Indoor CO2 Research Articles

Characteristics Analysis of CO2 Concentrations and Temperature in Residential Buildings in Severe Cold Area Based on Field Measurement

This paper provides references for the design and control of high-quality green building indoor environments during the transitional season in severe cold area. A residential building in severe cold area was selected as the research subject, where indoor pollutant CO2 concentrations and temperatures were measured at the beginning of the transitional season. The study explored the variations in indoor pollutant temperatures and CO2 concentrations under natural and non-natural ventilation conditions, in conjunction with an analysis of the occupants' activities. The results demonstrated clear relationships between indoor pollutant CO2 concentrations and temperatures under natural ventilation conditions. Based on these findings, recommendations for natural ventilation strategies that consider both indoor CO2 levels and thermal environment are proposed.

Study on indoor air quality of a newly built student dormitory in a university in Shenyang

During the heating season, a questionnaire survey was conducted among the test-occupancy staff of a newly built dormitory in a university in Shenyang, Liaoning Province, and the indoor air environment parameters of four dormitories were continuously monitored for 24h. The results show that the test residents have low satisfaction with the indoor air environment. The measured results show that the temperature of the four dormitories with high indoor air temperature ranges from 25.8 ℃ to 29.3℃, indoor air humidity meets the standard requirements, indoor CO2 and PM2.5 concentrations exceed the standard seriously, and HCHO and TVOC concentrations exceed the standard for a small amount of time.

One-year operation performance of a decentralised all-air HVAC system for a school room

Since the first COVID outbreak in 2020, schools have been considered a substantial issue with regard to the spread of the disease, as they represent indoor environments that are continuously occupied most of the time. Several studies have underscored the crucial role of mechanical ventilation systems in the fight against any pandemic caused by airborne pathogens. AiCARR, through its associated companies, donated a mechanical ventilation system to a public school in Rho, Milan province (IT). The primary objective of the installation was to enhance safety by diluting indoor contaminants, improving indoor air quality, and ensuring thermal comfort. During the course of the project, the focus included advancing energy efficiency and reducing operational and maintenance costs. This article presents the first year operational data recorded by the monitoring system that include outdoor and indoor air temperature, relative humidity, CO2 concentration and unit electric consumption.

Assessing the hidden dangers of volcanic CO2 exposure: a critical review of health impacts.

Volcanic eruptions pose significant health risks to inhabitants of affected regions, with volcanic gases, including carbon dioxide (CO2), being a notable concern. This review examines the implications of long-term exposure to volcanic CO2 emissions on public health, highlighting the shift in understanding from acute to chronic health effects. Recent studies have underscored the need to reevaluate the adverse health impacts of CO2 beyond acute toxicity symptoms. While previous guidelines deemed an indoor (residential) acceptable long-term exposure range (ALTER) of ≤3,000 parts per million (ppm) in residential housing areas, emerging evidence suggests that even concentrations within the range of 3,000 to 1,000 ppm may induce deleterious health effects. International agencies now advocate for lower safe indoor CO2 levels (600-1,000 ppm), necessitating a reassessment of public health strategies in volcanic areas. This review argues for increased awareness among local and public health authorities about the chronic toxicity of CO2 exposure and emphasizes the importance of safeguarding populations from the adverse health effects induced by CO2 exposure.

Enhancing Indoor Air Quality and Regulatory Compliance: An In-Depth Comparative Study on Ventilation Strategies and Their Impact on SARS-CoV-2 Transmission Risk

Enclosed-space ventilation plays a pivotal role in enhancing indoor air quality (IAQ). Various regulations and guidelines determine minimum fresh air requirements, varying by the application, country, etc. The present study employs real-time indoor CO2 measurements to calculate the actual air change rate (ACH) and models the building’s compliance with Chartered Institution of Building Services Engineers (CIBSE) guidelines to assess its impact on IAQ. The contaminant considered is the SARS-CoV-2 virus with multiple infectors, and the study calculates the virus’s transmission risk under different scenarios. Fresh air is assumed to be provided by mechanical or hybrid ventilation. The results reveal that the current building conditions are unacceptable, showing a significant gap from the recommended guideline rates. Meeting CIBSE recommendations ensures indoor air safety in terms of CO2 concentration. However, in extreme conditions with five infectors, findings show a 14% reduction in mechanical ventilation efficacy. Among the hybrid ventilation scenarios, combining CIBSE rates with natural ventilation, with a 30% door and window opening from the class outset, proves most effective in reducing the virus’s transmission risk, with a 58–70% reduction from the building’s current condition. Furthermore, implementing supplementary measures like air cleaners resulted in an additional 28–50% reduction in transmission risk.

