Low Ventilation Rates Research Articles

Unattached fractions and aerosol attached of radon progeny in indoor air

The present study summarizes the experimental data on the activity concentrations of222Rn gas , unattached and attached short-lived222Rn progeny 218Po, 214Pb and 214Po in indoor air of Jeddah City, K.S.A. Jeddah city lies on the eastern bank of the red sea, South West the Kingdom of Saudi Arabia. The city is located between latitudes 21° 27\ and 21° 30\ N, longitudes 39° 9\ and 31° 12\ E. By means of theoretical model calculation, the unattached fraction (fP) of 218Po, 214Pb of potential alpha energy of 222Rn progeny, the equilibrium factor (F), the attachment rate (X) to aerosol particles in the room air, the attachment coefficient (B) and the deposition rates of unattached (qf) and attached (qa) of 222Rn progeny on walls and other surfaces were calculated. The measurements were performed at different days in three different rooms of same size at low and moderate ventilation rates. An electrostatic precipitation method and a single wire-screen diffusion battery technique were both employed for the determination of 222Rn gas concentration and its unattached progeny, respectively. At low ventilation rate (υ ≤ 0.4 h–1) a mean unattached fraction (fP) of 0.096±0.01 was obtained at a mean aerosol particle concentration (Z) of 2.6×103 cm–3 and at a mean equilibrium factor (F) of 0.34 ± 0.02. The mean deposition rates of unattached (qf) and attached (qa) 222Rn progeny were found to be 94±13 h–1 and 0.12±0.05 h–1, respectively. The values of the recoil factor were neglected. At moderate ventilation rate of υ = 0.5 h–1 a mean value of fP = 0.059±0.006 was obtained at a mean aerosol concentration Z = 29×103 cm–3 and at a mean F = 0.24±0.014. In this case the mean value of the recoil factor was found to be 0.54±0.18. Key words: Unattached fraction, aerosol attached, theoretical model calculation, radon progeny.

Computational fluid dynamics simulation of air temperature distribution inside broiler building fitted with duct ventilation system

An investigation was conducted to develop ventilation systems to prevent cold air drafts during the winter season and create a suitable atmosphere inside the broiler rearing building. In the cold weather, ventilation ducts and low ventilation rates are used to maintain the required air temperature. Perforated ducts are preferred for heating spaces because they provide efficient and uniform distribution of the entire air volume. Four ventilation systems were designed in order to establish a comfortable zone for the broilers during winter season. To investigate these different systems under realistic conditions, computational fluid dynamic simulation was used. Field experiments were conducted to validate the designed cases. From the validation results, very low errors were observed. The improved designs were compared with the standard design in terms of ventilation rate, air temperature distribution and indoor gas concentration reduction. Case four (C-4) of the improved designs achieved the highest ventilation rate in the broiler zone. In C-4, theinlet duct was installed in building side and the outlet duct in the opposite side. It achieved about 54% of the ventilation in comparison to standard design. All improved designs showed high uniformity ranging around 60–70% compared to the standard design. For gas dilution in broiler zone, C-4 showed 15% ammonia reduction efficiency 3 min after operating the ventilator.

In China, Students in Crowded Dormitories with a Low Ventilation Rate Have More Common Colds: Evidence for Airborne Transmission

ObjectiveTo test whether the incidence of common colds among college students in China is associated with ventilation rates and crowdedness in dormitories.MethodsIn Phase I of the study, a cross-sectional study, 3712 students living in 1569 dorm rooms in 13 buildings responded to a questionnaire about incidence and duration of common colds in the previous 12 months. In Phase II, air temperature, relative humidity and CO2 concentration were measured for 24 hours in 238 dorm rooms in 13 buildings, during both summer and winter. Out-to indoor air flow rates at night were calculated based on measured CO2 concentrations.ResultsIn Phase I, 10% of college students reported an incidence of more than 6 common colds in the previous 12 months, and 15% reported that each infection usually lasted for more than 2 weeks. Students in 6-person dorm rooms were about 2 times as likely to have an incidence of common colds ≥6 times per year and a duration ≥2 weeks, compared to students in 3-person rooms. In Phase II, 90% of the measured dorm rooms had an out-to indoor air flow rate less than the Chinese standard of 8.3 L/s per person during the heating season. There was a dose-response relationship between out-to indoor air flow rate per person in dorm rooms and the proportion of occupants with annual common cold infections ≥6 times. A mean ventilation rate of 5 L/(s•person) in dorm buildings was associated with 5% of self reported common cold ≥6 times, compared to 35% at 1 L/(s•person).ConclusionCrowded dormitories with low out-to indoor airflow rates are associated with more respiratory infections among college students.

