Outdoor Air Supply Rate Research Articles

Evaluation of various activated carbons for air cleaning – Towards design of immune and sustainable buildings

There are increased demands for security, sustainability and indoor air quality in today's building design, construction, operation and maintenance. Installation of air cleaning systems can improve the indoor air quality by reducing the air pollution levels, and enhance the building security against sudden release of chemical and/or biological agents. At the same time, air cleaning techniques may reduce the building energy consumption by reducing the outdoor air supply rate, hence lowering the needs for conditioning of outdoor air. While the air filtration of particulate matter is well standardized, the standards against which the performance of air cleaning for gaseous contaminants is measured or classified are still under development. This study examined the performance of various granular activated carbons (GACs) for the removal of volatile organic compounds (VOCs) from mechanically ventilated buildings. Eight different GACs (three virgin and five impregnated) were tested against toluene using a dynamic test system. The virgin GACs showed better performance than impregnated ones, the percentage and the type of impregnation affected the removal efficiencies. Tests were also conducted with selected GACs against toluene, cyclohexane and ethyl acetate at relative humidity (RH) values of 30%, 50% and 70%. The effect of humidity was dependant on the VOC used. Both for toluene and cyclohexane, the removal efficiency decreased as RH increased. However, higher humidity showed a positive impact on the removal of ethyl acetate.

The Effects of Electrostatic Particle Filtration and Supply-Air Filter Condition in Classrooms on the Performance of Schoolwork by Children (RP-1257)

Two independent field intervention experiments involving a total of about 190 pupils were carried out in winter and early spring of 2005 in five pairs of mechanically ventilated classrooms that received 100% outdoor air. Each pair of classrooms was located in a different school. Electrostatic air cleaners were installed in classrooms and either operated or disabled to modify particle concentrations while the performance of schoolwork was measured. In one school, the used supply-air filters in a ventilation system without recirculation were also replaced with new ones to modify classroom air quality, while the filters in use in other schools were not changed. The conditions were established for one week at a time in a blind crossover design with repeated measures on ten-to-twelve-year-old children. Pupils performed six exercises exemplifying different aspects of schoolwork as part of normal lessons and indicated their environmental perceptions and the intensity of any symptoms. A sensory panel of adults judged the air quality in the classrooms soon after the pupils left. Operating the electrostatic air cleaners considerably reduced the concentration of particles in the classrooms. The effect was greater the lower the outdoor air supply rate. There were no consistent effects of this reduction on the performance of schoolwork, on the children's perception of the classroom environment, on symptom intensity, or on air quality as perceived by the sensory panel. This suggests there are no short-term (acute) effects of particle removal outside the pollen season. When new filters were installed, the effects were inconsistent, although this is believed to be due to sequential and unbalanced presentation of filter conditions and to the fact that the used filters retained very little dust.

Outdoor Air Supply Rate Affects Occupant's Perception and Intensity of SBS Symptoms

ISEE-135 Objective: The objectives of the study are to obtain the perceptual constructs of the subjective responses through the principal component analysis and to determine the effects of outdoor air supply rate on each perceptual construct or factor. Material and Methods: A blind intervention study was administered on 48 male and 48 female participants (age range: 20–23 years) using a counterbalanced order of exposure to different outdoor air supply rates, ie, 4.5, 9.0, and 18.0 liters per second per person (L/s/p) in a field environmental chamber operating with a total recirculation rate of approximately 6 air changes per hour and media filters. The subjects completed questionnaire on perception of air quality, thermal comfort, indoor parameters, and the intensity of SBS symptoms. Survey results were subjected to principal component analysis and several factors were extracted. The factor scores were subsequently analyzed for the main effects using the nonparametric Friedman test. Results: Ten factors were extracted with a cumulative explained variance of 72%. The most dominant factor (20%) was the neurobehavioral-related symptoms, which included symptoms like depression, difficulty to think, difficulty to concentrate, headache, and dizziness. Neurobehavioral-related symptoms diminished when outdoor air supply rate is increased from 4.5 to 9.0 L/s/p; however, the symptoms increased when outdoor air supply rate is increased from 9.0 to 18.0 L/s/p (P < 0.001). Another relevant factor was perceived odor and irritation, which incorporates the olfaction and chemesthesis responses. The perceived odor and irritation factor decreased with higher outdoor air supply rate (P < 0.0001). This is consistent with improved perception of air quality with elevated outdoor air supply rate (P < 0.02). Conclusions: Neurobehavioral-related symptoms have been identified to respond to exposures to outdoor air supply rate. Higher outdoor air supply rate (up to 9.0 L/s/p) is associated with better perception and lower intensity of symptoms.

