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This paper presents a theoretical study of an inertial actuator connected to an accelerometer by a local feedback loop for active vibration control on a floating raft. On the criterion of the minimum power transmission from the vibratory machines to the flexible foundation in the floating raft, the best mounting positions for the inertial actuator on the intermediate mass of the floating raft are investigated. Simulation results indicate that the best mounting positions for the inertial actuator vary with frequency. To control time-varying excitations of vibratory machines on a floating raft effectively, an automatic control system based on real-time measurement of a cost function and automatically searching the best mounting position of the inertial actuator is proposed. To the best of our knowledge, it is the first time that an automatic control system is proposed to move an actuator automatically for controlling a time-varying excitation.

Driven by wind and buoyancy effects in the urban environment, ventilation performance and pollutant transmission are highly related to human health. In order to investigate characteristics of the single-sided natural ventilation and interunit dispersion problem, this study conducted scaled outdoor experiments in summer and winter periods in two-dimensional street canyons. Tracer gas method was adopted to predict the ventilation rate and simulate the pollutant dispersion. It was found the ventilation performance of windward and leeward rooms showed different trends with wind velocities. Archimedes number Ar was used to examine the interactions of the buoyancy and the wind forces. It revealed that the non-dimensional ventilation rates of all rooms were generally smaller than the results of buoyancy effect only. It indicates that interactions between the buoyancy and wind effects were destructive, which reduced the ventilation rates. The interunit dispersion characteristics with the wind effect were highly dependent on source locations. The results of the tracer gas concentrations of the reentered rooms were not showing simple increasing or decreasing trends. This study provides authentic and instant airflow and pollutant dispersion information in an urban environment. The dataset of this experiment can offer validations for further numerical simulations.

This paper presented a theoretical study of the vibration control of a floating raft system using periodic structures. The band gap properties of the periodic structures, the power flow and the power transmissibility of the floating raft system were investigated by using the transfer matrix method. To minimize the power flow through periodic structures in a floating raft system, the geometrical parameters of the periodic structures were optimized by using a genetic algorithm. The numerical results demonstrated that the optimum periodic structure can provide broader stop band regions. The stop band regions of the optimum periodic structure contained all the harmonic frequencies of the force excitation in the floating raft system. The numerical results validated that the proposed optimization approach is sufficiently capable for the design of periodic structures. The proposed optimization approach has potential use for the development of vibration and shock isolation systems such as floating raft systems.

In this paper, an assessment model based on multi-layer fuzzy comprehensive evaluation method (FCE) of classroom acoustical environment is proposed. The model classifies five major factors affecting overall assessment model into several subsets alternatives. The weightings of these main criteria and alternatives were collected through questionnaires among students based on analytic hierarchy process methodology (AHP). An evaluation score was calculated from the proposed model with the weightings generated from AHP method. In this paper, classrooms in the Hong Kong Polytechnic University were used to develop the assessment model. The result shows that the evaluation score of PolyU classrooms is about 87.2, which refers to “Good” evaluation set. It indicates that classrooms in PolyU needs to be improved. The weightings generated from AHP method can be considered for the importance of each alternatives. The assessment model can provide proper recommendation to universities for acoustic treatment so as to increase the acoustic quality of the educational environment.

The importance of the quality of the soundscape to the total environment of urban parks has been widely realized. With the purpose of exploring more efficient and effective approaches for the evaluation and analysis of the soundscape quality of urban parks, the quality assessment theories and methods that used in the areas of quality management and service industry are adopted in this study. A quality evaluation method for the soundscape is then proposed based on two well-known service quality measurement (SQM) models, Importance-Satisfaction (I-S) model and Improvement index (Ii) model. By simultaneously assessing both importance and satisfaction of soundscape elements in urban parks, this method can provide detailed and comprehensive information that can be used for guiding the soundscape design and improvement of urban parks. Finally, the proposed method is applied to a case study in Hong Kong. Based on the analysis of the data collected by questionnaire survey in this case study, the practicality and effectiveness of the proposed method is demonstrated, and a practical decision-making strategy for soundscape quality improvement of urban parks is summarized. According to the authors’ best knowledge, this study is the first attempt to apply the SQM method of combining I-S model and Ii model to the soundscape study of urban park. The ideas and findings not only benefit the practical soundscape management, but also provide a valuable reference for the academic research of soundscape.

