A review of ventilation and the quality of ventilation air

Ventilation is pivotal in terms of securing optimum indoor air quality. In addition, it also has a major impact on energy use in buildings. It is important, therefore, that the role and impact of ventilation is fully understood and that ventilation is employed efficiently. The purpose of this paper is to review these aspects with particular reference to recent research and developments. Key aspects are concerned with identifying the role of ventilation and reviewing this role in the context of the other measures that must be taken to secure a healthy indoor environment. References are particularly made to the development of standards and recent related research. Although good progress is being made, areas that still need to be addressed include maintaining good outdoor air quality and preventing contaminated outdoor air from entering buildings. The outcome of recent research must also be disseminated in practical ways to policy makers, building occupiers and practitioners. Good indoor climate can be achieved, not so much by introducing expensive concepts, but by developing a rationale approach to identifying needs and applying the necessary tools to deal with each need.     

Day care center characteristics and children's respiratory health

Day care centers provide an important exposure arena with potential harmful health effects for children. This study has linked health effect data from a survey among 942 3-5-year-old Oslo children with information on day care center characteristics collected during inspection of the 175 day care centers these children attended. The aim of the study was to estimate associations between dampness problems and other building characteristics and several respiratory health outcomes. Dampness problems (sign of molds, water leakage, damage to floor/wall) were observed in 51% of the day care centers. In multiple logistic regression analyses none of the studied symptoms and diseases (nightly cough, blocked or runny nose without common cold, wheeze, heavy breathing or chest tightness, the common cold, tonsillitis/pharyngitis, otitis media, bronchitis, pneumonia, asthma, and allergic rhinitis) were systematically associated with dampness problems or type of ventilation in day care centers. None of the studied indicators of day care center exposures were found to have a clear effect on day care children's respiratory health. Even so this study does not rule out negative health effects of day care center exposures. The study demonstrates that population-based studies of these relations are demanding with regard to assessment of exposure and health outcomes. PRACTICAL IMPLICATIONS: Simple and easy-to-register indicators of exposures like dampness problems and type of ventilation assessed in 175 day care centers were not related to respiratory health among 3-5-year-old Norwegian children attending the day care centers. The study does not rule out negative health effects of day care center exposures, but demonstrates methodological challenges needed to be addressed in studies of health effects of the day care environment.     

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.     

The impacts of ventilation strategies and facade on indoor thermal environment for naturally ventilated residential buildings in Singapore

The impacts of various ventilation strategies and facade designs on indoor thermal environment for naturally ventilated residential buildings in Singapore are investigated in this study based on thermal comfort index. Four ventilation strategies, nighttime-only ventilation, daytime-only ventilation, full-day ventilation and no ventilation were evaluated for hot-humid climate according to the number of thermal discomfort hours in the whole typical year on the basis of a series of TAS simulations. Parametric studies of facade designs on orientations, window to wall ratios and shading devices were performed for two typical weeks by coupled simulations between building simulation ESP-r and CFD (FLUENT). The results indicate that full-day ventilation for indoor thermal comfort is better than the other three ventilation strategies. With various facade design studies, it was found that north- and south-facing facades can provide much comfortable indoor environment than east- and west-facing facades in Singapore. It is recommended that optimum window to wall ratio 0.24 can improve indoor thermal comfort for full-day ventilation and 600 mm horizontal shading devices are needed for each orientation in order to improve thermal comfort in further.     

Indoor air pollution from biomass combustion and respiratory symptoms of women and children in a Zimbabwean village

Rural areas of developing countries are particularly reliant on biomass for cooking and heating. Women and children in these areas are often exposed to high levels of pollutants from biomass combustion that is associated with a range of respiratory symptoms. Domestic exposure to carbon monoxide (CO) and respirable particles (RSPs) in association with respiratory symptoms among women and children in Zimbabwe was investigated in 48 households. Health status and household characteristics were also recorded. In this study, indoor levels of CO and RSPs exceeded World Health Organization (WHO) air quality guidelines in over 95% of kitchens. The level of indoor air pollutants was associated with the area of kitchen windows and the length of cooking time combined with the level of fire combustion. Prevalence of respiratory symptoms was 94% for women and 77% for children. In addition, women reporting respiratory symptoms were exposed to higher levels of RSPs when compared with those reporting no respiratory symptoms. The study results indicated that levels of indoor air pollutants in rural Zimbabwe may contribute to respiratory symptoms in both women and children. PRACTICAL IMPLICATIONS: Levels of respirable particles and carbon monoxide in kitchens in rural Zimbabwe are unacceptably high and measures to reduce levels should be undertaken. Based on the study findings, recommendations for increasing the area of kitchen windows may be considered as a practical method of reducing indoor air pollutants in rural Zimbabwe.     

