Optimization of air supply location,size, and parameters in enclosed environments using a computational fluid dynamics-based adjoint method

Optimal design of an indoor environment based on specific design objectives requires a determination of thermo-fluid control methods. The control methods include the air supply location, size, and parameters. This study used a computational fluid dynamics- (CFD) based adjoint method to identify the optimal air supply location, size, and parameters. Through defining the air distribution in a certain area (design domain) as a design objective in a two-dimensional, ventilated cavity, the adjoint method can identify the air supply location, size, and parameters. However, the air supply location, size, and parameters were not unique, which implied multiple solutions. By using any of the air supply location, size, and parameters identified as boundary conditions for forward CFD simulations, the computed air distribution in the design domain was the same as that used as a design objective. Thus, the computing costs did not depend on the number of design variables.     

Inverse design of an indoor environment using a filter-based topology method with experimental verification

In order to create a healthy, comfortable, productive, and energy-efficient indoor environment, the computational fluid dynamics (CFD)-based adjoint method with an area-constrained topology method can be used to inversely design the optimal number, size, location, and shape of air supply inlets and air supply parameters. However, this method is not very mature, and the distribution of retained inlets is always scattered. To solve that problem, this investigation introduced a filter method that smooths the intermediate results during the inverse design process. Using a three-dimensional, non-isothermal, asymmetrical office with pre-set air supply inlets as an example, this study verified the performance of the proposed filter-based topology method. The verified method was then used to solve a multi-objective design problem and design an optimal indoor environment for a room. The results indicate that the proposed method was able to find the optimal number, location, and shape of air supply inlets and the optimal air supply temperature, velocity, and angle that led to a thermally comfortable, healthy, productive, and energy-efficient indoor environment. Finally, this investigation installed the optimal inlets in an environmental chamber to mimic the room. The measured air temperature, velocity, and mean age of air in several typical locations in the environmental chamber matched the CFD simulation results very closely.     

Development of ventilation design strategy for effective removal of pollutant in the isolation room of a hospital

This paper investigates the airflow and pollutant distribution patterns in a “negative pressure” isolation room by means of objective measurement and computational fluid dynamics (CFD) modeling based on three ventilation strategies. An effective ventilation system is crucial to protect doctors, nurses and other health-care workers from patients with infectious disease. In the preliminary study with Strategy 1, the isolation room has two air supply diffusers and two extract grilles mounted on the ceiling. Strategy 2 retains the air supply diffusers in Strategy 1 but relocates the two extract grilles to the wall behind the bed at 0.3 m above the floor level. Strategy 3 has the same layout as Strategy 2 except the ceiling diffusers are replaced by supply grilles and relocated closer to the wall behind the bed.     

Inverse design of indoor environment using an adjoint RNG k‐ε turbulence model

The adjoint method can determine design variables of an indoor environment according to the optimal design objective, such as minimal predicted mean vote (PMV) for thermal comfort. The method calculates the gradient of the objective function over the design variables so that the objective function can be minimized along the fastest direction using an optimization algorithm. Since the objective function is controlled by the Reynolds‐averaged Navier‐Stokes (RANS) equations with the RNG k‐ε model during the optimization process, all the corresponding adjoint equations should be solved, rather than the “frozen turbulence” assumption used in previous studies. This investigation developed adjoint equations for the RNG k‐ε turbulence model and applied it to a two‐dimensional ventilated cavity and a three‐dimensional, two‐person office. Design processes with the adjoint RNG k‐ε turbulence model led to a near‐zero design function for the two cases, while those with the “frozen turbulence” assumption did not. This investigation has successfully used the new method to design a two‐person office with optimal thermal comfort level around the two occupants.     

Optimal design for a dual-airflow window for different climate regions in China

The dual-airflow window could be used to conserve energy and improve indoor air quality in buildings because it works like a heat exchanger and can introduce outdoor air into buildings. In order to optimize the window design, this investigation used the orthogonal method to evaluate the importance of these 13 design parameters of the dual-airflow window in energy conservation: outdoor air supply rate, window cavity width, window width, window height, thermal conductivity, glazing thickness, solar heat gain coefficient, emissivity, thermal conductivity of window frame, window frame width, window orientation, shading coefficient, and window blinds position. The outdoor air supply rate, window height, solar heat gain coefficient, and window orientation were found to be the most important. The first four parameters were further studied by using the listing method to identify their optimal values for the window design. With the optimal design, the dual-airflow window could save 25% energy in a warm climate region such as Guangzhou and 34% in a cold climate region such as Harbin. The dual-airflow window is recommended for use in colder climate regions.     