It is common to have two or more vibratory machines of the same type mounted on the same supporting structure. These vibratory machines transmit structure-borne sound to adjacent walls or floors and the structure-borne sound is eventually emitted as noise into indoor spaces. The interactions of the mounting points among coherent machines increase the structure-borne sound power transmission significantly at some frequencies and decrease it considerably at some other frequencies. However, there is still no general design frameworks of supporting structure optimization strategy that target on minimizing structure-borne sound power transmission by utilizing the interactions of the mounting points among coherent machines properly. This paper for the first time develops a practical design framework to obtain an optimal set of geometrical parameters for a supporting structure by using a genetic algorithm with parametric finite element models. A steel-made supporting structure with two coherent fans installed on were analyzed. Experiments were conducted to obtain the source mobilities and free velocities of the coherent fans that are required for the calculation of structure-borne sound power transmission. Parametric finite element analysis was conducted to obtain the receiver mobility of the supporting structure. A genetic algorithm solved the optimal solution. The results shown that the proposed approach is sufficiently capable of minimizing the structure-borne sound power transmission on a supporting structure with coherent machines mounted on a supporting structure.

Being healthy and energy saving have become two important principles of building development. Daylight is an influential factor with the characteristics of both photometry and radiometry. Irradiance brings solar heat gains that transfer to building cooling load, while illuminance provides a luminous environment and affects artificial lighting system at the same time. To balance the energy and daylighting performances, it is reasonable to minimize the environmental load under moderate comfort conditions. This study first quantified luminous comfort with a dynamic daylighting metric, average daylight autonomy (Ave. DA300), from a questionnaire survey and simulation work. The benchmark of this metric should range from 29.6% to 57.8% for high-rise residential buildings. With this guideline, the Hong Kong public housing units is found that part of units lack of daylight due to the high building floor and density, while some units have potential to save energy by compromising daylighting performance. Therefore, a new index, energy daylight rate (EDR), is proposed to help decide the best scenario of envelope design for both daylighting and shading purposes. The results show that opening a secondary window is an efficient way to bring more light in and lengthening overhang is an efficient way to block excessive sunlight. This method and the new index are proved to have the ability to help defining proper building envelope design at the early stage.

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.

Indoor environmental quality (IEQ) has significant impacts on office occupants' productivity and these impacts differ according to the type of office. The present study focuses on a special type of open-plan offices, university open-plan research offices (UOROs), and aims to study how the IEQ of this type of offices affects the occupants' productivity. A four-part IEQ assessment framework for the University Open-plan Research Office (UORO) is first proposed. Then the investigation is conducted based on survey responses collected from 231 people who are working in UOROs from 19 universities in China. The analysis results show a clear picture of (1) how the office productivity is affected by the five key IEQ aspects (layout, air quality, thermal comfort, lighting and acoustic environment), (2) how these five key IEQ aspects are affected by their corresponding sub-factors, such as conversation noise, and (3) how occupants' perception of sub-factors are affected by individual factors, such as occupant demographics and work activity. The results also emphasize the quality of acoustic environment has the greatest influence on the occupants' productivity in UOROs and imply occupants working in UOROs have higher requirements for acoustic environment than in other common types of open-plan offices. Based on the analysis, a decision-making strategy is also presented for the evaluation and improvement of the IEQ of UOROs.

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.

As regional drought conditions continue deteriorating around the world, residential water use has been brought into the built environment spotlight. Nevertheless, the understanding of water use behavior in residential buildings is still limited. This paper presents data analytics and results from monitoring data of daily water use (DWU) in 50 single-family homes in Texas, USA. The results show the typical frequency distribution curve of the DWU per household and indicate personal income, education level and energy use of appliances all have statistically significant effects on the DWU per capita. Analysis of the water-intensive use demonstrates the residents tend to use more water in post-vacation days. These results help generate awareness of water use behavior in homes. Ultimately, this research could support policy makers to establish a water use baseline and inform water conservation programs.

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.

Daylight has two characteristics: radiometry and photometry. Hong Kong is situated just south of the Tropic of Cancer and receives a lot of daylight which could generate more lighting energy savings but bring solar heat gain at the same time. This study appealed that the energy-efficient design should guarantee residents’ luminous comfort level first. A dynamic daylight metric, average DA300 (Daylight Autonomy), was first tested to quantify occupants’ luminous comfort by using statistical analysis with the data from questionnaire survey and climate-based simulation of 108 unit cases. The benchmark of Ave. DA300 is then found as 29.6 %. A new parameter EDR (Energy Daylight Rate) was also proposed to reflect the relation between daylighting performance and energy performance. Case study was conducted to optimize the green features’ design and validate the utilization of EDR. The result showed the EDR could help optimize the envelope design at the early stage.

