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.     

室内机位置对室内热舒适影响数值模拟分析

用CFD方法数值模拟了分体式空调器室内机在室内摆放位置不同时,在相同送风温度和送风速度下,对室内温度场、速度场以及热舒适性的影响.模拟结果表明:相同送风温度和送风速度情况下,不同的室内机位置产生了不同的室内温度场、速度场;与室内布局相适宜的室内机摆放位置可以改善室内舒适度.     

Unsteady thermal performance analysis of a room with serial and parallel duct radiant floor heating system using hot airflow

In this study, the unsteady thermal performance of a test room heated by circulating hot airflow under the floor was analyzed with a developed mathematical model based on heat transfer equilibrium among the air flow, the floor and the indoor air. The time variations in the indoor air temperature for the serial duct floor heating system were investigated theoretically and experimentally. The time variations in the floor surface and the indoor air temperatures were predicted theoretically for the parallel duct floor heating system. Experiments on the time variations of the dimensionless numbers such as Nu for the airflow in duct and the indoor air, Gr for the indoor air and the heat ratios of convection and radiation to total heat for the serial duct floor heating system were performed. The theoretical and experimental results showed a good agreement.     

Flow impact of an air conditioner to portable air cleaning

In order to reduce indoor pollutant exposure, people become increasingly interested in portable air cleaning devices, which can be positioned with flexibility. Such purification devices usually discharge cleaned air with strong momentum, which can interrupt indoor airflow created by air-conditioning units. If a well-organized air circulation to a portable air cleaner is not achieved, indoor air purification cannot be fully ensured. This study has used both measurement and computational fluid dynamics (CFD) modeling to investigate the flow interaction between an air conditioner and a portable air cleaner to purify indoor gaseous pollutants. A workshop environment conditioned by an air conditioner and cleaned by a portable air cleaner was mimicked in an environmental chamber to obtain data for validation of a CFD program. Then CFD was applied to evaluate factors that may affect air purification including: positioning of the air conditioner and air cleaner, air conditioner diffuser types, air-conditioning cooling or heating running mode, and location of pollutant sources. The study finds the simulation results are in good agreement with the corresponding experimental data. The positioning coordination of an air conditioner and an air cleaner, and selection of air conditioner diffuser types shall assure a good air circulation cycle to the air cleaner to improve air purification efficacy. In addition to the cleaner effectiveness, it is also recommended to evaluate an air cleaning device in terms of the absolute pollutant concentration, if the portable air cleaner is under the interaction of an air conditioner and the local performance data are interested.     

Outdoor Air Contaminants and Indoor Air Quality under Transient Conditions

The indoor concentrations of contaminants originating from outdoor sources have been measured and calculated under transient conditions. The results show that contaminants that are supplied to an office building via the ventilation system can reach considerably high concentration levels. The indoor/outdoor concentration ratio and time lag are dependent on the air change rate. In buildings with low air change rates the indoor concentration variations are smoothed out compared to buildings with high air change rates. The results from the theoretical model are compared to the results from both laboratory and field measurements and the model is verified for well mixed conditions in a 20 m³ test chamber. The model can be used to simulate different control strategies for reduction of indoor contaminant concentrations related to outdoor sources. One such control strategy is based on reduction of the outdoor air change rate during periods with peak outdoor contaminant concentrations.     

Control strategies for sub-micrometer particles indoors: model study of air filtration and ventilation

The effects of air filtration and ventilation on indoor particles were investigated using a single-zone mathematical model. Particle concentration indoors was predicted for several I/O conditions representing scenarios likely to occur in naturally and mechanically ventilated buildings. The effects were studied for static and dynamic conditions in a hypothetical office building. The input parameters were based on real-world data. For conditions with high particle concentrations outdoors, it is recommended to reduce the amount of outdoor air delivered indoors and the necessary reduction level can be quantified by the model simulation. Consideration should also be given to the thermal comfort and minimum outdoor air required for occupants. For conditions dominated by an indoor source, it is recommended to increase the amount of outdoor air delivered indoors and to reduce the amount of return air. Air filtration and ventilation reduce particle concentrations indoors, with the overall effect depending on efficiency, location and the number of filters applied. The assessment of indoor air quality for specific conditions could be easily calculated by the model using user-defined input parameters.     

