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Using solar chimneys in buildings can enhance the thermal insulation of the building envelope and provide sufficient ventilation and cooling. The performance of a solar chimney is strongly affected by its configurational factors. This work examines the effects of the opening heights on the flow field in the cavity of a wall solar chimney with a Computational Fluid Dynamics (CFD) model. Both cases of equal and unequal opening areas were considered. The results show that the induced flow rate increases with the opening height and gradually becomes constant as the opening height is about 2.0–3.0 and 5.0–6.0 times the air gap for heating the left wall (HLW) and the right wall (HRW) of the air cavity, respectively. Particularly, using equal inlet and outlet heights that are equal to the air gap reduces the flow rate of 27% for HLW and 85% for HRW compared to the maximum ones. The optimal design of a wall solar chimney to achieve maximum flow rate is proposed for two cases of heating, that is, (a) for HLW, equal opening heights which are twice the air gap, and (b) for RHW, the inlet height equal to the air gap, and the outlet height equal to five times the air gap.

The use of vertical greenery systems in buildings is becoming more and more common as they provide several benefits, particularly in improving indoor thermal comfort. This paper studies the influence of an indoor living wall on the air temperature and humidity in the test house in Ho Chi Minh City. Effects of the plants, irrigation and ventilation were examined. The temperature and humidity were monitored and analyzed during a 2–month period. The cooling effect of the living wall was proven, with an average reduction of 1°C of the room temperature. Higher air humidity levels were experienced near the green wall, increasing the overall humidity in the room. Irrigation for the plants also helped reduce the room temperature compared to that without irrigation. Therefore, these systems have been proven to be very useful and interesting for warm indoor environments due to the cooling effect.

In the studies of solutions for green buildings, the Computational Fluid Dynamics (CFD) method has been widely used, particularly for solar chimneys. Performance of a solar chimney for natural ventilation or cooling can be assessed numerically in terms of the induced flow rate and temperature rise through the chimney. As the CFD technique has been employed successfully by many researchers for small-scale solar chimneys, applications of this method to large-scale systems, particularly three-dimensional (3D) ones are extremely difficult due to computational cost. As an attempt to apply the CFD method to 3D solar chimneys, in this work, we built an Artificial Intelligence – based ANFIS (model) to predict performance of a simple 3D vertical solar chimney. The ANFIS model was trained with the data generated by an CFD model for various applied heat fluxes. The trained ANFIS model was then employed to predicted performance of the chimney at other heat fluxes. The results show that the ANFIS model is able to predict well the induced flow rate and temperature rise through the chimney with the maximum difference with the CFD results of less than 5.0%. Therefore, this study shows a possibility of combining CFD and ANFIS methods for large-scale solar chimneys.

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.

Natural ventilation for buildings using solar chimney is increasingly attracting the attention of many researchers. Many techniques have been introduced to research on solar chimneys such as experimental, analytical, computational methods. Recently, with the development of computer technology, computational method, particularly, Computational Fluid Dynamics (CFD) becomes more common and widely applied in solar chimney, but this method still exists limitation. One of the main limitations is using much computational source. In this study, CFD was combined with Adaptive Neuro-Fuzzy Inference System (ANFIS) to prevail against this limitation when predicting flow field and mass flow rate in a chimney. In particular, the fluid flow and heat transfer in chimney were simulated with CFD to create dataset. Two ANFIS models were built, trained, and validated using dataset from CFD. After the training, ANFIS models can predict flow temperature, velocity and induced mass flow rate, respectively, with R-squared (R2) of 0.97, 0.997 and 0.9996 for training set, while 0.9715, 0.994 and 0.9996 for testing set; similarly, root mean squared error (RMSE) are 0.032, 1.703, 3.45x10−5 for training set, and 0.042, 1.713 and 2.95x10−5 for testing set. It is expected that the combination of CFD and ANFIS can estimate more different scenarios but using less computational time.

Solid particles impair the performance of the photovoltaic (PV) modules. The results in power losses that lower the system’s efficiency also decrease the life expectancy of the panel. An Internet of Things (IoT) based system was made to monitor, detect dust accumulation, and a cleaning system that would automatically wipe the dust on the surface of the PV solar panels. Using a specific dust sensor, it detects and monitor the amount of dust in the panel. As the dust accumulated reaches its limit, the cleaning system triggers automatically. The ambient temperature was monitored using the temperature and humidity sensor. The data will be received via internet using the Blynk app. The system will address the panel’s dust accumulation problem as it was considered one of the biggest problems globally regarding solar energy reproduction.