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.

The pedestrian level wind environment is seriously worsen by moderated air flow in the built-up cities like Hong Kong. The lift-up design is therefore adopted in the building constructions to improve the weak wind condition. In order to evaluate the influence of lift-up design on the pedestrian level wind comfort, the wind flow around isolated buildings with and without Lift-up design are simulated respectively via CFD approach. The turbulence model and numerical method are firstly validated by comparing the simulated wind flow data with a wind tunnel test. Then the validated model is used to simulate the wind flows around the isolated buildings. Results show that the lift-up design can improve the wind comfort at pedestrian level and its effects are highly rely on the approaching wind direction. Specifically, the wind comfort is better under the oblique wind direction than the other wind directions.

Ventilation is needed in air-conditioned residential buildings, particularly the bedrooms in nighttime sleeping periods, to maintain an acceptable indoor air quality. Our previous on-site measurements evaluating various ventilation strategies suggest that short-term mechanical ventilation is overall the most appropriate ventilation strategy for air-conditioned residential buildings. However, there is still no a general design framework of short-term mechanical ventilation strategy, which can determine appropriate design parameters, including ventilation period, ventilation frequency, and start concentration of ventilation, based on various combinations of indoor CO 2 generation rate, net room volume, infiltration rate, and mechanical ventilation rate. This study for the first time develops such a design framework and then provides the detailed design guidelines. A whole sleeping period of 8 h is divided into many repeated single V -shape ventilation periods; each single ventilation period is comprised of a short-term mechanical ventilation period and a follow-up CO 2 build-up period. The single V -shape ventilation process is particularly investigated based on a criterion that the average indoor CO 2 concentration is less than but close to 1000 ppm. A high efficient ventilation strategy, namely requiring a minimum total mechanical ventilation period, is a short single ventilation period and a high ventilation frequency. The outcomes of this study are presented in the form of figures and tables, with most parameters normalized, which are useful to assist a rapid ventilation design.

More and more studies reported that there were insufficient ventilation and excessive CO2 concentration in air-conditioned residential buildings, but few solutions were provided. This study investigates the overnight evolution of CO2 concentration in air-conditioned residential buildings and then focuses mainly on the evaluation of three ventilation strategies, including overnight natural ventilation, short-term mechanical ventilation and short-term natural ventilation. On-site measurements were conducted in a typical residential bedroom in Hong Kong in September. The indoor and outdoor CO2 concentration, air temperature and relative humidity as well as the outdoor wind speed during the measurements were analysed. Ventilation rates were calculated based on the time series of CO2 concentration. This study confirms that additional ventilation is usually needed in air-conditioned residential buildings. Overnight natural ventilation with even a small opening is associated with excessive energy consumption and deteriorated indoor thermal environment. Short-term natural ventilation strategies are inefficient and uncontrollable. Compared to the best short-term natural ventilation strategy, a reasonably designed short-term mechanical ventilation strategy requires only a 41% of ventilation period to complete one full replacement of indoor air and to reach a lower indoor CO2 concentration. Nighttime case studies and a theoretical analysis suggest that a few several-minute mechanical ventilation periods could potentially maintain an acceptable indoor air quality for a normal sleeping period of 8 h.

A survey was conducted with a sample of 482 residents in high-rise residential buildings to investigate the impact of aspects of indoor environmental quality (IEQ) on occupants’ overall environmental satisfaction (OES). A three-step approach was proposed to structure the OES. The structure was first tested by the non-parametric tests and the results of statistical analysis showed that the combined aspect of air quality and thermal comfort had the greatest influence on OES in apartments, followed by luminous comfort and acoustic comfort. A detailed structure was then developed and proved residents’ subjective feelings about certain sub-factors, such as air freshness, had strong correlations with each IEQ aspect. The individual items, namely gender, age, physical environment, and adaptive behaviors, were further explored and tested. The results show that most of the items had significant impact on occupants’ feelings regarding sub-factors. The adaptive behaviors of shading and lighting affect luminous comfort significantly and activity intensity and mental stress decides acoustic comfort most. In further studies, the OES could be quantified with the data from both real condition simulation and questionnaire survey.