Comparison of strategies to improve indoor air quality at the pre-occupancy stage in new apartment buildings

Indoor air quality of new apartment buildings, which is known to cause Sick Housing Syndrome, has become a major concern among apartment residents as well as construction companies in Korea. Recently, the Indoor Air Quality Management Act, a regulation that limits concentration levels of formaldehyde and five volatile organic compounds in new apartment buildings, has been implemented. In this study, the effects of ventilation and decomposing agents were investigated and compared, which could be used at the pre-occupancy stage as solutions to high VOCs concentration levels in new apartment buildings. Six housing units were investigated under different conditions to assess the extent of the improvement in indoor air quality. The results demonstrate that ventilation is an effective way to control indoor air pollution caused by VOCs emissions, and the effect of decomposing agents on improving indoor air quality depends on the types of VOCs.     

The effect of housing characteristics and occupant activities on the respiratory health of women and children in Lao PDR

The paper presents the results of a study conducted into the relationship between dwelling characteristics and occupant activities with the respiratory health of resident women and children in Lao People's Democratic Republic (PDR). Lao is one of the least developed countries in south-east Asia with poor life expectancies and mortality rates. The study, commissioned by the World Health Organisation, included questionnaires delivered to residents of 356 dwellings in nine Districts in Lao PDR over a five month period (December 2005-April 2006), with the aim of identifying the association between respiratory health and indoor air pollution, in particular exposures related to indoor biomass burning. Adjusted odds ratios were calculated for each health outcome separately using binary logistic regression. After adjusting for age, a wide range of symptoms of respiratory illness in women and children aged 1-4 years were positively associated with a range of indoor exposures related to indoor cooking, including exposure to a fire and location of the cooking place. Among women, “dust always inside the house” and smoking were also identified as strong risk factors for respiratory illness. Other strong risk factors for children, after adjusting for age and gender, included dust and drying clothes inside. This analysis confirms the role of indoor air pollution in the burden of disease among women and children in Lao PDR.     

Analysis of thermal comfort and indoor air quality in a mechanically ventilated theatre

Theatres are the most complex of all auditorium structures environmentally. They usually have high heat loads, which are of a transient nature as audiences come and go, and from lighting which changes from scene to scene, and they generally have full or nearly full occupancy. Theatres also need to perform well acoustically, both for the spoken word and for music, and as sound amplification is less used than in other auditoria, background noise control is critically important. All these factors place constraints on the ventilation design, and if this is poor, it can lead to the deterioration of indoor air quality and thermal comfort. To analyse the level of indoor air quality and thermal comfort in a typical medium-sized mechanically ventilated theatre, and to identify where improvements could typically be made, a comprehensive post-occupancy evaluation study was carried out on a theatre in Belgrade. The evaluation, based on the results of monitoring (temperature, relative humidity, CO₂, air speed and heat flux) and modelling (CFD), as well as the assessment of comfort and health as perceived by occupants, has shown that for most of the monitored period the environmental parameters were within the standard limits of thermal comfort and IAQ. However, two important issues were identified, which should be borne in mind by theatre designers in the future. First, the calculated ventilation rates showed that the theatre was over-ventilated, which will have serious consequences for its energy consumption, and secondly, the displacement ventilation arrangement employed led to higher than expected complaints of cold discomfort, probably due to cold draughts around the occupants’ feet.     

Natural ventilation of indoor spaces while minimizing heat losses: Theoretical and experimental investigation

Limiting heat losses during ventilation of indoor building spaces has become a basic aim for architects, particularly since the oil crisis of 1970. Much experience has been gained in terms of ventilation of indoor spaces. Nevertheless, due to the complex applications, attempts to create a theoretical base for solving the problems related to the issue are limited, especially determining the minimum ventilation period required within a designated space. In this paper we have approached this matter, both theoretically and experimentally. The conclusion we reached was that controlled ventilation of spaces through vent holes that successively open and close at regular time intervals can limit the excessive circulation of air masses, which in turn limits heat losses.     

