A. Moret Rodrigues

Numerical and experimental study of the optical properties of venetian blinds

Shading devices are used to reflect direct sunlight, reduce glare and prevent overheating. A correctly designed shading system will strongly influence the entire building energy consumption, peak loads and indoor comfort. The use of the venetian blinds is particularly common due to its relatively low cost and high versatility. The present study focuses on the algorithms for calculating both short-wave (solar) and long-wave (infrared) transmittance, absorptance and reflectance of the venetian blinds. The model is based on the net radiation method, allows for different slat discretization schemes and is suitable for integration into the building energy simulation tools. Once the effective optical properties are computed, the system can be regarded as an additional layer in a multilayer glazing system. Computed blind solar transmittance has been compared with other numerical models and in situ experimental results. A general good agreement has been found, except in cases where incident radiation is mostly diffuse. In this study, the effect of different design parameters on effective optical properties of the venetian blinds is also investigated: (a) the sun profile angle, (b) the slat angle and (c) the venetian blind geometry. Moreover, the effect of the discretization of each slat is examined.

Evaluation of Vertical Solar-Air Collectors for Natural Ventilation Using Integral and CFD Models

Vertical solar-air collectors that are used for providing natural ventilation can be a viable solution in buildings where higher ventilation rate requirements for better indoor air quality cannot be met by traditional natural ventilation methods. Indoor air quality problems have been experienced in Portuguese school buildings where a study revealed that the CO2 concentrations in classrooms in winter were higher than the recommended health limits. To improve the environment in these classrooms, solar-induced ventilation has been suggested. In the design of these solar ventilators, simple models can only predict the main features of the flow but they can be useful tools in the first stages of the design process. However, CFD models can produce microscopic information about the state of all flow parameters and thus are recommended when a high degree of accuracy is needed. In this paper, a simplified model based on the integral equations of motion and heat transfer is developed for a vertical solar-air collector and applied to different boundary conditions. The results are compared and discussed with those computed from a CFD code specially designed for room ventilation.