基于室内空气品质的需求控制通风研究

本文研究的基于室内空气品质的需求控制通风，用CO2浓度作为室内人员相关污染物的控制指标，以TVOC作为室内建筑相关污染物的控制指标，从而容许在室内人员改变或建筑相关污染物浓度改变时调节入室新风量，实现了节能与提高室内空气品质的统一。文中对该方法理论和实验研究做了简要介绍。     

Indoor Air Quality: Exploring Policy Options to Reduce Human Exposures

Deciding between the different policy approaches available for reducing human exposures to indoor pollutants is an exceptionally complex task. These options can range from waiting until more definitive information is available to enacting regulatory standards, with many variations in between. This paper presents some of the factors policy-makers must consider in establishing indoor air quality policies, and the role researchers should play in ensuring that indoor air policies are based on the best available scientific information.     

A new virtual sphere method for estimating the role of thermal mass in natural ventilated buildings

The role of thermal mass is very important in natural ventilated buildings. Thermal mass can be classified as external thermal mass and internal thermal mass. In this paper, a heat balance model for naturally ventilated building is developed. The effect of external thermal mass is introduced by harmonic response method, and the effect of internal thermal mass is calculated by virtual sphere method which can lump different shapes and types into one virtual sphere. The effective convection heat transfer coefficient is presented to represents the effect of uneven distribution of internal thermal mass temperature. Through comparison with Li's model [1] and numerical calculation, it was found that the model is more suitable than the others, especially in estimating decrement factor of indoor air temperature. The errors of time lag become smaller when the fluctuation of indoor air temperature is smaller. Based on the model, a simple tool is developed to evaluate the indoor air temperature and required internal thermal mass for certain naturally ventilated buildings.     

Investigating the potential use of natural ventilation in new building designs in Turkey

The most economic air conditioning of living and working places can be achieved by natural ventilation if sufficient. This provides not only the circulation of clear air, but also the decrease of indoor temperature, especially, during hot summer days, provided that the temperature of clear air is lower than that of indoor. From the geometric optimization point of view, both size and position of windows in buildings are important parameters to obtain a uniform indoor air velocity distribution.In this study, the potential use of natural ventilation as a passive cooling system in new building designs in Kayseri, a midsize city in Turkey located at 38.44°N and 35.29°W, was investigated by computational fluid dynamics (CFD). Using the FLUENT 6.2 program, which employs finite element methods, indoor air velocity distributions with respect to changing wind direction and magnitude were obtained in living places of different dimensions. The simulation results suggest that natural ventilation can be used to provide a thermally comfortable indoor environment during the summer season in the study area. The study presents useful design guidelines for natural ventilation at both site planning and individual building levels.     

The effectiveness of stand alone air cleaners for shelter-in-place

Stand-alone air cleaners may be efficient for rapid removal of indoor fine particles and have potential use for shelter-in-place (SIP) strategies following acts of bioterrorism. A screening model was employed to ascertain the potential significance of size-resolved particle (0.1-2 microm) removal using portable high efficiency particle arresting (HEPA) air cleaners in residential buildings following an outdoor release of particles. The number of stand-alone air cleaners, air exchange rate, volumetric flow rate through the heating, ventilating and air-conditioning (HVAC) system, and size-resolved particle removal efficiency in the HVAC filter were varied. The effectiveness of air cleaners for SIP was evaluated in terms of the outdoor and the indoor particle concentration with air cleaner(s) relative to the indoor concentration without air cleaners. Through transient and steady-state analysis of the model it was determined that one to three portable HEPA air cleaners can be effective for SIP following outdoor bioaerosol releases, with maximum reductions in particle concentrations as high as 90% relative to conditions in which an air cleaner is not employed. The relative effectiveness of HEPA air cleaners vs. other removal mechanisms was predicted to decrease with increasing particle size, because of increasing competition by particle deposition with indoor surfaces and removal to HVAC filters. However, the effect of particle size was relatively small for most scenarios considered here. PRACTICAL IMPLICATIONS: The results of a screening analysis suggest that stand-alone (portable) air cleaners that contain high efficiency particle arresting (HEPA) filters can be effective for reducing indoor fine particle concentrations in residential dwellings during outdoor releases of biological warfare agents. The relative effectiveness of stand-alone air cleaners for reducing occupants' exposure to particles of outdoor origin depends on several factors, including the type of heating, ventilating and air-conditioning (HVAC) filter, HVAC operation, building air exchange rate, particle size, and duration of elevated outdoor particle concentration. Maximum particle reductions, relative to no stand-alone air cleaners, of 90% are predicted when three stand-alone air cleaners are employed.     