Previous studies on inter-unit dispersion are limited to isolated buildings. The influence of an upstream interfering building may significantly modify the indoor airflow characteristics of the wind-induced natural ventilated downstream interfered building. Motivated by the findings in previous studies, namely that infectious respiratory aerosols exhausted from a unit can re-enter into another unit in the same building through building envelope openings, this study investigates the inter-unit pollutant dispersion around a multi-story building in two wind directions by employing the computational fluid dynamics (CFD) method. The CFD model employed in this study has been validated against previous experimental data. The results show that the presence of an upstream building greatly changes the path lines around the downstream target building and the pollutant transportation routes around it. The presence of a low upstream building also greatly increases the average air exchange rate (ACH) values and the pollutant re-entry ratios (Rk) below the source unit on the windward side of the downstream target building for normal wind incidence. However, the presence of a high upstream building greatly increases the average ACH values on the windward side and increases the Rk on the leeward side of the downstream building for oblique wind incidence., Highlights • Interunit pollutant dispersion in a naturally ventilated building was investigated. • Effect of an upstream interfering building on the target building was examined. • A high and a low upstream buildings were considered. • An upstream building improves ventilation performance of the target building. • An upstream building enhances Interunit dispersion in the target building.

This paper presented an overview of the prediction methods used in building acoustics. The methods reviewed were based on analytical models, empirical models and numerical models. This review found that the analytical models had made significant contributions to the research literature in building acoustics in the past three years. Numerical models or experimental models were commonly used to verify the analytical models. Besides, the prediction methods used in building acoustics are those used for prediction in room acoustics and for air-borne sound, structure-borne sound, and duct-borne sound. Many of the literature found in this review were related to the prediction of sound in room acoustics and for air-borne sound.

Previous studies on single-sided natural ventilation are mostly limited to very simple physical models, such as a single-room or single-storey building. Our recent on-site measurements have shown that previous empirical models based on such simple physical models are inapplicable to multi-storey buildings. In order to explore why, this study systematically compares the ventilation characteristics of single-storey and multistorey buildings with single-sided natural ventilation. In addition to single-storey and multi-storey buildings with real rooms and openings, a solid block with the same dimensions as the single-storey building is created for comparison. Steady CFD simulation using the renormalization group (RNG) k - e turbulence model is employed to establish the mean flow fields, and the integration method is used to predict the ventilation rates. It is found that both the envelope flow pattern and the ventilation rate of a room in a multi-storey building are highly dependent on its three-dimen...

To protect and improve the built environment, the Hong Kong government recommends sunshades and balconies as two daylighting green features to be incorporated into new buildings. A questionnaire survey was conducted to investigate the effects of these green features on subjective luminous comfort in housing units. The results showed that some practical functions decided the preferences of residents for tilted or horizontal sunshades and balconies with glass walls and parapets. Both features had direct effects on reducing glare and overheating problems, but at the same time, they decreased daylight uniformity. Further, balconies provided poor privacy, which forced residents to use internal shading and artificial lighting more often. Based on the analysis, green features affected residents’ luminous comfort indirectly by unconsciously affecting their feelings and behavior. Practical application: These results may help the government to understand the status quo and establish appropriate guidelines and help researchers and architects improve green features that provide residents with better luminous environments. The data can be used for further studies that adopt the climate-based simulation to present the real luminous condition of the units whose residents were involved in this survey. The luminous comfort could then be quantified by some cumulative metrics, and those metrics can be treated as the standard for the energy-efficient building design.

Previous studies regarding interunit dispersion used Reynolds‐averaged Navier–Stokes (RANS) models and thus obtained only mean dispersion routes and re‐entry ratios. Given that the envelope flow around a building is highly fluctuating, mean values could be insufficient to describe interunit dispersion. This study investigates the wind‐induced interunit dispersion around multistory buildings using the large eddy simulation (LES) method. This is the first time interunit dispersion has been investigated transiently using a LES model. The quality of the selected LES model is seriously assured through both experimental validation and sensitivity analyses. Two aspects are paid special attention: (i) comparison of dispersion routes with those provided by previous RANS simulations and (ii) comparison of timescales with those of natural ventilation and the survival times of pathogens. The LES results reveal larger dispersion scopes than the RANS results. Such larger scopes could be caused by the fluctuating and stochastic nature of envelope flows, which, however, is canceled out by the inherent Reynolds‐averaged treatment of RANS models. The timescales of interunit dispersion are comparable with those of natural ventilation. They are much shorter than the survival time of most pathogens under ordinary physical environments, indicating that interunit dispersion is a valid route for disease transmission.

