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Solar chimney has been applied on various aspects of building physics and green design. It makes natural ventilation based on stack effect from absorbing solar radiation. A Computational Fluid Dynamics (CFD) method has been widely utilized to model the heat transfer and air flow inside the chimney. The appearance of reverse flow is one of the elements affecting induced results from CFD models. In this study, we examined influences of the suction flow to suppress the reverse flow at the outlet of the air channel. The suction height, suction width and the velocity of the exhaust fan were investigated. The induced flow rate and temperature rise of the chimney were compared to the base case, which has no suction flow. It is observed that the ratio of Qsc and Qbase, which are the induced flow rate at the outlet of the chimney which has exhaust fan and induced flow rate of the base case, respectively, increases with the width, w, and the height above the inlet, h, of the suction port then gradually approaches a constant of about 1.25 when w and h are higher than 0.02 m and 0.15 m correspondingly. Additionally, one advantage of the suggested solution is to lower the noise from the fan to the room.

Using solar energy, a Trombe wall is a passive solar design in an attempt to improve the energy efficiency inside buildings. Trombe walls absorb thermal energy through a glass panel on the outside. This energy is used to heat the cold air from inside the buildings through the inlet at the bottom of the air gap between the glaze and the wall. The warm air rises and it is redirected back into the building through the outlet at the top of the air gap. The performance of Trombe walls can be improved by adding discrete heat sources. In this study, an investigation on the temperature rise and the induced flow rate of the air flow was studied with the presence of a heat source placed at different positions on the air channel. By Computational Fluid Dynamics (CFD) technique, the dimension of the heat source was varied to obtain their effects on the efficiency of the Trombe wall. An increase of 18°C in temperature was attained when the heat source was placed near the outlet of the air gap. The presence of discrete heat sources is an approach to improve the performance of Trombe walls.

Numerical simulations have been widely employed in buildings, particularly for prediction of natural ventilation. The Computational Fluid Dynamics (CFD) has been utilized successfully for prediction of the airflow and heat transfer in solar chimney, one of the common devices for natural ventilation. However, CFD requires expensive computational resources. In this study, an Adaptive Neuro-Fuzzy Inference System (ANFIS) model was tested for quick prediction of the heat transfer in a vertical solar chimney based on the data provided by a CFD model. The Nusselt number in solar chimneys at different heights and heat flux were predicted with the CFD model. The generated data were used to train two ANFIS models which were then validated with the remaining CFD data. The results show that the ANFIS models can predict the Nusselt number and mass flow rate with the maximum discrepancy between the two results of less than 5.0%.

Natural ventilation, one of the key elements of green buildings, can be achieved with solar chimneys. This device based on buoyancy effects induced by solar radiation to create air flow for ventilation. Among the factors influencing performance of a solar chimney is the area of the inlet. In this study, effects of reducing the inlet area on the performance of a vertical solar chimney was examined numerically. A CFD (Computational Fluid Dynamics) model was built on the ANSYS Fluent CFD code to simulate the air flow and heat transfer inside the solar chimney at different heights and gaps. The results showed that, as the inlet area decreases, the flow rate is almost unchanged until a critical ratio of the inlet area and the gap of the air channel. As the inlet area decreases further, the flow rate decreases at a constant rate. The temperature rise is always enhanced as the inlet area decreases. The changes of the thermal efficiency depend on the gap – to -height ratio. These observations can serve as references for design of air damper at inlet of solar chimney for a specific application, such as ventilation where higher flow rate is desired, or heating where higher temperature rise is preferred.

Exploring solar radiation, solar chimneys are widely used in sustainable building design. Solar chimneys can ensure thermal comfort in a house by generating a heating or cooling air flow. For heating applications, the induced air flow is heated and supplied back to the house. In this study, the air flow and heat transfer in a solar chimney for heating were modelled by a numerical simulation based on Computational Fluid Dynamics (CFD) technique. An investigation on the system performance was carried out with the presence of a heated cavity above the top and below the bottom of the air channel. The length and the width of the cavity and the chimney gap have a strong influence on the flow rate and temperature rise through the chimney. The results showed that an appropriate dimension of the heated cavity can enhance the performance of the solar chimney.

