Springtime Monitoring of Passive Cool Roofs in Subtropical Climate

Passive strategies for acclimatization of buildings have been studied by several authors in many countries, especially the evaporative and radiant cooling techniques. Fiber cement tiles are very common in popular constructions due to their low cost. However, they have over twice of the value thermal transmittance indicated to this bioclimatic zone according to Brazilian guidelines. The objective is to present an alternative to reduce high temperatures on fiber cement tiles. In this paper, the monitoring of passive cooling of roofing during the spring season in a city with subtropical climate is described. Single and combined reflective and evaporative cooling systems were studied in different environmental conditions. Internal surface temperatures of tiles were monitored together with weather variables. Results show a decrease of about 6 ℃, 9 ℃, 10 ℃ and 11 ℃ as compared to the original tiles according to environment conditions and the combined passive cooling techniques. These results allow for the conclusion that the use of passive cooling techniques opens up new possibilities to attenuate the internal surface temperatures of tiles and to consequently decrease the roofing solar heat gain into buildings, thus, providing less air cooling energy consumption.     

Syngas production by the CO2 reforming of CH4 over Ni–Co–Mg–Al catalysts obtained from hydrotalcite precursors

The catalytic performance of the Ni, Co, Mg, and Al mixed-oxide solids, synthesized via hydrotalcite route, was investigated towards the dry reforming of methane for hydrogen production. The hydrotalcite structure was successfully obtained upon the synthesis. After calcination at 800 °C under an air flow, this structure was completely decomposed and the resulting oxides (Co_xNi_yMg_zAl₂800, x and y = 0; 1; 2; 3; 4, z = 2; 4, x + y + z = 6, x, y, and z are the molar ratios) were used as catalysts and were characterized using X-ray diffraction and Temperature-Programmed Reduction. The dry reforming of methane was carried out using a mixture of CH₄:CO₂ (1:1) after 2 h of reduction under an H₂ flow at 800 °C. Co₂Ni₂Mg₂Al₂800 showed the highest catalytic activity in the studied series, ascribable to an interaction between Ni and Co, which is optimal for such Co/Ni ratio. The post-reaction characterization of the catalytic samples by X-ray diffraction and Differential Scanning Calorimetry evidenced a better resistance towards carbon deposition for the catalysts where Co molar ratio is higher than Ni.     

Influence of external surface colour on the periodic heat flow through a flat solid roof with variable thermal resistance

In this research, the influence of external colour on the dynamics of the heat flow through a flat solid roof, with variable thermal resistance, has been studied analytically. The chromatic effect on the density of heat flow through the roof has been analysed using periodic solutions of the heat conduction equation, by means of Fourier analysis. The simulation has been carried out over a period of 24 h, for the summer design day of Campinas, in the State of São Paulo, Brazil, and its composite climate. An almost linear relationship between heat flow amplitudes (Δq_i) and the thickness of a concrete roof has been noticeable in the range from 5 to 14 cm for a grey coloured exterior surface and a corresponding white one. Conversely, from 15 cm and more, this relationship starts flattening. It may be concluded that as the thermal resistance of the concrete roof increases (>15 cm), the effect of the exterior colour surface on the periodic heat transfer through the roof is attenuated. As a consequence, the conflict between choosing colour for aesthetics and assuring energy efficiency of opaque building components in hot climates can be mitigated, if building designers make proper use of thermal inertia. Copyright © 2003 John Wiley & Sons, Ltd.     

Simulation of NO and NO2 sorption–desorption–reduction behaviours on Pt-impregnated HPW supported on TiO2

NO and NO₂ (NO_x) sorption, desorption and reduction by hydrogen, carbon monoxide and/or propene were investigated on a TiO₂-supported heteropolyacid, 12-tungstophosphoric acid hexahydrate (HPW), promoted by platinum. A model taking into account NO_x sorption, desorption and reduction was established. Kinetic constants for NO_x sorption, desorption and reduction were extracted by modelling for the investigated range of temperature (170–300 °C).     

Coupled horizontal and rocking vibrations of a rigid circular plate on a transversely isotropic bi-material interface

This paper investigates the coupled rocking and horizontal vibratory response of a rigid circular plate embedded in viscoelastic, transversely isotropic, three-dimensional unbounded media. The boundary-value problem corresponding to the case of distributed horizontal and rocking ring loads at a bi-material interface is solved to obtain the required influence functions for the solution of the present problem. The case of an embedded rigid plate is formulated in terms of a discretized integral equation, which couples the rigid body displacements of the plate with the tractions acting over its contact surface through a set of displacement influence functions. The system of resulting discretized integral equations is solved numerically. The solution results in the tractions over each disc element. This paper carefully takes into account the coupling of the rocking and horizontal responses of the plates that is typical of non-homogeneous interfaces, i.e., their horizontal displacements due to rocking moments and their rotations due to horizontal loads. The dynamic direct and cross compliances of the embedded plate are shown for different governing parameters such as frequency of excitation and bi-material configuration. The present results are useful to the study of dynamic response of deeply buried foundations and anchors in non-homogeneous soils.     

Natural Ventilation by Air Captors and Extractors Sheds in Hospitals in Brazil： Wind Tunnel Measurements

Natural ventilation is an efficient design strategy for the passive cooling of buildings, especially in tropical countries such as Brazil. Among the ventilation strategies, sheds can be highlighted. These structures consist of roof openings that work as air captors or extractors depending on their location in relation to the prevailing wind directions. The hospitals of the Sarah Network, designed by the Brazilian architect Joao Filgueiras Lima, Lele, are worldwide known for using these elements to improve natural ventilation. This paper analyses the natural ventilation performance of sheds for air collecting and extracting in two Sarah hospitals located in the cities of Salvador and Rio de Janeiro. In each building, the sheds were analyzed for air extracting and collecting. The analyses were carried out by reduced physical models in an atmospheric boundary layer wind tunnel. The wind velocity was measured at external and internal points of the buildings, using hot-wire anemometers. The results show that the wards in Rio de Janeiro hospital are 17% more ventilated than the ones in the Salvador hospital. However, this difference occurs not only because of the collecting sheds but also because of set of openings and the configuration of the covering in hospitals in Rio de Janeiro.