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.

With the limited water temperature dispensed by current water dispensers and the varying water temperature desired by consumers, a multiple temperature selections thermoelectric water dispenser was designed to provide the consumer’s demand. This design uses a Thermoelectric module that operates based on the Peltier effect to heat and cool the water in the respective container, thereby eliminating the harmful effects of Freon, a refrigerant used by the current water dispensers process. Arduino Uno’s implementation as a microcontroller provided consumers with a chance to input and be served with their desired water temperature. The experiment results showed that the design is accurate in providing the consumers with their desired water temperature. Thus, the implemented design is successful in meeting the objectives of the study.

Solar chimney has been studied extensively by many researchers and proved to be an effective method for natural ventilation of buildings. Once properly designed, a solar chimney can help to save energy significantly and maintain thermal comfort conditions inside the building. In ideal configurations, a vertical solar chimney has been studied in the form of a straight air channel with constant flow area. In this study, we considered a solar chimney in practical applications where the outlet area of the air channel may be contracted due to other required elements, such as those for weatherproofing. The flow and heat transfer inside the air channel were simulated with a Computational Fluid Dynamics model. Effects of reducing the outlet area were examined under different heights and gaps of the air channel. The results show that reducing the outlet area significantly reduces the flow rate but increases the temperature rise through the chimney. Based on the results, one may select suitable configurations depending on the priority of the application of the chimney, i.e. higher flow rate for ventilation or higher temperature rise for heating applications.

With a good design, solar chimney is able to provide sufficient natural ventilation for buildings. In practice, natural ventilation performance depends on many factors, such as solar radiation, which is intermittent. Therefore, in this study, a proposed combined natural–forced flow solar chimney is investigated. Induced ventilation rate is estimated under the effects of the temperature of the forced flow and compared to that of the base case which has no forced flow. The results show that, with a forced flow velocity of 1.0 m/s and a heat flux of 500 W/m2, the induced mass flow rate increases when the forced flow temperature increases from 20 to 35oC. Compared with the base case, the combined natural–forced flow offers more flow rate as the gap G is above 0.05 m at the height, H, of solar chimney H of 0.45 m; 0.1 m at H=0.95 m; 0.15 m at H=1.45 m, and 0.2 m at H=2.0 m. It is expected that with a proper design, improvement of ventilation performance of a solar chimney can be achieved by this combined natural–forced flow.

Power efficiency and responsible electricity usage are the topmost global concern nowadays, as significant electricity resources are mostly non-renewable. In industries, power factor correction dramatically reduces system power losses, increases the load carrying capabilities, maintains an efficient electrical system, and more. Power factor (PF) measures an electrical system’s power efficiency and is an essential aspect in improving the quality of supply. In terms of induction motors, the power factor drastically changes as the motor changes load; therefore, automatic power factor correction deals the most significant part in maintaining the efficiency of the power supplied to the machine. The study aims to build an Automatic Power Factor Correction (APFC) Unit with embedded Internet of Things (IoT)-Based energy consumption monitoring system that will automatically improve the system’s power factor. An open-source energy monitoring library was implemented to design accurate power calculations to display the system’s voltage, current, power, power factor, energy consumption, and frequency. Through a wireless sensor network, the real-time data reading from the IoT-Based energy monitoring system can be accessed and obtained from the IoT-Based web server through the Blynk IoT platform. Energy measurement and monitoring are done in the sensor microcontroller unit (MCU). The data is then calculated and transmitted to the capacitor bank MCU that handles the switching of relays to the capacitor bank to compensate for the system’s lagging power factor. The result shows that APFC provides the ease of monitoring more efficiently and can be achieved due to reduced power losses and reduced electric consumption.

Existing buildings without a fire alarm monitoring system need an alternative installation cost-effective, flexible, and scalable and will not affect the building’s aesthetics. In place of the conventional fire alarm monitoring system, an Internet of Things (IoT)fire sensor nodes were designed to monitor each room’s temperature and analog CO level and deploy through point to point technique. An IoT fire alarm monitoring system using a wireless sensor network was developed through which real-time data of temperature and analog CO level were obtained from the fire sensor nodes. The IoT fire sensor nodes were deployed from rooms LB384 to LB387. Each room has a node, and each node has its designated Internet Protocol (IP) address. The data can be easily obtained and accessed through the cloud web server, and each IoT fire sensor node will send a notification to the user of the room through the IoT ThingSpeak monitoring widget. The IoT fire alarm monitoring system reduced the installation time and did not require significant building renovations based on the assessment. With the advancement of IoT, fire detection could then be realized such that people within buildings can have a good understanding of the safety of their living environment.

