G. Álvarez

EVALUATION OF ENERGY ABSORPTION PERFORMANCE OF STEEL SQUARE PROFILES WITH CIRCULAR DISCONTINUITIES

This article details the experimental and numerical results on the energy absorption performance of square tubular profile with circular discontinuities drilled at lengthwise in the structure. A straight profile pattern was utilized to compare the absorption of energy between the ones with discontinuities under quasi-static loads. The collapse mode and energy absorption conditions were modified by circular holes. The holes were drilled symmetrically in two walls and located in three different positions along of profile length. The results showed a better performance on energy absorption for the circular discontinuities located in middle height. With respect to a profile without holes, a maximum increase of 7% in energy absorption capacity was obtained experimentally. Also, the numerical simulation confirmed that the implementation of circular discontinuities can reduce the peak load (Pmax) by 10%. A present analysis has been conducted to compare numerical results obtained by means of the finite element method with the experimental data captured by using the testing machine. Finally the discrete model of the tube with and without geometrical discontinuities presents very good agreements with the experimental results.

Effect of Tree Shading on the Thermal Load of a House in a Warm Climate Zone in Mexico

This paper presents the effect of the shade of a tree on the indoor temperature and thermal loads of a house (test house) located in the State of Morelos, Mexico, 18° 50′ 43″ north latitude and 99° 10′ 44″ west longitude. Energy Plus was used to simulate different geometries of the shadow of a tree and the simulation results were compared with experimental measurements of the house without air-conditioning, for one warm and one cold week of the year 2011. The results showed that the maximum temperature difference between the measured and simulated temperatures with both geometry models of tree-shading was 1.7°C. When the effect of tree shading is not considered, it was found that there is a maximum temperature increase of 4°C in the warm week compared with the measured results. In the cold week, the temperature increase was 1.3°C compared with the measured results. Simulation results for an air-conditioned tree-shaded test house show that total annual energy consumption for cooling and heating to achieve thermal comfort represents a substantial energy savings of 76.6% when compared with an unshaded house.© 2012 ASME

Thermal Performance of a Natural Ventilation System

Natural ventilation in buildings using solar passive systems, such as solar chimneys, has emerged in the last years. Several theoretical and experimental studies in the literature show that their design parameters strongly depend on the ambient conditions, in which they are installed. In order to increase the knowledge of this kind of systems, this work presents the thermal behavior of a stand alone experimental solar chimney during one year. The dimensions of the solar chimney are 5.60 m high, 1.0 m width, and 0.52 m depth. The absorber plate is made of a common reinforced concrete wall of 4.5 m high, 1.0 m wide and 0.15 m depth. This system was designed by Marti J., and Heras M.R. in 2003 [1,2] and it is located in the L aboratorio de E nsayos Energeticos para C omponentes de la E dificacion (LECE ) in the P lataforma S olar of A lmeria (PSA ) in Spain. The entrance of this solar chimney was redesigned in 2007 by Arce et al. [3] and also the instrumentation of the system was increased and improved. During one year, the solar chimney was monitored and several experimental variables were measured. The results present the temperature profiles of the different measured elements of the solar chimney as well as the air mass flow rate through the solar chimney channel. It was observed that the effect of the outdoor wind added to the thermal effects plays an important role affecting the performance of the solar chimney studied.Copyright

A Simulation of the Thermal Performance of a Small Solar Chimney Already Installed in a Building

In this paper we present the theoretical and experimental study of a small solar chimney. The dimensions of the solar Chimney channel are 1.95 m high, 1.70 m width and 0.24 m depth. The channel of the solar chimney has in its backside a metallic plate as a solar heat absorber, and it is attached to a concrete wall, which acts as a storage and thermal isolation. On the front part of the chimney there is a glass plate used to decrease the heat losses to the exterior. Because the metallic plate is heated, air circulates from the lower side to the top side of the chimney channel. For the theoretical study, the steady state energy balance equations were solved for each element of the solar chimney following the methodology proposed by Ong in 2003 [8]. A numerical code was developed and reduced to cases of literature in order to validate it (Ong and Chow in 2003 [12]). The results showed the temperature distributions of the glass, the air inside the channel and the metallic plate. Also, the air mass flow rate was determined. For an hourly Irradiance of 400 W/m2 , the efficiency of the solar chimney decreased from 38 to 15% as the height of the chimney increased from 0.25 to 1.95 m.Copyright