Abstract: The use of low exergy high temperature radiant cooling in the tropics is only possible with adequate dehumidification. We analyze the adaption of a decentralized ventilation system to supply dehumidified air using models and experimental prototypes. The decentralized air supply prototype was developed and initially tested at the ETH Zurich, then installed in a building laboratory that was shipped to Singapore-ETH Centre, and it was modeled and evaluated in collaboration with the National University of Singapore. We present the findings on its performance and ability to mitigate the risk of condensation for high performance radiant cooling surfaces for buildings in the tropics from models and experiments. We show that adequate dehumidification can be achieved in the decentralized supply unit by our expanded cooling coil. Our model shows that when the supply air has a humidity ratio of 13 g/kg then sufficient mitigation of condensation on the chilled panels is achieved. Experiments in the laboratory showed supply air down to 11 g/kg, which should be sufficient, but also showed the potentially large impact of infiltration of humid outdoor air in the tropics because humidity in the space remained higher than expected, and was also very sensitive to infiltration in our models.
Permalink: https://doi.org/10.1016/j.enbuild.2013.08.015

Abstract: Shock-wave propagation through different arrays of solid obstacles and its attenuation are analyzed by means of numerical simulations. The two-dimensional compressible Navier–Stokes equations are solved using a fifth-order weighted essentially non-oscillatory scheme, in conjunction with an immersed-boundary method to treat the embedded solids within a cartesian grid. The present study focuses on the geometrical aspects of the solid obstacles, particularly at lower effective flow area, where the frictional forces are expected to be important. The main objective is to analyze the controlling mechanism for shock propagation and attenuation in complex inhomogeneous and porous medium. Different parameters are investigated such as the geometry of the obstacles, their orientation in space as well as the relaxation lengths between two consecutive columns. The study highlights a number of interesting phenomena such as compressible vortices and shock–vortex interactions that are produced in the post-shock region. This also includes shock interactions, hydrodynamic instabilities and non-linear growth of the mixing. Ultimately, the Kelvin–Helmholtz instability invokes transition to a turbulent mixing region across the matrix columns and eddies of different length scales are generated in the wake region downstream of the solid blocks. The power spectrum of instantaneous dynamic pressure shows the existence of a wide range of frequencies which scales nearly with f −5/3. In terms of shock attenuation, the results indicate that the staggered matrix of reversed triangular prism (where the base of the triangular prism is facing the incoming shock) is the most efficient arrangement. In this case, both static and dynamic pressure impulses show significant reduction compared to the other studied configurations, which confirms the effectiveness of this type of barrier configuration. Furthermore, the use of combination of reverse–reverse arrangement of triangular prism obstacle maze is found more effective compared to the forward–reverse or forward–forward arrangements.
Permalink: https://doi.org/10.1007/s00193-012-0362-2

Abstract: In this paper, 2D numerical simulation of the Trombe wall performance and indoor air environment under unsteady state condition for a room located in Yazd, Iran are studied. The governing equations involve mass, momentum and energy conservation, which are discretized by the finite volume method after non-dimensionalization. The SIMPLER algorithm is used for coupling the velocity and pressure. The average absorbed solar radiation on the Trombe wall has been defined for different hours of the coldest period of the year (21 January–19 February) in Yazd. All equations have been solved together using a FORTAN code. The main aim of this research is to investigate the time duration of room heating during the non-sunny periods. The stored energy of the wall being delivered to the inside room was defined for different materials of the Trombe wall. The results show that the Trombe wall made of paraffin wax can keep the room warmer in comparison with other materials for about 9 h.
Permalink: https://doi.org/10.1007/s00231-013-1175-2