Wind-Thermal Environmental Characteristic of Multi-Variable Passive Enhanced Natural Ventilation System for High and Large Space Building

Natural ventilation effects in high and large space buildings of tropical areas greatlya ffect the air conditioning energy consumption.Aiming at nearly zero energy building design,thisp aper mainly contributes to provide theoretical basis and reference for thermal comfortable air conditioning system design of high and large space buildings.Taking a theatre in Hainan as study object,a newly composite enhanced natural ventilation system is proposed by integrating theu nderground tunnel-based earth to air heat exchange system and the solar chimney.Ventilationq uantity,air velocity and air temperature field,human vertical temperature gradient differenceu nder24simulation working conditions are considered and analyzed by using ANSYS Fluent.Fort he underground tunnel,results show that Group Two with double underground tunnels and side airs upply location shows its advantages in cooling effects and air supply uniformity.Then for the solar chimney,results show that the solar radiation intensity contributes to larger difference int ransmission power and leads to different cooling effects.On the whole,the system under workingc ondition No.7with120m long,side air supply,double underground tunnel and20m high,1mw ide,0.6°absorber plate angle solar chimney shows its priority in better comprehensive performance.

Thermal comfort in naturally ventilated indoor environment in hot and humid climate zone in P. R. China

To identify human thermal comfort in naturally ventilated buildings,the research based on both subjective and objective data was carried out in Chongqing,P. R. China. The characteristics of subjects' clothing regulation function,changes of actual mean thermal comfort vote (AMV) varying with time and acceptable operative temperature in natural conditions were analyzed. In addition,the indicator actual mean vote-actual percentage dissatisfied (AMV-APD) was used to study the actual dissatisfaction with thermal environment. The results indicate that regulative ability by changing clothing under natural ventilated conditions is very significant but limited simultaneously,about 1.7 ℃ per 0.1 clo. Under naturally ventilated conditions,people may have an acceptable operative temperature of 16-28 ℃. Based on the AMV-APD,the actual minimum percentage dissatisfied can reach 4% at AMV of -0.36.

Impact of indoor heat load and natural ventilation on thermal comfort of radiant cooling system:An experimental study

Construction and operation of buildings are responsible for about 20%of the global energy consumption.The embodied energy of conventional buildings is high due to the utilization of energy-intensive construction mate-rials and traditional construction methodology.Higher operational energy is attributed to the usage of power-consuming conventional air-conditioning systems.Therefore,moving to an energy-efficient cooling technology and eco-friendly building material can lead to significant energy savings and CO 2 emission reduction.In the present study,an energy-efficient thermally activated building system(TABS)is integrated with glass fiber rein-forced gypsum(GFRG),an eco-friendly building material.The proposed hybrid system is termed the thermally activated glass fiber reinforced gypsum(TAGFRG)system.This system is not only energy-efficient and eco-friendly but also provides better thermal comfort.An experimental room with a TAGFRG roof is constructed on the premises of the Indian Institute of Technology Madras(IITM),Chennai,located in a tropical wet and dry climate zone.The influence of indoor sensible heat load and the impact of natural ventilation on the thermal comfort of the TAGFRG system are investigated.An increase in internal heat load from 400 to 700 W deteriorates the thermal comfort of the indoor space.This is evident from the increases in operative temperatures from 29.8 to 31.5℃ and the predicted percentage of dissatisfaction from 44.5%to 80.9%.Natural ventilation increases the diurnal fluctuation of indoor air temperature by 1.6 and 1.9℃ for with and without cooling cases,respectively.It reduces the maximum indoor CO 2 concentration from 912 to 393 ppm.

