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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.

PTHs are massively deployed for disaster-relief after various natural disasters. Following a previous experimental study on applying PCMs to an experimental PTH, where only a very limited number of designs were experimentally examined, in this paper, different designs of applying PCMs to a disaster-relief PTH were numerically examined and the best one identified for guiding future practical applications. A numerical model for a full-scale PTH was established using EnergyPlus and experimentally validated. Using the validated model, a two-part numerical study was carried out. In the first part, a total of 16 different designs were defined and D10 identified as the most effective one, resulting in the highest number of acceptable hours at 90. In the second part, increasing PCM's thickness to beyond 20 mm would lead to negligible effects on further improving indoor thermal environment. Hence, 20 mm thickness was recommended as a reference value for future practical applications. Furthermore, the developed EnergyPlus based model for the experimental PTH may be adapted for other types of PTHs used in different climates. Hence, the outcomes of the numerical study may also guide the future applications of PCM to disaster-relief PTHs of various configurations, and located in different climates.

We assessed whether increasing airflow with an electric fan is similarly effective as decreasing air temperature with air cooling (AC) in preventing heat-related reductions in productivity, and elevations in body temperatures and discomfort in a warm/humid indoor environment. In 48 experimental trials, we compared the reduction in the human heat stress response of sixteen participants during 135 min of intermittent arm ergometry at a fixed heart rate of 110 beats min−1, from a simulated tropical environment (HOT; 30 °C, 70%RH; wind °C, 70%RH, wind °C, 70%RH, wind = 4.2 m s−1). Cumulative work was similarly improved (+11%) by FAN compared to AC. Likewise, reductions in rectal temperature, thermal sensation, and thermal discomfort were similar with the two different cooling strategies. Sweat losses in the FAN trial were higher compared to AC but lower than HOT without fanning. In conclusion, fanning offers an effective method for alleviating thermal stress and preventing productivity losses for workers exposed to environmental heat. Moving air instead of chilling it may require a little more sweating, but it can save electricity and hence lower greenhouse gas emissions compared to AC.

In disaster relief reconstructions, the severe indoor thermal environment of the prefabricated temporary house (PTH) limits its massive utilization. Here, the application of phase change material energy storage system (PESS) has been proposed in the full-scale experimental PTH. In the experimental investigations, a movable PESS was designed aiming at regulating the indoor environment of the PTH during the daytime in hot summer, by charging the cool energy during the nighttime. The movable PESS revealed positive impacts on the indoor environment regulation in the experimental PTH. In addition, the distance between the PESS and the west wall also had influences on the cool energy discharging of the PESS and the indoor thermal environment of the experimental PTH.

Latent heat thermal energy storage (LHTES) using phase change material (PCM) has many application potentials, in view of the fact that it has higher thermal energy storage capacity than the sensible heat thermal energy storage such as stratified water storage (SWS). However, the stored thermal energy in an LHTES system is not all effective in discharging due to the additional heat transfer resistance between PCM and heat transfer fluid (HTF). An LHTES system could have a higher effective storage capacity than an SWS system only if it is well designed. The optimal design of an LHTES system could be realized only after the effective energy storage ratio, Est, is analyzed in the design stage. In comparison to the laborious computational analysis method, in this work, we developed an analytical technique from the effectiveness-NTU theory to calculate the required heat transfer length and predict Est of the basic unit in any tube-in-tank LHTES system. The technique was first compared with the numerical simulation method we reported earlier, and then used to find the optimal design under various constraints. It was shown that heat transfer enhancement in PCM could effectively improve the effective storage capacity of an optimal design. However, the maximum Est was limited by the thermal resistance in HTF when the enhancement in PCM was over a certain threshold. It was demonstrated that the use of HTF in a low-Re turbulent region could enhance heat transfer in HTF and achieve an Est as high as that in a laminar region while obtaining a higher discharging rate if heat transfer in PCM was well enhanced. This analysis provided quantitative guidelines on designing optimal tube-in-tank LHTES systems.

During disaster relief reconstructions, prefabricated temporary houses (PTHs) have been extensively used for resettling disaster victims. However, due to the nature of disaster relief, PTHs are normally light-weighted, without an electrical thermal environmental control systems installed. Hence, the thermal environments inside these PTHs can become intolerably hot in summer. Therefore, simple and low cost measures should be applied to disaster-relief PTHs for improving their indoor thermal environments. In this paper, an experimental study on applying PCMs to disaster-relief PTHs is reported. Two different designs of applying PCMs were examined. In Design 1, PCMs were fixed to the internal surfaces of a model PTH and the related experimental results demonstrated that both indoor air temperature and internal surface temperature of the model PTH can be reduced at daytime. However, in Design 2, a movable PCM based energy storage system (PESS) was used and the related experimental results suggested the use of the mobile PESS with a total charge of 148.8 kg PCM helped reduce the average indoor air temperature by 3.2–3.6 °C. The experimental results from both Designs suggested that, due to the nature of disaster relief and since outdoor air at a lower temperature may be the only cooling energy source for charging the PCM, a movable PESS system was preferred, so that it can be moved to outdoor at nighttime for being charged with more cooling energy using lower temperature outdoor air not adversely increasing the air temperature inside PTHs.

Thermal Energy Storage (TES) systems are normally utilized to assist water chillers to cut down operational cost. With the development of heat-transfer-enhancement technique, there is potential for TES systems using the latent heat of Phase Change Materials (PCMs) for emergency cooling applications. The Latent Heat Storage (LHS) systems might be able to provide thermal energy around PCM melting temperature. This study numerically calculated the basic unit of the system in a tube-in-tank design and analyzed the results by the characteristic figure, which shows the relationship between the capacity effectiveness and the heat transfer effectiveness. The parameter of the equivalent thermal conductivity of the PCM is investigated to improve the characteristic capacity effectiveness of the LHS, and the parameter of inlet temperature is evaluated by testing the operational stability of the LHS when the thermal load is unsteady. According to the numerical results, most of the stored thermal energy in the LHS can be discharged effectively around the PCM melting temperature. The characteristic capacity effectiveness can reach approximate 3 at 80% heat transfer effectiveness, indicating a three times quantity of the thermal energy provided by an equivalent water tank.