Indoor air quality at the Correr Museum, Venice, Italy.

Two multidisciplinary field surveys, one in winter and the other in summer have monitored the indoor microclimate, air pollution, deposition and origin of the suspended particulate matter and microorganisms of the Correr Museum, Venice. In addition, this study was focused to identify the problems caused by the heating and air conditioning system (HAC) and the effects due to the presence of carpets. Heating and air conditioning systems (HACs), when chiefly designed for human welfare, are not suitable for conservation and can cause dangerous temperature and humidity fluctuations. Improvements at the Correr Museum have been achieved with the assistance of environmental monitoring. The carpet has a negative influence as it retains particles and bacteria which are resuspended each time people walk on it. The indoor/outdoor pollutants ratio is greater in the summertime, when doors and windows are more frequently open to allow for better ventilation, illustrating that this ratio is mainly governed by the free exchange of the air masses. The chemical composition, size and origin of the suspended particulate matter have been identified, as well as the bacteria potentially dangerous to the paintings. Some general suggestions for improving indoor air quality are reported in the conclusions.     

铁路客车空调系统多工况节能控制

铁路客车空调系统一般按照夏、冬两季室外空气处于设计参数、室内负荷处于最不利条件下进行设计。但是从全年来看，室外空气状态等于设计参数的时间极少，室外空气状态随季节不断变化，对客车空调系统影响很大。因此，客车空调系统的设计与运行必须考虑在室外气象条件和室内热、湿负荷变化时的调节和控制，才能既满足室内温湿度要求，又达到经济运行的目的。本文介绍了客车空调系统多工况节能控制方法。该方法根据送风状态点与室内、室外空气状态的相对位置关系，采用多工况分区方式能达到节能的目的。方法简单，应用方便，为客车空调系统设计和控制提供了理论依据。     

Window and roof configurations for comfort ventilation

This paper assesses the applicability of some architectural design elements to provide comfort ventilation in humid tropical regions: size and location of windows, building eaves and roof shapes for a single unit house. Most window and roof configurations are sufficent to produce only a slightly more comfortable level although they can certainly increase the indoor air velocity. The improvement of indoor air velocity can minimize the physiological effect of the high humidity. Among the tested models, the room with a high gable roof combining with eaves improves significantly the indoor air velocity. Cet expose evalue l'applicabilite de certains elements de configuration visant a assurer une ventilation de confort daus les regions tropicales humides: dimensions et emplacement des fenetres, formes d'avant-toit et de toiture pour une maison individuelle. La plupart des configurations de fenetre et de toiture suffisent seulement a fournir un minime supplement de confort, bien qu'elles puissent effectivement ameliorer la circulation interieure de l'air. Une amelioration de circulation interieure de l'air peut attenuer les effets physiologiques d'une forte humidite. Parmi les modeles essayes, le local comportant une toiture a pignon eleve associee a des avant-toits offre une nette amelioration de circulation interieure de l'air.     