Numerical investigation of the influence of room factors on HAM transport in a full-scale experimental room

Abstract To model the indoor environment influenced by room factors including moisture loads and ventilation conditions, the governing equations of heat, air and moisture (HAM) transport inside the room and through the envelope, including the coupling process of the interaction of heat and moisture between indoor air and envelope, need to be solved. This paper presents a CFD model of the indoor environment that takes into account the heat and moisture transfer through the envelope in a single simulation environment. The comparisons between experimental data and simulation results show close agreement. This model is then implemented in 12 cases to study the influence of moisture loads, ventilation rates, and positions of the air inlet and outlet on the indoor environment and on the heat and moisture transport through the envelope. Simulation results show that the humidity responses of the test room vary significantly for different moisture loads from 42 g/h to 91 g/h and for different ventilation rates from 0.5 air change per hour (ach) to 1 ach. Changing the positions of the ventilation vents alters the air flow pattern significantly, thus affecting the ventilation efficiency. With a heat and moisture source inside the test room, the changed ventilation efficiency influences the indoor environment significantly, especially under low ventilation rates. The increased ventilation rate carries away more heat and moisture, which reduces both temperature and moisture levels inside the room. Under the mixed convection condition, the indoor temperature and moisture levels dominate the heat and moisture transport through the wall system.

Ventilation rates in schools and pupils’ performance

This paper is a development of our earlier work [5,6,11]. The effects of classroom ventilation on pupils’ performance were investigated in 8 primary schools in England. In each school the concentrations of carbon dioxide and other parameters were monitored for three weeks in two selected classrooms. In 16 classrooms interventions were made to improve the ventilation rate and maintain the temperature within an acceptable range using a purpose-built portable mechanical ventilation system. As a result of the interventions the provision of outdoor air to the classrooms was improved from the prevailing levels of about 1 l/s per person to about 8 l/s per person. The pupils and teachers in the classrooms studied were usually exposed to unacceptably poor air quality conditions, with CO 2 concentrations of up to 5000 ppm, much higher than the average recommended levels of 1500 ppm and the preferred level of 1000 ppm. The results of computerized performance tasks performed by more than 200 pupils showed significantly faster and more accurate responses for Choice Reaction (by 2.2%), Colour Word Vigilance (by 2.7%), Picture Memory (by 8%) and Word Recognition (by 15%) at the higher ventilation rates compared with the low ventilation conditions. The present investigation provides strong evidence that low ventilation rates in classrooms significantly reduce pupils’ attention and vigilance, and negatively affect memory and concentration. The physical environment therefore affects teaching and learning.

Experimental analysis of energy performance f a ventilated window for heat recovery under controlled conditions

A ventilated window in cold climates can be considered as a passive heat recovery system. This study carried out tests to determine the thermal transmittance of ventilated windows by using the Guarded Hot Box. By testing under defined boundary conditions, the investigation described the heat balance of the ventilated window and clarified the methodology for thermal performance evaluation. Comparison between windows with and without ventilation using the window-room-ventilation heat balance revealed that a ventilated window can potentially contribute to energy savings. In addition, it was found that a significant part of preheating occurred through the window frames, which positively influenced the heat recovery of the window but increased the heat loss. Results also showed that increasing air flow decreased the recovery efficiency until the point when the additional thermal transmittance introduced by the ventilation was higher than the effect of heat recovery. Accordingly, the use of the ventilated windows might be most suitable for window unit with low ventilation rates. The results correlated with theoretical calculations in standards and software. However, the concept of a window thermal transmittance ( U w) value is not applicable for energy performance evaluation of ventilated window and requires deeper analysis.