The Effectiveness of Exhaust Fan Rotation with Microcontroller for Indoor CO2 Gas Concentration Control System

A dangerous gas that is harmful to human health and is generally found in the room is carbon dioxide (CO2) gas, which is produced from the accumulation of cigarette smoke. In order to overcome the CO2 gas concentration in the room, it is necessary to develop a device that can control the CO2 gas concentration in the room and that processes the CO2 gas detection results from the MQ-2 sensor. In this research, a device simulation was created that can control the CO2 gas concentration produced by accumulated cigarette smoke in a simulation room measuring 15 cm long, 20 cm wide, and 15 cm high with two CO2 gas release ventilation holes, each with a diameter of 3.5 cm, using the exhaust fan rotation and a microcontroller type Arduino UNO as the control unit. The effectiveness of using a microcontroller of the type Arduino UNO to process the CO2 gas detection results from the MQ-2 sensor can be seen in how the exhaust fan works to release CO2 gas from the simulation room. From the results of this research, it can be seen that the effectiveness of the exhaust fan rotation in controlling the CO2 gas concentration detected by the MQ-2 sensor looks good where the CO2 gas concentration can be controlled under 350 ppm.

Development and Validation of a Methodology to Measure Exhaled Carbon Dioxide (CO2) and Control Indoor Air Renewal

The measurement of carbon dioxide (CO2) has emerged as a cost-effective and straightforward technique for indirectly managing indoor air quality, aiding in the reduction of the potentially pathogen-laden aerosol concentrations to which we are exposed. Unfortunately, inadequate practices often limit the interpretation of CO2 levels and neglect methodologies that ensure proper air renewal. This study presents a novel methodology for measuring and controlling indoor CO2 levels in shared spaces, comprising four stages: analysis, diagnosis, correction protocols, and monitoring/control/surveillance (MCS). This methodology underwent validation in practical settings, including a cultural center (representing spaces with uniform activities) and 40 commercial spaces (with diverse activities) in Zaragoza, Spain. The results indicate the feasibility of swiftly implementing measures to enhance shared air renewal, with the immediate opening of doors and windows being the most direct solution. The proposed methodology is practical and has the potential to mitigate the risk of the aerosol transmission of respiratory diseases. Consequently, we anticipate that this work will contribute to establishing methodological foundations for CO2 measurement as a valuable, standardized, and reliable tool.

Ventilation causing an average CO2 concentration of 1,000 ppm negatively affects sleep: A field-lab study on healthy young people

Poor bedroom ventilation, leading to poor indoor air quality (IAQ), has been shown to reduce sleep quality. Ventilation causing a carbon dioxide (CO2) concentration of 1,000 ppm is assumed to permit optimal sleep quality. The effects of three ventilation levels causing average indoor CO2 concentrations of 750 ppm, 1,000 ppm and 1,300 ppm, on sleep quality, physiological response and next-day work performance were examined. After a first night for adaptation, thirty-six young and healthy participants slept alone in simulated bedrooms for two nights at each of the three ventilation levels in balanced order. Sleep quality was recorded by a wrist-worn sleep tracker. Physiological parameters were measured before sleep and after waking. The participants’ ratings of the bedroom environment, the intensity of the health symptoms they experienced, and cognitive performance were obtained using questionnaires and tests.Compared with ventilation causing an average CO2 concentration of 750 ppm, sleep quality was significantly reduced at the ventilation rates causing CO2 concentrations of 1,000 ppm and 1,300 ppm: Sleep efficiency was reduced by 1.3 % and 1.8 % and time awake increased by 5.0 min and 7.8 min, respectively. Deep sleep duration decreased at the ventilation rate causing CO2 concentration of 1,300 ppm as compared to 750 ppm along with a significant increase in salivary cortisol after waking, which suggests increased stress and sympathetic activity. Ventilation causing an average CO2 concentration of 1,000 ppm or above in bedrooms should therefore be avoided. Participants whose sleep quality was poorer performed worse on tests of cognitive performance the next day.