空调大温差研究(2):空调大温差送风系统设计方法

提出用定露点法计算常规空调大温差系统,逐项介绍了设计步骤;认为定露点法不但可以较准确地控制室内设计参数,掌握室内实际空气状态,而且可以利用计算机,使大温差送风的设计计算更加简捷、直观。强调采用定露点法计算时,单个系统不宜过大,热湿比不同的房间宜采用不同的空调系统,空调机组风量或风压较大时,宜采用风机压出式布置。     

建筑节能与改善功能

建筑节能与改善建筑功能是矛盾对立的两方面, 讲节能, 限制了通风, 产生了房间空气质量问题;而满足了房间空气质量的通风,会产生能量大的损失,经济负担太大,一般住户难以承担。也是国家政策所不允许。所以,处理好这一对矛盾是解决建筑节能的关键问题。中国四合院建筑是既解决建筑节能又改善功能的典型,作者将对此进行论证。对被动太阳房因能量有限是绝对不能通风的,也产生室内空气质量问题,这可采用在四合院建筑形成被动太阳房来解决房间空气质量的问题。还研究了大气长波辐射的利用、强化和减弱的措施。     

Evaluation of professional choice of sampling locations for indoor air quality assessment

The uncertainties of professional choice of ‘representative’ sampling locations for general indoor air quality (IAQ) assessment are reported from the perspective of probable errors deviated from the sample-spatial average pollutant concentration of an indoor environment. In this study, associations between the professional choices of the sampling locations and attributes of the assessors were examined to quantify the uncertainties of the IAQ assessment results for a typical air-conditioned office in Hong Kong. In particular, a long-term (one-year) measurement result of the spatial indoor carbon dioxide (CO₂) concentrations in this office was used as a basis to investigate the probable errors due to the choices of sampling locations. Comparing with the random choices, the assessment accuracy with the expert choices would be significantly improved for coarse sampling point densities at certain engineering acceptable error limits. It was reported that the location choices and assessment accuracy would be significantly influenced by the academic background of the assessors. An assessor group with higher academic level would make a choice leaning towards more accurate assessment results. To avoid an inappropriate level of reliance on the assessment results, uncertainties must be quantified for IAQ assessment. This study provided a template for further investigations into the uncertainties of IAQ assessment results involving professional choice of ‘representative’ sampling locations and the results might be a useful reference for assessing indoor environment elsewhere.     

Mapping indoor overheating and air pollution risk modification across Great Britain:A modelling study

Housing has long been thought to play a significant role in population exposure to environmental hazards such as high temperatures and air pollution.However,there is sparse data describing how housing may modify heat and air pollution exposure such that housing's role in poor health and mortality from these hazards may be estimated.This paper describes the development of individual-address level indoor overheating and air pollution risk modifiers for Great Britain,for use alongside historical weather,outdoor air pollution,population socio-economic data,and mortality data in a large-scale epidemiological investigation.A geographically-referenced housing stock database was developed using the Homes Energy Efficiency Database(HEED)and the English Housing Survey(EHS).Simulations of unique combinations of building,fabric,occupation,and environment were run using a modelling framework developed for Energy Plus8.0,estimating indoor temperature metrics,indoor/outdoor ratio of pollution from outdoor sources,and indoor air pollution from multiple indoor sources.Results were compiled,matched back to individual properties in HEED,and mapped using Geographical Information Systems(GIS).Results indicate urban areas had higher numbers of buildings prone to overheating,reduced levels indoor air pollution from outdoor sources,and higher air pollution from indoor sources relative to rural areas,driven largely by variations in building types.The results provide the first national-scale quantitative estimate of heat and indoor air pollution modification by dwellings,aggregated at levels suitable for inclusion in health analysis.     

低温地板辐射采暖预见性间歇运行特性的研究

本文针对采用辐射采暖系统的房间,采用UDF(User Define Function)嵌入数值模拟软件FLUENT方法进行模拟。根据我国夏热冬冷地区(长沙)冬季昼夜温差大的特殊气候,考虑室外温度波动,提出预见性的间歇运行方案,并模拟计算不同运行参数下间歇运行所带来的房间温度变化情况。研究表明:在夏热冬冷地区,室内温度受室外温度波动影响显著,在该地区设置间歇运行策略应根据室外逐时综合温度变化趋势来决定,考虑到地板的预热过程,进行预见性提前开机可以满足室内热舒适需求,并且节约能源。