FACTORS AFFECTING VENTILATION, INDOOR-AIR QUALITY AND ACOUSTICAL QUALITY IN ‘GREEN’ AND NON-‘GREEN’ BUILDINGS: A PILOT STUDY

This paper discusses a pilot project involving the direct monitoring of ventilation, indoor-air quality and the acoustical conditions in selected nominally ‘green’ and non-‘green’ buildings located on a university campus. The objectives were to measure parameters quantifying these three aspects of indoor environmental quality, determine the relationships between them and the building-design concepts, and evaluate the implications of the results for ventilation-system design, especially in ‘green’ buildings. Measurements were made in rooms, with and without acoustical treatment, in buildings with natural ventilation or mechanical (displacement and/or mixed-flow) ventilation systems. Measurements were made of ventilation rates (air changes per hour), indoor air quality (respirable-fibre, total-VOC and ultrafine-particulate concentrations), and the acoustical conditions (noise levels and reverberation times). Correlations between the environmental results, the building concept, the ventilation concept and the building window status were explored. In rooms with natural ventilation, low-frequency noise and total sound-pressure levels were lower; however, the rooms had higher ultrafine-particulate counts and lower ventilation rates. Rooms with mechanical ventilation had higher low-frequency and total sound-pressure levels, higher ventilation rates and fibre concentrations, but lower concentrations of ultrafine particulates. It was concluded that, in general, mechanical ventilation can provide better indoor air-quality, but that HVAC noise is an issue if the system is not properly designed. In ‘green’ buildings, noise levels were acceptable when the windows were closed, but increasing the ventilation rate by opening the windows resulted in higher noise levels. The results suggest that the acceptability of environmental factors in buildings depends on the degree of compliance of the design and its implementation with standards and design guidelines (i.e. for ventilation, air quality, thermal comfort, etc.), whether the original design concept is ‘green’ or non-‘green’.

Removing indoor particles using portable air cleaners: Implications for residential infection transmission

Reducing indoor exposure to influenza particles can be an important strategy to manage residential infections. Many portable air cleaning (PAC) technologies are currently employed in residential environments but very little research has been performed to evaluate and compare their performance in terms of particle removal associated with influenza. This study evaluates the effectiveness of portable air cleaners at removing airborne NaCl particles as an analogue to the influenza virus and applies the results to an IAQ mass balance model to evaluate the performance in controlling residential exposures and mitigating infection risks. Various devices representing different PAC technologies were tested using a pull down particle challenge in a full scale stainless steel chamber. Particle generation and measurement were conducted using a 6-jet atomizer and a paired aerodynamic particle sizer (APS)-scanning mobility particle sizer (SMPS), respectively. PAC incorporating HEPA filtration, electrostatic precipitation, ion generation and electret filtration were tested. We found that particle exposures released during a cough or sneeze event in a typical Quebec City residential room in Canada can significantly be reduced using HEPA, electrostatic precipitation and electret filtration PACs when compared with a situation where no PAC is being used. Modelling analysis demonstrates that the use of these PACs can mitigate the risks of influenza infection via airborne route for a caregiver or a spouse sharing the same room. The implications of this study are significant considering low ventilation rates of Quebec City residences.