Comparison of the air change per hour measured over four seasons in the residential buildings of the urban, rural, and industrial areas of South Korea: K-IOP Study

Air infiltration, calcuated by air changes per hour (ACH) is a key factor in assessing the potential amount of air borne pollutants moving from outdoor into indoor spaces. We measured the natural ACH through fall, winter, spring, and summer (2 weeks/season), in 81 nonsmoking elderly houses located in urban (n = 29), industrial (n = 26) and rural (n = 26) areas from 2021 to 2022 consecutively. Indoor CO2 data measured at dawn (01:00 to 05:00 a.m.) over four season was used to estimate the ACH. Moreover, morning ACHs were also calculated from the CO2 level monitored in the morning, when the levels were dropped significantly with opening a window during fall, winter, and spring. The ACH at dawn over the four seasons ranged from 0.02 to 0.03,while that in the morning with opening a window was 0.2 to 0.3. Our multivariate regression models demonstrated that the difference in CO2 concentration during dawn was positively associated with the ACH change after adjusting for seasonality. In addition, after controlling for the study area, ACH was approximately 50 % higher during summer than during the other seasons (p < 0.05). This study elucidates the seasonal and regional distributions of ACH; a determination of these patterns may further contribute to future simulation or prediction studies assessing the associations among indoor air quality, activity patterns and ventilation practices among Korean elderly population.

A Microalgae Photobioreactor System for Indoor Air Remediation: Empirical Examination of the CO2 Absorption Performance of Spirulina maxima in a NaHCO3-Reduced Medium

Microalgae-based photobioreactors (PBRs) have gained attention as a sustainable solution for indoor air quality (IAQ) control. This study investigates indoor CO2 absorption performance of Spirulina maxima (S. maxima) in NaHCO3-limited cultivation (standard: NaHCO3-free medium = 1:1 v/v%) of a lab-scale PBR system. Cultivation performance of three medium amendments (standard, 50% NaHCO3, and NaHCO3-free) was compared by observing cell growth for 30 days in a controlled environment. Empirical examinations were conducted to evaluate the algal CO2 uptake, and overall system performance in the culture volumes of 2, 4, and 7 L and natural indoor CO2 concentration of ~1100 ppm. We found CO2 was reduced by ~55%, in an air chamber of 0.064 m3, showing the greatest mitigation rate (~20%) on Day 4. Under a high concentration of CO2 (10,000 ppm), the CO2 levels were decreased up to ~90% before saturation. This research provides valuable insights into the development of S. maxima-activated IAQ control systems for airtight buildings.

Air quality in the car: How CO2 and body odor affect drivers' cognition and driving performance?

Elevated indoor levels of CO2 and the presence of body odor have been shown to have adverse effects on the cognitive function of building occupants. These factors may also contribute to impaired in-car driving performance, potentially posing a threat to transportation and public safety. To investigate the effects of CO2 and body odor on driving performance, we enrolled 25 participants in highway driving tasks under three indoor CO2 levels (800, 1800, and 3500 ppm) and two body odor conditions (presence and absence). CO2 was injected in the cabin to increase CO2 levels. In addition, we assessed working memory and reaction time using N-back tasks during driving. We found that driving speed, acceleration, and lateral control were not significantly affected by either CO2 or body odor. We observed no significant differences in sleepiness or emotion under varying CO2 or body odor conditions, except for a lower level of emotion valence with exposure to body odor. Task load was also not significantly impacted by CO2 or body odor levels, except for a higher reported effort at 1800 ppm compared to 800 ppm CO2. However, participants did demonstrate significantly higher accuracy with increased body odor exposure, suggesting a complex effect of volatile organic compounds on driver cognition. Our findings also revealed moderating effects of task difficulty of N-back tests and exposure duration on cognition and driving performance. This is one of the first few in-depth studies regarding environmental factors and their effect on drivers' cognition and driving performance, and these results provide valuable insights for car-cabin environmental design for air quality and driving safety.

