| Green building and sustainable architecture are known to be energy-conserving and environmental-protective by utilizing new and renewable energies for HVAC. Trombe walls are regarded as a sustainable architectural technology for heating and ventilation. A new invention is the PV-Trombe wall, in which the front side of the glazing is composed of photovoltaic panels that simultaneously convert solar radiation into heat and power. However, the PV panel on the front cover hinders the penetration of solar rays into the Trombe wall channel between the walls and glazing. Therefore, the efficiency of the Trombe wall is reduced in terms of heat gain. In order to improve the solar efficency of Trombe wall, a novel built-in photovoltaic-Trombe wall (BiPV-TW) was proposed in this thesis. In this new model, PV panels are attached to the interior absorbor wall, thus, solar radiation could almost completely passes through the glass cover and absorbed by the PV panels and the air in the channel. A part of the solar energy will be converted into electricity by the PV panels and the remained will be converted into thermal energy. The air inside the channel is then heated by natural convection and natural ventilation is generated.Based on the principle of Computational Fluid Dynamics, the air flow and heat transfer inside the channel in the BiPV-TW model with a horizontal inlet were simulated by the commercial software FLUENT 6.3. The RNG κ-ε turbulence model, DO radiation model and SIMPLEC algorithm were used to calculate the temperature and flow fields of air. The effects of solar radiation and geometric parameters of the BiPV-TW on the ventilation and heat transfer, e.g., the distribution of air temperature, velocity, local heat transfer coefficient and ventilation rate were studied and discussed. Dimensionless numbers, i.e., Nusselt number, Nu, Reynolds number, Re, a modified Rayleigh number, Ra*, and thermal efficiency ηth, etc, were defined and were correlated for the calculation of the heat transfer coefficient and ventilation rate in the built-in PV-Trombe wall based on the least squares method and linear regression analysis method. The following main conclusions can be drawn from the results.(1) The temperature and velocity distribution of the air in the channel is not uniform at the same level along the width direction. There were obvious temperature and velocity boundary layers near the right wall of the channel, and the thickness of the layers increase with the solar radiation. Larger temperature and velocity gradients were found in the boundary layers, while the temperature and velocity gradients could be neglected at the main area away from the heated wall.(2) The air flows in the vertical channel were naturally regarded as natural convection in confined space, and air flow patterns can be judged by the Ra* number which was defined by the channel width as the characteristic dimension. The airflow streamlines and theoretical analysis illustrated that the air flow patterns changed slightly with solar radiation and channel height and the channel width was the key parameter to affect the flow patterns.(3) There was a big difference on local heat transfer coefficient distribution of the air between the inlet and fully developed regions. The increase of solar radiation and channel height could improve the ventilation performance. However, the ventilation rate increased first to a maxixmum and then decreased slowly as the channel width increased. The reverse flow which appeared within the channel could strengthen the local heat transfer, but it will obstruct the air flow and resulted in a decresed ventilation rate.(4) The dimensionless numbers, Nu, Re, Ra*, and thermal efficiency ηth are introduced to correlate the empirical formula of heat transfer coefficient and the ventilation rate by linear fitting method, which could help for further research and engineer applications. |
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