The Effects of Moderately Raised Classroom Temperatures and Classroom Ventilation Rate on the Performance of Schoolwork by Children (RP-1257)

Two independent field intervention experiments were carried out in school classrooms in late summer (in 2004 and 2005). The air temperature was manipulated by either operating or idling split cooling units installed for the purpose. In one of these experiments, the outdoor air supply rate was also manipulated. The conditions were established for one week at a time in a blind crossover design with repeated measures on two classes of 10- to 12-year-old children. Six to eight exercises exemplifying different aspects of schoolwork (numerical and language-based) were performed as part of normal lessons. Pupils indicated their environmental perceptions and the intensity of any symptoms on visual analogue scales. Their thermal sensation changed from slightly too warm to neutral, and the performance of two numerical and two language-based tests was significantly improved when the temperature was reduced from 25°C to 20°C (77°F to 68°F). When the outdoor air supply rate was increased from 5.2 to 9.6 L/s (11.0 to 20.3 cfm) per person, their performance of four numerical exercises improved significantly, confirming the results of previously reported experiments in the same series. The above improvements were mainly in terms of the speed at which tasks were performed, with negligible effects on error rate. Most school classrooms worldwide experience raised air temperatures during increased thermal loads, e.g., in warm weather; these results show that providing some means of avoiding elevated temperatures would improve educational attainment.

The Effects of Outdoor Air Supply Rate and Supply Air Filter Condition in Classrooms on the Performance of Schoolwork by Children (RP-1257)

Two independent field intervention experiments were carried out in mechanically ventilated classrooms receiving 100% outdoor air. Outdoor air supply rate and filter condition were manipulated to modify indoor air quality, and the performance of schoolwork was measured.The conditions were established for one week at a time in a blind crossover design with repeated measures on 10- to 12-year-old children in two classes. Seven exercises exemplifying different aspects of schoolwork (numerical or language-based) were performed as part of normal lessons by pupils who also marked visual analogue scales to indicate their environmental perceptions and the intensity of any symptoms. The children indicated that the air was fresher but otherwise perceived little difference when the outdoor air supply rate increased from 3.0 to 8.5 L/s (6.4–18 cfm) per person, while the speed at which they performed two numerical and two language-based tasks improved significantly. A significant effect of ventilation rate was observed in 70% of all the statistical tests for an effect on work rate, but there were no significant effects on errors. The effects were probably due to improved air quality in the classrooms as judged by a sensory panel of adults blind to conditions, as perceived by children, and as indicated by the reduction in the average CO2 concentration from 1300 to 900 ppm, taking this as a marker of reduced bioeffluent concentration. It was not possible to test the effect of replacing a soiled filter with a new one because very little dust had been retained by the “used” filter and because of an incompletely balanced design. The unbalanced design also made it impossible to test for an interaction between filter condition and ventilation rate. These results indicate the importance of improving indoor air quality and ventilation in classrooms.

Pollutants emission from building materials and their influence on indoor air quality and people performance in offices

Abstract New technologies and materials have introduced a large quantity of new pollutants emitted to the indoor air. Energy conservation for economical reasons, resulting in low outdoor air supply rates, can become the reason of a poor indoor air quality. The cost of the deteriorated indoor climate, resulting in reduced comfort and losses in productivity, for the society is higher than the costs for the heating energy or ventilation systems in the same building. An experiment was conducted to determine how poor indoor air quality could cause involuntary changes in performance and occurring sick building syndrome symptoms. Twenty‐four female subjects were exposed to three environmental conditions, while performing normal office tasks in a low‐polluting room. Sick building syndrome symptoms, the perceived air quality and performance data were obtained. The acceptability of air quality was significantly better and the odour intensity was much lower under the conditions of high ventilation. The performance o...