Direct Air Capture Technology and Its Application

Direct air capture technology (DAC) is integral to achieving carbon emission targets. This paper briefly analyses the application of DAC technology in indoor CO2 removal and CO2 mineralisation. Thanks to the elevated concentration of CO2 in the air (1000ppm) and the integrated DAC unit and air conditioning unit, the indoor CO2 removal system significantly reduces energy consumption. CO2 mineralisation, combined with DAC technology, offers a safe solution for permanent carbon storage and the possibility of obtaining a valuable end product by selecting the right mineralised feedstock. Future research should continue to focus on the development of adsorbent materials and the integration of CO2 capture with subsequent applications to achieve sustainability.

Strategies for Effective Management of Indoor Air Quality in a Kindergarten: CO2 and Fine Particulate Matter Concentrations.

The educational and play-related activities of children proceed mainly indoors in a kindergarten. High concentrations of indoor PM2.5 and CO2 have been linked to various harmful effects on children, considerably impacting their educational outcomes in kindergarten. In this study, we explore different scenarios involving the operation of mechanical ventilation systems and air purifiers in kindergartens. Using numerical models to analyze indoor CO2 and PM2.5 concentration, we aim to optimize strategies that effectively reduce these harmful pollutants. We found that the amount of ventilation required to maintain good air quality, per child, was approximately 20.4 m3/h. However, we also found that as the amount of ventilation increased, so did the concentration of indoor PM2.5; we found that this issue can be resolved using a high-grade filter (i.e., a MERV 13 grade filter with a collection efficiency of 75%). This study provides a scientific basis for reducing PM2.5 concentrations in kindergartens, while keeping CO2 levels low.

Investigation on indoor thermal environment of industrial heritage during the cooling season and its impacts on thermal comfort

Global warming has increased the cooling energy consumption for the operation of built heritages, especially for industrial heritage which suffers from thermal performance deficiencies and are facing the dilemma of functional conversion. In order to satisfy the thermal comfort of users while preserving the value of the heritage, it is necessary to monitor the indoor environment and to analyze its impacts on thermal comfort of human beings. In present study, a cotton textile factory heritage located in Qingdao, Shandong Province, China, was selected, where a long-term investigation of indoor environmental conditions as well as thermal comfort were conducted over a period of 78 days. What's more, the temperature distribution in space field was analyzed by applying CFD simulation. The obtained results show that: i) the indoor temperature fluctuates greatly and the relative humidity as well as CO2 concentration maintain at a high level, failing to provide a satisfactory indoor environment; ii) For most of the time, users report complaints about thermal discomfort, with the hottest mean thermal sensation vote (TSV) being close to warm (1.76) and the worst mean thermal comfort vote (TCV) reaching uncomfortable (−1.60); iii) The deviation between PMV and TSV demonstrates the limitations of the Fanger's model when applied in industrial heritage, and the thermal comfort perception of users are influenced by indoor humidity, CO2 concentration and outdoor temperature. The performed analyses suggest that the indoor thermal environment of industrial heritage fails to keep pace with the transformation of its nature and function. These findings will provide basic research for the retrofitting of industrial heritage.

