Outdoor Air Supply Rate Research Articles

Unlocking ventilation flexibility of large airport terminals through an optimal CO2-based demand-controlled ventilation strategy

Large airport terminals consume significant energy due to their extensive ventilation demands. Optimizing the operation of ventilation systems is a crucial aspect of achieving greater energy flexibility and efficiency. In this study, we proposed an optimal CO2-based demand-controlled ventilation (DCV) strategy that utilizes the large indoor space of airport terminals to shift ventilation loads, reduce operating cost, and enable demand response (DR) programs. The effect of air infiltration on ventilation demand is considered in the DCV strategy through on-site CO2 measurement. A passenger dwell model is integrated to estimate the occupancy of airport terminal based on flight schedules for dynamic ventilation control. Considering the DR signal and time-of-use tariff, an advanced evolutionary algorithm is employed to locate optimal ventilation solutions that deliver better economic performance and energy flexibility while meeting indoor air quality constraints. Using an airport terminal in Beijing, China, as a testbed, the superior performance of the proposed DCV strategy was demonstrated against a baseline strategy with a fixed outdoor air supply rate under three scenarios. Simulation results showed that the proposed DCV strategy can reduce peak energy consumption by up to 60.9% and operating costs by up to 48.6% in different scenarios. Moreover, the DCV strategy can provide a flexible trade-off between the overall energy efficiency and DR capability in the adjustable DR scenario. This study revealed great opportunities for improving the flexibility of ventilation in large-space buildings and provided an instructive case study.

CO2 concentration as an indicator of indoor ventilation performance to control airborne transmission of SARS-CoV-2

BackgroundThe Wells-Riley equation has been extensively used to quantify the infection risk of airborne transmission indoors. This equation is difficult to apply to actual conditions because it requires measurement of the outdoor air supply rate, which vary with time and are difficult to quantify. The method of determining the fraction of inhaled air that has been exhaled previously by someone in a building using a CO2 concentration measurement can solve the limitations of the existing method. Using this method, the indoor CO2 concentration threshold can be determined to keep the risk of infection below certain conditions. MethodsBased on the calculation of the rebreathed fraction, an appropriate mean indoor CO2 concentration and required air exchange rate to control SARS-CoV-2 airborne transmission was calculated. The number of indoor occupants, ventilation rate, and the deposition and inactivation rates of the virus-laden aerosols were considered. The application of the proposed indoor CO2 concentration-based infection rate control was investigated through case studies in school classrooms and restaurants. ResultsIn a typical school classroom environment with 20–25 occupants and an exposure time of 6–8 h, the average indoor CO2 concentration should be kept below 700 ppm to control the risk of airborne infection indoors. The ASHRAE recommended ventilation rate is sufficient when wearing a mask in classrooms. For a typical restaurant with 50–100 occupants and an exposure time of 2–3 h, the average indoor CO2 concentration should be kept below about 900 ppm. Residence time in the restaurant had a significant effect on the acceptable CO2 concentration. ConclusionGiven the conditions of the occupancy environment, it is possible to determine an indoor CO2 concentration threshold, and keeping the CO2 concentration lower than a certain threshold could help reduce the risk of COVID-19 infection.

Association of indoor temperature and air quality in classrooms based on field and intervention measurements