The performance and subjective responses of call-center operators with new and used supply air filters at two outdoor air supply rates

A 2 x 2 replicated field intervention experiment was conducted in a call-center providing a telephone directory service: outdoor air supply rate was adjusted to be 8% or 80% of the total airflow of 430 l/s (3.5 /h) and the supply air filters were either new or had been in place for 6 months. One of these independent variables was changed each week for 8 weeks. The interventions did not affect room temperature, relative humidity or noise level. The 26 operators were blind to conditions and each week returned questionnaires recording their environmental perceptions and Sick Building Syndrome (SBS) symptoms. Their performance was continuously monitored by recording the average talk-time every 30 min. Replacing a used filter with a clean filter reduced talk-time by about 10% at the high ventilation rate but had no significant effect at the low rate. Increasing the outdoor air supply rate reduced talk-time by 6% with a new filter in place but increased talk-time by 8% with a used filter in place. The interventions also had significant effects on some SBS symptoms and environmental perceptions. The present results indicate that increasing outdoor air supply rate and replacing filters can have positive effects on health, comfort and performance. Supply air filters should be changed frequently not just because their airflow resistance increases progressively but because they degrade air quality with negative consequences for health, comfort and the performance of office work, all of which are factors that affect office productivity (profitability). Increasing outdoor air supply rates may only be beneficial when new filters are installed. Unwanted negative effects may be produced when used filters are in place. Filter condition (used or new) should always be recorded to make it possible to draw sound conclusions in studies of the effects of outdoor air supply rates on building occupants.

The effects of indoor air quality on performance and productivity.

The main justification for ventilation has historically been to create a healthy indoor environment. Ventilation removes air pollutants originating inside the building, including bio-effluents. The outdoor air supply rate that has been found by experience to provide subjectively acceptable indoor air quality and to prevent the accumulation of moisture in the building is generally sufficient to maintain the concentration of pollutants at healthily low levels. Until 5 years ago this would have been the justification for current ventilation practices, but in 1999 the first of a series of experiments was published, revealing new mechanisms by which raised levels of indoor air pollution may reduce productivity, either in addition to or instead of having negative effects on comfort and health. It was shown in realistic experimental exposures lasting up to 5 h that the performance of simulated office work could be significantly increased by removing common indoor sources of air pollution, such as floor-coverings, used supply air filters and personal computers, or by keeping them in place and increasing the rate at which clean outdoor air was supplied from 3 to 10 to 30 l s(-1) per person. These short-term effects were demonstrated repeatedly even at pollutant levels that had no measurable effects on the perception of air quality by the occupants themselves, although there were effects on subclinical SBS symptoms such as headache. Temperature and noise distraction have since been studied in directly comparable exposures. The prediction arising from these experiments, that the performance of real office work over time would be significantly and substantially affected by the changes in indoor environmental quality that take place in the course of normal building operation, have recently been validated in 8-week field intervention experiments carried out in call-centers in northern Europe and the Tropics. These findings have far-reaching implications for the efficient use of energy in buildings. It has now been shown beyond reasonable doubt that poor indoor air quality in buildings can decrease productivity in addition to causing visitors to express dissatisfaction. The size of the effect on most aspects of office work performance appears to be as high as 6-9%, the higher value being obtained in field validation studies. It is usually more energy-efficient to eliminate sources of pollution than to increase outdoor air supply rates. The experiments summarized in this article have documented and quantified relationships that can be used in making cost-benefit analyses of either solution for a given building. The high cost of labor per unit floor area ensures that payback times will usually be as low as 2 years.

Detection of Airborne Rhinovirus and Its Relation to Outdoor Air Supply in Office Environments

Rhinoviruses are major causes of morbidity in patients with respiratory diseases; however, their modes of transmission are controversial. We investigated detection of airborne rhinovirus in office environments by polymerase chain reaction technology and related detection to outdoor air supply rates. We sampled air from 9 A.M. to 5 P.M. each workday, with each sample run for 1 work week. We directly extracted RNA from the filters for nested reverse transcriptase-polymerase chain reaction analysis of rhinovirus. Nasal lavage samples from building occupants with upper respiratory infections were also collected. Indoor carbon dioxide (CO2 concentrations were recorded every 10 minutes as a surrogate for outdoor air supply. To increase the range of CO2 concentrations, we adjusted the outdoor air supply rates every 3 months. Generalized additive models demonstrated an association between the probability of detecting airborne rhinovirus and a weekly average CO2 concentration greater than approximately 100 ppm, after controlling for covariates. In addition, one rhinovirus from a nasal lavage contained an identical nucleic acid sequence similar to that in the building air collected during the same week. These results suggest that occupants in buildings with low outdoor air supply may have an increased risk of exposure to infectious droplet nuclei emanating from a fellow building occupant.