Wind flow turbulence is known to have a major influence on the pedestrian-level wind (PLW) environments, particularly around a building. The elevated design of a building, as a special feature, proved to improve pedestrian-level weak wind conditions in high-density cities. The present study aims to assess three turbulence models, the detached eddy simulation (DES), the steady-state RANS (SRANS), and the unsteady-state RANS (URANS), in their simulation of the PLW flow turbulence concerning wind gust. The simulated mean wind velocities around isolated buildings with and without an elevated design were compared with those obtained from a wind tunnel experiment. The effects of mesh resolution and inflow fluctuating algorithm on the performance of the DES model were thoroughly evaluated. The DES model can better reproduce the mean flow fields than the other two models. Finally, the unsteady fluctuations of wind flow around the buildings with and without the elevated design are analyzed in terms of instantaneous wind velocity, lift coefficient, energy spectral density, and turbulence intensity. The predicted lift coefficient and Strouhal number are approximately 0.01 and 0.09, respectively, which is consistent with what are reported in the literature. Modifications of the frequency of vortex shedding, periodical wind flow pattern, and the normalized wind gust flow fields around the two types of buildings are compared in detail. The work reveals that transient turbulent flow pattern can be reasonably obtained with the DES model, indicating the potential of using the DES for PLW gust assessments in urban planning.

City residents wish to have pleasant experience in outdoor space, which are often impeded by thermally uncomfortable conditions, particularly in hot and humid summer. Lift-up design can provide comfortable microclimate in summer but the effects of lift-up design on thermal comfort in a built-up environment have not been systematically studied. This paper aims to investigate the effects of lift-up design on outdoor thermal comfort comprehensively, as well as the effects on pedestrian level wind environment. The thermal comfort assessments are carried out by using a proposed integrated method, which combines wind tunnel tests and on-site monitoring to calculate Physiologically Equivalent Temperature (PET) values. The Hong Kong Polytechnic University (HKPolyU) campus is selected as study area. The investigation mainly focuses on summer and winter seasons. Four typical days in a year were chosen to carry out on-site monitoring for obtaining environmental parameters. This study demonstrates that the proposed integrated method can be used to predict outdoor thermal comfort. Results also show that lift-up design can effectively improve pedestrian level wind environment and thermal comfort. Moreover, lift-up design can provide a comfortable microclimate in summer while not cause strong cold stress in winter. These findings provide solid evidence bases to city planners and architects of available options for creating pleasant outdoor microclimate in precinct planning.

Radiant cooling systems are currently used in many parts of the world. However, the relatively long thermal response time of such a system causes numerous concerns regarding their operation. This study emphasizes the operation dynamic of radiant systems through on-site measurement and simulation. The results of on-site measurement imply that the capacity of heat extraction at a cooling surface can be improved by altering the operational strategy of the radiant system based on Beijing weather. The feasibility in a typical office building with a same radiant system can be studied by simulation. The results show that 9–15% of cooling energy is required during the occupied period that can be conserved in the thermal mass in advance, and the peak sensible cooling loads of terminal devices decrease at 32–39% compared with that in the conventional scheduling. Although the altered operation strategies lead to increased cooling demands, the electricity consumption and costs decrease because of the improved coefficient of performance and low electricity tariffs at night. The convectional strategy is still recommend for the radiant system with less thermal mass because the indoor environment can be controlled precisely.

Owing to the void space at lower heights, lift-up buildings have high building permeability at ground level and subsequently improve the air circulation in congested urban areas. Despite this advantage, the lift-up design has been sparsely adopted for buildings in urban areas partly because of the lack of understanding of the combined effects of building dimensions and lift-up design on the surrounding pedestrian level wind (PLW) field. Therefore, this study aims to investigate the influence of lift-up buildings with different aspect ratios (height/width) on the surrounding PLW field and pedestrian wind comfort level. Five lift-up buildings with aspect ratios 4:1 to 0.5:1 were tested in a boundary layer wind tunnel and results were compared with those of five buildings with similar dimensions but without lift-up design. The results reveal a strong dependence of the maximum wind speed in lift-up areas with building height, which results subsequently a small area of acceptable wind conditions near tall and slender lift-up buildings. Lift-up designs adopted for short and wide buildings produce larger areas of pedestrian wind comfort. The central cores modified with corner modifications are effective in increasing the pedestrian wind comfort in the lift-up area of tall and slender buildings., Highlights • Tall and slender buildings generate high-speed wind flows in lift-up areas. • Modified corners of lift-up cores improve the pedestrian wind comfort. • Lift-up cores with modified corners are recommended for tall and slender buildings.

Modern megacities are teeming with closely-spaced tall buildings, which limit air circulation at the pedestrian level. The resultant lack of air circulation creates poorly ventilated areas with accumulated air pollutants and thermal discomfort in the summer. To improve air circulation at the pedestrian level, buildings may be designed to have a ‘lift-up’ shape, in which the main structure is supported by a central core, columns or shear walls. However, a lack of knowledge on the influence of the ‘lift-up’ design on the surrounding wind environment limits the use of ‘lift-up’ buildings. This study aims to investigate the influence of ‘lift-up’ buildings and their dimensions on the pedestrian-level wind environments using wind tunnel tests. A parametric study was undertaken by using 9 ‘lift-up’ building models with different core heights and widths. The results were compared with the surrounding wind environment of a control building with similar dimensions. The results reveal that the ‘lift-up’ core height is the most influential parameter and governs the area and magnitude of high and low wind speed zones around such buildings. Based on wind tunnel test results and a selected comfort criterion, appropriate core dimensions could be selected to have acceptable wind conditions near lift-up buildings., Highlights • The effects of ‘lift-up’ buildings and their dimensions on the surrounding wind environments are studied. • The ‘lift-up’ core height is the most important parameter of a ‘lift-up’ design. • Appropriate lift-up dimensions are selected by combining wind speed data with a predetermined wind comfort criterion.