This article analyzes students' opinions about thermal comfort in air-conditioned classrooms. This field study monitored and recorded the following variables: Air temperature (°C), Mean radiant temperature (°C), Humidity (%), and Air velocity (m/s). In addition, a survey was answered by 169 students to collect the students' thermal sensation and preferences according to the ASHRAE sensory scale. The results show the neutral temperature found from the votes was 28.2°C with 98% of students feeling it at neutral. The results also show that the neutral temperature was also higher than the one obtained from the Predicted Mean Vote (PMV) model. The findings from this study can contribute to the design of air-conditioning systems to achieve thermal comfort with efficient energy usage.

In this paper, we investigated the feasibility of harvesting wave energy in Phan Thiet sea area. In Viet Nam seas, Phan Thiet sea area is the most suitable for exploiting wave energy. This paper studies exploiting sea wave energy by the point absorber method for Phan Thiet sea area. The point absorber is a popular harvesting sea wave energy method, it is suitable for areas with small wave energy as Phan Thiet sea area. This work build the floating body dynamics equation for point absorber buoy. By solving this equation, we have determined the efficiency of sea wave energy exploitation for Phan Thiet sea area. The result showed the wave energy in Phan Thiet sea area can be exploited effectively.

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%.

Certain areas suffer frequent energy shortages due to their limited access to the power grid. With this notion, it is very recommended that these areas utilize alternative forms of producing electric energy. The Solar Home System (SHS) has helped millions of families gain access to electricity in Asia and requires the simplest form of a panel and battery. This setup provides a household with sufficient power for their basic needs, particularly the electrification of essential lightings and appliances. The Swarm Solar Household System (SSHS) is one of the potential ways of enjoying energy for every household for in this process, the households that need more power can connect to the interconnected households and use their energy. This research establishes a proof-of-concept for the idea of swarm solar household systems (SSHS) as an additional but beneficial feature for existing solar home systems (SHS). The IoT-based information and control system will be used to utilize SSHS powerfully. SSHS has been installed readily by each of these modeled households. Every household includes a swarm solar household system wireless connection. Monitoring the mutual power and cost process associated with this SSHS can determine the owner’s total payment. In this study, an IoT-based swarm solar household system was successfully obtained using sensors, controllers, Wi-Fi modules, and software applications via Blynk with a built-in cloud server for monitoring and controlling the connection between households; energy sharing is enabled.

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.

An accurate simulation will assist to understand the behavior of rarefied gas flows in MEMS devices. This is useful for obtaining an optimal design for these devices. In this paper, we will comprehensively investigate the effect of viscous heat generation on the rarefied gas microflows in the microcavity and Couette flows. The considered cases have the Knudsen number ranging from 0.05 to 1, and working gas as argon. Both of the temperature jump conditions were recently derived including the viscous heat generation term such as the new type of Smoluchowski and the modified Patterson temperature jump conditions are adopted in the present work. The simulation results show that the viscous heat generation significantly affects the gas temperatures, and it makes a reduction of the gap between the CFD and DSMC data. The simulation results of the modified Patterson jump condition are close to the DSMC data for the high Kn cases, Kn = 0.5 and 1 while those of the new type of Smoluchowski jump condition are not.

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.

Integrated passive cooling technique in building is expected to save energy and create thermal comfort. Solar chimney has been adopted to building design as an effective technique for natural ventilation. The working principle of solar chimney is based on thermal effect, particularly natural convection heat transfer. In this paper, heat transfer performance of a solar chimney with different contracting inlet areas is presented. Furthermore, the effects of major dimension, i.e. ratio of chimney gap and height G/H, are also investigated. As the ratio of the inlet area and the gap, Ai/G, from 90% to 20%, the Nusselt number is strongly affected for G/H below or equal to 5%; while for G/H above or equal to 20%, it showed minor influence. In addition, with G/H of 10% and inlet area from 40% to 60% of the gap, heat transfer coefficient have considerable improvement from 5.3% to 6.1%. The result suggests that G/H = 10% and Ai/G in the range of 40% to 60% are optimal design.