Characterization of indoor air quality using multiple measurements of nitrogen dioxide

Indoor air quality can be affected by indoor sources, ventilation, decay and outdoor levels. Although technologies exist to measure these factors, direct measurements are often difficult. The purpose of this study was to develop an alternative method to characterize indoor environmental factors by multiple indoor and outdoor measurements. Daily indoor and outdoor NO2 concentrations were measured for 30 consecutive days in 28 houses in Brisbane, Australia, and for 21 consecutive days in 37 houses in Seoul, Korea. Using a mass balance model and regression analysis, penetration factor (ventilation rate divided by the sum of ventilation rate and deposition constant) and source strength factor (source strength divided by the sum of ventilation rate and deposition constant) were calculated using multiple indoor and outdoor measurements. Subsequently, the ventilation rate and NO2 source strength were estimated. Geometric means of ventilation rate were 1.44 air change per hour (ACH) in Brisbane, assuming a residential NO2 deposition constant of 1.05/h, and 1.36 ACH in Seoul, with the measured residential NO2 deposition constant of 0.94/h. Source strengths of NO2 were 15.8 +/- 18.2 and 44.7 +/- 38.1 microg/m3/h in Brisbane and Seoul, respectively. In conclusion, indoor environmental factors were effectively characterized by this method using multiple indoor and outdoor measurements.     

Valuing the health benefits of improving indoor air quality in residences

Unlike commercial premises, the indoor air quality of residences is more dynamic, uncontrolled, and prone to human behavioral changes. In consequence, measuring the health benefit gains derived from improving indoor air quality in residences is more complicated. To overcome this, a human thermal comfort model was first integrated with indoor microenvironment models, and subsequently linked with appropriate concentration-response and economic data for estimating the economic benefit gains derived from improving indoor air quality in residences for an adult and an elderly person. In this study, the development of the model is illustrated by using a typical residential apartment locating at the worst air quality neighborhood in Hong Kong and the daily weather profiles between 2002 and 2006. Three types of personal intervention measures were examined in the study: (i) using air cleaner in residence, (ii) changing time spent in residence, and (iii) relocating to a better air quality neighborhood. Our results revealed that employing air cleaners with windows closed in residence throughout the entire year was the most beneficial measure as it could provide the greatest annual health benefit gains. It would give a maximum of HK$2072 in 5-year cumulative benefit gain for an adult and HK$1700 for an elderly person. Employing air cleaners with windows closed in only cool season (October through March) could give the highest marginal return per dollar spent. The benefit gains would become smaller when windows were opened to a greater extent. By contrast, relocating to a better air quality neighborhood and changing the time spent in residence did not appeal to be beneficial intervention measures.     

The effect of environmental and structural factors on indoor air quality of apartments in Korea

The indoor air quality (IAQ) was measured in newly built Korean apartments before and after occupancy in a survey of 158 residences in 24-apartment complexes nationwide. Factors that might affect pollutant concentration, such as temperature, humidity, housing size, and duration of occupancy, were analyzed in relation to the measured concentrations. Average pollutant levels were consistent with the Ministry of the Environment's recommended standards; however, pollutant levels in some apartments exceeded the current standards. We found that the concentrations of formaldehyde and toluene often exceeded the more stringent guidelines that will soon be enacted. Our results suggest that stronger countermeasures are therefore required to control these two chemicals. The results show that the pollution concentration was generally proportional to temperature and humidity, but that, in some cases, the concentration measurements were inversely proportional to these two factors, and in a few others the relationship between these factors was not clear. Indoor air pollution readings were highest in the 30-pyeong apartments, followed by 10-, and 20-pyeong residences. The pollutant concentrations decreased to about half of their initial levels after one year of occupancy, but the concentration of formaldehyde in indoor air persisted for a longer period. The duration of the apartment's occupancy affected indoor air pollutant concentrations more so than other factors such as temperature, humidity, and apartment size.     

Uncertainty in indoor air quality and grey system method

Based on analysis of uncertainty, this paper presents grey system theory to handle the “grey” characteristic of IAQ. Grey comprehensive analysis of indoor air quality reveals that we should pay more attention to the air purification and humidity control in the design and maintenance of HVAC. In order to represent grey characteristic of IAQ system, the educed grey IAQ models can identify the variation intervals of key IAQ model parameters that are lack of directly measurable messages in practical situations. Furthermore, grey assessment is an effective multifactor comprehensive assessment method that can express the integrative influence of contamination indexes on indoor air quality. We can determine the IAQ grade and make comparison according to the grey incidence matrix R.     