To investigate the variation of classroom environment during typical lecture hours, repeated field measurements and intervention experiments for indoor temperature were carried out in a typical class (95 min in duration, 0.32–0.39 person/m2 of occupants density) in a spring semester of a university in Beijing. Environmental data were recorded every 5 min, including indoor temperature, relative humidity and carbon dioxide (CO2) concentration. Additionally, volatile organic compounds (VOCs) were sampled and indoor air quality (IAQ) were evaluated repeatedly. The results of field measurements showed the average air temperature in the classroom ranged from 21.2 ± 0.8 °C to 26.8 ± 0.7 °C, relative humidity ranged from 23.1 ± 1.8% to 57.5 ± 0.2%, and the average concentrations of CO2 and total volatile organic compounds (TVOC) were 1,291–1,833 ppmv and 159-1,178 ppbm respectively. The subjective evaluations collected during intervention experiments showed that perceived odor intensity by visitors upon entering the room increased significantly, meanwhile the satisfaction and acceptability of air quality reduced considerably at the indoor temperature of 27 °C than that at 24 °C. Present results suggest when the indoor temperature rises, it is necessary to increase the outdoor air supply rate to ensure air freshness in classrooms. Subsequently, the calculated CO2 emission rate by students increased by 0.54 L/h per person for every 1 °C rise in indoor temperature. Corresponding to the control target of indoor CO2 concentration of 1,000 ppmv, the outdoor air ventilation rate required to eliminate occupant-generated pollution needs to be increased by 0.25 L/s per person.

The effects of warmth and CO2 concentration, with and without bioeffluents, on the emission of CO2 by occupants and physiological responses.

The emission rate of carbon dioxide (CO2 ) depends on many factors but mainly on the activity level (metabolic rate) of occupants. In this study, we examined two other factors that may influence the CO2 emission rate, namely the background CO2 concentration and the indoor temperature. Six male volunteers sat one by one in a 1.7m3 chamber for 2.5h and performed light office-type work under five different conditions with two temperature levels (23 vs. 28°C) and three background concentrations of CO2 (800 vs. 1400 vs. 3000ppm). Background CO2 levels were increased either by dosing CO2 from a cylinder or by reducing the outdoor air supply rate. Physiological responses to warmth, added CO2 , and bioeffluents were monitored. The rate of CO2 emission was estimated using a mass-balance equation. The results indicate a higher CO2 emission rate at the higher temperature, at which the subjects were warm, and a lower emission rate in all conditions in which the background CO2 concentration increased. Physiological measurements partially explained the present results but more measurements are needed.

Cabin air quality on non-smoking commercial flights: A review of published data on airborne pollutants.

We reviewed 47 documents published 1967-2019 that reported measurements of volatile organic compounds (VOCs) on commercial aircraft. We compared the measurements with the air quality standards and guidelines for aircraft cabins and in some cases buildings. Average levels of VOCs for which limits exist were lower than the permissible levels except for benzene with average concentration at 5.9±5.5μg/m3 . Toluene, benzene, ethylbenzene, formaldehyde, acetaldehyde, limonene, nonanal, hexanal, decanal, octanal, acetic acid, acetone, ethanol, butanal, acrolein, isoprene and menthol were the most frequently measured compounds. The concentrations of semi-volatile organic compounds (SVOCs) and other contaminants did not exceed standards and guidelines in buildings except for the average NO2 concentration at 12ppb. Although the focus was on VOCs, we also retrieved the data on other parameters characterizing cabin environment. Ozone concentration averaged 38ppb below the upper limit recommended for aircraft. The outdoor air supply rate ranged from 1.7 to 39.5 L/s per person and averaged 6.0±0.8L/s/p (median 5.8L/s/p), higher than the minimum level recommended for commercial aircraft. Carbon dioxide concentration averaged 1315±232ppm, lower than what is permitted in aircraft and close to what is permitted in buildings. Measured temperatures averaged 23.5±0.8°C and were generally within the ranges recommended for avoiding thermal discomfort. Relative humidity averaged 16%±5%, lower than what is recommended in buildings.