A structural model of perfusion and oxygenation in low-flow states

Background Recent investigations underscore the critical importance of ventilation strategies on resuscitation outcomes. In low perfusion states, such as cardiac arrest and traumatic shock, the rise in intrathoracic pressure that accompanies positive-pressure ventilation can significantly impede venous return and lead to a decrease in cardiac output. The optimal ventilation strategy in these “low-flow” states remains unclear. Objective To create a mathematical model of perfusion and oxygenation to predict the effects of PPV with both normotension and hypotension. Methods The lung pressure–volume relationship was modeled using a novel formula allowing manipulation of various lung characteristics. A separate formula was then derived to predict mean intrathoracic pressure (MITP) for specific minute ventilation values using the pressure–volume formula. The addition of positive end-expiratory pressure was also modeled. Finally, a formula was derived to model oxygen absorbance as a function of alveolar surface area and flow based on ventilation rate and MITP. Results Mathematical models of the lung pressure–volume relationship, MITP, and absorbance were successfully derived. Manipulation of total lung capacity, compliance, upper and lower inflection points, positive end-expiratory pressure, and minute ventilation allowed prediction of optimal ventilation rate and tidal volume for a normal lung and with various abnormal characteristics to simulate particular disease states, such as acute respiratory distress syndrome (ARDS). For a normal lung, ventilation rates of 4–6 breaths/min with higher tidal volumes (15–20 mL/kg) resulted in the lowest predicted MITP values (5 cm H 2O) and the highest absorbance. The input of lung parameters that would simulate ARDS resulted in optimal ventilation rates of 10–12 breaths/min with lower tidal volumes (8–10 mL/kg) and higher predicted MITP values (10–15 cm H 2O). Conclusions A mathematical model of ventilation was successfully derived allowing manipulation of multiple pulmonary physiological variables to predict MITP and potentially identify optimal ventilation strategies. This model suggests the use of lower ventilation rates and larger tidal volumes to minimize the hemodynamic effects of positive pressure ventilation in patients with hypoperfusion but normal lung characteristics.

Serial MRI characterization of the functional and morphological changes in mouse lung in response to cardiac remodeling following myocardial infarction

The temporal evolution of heart failure and associated pulmonary congestion in rodent heart failure models has not yet been characterized simultaneously and noninvasively. In this study, MRI was used to assess the serial progression of left-ventricular dysfunction and lung congestion in mice following myocardial infarction (MI). Cardiac and lung (1) H MRI was performed at baseline and every 3 days up to 13 days postsurgery in sham and MI mice. Respiratory parameters and terminal lung mechanics were assessed followed by histological analysis. MRI revealed that the MI induced significant pulmonary congestion/edema as detected by increased MRI signal intensity and was associated with increased lung volume and reduced cardiac contractility. Pulmonary function was also depressed in MI-mice, reflected by a reduced tidal volume and a low minute ventilation rate. Additionally, MI significantly increased lung resistance, markedly reduced lung compliance and total lung capacity and significantly increased lung weights by 57%. Significant correlations were observed between the MRI measured lung congestion, lung volume, ejection fraction, and lung wet-weight parameters. This study demonstrates that MRI may be of significant value in evaluating therapies aimed at primary intervention for lung congestion and secondary prevention of unfavorable cardiac remodeling.

Ventilation rates and health: multidisciplinary review of the scientific literature

The scientific literature through 2005 on the effects of ventilation rates on health in indoor environments has been reviewed by a multidisciplinary group. The group judged 27 papers published in peer-reviewed scientific journals as providing sufficient information on both ventilation rates and health effects to inform the relationship. Consistency was found across multiple investigations and different epidemiologic designs for different populations. Multiple health endpoints show similar relationships with ventilation rate. There is biological plausibility for an association of health outcomes with ventilation rates, although the literature does not provide clear evidence on particular agent(s) for the effects. Higher ventilation rates in offices, up to about 25 l/s per person, are associated with reduced prevalence of sick building syndrome (SBS) symptoms. The limited available data suggest that inflammation, respiratory infections, asthma symptoms and short-term sick leave increase with lower ventilation rates. Home ventilation rates above 0.5 air changes per hour (h(-1)) have been associated with a reduced risk of allergic manifestations among children in a Nordic climate. The need remains for more studies of the relationship between ventilation rates and health, especially in diverse climates, in locations with polluted outdoor air and in buildings other than offices. Ventilation with outdoor air plays an important role influencing human exposures to indoor pollutants. This review and assessment indicates that increasing ventilation rates above currently adopted standards and guidelines should result in reduced prevalence of negative health outcomes. Building operators and designers should avoid low ventilation rates unless alternative effective measures, such as source control or air cleaning, are employed to limit indoor pollutant levels.

