CFD study of exhaled droplet transmission between occupants under different ventilation strategies in a typical office room

This paper investigated the transmission of respiratory droplets between two seated occupants equipped with one type of personalized ventilation (PV) device using round movable panel (RMP) in an office room. The office was ventilated by three different total volume (TV) ventilation strategies, i.e. mixing ventilation (MV), displacement ventilation (DV), and under-floor air distribution (UFAD) system respectively as background ventilation methods. Concentrations of particles with aerodynamic diameters of 0.8 μm, 5 μm, and 16 μm as well as tracer gas were numerically studied in the Eulerian frame. Two indexes, i.e. intake fraction (IF) and concentration uniformity index R_C were introduced to evaluate the performance of ventilation systems. It was found that without PV, DV performed best concern protecting the exposed manikin from the pollutants exhaled by the polluting manikin. In MV when the exposed manikin opened RMP the inhaled air quality could always be improved. In DV and UFAD application of RMP might sometimes, depending on the personalized airflow rate, increase the exposure of the others to the exhaled droplets of tracer gas, 0.8 μm particles, and 5 μm particles from the infected occupants. Application of PV could reduce R_C for all the three TV systems of 0.8 μm and 5 μm particles. PV enhanced mixing degree of particles under DV and UFAD based conditions much stronger than under MV based ones. PV could increase the average concentration in the occupied zone of the exposed manikin as well as provide clean personalized airflow. Whether inhaled air quality could be improved depended on the balance of pros and cons of PV.     

住宅室内空气品质与通风换气

当今，国际上一些环保专家巳将“室内空气污染”问题列为继“煤烟型污染”、“光化学烟雾型”污染之后的第三代空气污染问题。ASHRAE(美国暖通空调和制冷工程师协会)标准62—1989R中，首次提出了可接受的室内空气品质的概念，定义如下：房间内绝大多数人(80％或更多)没有对室内空气表示不满意，并且空气中没有巳知的污染物达到了可能对人体健康产生严重威胁的浓度。     

板式儿童家具中挥发性有机物（TVOC）对室内空气质量影响的研究

对北京流通领域的板式儿童家具分别进行抽样,参照国际标准ISO16000-9对其TVOC释放量进行了试验研究。测试结果表明：测量获得挥发性有机化合物种类高达60种,有酸、醛、醇、芳香烃、烷烃等多大类型。4个样品舱内TVOC含量,均未达到室内空气质量标准的TVOC限量要求。儿童家具是形成儿童房室内空气中挥发性有机物的一个主要来源。提出了可行、有效的家具检测测试方案。     

室内空气品质研究的探讨

针对室内空气品质是人们生活和工作最重要的环境因素之一,并通过目前国内外室内空气品质的定义和评价,分析了几种可能影响室内空气品质的因素,并探讨了空气质量的控制问题,从而充分改善室内空气品质。     

Effect of internal partitions on the performance of under floor air supply ventilation in a typical office environment

This paper presents a case to investigate the effect of partitions in an office on the performance of under floor air supply ventilation system via computational fluid dynamics. The assessment is in terms of thermal comfort and indoor air quality with the use of a validated computer model. The results indicate that the partitions may significantly affect airflow and performance of a under floor air supply ventilation system. In particular, the presence of a gap above the partition wall is able to improve air distribution owing to less air re-circulation in the upper zone. Its effect on thermal comfort and indoor air quality indicators are evaluated.     

Evaluation on four sampling schemes for assessing indoor air quality

Continuous sampling is one of the common approaches for assessing indoor pollutant level. It is believed that the longer the measurement time, the higher the accuracy and confidence level of the measurement can be achieved. In 2003, the Hong Kong Environmental Protection Department (HKEPD) launched an Indoor Air Quality (IAQ) certification scheme to promote an acceptable IAQ in workplaces. However, measurement efforts and uncertainties associated with the sampling method have not been addressed. Alternative sampling schemes taking shorter measurements in the sampling period were proposed in some circumstances. In this study, the average carbon dioxide (CO₂) concentration of a workplace is selected as an indicator of the indoor air quality to investigate the probable errors and measurement efforts in four sampling schemes, regarding the sampling period: in Scheme A, it is from a continuous sampling throughout the measurement; in Scheme B, it is from two sampling periods of two equal sessions of the measurement; in Scheme C, it is from two structural sampling periods of the two sessions; and in Scheme D, the average concentration is from four sampling periods in four equal sessions of the measurement. In particular, a year-round indoor CO₂ concentration at 17 locations in a typical office in Hong Kong was used to evaluate the probable errors using these four sampling schemes. At certain confidence levels, the required measurement times of the alternative sampling schemes (Schemes B, C, D) were evaluated and compared with that of an 8-hour continuous one (Scheme A). It was found that Scheme C would offer a reduction of measurement effort up to 30%. It is recommended to specify the uncertainties and efforts of measurement in future codes, and to consider these sampling schemes in determining practical strategies for IAQ measurement.     