Method of test for CO2-based demand control ventilation systems: Benchmarking the state-of-the-art and the undervalued potential of proportional-integral control

Carbon dioxide (CO2) based demand control ventilation (DCV) adjusts a building’s outdoor air ventilation rate in response to indoor CO2 concentration to save energy while maintaining indoor air quality. Packaged heating, ventilation, and air-conditioning systems often contain DCV controllers with embedded proprietary algorithms that lack transparent performance data. A test method was developed to assess the ability of a DCV controller to maintain the indoor CO2 concentration at a setpoint in response to a series of CO2 generation functions that represent three different building occupancy densities and two occupancy schedules. Six commercially available controllers were tested to demonstrate the method and provide directly comparable results. The performance (in terms of CO2 control and damper movement) of each controller tested was compared to the performance of an ideal controller which knows the CO2 generation function. Finally, the performance of a proportional-integral (PI) controller with preset gains was developed and tested to determine the potential maximum performance achievable with this control strategy. The best performing commercially available controller achieved CO2 control (within 75 ppm of the setpoint) approximately 80 % of the time with damper movement slightly less than an ideal controller. However, most of the commercially available controllers had marginal or poor performance for CO2 control and damper movement. Two controllers had damper movement more than three times the ideal controller. Notably, a PI algorithm configured and tested by the research team achieved superior performance with CO2 control 92 % of the time and damper movement 1.5 times the ideal controller.

Smart digital campus UniTO: data gathering and visualisation to support sustainability and indoor comfort

This research aims to identify and investigate the best digital tools to improve indoor comfort conditions and sustainability through energy efficiency enhancement in educational buildings, integrating data gathered from sensors. By leveraging an existing asset management platform that integrates Building Information Modelling (BIM) and Geographic Information Systems (GIS), data from Internet of Things devices were linked to the BIM model of a test case building creating a digital shadow in order to gather real-time data on indoor conditions, including temperature, humidity, and CO2 levels. The methodology enables continuous evaluation of the building’s state of usage and calls for automatic and frequent updates of data. The digital shadow can display current usage conditions and alarms when conditions exceed what is comfortable, and it allows for immediate feedback through colours based on the internal detected conditions. The platform can be used with business intelligence tools to support strategic choices and enable future innovations, including machine learning techniques to estimate building occupancy and identify any deviations from expected usage patterns. This study presents a promising workflow for creating sustainable and comfortable educational buildings, which could be replicable and scalable in the future.

Exploration of the relationships between perceived and observed parameters of IEQ using Bayesian analysis

Seeking to bridge the gap between observations and predictions of thermal comfort, recent work has explored novel predictive frameworks to improve the prediction accuracy of occupants’ thermal satisfaction in office spaces. Recent contributions include the development of a Bayesian framework to estimate the probability of an occupant feeling thermally satisfied as a function of not only psychrometric IEQ parameters but also non-thermal metrics of IEQ. A predictive relationship between indoor CO2 concentrations and thermal satisfaction was found, though the underlying causal relationship is not yet clear. An occupant unhappy about air quality is more likely than not found to be unhappy with other parameters, including indoor air temperature. To quantify these relationships, further analysis with new modelling methods and data is required. This paper presents a new formulation of prior work, using a new Bayesian logistic regression model and counterfactual inference to assess the combined relationships between many subjective and objective IEQ factors. This work sets out to provide the first-known Bayesian analysis of the underlying causality of observed statistical relationships between divergent parameters of subjective and objective IEQ.

The Influence of Bedroom CO2 Concentration on Sleep Quality

A person spends about a third of their life sleeping, and high sleep quality is very important for health. Environmental factors are one of the most important factors affecting sleep quality, and indoor carbon dioxide (CO2) concentration while sleeping has a significant effect on sleep quality. In an indoor bedroom with no open windows and no fresh air system, different numbers of people sleeping will lead to changes in indoor CO2 concentration. In order to study the changes in sleep quality caused by differences in CO2 concentration, experimental research was performed. Objective sleep quality data are collected with polysomnography (PSG) and a subjective questionnaire. The sleep quality of the subjects is tested under three different CO2 concentration levels; the average carbon dioxide concentration of three conditions is 680, 920, and 1350 ppm, which simulate a room with 1, 2, and 3 people sleeping, respectively. Other environment parameters are controlled as follows: test environment temperature is 26 ± 0.5 °C, relative humidity is 50 ± 5%, there is no obvious heat source in the test room, and the radiation temperature and air temperature difference is less than 1 °C. A total of 30 subjective tests were carried out with 10 subjects; the test lasted more than one month. The data subsequently underwent statistical analysis to determine the influence of CO2 concentration on sleep quality. The results show that as the CO2 concentration level increased, the sleep quietness and satisfaction of the subjects gradually decreased, the sleep duration gradually decreased, and symptoms such as throat discomfort, dyspnea, dry and itchy skin, difficulty falling asleep, difficulty waking up, congested nose and bad air smell become more obvious. The PSG test results showed that CO2 concentration has a significant impact on the proportion of the N3 period. According to the group of CO2 concentration conditions, the mean of the N3 period proportion under the conditions of one person, two persons, and three persons is 20.4%, 17.3%, and 14.4%, respectively. Finally, there was also an increase in turning over or awakening during sleep, indicating that sleep quality was reduced under higher CO2 concentrations.