Investigation of volatile organic compounds in office buildings in Bangkok, Thailand: Concentrations, sources, and occupant symptoms

To conserve energy, office buildings with air-conditioning systems in Thailand are operated with a tight thermal envelope. This leads to low fresh-air ventilation rates and is thought to be partly responsible for the sick building syndrome symptoms reported by occupants. The objectives of this study are to measure concentrations and to determine sources of 13 volatile organic compounds (VOCs) in office buildings with air-conditioning systems in the business area of Bangkok. Indoor and outdoor air samples from 17 buildings were collected on Tenax-TA ™ sorbent tubes and analyzed for individual VOCs by thermal desorption-gas chromatography/mass spectrometry (TD–GC/MS). Building ventilation was measured with a constant injection technique using hexafluorobenzene as a tracer gas. The results show that the VOC concentrations varied significantly among the studied buildings. The two most dominant VOCs were toluene and limonene with average concentrations of 110 and 60.5 μg m −3, respectively. A Wilcoxon sum rank test indicated that the indoor concentrations of aromatic compounds and limonene were statistically higher than outdoor concentrations at the 0.05 level, while the indoor concentrations of chlorinated compounds were not. Indoor emission factors of toluene and limonene were found to be highest with the average values of 80.9 and 18.9 μg m −2 h −1, respectively. Principal component analysis was applied to the emission factors of 13 VOCs, producing three components based on source similarities. Furthermore, a questionnaire survey investigation and field measurements of building air exchange pointed to indoor air complaints related to inadequate ventilation.

The effects of outdoor air supply rate on work performance during 8-h work period

The purpose of this study is to evaluate the effect of ventilation rate on work performance and perceived air quality through short-term laboratory experiments. The experiment was designed to simulate office work, and a laboratory space was modified using new finish materials to become a typical office space. High levels of volatile organic compounds (VOCs) were found in the exposure chamber, most probably originating from the new finishing materials that were present. Twenty-four subjects were divided into six groups that were randomly exposed to the three ventilation rates, 5, 10, and 20 l/s per person. The subjects performed work tasks three separate times for each ventilation rate over an 8-h exposure period. The work performance of the subjects logarithmically improved with increased ventilation rates, which was similar to the previous research findings. Statistical significance was found for addition task, text-typing task, and memorization task. Increased work performance in this experiment was slightly lower than the results of previous short-term laboratory experiments, yet remained higher than results of previous long-term field experiments. However, it was difficult to directly compare the results of this experiment with those of previous experiments, because of the higher concentration of VOC present in the office rooms and the learning effect associated with the repeated tasks. The results of this experiment show that ventilation had positive impacts on perceived air quality and work performance for the subjects tested. Work performance logarithmically increased by approximately 2.5-5% as ventilation rates were increased from 5 to 20 l/s per person. The positive effect of ventilation rate on work performance was shown to be limited at the low ventilation rate. The positive effects on work performance were at lower ventilation rates. The learning effect in repeated work performance tasks could increase the uncertainty of the work performance analysis in 8-h exposure period.

Effectiveness of Multi-Stage Scrubbers in Reducing Emissions of Air Pollutants from Pig Houses

Emissions of air pollutants from livestock houses may raise environmental problems and pose hazards to public health. They can be reduced by scrubbers installed at the air outlets of livestock houses. In this study, three multi-stage scrubbers were evaluated in terms of their effectiveness in reducing emissions of airborne dust, total bacteria, ammonia, and CO2 from pig houses in winter. The three multi-stage scrubbers were one double-stage scrubber (acid stage+ bio-filter), one double-stage scrubber (acid stage + bio-scrubber), and one triple-stage scrubber (water stage + acid stage + bio-filter). Results showed that these scrubbers reduced concentrations of PM10 by 61% to 93%, concentrations of PM2.5 by 47% to 90%, concentrations of airborne total bacteria by 46% to 85%, and concentrations of ammonia by 70% to 100%. Concentrations of CO2 were not affected. Most of the airborne bacteria emitted from the pig houses were larger than 3.3 m (73% to 95%). The multi-stage scrubbers removed 53% to 92% of them, compared with -42% to 20% removal effectiveness of the bacteria in the size range of 0.65 to 3.3 m. The triple-stage scrubber was the most efficient in removing dust and ammonia. Compared to single-stage scrubbers, all three multi-stage scrubbers performed more consistently in reduction of PM10, PM2.5, total bacteria, and ammonia emissions from livestock houses and removed these pollutants more efficiently. It should be noted that all measurements were performed in winter at low ventilation rates, thus at low loadings of the multi-stage scrubbers.