The pedestrian level wind environment is seriously deteriorated by moderated local wind flow in a densely built-up subtropical city like Hong Kong. In order to improve the weak wind condition, the lift-up design has been used for some time. However, there is a lack of understanding and quantitative assessment of its modification on the pedestrian level wind comfort around different building configurations under different wind directions. This paper aims to study the effects of lift-up design in four common building configurations on the wind comfort via computational fluid dynamics (CFD) simulations. The turbulence model and numerical method are firstly validated by comparing the simulated wind flow data with the wind tunnel test results. The validated model is then utilized to simulate the four building configurations, including the “─”, “L”, “U” and “□” shaped buildings. The mean wind velocity ratio ( MVR ) and mean wind velocity change ratio ( Δ MVR ) are employed to identify the wind comfort and to quantitatively evaluate the improvements due to the lift-up design. Results show that the lift-up design can improve the wind comfort in building surroundings and its influence is highly dependent on the incident wind direction. Specifically, the wind comfort is better under the oblique wind direction than the other two wind directions. These findings can provide us a better understanding of the lift-up design and will be helpful in better precinct planning.

This study aims at further investigating the respiratory infectious diseases transmission in typical high-rise residential (HRR) environments, and at developing reliable CFD modeling method. The inter-building dispersion under wind effect was focused on and the cross-infection risk was assessed. The URANS model and DES model were compared, and the representation of surroundings was evaluated to improve the prediction of airflow and pollutant dispersion among a group of buildings. The DES model can better reproduce unsteady fluctuations of airflow around the buildings, and can accurately predict the frequency of vortex shedding. The predicted Strouhal number is approximately 0.15, which is consistent with the reported value in literature, whereas the URANS model fails to reproduce the whole features of unsteady airflow and significantly under-estimates the vortex shedding frequency. Ignoring the surrounding buildings in the simulation will significantly over-estimate the downward dispersion and over-estimate the risks in lower heights. The tracer gas concentrations near the downstream buildings are four orders lower than the concentration in the index/source unit, but only one order lower than the concentration in the leeward side and on the roof of the index building, and therefore the risk is comparable to that of intra-building dispersion within the index building. The tracer gas can diffuse to a long distance with slow concentration decay in empty areas. The cross-infection risk of inter-building dispersion should not be overlooked, especially when a super infector with high pathogen generation rate exists.

Wind flow turbulence plays a critical role in the pedestrian level wind environment, particularly for the airflow around buildings with specific architectural features. The elevated design, a feature was proved to improve the pedestrian level weak wind conditions in high-density cities in our earlier study. This present study aims to further investigate the pedestrian level wind flow turbulence in an elevated building surrounding. The predictions were conducted by comparing the CFD simulation and a wind tunnel experiment. Specifically, the Detached Eddy Simulation (DES), the Steady-state and the Unsteady-state RANS (SRANS and URANS), were assessed. The effects of mesh resolutions and inflow fluctuating algorithms on the performance of the DES model were thoroughly evaluated. DES can better reproduce the mean flow fields than the other two models. The unsteady flow fluctuations around the elevated building are analyzed with energy spectral density. Meanwhile, the periodical wind flow fields around the elevated building are accurately obtained.

Outdoor activities are believed to provide citizens with various benefits, including stress reduction, livability improvement and energy conservation. Encouraging outdoor activity becomes an effective way to evocate positive emotions. Thus, numerous studies were established to enhance respondent outdoor thermal comfort by investigating landscape design and building morphology. Yet, studies on the outdoor microclimate and thermal comfort in the underneath-elevated-building (UEB) area were scarce. In this study, on-site measurements and questionnaire surveys were conducted from March to December in 2016. Comparisons of meteorological parameters and respondent thermal perceptions between the underneath-elevated-building area and the direct-radiated (DR) area were presented. Results indicated that occupants were more comfortable in UEB area. It appeared that solar radiation and wind speed were two major issues affecting respondent outdoor thermal comfort and highly relative to occupants’ thermal sensation, which can be helpful references for urban planners to optimize outdoor microclimates by altering building designs.

As one of the leading journals in building energy studies, Energy and Buildings has witnessed the great efforts in the research community and professional society in advancing the state-of-the-art of HVAC systems since its founding. In this paper, a critical review on the development of advanced, energy-efficient HVAC systems in the past 30 years is presented. Specifically, attention is paid on stratified ventilation, heat recovery ventilation, thermal storage, indirect evaporate cooling technology, and the independent control of temperature and humidity design which involves radiant cooling system and solid/liquid desiccant system. The review covers, but is not limited to, mechanism investigation, numerical model development, experimental verification/calibration, and equipment development. Areas that have not yet been studied in-depth were exposed. The limits and future application potentials of each technology were also discussed.

Single-sided natural ventilation is an energy efficient ventilation strategy that could provide satisfactory indoor air quality and thermal comfort. However, one of its possible negative influences is the cross-infection between households due to the two-way airflow. The present study aims at assessing the efficacy of mechanical exhaust (ME) devices to eliminate this possible cross-infection. CFD method was employed to simulate the buoyancy driven single-sided natural ventilation and the cross-contamination. Different occupant behaviour scenarios, such as ME-on centrally or ME-on individually, were compared with the no-ME case. It is found that mechanical exhaust could reduce the outflow of indoor air and increase the inflow of fresh air. However, the weakened outflow tends to be more attached to the facade and the re-entry risk may be increased. As the exhaust rate is large enough, the two-way airflow will turn into one-way inflow, and accordingly the vertical cross-household infection can be avoided. With ME-on in both floors, a low exhaust rate of 5 h −1 could reduce the presence of the tracer from the lower floor in the upper floor by an order of magnitude. But if the ME is on only in one of the two floors, the re-entry of outflow to the upper floor may be aggravated at some specific exhaust rate. Therefore, in epidemic seasons, appealing residents to switch on their individual exhaust fans, or alternatively switching on a central exhaust system is recommended. The results will contribute to the control of airborne transmission infectious diseases in high-rise residential buildings.