Effective improvement of a local thermal environment using multi-vent module-based adaptive ventilation

Indoor thermal comfort is essential as it improves living standards.Activity scenarios of personnel are in the process of a dynamic change.In most interior spaces with fixed working stations,people directly blown by cold air have a poor thermal experience.Therefore,to meet the differentiated environmental demands,one challenge is to explore novel ventilation strategies to satisfy the changing environmental needs.An adaptive strategy,multi-vent module-based adaptive ventilation(MAV),was designed to increase the adjustability of air distribution and better adapt to variable demands.A classroom was chosen as a representative model with multiple scenarios during its use.Simulations were conducted to verify the three-level control effect of MAV on improving the thermal environment.The results revealed that different vent solutions create different airflow patterns and thermal environments,which can be matched to the scenarios.The scale for ventilation efficiency No.4,which measured the influence scope of supply air,was used to evaluate the zoning division control in MAV.The space under the charge of a concerned MAV module showed a higher SVE4 than that at other zones.This implied that the zoning division can be effectively implemented.Thermal comfort measured using the air diffusion performance index,predicted mean vote,and draught rate showed that the application of MAV is better than that of the fixed MV mode,and the discomfort experienced when exposed to cold air can be avoided.It is believed that these results will help extend the research of adaptive ventilation strategies.

Adaptive thermal comfort in naturally ventilated hostels of warm and humid climatic region,Tiruchirappalli,India

Thermal comfort is an important factor in hostel buildings when the aim is to maximize the productivity of the students.Due to the extreme weather conditions,achieving thermal comfort in a hostel building in a hot and humid climate is even more difficult.Studies conducted in naturally ventilated hostel buildings in warm-humid climates involved the influence of outdoor air temperature only up to 34.4℃ and have been conducted in a specific season.In contrast,the Tiruchirappalli climate is characterized by a higher range of environmental variables.Therefore,to understand the thermal comfort conditions and usage of the environmental controls in naturally ventilated hostel buildings at the higher range of the environmental variables,a thermal comfort field study spread over one year was carried out at the National Institute of Technology,Tiruchirappalli,India,in twenty-seven hostel buildings.This study relies on field observation and thermal comfort responses from 2028 questionnaires collected from the students between September 2019 to August 2020.The analysis revealed a neutral temperature of 29.5℃ and a comfort range from 26.1℃ to 32.8℃,indicating a wide range of ther-mal adaptation than suggested by the National Building Code of India and ASHRAE standard 55.The preferred temperature was 27.8℃,indicating that students preferred a cooler environment.Acceptability with sweating conditions extended the upper limit of thermal acceptability from 31.8℃ to 32.4℃.The use of a mosquito net can increase the probability of opening a window.Results indicated that overall behavioral adjustment could extend the comfort limits.The study results would be helpful to develop guidelines and designs for naturally ventilated hostel buildings in warm and humid climates that will contribute to reducing energy demand.

Model-based adaptive controller for personalized ventilation and thermal comfort in naturally ventilated spaces

This work develops a standalone autonomously controlled personalized ventilation(PV)unit in a naturally ventilated(NV)office space to maintain acceptable thermal comfort{TQ under steady and transient indoor conditions and activity levels.The NV-PV proportional integral derivative(PID)controller adjusts the PV supply temperature(7spv)at the occupant set flow rate(Qspv)based on predicted TC using a regression model.The target TC level that the controller attains at all times is between 0(neutral)and 1(slightly comfortable).Process transfer functions were developed and then used to find the adaptive PID tuning coefficients using the Internal Model Control(IMC)method.The controller was tested in a case study at indoor temperature range of 25 to 33℃ with relative humidity range of 55%and 80%.It was shown that the NV-PV controller adjusted Tspv to maintain acceptable TC under transients of indoor conditions and metabolic rates.