Risk of indoor airborne infection transmission estimated from carbon dioxide concentration.

The Wells-Riley equation, which is used to model the risk of indoor airborne transmission of infectious diseases such as tuberculosis, is sometimes problematic because it assumes steady-state conditions and requires measurement of outdoor air supply rates, which are frequently difficult to measure and often vary with time. We derive an alternative equation that avoids these problems by determining the fraction of inhaled air that has been exhaled previously by someone in the building (rebreathed fraction) using CO2 concentration as a marker for exhaled-breath exposure. We also derive a non-steady-state version of the Wells-Riley equation which is especially useful in poorly ventilated environments when outdoor air supply rates can be assumed constant. Finally, we derive the relationship between the average number of secondary cases infected by each primary case in a building and exposure to exhaled breath and demonstrate that there is likely to be an achievable critical rebreathed fraction of indoor air below which airborne propagation of common respiratory infections and influenza will not occur.

Air quality in a simulated office environment as a result of reducing pollution sources and increasing ventilation

Air quality was studied in an office space classified as low-polluting and ventilated with outdoor air at a rate of 1 h −1. The pollution load in the space was changed by introducing or removing common building-related indoor pollution sources (linoleum, sealant and wooden shelves with books and paper documents) so that the space could no longer be classified as low-polluting. The outdoor air supply rate in the office was altered from 1 to 3 h −1 (0.83 and 2.5 l/s per m 2 floor, respectively) when sources were present and absent. Air temperature of 23 °C, relative humidity of 50% and noise level of 35 dB(A) remained unchanged. Under each of the four conditions of air quality in the office, concentrations of volatile organic compounds (VOCs) were measured and perceived air quality was assessed by a panel of 30 female subjects. Removing the sources reduced the chemical and sensory pollution load in the office, and increasing the outdoor air supply rate decreased concentrations of many VOCs, including those emitted by building materials and furnishing, and human bioeffluents. The perceived air quality in the office was consequently improved. The improvement in air quality obtained by removing the sources was similar to that obtained by increasing the outdoor air supply rate. The study, thus, confirmed that the systematic use of low-polluting building materials will lead to improved air quality.

Risk of sick leave associated with outdoor air supply rate, humidification, and occupant complaints.

We analyzed 1994 sick leave for 3,720 hourly employees of a large Massachusetts manufacturer, in 40 buildings with 115 independently ventilated work areas. Corporate records identified building characteristics and IEQ complaints. We rated ventilation as moderate (approximately 25 cfm/person, 12 ls-1) or high (approximately 50 cfm/person, 24 ls-1) outdoor air supply based on knowledge of ventilation systems and CO2 measurements on a subset of work areas, and used Poisson regression to analyze sick leave controlled for age, gender, seniority, hours of non-illness absence, shift, ethnicity, crowding, and type of job (office, technical, or manufacturing worker). We found consistent associations of increased sick leave with lower levels of outdoor air supply and IEQ complaints. Among office workers, the relative risk for short-term sick leave was 1.53 (95% confidence 1.22-1.92) with lower ventilation, and 1.52 (1.18-1.97) in areas with IEQ complaints. The effect of ventilation was independent of IEQ complaints and among those exposed to lower outdoor air supply rates the attributable risk of short-term sick leave was 35%. The cost of sick leave attributable to ventilation at current recommended rates was estimated as $480 per employee per year at Polaroid. These findings suggest that net savings of $400 per employee per year may be obtained with increased ventilation. Thus, currently recommended levels of outdoor air supply may be associated with significant morbidity, and lost productivity on a national scale could be as much as $22.8 billion per year. Additional studies of IEQ impacts on productivity and sick leave, and the mechanisms underlying the apparent association are needed.