Green building design is presently among the hottest research topics in the world. Maintaining a comfortable indoor environment with minimum energy consumption is a challenging task that attracts the attention of experts around the world. With the recent advances in building performance simulation tools, it is now possible to predict and assess building performance at the design stage. Simulation-based optimization of building design is a potential application that connects building performance simulation with optimization algorithms. In this paper, numerous studies on the optimization of building envelope design were assembled and reviewed. Popular optimization algorithms were compared and discussed. Targeted objectives were collected and summarized. Based on the statistical results, the limitations in this research area were identified, and some potential breakthroughs were suggested.

The choice of proper turbulence models in computational fluid dynamics is still a challenging issue for accurately predicting outdoor microclimate and thermal comfort conditions in urban planning. This study compared the performances of the Steady Reynolds Averaged Navier–Stokes (SRANS) RNG k-e , Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) modeling approaches in simulating the wind flow around an isolated building (with a 1:1:2 shape). The effects of the computational parameters were analyzed, including the grid resolution for all cases, and the discretization time step ( Δt ) and non-dimensional sampling time ( t * ) for the LES and DES cases. The results of the LES and DES simulations were affected by the gradual decrease in Δt and increase in t * until the two parameters reached 0.005 s and 288, respectively. The mean velocity fields on the windward side of the building predicted by the three models were in good agreement with the wind tunnel results. However, the results of the LES and DES cases were in better agreement with the experimental results for the leeward and lateral regions in both vertical and horizontal planes. The DDES (Delayed Detached Eddy Simulation) and LES models predicted similar results in the wake region, but the DDES has a lower overall mesh requirement. It is encouraging that the DDES model provides not only the mean flow field, but also the instantaneous wind characteristics, which can be useful for more accurate analysis of outdoor wind and thermal comfort.

Local air circulation is influenced by the drag forces exerted by urban vegetation. In this study, tree canopy parameterization in computational fluid dynamics (CFD) with source term modifications is conducted at the tree scale, which builds upon the models previously used in the literature. A simplified three-dimensional model representing tree canopies is resolved and validated against available wind tunnel experiment. The prediction of turbulence kinetic energy (TKE) is shown to be highly sensitive to the model coefficients in the source term of turbulence dissipation rate (TDR). No optimal set of the model coefficients in the TDR source term can be identified. However, C e 4 > C e5 is found to better reproduce the turbulent quantities behind the canopy than C e4 = C e5 . The reduction of C e 5 value from 1.5 to 0.4 yields a higher TDR source term level by one order of magnitude. The prediction of the mean velocity is primarily controlled by the form drag coefficient, which is heavily correlated to all source terms and their components. Results indicate the feasibility of using a more straightforward modification method in the vegetated microclimate simulations by only adding momentum source terms.

Low airflow or poor outdoor ventilation around building blocks can negatively influence pollutant dispersion in the surroundings and indoor air quality, and increase the risks of airborne transmission of infectious diseases. However, there have been few studies addressing the wind environment, thermal comfort and other concerns at the pedestrian level. Buildings with a lift-up design may have a number of impacts on the pedestrian-level wind and thermal environments. Three building configurations that resulted in the lowest wind speed zones were identified from a previous study. A 3.5 m high open ground floor was added to each of the three configurations, and scale models of the three designs were studied in a wind tunnel to assess their influences on airflow and ventilation around the buildings. Undesirable areas of low wind speed leading to poor air ventilation and, on the other side of extreme, areas of discomfort due to strong wind conditions were both identified, and their practical implications are discussed.

A stratified air distribution (STRAD) system is a feasible air conditioning design for large space buildings that satisfies the energy conservation and thermal comfort requirements. In this paper, a novel energy efficiency index for STRAD systems is developed using theoretical analysis to properly evaluate the system's energy saving potential. Using a validated numerical model, two typical stratified air distribution designs in a hypothetical terminal building are evaluated based on thermal comfort and energy savings. The influence of supply and return diffuser distributions on the ventilation performance of these two ventilation designs is studied. When the air is supplied at mid-height, the local thermal comfort is greatly improved without sacrificing the energy efficiency due to additional return grilles located at exterior walls. When the air is supplied at floor level, installing additional return grilles at exterior walls slightly alleviates the local draft risk, but doing so largely impairs the energy saving capacity of the ventilation system. To achieve better thermal comfort and higher energy efficiency, a more uniform distribution of supply diffusers surrounding the occupied zone is suggested. When the air is supplied at the floor level, increases in solar radiation intensity can be mitigated by utilizing external shading designs, which are particularly important in preventing too large of a temperature gradient in the region exposed directly to the solar radiation.

To achieve a more comfortable indoor environment while still retaining low energy consumption level is an exciting challenge for designers and owners of buildings. In this paper, a silica-aerogel filled super-insulating glazing system was proposed. A numerical study was conducted to analyze the energy performance and visual performance of the proposed glazing system. Two popular building simulation programs namely EnergyPlus and Radiance were applied in the numerical study. In the study of the energy performance, three control strategies (space temperature control, operative temperature control and PMV control) were applied to simulate the occupant’s control behavior toward the air-conditioning system in reality. The result indicated that compared with conventional single clear glazing, the silica aerogel glazing could retain a 4% longer thermally comfort period, while the energy consumption of HVAC system was reduced by 4–7%. The performance of the silica aerogel glazing was almost equal to that of the state-of-art low-e glazing. It is also concluded that as the occupant’s request on thermal comfort got stricter, the performance of the silica aerogel glazing would became better. In the visual comfort point of view, it can be concluded that the glare effect and near-window bright zone could be reduced significantly while indoor illumination level still met the requirement.