不同通风方式下室内空气质量的研究

介绍了国内外不同的研究背景,综述了不同通风方式下室内空气质量的研究情况。指出了新型通风方式———碰撞射流通风存在的研究难点和今后的研究方向。     

谈办公空间中家具的摆放对营造空间的影响

简要阐述了家具的概念以及发展现状,分析了家具在办公空间内的地位,系统地研究了家具的摆放对办公空间的影响,以期营造出具有积极氛围的工作空间,进而提高办公空间内的工作效率。     

Effect of mechanically induced ventilation on the indoor air quality of building envelopes

Experiments were conducted to study the effect of mechanically induced fresh-air ventilation on the indoor air quality (IAQ) of the Tuskegee Healthy House (THH), selecting the outdoor weather conditions almost identical during the “fan OFF” and “fan ON” periods. Measurements of outdoor and indoor temperature and relative humidity (RH), in addition to the indoor dust particle concentration levels and interior wall moisture content, were systematically carried out during the summer month of August 2008. Results show that the effect of mechanically induced ventilation (“fan ON” period) is to raise the indoor RH, interior wall moisture content, and indoor dust particle concentration values significantly above those measured during the “fan OFF” period. The indoor temperature increases only slightly during the “fan ON” period.     

Relating actual and effective ventilation in determining indoor air quality

Ventilation is both a mechanism for removing indoor air pollutants, and a potential energy load on the heating or cooling system of a building. Quantitative estimates of the ventilation rates, important for both of these applications, necessitate determining time-averaged quantities. The time-averaged ventilation rate appropriate for indoor air pollution, however, is different from that associated with energy load. We derive ventilation efficiencies for well-mixed, homogeneous, time-varying concentrations and corroborate findings with field data from a test house in Edmonton, Alberta, which indicate that monthly ventilation efficiency ranges from 79% to 92% with an annual average of 80%, and that hourly temporal ventilation efficiencies vary over a much larger range than time-averaged quantities.     

Exhaust ventilation in attached garages improves residential indoor air quality

Previous research has shown that indoor benzene levels in homes with attached garages are higher than homes without attached garages. Exhaust ventilation in attached garages is one possible intervention to reduce these concentrations. To evaluate the effectiveness of this intervention, a randomized crossover study was conducted in 33 Ottawa homes in winter 2014. VOCs including benzene, toluene, ethylbenzene, and xylenes, nitrogen dioxide, carbon monoxide, and air exchange rates were measured over four 48‐hour periods when a garage exhaust fan was turned on or off. A blower door test conducted in each garage was used to determine the required exhaust fan flow rate to provide a depressurization of 5 Pa in each garage relative to the home. When corrected for ambient concentrations, the fan decreased geometric mean indoor benzene concentrations from 1.04 to 0.40 μg/m³, or by 62% (P<.05). The garage exhaust fan also significantly reduced outdoor‐corrected geometric mean indoor concentrations of other pollutants, including toluene (53%), ethylbenzene (47%), m,p‐xylene (45%), o‐xylene (43%), and carbon monoxide (23%) (P<.05) while having no impact on the home air exchange rate. This study provides evidence that mechanical exhaust ventilation in attached garages can reduce indoor concentrations of pollutants originating from within attached garages.     

Domestic ventilation with heat recovery to improve indoor air quality

Recently in the U.K., and particularly in Scotland, domestic ventilation systems have been considered as means of reducing condensation in existing housing stock. A simple ventilation model which is suitable for ventilation systems with a heat recovery unit is presented. Using field data of temperature and relative humidity, air supply and extract rates for individual rooms are estimated by applying this model. Unlike conventional systems, extract from bedrooms is considered necessary for the type of dwellings considered to reduce surface condensation.     

室内空气质量控制策略初探

由于经济快速增长及生产活动导致的大气污染问题越来越严重,且是一个不可能在短期内解决的问题,现代人80%-90%的时间在室内度过,因此室内的空气品质对人体健康有着很大的影响。室外雾霾天气及室内材料散发的甲醛、TVOC等污染物,使我国室内空气环境处于内忧外患的状态。本文总结了目前常见的新风系统形式及典型的气流分布模式,总结了市面上常用的过滤器类型及空气净化器类型,为绿色建筑及被动房建设提供技术参考。     

多区域空气流动网络模型用于室内空气品质和通风模拟研究

介绍了用于研究建筑物内空气流动和污染物传播的多区域模拟软件CONTAMW，其使用条件和可以实现的模拟组合。着重分析了该模型在建筑通风、空内空气品质研究及防排烟领域的重要应用前景。     

新装修办公室内空气污染的消除试验

以一个新装修的办公室为研究对象,对室内的污染状况进行了检测。从控制污染源和消除室内空气污染两方面进行了净化试验。试验结果表明,在有紫外线灯照射时,用臭氧水对空间和人造板表面进行喷雾,同时保持室内高臭氧浓度的方法对降低人造板的甲醛散发量有明显效果;利用夜间产生高浓度臭氧、白天产生低浓度臭氧结合活性炭吸附的方法能有效消除室内空气中的甲醛和氨气。     

Improving energy performance of school buildings while ensuring indoor air quality ventilation

Energy conscious design of school buildings, as well as deemed-to-satisfy provisions in a Performance Based Energy Code, should address the problem known as the energy efficiency—thermal comfort—indoor air quality dilemma (EE-TC-IAQ Dilemma). In warm and moderate climates, the large internal heat sources usually found in school buildings prevent achieving thermal comfort without active cooling in summer, but are not sufficient to eliminate the need for heating in winter. Commonly used air-conditioners do not improve air quality, while natural ventilation induces uncontrolled energy losses. In this study, a step by step process was used for the development of deemed-to-satisfy design solutions, which cope with the EE-TC-IAQ Dilemma, for a performance based code. A distinction is made between improving building design variables and improving ventilation schemes. Results indicate that implementation of improved ventilation schemes in an otherwise well designed energy-conscious building result in savings of 28–30% and 17–18% for northern and southern classroom orientations, respectively.     