Inverse modeling methods for indoor airborne pollutant tracking: literature review and fundamentals

Reduction in indoor environment quality calls for effective control and improvement measures. Accurate and prompt identification of contaminant sources ensures that they can be quickly removed and contaminated spaces isolated and cleaned. This paper discusses the use of inverse modeling to identify potential indoor pollutant sources with limited pollutant sensor data. The study reviews various inverse modeling methods for advection-dispersion problems and summarizes the methods into three major categories: forward, backward, and probability inverse modeling methods. The adjoint probability inverse modeling method is indicated as an appropriate model for indoor air pollutant tracking because it can quickly find source location, strength and release time without prior information. The paper introduces the principles of the adjoint probability method and establishes the corresponding adjoint equations for both multi-zone airflow models and computational fluid dynamics (CFD) models. The study proposes a two-stage inverse modeling approach integrating both multi-zone and CFD models, which can provide a rapid estimate of indoor pollution status and history for a whole building. Preliminary case study results indicate that the adjoint probability method is feasible for indoor pollutant inverse modeling. PRACTICAL IMPLICATIONS: The proposed method can help identify contaminant source characteristics (location and release time) with limited sensor outputs. This will ensure an effective and prompt execution of building management strategies and thus achieve a healthy and safe indoor environment. The method can also help design optimal sensor networks.     

低温送风条件下风口结露实验研究

对3种普通风口在低温送风条件下的结露特性进行了实验研究,针对实验现象分析了各种风口的结露机理,为普通风口在低温送风条件下的使用制定了软启动控制策略,认为若无软启动措施,低温送风系统宜采用专用风口。     

Principles and applications of probability-based inverse modeling method for finding indoor airborne contaminant sources

Building indoor air quality (IAQ) has received growing attentions lately because of the extended time people spend indoors and the increasing reports of health problems related to poor indoor environments. Recent alarms to potential terrorist attacks with airborne chemical and biological agents (CBA) have further highlighted the research needs on building vulnerability and protection. To maintain a healthful and safe indoor environment, it is crucial to identify contaminant source locations, strengths, and release histories. Accurate and prompt identification of contaminant sources can ensure that the contaminant sources can be quickly removed and contaminated spaces can be effectively isolated and cleaned. This paper introduces a probability concept based prediction method—the adjoint probability method-that can track potential indoor airborne contaminant sources with limited sensor outputs. The paper describes the principles of the method and presents the general modeling algorithm and procedure that can be implemented with current computational fluid dynamics (CFD) or multi-zone airflow models. The study demonstrates the application of the method for identifying airborne pollutant source locations in two realistic indoor environments with few sensor measurement outputs. The numerical simulations verify the feasibility and accuracy of the method for indoor pollutant tracking applications, which forms a good foundation for developing an intelligent and integrated indoor environment management system that can promptly respond to indoor pollution episodes with effective detection, analysis, and control.     

CFD study of the thermal environment in an air-conditioned train station building

This study used the computational fluid dynamics (CFD) method to evaluate the indoor thermal environment of an air-conditioned train station building under three types of air-conditioning design schemes. The impacts of air-conditioning design parameters such as supply air temperature, velocity, altitude and angle of incidence were also investigated. The numerical results showed that if the waiting hall and entrance hall of the train station building were connected to each other and served with the cooling air respectively, when the cooling loads in the two halls were fixed and air-conditioning systems were designed properly, altering largely the cooling air supply scheme in the waiting hall while keeping the cooling air supply scheme in the entrance hall unchanged would have significant effects on the air distribution and thermal comfort in the occupied region of the waiting hall but may have some minor effects on those in the occupied region of the entrance hall. The uniformities of velocity and temperature distributions in the occupied region of waiting hall were satisfactory when side supply scheme was applied. Changing supply air temperature, velocity, altitude and angle of incidence would yield great effects on the thermal environment in the train station building. For the stratified air-conditioning design in the train station building, in order to obtain the satisfactory thermal comfort in the occupied region, the mid-height of the building was found to be a good position for the cooling air supply and the supply angle of 0° from the horizontal could be recommendable. The results also indicated that analyzing the effects of air-conditioning design parameters on the building environment with CFD was an effective method to find the way to optimize the air-conditioning design scheme.     