Solar radiation through glazing area is one major source of the space cooling load in subtropical cooling-dominant climates. Application of energy-efficient glazing system can significantly reduce the energy consumption of air-conditioning systems in summer, thus has become a hot research topic. In this paper, a super-insulating glazing system was studied, which was formed by two layers of conventional single clear glass panes and a layer of silica aerogel filled in between. Several glazing samples were prepared. The thermal and optical parameters were measured. An annual HVAC (heating, ventilation and air conditioning) system energy analysis was also conducted based on the space cooling load simulation. The result indicated that in humid subtropical climates like Hong Kong, the application of silica aerogel glazing system can reduce the annual space cooling load by around 4% in a typical commercial building. With respect to the envelope heat gain, the reduction could be around 60%. It was also found that the silica aerogel glazing system performed better if the internal heat source in a building took a small proportion in the total space cooling load.

Conducting energy-efficient designs on building window can be a solution to relieving the pressure caused by growing building energy consumption. In this paper, a series of simulation studies were carried out to evaluate the performance of several popular energy-efficient window designs in cooling-dominant climates. Both thermal and daylighting performance were considered during the analysis. Results indicate that among all designs studied, low-e glazing achieves a best performance, while double-layer glazing performs the worst. Energy-efficient designs on the east and west orientations are the most cost-effective in cooling-dominant climates. As latitude rises, the performance of window designs on the south orientation is getting better. It is also discovered that only in area very close to equator performance of north facing window designs is satisfactory. Furthermore, as the reflectivity of blind louver decreases, both thermal and daylighting performances drop.

In this paper, using a newly defined cooling coil load calculation method for stratified air distribution (STRAD) systems, the effects of separate location of the return and exhaust grilles on thermal comfort and energy saving are experimentally investigated. The results clearly demonstrated the extra energy saving potentials for STRAD systems with separate locations of return and exhaust grilles. After using the experimental results to validate our CFD method, numerical investigation is carried out for an office setting. Decreasing the height of return grille will increase exhaust air temperature and significantly reduce the cooling coil load. However, the risk of poor thermal comfort caused by too large temperature difference between the head and foot levels also increased, when the return inlet is located close to the floor level. Locating the exhaust grilles at ceiling level and close to external wall while locating the return grilles at the upper boundary of the occupied zone are recommended in practice. It is demonstrated that the purpose to simultaneously achieve satisfied thermal comfort and prominent energy saving can be attained with a STRAD system via deliberate locations of supply outlets and return and exhaust grilles in relation to the heat source locations.

Balconies are green features commonly used in residential buildings to improve natural ventilation and air quality. Small vents, if mounted with an acoustic silencer, can reduce noise penetration while still allowing natural ventilation to occur. In this study, the computational fluid dynamics method is used to investigate numerically the effect of balconies with small upper and lower vents on the ventilation and air quality of the 4th, 5th and 6th floors of a 10-storey building. The results show that balconies can significantly increase the natural ventilation on these floors and generally have a more positive effect on the improvement of natural ventilation and the reduction in pollutant concentration on the floor on which they are located rather than on the levels above or below. Practical application: This study will help designers and engineers understand more about the effect of balconies and lower and upper vents on natural ventilation and indoor air quality in buildings. This study will also help them to incorporate with confidence the design of balconies with lower and upper vents.

Compared with the buoyancy-dominated upward spread, the interunit dispersion of pollutants in wind-dominated conditions is expected to be more complex and multiple. The aim of this study is to investigate the wind-induced airflow and interunit pollutant dispersion in typical multistory residential buildings using computational fluid dynamics. The mathematical model used is the nonstandard k-ε model incorporated with a two-layer near-wall modification, which is validated against experiments of previous investigators. Using tracer gas technique, the reentry of exhaust air from each distinct unit to other units on the same building, under different practical conditions, is quantified, and then, the possible dispersion routes are revealed. The units on the floor immediately below the source on the windward side, and vertically above it on the leeward side, where the reentry ratios are up to 4.8% and 14.9%, respectively, should be included on the high-infection list. It is also found that the presence of balconies results in a more turbulent near-wall flow field, which in turn significantly changes the reentry characteristics. Comparison of the dispersion characteristics of the slab-like building and the more complicated building in cross (#) floorplan concludes that distinctive infectious control measures should be implemented in these two types of buildings.

The thermal performance of building envelopes is the determinant factor of building energy consumption, and especially envelope retrofitting is an effective way of reducing energy consumptions in existing building. For different climates, there may exist different optimal retrofitting schemes. In this paper, two most popular retrofitting methods, namely thermal insulation and high-reflectivity coating on building walls in cooling dominate cities are investigated. Four cities with different climates are selected, and the impacts of internal versus external thermal insulation are investigated. Result indicates that in cooling-dominant cities employing both thermal insulation and high reflectivity coating could significantly reduce cooling load through building external wall. Also, performance of retrofitting on different wall surface varies with different orientations. In climates with little diurnal temperature change in the summer season, internal insulation performs better than external insulation in reducing air-conditioning load, which typically operates during part of a day, whereas in climates in which there is a free cooling period during the night, external insulation will perform better.

Re-ingestion of the contaminated exhaust air from the same building is a concern in high-rise residential buildings, and can be serious depending on wind conditions and contaminant source locations. In this paper, we aim to assess the prediction accuracy of three k-ɛ turbulence models, in numerically simulating the wind-induced pressure and indoor-originated air pollutant dispersion around a complex-shaped high-rise building, by comparing with our earlier wind tunnel test results. The building modeled is a typical, 33-story tower-like building consisting of 8-household units on each floor, and 4 semi-open, vertical re-entrant spaces are formed, with opposite household units facing each other in very close proximity. It was found that the predicted surface pressure distributions by the two revised k-ɛ models, namely the renormalized and realizable k-ɛ models agree reasonably with experimental data. However, with regard to the vertical pollutant concentration distribution in the windward re-entrance space, obvious differences were found between the three turbulence models, and the simulation result using the realizable k-ɛ model agreed the best with the experiment. On the other hand, with regard to the vertical pollutant concentration distribution in the re-entrant space oblique to the wind, all the three models gave acceptable predictions at the concentration level above the source location, but severely underestimated the downward dispersion. The effects of modifying the value of the turbulent Schmidt number in the realizable k-ɛ model were also examined for oblique-wind case. It was confirmed that the numerical results, especially the downward dispersion, are quite sensitive to the value of turbulent Schmidt number.