The effects of outdoor air supply rate in an office on perceived air quality, sick building syndrome (SBS) symptoms and productivity.

Perceived air quality, Sick Building Syndrome (SBS) symptoms and productivity were studied in a normally furnished office space (108 m3) ventilated with an outdoor airflow of 3, 10 or 30 L/s per person, corresponding to an air change rate of 0.6, 2 or 6 h-1. The temperature of 22 degrees C, the relative humidity of 40% and all other environmental parameters remained unchanged. Five groups of six female subjects were each exposed to the three ventilation rates, one group and one ventilation rate at a time. Each exposure lasted 4.6 h and took place in the afternoon. Subjects were unaware of the intervention and remained thermally neutral by adjusting their clothing. They assessed perceived air quality and SBS symptoms at intervals, and performed simulated normal office work. Increasing ventilation decreased the percentage of subjects dissatisfied with the air quality (P < 0.002) and the intensity of odour (P < 0.02), and increased the perceived freshness of air (P < 0.05). It also decreased the sensation of dryness of mouth and throat (P < 0.0006), eased difficulty in thinking clearly (P < 0.001) and made subjects feel generally better (P < 0.0001). The performance of four simulated office tasks improved monotonically with increasing ventilation rates, and the effect reached formal significance in the case of text-typing (P < 0.03). For each two-fold increase in ventilation rate, performance improved on average by 1.7%. This study shows the benefits for health, comfort and productivity of ventilation at rates well above the minimum levels prescribed in existing standards and guidelines. It confirms the results of a previous study in the same office when the indoor air quality was improved by decreasing the pollution load while the ventilation remained unchanged.

Carbon Dioxide Concentrations and Minimum Air Change Rates in a High-Rise Office Building

The carbon dioxide concentration patterns in a large, high-rise, office building in Ottawa were examined experimentally using an automated data acquisition system. Daily CO2 concentration profiles throughout the building and air change rates, using SF6 as a tracer gas, were measured at minimum outdoor air supply rates during much of a heating season. Of particular interest was how well mixed the indoor air was and how well the CO2 concentrations that were measured in the central ventilation system's return air plenum represented the average CO2 concentration behaviour in the building as a whole. CO 2 concen tration profiles were also measured on individual floor spaces in the building to determine the range of variability in the concentration behaviour. The mea surement results are presented and discussed in the context of demand-con trolled ventilation.

Field Evaluation of CO2 Detector Tubes for Measuring Outdoor Air Supply Rate in the Indoor Environment

Indoor carbon dioxide (CO2) concentration can be used to estimate the degree of air recirculation and outdoor air supply rate. Three types of CO2 detector tubes were evaluated by using Fourier Transform Infra-Red (FTIR) Spectroscopy as a reference method. Two types of detector tubes (Draeger CH 30801 and Kitagawa 126 B) showed a good correlation with the reference method (r = 0.98), the 95% confidence interval of the slope being 0.89-1.06 and 0.80-0.95, respectively in linear regression analysis. The third type (Gastec 2LL.) showed lower correlation (r = 0.91) and a wider 95% confidence interval (0.52-0.80) of the slope. A t CO2 concentrations in the range 800-1000 5 l/l(ppm), control values suggested for the indoor environment, the Draeger and the Gastec tubes underestimated the CO2 concentration, while the Kitagawa tube showed a correct value. The difference in reading between observers was similar for all three brands of detector tubes (5-7%), expressed as relative standard error No significant influence of the air humidity or temperature on the readings could be demonstrated. It is concluded that some brands of CO2 detector tubes can be used to measure indoor carbon dioxide concentration with sufficient precision and accuracy. Since the relative error is relatively large at lower CO2 concentrations, the use of such tubes for the determination of air recirculation in ventilation systems should be avoided. As a crude estimate of the outdoor air supply rate, however, CO2 detector tubes may be used. In order to minimize the error in reading, the type of detector tube and the need for recalibration should be considered. When using CO2 measurements as an estimate of outdoor air supply rate, the influence of age and work-load on the individual's emission of CO2 and the time needed to reach equilibrium, should also be taken into consideration.