Wind-induced single-sided natural ventilation in buildings was widely investigated based on isolated buildings. However, owing to the presence of surrounding buildings, the wind flow pattern around a building in an urban area becomes very different from that around an isolated building. Considering an urban context, this study investigates the wind-induced single-sided natural ventilation in buildings near a long street canyon under a perpendicular wind direction using CFD method. Four aspect ratios (AR) of the street canyon, from 1.0, 2.0, 4.0 to 6.0, are investigated to examine the influence of street configuration, while eight envelope features are compared to explore the possibility of envelope design in improving natural ventilation performance of urban buildings. Ventilation rate of rooms in buildings is particularly analyzed. AR influences ventilation rate and its distribution among rooms along height of buildings. The percentage decrease of ventilation rate of buildings reaches 67% when AR of a street canyon is increased from 1.0 to 6.0. Envelope design provides a possibility to enhance the adaptability of buildings to dense urban environments. A good envelope design, such as a horizontal feature at the middle of an opening, can break effectively the along-facade flow and thus create a large pressure difference to drive ventilation. The findings of this study are intended to increase the understanding of natural ventilation performance in urban buildings and thus provide information for urban planning and building design.

The acoustic performance of the ducted Helmholtz resonator (HR) system is analyzed theoretically and numerically. The periodic HR array could provide a wider noise attenuation band due to the coupling of the Bragg reflection and the HR's resonance. However, the transmission loss achieved by a periodic HR array is mainly dependent on the number of HRs, which restricted by the available space in the longitudinal direction of the duct. The full distance along the longitudinal direction of the duct for HR's installation is sometimes unavailable in practical applications. Only several pieces of the duct may be available for the installation. It is therefore that this paper concentrates on the acoustic performance of a HR array consisting of several periodic parts. The transfer matrix method and the Bragg theory are used to investigate wave propagation in the duct. The theoretical prediction results show good agreement with the Finite Element Method (FEM) simulation results. The present study provides a practical way in noise control application of ventilation ductwork system by utilizing the advantage of periodicity with the limitation of available completed installation length for HRs.

This paper examines the problem of broadband vibration control of nonrigid systems employing periodic structures with tunable parameters. It investigates this by using a semi-two-dimensional model that applies a dual-beam periodic structure with transverse branches as a parameter-tunable isolator. Conventional study of vibration control problems, including the problem of vibration control by periodic structures, usually reduces systems to equivalent single- or multi-mount models with only a unidirectional translation at a mounting point. This assumption of decoupling leads to the erroneous prediction of vibratory power transmission when designing an isolator for a nonrigid system. Such a periodic structure involves the coupling of vibrations between different mounting points and different directions of motion and is therefore a reasonable simulation of the real-life problem. However, its application as a periodic isolator has not been proposed previously. The configuration of shape memory alloy (SMA) branches and non-SMA dual beams is proposed in order that this structure can effectively exploit the advantages of SMA materials, namely their significantly varying Young׳s moduli which can be tuned to adjust and widen the stop bands, and can prevent the associated limitation of hysteresis. Equations are derived governing the vibration transmitted through any number of periodic mounts between nonrigid machines and foundations. Based on the derived results, two methodologies are developed to determine the proper Young׳s moduli of the SMA branches and minimize the transmitted power. The numerical results demonstrate that the adaptive SMA branches at the proper temperatures are able to attenuate broadband vibration by adjusting the locations and broadening the widths of stop bands. With the application of a semi-two-dimensional periodic structure to broadband vibration isolation, this paper provides an approach and supporting methodologies for broadband vibration control using periodic structures.

A questionnaire survey was conducted to investigate the effects of daylighting and human behavior patterns on subjective luminous comfort in Hong Kong housing units. The participants were recruited via mail, and included residents of both public and private housing units. 340 questionnaires were returned and analyzed by using SPSS 19.0. In analyzing the response statistics, the Cronbach's alpha coefficient, Spearman rank correlation coefficient, Chi-square test, Kruskal–Wallis test and stepwise regression were adopted to identify the effects of particular aspects of human behavior and daylighting quality. The results confirmed that luminous comfort is a function of both behavior patterns and daylighting conditions. Behavior factors have a significant influence on luminous comfort among people who grade their satisfaction with daylighting as moderate. In general, the degree of luminous comfort is most affected by satisfaction with daylighting. External obstruction is the major physical factor affecting luminous comfort, while the perception of uniformity is the major factor of residents' feelings toward daylight. The use of artificial lighting is the most relevant behavior factor affecting luminous comfort, as using artificial lighting for many hours per day indicates poor daylighting conditions and decreased luminous comfort. These results should help to raise awareness of the detailed factors that influence the luminous environment. Our findings may also assist planners and architects to implement better daylighting for housing projects and provide residents with greater luminous comfort.

