Ita

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This paper illustrates a numerical investigation on a prototypal ventilated roof for residential use, under summer and winter conditions. The roof is modeled as a single flap, due to its geometric and thermal symmetry, and it is analyzed as two-dimensional, in air flow, thanks to the commercial code Ansys-Fluent. The governing equations are given in terms of k- turbulence model taking into account the radiation effect inside the channel. The analysis is performed in order to evaluate thermofluidodynamic behaviours of the ventilated roof, in transient regime with radiative heat transfer presence, as a function of the solar radiation applied on the top wall of the ventilated roof. The discrete transfer radiation model (DTRM) is chosen. Typical summer and winter conditions with heat transfer from the channel top wall toward the external ambient are examined. The bottom wall of the ventilated channel is simulated as isothermal, considering optimal temperature values for the internal ambient in summer and winter regimes. 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 fluid dynamic conditions in summer and winter regimes. In summer period, when the effect of solar radiation is more evident thanks to the convective effect within the channel, temperature values are higher and the effect of the ventilated channel is significative to reach comfort conditions. In winter, the effect of the ventilated layer is very important to reach optimal thermal and hygrometric conditions. NOMENCLATURE b: channel width, [m] C 1 , C 2 , C μ : empirical constants in the k-ε turbulence model D: Extra term in Turbulence kinetic energy equation E: Roughness parameter f 1 , f 2 , f μ : Wall damping function G b : Production of turbulent kinetic energy due to buoyancy G k : Production of turbulent kinetic energy due to mean velocity gradient h: hipped roof height, [m] k: kinetic energy of turbulence k ext : total thermal conductance of the upper layers of ventilated roof (between the channel and the external ambient, [W/m 2 K] k f , k s : fluid and solid thermal conductivity, [W/K m] L: channel length, [m] L x , L y : reservoir dimensions, [m] T avg : average value of the temperature in the exit section of the channel, [K] T havg : average value of the temperature on the top wall of the ventilated channel, [K] T i : Room temperature, [K] T e : Cavity temperature, [K] T max : maximum value of the temperature in the channel. T ∞ : Flow temperature, [K] T s : Channel wall (surface) temperature, [K] T o : Environment temperature, [K] T S : Summer condition temperature, [K] T W : Winter condition temperature, [K] v avg : average value of the velocity in the ventilated channel, [m/s] v max : maximum value of the velocity in the ventilated channel, [m/s] X, Y ,Z: Cartesian coordinates...

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Impact of Heat Reflective Coatings on Heat Flows Through the Ventilated Roof With Steel Coatings

Cited by 6 publications

References 10 publications

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

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

Heat transfer on residential roofs with the HT-Flux software

Radiation Effect on Transient Natural Convection in Ventilated Roofs

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