Comparative-experimental study of different roof types in a tropical climate

Introduction: The implementation of green roofs in buildings has become increasingly common, because it is an ecological construction alternative that provides great benefits, which range from reducing air pollution to improving air conditioning inside of the buildings. Objective: This article aims to evaluate whether extensive green roofs are an energy-valuable option in a tropical climate compared to a thermoacoustic, clay tile, and concrete roof. Methodology: An experimental study was carried out in summer (December) in a tropical climate, where the internal temperature of two identical small buildings was compared except for the roof type. Both small buildings were built with a low construction standard according to buildings of families with low income in this region. Data of internal temperatures and other climatic conditions were analyzed to compare the influence of the roof type on the inner shelter temperature. Results: In these experiments, the average inner shelter temperature of green roofs was lower than the same temperature for thermoacoustic, clay tile and concrete roof and resulted in average temperature differences of 1.8 °C, 0.9 °C and 1.5 °C, respectively (depending on environmental conditions). Conclusions: It was possible to show that the green roof has a greater thermal inertia compared to the others. However, the temperature difference between the green roof and the other roof types was in the same range as in studies conducted in other climatic regions, therefore no special benefit of the green roof has been derived in a warm-tropical climate in this study. However, the low building standard can be of great interest for a final evaluation and the authors recommend to conduct further studies.Resumen Introducción: La implementación de techos verdes en las edificaciones se ha vuelto cada vez más común, debido a que es una alternativa de construcción ecológica que brinda grandes beneficios que van desde la reducción de la contaminación en el aire, hasta la mejora de la climatización dentro de los edificios. Objetivo: Este artículo tiene como objetivo evaluar si los techos verdes extensivos son una opción energéticamente valiosa en un clima tropical en comparación con un techo termoacústico, de tejas de barro y concreto.  Metodología: Se realizó un estudio experimental en verano (diciembre) en clima tropical donde se comparó la temperatura interna de dos cubículos idénticos excepto del tipo de techo. Los cubículos fueron construidos de bajo estándar de construcción como se construyen casas unifamiliares de personas de bajos ingresos. Los datos de temperaturas internas y demás condiciones climáticas se analizaron para comparar la influencia del tipo de techo en la temperatura interna del cubículo.  Resultados: En los experimentos realizados, la temperatura interna promedio en los techos verdes fue menor que la misma temperatura de los techos termoacústicos, de tejas de barro y concreto, con diferencias de 1.8 °C, 0.9 °C y 1.5 °C, respectivamente (dependiendo de las condiciones ambientales). Conclusiones: Se pudo evidenciar que el techo verde presenta una mayor inercia térmica con respecto a los demás. Sin embargo, la diferencia de temperatura entre el techo verde y los otros tipos de techo estuvo en el mismo rango que en los estudios realizados en otras regiones climáticas, por lo tanto, no se ha derivado ningún beneficio especial del techo verde en un clima cálido tropical en este estudio. Sin embargo, el bajo estándar de construcción puede ser de gran interés para una evaluación final y los autores recomiendan realizar más estudios

Energetic recovery and thermal analysis of the cooking process in the ceramic industry

Las investigaciones encontradas en la literatura no son específicas para hornos colmena, que son los más usados en la industria ladrillera (cerámica) en Colombia. Es por esto que en este trabajo se desarrolla un modelo matemático analítico que simula el comportamiento de los gases de combustión en esos hornos. En el horno se modela la combustión, la transferencia de calor y masa a los productos y las pérdidas por las paredes. El modelo matemático usado es validado con resultados experimentales. Además, con los datos experimentales medidos en el ducto de descarga y chimenea, se selecciona un sistema recuperador para aprovechar la energía residual.Previous scientific research has not focused on downdraught beehive kilns, which are the most used in the Colombian brick (ceramic) industry. Hence, in the present paper, an analytical mathematical model is developed in order to simulate the exhaust gas behavior. To do so, gas combustion and heat and mass transfer to the products and the walls are modelled within the kiln. The obtained model is validated by experimental data. Finally, with the experimental data acquired in the discharge duct and chimney, a heat recovery system is proposed to make use of the residual energy. &nbsp