办公建筑中旋流风口地板送风系统的设计及实验研究

基于地板送风与置换通风原理的相似性,参考办公室中置换通风的设计方法,结合旋流风口地板送风系统的特性,提出旋流风口地板送风系统的设计方法。通过实验对设计方法进行了验证,并对室内热舒适性进行了评价。     

Optimization of indoor climate conditioning with passive and active methods using GA and CFD

This study aims at the development of an optimal design tool using a genetic algorithm (GA) and computational fluid dynamics (CFD). Random variables (fluctuating outdoor conditions), passive design elements (model variables) and active design elements (HVAC system) were set up to represent a realistic building environment. A combination of designs is determined based on the relationship between fluctuating outdoor conditions and the HVAC system in the optimal design search. Building environment designs should consider both active and passive design elements because the HVAC system keeps adjusting the supply air flow rate until the indoor climate reaches target conditions when outdoor conditions are changing.     

Schallschutz mit schalldämmenden Lüftungsgittern

Sound protection using sound‐absorbing ventilation grilles. Sound‐absorbing ventilation grilles are used for supply and exhaust air openings in buildings, in naturally ventilated multistorey car parks, and for screening noise‐emitting equipment requiring a flow of air. The sound insulation of different ventilation grilles was measured in the laboratory. A nomogram taking account of the gap length and width was developed for estimating the weighted sound reduction index of typical sound‐absorbing ventilation grilles. Suggested spectrum adjustment values for the weighted sound reduction index are provided.     

Testing of Localized Ventilation Systems in a New Controlled Environment Chamber

This paper describes tests of thermal comfort and air distribution performance of two relatively new occupant-controlled localized ventilation (also called task ventilation) systems. The first is a raisd-floor distribution system providing air through grilles in the floor panels, and the second is a desk-mounted unit supplying conditioned air at desktop level. The tests were performed in a new controlled environment chamber (CEC) having unique capabilities for detailed studies of space conditioning and thermal comfort in office environments. Measurements were made in a mockup of a typical partitioned open-plan office, and the resulting temperature and air velocity distributions are reported for a variety of system- and locally controlled conditions. Comfort model predictions are presented to describe the degree of environmental control and range of occupant comfort levels produced in the workstations. The results are also compared to those produced by a conventional ceiling supply system. The tests investigated the effects of supply volume, supply location, supply vent orientation, supply/return temperature difference, heat load density, and workstation size and layout. Temperature differences in the range of 1–2.5°C were observed between adjacent workstations, and local air velocities in the vicinity of outlets could exceed 3 m/s. Such wide-ranging values could violate existing comfort standards (ASHRAE, 1981; ISO, 1984), if strictly interpreted. However since these systems put the local thermal conditions within the workstations under the direct control of their occupants, it is recommended that the standards grant exceptions to such systems.     

富华国际会议及展览中心空调设计

结合高大空间特点,介绍了各展厅空调系统设计,包括气流组织的确定、系统的划分及机房的设置。第一展厅外区采用下送下回方式、双层百叶风口,内区采用上送下回方式、旋流风口;第二、三展厅均为内区,采用上送下回方式、旋流风口;共享大厅采用侧送下回方式、球型喷口。水系统采用变水量、两管制系统。介绍了通风、自控设计。     

Comfort and airflow evaluation in spaces equipped with mixing ventilation and cold radiant floor

In this work the comfort and airflow were evaluated for spaces equipped with mixing ventilation and cold radiant floor. In this study the coupling of an integral multi-nodal human thermal comfort model with a computational fluid dynamics model is developed. The coupling incorporates the predicted mean vote (PMV) index, for the heat exchange between the body and the environment, with the ventilation effectiveness to obtain the air distribution index (ADI) for the occupied spaces with non-uniform environments. The integral multi-nodal human thermal comfort model predicts the external skin and clothing surfaces temperatures and the thermal comfort level, while the computational fluid dynamics model evaluates the airflow around the occupants. The air distribution index, that was developed in the last years for uniform environments, has been extended and implemented for non-uniform thermal environments. The airflow inside a virtual chamber equipped with two occupants seated in a classroom desk, is promoted by a mixing ventilation system with supply air of 28 °C and by a cold radiant floor with a surface temperature of 19 °C. The mechanical mixing ventilation system uses a supply and an exhaust diffusers located above the head level on adjacent walls.     