Development of a CFD model for simulating vehicle cabin indoor air quality

As the level of CO2 within the vehicle cabin increases, the risk of accidents as a result of driver drowsiness and a slowing of the reactions also increases. Accordingly, a CFD simulation model was developed in this study to explore the effects of outdoor air ventilation rate on vehicle cabin indoor air quality and the amount of outdoor air required for each person in a vehicle. The results show that using the outdoor air supply rate recommendations of ASHRAE Standard 62.1 (i.e. 2.5 l/s per person) the mean CO2 concentrations in the cabin are around 2850 ppm. The results also show that using the outdoor air supply rate recommendations of 4.0 l/s per person for improved human wellbeing, the corresponding mean CO2 concentrations in the cabin are around 1810 ppm. Moreover, the present study found that an outdoor fresh air flow rate of 9.2 l/s per passenger was sufficient to reduce the carbon dioxide concentration within the cabin to a safe value of 1000 ppm. Furthermore, an outdoor fresh air flow rate of 3.6 l/s per passenger resulted in a carbon dioxide concentration of around 2000 ppm.

An experimental evaluation on air purification performance of Clean-Air Heat Pump (CAHP) air cleaner

The escalation of energy consumption in buildings and heightened concerns about acceptable indoor air quality stimulate interest in the usage of air cleaner as an adjunct for indoor environmental conditioning. A regenerative desiccant wheel integrated into a ventilation system termed Clean-Air Heat Pump (CAHP) can improve the air quality during the process of dehumidification without using additional energy. An experimental study in a field lab was performed to investigate the air cleaning performance of CAHP. Photoacoustic gas analyzer-INNOVA was used to characterize chemical removal of indoor air pollutants by the CAHP. The results revealed that all the detected VOCs were removed effectively by the CAHP with an average single pass efficiency of 82.7% when the regeneration temperature for desiccant wheel was 60 °C. The mass balance between adsorption and desorption of the desiccant wheel was 96.8%, which indicated that the most of gaseous pollutants were not accumulated in the CAHP. The regeneration temperature for the wheel could affect the air purification performance of CAHP. At 70 °C of regeneration temperature, the air-cleaning efficiency reached 96.7%. Up to 70% of the outdoor air ventilation can be saved with the operation of CAHP. The clean air deliver rate (CADR) was over threefold of the outdoor air supply rate when CAHP was in operation.

Experimental analysis of indoor air quality improvement achieved by using a Clean-Air Heat Pump (CAHP) air-cleaner in a ventilation system

This study investigated the air purification effect of a Clean-Air Heat Pump (CAHP) air-cleaner which combined a silica gel rotor with a heat pump to achieve air cleaning, heating and ventilation in buildings. The experiments were conducted in a field laboratory and compared a low outdoor air supply rate with CAHP air purification of recirculated air with three different outdoor air supply rates without recirculation or air cleaning. Sensory assessments of perceived air quality and chemical measurements of TVOC concentration were used to evaluate the air-cleaning performance of the CAHP. The results of the experiment showed that the operation of the CAHP significantly improved the perceived air quality in a room polluted by both human bio-effluents and building materials. At the outdoor airflow rate of 2 L/s per person, the indoor air quality with CAHP was equivalent to what was achieved in the same room with 10 L/s per person of outdoor air ventilation without air cleaning. The percentage dissatisfied was as low as 5.2% with the CAHP in operation, based on adapted perception assessment. The outdoor air supply rate can be reduced by 76% by using CAHP, as the Clean Air Delivery Rate (CADR) was over three times the outdoor air supply rate when the CAHP was in operation. The chemical measurements indicated a single-pass efficiency of over 92% for the removal of indoor air pollutants when the regeneration temperature was 60 °C. No VOC accumulation on the desiccant wheel was observed.