Improving thermal comfort in mosques of hot-humid climates through passive and lowenergy design strategies

Mosques have intermittent operational schedules with short-term occupancy during the five daily prayers.The occupancy level of the daily prayers is a fraction compared to the mandatory Friday prayers with full occupancy.Usually,the same thermal control mechanism is operated within the same large prayer hall to maintain the thermal comfort of the occupants.Yet,the comfort requirements are often not met due to the short span of operation during prayer times.Nevertheless,mosques have a very high energy usage as the same energyintensive system is operated even during minimal occupancy profiles.The current research aims at using a passive approach towards design to achieve the comfort conditions during the low occupancy daily prayer times without employing mechanical intervention.Numerical simulations are carried out on a validated model of the case study building to investigate the impact of the west-facing Qiblah wall as the congregation stands in proximity to this wall.The design alternatives are tested in conjunction with ventilation strategies to holistically assess the thermal comfort of the occupants.Results show that as much as 4-6℃reduction in indoor wall surface temperature can be achieved with a suitable Qiblah wall design,which reduces the mean radiant temperature of the occupants by 2-4℃.Combined with ventilation strategies,thermal comfort can be significantly improved by at least 40%for the prayers during the hottest times of the day,and as much as 80%for night-time prayers.Results suggest that suitable comfort conditions can be achieved without the need for air-conditioning for at least two or three of the five daily prayers.

Thermal comfort in classrooms considering a traditional wind tower in Trabzon through simulation

The spaces must be designed in accordance with certain design principles for people to feel comfortable.In accordance with that,building ventilation is particularly important during hot periods to ensure thermal comfort.In this study,the effect of ventilation realized using a wind tower on the thermal quality of a classroom was investigated.In the study,two popular models(unidirectional and multidirectional wind tower)were studied,and the model that provided more ergonomic ventilation to sitting users based on climate conditions of the province of Trabzon(Turkey)during the month of August was determined.The more efficient model was studied further.Some dimensional changes in width,height,and shelf height were applied to it to find a model that provided more comfort for the used thermal conditions.The models were modelled and simulated using ANSYS FLUENT.Velocity distributions were generated to ease the interpretation of the results.With the calculated average wind speeds in different regions in the classroom,the thermal sensation in the space was evaluated.Furthermore,the thermal perception of users of the retained model was evaluated by entering thermal comfort parameter values calculated for the relevant region into the CBE thermal comfort tool available online.The change in the dimensional features of the wind tower had an impact on wind tower performance.Ventilation provided by wind towers under the thermal conditions of Trabzon in August often caused thermal discomfort.

Evaluation of thermal comfort and air quality of low-income housing in Kampala City,Uganda

This paper presents the results of thermal comfort and air quality studies in naturally ventilated residential buildings in Kampala City,Uganda.Questionnaire surveys were used for obtaining occupant subjective thermal sensation votes.Indoor and outdoor measurements for air temperature(T_(a)),Mean Radiant Temperature(MRT),relative humidity,air speed,and air quality were done for seven buildings over fifteen days during the month of June 2019.DesignBuilder software was used to develop the reference building model and to simulate strategies for improvement of thermal comfort.Survey results showed that 67.8%of the respondents were comfortable with the indoor thermal environment.The indoor air temperature range was 22.7℃-27.9℃ which lies within the 80%acceptable limits set by ASHRAE 55.The measured indoor MRT range was 24.24℃-25.57℃.Measured levels of indoor PM_(2.5)were double the World Health Organization recommended limits,while the levels of PM 10 were thrice the recommended limits of ASHRAE 62.1.The CO_(2)concentrations were within the limits set by ASHRAE 62.1.The developed model predicted comfortable indoor conditions with a temperature range of 23.6℃-25.3℃ based on the 80%acceptable limits set by ASHRAE 55.The results show that majority of occupants preferred cooler temperatures during the day which is justified by the use of adaptive measures to obtain thermal comfort.

