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A CFD based procedure is described to identify the optimum inclination angle of a small-scale roof-top solar chimney for maximum ventilation performance. The absorber wall of the chimney under consideration is 500-mm long and the air gap width is 40 mm. Firstly, CFD simulations are performed on a two-dimensional solar chimney model with inclination angles varying from 30° to 90° relative to the horizontal plane under different heat fluxes. Subsequently, a mathematical procedure using the CFD data to estimate the ventilation performance of the solar chimney at different inclination angles under real climate conditions is described. The procedure accounts for the effect of the inclination angle on receivable solar irradiance and is applied to three Australian cities, corresponding to three different latitudes. It is found that the optimum inclination angle varies from 45° to 60°, depending on the latitude and season of operation.

A transient heat balance model (THBM) based on energy conservation is developed for predicting the thermal performance of a semi-transparent water wall system. In order to validate the THBM against field measurements, real climate conditions in Sydney, Australia are adopted and the time variations of both internal and external convective and radiative heat transfer coefficients are calculated using empirical correlations from the literature. An alternative concrete wall model is also developed for further validation of the THBM. Good agreements between the THBM simulation and field data are achieved for both the water wall and concrete wall systems. The validated THBM is then adopted in a sensitivity analysis in order to assess the thermal performance of the semi-transparent water wall system under different configurations. It is found that the daily maximum water and air temperatures decrease significantly with the decrease of the transmissivity of the semi-transparent panels, whereas an increase of the attenuation coefficient of solar radiation in water has an insignificant impact on the water and air temperatures. The present results also indicated that increasing the thickness of the water column can reduce the fluctuations of the water temperature and the diurnal peak air temperature. From the practical application point of view, reducing the transmissivity of the external panel provides the most effective way to mitigate over-heating in the semi-transparent water wall system.

The thermal performance of an opaque water wall system is numerically investigated using the shear-stress transport (SST) k–ω turbulence model and the Discrete Ordinates radiation model for typical winter and summer climate conditions in Sydney, Australia. With a periodic sol-air temperature specified on the outside Perspex panel, the energy performance of the water wall system is examined over a range of water wall thicknesses. The computational fluid dynamics (CFD) model is compared with an experimentally validated transient heat balance model (THBM), and a fair agreement between the CFD model and the THBM results is achieved. The present numerical results indicate that the performance of the opaque water wall system is improved by increasing the thickness of the water column under the winter climate condition in Sydney. It is also found that less supplementary energy is required in winter than that in summer in order to maintain a comfortable interior temperature. Further, a comparison between the present water wall system and a conventional concrete wall system shows that the water wall system performs significantly better than the concrete wall system of the same thickness in the winter climate of Sydney, whereas both the water wall and concrete wall systems have a similar performance in terms of energy savings in the summer climate of Sydney.

Ongoing investigations into solar chimney development have resulted in constantly evolving new designs. In this study, experiments are carried out with an inclined passive wall solar chimney (IPWSC) model with a uniform heat flux on the active (absorptive) wall. The effectiveness of this design has been examined for the heat flux range of 100 W/m2–500 W/m2 with a fixed base air gap width of 0.1 m and inclination angles of the passive wall in the range of 0–6 degrees. The experimental results show that the inclination angle of the passive wall has no significant effect on the temperature distribution across the air gap width and along the chimney height. On the other hand, the averaged air flow velocity across the air gap width is strongly affected by the inclination angle. The experimental results also show that the IPWSC with 0.7 m absorber height and 0.1 m air gap width at an inclination angle of 6° and input heat flux of 500 W/m2 can produce sufficient ventilation for a 27 m3 room based on ASHREA standards. Further, the present experimental results show that the IPWSC design can significantly improve the ventilation performance of a solar chimney in comparison to the conventional chimney design with vertical passive wall configuration. The experimental results are supported by flow visualization experiments and are consistent with scaling predictions.

This paper reports a numerical investigation of flow reversal effects on the buoyancy induced air flow in a solar chimney for ventilation applications over a range of controlling parameters. The reverse flow phenomenon is quantitatively examined by calculating its penetration depth. In order to suppress the reverse flow and enhance ventilation performance, a configuration with an inclined passive wall is proposed as a new design; the effectiveness of this design has been examined over the Rayleigh number range of 10 9 ⩽ Ra ⩽ 10 11 . It is identified that there exists an optimum inclination angle corresponding to an optimum aspect ratio at which the mass flow rate is the maximum for a given Rayleigh number. The numerical results are supported by a scaling argument and a flow visualization experiment.