Hot spots have been a significant problem for photovoltaic (PV) installations until the present. Hot spots reduce the power production performance and speed up cell degradation of the PV system. Hot spotting is a reliability problem where mismatched cells heat up due to the reverse biasing of these cells and cause permanent damage to the PV panel. Hot spot occurrences are due to several factors such as shading, panel defect, electrical characteristics mismatching, and bypass diode failures. Bypass diodes are used as a protective device to reduce the severity of cell mismatching, particularly the effect of overcurrent per cell, but these can sometimes be inefficient for hot spot prevention. Through a camera and an IR thermal sensor, the hot spot detection technology implementation is possible with an Arduino-based program of which the results of the hot-spotted (affected strings or cells) are analyzed using Simulink. Furthermore, to mitigate the effect of hot-spotting in the cells, a modified transistor circuit is configured to carry the excess currents running in the cells due to overcurrent (OC). The solutions presented have considerably improved the performance and power output of the solar panels studied through the system’s corrective actions. It has been observed that there was an increase in the attention given to the solar panels by having been able to check which part of the panel’s cells were affected by hot spots as well. The proposed system design can be used in households that rely moderately on photovoltaic systems for energization.

The paper focuses on the flow in the coastal area of Ho Chi Minh City in stormy conditions. In this study, using hydraulic model MIKE 21 with wind and pressure conditions in Tropical Storm Pakhar (2012). The model is calibrated and verified by actual water level data measured at Nha Be, Vam Co, Vam Sat, Dong Tranh, Nga Bay and Cai Mep stations, showing good correlation, ensuring tissue reliability. The simulation results show that, when there is a storm, the average water level rise is about 10 cm in estuary areas, while at rivers, the water level rises by 5 cm. The results show the influence of the storm on the study area, which if combined with rain could cause flooding.

Solar chimney has been widely employed for natural cooling or heating of buildings. Of its forms, wall-attached solar chimney is common. Most of previous studies examined solar chimneys with the heat source on one side of the air channel of a solar chimney. In practical applications, depending on the materials, the absorption of solar radiation can be on both sides of the air channel. Therefore, this study examines a wall-attached solar chimney with the heat source distributed on both sides of the air channel. The Computational Fluid Dynamics (CFD) model was utilized to simulate the flow dynamics and heat transfer of the problem. Performance of the solar chimney was described in terms of the heat transfer coefficient, or Nusselt number, the induced flow rate, and the temperature rise through the chimney. The results shows that the examined parameters can be improved, reduced, or unchanged depending on the gap of the air channel and the heat distribution ratio. The findings may be useful for designing wall-attached solar chimney as they show the conditions for maximizing the flow rate or the temperature rise.

This study aimed to compare prediction performance between ANFIS models which use different input partitioning methods in case of predict temperature and flow field in a solar chimney. In this study, a fixed geometry solar chimney is simulated by CFD software to create dataset for ANFIS models. Three different ANFIS models consist of ANFIS1, ANFIS2, ANFIS3 was trained to predict temperature and flow field in the solar chimney and their prediction performances are compared and analyzed to figure out which model is the best model to predict temperature and flow field in the solar chimney. The result shows that the ANFIS2 model is the best model with RMSE for T, V prediction equal to 0.94, 0.0202 for the training set and 0.97, 0.0218 for the testing set.

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.

As one of the most common methods for natural ventilation of building, solar chimney has been studied widely in the literature. Various forms of solar chimney have been proposed for enhancing its performance for a specific application, i.e ventilation and/or heating. In this work, we examined performance of an L-shaped comprising horizontal and vertical air channels connected serially by a numerical model based on the Computational Fluid Dynamics (CFD) method. Two different total lengths and gaps of the chimney were tested. The considered parameters included the flow rate, temperature rise, and thermal efficiency. The results show that as the horizontal portion is longer than the vertical one, the flow rate decreases while the temperature rise increases. The variation of the thermal efficiency depends on the ratio between the gap and the total length of the air channel. The findings can help to select suitable configurations of an L-shaped for a specific cooling or heating application.

A Trombe wall can be installed in buildings to reduce electricity consumption. Trombe walls are designed to absorb and store solar radiation. By thermal effects, cool air enters the air channel from the inlet and is heated during the channel’s passage. The warm air rises and is fed back into the building to achieve energy efficiency. In this study, an investigation on the induced flow rate and temperature rise was carried out with a fin’s presence by a numerical method based on Computational Fluid Dynamics (CFD) technique. The location and length of the fin were changed to improve the system performance. This work demonstrated that an increase of 16° C in temperature at the outlet can be achieved with a distance of 0.1 m between the fin and the inlet. The fin added inside the Trombe wall channel is an approach to achieve thermal comfort in sustainable building design.