Coupled urban wind flow and indoor air flow is an important flow problem that is associated with many environmental processes. This paper provides detailed sensitivity analyses of some important computational parameters that may influence the prediction accuracy of such a flow problem. The CFD prediction of single-sided ventilation rate is taken as a case study. Based on both the RANS and LES turbulence models, the most commonly used predictive methods, namely the integration and tracer gas decay methods, are examined. A range of wind directions are considered, since the characteristics of both building aerodynamics and ventilation mechanics are distinctive under different wind directions. The performance of numerical model is thoroughly evaluated, including validation against field measurements. Specific attention is paid to sensitivity analyses of the near-wall mesh density. The implications for accurate CFD prediction of the single-sided ventilation rate are summarized, which are also applicable to other coupled flows.

For the active vibration control (AVC) of periodically time-varying systems, the filtered-x least mean squares (FXLMS) method is widely applied. Many AVC systems based on FXLMS employ two coupled adaptive processes – online modeling or identification and controller updating – to track the parametric change and realize the real-time updating of the control signal. Errors in one process can affect the other. When one process converges, it takes several steps for the other process to converge. After they both converge, it is difficult to tell whether the controller is optimal or not. Therefore, it is difficult to evaluate the influence of the coupling effect and perform a rigorous derivation. In this study, the new AVC system adopts adaptive identification and non-adaptive control to avoid the coupling effect, and the necessary condition for decoupling is obtained. This condition guarantees that the optimal controller can be obtained the moment the system identification process converges, and meanwhile boosts the convergence of the identification process. The robustness of the identification process with the self-tuning mechanism and the optimization of the controller are proved by rigorous derivation. A simple but representative numerical verification is presented to verify the effectiveness of the proposed AVC system.

This study aims to evaluate the performance of different methods in determining single-sided ventilation rates in multistory buildings. The study is motivated by the fact that the methods established from very simple physical models, such as a single-room building, have been applied directly to multistory buildings. On-site measurement in a multistory building was conducted to verify the applicability of existing empirical models. A computational fluid dynamics (CFD) simulation was performed to (a) examine the integration method and the tracer gas decay method and (b) investigate the ventilation characteristics of a multistory building and how these differ from the ventilation characteristics of a single-room building. The empirical models are not applicable to multistory buildings as they cannot account for the difference in ventilation rate between different rooms in the same building. This study finds that the CFD method is particularly suitable for the determination of ventilation rates in multistory buildings despite the fact that the methods reproduced by CFD simulation are compromised by the accuracy of the velocity and turbulence fields generated by the selected numerical model. Finally, a parametric study shows that an increase in the incident k profile leads to a significant decrease in ventilation rate to the leeward rooms.

This paper presents a method for the prediction of flow noise from in-duct spoilers using Computational Fluid Dynamics (CFD). Previous work conducted by Mak [Mak CM. A prediction method for aerodynamic sound produced by multiple elements in air ducts. J Sound Vib 2005;287:395–403] and Mak et al. [Mak CM, Wu J, Ye C, Yang J. Flow noise from spoilers in ducts. J Acoust Soc Am 2009;125:3756–65] provides a method for such a prediction based on experimental data. In this work, the advanced Large-eddy Simulation turbulence model (LES) is used to compute the mean pressure drop across spoilers and the fluctuating drag forces acting on them. The predictions of the numerical simulation agree well with those based on experimental data and the actual, measured levels. With the aid of CFD simulation, engineers are now able to use the prediction method developed by the authors to predict the flow noise from in-duct spoilers using the LES turbulence model.

Transient noise is a typical real-life noise problem. In order to develop efficient methods of dealing with it, the generating and transmitting mechanisms of transient noise radiating from a vibrating structure have been widely studied. The analytical methods used differ according to the properties of the excitation, structure, and acoustic environment. Focusing on plate-like structures, this paper provides an overview of commonly-used approaches to the analysis of structural transient vibration and sound radiation (TVSR). A general process for solving this type of problem is presented, together with suggestions for future work in this field.