Influencing factors and energy-saving control strategies for indoor fine particles in commercial office buildings in six Chinese cities

Experimental studies on indoor fine particles were performed in actual commercial offices in six Chinese cities: Beijing, Shanghai, Guangzhou, Tianjin, Shijiazhuang and Chengdu. Particle introduced through outdoor air supply (OA) system was the most significant contributor to indoor PM2.5. In most cases, the OA systems of the six office buildings could not provide enough protection for staff. The first reason was the insufficient filtration efficiency of the OA system for PM2.5 due to filter bypass and design shortage. The tested filtration efficiency of the OA system for PM2.5 ranged from 17.0±0.9% to 55.7±2.8%. The gaps between the tested and rated filtration efficiencies ranged from 4.4% to 26.3%. The gaps between the rated and required filtration efficiencies ranged from 7.4% to 64.5%. The second reason was the superfluous outdoor air supply rate. The outdoor air supply rates per staff could reach 7.5L/s to 12.8L/s with the operating OA systems, much higher than the ASHRAE guideline. Five control strategies (including higher level filters, minimum outdoor air supply rates, portable air cleaners and combinations of these options) were proposed for HVAC system to reduce indoor PM2.5 concentration level to 35μg/m3. The reduced indoor PM2.5 exposure per power under strategy 2 (minimum outdoor air supply rate+higher level filters) was the highest in all cases. The total energy consumption of HVAC systems under strategy 2 was only 42%-71% of the current energy consumption.

Responses to Human Bioeffluents at Levels Recommended by Ventilation Standards

The purpose of this study was to examine whether exposure to human bioeffluents, at the levels recommended by the current ventilation standards, would cause any effects on humans. Ten subjects were exposed in a low-emission stainless-steel climate chamber for 4.25 hours. The outdoor air supply rate was set to 33 or 4 l/s per person, creating two levels of bioeffluents with carbon dioxide (CO2) at 500 or 1600 ppm. Subjective ratings were collected, cognitive performance was examined and physiological responses were monitored. The results show that exposures to human bioeffluents at ventilation rate of 4 l/s per person caused sensory discomfort of visitors, reduced pNN50 (a domain of ECG measurement), but did not produce negative effects on cognitive performance or health symptoms.

Effects of exposure to carbon dioxide and bioeffluents on perceived air quality, self-assessed acute health symptoms, and cognitive performance.

The purpose of this study was to examine the effects on humans of exposure to carbon dioxide (CO2 ) and bioeffluents. In three of the five exposures, the outdoor air supply rate was high enough to remove bioeffluents, resulting in a CO2 level of 500ppm. Chemically pure CO2 was added to this reference condition to create exposure conditions with CO2 at 1000 or 3000ppm. In two further conditions, the outdoor air supply rate was restricted so that the bioeffluent CO2 reached 1000 or 3000ppm. The same 25 subjects were exposed for 255min to each condition. Subjective ratings, physiological responses, and cognitive performance were measured. No statistically significant effects on perceived air quality, acute health symptoms, or cognitive performance were seen during exposures when CO2 was added. Exposures to bioeffluents with CO2 at 3000ppm reduced perceived air quality; increased the intensity of reported headache, fatigue, sleepiness, and difficulty in thinking clearly; and reduced speed of addition, the response time in a redirection task, and the number of correct links made in the cue-utilization test. This suggests that moderate concentrations of bioeffluents, but not pure CO2 , will result in deleterious effects on occupants during typical indoor exposures.

Human responses to carbon dioxide, a follow-up study at recommended exposure limits in non-industrial environments

To extend the results of a previous study on the effects of carbon dioxide (CO2) and bioeffluents on humans, the new study reported in this paper was carried out. The purpose of this study was to examine, whether exposure to CO2 at 5000 ppm would cause sensory discomfort, evoke acute health symptoms, reduce the performance of cognitive tasks, or result in changes in physiological responses. The outdoor air supply rate was set high enough in a low-emission stainless-steel climate chamber to create a reference condition with CO2 at 500 ppm when subjects were present, and chemically pure CO2 was added to the supply air to create an exposure condition with CO2 at 5000 ppm (the measured exposure level was ca. 4900 ppm). Ten healthy college-age students were exposed twice to each of the two conditions for 2.5 h in a design balanced for order of presentation. The raised CO2 concentration had no effect on perceived air quality or physiological responses except for end-tidal CO2 (ETCO2), which increased more (to 5.3 kPa) than it was in the reference condition (5.1 kPa). Other results indicate additionally that a 2.5-h exposure to CO2 up to 5000 ppm did not increase intensity of health symptoms reported by healthy young individuals and their performance of simple or moderately difficult cognitive tests and some tasks resembling office work. These results accord well with the current occupational exposure limit recommendation for CO2 and with many other reports published in the literature.

