不同气流组织形式下空气龄的实验研究

空气龄是评价室内空气品质的指标之一,本文利用CO2示踪气体得出了常用的6种气流组织形式下标准气室中各测点处的浓度衰减曲线,并计算出各测点的空气龄。实验可重复性较好,测得的空气龄反映了标准气室各点空气的新鲜程度,描述了不同气流组织形式通风效率的高低,揭示了室内空气的流动形态,也给空调房间气流组织形式的合理选择提供了依据。     

示踪气体跟踪测量方法在空调通风上的应用

论述了示踪气体跟踪测量的基本原理和基本方法。详细介绍了空调、通风工程中使用示踪气体进行检测的内容、计量和过程等,指出了该方法的优点和不足。认为示踪气候跟踪测量在空调、通风工程中能解决系统调节、测量等工作中的具体问题,应用前景广阔。认为“空气龄”应作为评价人空气质量的主要指标之一。     

外窗通风换气性能测试与流场模拟

采用示踪气体法(选取二氧化碳作为示踪气体)中的下降法(将一定量的示踪气体充入测试区域,在测试区域空气中示踪气体体积分数均匀后开始记录示踪气体体积分数的下降过程,通过记录数据可以计算出房间换气次数,从而得出待测外窗的通风换气性能),对上悬窗、内平开窗、外平推窗的通风换气性能进行测试。外平推窗的通风换气能力最强,上悬窗的通风换气能力最弱,内平开窗的通风换气能力居中。流体力学数值模拟结果表明,在测试期间,由于室内温度高于室外温度,在热压作用下,室内高温空气与室外低温空气在外平推窗的窗口处完成了换热。类似风帽的外平推窗,既促进了自然通风的进行,又避免了室外空气对室内气流组织的干扰。     

用数值方法计算通风房间的空气年龄

利用STACH－3软件对8种不同通风方式进行数值模拟,得到实验小室的速度场和空气年龄场,将模拟计算结果与示踪气体实验结果进行了对比,并对典型工况的室内空气流动进行了分析。结果表明,STACH－3软件计算通风房间的空气年龄可靠性较高,可用于分析房间的通风效率。     

重庆地区高层住宅双窗设计及自然通风实测分析

为推进自然通风在重庆地区的应用,针对某住宅小区进行了楼栋开槽和双窗卧室的优化设计,并对设计的实际住宅进行了通风效果测试。采用示踪气体浓度衰减法对卧室内的气流进行了测量,并用局部空气龄及换气次数作为通风效果的评价指标。测试结果表明,在重庆地区楼栋开槽和双窗设计能将卧室的局部空气龄缩短至1/10,将换气次数提高2~4倍。     

婴儿躺卧场景下个性化送风有效性实验研究

提出在婴儿躺卧场景下应用个性化送风方案。基于婴儿暖体假人进行实验,利用示踪气体衰减法测算房间内不同位置的空气龄和污染物残留浓度,以此评价个性化送风系统的有效性,并与织物风管混合通风系统进行了对比。基于3～11 L/s的送风量和50～90 cm的送风距离,针对个性化送风设计了15组工况;基于11,40 L/s的送风量,针对织物风管混合通风设计了2组工况。结果显示:采用个性化送风,仅在不利工况下新风无法穿透婴儿热羽流,其他工况呼吸区空气龄均小于36 min,最小达到19.13 min;个性化送风在运行前4 min内污染物浓度下降即超过50%,显著快于织物风管混合通风;送风量相同时,个性化送风下呼吸区空气龄较混合通风小51%。     

不同示踪气体对房间通风量测试效果的探讨

示踪气体法是一种常用的室内通风量测试方法,目前已有多种测试模式及示踪气体种类。针对示踪气体的种类和测试条件的不同,来对测量通风量的测试效果进行实验研究分析。在设定标准工况下,通过多组工况的测试结果发现,在自然混合或机械混合的条件下,SF_6与CO_2作为示踪气体的测试效果差异不是很明显,当室内存在机械混合时,测试效果明显比自然混合状态要好很多,更接近于标准设定工况,此时SF_6在作为示踪气体测量通风量比CO_2的测试效果更佳。     

室内换气排污效果的评价指标

就空调送风气流组织排除室内污染物能力的评价，介绍了北欧及英国学者采用拉格朗日法提出的空气龄，换气效率，排污效率等概念，详细推导了示踪气体浓度与局部平均空气龄的关系，阐述了换气效率与排污效率的关系。     

万科住宅产业化样板房自然通风效果的实验研究

采用CO_2示踪气体浓度衰减法,对万科产业化住宅某一典型户型的自然通风进行实验研究,以空气龄为评价指标,实验结果表明在风压作用下风速和风频、窗户开口情况对住宅自然通风舒适性的影响,并进一步分析户型的布局,优化设计。最后总结了此实验方法在自然通风研究方面的其他用途。     