This article presents an integral approach to sustainable noise control system design for building ventilation systems in Hong Kong. This approach combines the analytic hierarchy process and life cycle analysis (LCA) to obtain a holistic view of the system performance in terms of human, economic, and environmental impacts. The approach was applied to the evaluation of various noise control systems including duct liners, silencers, semi-active noise control, and active noise control for ventilation systems. Although passive systems such as duct liners and silencers seem to consume more material resources than semi-active and active systems, the latter require sensors, controllers, resonators or loudspeakers, and electricity. In fact, the LCA showed little difference between the semi-active and active systems and the passive systems in term of resource depletion and carbon emission. As human impact and economic impact dominated the experts’ views on sustainability, the analysed results indicated that the most sustainable design was duct liners, followed by silencers, active noise control, and semi-active noise control.

Single-sided ventilation rate is difficult to accurately predict because it has a complex relationship with many factors, including the direction of the approaching wind and building envelope features. In addition, the incursion of outdoor pollutants into the interior through a ventilation opening has been recognized as a serious threat to indoor air quality (IAQ). This article presents on-site measurements of the ventilation performance and IAQ in four high-rise residential rooms in Hong Kong. Key parameters including the air changes per hour, respirable suspended particulate matters (PM: PM10 and PM2.5), and total volatile organic compounds were continuously recorded over a specified period. A comparison of cases with floor-extended and window-like openings is made. The results indicate that single-sided ventilation performs well regardless of the orientation of the apartment room and the configuration of the opening. Previous empirical models based on single-room buildings are not reliable in determining the ventilation rate of high-rise buildings. The measurements reported here also identify an important route for the incursion of outdoor pollutants, namely the downward re-entry of aerosol particles from an upper unit to a lower unit in the same building. A combination of gravitational and wind effects means this downward transport route significantly increases the PM10 and PM2.5 concentrations in the lower room.

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.

It is known that the commonly used performance indicator for vibration isolation − force transmissibility − over-simplifies the vibration problem. Therefore, Mak and Su propose a power transmissibility approach that includes the effect of floor dynamics and the interactions of the mounting points between machine and floor. However, their model does not consider transient vibration excitation. The question motivating this study is the occasional problem which arises due to the sudden or frequent starting and stopping of vibratory machines. In this paper, a transient power transmissibility approach is proposed to assess the performance of isolators in a transient vibration excitation. A spring-mass-movable floor system is considered in the simulation, and the spring isolator is first selected using the steady-state power transmissibility approach of Mak and Su. A system disturbed by two transient excitations as typically experienced by building services equipment is then analyzed. The results indicate the necessity of using transient power transmissibility in the selection of isolators for a transient vibration.

The transient vibration and sound radiation (TVSR) of a stiffened plate was investigated using the time-domain finite element method and time-domain boundary element method. A four-noded stiffened-plate element was adopted in this method; this allowed the plate to have arbitrary elastic boundary conditions and the stiffeners with any shape to be located at arbitrary positions inside the plate. The in-plane deformation of the plate was taken into account. The transient vibration predicted by the present approach showed a good agreement with earlier published results. The proposed method was subsequently applied to a parametric study that examined the effects of the stiffeners on the TVSR of a window, which is a typical plate structure. The results showed that the stiffeners (or their locations) notably influenced the window’s TVSR responses, thereby demonstrating the possibility of using appropriate stiffeners to improve the transient vibration and noise isolation performance of a practical window.

Mechanical ventilation poses some challenges for control of pollutants in a fully enclosed dental clinic. Natural ventilation is used in some clinics because of its high exhausting efficiency and low non-renewable energy consumption. In this study, a dental clinic model was built using a computational fluid dynamics platform. The objective was to study the effect of natural ventilation on pollutant dispersion in this setting. The evaluations were conducted using the advanced turbulence model, large eddy simulation for the flow field and the discrete phase modelling for pollutant tracks. Three basic ventilation paths were identified, the ‘single narrow path’, ‘narrow path’ and ‘dispersive path’. The results show that the first of these had the highest efficiency, with an escape time of about 1/30 and 1/100 of the narrow and dispersive paths, respectively. Despite the position of the pollutant source and facilities such as bulkheads, escape time was significantly reduced when the ventilation flow rate was increased under the single narrow and dispersive paths. However, for the narrow path, these factors played a more dominant role in the escape time than the ventilation flow rate. Practical application: This study is expected to provide information and guidance in understanding the pollutant spread in a naturally ventilated room such as a dental clinic.