Laboratory air quality and room ventilation rates: An update

This report extends previously published empirical testing of laboratory air quality at varying room air change per hour (ACH) rates under controlled releases of organic solvents. Additional testing was performed after modifying the ventilation controls to enable reliable operations at room ventilation rates as low as 2 ACH, and with additional solvents for some test conditions. The accumulation, peak concentration, and clearance of airborne contaminants continued to be inversely proportional to the overall room ACH rate, demonstrating that low laboratory ventilation rates require exceptionally long times to clear.

Automobile proximity and indoor residential concentrations of BTEX and MTBE

Attached garages have been identified as important sources of indoor residential air pollution. However, the literature lacks information on (1) how the proximity of cars to the living area affects indoor concentrations of gasoline-related compounds, such as benzene; and (2) the origin of these pollutants, i.e., vapor or tailpipe emissions. We analyzed data from the Relationships of Indoor, Outdoor, and Personal Air (RIOPA) study to evaluate indoor ( C in) and outdoor ( C out) concentrations for 114 residences with cars either in an attached garage, a detached garage or carport, or without cars. Results indicate that single-family detached homes with cars in attached garages were affected the most by parked vehicles, followed by homes with vehicles in carports. Concentrations in homes with cars in detached garages were similar to those in residences without cars. Low ventilation rates exacerbated C in in homes with attached garages. In general, the contribution from gasoline-related sources to indoor benzene and MTBE concentrations appeared to have been dominated by car exhaust, or by a combination of tailpipe and gasoline vapor emissions. Residing in a home with an attached garage could lead to benzene exposures that are an order of magnitude higher than exposures from commuting in a car in heavy traffic, with a risk of 17 excess cancers in a population of a million. Strategies to lower exposure to gasoline-related contaminants in homes include improving construction practices to prevent the infiltration of pollutants into the living quarters or incorporating detached garages.

Hydrogen permeation from CGH2 vehicles in garages: CFD dispersion calculations and experimental validation

The time and space evolution of the distribution of hydrogen in confined settings was investigated computationally and experimentally for permeation from typical compressed gaseous hydrogen (CGH2) storage systems for buses or cars. The main goal was to examine whether hydrogen is distributed homogeneously within a garage-like facility or whether stratified conditions are developed, under certain conditions. The nominal hydrogen flow rate considered was 1.087 L/min in a bus facility with a volume of 681 m 3. The release was assumed to be directed upwards from a 0.15 m diameter hole located at the middle part of the bus cylinders casing. Ventilation rates up to 0.03 air changes per hour (ACH) were considered. Simulated time periods extended up to 20 days. The CFD simulations performed with the ADREA-HF code showed that fully homogeneous conditions exist for low ventilation rates, while stratified conditions prevail for higher ventilation rates. Regarding flow structure it was found that the vertical concentration profiles can be considered as the superposition of the concentration at the floor (driven by diffusion) plus a concentration difference between floor and ceiling (driven by buoyancy forces). In all cases considered this concentration difference was found to be less than 0.5%. The dispersion experiments were performed in a large scale garage-like enclosure of 40 m 3 using helium (GARAGE facility). Comparison between CFD simulations and experiments showed that the predicted concentrations were in good agreement with the experimental data. Finally, simulations were performed using two integral models: the fully homogeneous model and a two-layer model and the results were compared both against CFD and the experimental data.

Response of direct thoron progeny sensors (DTPS) to various aerosol concentrations and ventilation rates

Direct thoron/radon progeny sensors (DTPS/DRPS) are absorber mounted LR115 type track detectors for measuring the time-averaged progeny concentrations. Through a large number of experiments, the sensitivity factor of these sensors in natural indoor environment was found to be nearly constant at a value of 0.94 Tr cm−2 d−1/EETC (Bq m−3) for DTPS and 0.09 Tr cm−2 d−1/EERC (Bq m−3) for DRPS. The constancy of the sensitivity factor in the natural environments is attributed primarily to the presence of large aerosol concentrations and relatively low ventilation rates in time-averaged measurements. However, detailed model calculations suggest that in extreme scenario i.e. at high ventilation rate and low aerosol concentrations, the sensitivity factor can be quite different. Such situations are likely to occur in occupational plant areas. Therefore systematic chamber experiments were carried out to using DTPS, to estimate the variability of the sensitivity factor in these extreme conditions. In the first set, the sensitivity factor of DTPS was measured in 6 different aerosol concentrations at zero ventilation rates. The sensitivity factor showed a steep decrease as the aerosol concentration increased to about 8554 particle cm−3, after which it remained almost constant with increase in aerosol concentration. The second set of experiments was conducted at ∼5000 particles cm−3 at three different ventilation rates. The sensitivity factor was found to increase with increase in ventilation rate. The results are further discussed.