Complaints on thermal comfort and confusions on cooling load calculation are still two main issues for the design of stratified air distribution (STRAD) system. This paper investigated these two issues for STRAD systems applied in a large space lecture theatre. The simulation results revealed that best satisfied thermal environment was obtained when supplied air from floor level, terrace and desk-edge mounted grilles simultaneously. A new method for the calculation of the occupied zone cooling load, which is based on CFD (computational fluid dynamics) simulation was proposed and tried. The effective cooling load factor concept was further clarified, which can be conveniently used to calculate the occupied zone cooling load and then determine the supply airflow rate. The concepts of occupied zone cooling load reduction and the associated but different cooling coil load reduction were differentiated, and it was illustrated that cooling coil load reduction up to 16.5% of the space cooling load can be achieved with split location of return and exhaust grilles. These simulation works provide a good basis for full-scale experimental validation of the key energy saving features of a well-designed stratified air distribution system.

Microencapsulated phase change material (MPCM) slurry provides a good kind of medium for thermal energy storage due to its thermal properties, especially proper working temperature, which is appropriate for maximized utilizations of nature cooling sources. In this study, a novel MPCM slurry storage system is investigated by combining MPCM slurry storage with a nocturnal radiative cooling system. The cooling energy consumption and the effect of energy-free nocturnal radiation application were simulated using the energy simulation code ACCURACY and MATLAB model based on hour-by-hour calculations in five typical cities across China. It can be concluded that MPCM slurry appears to be a good medium for the combined application of passive cooling technology in air conditioning system. The results showed the energy saving potential in Lanzhou and Urumqi can reach 77% and 62% for low-rise buildings, which exhibits strong attractions for building energy conservation and emission reduction. Hong Kong has the weakest effect in the five typical cities under the same operating condition due to the hot and humid climate condition. The present hybrid system is recommended to be used in northern and central China cities where the weather is dry and the ambient temperature is low at night.

A number of radiant heating/cooling systems have been applied in Mainland China in recent years for its improved thermal comfort and inherent energy saving potential. Because the systems require relatively higher temperatures for cooling and lower temperatures for heating, many natural low-grade energy sources can be directly or indirectly used. However, because of a lack of information about prior practical projects, a number of difficulties in design, construction and management of the systems have been encountered, and energy efficiency is not necessarily achieved in all situations. This paper reviews the practical applications in four major projects involving different building types located in different climatic cities and presents the associated considerations in system design. Other factors affecting the energy efficiency of the systems are identified, such as the spatial convection and radiation heat transfer processes in indoor environments and the envelope thermal properties. Further studies are needed to achieve system optimization and to realize the full energy saving potentials of radiant systems by developing analytical design methods and monitoring the actual energy use of such systems in completed projects.

Energy-efficient retrofitting of existing building is a huge contribution to the sustainability of the society since building energy consumption takes more than one fourth of total energy consumption. The application of external shading system could block out unwanted radiant heat gain, thus reduces the cooling load of the air-conditioning system. During the assessment of energy-efficient retrofitting projects, apart from annual saving figures and economic payback time, energy and CO 2 emission payback periods should also be taken as indispensable references. In this paper, a methodology is described for analyzing the energy and CO 2 emission payback periods of external overhang shading in a university campus in Hong Kong. Result shows that due to requirements of structural strength under typhoon situation, although introducing overhang shading system could reduce almost half of the cooling load in the related area, the energy and CO 2 emission payback periods of the project are still unrealistically long. This case study presents an example of multi-disciplinary approach being not only important to the energy-efficient retrofitting but also necessary for policy making in different climatic and geographic regions.

Thermal comfort may be achieved more energy-efficiently in non-uniform thermal environments than in uniform ones, and such environments are also frequently transient, so developing a thermal comfort model to evaluate thermal comfort asymmetrical environments or transient conditions has being an hotspot of recent study. This paper first reviews several thermal comfort models that address local thermal sensations and attempts to distinguish these models by their advantages, limitations and suitable ranges of applications. Then, two typical thermal comfort models, the simple ISO 14505 standard method and the comprehensive UC Berkeley thermal comfort model (UCB model), were coupled to computational fluid dynamic (CFD) numerical simulation with different process to evaluate thermal environment of a small office. The results indicated that compared with the UCB model, the ISO 14505 index could be applied with caution as a convenient method to evaluate thermal comfort in non-uniform, overall thermally neutral environments.

The windcatcher system is a green architectural feature that uses natural ventilation to induce external airflow into residential buildings. This paper presents different configuration and ventilation strategies for the windcatcher to evaluate the performance of the system in relation to ventilation and indoor particle dispersion. A commercial computational fluid dynamic (CFD) code is used to evaluate the windcatcher’s performance using different numbers of louvers and louver lengths. The effects of buoyancy and window positions on the system’s performance are considered. The flow rate of air induced into the windcatcher is found to increase with the number of louver layers and the highest ventilation rate is reached when the louver length equates with the reference length. With respect to the buoyancy effect, the results show that the system performs well in stimulating airflow and removing contaminants when a window is positioned on the leeward side. A uniform and low particle concentration is created when a window is positioned on the leeward side. However, due to the high air velocity below the windcatcher, the general airflow distribution of the system is not uniform. A damper or egg crated grill should be installed at the terminal of the system, especially when the external wind is strong.