Indoor air quality and thermal comfort studies of an under-floor air-conditioning system in the tropics

This paper reports thermal comfort and indoor air quality (IAQ) studies of an under-floor air-conditioning (UFAC) system in hot and humid climate. Thermal comfort parameters were measured at predetermined grid points within an imaginary plane to predict the airflow pattern of the supply air jet as well as to determine the occurrence of thermal stratification in the office space. Fanger’s [Thermal Comfort Analysis and Applications in Environmental Engineering, McGraw-Hill, New York, 1970] thermal comfort index was also computed to detect the occupants’ thermal sensation. Besides, the concentration levels of dust and carbon dioxide were recorded with the intention to examine the quality of the indoor air. Statistical methods were applied to derive the relationship between air velocity and the other parameters as mentioned earlier. The main findings from the study revealed reasonable level of acceptability of IAQ associated with the UFAC system. However, occupants are likely to experience localised thermal discomfort near the supply diffusers due to the existence of large temperature gradients. In addition, a stagnant zone is discovered at sedentary level, which is caused by the parabolic airflow nature of the primary air jet.     

Momentum source model for CFD-simulation of nozzle duct air diffuser

Development of simplified models for air diffusers is essential for the applicability of CFD-modelling to room air flow simulation. The geometry of a diffuser is usually complex and, therefore, it is not possible to use an exact geometrical model in practical CFD-simulations. The model should be simple enough to enable the modelling of a room with several diffusers. In this study, a simplified model was developed for the nozzle duct diffuser. The diffuser consists of a duct, which is partly covered with small nozzles creating high-velocity jets. A complex circulating flow pattern is created between the jets. The room air enters the flow from the nozzle-free sector and is mixed with the supply air. The flow field near the diffuser was investigated with laboratory measurements in order to determine the boundary conditions for the simplified model. The developed model is based on momentum sources describing the induction of secondary air caused by the jet system. The model was validated with laboratory test cases by comparing the simulation results with measurements. The measured flow patterns in the four test cases with different Archimedes numbers were well reproduced by the simulations.     

多分支风道系统静压复得计算法的新算法

分析了传统的静压复得法的几种不同算法，指出了现行的静压复得计算法存在的问题，提出了静压复得计算法的新算法，经工程实践验证，解决了多分支风道无风量调节阀的匀送风的难题，提高了计算速度，改善了风道系统的平衡性。     

Airflow and air temperature distribution in the occupied region of an underfloor ventilation system

Measurements were carried out in an office-type experimental room ventilated by a floor return-type underfloor ventilation system to investigate the distributions of airflow velocity and air temperature. A fan-powered floor air unit (FAU) with rectangular supply and return air outlets covered by straight-profile linear bar-type air diffusers was installed to deliver the conditioned air in the experimental room. Turbulence intensity and draught rate distributions inside the room were also calculated by using the measured data. From the experimental results, it is found that undesirable high air velocities and high draught rates were created within a small region near the supply outlet of the FAU. Temperature differences between different height levels were maintained within an acceptable comfort level under the tested supply air conditions and heat loads. The results indicated that the temperature stratification could be maintained at an acceptable comfort level by designing the supply air conditions properly. A clearance zone is suggested as a design consideration for locating the FAUs and occupants to avoid undesirable draught discomfort to the occupants.     

室内空气流动的简捷数值模拟方法

概要介绍了N点风口动量模型、新零方程湍流模型及误差预处理数值算法，利用这些模型和方法对某采用百叶风口的办公室内温度场和速度场进行模拟计算，并与实验数据进行比较，表明计算值与实测值吻合得较好；在普通微机上能快速合理地模拟室内温度场和速度场，可用于实际工程指导通风空调气流组织设计和分析。