Towards Enhancing the Effectiveness of Classroom Designs for Natural Ventilation Comfort in Yola, Nigeria

Given the perennial incidence of thermal discomfort, health issues, as well as energy costs associated with naturally ventilated classrooms in Yola, the study aimed at enhancing the effectiveness of classroom designs for natural ventilation comfort by examining the effects of six architectural design variables—size and position of openings, form of buildings, orientation of buildings, site planning, topography, and physical features, on the ventilation coefficients of 61 classrooms selected from nine stratified clusters in Yola, Adamawa State, Nigeria. Data were analyzed using percentages, ratios, means as well as standard deviation, and then sorted in groups using tables. The study revealed that the form and orientation of the classroom-buildings, as well as topography, site planning and other physical features, have no significant effect on ventilation coefficient. In addition, a new mean ventilation coefficient was obtained in ten classrooms against an earlier claim that ventilation coefficient cannot exceed a fixed average regardless of the ratio of wall opening to floor area.

Application of natural ventilation of residential buildings in hot-humid regions

The current ventilation condition of the hot and humid regions was analyzed through on-site investigation. It is found that residents in this region expect to improve indoor thermal environment through natural ventilation as much as possible. Then,it comes to a conclusion by the field test that natural ventilation has certain practical effect on improving indoor thermal environment. CFD simulation software is employed to verify the test result. Based on PMV modified model,and according to norms,geography and climate combined with the measured and simulated results,the application of the time and effectiveness of natural ventilation in hot and humid region were analyzed,to some extent,providing a basis for reducing the air-conditioner's runtime with natural ventilation.

夏热冬冷地区住宅浴室热湿环境与洗浴行为研究

对上海地区住宅浴室热湿环境进行了实地测量,分析了浴室热湿环境特征,并通过网络问卷调研了典型人群的洗浴行为。结果表明:浴室热湿环境受洗浴行为影响明显,淋浴开始后空气温度迅速升高,相对湿度接近饱和状态,淋浴结束后相对湿度需要较长时间才能恢复至初始状态,与常规居家场景相比,洗浴过程中的浴室热湿环境偏离常规热舒适区;夏热冬冷地区居民洗浴行为受季节影响明显,淋浴水温冬季偏暖(43.3℃左右)、夏季偏凉(一般36~40℃);洗浴频次以1天1次或2天1次为主;洗浴时长夏季多为5~10 min、冬季多为10~20 min。本文还探讨了浴室环境改善措施和浴室热舒适的特殊性。

自然通风、冷屋顶与外遮阳对室内热环境改善效果实验研究

对自然通风、冷屋顶与外遮阳3种被动技术在夏热冬冷地区的综合隔热降温作用及对室内热环境的改善效果进行了测试分析。结果显示:当三者协同作用时,外遮阳可以遮挡太阳辐射,有效降低窗户的得热量,实验房间玻璃外表面温度较对比房间最高降幅达到7.6℃;高反射涂料的应用使屋顶表面降温幅度达到10.3℃,有效减少了屋顶的温差传热;自然通风系统成功诱导了连续并具有周期性波动的气流,并对埋管内空气有着良好的预冷效果;实验房间室内温度稳定在26.8~27.9℃之间,室内热环境得到了明显的改善。

天津既有住宅自然通风调控模式有效性研究

为提升既有住宅夏季自然通风有效性,设计了基于室内外温度变化的反馈开窗控制模式,对比无调控开窗和分时段开窗控制模式,利用FLUENT软件分别进行室内风环境模拟。以满足室内适应性平均热感觉指标(APMV)一级的时长百分比,和温度平均绝对偏差值(MAD)为评价指标,通过分析室内风热环境的仿真结果发现自然通风成效与开窗控制模式的规律,以及在不同调控策略下的差异化表现。实验结果显示,相较于无调控开窗和分时段开窗控制模式,温度反馈开窗控制模式下室内APMV一级百分比分别提高了9.09%和6.06%,MAD数值分别提高了0.19℃和0.1℃,温度反馈开窗控制模式能够更大幅度地提升自然通风有效性和室内热舒适度,但三种模式下住宅室内热舒适的分布规律相同。