空气渗透

一、测定空气渗透的方法一个空间内的换气次数,可以从一种与空气充分混合的示踪气体的消失速度来确定。示踪气体浓度随着空气渗透而下降的理论公式为: C_t=C_0e~(-Nt) (1)式中 C_t——t时间后示踪气体的浓度(米~3/米~3); C_0——示踪气体的初浓度(米~/米~3); N——单位时间内房间的换气次数(次/秒); t——时间(秒)。一种最适合的示踪气体是N_2O,用带有CO_2和H_2O吸收过滤器的红外线气体分析器来检测。其方法是将一已知量按照计算的N_2O放入室内,造成所     

Air Change Effectiveness Measurements in Two Modern Office Buildings

Local age of air and air change effectiveness were determined in two office buildings using tracer gas techniques to study the applicability of the associated measurement procedures in mechanically ventilated office buildings. Measurement issues examined include the establishment of a uniform tracer gas concentration at the start of the test and the relationship of ventilation system configuration and system operation to the test procedure. Air change effectiveness was determined at locations in the occupied space based on the local age of air at that location and the age of air in the corresponding ventilation system return duct. Values of the air change effectiveness in the occupied space were generally close to one, which is consistent with good mixing of the Ventilation air within the occupied space. Deviations from 1.0, on the order of 10%, did occur, but given the limited experience with these measurement procedures in the field it is not clear whether these deviations are significant. These tests provide data on air change effectiveness to supplement the limited database on mechanically ventilated office buildings in the US. In addition, the experience obtained with the measurement procedures will assist in the development of a standardized approach to measuring air change effectiveness in the field.     

Sensory Characterization of Emissions from Materials

Abstract The exposure-response relationship between the concentration of air pollutants and perceived air quality was studied for eight materials often found indoors and for a mixture of three of the materials. Samples of the materials were placed in a ventilated test chamber. The exhaust air from the test chamber was diluted with different rates of unpolluted air to obtain five different concentrations of polluted air. A sensory panel assessed the perceived quality of the five concentrations of polluted air. The exposure-response relationship differed between the materials and also from the corresponding relationship for human bioeffluents. The exposure-response relationships can be described by straight lines in a log-probit plot and be defined by two constants characteristic for each material. Determination of the two constants characterizing each material requires sensory assessments at least at two pollution concentrations. The sensory pollution load for a material may change with the pollution concentration in the air. The use of a simple measurement method based on a dilution system connected to a ventilated small-scale test chamber is proposed to characterize the emissions from materials in sensory and chemical terms.     

Impact of varying area of polluting surface materials on perceived air quality

A laboratory study was performed to investigate the impact of the concentration of pollutants in the air on emissions from building materials. Building materials were placed in ventilated test chambers. The experimental set-up allowed the concentration of pollution in the exhaust air to be changed either by diluting exhaust air with clean air (changing the dilution factor) or by varying the area of the material inside the chamber when keeping the ventilation rate constant (changing the area factor). Four different building materials and three combinations of two or three building materials were studied in ventilated small-scale test chambers. Each individual material and three of their combinations were examined at four different dilution factors and four different area factors. An untrained panel of 23 subjects assessed the air quality from the chambers. The results show that a certain increase in dilution improves the perceived air quality more than a similar decrease in area. The reason for this may be that the emission rate of odorous pollutants increases when the concentration in the chamber decreases. The results demonstrate that, in some cases the effect of increased ventilation on the air quality may be less than expected from a simple dilution model.     

Empirical validation and modelling of a naturally ventilated rainscreen façade building

In this paper the thermal behaviour of a rainscreen ventilated façade has been investigated both experimentally and numerically. Field measurements were performed during the 2009/10 winter season in a test building located in San Mauro Pascoli (Italy) having a squared base of internal dimension of 2.89 m and a total internal height of 7.75 m. The external walls of this tower are rainscreen ventilated façades with a 24 cm air cavity and an external side composed of stoneware with open joints. Ventilation grills are located at the top and at the bottom of the tower. In this work the modelling of the test building using a dynamic thermal simulation program (ESP-r) is presented and the main results discussed. In order to study the rainscreen ventilated façade three different multi-zone models were defined and the comparison with the experimental results has been used in order to select the best ESP-r air flow network for the modelling of this kind of envelope component. The thermal analysis of this envelope component evidenced that the ventilated façade is able to reverse the direction of the heat flux through the envelope in regions characterized by large solar irradiation during the winter and moderate wind velocity, when the indoor-outdoor air temperature difference is small, thereby reducing the energy consumption required for indoor heating.     