Highlights ► We examine unsteady characteristics of cross-contamination in high-rise building. ► The values of concentration fluctuation intensity were greater than 1 and can be up to 10. ► The intermittency factor and peak-to-mean ratio can be up to 0.8 and 70, respectively. ► The concentration fluctuation is increased under open-window conditions. ► Instantaneous peak infection risk is below 0.1% under open-window condition., This article presents experimental results that illustrate the unsteady characteristics of gas dispersion around a complex-shaped high-rise building for different incident wind directions. A series of wind tunnel experiments were conducted using a 1:30 scale model that represented the real structures under study. The objective of this paper is to study the behaviour of concentration fluctuations through transient analysis. Tracer gas was continuously released from a point source located at different positions, and a time series of fluctuating concentrations were recorded at a large number of points using fast flame ionization detectors. The experimental data were analysed to provide a comprehensive data set including variances and associated statistical quantities. Both the unsteady characteristics of the system and their potential practical impact are presented and discussed. Under crowd living conditions, the air pollutant exhausted from one household could probably re-enter into the neighbouring households, traveling with ambient airflow. Such pollutant dispersion process is defined as air cross-contamination in this study. The results indicate that the wind-induced cross-contamination around the studied type of high-rise building should not be overlooked, and the fluctuating concentrations should be paid attention to particularly during the evaluation of a potential contamination risk. This study can help deepen our understanding of the mechanisms of air cross-contamination, and will be useful for implementing optimization strategies to improve the built environments in metropolitan cities such as Hong Kong.

This article presents a numerical study of ventilation performance of balconies using computational fluid dynamics. The pressure coefficients distributed on the opposite walls of a five-storey building model, both with and without balconies, were studied under variation of the wind direction, balcony dimensions and building height. The effect of balconies on the capacity for wind-induced natural ventilation is discussed. The numerical results show good agreement with the experiments of Chand et al. They also indicate that a balcony enhances the cross-ventilation of intermediate floors but weakens that of the ground and top floors, by significantly changing the pressure distribution on the windward wall. Finally, the ventilation performance of a balcony is not greatly affected by variations in its size but is slightly weakened as the height of the building increases. Practical application: This study provides information and guidance in how best to incorporate the use of a balcony in building development at the design stage.

Chand et al. conducted experiments in a low speed wind tunnel to study the effect of balconies on the ventilative force on low-rise buildings without openings. Using their model, this study intends to investigate indoor ventilation performance by examining mass flow rate and average velocity on the working plane using computational fluid dynamics. Simulations were validated against their experiments. The numerical results indicate that, for single-sided ventilation, the provision of balconies increases mass flow rate and reduces average velocity on the working plane in most rooms, but for cross ventilation, this provision has no significant effect under normally or obliquely incident wind conditions. After the addition of balconies, the worst ventilation circumstances on the windward side under single-sided ventilation conditions were found on the intermediate floor. The simulation results also showed that, in many cases, wind flows into and out of the rooms through the left or right side of the opening rather than through the bottom and top of the opening, especially in the case of buildings that are obliquely oriented to the air stream. This phenomenon demonstrates that predictions of single-sided ventilative force using data relating to the bottom and top parts of the opening are not accurate enough.

The presence of the parapet and floor of a balcony is expected to have a range of effects on a building’s environmental behaviour, in terms of aspects, such as natural ventilation, thermal comfort, pollutant transportation and shading and daylighting. The authors have previously reported that the presence of a balcony can significantly increase the air flow rate of most rooms in a naturally ventilated building. In this study, the CFD technique and Fanger and Toftum’s extended PMV—PPD model are combined to investigate numerically the effect of a balcony on thermal comfort for naturally ventilated buildings in tropical-humid regions. The results show that although a balcony reduces the indoor average velocity for most rooms, and in turn increases the PMVnv value in both the seated and standing positions, it does not change the indoor thermal comfort level. However, the presence of a balcony improves comfort by increasing the uniformity of indoor air distribution. PMVnv is also shown to be less sensitive to velocity than PMV, allowing for a wider thermal comfort range for naturally ventilated buildings. Practical application: This study will help designers and engineers who are considering the use of a balcony at the design stage to have a better understanding of its effect on thermal comfort in naturally ventilated buildings.

This paper investigated the transmission of respiratory droplets between two seated occupants equipped with one type of personalized ventilation (PV) device using round movable panel (RMP) in an office room. The office was ventilated by three different total volume (TV) ventilation strategies, i.e. mixing ventilation (MV), displacement ventilation (DV), and under-floor air distribution (UFAD) system respectively as background ventilation methods. Concentrations of particles with aerodynamic diameters of 0.8 μm, 5 μm, and 16 μm as well as tracer gas were numerically studied in the Eulerian frame. Two indexes, i.e. intake fraction (IF) and concentration uniformity index RC were introduced to evaluate the performance of ventilation systems. It was found that without PV, DV performed best concern protecting the exposed manikin from the pollutants exhaled by the polluting manikin. In MV when the exposed manikin opened RMP the inhaled air quality could always be improved. In DV and UFAD application of RMP might sometimes, depending on the personalized airflow rate, increase the exposure of the others to the exhaled droplets of tracer gas, 0.8 μm particles, and 5 μm particles from the infected occupants. Application of PV could reduce RC for all the three TV systems of 0.8 μm and 5 μm particles. PV enhanced mixing degree of particles under DV and UFAD based conditions much stronger than under MV based ones. PV could increase the average concentration in the occupied zone of the exposed manikin as well as provide clean personalized airflow. Whether inhaled air quality could be improved depended on the balance of pros and cons of PV.

Ice storage is currently the dominant cooling energy storage method. To more effectively utilize natural, renewable cooling sources, such as evaporative cooling and sky-radiative cooling, diurnal storage media operated on a daily basis at the temperate range between 10 and 20 °C are the most desirable. This paper will present the experimental investigation of microencapsulated paraffin slurry as cooling storage media for building cooling applications. The water slurry of microencapsulated n-hexadecane with a melting temperature of 18 °C was cooled to 5 °C and heated to 25 °C cyclically in a storage tank of 230 l, and it was observed that full latent heat storage can only be realized at around 7 °C due to supercooling, and the effective cooling storage capacity at the cooling temperature range between 5 and 18 °C are obtained, which can be used to realistically estimate cooling storage capacity with various natural cooling schemes.

Microencapsulated phase change material (MPCM) slurry is advantageous for thermal storage systems to use as a heat transfer and storage medium. In this paper, a new design of air-conditioning system is proposed, which is a combination of CC and a MPCM slurry storage tank. The mathematical model of the combined system is provided and used to predict the system performance of an office room under Hong Kong weather condition using hour-by-hour calculations. A feasibility analysis for the combined system was also made with computer calculations. The results indicate that a small MPCM slurry storage tank is able to shift the part of cooling load from the daytime to nighttime. It is also revealed that the proposed combined system is an energy saving and economy-favorable air-conditioning system.