The purpose of this study was to investigate the effect of a new building which can impose on its immediate ambient environment, on air movement and thermal comfort of people using the area. The effect of eight prevailing wind directions around the building was simulated using computational fluid dynamics (CFD). The CFD simulation was validated by two wind tunnel experiments. The CFD results were used to conduct an air ventilation assessment using velocity ratio (VR) indicator and to assess thermal comfort by an extended predicted mean vote (PMV) evaluation. An analysis of the relationship of VR and PMV with the to-be-built building (the front area index λf and plan area density λp) was also conducted. The result indicates that the PMV trend was generally opposite to the VR trend. The λp would increase due to the new building and the λf would increase in all wind directions except East-South-East and South-East. There could be a significant change in thermal comfort when the λf became smaller than 12% and a significant change in ventilation efficiency if the λf was smaller or larger than 12%. It means that λf can be used as an urban planning parameter for the thermal comfort study in the natural ventilated urban environment.

The acoustic diffusion performance of a terraced classroom was investigated using a two-dimensional boundary element method. Quadratic residue diffuser (QRD) and porous material were employed on the ceiling and rear wall, respectively, to improve the diffusion performance. The diffusion gains of various models were calculated to compare the diffusion performance. It is found that terraces in a rectangular classroom raise the lowest sound pressure level and provide slight diffusion improvement. The QRD ceiling enhances the diffusion by scattering the sound wave to be more evenly distributed, but at some frequencies the diffusion improvement is minor or even negative. The absorption rear wall provides useful diffusion gain mainly at higher frequencies by absorbing parts of the reflected sound. When the parameters of the QRD ceiling and porous material change, the diffusion improvement first increases and then begins to decrease. In a terraced classroom with both treatments, the diffusion at lower frequencies is similar to that with the QRD ceiling, while at higher frequencies it resembles that with the absorption rear wall. The results clearly indicate that the combination of the two treatments produces the most desirable diffusion performance of the tested models.

This article reports the results of a questionnaire survey examining the effects of sound on office productivity and assessing the relationship between changes in office productivity and noise sources as well as five environmental and office design factors, namely temperature, air quality, office layout, sound and lighting. The convenience sample for the survey comprised 259 office workers in 38 air-conditioned offices in Hong Kong. The subjects were requested to complete the questionnaires themselves. The results show that among the five environmental and office design factors examined, sound and temperature were the principal factors affecting office productivity. A strong and significant correlation was also found between changes in office productivity and sound, temperature and office layout. Participants were separated into low- and high-productivity groups using the mean productivity score of all participants as the cut-point. The three most annoying noise sources, including conversation, ringing phones and machines, differed little in mean annoyance scores for the low- and high-productivity participants, indicating that they had a significant negative impact on all participants. The results also indicate that low-productivity participants were easily influenced by noises such as background noise, closing doors, and human activity, as well as those coming from both inside and outside the office. Practical applications: This study evaluates the effects of sound and other environmental and office design factors on office productivity. It suggests that sound is a principal factor affecting office productivity in modern air-conditioned offices.

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.

Commercial wind towers have been the focus of intensive research in terms of their design and performance. There are two main forces which drive the flow through these devices, external wind and buoyancy due to temperature difference. This study examines the relationship between these two forces and the indoor ventilation rate achieved. The work uses computational fluid dynamics (CFD) modeling to isolate and investigate the two forces and draw comparisons. The study found that as expected the external driving wind is the primary driving force providing 76% more internal ventilation than buoyancy driven flow, which is deemed secondary. Moreover the study found that the effect of buoyancy is insignificant without an external airflow passage other than the wind tower itself. The addition of an external airflow passage such as a window in combination with buoyancy force increased the indoor ventilation by 47%. Therefore the careful positioning of windows in conjunction with internal heat source has the potential to overcome the lack of external wind driven forces in dense urban environments.

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.

Concrete plinths are commonly used by engineers as a base for vibratory building services machines. However, it is not clear what effects they have on the structure-borne sound power transmission and the eigenfrequencies of floors. In this paper, the modal functions, eigenfrequencies, and mobility expression of a floor with a concrete plinth attached are deduced. The power transmissibility method is used to analyze the effect of a concrete plinth on the power transmissibility that is used to assess the performance of vibration isolation. It is found that the effect of a concrete plinth is mainly to decrease the eigenfrequencies of the floor, and changing the thickness of the concrete plinth has a greater effect on the eigenfrequencies of the floor and the power transmissibility than does changing the area of the concrete plinth. An estimated equation for power transmissibility is formulated.

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.