Energetic recovery and thermal analysis of the cooking process in the ceramic industry

Las investigaciones encontradas en la literatura no son específicas para hornos colmena, que son los más usados en la industria ladrillera (cerámica) en Colombia. Es por esto que en este trabajo se desarrolla un modelo matemático analítico que simula el comportamiento de los gases de combustión en esos hornos. En el horno se modela la combustión, la transferencia de calor y masa a los productos y las pérdidas por las paredes. El modelo matemático usado es validado con resultados experimentales. Además, con los datos experimentales medidos en el ducto de descarga y chimenea, se selecciona un sistema recuperador para aprovechar la energía residual.Previous scientific research has not focused on downdraught beehive kilns, which are the most used in the Colombian brick (ceramic) industry. Hence, in the present paper, an analytical mathematical model is developed in order to simulate the exhaust gas behavior. To do so, gas combustion and heat and mass transfer to the products and the walls are modelled within the kiln. The obtained model is validated by experimental data. Finally, with the experimental data acquired in the discharge duct and chimney, a heat recovery system is proposed to make use of the residual energy. &nbsp

Vertical Axis Wind Turbine Design and Installation at Chicamocha Canyon

The use of vertical axis wind turbines (VAWT) in Colombia could tackle the energy distribution difficulties as large parts of the territory are not connected to the electrical grid. The present chapter explains how to design and select an accurate VAWT for a mountain site, (the Chicamocha’s canyon) by characterizing the wind energy potential, selecting the appropriate blade’s airfoil, and design its corresponding blades to obtain an accurate VAWT performance. This methodology can be used to design and allocate a VAWT for residential use, as it tackles the critical point on wind energy design and selection. It is found feasible the use of wind energy at the location where the mean year density power is 485 [W/m2], and the DU06W200 airfoil is suggested as its aerodynamic efficiency (cl/cd) overcomes by 14% the commonly used NACA0018. Finally, straight blades are recommended to overcome the inertial effects of the low wind velocity at the location

Numerical study of natural convection heat transfer from an isothermal thin plate.

In this work detailed numerical simulations of natural convection heat transfer around an isothermal thin plate with different inclinations are carried out. The numerical approach is based on the finite volume technique for the study of air movement around the plate and its surroundings using symmetry-preserving formulation. To solve turbulence, Direct Numerical Simulation (DNS) or Large Eddy Simulation (LES) are selected. After verification of the numerical solutions and comparison of the results from different turbulence models, a data reduction of the numerical results is carried out in order to determine local and global heat transfer coefficients. Furthermore, the influence of Rayleigh number and plate inclination on flow characteristics and heat transfer coefficients is investigated.Peer ReviewedPostprint (published version

Detailed numerical study of turbulent flows in air curtains

Air curtains are generally a set of vertical or horizontal plane jets used as ambient separator. In order to prevent entrainment, a good air curtain should provide a jet with low turbulence level, enough momentum to counteract pressure differences across the opening. Consequently, the analysis of the plenum before discharge should be taken into consideration. Hence, the main object of this paper is to study the discharge chamber geometry and the presence of blades for flow orientation at the exit of air curtains. This analysis is carried out in order to understand their influence on the characteristics of the jet produced.Studies presented are based on the detailed numerical simulation of the air curtain discharge plenum by meaans of Computational Fluid Dynamics method using symmetry-preserving formulation and unstructured meshes. The numerical solutions are compared and the influence of the turbulence model used, boundary conditions and computational domain selected are also investigated. Furthermore, experimental measurements of an air curtain prototype using Hot-Wire Anemometry technique are presented.Peer ReviewedPostprint (published version

Numerical study of natural convection heat transfer from an isothermal thin plate.

