In the planning process for inclusion of renewable energy systems, after the definition coming from a multiple criteria approach ( energy resources, socio-economic indicators, indices of non­electrification, among others) of the localities to be benefited, a dimensioning of the energy systems is necessary. The SIGA SOL permits the realization of dimensioning or simplified calculus for the following systems:

Figure 10 — SIGA-SOL functionalities, PV macro-planning, aptitude for the sugar cane and castor

bean plant for the state of Pernambuco

Figure 11 — SIGA-SOL functionalities, PV macro-planning, mean annual wind speed and prevailing

direction of the winds

Autonomous photovoltaic system[2];

Photovoltaic system interconnected to the network;

Photovoltaic pumping system with given demand and depth of well [2];

Photovoltaic pumping system with given capacity and depth of well;

Annual electric energy generated by sugar cane bagasse and Annual electric energy generated by wind energy[3,4].

Acknowledgements

We thank the National Research Council (CNPq) , Brazilian Electric Centers SA (ELETROBRAS), The Sao Francisco Hydro Eletric Company (CHESF)and Coordination for Perfection of High Level Personnel (CAPES) for the aid in research projects on solar energy that provided material means and scientific ambient for carrying out this research.

References

[1] SIGA SOL 1.0 (2007) Sistema de informagao geografica aplicada a energia solar, Projeto ANEEL — CHESF, CT-I-192.1760.0.

[2] Tiba, C. , Fraidenraich, N. e Barbosa, E. M. S. (1998) Instalagao de sistemas fotovoltaicos para residencias rurais e bombeamento de agua, ISBN 85-7315-118-8, Ed. Universitaria da UFPE, Recife, Pernambuco.

[3] Amarante, O. C. , Brower, M., Zack, J. and Leite de Sa, A. (2001) Atlas do potencial eolico brasileiro, MME — ELETROBRAS-CEPEL.

[4] RETScreen (2007) Photovoltaic projects analysis, www. retscreen. net, Acess in April 2007.

Computational simulation of the temperature field behavior in a
confined space: Interference of the incident solar radiation on flat roofs

P. R. C. Drach 1* and J. Karam F.2

1 PROURB-UFRJ, Faculdade de Arquitetura e Urbanismo da Universidade Federal do Rio de Janeiro, Brasil

2 Laboratorio Nacional de Computagao Cientifica, LNCC/MCT, Av. Gethlio Vargas 333, Petropolis, Brasil

* Corresponding Author, pdrach@lncc. br

Abstract

In this work we studied the temperature field behavior inside the third-floor of House VI in Vila 37. A “vila” in Brazil is a small private cul-de-sac with terraced houses. In this specific “vila” the original houses were very small and had no space between them, so they had to grow vertically. Nowadays the indoor air circulation presents a decreased state because the indoor ventilation is restricted to the facade windows and the urban volumes swallowed these houses.

In attempt to increase and promote better ventilation, we imposed some changes by introducing a wind-catch on the third-floor in this particular house. We also considered the incident solar radiation interference on the flat roof because this pavement receives the solar radiation directly. Computational simulations were carried out in both cases; with and without wind-catch. The analysis start by solving the air circulation problems, using a Petrov-Galerkin mixed stabilized finite element method applied to the full Navier-Stokes equations. The thermal problem is analyzed through a SUPG — Streamline Up-wind Petrov-Galerkin stabilized finite element method. The results obtained were compared and they suggest that this strategy shows good potential in achieving significant quality with reduced environmental and economical costs. Keywords: passive cooling, ventilation, wind-catch, solar radiation, finite element method

1. Introduction

In this work we study the temperature field behavior on the third-floor of House VI in “Vila” 37. A “vila” in Brazil is a small private cul-de-sac with terraced houses, which share a common area and entrance gate. Vila 37 was built in the year of 1890 and is located in the neighborhood of Catete in Rio de Janeiro city, a tropical climate city, therefore hot. This “vila” initially was formed by a group of 24 one-floor houses and only one two-storey house located in its entrance. Figure 1(a) shows the photo of the entire original project. And some details such as the "facade of the street", Figure 1(b), in reference to the two-storey house located at its entrance and the facade of the standard one-floor house in Figure 1(c). Figures 2(a) and 2(b) present the plants of the house pattern and of the location of the group of houses where it is possible to observe how the houses were very small and that there was not space around them. These houses were constructed by a hard working population. They had originally just one room, one corridor, one bedroom and kitchen (Figure 2(a)). In agreement with old residents, the bathroom was located in the internal small street of the “vila” and it was collective in use and as a place for clothes washing. These documents were obtained in 2006 through the General Archive of Rio de Janeiro City — AGCRJ [1].