By contrast with the conventional heat transfer fluid (water), the microencapsulated phase change material (MPCM) suspension, with a small temperature difference between storing and releasing heat, is of much larger apparent specific heat and much higher thermal energy storage capacity. It has been suggested to serve as a dual-functional medium for thermal energy transport and/or storage. The heat transfer characteristics of a kind of MPCM suspension, formed by microencapsulating industrial-grade 1-bromohexadecane (C16H33Br) as phase change material, were experimentally studied for laminar flow in a circular tube under constant heat flux. A new expression of Ste is put forward in the paper, according to the physical definition of Stefan number. The results in the experiments show: (a) the dimensionless internal wall temperature of the MPCM suspension is lower than pure water, and the decrease can be up to 30% of that of water; (b) the heat transfer enhancement ratio can be 1.42 times of that of water at x+ = 4.2 × 10−2 for 15.8 wt% MPCM suspension, which is not as much as in some references; and (c) the pump consumption of the MPCM suspension system decrease greatly for the larger heat transfer rate compared with water, due to phase change, the decrease can be up to 67.5% of that of water at q = 750 W (15.8 wt%). The kind of MPCM suspension has good application feasibility in practice.

Evaporative cooling is able to generate the cooling medium at a temperature approaching to the ambient wet bulb temperature. In this paper, a low-energy air-conditioning strategy is proposed, which is a combination of cooled ceiling (CC), microencapsulated phase change material (MPCM) slurry storage and evaporative cooling technologies. The assessment of evaporative cooling availability and utilization is done for five representative climatic cities, including Hong Kong, Shanghai, Beijing, Lanzhou and Urumqi in China, and the energy saving potential of the proposed air-conditioning system is analyzed by using a well validated building simulation code. The results indicate that the new system offers energy saving potential up to 80% under northwestern Chinese climate and up to 10% under southeastern Chinese climate. The optimal design method of the slurry storage tank is also proposed based on the slurry cooling storage behaviors and cooling demand variations of the ceiling panels.

UNLABELLED In the worldwide spread of Severe Acute Respiratory Syndrome (SARS) in 2003, cluster of cases occurred in a number of large high-rise residential building blocks, especially in Hong Kong. In this study, we examined one of the most likely virus-spread mechanisms, which is related to the inter-flat or inter-zonal airflow through open-windows caused by buoyancy effects. Dual tracer gases of CO2 and SF6 are employed simultaneously to quantify the amount of the exhaust air coming out of the upper part of the window of a floor that re-enters the lower part of the open-window at the immediate upper floor. It was found that the room air could contain up to 7% of the exhaust air from the lower floor, and this occurs at low wind conditions with a combination of indoor-outdoor temperature difference. The results can well explain the earlier governmental finding that DNA strings of SARS Corono-Virus were detected within the sampled deposits on the window sills of the upper floors of the two index patients' flats. The preliminary and yet alarming conclusion may be that, in high-rise buildings, windows flush with a flat facade can be a major route for the vertical spread of pathogen-containing aerosols. PRACTICAL IMPLICATIONS The confirmation of the transmission route can have a number of implications to both building design and infectious disease control. With respect to the former, considerations should be given to minimize the inter-flat airflow via windows flush with facade for high-rise buildings with natural ventilation; and with respect to the latter, more targeted and earlier intervention can be implemented in case of any highly infectious disease outbreaks.

Larger window openings in the walls of a building may provide better natural ventilation. However, it also increases the penetration of direct solar radiation into indoor environment. The use of wing wall, one of the green features, is an alternative to create effective natural ventilation. Givoni conducted experiments in a wind tunnel to study the ventilation performance of wing walls. This paper presents a numerical study of the ventilation performance of wing walls using computational fluid dynamics (CFD). Two-dimensional and three-dimensional simulations are compared with the results of the experiments of Givoni. The results indicate that wing wall can promote natural ventilation by increasing the air change per hour and the mean indoor air speed relative to wind speed at various wind speeds and wind directions. The best performance of wing wall is at the wind angle of around 45°. The study also shows that 3D CFD simulation produces similar trend to the experimental results though there are some discrepancies.

Building envelopes are usually comprised of several different layers of building materials, which may alternatively act as VOC sources or sinks depending on their emission and sorption potentials and the indoor environmental conditions as well. In this research, a whole room IAQ model consisting of multi-phase emission/sorption model for wall materials and room volume mass balance model catering for practical ventilation schemes was developed. The interactions of VOC and building materials composing different building components can be modeled based on fundamental mass transfer theories. The effects of various construction materials and ventilation strategies on the emission characteristics were investigated. Results show that measures like pre-occupancy flush-out, lead-time ventilation, etc. have substantial impacts on indoor VOC concentration and the model can successfully handle different building scenarios. Although more rigorous validation, in particular more experimental verification, is needed, the proposed model has proven to be valuable in handling different building scenarios. It is useful in analyzing the levels of contaminant buildup that would occur during no ventilation period for intermittent ventilation situations and in determining the amount of outdoor air and the lead-time period required to flush out the contaminants prior to occupancy. It is likely to be a simple routine tool for building owners, designers and operators to attain acceptable indoor VOC concentration level.

In this paper, we investigated the pollutant exposure reduction and thermal comfort that can be achieved with personalised ventilation (PV) design when a PV system is combined with two types of background air conditioning systems. For the investigation of inhaled air quality, pollutants emitted from building materials are the targeted pollutants; and for the investigation of thermal comfort, local discomfort associated with nonuniform thermal environment is focused upon. These investigations were performed by combining CFD simulation of the 3D air flow and a multi-nodal humanbody thermo-regulation model. The results reveal some new characteristics of the three typical air distribution designs, i.e. mixed ventilation, displacement ventilation and PV, and provide insight into the possible optimisation of system combinations.