The effect of increased classroom ventilation rate indicated by reduced CO2 concentration on the performance of schoolwork by children.

The article reports on an experiment which investigated the effect of increased classroom ventilation rate on the performance of children aged 10-12years. The experiment was executed at two different schools (two classrooms at each school) as a double-blind 2×2 crossover intervention where four different performance tests were used as surrogates for short-term concentration and logical thinking. Only complete pairs of test responses were included in the within-subject comparisons of performance, and data were not corrected for learning and fatigue effects. Analysis of the total sample suggested the number of correct answers was improved significantly in four of four performance test, addition (6.3%), number comparison (4.8%), grammatical reasoning (3.2%), and reading and comprehension (7.4%), when the outdoor air supply rate was increased from an average of 1.7 (1.4-2.0) to 6.6l/s per person. The increased outdoor air supply rate did not have any significant effect on the number of errors in any of the performance tests. Results from questionnaires regarding pupil perception of the indoor environment, reported Sick Building Syndrome symptoms, and motivation suggested that the study classroom air was perceived more still and pupil were experiencing less pain in the eyes in the recirculation condition compared to the fresh air condition.

Providing better thermal and air quality conditions in school classrooms would be cost-effective

This paper is an overall summary of research by the authors on how classroom conditions affect the performance of schoolwork by children, motivated by the fact that the thermal and air quality conditions in school classrooms are now almost universally worse than the relevant standards and building codes stipulate that they should be. This is sometimes because financial resources for the maintenance and upgrade of school buildings are inadequate, but it is also because schools are increasingly allowing classroom temperatures to drift above the recommended range of 20–22 °C in warm weather and allowing outdoor air supply rates to remain so low that carbon dioxide (CO2) levels during school hours exceed 1000 ppm for long periods, in order to conserve energy. The research that is summarized in this paper shows that the indoor environmental consequences of either of these investment-free but ill-advised energy conservation measures can reduce children's performance of schoolwork by as much as 30%, so a more sophisticated approach to maintaining good classroom indoor environmental quality (IEQ) is required.

CO2–Based Demand–Controlled Ventilation and Its Implications for Interior Design

CO2–based demand–controlled ventilation (DCV) is a ventilation method that resets outdoor air supply rates using CO2 as an operating parameter ( ASHRAE, 2007a ). Even though CO2 itself is not harmful, high levels of CO2 concentration in indoor environments displace oxygen in the air and can cause a deficiency of oxygen for breathing. The most important aspect of CO2 in DCV is that it is a good indicator of occupancy in indoor spaces. Therefore, CO2 is an effective parameter for controlling ventilation based on occupancy level. CO2–based DCV has been increasingly used in recent years to optimize the energy consumption in ventilation systems as technological advances make its implementation more feasible and interest in environmentally responsible building design grows. This study aims to provide information about CO2–based DCV and suggest implications for interior design practitioners and educators. To achieve this purpose, this study reviewed previous studies and examined the current practices in CO2–based DCV in order to suggest guidelines for CO2–based DCV implementation for interior designers. The guidelines focused on proper CO2 sensor location design, taking into consideration the activities and other equipment in the room. In addition, a study of CO2–based DCV in the lecture halls of a university campus was conducted. Physical measurements were done in the lecture halls, and trends data were collected from the university's facility management department to compare the measurements. A perceived indoor environmental quality survey was also done to explore the occupants’ responses about CO2–based DCV.

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.