Hydraulic conductivity is vital in estimating an aquifer's water level and water budget on a regional scale in a refinement grid. Currently, hydraulic conductivity is mainly determined through field tests. However, since the pumping tests are expensive and complex to operate, the available hydraulic conductivity data is limited. Hence, the paper applied a geostatistical method to estimate hydraulic conductivity distribution in porous media of the Saigon river basin. The study utilized the available hydraulic conductivity data via pumping test from DWRPIS. The Kriging method shows better performance than the Natural Neighbor method on interpolation hydraulic conductivity in the Saigon river basin. Thus, the hydraulic conductivity distribution could characterize the quality of the aquifer on a local scale. For better distributed hydraulic conductivity maps, further study should increase the number of samples via estimated hydraulic conductivity base on the particle size and resistivity.

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.

This study investigates flow field around a building with triangular cross section by experiments and numerical simulations. The experiments were conducted in an open wind tunnel. Pressure distribution on the surfaces of a scaled model of the building was recorded at different wind speeds and wind angles. The simulation was based on Computational Fluid Dynamics (CFD) technique with computational conditions similar to those in the experiments. It was revealed that the pressure distribution on the building surfaces changed significantly with the wind angles, the direction of the surface relative to the wind angle, and position on the surface. The effect of the different wind angles in determining the drag coefficient on the building was also performed. Flow visualization with smoke and the CFD results reveal flow structure around and behind the building which strongly correlate with the measured pressure distribution on the building surface.

In this study, a passive ventilation and cooling technique which is widely used in sustainable building designs was investigated by a numerical simulation based on computational fluid dynamics (CFD). A system of a solar chimney (SC) and an Earth-to-Air Heat Exchanger (EAHE) is able to ensure thermal comfort in a house by generating an air flow which is induced by the thermal effect. The solar chimney drew ambient air (at 35°C) through the inlet of EAHE; the air flow was cooled by a lower temperature of the underground pipes (at 20°C) before circulating inside the house and leaving through the outlet of the solar chimney. Both the openings of the system were exposed to the atmosphere, and the atmospheric pressure was set at the inlet of the EAHE pipe and the outlet of the solar chimney. The performance of this ventilation and cooling system was analyzed under effects of design parameters, including the gap of the chimney, the diameter and length of the EAHE pipe as well as the solar heat flux applied on the wall of the air channel of the chimney. The results of the assessed parameters, such as temperature inside the house, show that the indoor temperature was reduced to 25°C and 26°C, respectively for the forced ventilation case of 0.2 m/s and natural ventilation case in the configuration with the EAHE pipe length of 11m. The coupled solar chimney and EAHE system can achieve the thermal comfort conditions for both cases of natural and forced ventilation.

Solar chimneys have been intensively studied as an effective method for natural ventilation of buildings. Though numerical methods, such as Computational Fluid Dynamics (CFD), have been widely utilized in such studies, they usually require extensive computational resources. Moreover, experimental study is quite complicated and costly. In recent years, machine learning has started to be used as a tool in the thermal-fluid field. In this study, in order to save time and cost, Adaptive Neuro-Fuzzy Inference System (ANFIS) technique, a class of adaptive networks that incorporate both neural networks and fuzzy logic principles, is combined with CFD. A simulation model was first validated by experiment from another study in the field. The result was documented as a dataset using CFD code ANSYS Fluent (Academic version 2020 R2). Then, they are used to train and validate the ANFIS model. In particular, the study is to predict the fluid flow field in a 2-dimensional typical solar chimney when heat flux changes in the range of 400 to 1000 W/m2. Inputs of the ANFIS model are position and heat flux, while outputs are temperature and velocity at that location. As a result, the 2 ANFIS models could achieve R2 values of 0.997, 0.97 (training set) and 0.994, 0.9715 (testing set); RMSE are 1.009, 0.00224 (training set) and 1.074, 0.0204 (testing set) for outputs of temperature and velocity, respectively. Those results are acceptable. By using the ANFIS model, large amounts of flow fields with different scenarios can be estimated simultaneously. Therefore, it is expected that engineers and architects can have a quick tool in the process of design.