Solar chimney has been applied widely in many aspects, such as civil engineering and building physics and demonstrated to be a good solution for natural ventilation of dwellings. It uses absorbed solar radiation to create stack effect which induces air flow and increases ventilation of building. Therefore, solar chimney is one of the most common methods used for energy saving, especially in the field of green design. In this study, we examined a solar chimney integrated with a cover plate at the outlet of the chimney. In other words, the outlet area of the chimney is contracted. A Computational Fluid Dynamics (CFD) model was utilized to simulate the air flow and heat transfer throughout the air channel. The effects of lowering the outlet area were investigated at various air channel heights and gaps. The results indicate that limiting the outlet area strongly affected the computed Nusselt number.

Solar chimneys have been widely used for natural ventilation of buildings. It absorbs solar radiation to create stack effect to induce air flow for ventilation. To model air flow and heat transfer inside solar chimneys, numerical models based on Computational Fluid Dynamics (CFD) have been broadly employed. The size of the computational domain is one of the factors influencing computed results from CFD models. In this study, we investigated effects of the extension of the domain above the outlet of the air channel as the gap and the height of the air channel changes. Two types of the computational domains were studied. The small domain has identical physical size with a cavity inside the solar chimney while the large domain contains both the cavity and the ambient air surrounding the chimney. The induced flow rate and temperature rise of the chimney were computed and compared between those domains. It is seen that to ensure the changes of both flow rate and temperature below 1.0%, the required extension, h, of the domain above the outlet of the air channel is a function of the gap – to – height ratio G/H, not only the gap. Specifically, for G/H in the range of 0.1 – 0.4 in this study, the required h/G rises from 10 to 30.

With passive designs, such as solar chimney, solar radiation absorbed on building envelopes can help to reduce the energy consumption of the building. Solar chimneys can be employed for natural ventilation and/or heating. The performance of a solar chimney has been reported in the literature to depend mainly on the dimensions and designs of the air channel where the air flow is induced. Particularly, the design of the inlet area plays an important role. In this study, effects of the expansion of the inlet area of a vertical solar chimney were investigated numerically with a Computational Fluid Dynamics (CFD) model. The induced flow rate and temperature rise through the chimney were assessed when the inlet area was expanded in both horizontal toward the right side of the air channel and vertical directions and at different heat fluxes. With the expansion, the induced flow rate is always enhanced as the expanded height is equal to and more than the gap of the air channel due to the reduction of the area of the recirculation zone in the air channel. However, no significant enhancement of the temperature rise or the thermal efficiency is seen as the thermal boundary layer along the heated (left) wall changes insignificantly. Similar trends are seen for both values of the heat fluxes. The findings in this study can serve as a reference for different design options for the inlet of solar chimneys.

Solar chimneys absorb solar radiation heat to create stack effect which induces airflow for natural ventilation of buildings. Solar chimneys have been studied mainly in two forms: vertical air channel and inclined one. In this paper, a solar chimney with a horizontal absorber surface was proposed. Its performance in term of the induced air flowrate through the channel and the thermal efficiency was predicted by a CFD (Computational Fluid Dynamic) model. Examined factors included the heat flux and major dimensions of the chimney: length of the absorber surface, gap of the air channel, and height and width of the inlet and outlet sections. The results show that increasing of all examined factors enhances the flowrate but has minor effect on the thermal efficiency. However, excessive large outlet width results in reduction of the flowrate and thermal efficiency due to appearance of reverse flow at the outlet.

Solar chimneys absorb solar radiation heat and induce natural convective airflow for natural ventilation of buildings. In this study, we simulate induced airflow in a two-dimensional vertical solar chimney by Lattice Boltzmann Method (LBM) and focus on laminar flow region at low Rayleigh (Ra) number. Standard D2Q9 and D2Q4 models with single relaxation time are used for flow and temperature fields, respectively. Airflow and air temperature distributions inside the chimney are investigated under effects of main parameters of solar chimneys: heat flux, chimney height H, and chimney width b. Typical characteristics of a solar chimney were well reproduced in our simulations. Particularly, we analyze flow reversal region near the outlet of the chimney. The flow separation regions were observed at low ratio of H/b at a given Ra number or at high Ra number at a given H/b ratio and significantly reduced the induced flowrate. To suppress the flow reversal, we propose a simple method of rearranging the heat transfer surface on the opposite side in the upper and lower halves of the chimney. The results show that this method can eliminate the separation region and increases the induced flowrate at low ratio of H/b at a given Ra number.