Optimal design for a dual-airflow window for different climate regions in China

The dual-airflow window could be used to conserve energy and improve indoor air quality in buildings because it works like a heat exchanger and can introduce outdoor air into buildings. In order to optimize the window design, this investigation used the orthogonal method to evaluate the importance of these 13 design parameters of the dual-airflow window in energy conservation: outdoor air supply rate, window cavity width, window width, window height, thermal conductivity, glazing thickness, solar heat gain coefficient, emissivity, thermal conductivity of window frame, window frame width, window orientation, shading coefficient, and window blinds position. The outdoor air supply rate, window height, solar heat gain coefficient, and window orientation were found to be the most important. The first four parameters were further studied by using the listing method to identify their optimal values for the window design. With the optimal design, the dual-airflow window could save 25% energy in a warm climate region such as Guangzhou and 34% in a cold climate region such as Harbin. The dual-airflow window is recommended for use in colder climate regions.

Can a photocatalytic air purifier be used to improve the perceived air quality indoors?

The effect of a photocatalytic air purifier on perceived air quality (PAQ) was examined in rooms polluted by typical sources of indoor pollution. The rooms were ventilated at three different outdoor air supply rates. The air quality was assessed by a sensory panel when the purifier was in operation as well as when it was off. Operation of the purifier significantly improved PAQ in the rooms polluted by building materials (used carpet, old linoleum, and old chipboard), and a used ventilation filter as well as a mixture of building materials, used ventilation filter and cathode-ray tube computer monitors. The effect corresponded to approximately doubling the outdoor air supply rate. Operation of the purifier significantly worsened the PAQ in rooms with human bioeffluents, probably due to incomplete oxidation of alcohols which are one of the main pollutants emitted by humans. Present results show that the photocatalytic air purifier can supplement ventilation when the indoor air is polluted by building-related sources, but should not be used in spaces where human bioeffluents constitute the main source of pollution. The present results suggest that a photocatalytic air purifier can supplement ventilation when the indoor air is polluted mainly by building-related sources, for example in unoccupied buildings outside working hours when ventilation is considerably reduced or turned off and pollutants build up and adsorb on indoor surfaces. The results also suggest that use of a photocatalytic air purifier should be avoided when humans are present and constitute main source of pollution.

THERMAL/AIR ENVIRONMENT EFFECTS ON ACADEMIC PERFORMANCE OF LATE-TEEN STUDENTS

This study investigated the IEQ effects on learning performance by means of field survey, and the target group was late-teen students. The field experiments were carried out at two technical colleges in Japan. At each college, a ordinary use classroom was adopted for the experiment. In order to evaluate the effects of indoor temperature and outdoor air supply rate, air conditioning units and ventilation fans were controlled at 3 levels (22, 25, 28 °C; 5, 10, 20 m3/s/person) and 5 combinations of them were adopted as the experimental cases. In every case, the learning performance was evaluated with a 30-minute examination after a 180-minute video image lecture. The results showed that the examination score decreased in the case of low temperature or low outdoor air supply rate. However, the examination score was not changed in the case of high temperature, which might be caused by seasonal effect. According to comparisons with previous studies, the learning performance of late-teen people was considered to be less affected by indoor environment than that of older people, if their background knowledge of the learning subjects was equivalent to the older people.