Solar chimneys absorb solar radiation for natural ventilation or cooling of buildings. In typical solar chimneys, the air flow is induced by the thermal effect which causes pressure gradient inside the chimney to deviate from that of the ambient air. The induced flow is employed to ventilate the connected building naturally. In this study, we aimed to boost the induced flow rate through a typical solar chimney by a forced flow at the inlet of the air channel which is divided into two ports for the forced and the induced flows. The air flow and heat transfer were modeled with a Computational Fluid Dynamics (CFD) model with the ANSYS Fluent CFD code. Changing factors included the forced velocity, the dimensions of the inlet port for the forced air flow and the length of the partition between the ports of the naturally induced and forced air flows. It is seen that the forced flow significantly reduces the pressure in the air channel compared to that of a typical chimney; hence increasing the induced flow rate. The flow rate was significantly enhanced as the forced velocity was above 0.2 m/s; the area of the inlet port for the forced flow was 12.4% of the total inlet area; and the partition height was less than 5.0% of the total height of the air channel. In this configuration, the forced flow can be the waste exhaust air flow from other mechanical ventilation systems of the building. Therefore, no additional energy is required for this solution.

Numerical simulations, particularly those based on the Computational Fluid Dynamics (CFD) Method, have been widely employed in engineering and design, such as design of green buildings. In this study, we investigated effects of the computational domain, a factor influencing the accuracy of a CFD simulation, of a solar chimney, a device for natural ventilation of buildings, on the predicted performance of a solar chimney attached to a building. Four different domains which, in turn, included both the chimney and the house, the chimney and the inlet length, the chimney with the horizontal inlet, and only the air channel of the chimney, were examined. The CFD model was based on the RANS equations and RNG k – ∊ turbulence model. The chimney had different heights, gaps, heat fluxes, and the location of the heat source in the air channel. The results show that the differences in the predicted flow rate and temperature rises through the chimney among the domains changed with the height, gap, and the location of the heat source. The simplest domain, which was a simple vertical rectangular channel, over – predicted the flow rate and under – predicted the temperature rise. The main cause of its worse performance is because of its inability to model the separation zones near the inlet of the air channel. Therefore, it is not recommended for high accuracy – simulations. Two other simpler domains, which included the inlet length and only the inlet, can be used when the required accuracy is within 10.0%. The full domain consisting of both the chimney and the building is preferred for the highest accuracy.

In this study, effects of the contractions of the inlet and outlet areas of a vertical solar chimney were examined with a Computational Fluid Dynamics. The results show that the flow rate decreased with both the inlet and outlet areas. The outlet area influenced more than the inlet area did. The flow rate decreased linearly with the outlet area, however, was affected significantly only when the inlet area was below half of the air gap.

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.

Formation of the initial bedforms, known as sand-wavelets, developing from a flat erodible bed in hydrodynamically smooth flow has been studied numerically. The computational model consists of hydrodynamic and sediment transport equations. The unsteady hydrodynamic equations are solved by Large-Eddy-Simulation (LES) and Immersed-Boundary-Method (IBM) on a non-bodyfitted grid. Dynamics of individual grains are neglected and only bedload is considered, as calculated from Van Rijn's equation (1984, Journal of Hydraulic Engineering, Vol. 110) . Two-dimensional (2D) bed evolution is coupled with the above 3-dimensional (3D) hydrodynamic equations. The computed wavelength agrees with linear stability analysis and with experimental data in the literature. The length of the sand-wavelets is observed to correspond to the disturbance region of bed shear stress caused by discontinuities on the bed surface, as postulated by Yalin (1977, Mechanics of Sediment Transport, Pergamon press) .

Experiments to examine the effects of surface roughness on the strength of rebounds from particle-wall collisions, in liquids and in air, are presented. The target walls are glass plates and have three different values of surface roughness: less than 0.3 μm, 10.5 μm, and 40.1 μm. Particles are glass beads with diameters from 1.05mm to 2.35mm. The experiments are conducted in tap water, sugar-water, and in air. Pre-impact Stokes numbers in liquids are in the range 20–170. For impacts in air, no significant effect of the surface roughness on rebound velocity is observed. In liquids, rough surfaces yield stronger rebounds than smooth surfaces. For a given ratio of surface roughness/particle’s radius, the enhancement of the surface roughness on the rebound compared to the smooth one increases when the impact Stokes number decreases toward the “rebound threshold”. These observations are in qualitative agreement with suggestions in the literature.Copyright © 2005 by ASME