Impacts of ventilation strategies on energy consumption and indoor air quality in single-family residences

This report compares the impacts of five different ventilation strategies on the overall energy consumption of superinsulated houses in the Northwestern United States. The strategies examined are: (1) natural ventilation, (2) balanced ventilation with an air-to-air heat exchanger, (3) exhaust ventilation without heat recovery, (4) exhaust ventilation connected to a heat pump to provide space heating, and (5) exhaust ventilation connected to a heat pump to heat domestic water. A modified Transient System Simulation (TRNSYS) residential load model incorporating the Lawrence Berkeley Laboratory (LBL) infiltration model, and a modified TRNSYS domestic hot water model, are used to simulate the energy consumption associated with each strategy. The domestic hot water model is used to determine the amount of useful heat supplied by an exhaust ventilation heat pump as a function of hot water demand schedule and storage tank size. The simulations are made for cities with: (1) a moderate coastal climate, (2) a windy cold climate, and (3) a calm cold climate. They show that total energy consumption (space heat + domestic hot water) can be reduced by 9 to 21% by using mechanical ventilation systems with heat recovery. These savings, compared with energy savings of 18 to 21% achieved by superinsulating the same houses, indicate that the choice of ventilation strategy can have a significant effect on energy consumption. The comparisons also show that for the same effective ventilation rate, houses with mechanical ventilation systems (especially those with exhaust fans) have uniform ventilation and therefore better indoor air quality.     

The effects of an energy efficiency retrofit on indoor air quality

To investigate the impacts of an energy efficiency retrofit, indoor air quality and resident health were evaluated at a low‐income senior housing apartment complex in Phoenix, Arizona, before and after a green energy building renovation. Indoor and outdoor air quality sampling was carried out simultaneously with a questionnaire to characterize personal habits and general health of residents. Measured indoor formaldehyde levels before the building retrofit routinely exceeded reference exposure limits, but in the long‐term follow‐up sampling, indoor formaldehyde decreased for the entire study population by a statistically significant margin. Indoor PM levels were dominated by fine particles and showed a statistically significant decrease in the long‐term follow‐up sampling within certain resident subpopulations (i.e. residents who report smoking and residents who had lived longer at the apartment complex).     

Energy saving potential and repercussions on indoor air quality of demand controlled residential ventilation strategies

Ventilation is ambiguously related to the energy saving rationale originating from the mitigation of global warming, the reaching of peak oil or health concerns related to fossil fuel burning. Since it makes up for about half of the energy consumption in well-insulated buildings, it is an attractive target for energy saving measures. However, simply reducing ventilation rates has unwanted repercussions on the indoor air quality. Two main strategies have been developed to reconcile these seemingly opposing interests: heat recovery and demand control ventilation. This paper focuses on the energy saving potential of demand controlled mechanical exhaust ventilation in residences and on the influence such systems may have on the indoor air quality to which the occupants of the dwellings are exposed. The conclusions are based on simulations done with a multi-zone airflow model of a detached house that is statistically representative for the average Belgian dwelling. Four approaches to demand based control are tested and reported. Within the paper exposure to carbon dioxide and to a tracer gas are used as indicators for indoor air quality. Both energy demand and exposures are reported and compared to the results for a standard, building code compliant, exhaust system, operating at continuous flow rates. The sensitivity of the control strategies to environmental and user variations is tested using Monte-Carlo techniques. Under the conditions that were applied, reductions on the ventilation heat loss of 25–60% are found, depending on the chosen control strategy (with the exclusion of adventitious ventilation and infiltration).     

CFD study on effect of the air supply location on the performance of the displacement ventilation system

The purpose of this paper is to investigate using a numerical simulation (computational fluid dynamics or CFD) the effect of the air supply location on the design and performance of the displacement ventilation (DV) system. The results are reported in terms of thermal comfort and indoor air quality. The study focuses on the typical Hong Kong office under local thermal and boundary conditions. This includes the high cooling load used in Hong Kong. Several pollutants typically found in the office such as carbon dioxide and volatile organic compounds (VOCs) were investigated. The results indicate that the supply should be located near the center of the room rather than to one side of the room. This will provide a more uniform thermal condition in the office. The DV system was found to be effective in dispersing VOCs within an office environment for all cases studied. The exhaust was found to have minimal effect on the thermal comfort. For a DV system in Hong Kong, it is possible to use 100% fresh air without extra energy consumption.