透壁式通风管–块石复合路基降温效果模型试验及数值模拟

为研究透壁式通风管–块石复合气冷路基的降温效果,针对年均气温-3.5℃,平均风速2.5 m/s,主导风向为西北方向的高原环境条件开展了室内模型试验,对比分析了单一块石路基和透壁式通风管–块石复合路基的孔隙空气对流速度、特征点地温及模型整体温度场变化过程。试验结果表明:在透壁式通风管的疏导作用下,通风管与块石层复合结构能够起到强化路基体对流的效果,复合路基块石孔隙中的空气流速比单一块石路基提高约20%,使得复合路基模型底部的降温幅度是单一块石路基模型的2.2倍。建立了透壁式通风管–块石复合路基数值计算模型,对通风管内空气流速分布、路基温度场变化进行了预测分析。结果表明:空气流速在通风管中心达到最大值4.06 m/s,在管壁处流速出现跃变陡降,在块石介质区域里速度的数量级为10-1,与室内试验的结果较为一致。模型试验和数值计算结果均表明复合路基能够起到储存冷量、降低下伏多年冻土地温的作用。     

Investigation of the performance of a ventilated wall

The need for environmental friendly and energy efficient building design has stimulated the design of new facade technologies, including various configurations of double skin facades. This paper investigates the thermal performance of a ventilated wall, both for heating and cooling. A thermal analysis was carried out, paying special attention to the characterization of the heat convection resulting from the buoyancy-induced flow in the open air channel which proved to be a critical aspect of the ventilated wall's behaviour. An integrated thermal and air flow model for the entire system was developed. A model of the ventilated wall construction was developed with the ESP-r simulation program and checked against experimental data from a real-scale test cell facility.The thermal benefits of adding a radiant barrier layer were also investigated. The results showed that this layer was beneficial in terms of the energy performance of the construction. Also, the comparison between the experimental and simulation model results showed satisfactory levels of convergence with the exception of the night hours during the summer period. A sensitivity analysis was also undertaken in order to investigate the main factors and the extent of their effect on the temperature variation inside the ventilated facades.     

Indoor Air Flow and Pollutant Removal in a Room with Task Ventilation

We studied the performance of a task ventilation system that permits occupants to control the flow rate and direction of air supplied to their work space through four floor-mounted supply grill. Air exited the room through a ceding-mounted return grill. To study air-flow patterns, we measured the age of air at multiple locations using a tracer gas stepup. To study the intra-room transport of tobacco smoke particles, cigarettes were smoked mechanically in one workstation and particle concentrations were measured at multiple locations. Our major findings were as follows: (1) deviations from uniform age of air, and uniform particle concentration, were generally less than 30 percent; (2)some supply air short-circuits to the return grill when directed toward the return with high velocity; (3) low supply velocities resulted in a floor-to-ceiling displacement flow; (4) directing the supply air toward the occupant, of partially toward the occupant, typically yielded an age of air at the occupant's breathing level that was 15 to 25 percent lower than the age at other breathing-level locations; (5) with low supply velocities und air directed toward the occupants, tobacco smoke particle concentrations in a ventilated non-smoking workstation were 50 percent of the chamber-average concentration.     

Influence of ozone-limonene reactions on perceived air quality

This study conducted short-term assessments of perceived air quality (PAQ) for six different realistic concentrations of ozone and limonene, separately or together, in room air. The impact of filtration and the influence of the ozone generation method were also examined. The evaluations were made in four identical 40 m3 low-polluting test offices ventilated at 1.4 h(-1) or in two identical 30 m3 stainless-steel chambers ventilated at 1.9 h(-1). Concentrations of ozone, total volatile organic compounds and size-fractionated particles were continuously monitored in each experiment. The results indicate that, for each of the six conditions, the PAQ was poorer when ozone and limonene were present together compared with when only ozone or only limonene was present. In the test offices a correlation was observed between the number of secondary organic aerosols produced by a given ozone/limonene condition and the sensory pollution load for that condition. The particles themselves do not appear to be the primary causative agents, but instead are co-varying surrogates for sensory offending gas-phase species. PRACTICAL IMPLICATIONS: Although the health consequences of long-term exposures to the products of ozone-initiated indoor chemistry remain to be determined, we judge that the sensory offending nature of selected products provides an additional reason to limit indoor ozone levels. Devices that emit ozone at significant rates should not be used indoors. Ozone-filtration of make-up air should also be beneficial in mechanically ventilated buildings located in regions that repeatedly violate outdoor ozone standards. Additionally, the use of limonene containing products should be curtailed during periods when indoor ozone levels are elevated.     

Field Measurements of Ventilation and Ventilation Effectiveness in an Office/Library Building

Mechanical ventalation system performance involves the provision of adequate amuunts of outdoor air, uniform distribution of ventilation air within the occupied space, and the maintenance of thermal comfort. Standard measurement techniques exist to evaluate thermal comfort and air change rates in mechanically ventilated buildings; procedures to evaluate air distribution or ventilation effectiveness in the field are still being developed. This paper presents measuremetlts of air change rates and ventilation effectivenes in an office/library building in Washington, DC. The tracer gas decay technique was used to measure whole building air change rates. The air change rates during the measurement period were essentially constant at about 0.8 air changes per hour, somewhat below the design specification and above the minimum recmmmded in ASHRAE Standard 62-1989. Ventilation effectiveness was investigated at several locations within the building through the measurement of local tracer gas decay rate and mean local age of air. The ventilation effectiveness measurements serve as an investigation of the applicability of the m e a s u r r n procedures employed, providing insight into the measurement issue of establishing initial conditions, the spatial variation in test results within a building, and the repeatabildy between tests. The results of the ventilation effectiveness meusurements are consistent with good distrhtion of the outdoor air by the ventilation system and good mixing within the occupied space.