Two-storey house

Houses

(a)

Fig. 2. Original details (1890): house pattern plan (a) and house group location (b).

New buildings were constructed everywhere in the growing city and even the old two-floor house located in the vila’s entrance gave place to an eight-floor building in 1955. Around this date, the Secretaria de Obras da Cidade do Rio de Janeiro (Repairing Work Secretariat of Rio de Janeiro City) received a request to authorize the reform of several Vila 37 houses. It is interesting to know that in the year of 1995 only 3 houses (Houses XXII, XVII and II) continued with a single pavement and 18 out of the 24 houses already had more than 2 pavements. So, most of the houses were out of pattern. They had to grow vertically due to the lack of space between the houses (Figure 2(b)).

Nowadays these houses and the internal small street have been suffering a decrease of air circulation. Some factors have been contributing to the current situation among them the fact that indoor ventilation is restricted to the windows in the main facade and the fact that these houses are swallowed by urban volumes.

Aiming to analyze the changes that took place in the ventilation of these confined spaces, the project of House VI was checked. In this house with three-floors the ventilation is restricted to the windows in the facade. The plans of the three-floors can be observed in Figure 3. and the sections and the facade in Figure 4.. These sketches are reproductions of the originals from August 2000, according to the last construction increment. Actually these sketches are filed at the Secretaria Municipal de Urbanismo

(Urbanization District Secretariat — Division of Property and Constructions Bureau) of Rio de Janeiro City.

Fig. 3. Plans of the three floors; first-floor (a), second-floor (b) and third-floor (c).

It is known that naturally ventilated environments have thermal conditions directly related to air circulation and the characteristics of the built environment. North Africa vernacular architecture brought us a legacy of solutions to increase the ventilation without any energy consumption, therefore, adopting passive cooling [2, 3]. One of these strategies is wind-catch which was developed in hot areas to improve ventilation by catching wind from high above where the air is cooler, stronger and cleaner and channeling it down into the building. In previous studies as for instance [4, 5] we tested the use of wind-catches and its effect on indoor environments as well as its possible introduction. With the intention of increasing and promoting better ventilation, we imposed some changes to the original project of the House VI by introducing a wind-catch on the third-floor. Besides scarce ventilation this pavement receives solar radiation directly. So we also considered the interference of incident solar radiation on the flat roof, taking into consideration its respective materials. The thermal changes between outdoor and indoor environments include a solar gain factor related to three specific hours; 7

a. m., 12 a. m., 4 p. m. and also includes no gain factor in one of the cases: at night. We carried out computational simulations for both cases; with and without wind-catch.

The meshes generated for the computational simulation comprise areas bigger than the ones on the plans, by doing that we can impose boundary conditions on the border of the meshes and leave the velocities and temperatures unknown at the entrances of the plans. So the velocities and temperatures could be determined by the solution of air circulation and thermal problems. The analysis starts by solving the air circulation problem to determine the wind fields, using a mixed stabilized finite element method — Petrov-Galerkin type — applied to the full Navier-Stokes equations written in velocity and pressure variables [6]. Then, with these wind fields, using a stabilized finite element method — Streamline Up-Wind Petrov-Galerkin (SUPG) [7], the heat transfer problem, taking into account the heat conduction and convection, was solved and analyzed. The results obtained with the new scenario (with wind-catch) are compared with the ones of the original situation (without wind-catch). These computational results suggest that the use of a wind-catch associated with an appropriate arrangement of openings deserves more attention and research because they show an improvement in air circulation and an ability to promote cooling.