孔隙率对多孔板弥散送风效果的影响研究

弥散送风系统(DCV)由上部静压室、多孔吊顶板、下部房间三部分组成,送风气流通过多孔吊顶板进入下部房间,吊顶板的孔隙大小与弥散送风过程密切相关,目前缺乏吊顶板孔隙率对弥散送风效果的影响研究。采用CFD数值模拟方法,建立了某采用弥散送风系统的办公室的数值计算模型,分析了不同孔隙率下吊顶板对流和辐射传热、室内热环境、热舒适性和空气龄。结果表明:孔隙率由5%增加至20%时,室内垂直温度梯度随之增加;孔板与下部房间的对流和辐射换热量随孔隙率增加而降低,对流换热量占比由6%降低至-3.2%,辐射换热量占比由32%降至17%;人员的热舒适性和平均空气龄随孔隙率增加而变差,PMV值由±0.5变化至±0.8,空气龄由467s变化至541.4s。

北方滨海地区自然通风乒乓球馆冬季风热环境调查研究

文章通过现场测试及主观问卷调查,分析了初冬非采暖期青岛市某高校乒乓球馆在自然通风条件下运动人群在热舒适、室内空气品质、风速干扰性三方面的主观感受。研究发现:与非运动人群相比,运动人群感觉偏暖,可接受的舒适温度下限更低;运动人群可接受的CO_(2)浓度更高,但同时对CO_(2)浓度的变化表现出更高的敏感度;虽然乒乓球馆室内平均风速仅为0.09m/s,但仍有65.67%的运动者认为风速干扰较大。乒乓球资深运动人群有习惯性关窗的行为,避免运动区域的风场干扰是乒乓球馆中引入自然通风亟须解决的首要问题。

针对有热源情况下大空间厂房内两种送风方式的对比研究

通过数值模拟的方法对比研究机械通风(mechanical ventilation,MV)与自然通风(natural ventilation,NV)有室内发热源的情况下,室内热环境的动态变化特征。结果表明,在有热源情况下,室内房间会在高度方向形成明显的热力分层现象,从而导致工作台位置温度较高,降低人体热舒适性。MV和NV房间内,靠近进风百叶位置处的热环境明显优于室内其他位置的热环境。另外,无论是机械通风还是自然通风,在室内局部位置均存在气流死角,导致局部环境恶化,温度过高,不利于设备散热。

电风扇舒适性自然风特征测试方法研究

目前很多电风扇产品能够模拟自然风,但是电风扇的自然风功能处理后的风是否真正接近自然风,尚缺少统一的测试方法。研究人员经过大量的试验和研究发现湍流强度可以表征气流紊动的特点,同时自然风的脉动特性由其自身的1/f紊动特性决定。考核室内环境热舒适性的常用指标中与电风扇产品相关度较高的是吹风感指数和预计平均热感觉指数,研究了利用吹风感指数和预计平均热感觉指数进行电风扇产品自然风挡位的热舒适性测试方法,并对多个电风扇样品进行测试验证。经测试验证,满足自然风要求的电风扇产品的热舒适性明显好于不满足自然风要求的电风扇产品。

城市住区与建筑环境通风控制关键技术及应用

城市住区热环境问题日益严重,建筑内部空气污染与环境质量提升迫在眉睫,通风关键技术是室内外环境质量的重要保障。项目围绕建筑通风领域中环境场仿真技术不完善、快速模拟分析工具缺失等瓶颈问题,开展基础理论与应用技术研究。攻克了城市住区“风-热-湿”多场耦合精确计算关键技术;首次建立了建筑风环境分析用风参数统一确定方法;揭示了建筑环境气载污染物的传输规律,首次实现了高精度的暴露风险预测技术;突破了非稳态自然通风波动型边界条件生成关键核心技术;提出了典型建筑自然通风协同设计方法。研发了住区和建筑通风模拟软件各一套,开发了基于蒸发冷却技术的垂直降温系统和双板双冷源新风机组,制定了多部地方标准和通风设计导则。依托本项目所开发的通风技术、软件工具和节能产品在绿色住区和建筑的设计与建设中得到广泛应用,取得良好的社会、环境、经济效益。