Specific Indoor Environmental Quality Parameters in College Computer Classrooms

The indoor environmental quality parameters, including temperature, relative humidity, air velocity, particulate matter concentration, illumination level, sound level, carbon dioxide concentration and ventilation rate in two computer classrooms and one general classroom were evaluated. Analytical results reveal average carbon dioxide concentration in the three classrooms during daytime classes was 785"1681 ppm. These values exceeded the exposure limits for indoor air quality suggested by the Environmental Protection Administration of the Republic of China, Taiwan (ROCEPA). The particulate matter concentration in the general classroom was 0.087 mg/m3, which exceeded the indoor air quality exposure limit for Type-1 venues recommended by the ROCEPA. Illumination level in the two computer classrooms was 386 and 176 Lux; these values are far lower than the illumination level for school classrooms suggested by Ministry of Education, Taiwan. Indoor sound levels in the three classrooms during non-class (51.4"61.9 dB(A) and class times (61.0"73.6 dBA exceeded the limit recommended by the Ministry of Education, Japan. The ventilation rates for the three classrooms were 0.41"0.65 h-1; such low ventilation rates were likely responsible for the very high indoor carbon dioxide concentrations in the three classrooms during class periods. These analytical results indicate schools should examine the efficacy of air-conditioning equipment in classrooms, particularly computer classrooms. Schools should also pay attention to ventilation rates and sound levels. Due to the poor ventilation rates in computer classrooms, this study suggests that problems arisen from the accumulation of specific toxicants dispersed by computer equipment, such as polybrominated diphenyl ethers, need further investigations.

Airflow characteristics at the surface of manure in a storage pit affected by ventilation rate, floor slat opening, and headspace height

To inform the modelling ammonia of emissions from manure surfaces and provide basic knowledge of the characteristics of airflow at the emission surface, laboratory experiments were performed using a scale model of a growing/finishing pig house with water in the pit and a clean slatted floor with various opening areas: 100%, 33.3% and 16.7%. At 100% opening area the headspace formed an integral part of the room airspace and this configuration was used as the reference treatment. The pig house model had two sidewall inlets and exhaust in the middle of the ceiling. The effects of room ventilation rate, slatted floor opening and headspace height in slurry pit on air velocity, turbulence intensity (Ti) and airflow pattern at manure surface were investigated. The mean air velocity at manure surface increased as ventilation rate increased with a constant inlet opening. Increasing the opening ratio of the slatted floor increased the air exchange rate in the slurry pit, resulting in a higher air velocity above manure surface. For 33.3% and 16.7% floor slat openings, the mean air velocity at the manure surface decreased as headspace height increased and this resulted in an increased mean Ti above the manure surface for 50 mm and 82 mm headspace heights, respectively. However, no significant differences were found in the mean Ti between four ventilation rates for 26 mm headspace height. Tests using smoke visualisation showed that the supply air travelled longer distances parallel to the manure surface at lower headspace heights than at higher heights before returning to the room space. Ammonia emission results from previous experiments can be explained by using the results of measurements of air velocity and Ti. A statistical model was developed to calculate the mean air velocity as a function of ventilation rate, opening ratio of the slatted floor and headspace height in the slurry pit (coefficient of determination R2 = 0.97). The mean air velocity was more sensitive to the ventilation rate than to the slatted floor opening ratio and the headspace height in the pit. Moreover, the mean air velocity was much more sensitive to variations in the ventilation rate at higher ventilation rates than at lower ventilation rates. However, the mean air velocity was much more sensitive at lower floor slat opening ratios and headspace heights than at higher ones.