The most cited articles inIndoor Air, through 18 years

Indoor Air started in the year 1991; we will soon turn 20 years. We have published more than 700 articles (and have rejected more than 1300 submissions). It is impossible to rank the best or most important articles, but we do have information about which articles have been the most cited. From 1994 Indoor Air has full citation coverage through ISI’s Web of Knowledge. The ten most cited articles published since 1994 are these (with citation statistics through 18 February 2009): Cited 196 times. Dampness in buildings and health – Nordic interdisciplinary review of the scientific evidence on associations between exposure to ‘dampness’ in buildings and health effects (NORDDAMP). Bornehag CG, Blomquist G, Gyntelberg F, et al. 2001: 11(2), 72–86. Cited 164 times. Concentrations of volatile organic compounds in indoor air – a review. Brown SK, Sim MR, Abramson MJ, et al. 1994: 4(2), 123–134. Cited 103 times. Ozone in indoor environments: concentration and chemistry. Weschler CJ. 2000: 10(4), 269–288. Cited 96 times. The effects of outdoor air supply rate in an office on perceived air quality, sick building syndrome (SBS) symptoms and productivity. Wargocki P, Wyon D, Sundell J, et al. 2000: 10(4), 222–236. Cited 94 times. Perceived air quality, sick building syndrome (SBS) symptoms and productivity in an office with two different pollution loads. Wargocki P, Wyon D, Baik YK, et al. 1999: 9(3), 165–179. Cited 84 times. Dust and the sick building syndrome. Gyntelberg F, Suadicani P, Nielsen JW, et al. 1994: 4(4), 223–238. Cited 80 times. Impact of temperature and humidity on the perception of indoor air quality. Fang L, Clausen G, Fanger PO. 1998: 8(2), 80–90. Cited 79 times. Estimates of improved productivity and health from better indoor environments. Fisk WJ, Rosenfeld AH. 1997: 7(3), 158–172. Cited 78 times. Association of ventilation rates and CO2 concentrations with health and other responses in commercial and institutional buildings. Seppanen OA, Fisk WJ, Mendell MJ. 1999: 9(4), 226–252. Cited 73 times. Indoor air quality, ventilation and health symptoms in schools: an analysis of existing information. Daisey JM, Angell WJ, Apte MG. 2003: 13(4), 53–64. For articles published in the first three volumes of Indoor Air, there is citation information in Google Scholar. This source also counts some citations in reports and other non-peer reviewed publications. The most cited articles from 1991 to 1993 are these: Cited 160 times (Google). Non-specific symptoms in office workers: a review and summary of the epidemiologic literature. Mendell MJ. 1993: 3(4), 227–236. Cited 124 times (Google). Volatile organic compounds, indoor air quality and health. Mølhave L. 1991: 1(4), 357–376. Cited 86 times (Google). The interaction of vapour phase organic compounds with indoor sinks. Tichenor BA, Guo Z, Dunn JE, et al. 1991: 1(1) 23–35. Combining these citation sources and allowing for intercomparison uncertainty, a possibly correct top ten list of the most cited articles published in Indoor Air to date would be these: Bornehag et al., 2001; Brown et al., 1994; Mendell, 1993; Mølhave, 1991; Weschler, 2000; Wargocki et al., 2000; Wargocki et al., 1999; Gyntelberg et al., 1994; Fang et al., 1998; Fisk and Rosenfeld, 1997. A large majority of these articles are reviews that address both exposures and health. All except Brown et al. (1994, Australia) are from Nordic countries or the USA. The median age of articles in the list is about a decade. This long age reflects that it takes time to be cited; the geographic concentration indicates that, early on, science within this field was mainly conducted in the Nordic countries and the USA. However, this situation is changing. If we look at the 100 most cited articles since 1994 (each of which has been cited more than 20 times), the most common publication year on this list is 2002 (11 articles of the top 100), and more than 50% of the top 100 were published in 2000 or later. We also see the emergence of influential research from eastern Asia in this longer list, a trend we expect to continue. The focus on reviews also reflects that few large multidisciplinary studies have been conducted. A consequence is that there is a need to conduct reviews or meta-analyses to gather enough important data with which to gain robust insights into the complex relationships between indoor environmental quality and health. In today’s economic climate, the possibility to conduct larger studies is limited (IAQ and health is still not adequately recognized as an important research area in this world). A solution may be more collaboration among institutions, each bringing their own (too small) funding together to support larger projects. But hopefully the broader situation will change, so that the general public and (then) the politicians will gain a greater (and proper) understanding of the importance of our research field.