The biofiltration of indoor air: implications for air quality

An alternative method of maintaining indoor air quality may be through the biofiltration of air recirculating within the structure rather than the traditional approach of ventilation. This approach is currently being investigated. Prior to its acceptance for dealing with volatile organic compounds (VOCs) and CO2, efforts were made to determine whether the incorporation of this amount of biomass into the indoor space can have an (negative) impact on indoor air quality. A relatively large ecologically complex biofilter composed of a ca. 10 m2 bioscrubber, 30 m2 of plantings and a 3,500 litre aquarium were established in a 160 m2 'airtight' room in a recently constructed office building in downtown Toronto. This space maintained ca. 0.2 air changes per hour (ACH) compared to the 15 to 20 ACH (with a 30% refresh rate) of other spaces in the same building. Air quality parameters of concern were total VOCs (TVOCs), formaldehyde and aerial spore counts. TVOC and formaldehyde levels in the biofilter room were the same or significantly less than other spaces in the building despite a much slower refresh rate. Aerial spore levels were slightly higher than other indoor spaces but were well within reported values for 'healthy' indoor spaces. Levels appeared to be dependent on horticultural management practices within the space. Most genera of fungal spores present were common indoors and the other genera were associated with living or dead plant material or soil. From these results, the incorporation of a large amount of biomass associated with indoor biofilters does not in itself lower indoor air quality.     

The effect of structures on indoor humidity--possibility to improve comfort and perceived air quality

The research presented in this paper shows that moisture transfer between indoor air and hygroscopic building structures can generally improve indoor humidity conditions. This is important because the literature shows that indoor humidity has a significant effect on occupant comfort, perceived air quality (PAQ), occupant health, building durability, material emissions, and energy consumption. Therefore, it appears possible to improve the quality of life of occupants when appropriately applying hygroscopic wood-based materials. The paper concentrates on the numerical investigation of a bedroom in a wooden building located in four European countries (Finland, Belgium, Germany, and Italy). The results show that moisture transfer between indoor air and the hygroscopic structure significantly reduces the peak indoor humidity. Based on correlations from the literature, which quantify the effect of temperature and humidity on comfort and PAQ for sedentary adults, hygroscopic structures can improve indoor comfort and air quality. In all the investigated climates, it is possible to improve the indoor conditions such that, as many as 10 more people of 100 are satisfied with the thermal comfort conditions (warm respiratory comfort) at the end of occupation. Similarly, the percent dissatisfied with PAQ can be 25% lower in the morning when permeable and hygroscopic structures are applied.     

Penetration of nitrogen oxides and particles from outdoor into indoor air and removal of the pollutants through filtration of incoming air

We studied the effect of ventilation and air filtration systems on indoor air quality in a children's day-care center in Finland. Ambient air nitrogen oxides (NO, NO2) and particles (TSP, PM10) were simultaneously measured outdoors and indoors with automatic nitrogen oxide analyzers and dust monitoring. Without filtration nitrogen oxides and particulate matter generated by nearby motor traffic penetrated readily indoors. With chemical filtration 50-70% of nitrogen oxides could be removed. Mechanical ventilation and filtration also reduced indoor particle levels. During holidays and weekends when there was no opening of doors and windows and no particle-generating activity indoors, the indoor particle level was reduced to less than 10% of the outdoor level. At times when outdoor particle concentrations were high during weekdays, the indoor level was about 25% of the outdoor level. Thus, the possible adverse health effects of nitrogen oxides and particles indoors could be countered by efficient filtration. We also showed that inclusion of heat recovery equipment can make new ventilation installations economical.     

The effect of a photocatalytic air purifier on indoor air quality quantified using different measuring methods

The effect on indoor air quality of an air purifier based on photocatalytic oxidation (PCO) was determined by different measuring techniques: sensory assessments of air quality made by human subjects, Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) and chromatographic methods (Gas Chromatography/Mass Spectrometry and High-Pressure Liquid Chromatography with UV detection). The experiment was conducted in a simulated office, ventilated with 0.6 h⁻¹, 2.5 h⁻¹ and 6 h⁻¹, in the presence of additional pollution sources (carpet, chipboard and linoleum). At the lowest air change rate, additional measurements were made with no pollution sources present in the office. All conditions were tested with the photocatalytic air purifier turned on and off. The results show that operation of the air purifier in the presence of pollutants emitted by building materials and furniture improves indoor air quality, as documented by sensory assessments made by human subjects. It also reduces concentrations of many chemical compounds present in the air as documented by the PTR-MS technique. For the lowest ventilation, results from measurements using the chromatographic methods have similar tendency, however many of the 50 compounds that were targeted for analysis were not detected at all, independent of whether the purifier was on or off. For the two conditions with higher ventilation the results were inconclusive.     

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。