Examining the Risk of Summertime Overheating in UK Social Housing Dwellings Retrofitted with Heat Pumps

The UK government has announced its ten-point plan to annually install 600,000 low-carbon heat pumps by 2028. However, there is a lack of evidence showing potential overheating risk in dwellings retrofitted with heat pumps. This paper examines the prevalence and magnitude of summertime overheating across 24 naturally ventilated social housing dwellings retrofitted with ground source heat pumps (GSHPs). The dwellings are located in a socially deprived area in Oxford (UK). The empirical study included longitudinal monitoring of indoor temperatures in the living rooms and bedrooms during the non-heating seasons of 2021 and 2022 (May–September), which included a record-breaking heatwave in July 2022. Indoor temperature and CO2 levels in bedrooms were monitored across a subset of six dwellings alongside the monitoring of window opening state in three bedrooms to understand the effect of natural ventilation in removing excess heat. About 136 thermal comfort surveys were conducted to ascertain the subjective responses of residents. Overheating risk assessment was carried out using CIBSE static and adaptive methods, which revealed that summertime overheating was prevalent across half of the dwellings in the non-heating season of 2022, as compared to 17% overheated dwellings in 2021. Bungalows with upgraded cavity wall insulation and top floor flats facing south and south-west had a propensity to overheat. The variation in indoor temperature and CO2 levels across a small sample also indicated the relationship between overheating and residents’ behaviour. Given that the majority of the dwellings were occupied by retired elderly people with low incomes who are vulnerable to heat and cannot afford active forms of cooling, it is vital to deploy passive design measures, such as appropriate shading devices that are suitable for a heating-dominated climate and enhanced ventilation, as part of home energy retrofits. Implementing reversible heat pumps coupled with solar PVs can provide cooling during heatwaves while delivering low-carbon heat in the winter.

Effects of short-term exposure to moderate pure carbon dioxide levels on cognitive performance, health symptoms and perceived indoor environment quality

Educational buildings frequently experience elevated CO2 concentrations with inadequate ventilation and high occupancy, sometimes exceeding building guideline levels. Some studies reported detrimental impacts on cognitive performance of indoor CO2 levels, while others did not. To generate further evidence, we conducted an experiment in an environmentally controlled chamber. Sixty-nine healthy university students were exposed individually for 70 min, in three separate sessions, to three CO2 conditions of 600, 1500 and 2100 ppm (crossover design). With fixed ventilation rates, pure CO2 was injected to achieve different exposure levels. A validated neurobehavioral BARS test battery was used to assess participants’ cognitive performance. Participants gave subjective ratings of indoor environment and reported any health symptom through questionnaires. Comparing elevated CO2 levels to 600 ppm, after adjusting for potential confounders, results showed significant improved performance, that is, responses were quicker in two out of ten tests, and no significant differences in accuracy for any test. Under 1500 ppm, participants rated the air quality significantly higher than at 600 ppm, but there were no differences at 2100 ppm. Differences were not significant on thermal sensation, perceived lighting quality, perceived noise level, or health symptoms for comparisons between conditions. Results indicate no clear link between pure CO2 levels below 2100 ppm and cognitive performance, perceived indoor environment quality and health symptoms. The findings are consistent with some prior studies, indicating that pure CO2 below 2100 ppm implies no harm in adults and should not be treated as a potential indoor pollutant in higher educational environments.