In this work detailed numerical simulations of natural convection heat transfer around an isothermal thin plate with different inclinations are carried out. The numerical approach is based on the finite volume technique for the study of air movement around the plate and its surroundings using symmetry-preserving formulation. To solve turbulence, Direct Numerical Simulation (DNS) or Large Eddy Simulation (LES) are selected. After verification of the numerical solutions and comparison of the results from different turbulence models, a data reduction of the numerical results is carried out in order to determine local and global heat transfer coefficients. Furthermore, the influence of Rayleigh number and plate inclination on flow characteristics and heat transfer coefficients is investigated.Peer Reviewe

Detailed numerical study of turbulent flows in air curtains

Air curtains are generally a set of vertical or horizontal plane jets used as ambient separator. In order to prevent entrainment, a good air curtain should provide a jet with low turbulence level, enough momentum to counteract pressure differences across the opening. Consequently, the analysis of the plenum before discharge should be taken into consideration. Hence, the main object of this paper is to study the discharge chamber geometry and the presence of blades for flow orientation at the exit of air curtains. This analysis is carried out in order to understand their influence on the characteristics of the jet produced.Studies presented are based on the detailed numerical simulation of the air curtain discharge plenum by meaans of Computational Fluid Dynamics method using symmetry-preserving formulation and unstructured meshes. The numerical solutions are compared and the influence of the turbulence model used, boundary conditions and computational domain selected are also investigated. Furthermore, experimental measurements of an air curtain prototype using Hot-Wire Anemometry technique are presented.Peer Reviewe

Analysis of the dynamic behavior of refrigerated spaces using air curtains

This article is devoted to the study of air curtains applied to reduce the refrigerated chambers heat gains. The proposed strategy is based on the numerical simulation of air curtains by means of computational fluid dynamics (CFD) using RANS modeling and their corresponding experimental validation. Further work on the reduction of the detailed numerical results into overall energetic parameters is also presented. Unsteady three-dimensional numerical parametric studies are carried out, simulating the process of refrigerated chamber sudden door opening. The numerical solutions are verified and the influence of the turbulence model used is also investigated. The studies are centered on the influence of air curtain location, the air suction combination, and both the air discharge velocity and the discharge angle.Peer Reviewe

Turbulence modelling and numerical issues: from RANS to DNS and LES

The objective of this work is to show possibilities and limitations of different turbulence models from RANS to DNS and LES. Firstly, standard approaches based on time averaging the governing equations (the so called Reynolds Averaged Navier-Stokes equations or RANS models) are presented. Attention is focused on explicit algebraic and eddy-viscosity linear and non-linear two-equation models. Aspects related to forced and natural convection, low-Reynolds number approaches, numerical issues, etc. are shown. A different simulation level is then presented: the Direct Numerical Simulation or DNS approach. This kind of analysis describes the whole range of the turbulent motion scales, from the largest ones (similar to the domain size) to the smallest ones (also called dissipative or Kolmogorov scales), where the fluctuations are damped and turbulent energy is irreversibly converted into internal energy. Aspects related to the discretization of the governing equations and the necessity of preserving some properties of the Navier-Stokes equations are pointed out. Examples are shown with emphasis on the possibilities and limitations of this important approach where no empirical inputs are needed at all. The paper ends with promising turbulence models based on the full simulation of the largest scales of the turbulent flow, while the smaller ones are modelled. This is called Large Eddy Simulation or LES approach. Discussion starts with classical techniques based on modelling the non-linear interactions of the convective operator as a diffusion term. Afterwards, the use of regularization techniques as a large eddy simulation model is discussed. The formulation is based on symmetry-preserving discretization methodology on non-structured and collocated meshes. In this approach, the length of the filter is the only empirical parameter used by the model. Examples of both natural and forced convection in well-known benchmark cases, and also in industrial applications, are presented.Peer ReviewedPostprint (published version