Associations between indoor CO2 concentrations and sick building syndrome symptoms in U.S. office buildings: an analysis of the 1994-1996 BASE study data

Higher indoor concentrations of air pollutants due, in part, to lower ventilation rates are a potential cause of sick building syndrome (SBS) symptoms in office workers. The indoor carbon dioxide (CO2) concentration is an approximate surrogate for indoor concentrations of other occupant-generated pollutants and for ventilation rate per occupant. Using multivariate logistic regression (MLR) analyses, we evaluated the relationship between indoor CO2 concentrations and SBS symptoms in occupants from a probability sample of 41 U.S. office buildings. Two CO2 metrics were constructed: average workday indoor minus average outdoor CO2 (dCO2, range 6-418 ppm), and maximum indoor 1-h moving average CO2 minus outdoor CO2 concentrations (dCO2MAX). MLR analyses quantified dCO2/SBS symptom associations, adjusting for personal and environmental factors. A dose-response relationship (p < 0.05) with odds ratios per 100 ppm dCO2 ranging from 1.2 to 1.5 for sore throat, nose/sinus, tight chest, and wheezing was observed. The dCO2MAX/SBS regression results were similar.     

The link between symptoms of office building occupants and in-office air pollution: the Indoor Air Pollution Index

The lack of an effective indoor air quality (IAQ) metric causes communication concerns among building tenants (the public), building managers (decision-makers), and IAQ investigators (engineers). The Indoor Air Pollution Index (IAPI) is developed for office buildings to bridge this communication discord. The index, simple and easily understood, employs the range of pollutant concentrations and concentrations in the subject building to estimate a unitless single number, the IAPI, between 0 (lowest pollution level and best IAQ) and ten (highest pollution level and worst IAQ). The index provides a relative measure of indoor air pollution for office buildings and ranks office indoor air pollution relative to the index distribution of the US office building population. Furthermore, the index associates well with occupant symptoms, percentage of occupants with persistent symptoms. A tree-structured method is utilized in conjunction with the arithmetic mean as the aggregation function. The hierarchical structure of the method renders not only one index value, but also several sub-index values that are critical in the study of an office air environment. The use of the IAPI for IAQ management is illustrated with an example. The decomposition of the index leads to the ranking of sampled pollutants by their relative contribution to the index and the identification of dominant pollutant(s). This information can be applied to design an effective strategy for reducing in-office air pollution.     

Evaluation of distributed environmental control systems for improving IAQ and reducing energy consumption in office buildings

Conventional heating, ventilation, and air conditioning (HVAC) systems are incapable of providing control over individual environments or adjusting fresh air supply based on the dynamic occupancy of individual rooms in an office building. This paper introduces the concept of distributed environmental control systems (DECS) and shows that improvement in indoor air quality (IAQ) and energy efficiency can be achieved by providing required amounts of fresh air directly to the individual office spaces through distributed demand controlled ventilation (DDCV). In DDCV, fresh air is provided to each micro-environment (room or cubicle) based on input from distributed sensors (CO₂, VOC, occupancy, etc.) or intelligent scheduling techniques to provide acceptable IAQ for each occupant, rather than for groups or populations of occupants. In order to study DECS, a numerical model was developed that incorporates some of the best available models for studying building energy consumption, indoor air flow, contaminant transport and HVAC system performance. The developed model was applied to a DECS in a model office building equipped with a DDCV system. By implementing DECS/DDCV and intelligent scheduling techniques it is possible to achieve an improvement in IAQ along with a reduction in annual energy consumption compared to conventional ventilation systems.     

Evaluation on sampling point densities for assessing indoor air quality

In Hong Kong, the Environmental Protection Department (HKEPD) has launched an indoor air quality (IAQ) certification scheme to promote an acceptable IAQ in workplaces. However, the associated uncertainties and measurement efforts have not been detailed for practical measurement in indoor spaces. In this study, indoor carbon dioxide (CO₂) concentration is selected as an indicator of the IAQ to investigate the probable errors and measurement efforts in different sampling schemes regarding the sampling point density. In particular, a one-year measurement for sample-spatial average indoor CO₂ concentration at 17 sampling locations in a typical large office (floor area=1200 m²) has been used to evaluate the probable errors of the sample-spatial average concentrations using different sampling point densities. The result shows that the measured concentration at a single sampling point could not be representative for the space and more than one sampling locations would be required in order to increase the measurement accuracy. Mathematical expressions for the sample-spatial average concentration at a confidence level at certain sampling point densities are proposed. When doubled the required measurement points, it was found that the probability of obtaining a measured CO₂ concentration at the confidence level of 95% could be increased from 70% to 90%, as compared with the current sampling practice. It is recommended to specify the measurement uncertainties in future codes so that effort for IAQ measurements in indoor spaces could be determined for practical strategies.     

Assessment of ventilation and indoor air pollutants in nursery and elementary schools in France

The aim of this study was to characterize the relationship between Indoor Air Quality (IAQ) and ventilation in French classrooms. Various parameters were measured over one school week, including volatile organic compounds, aldehydes, particulate matter (PM_2.5 mass concentration and number concentration), carbon dioxide (CO₂), air temperature, and relative humidity in 51 classrooms at 17 schools. The ventilation was characterized by several indicators, such as the air exchange rate, ventilation rate (VR), and air stuffiness index (ICONE), that are linked to indoor CO₂ concentration. The influences of the season (heating or non‐heating), type of school (nursery or elementary), and ventilation on the IAQ were studied. Based on the minimum value of 4.2 l/s per person required by the French legislation for mechanically ventilated classrooms, 91% of the classrooms had insufficient ventilation. The VR was significantly higher in mechanically ventilated classrooms compared with naturally ventilated rooms. The correlations between IAQ and ventilation vary according to the location of the primary source of each pollutant (outdoor vs. indoor), and for an indoor source, whether it is associated with occupant activity or continuous emission.     

A performance comparison of passive and low-energy buildings

This paper compares apartments in two residential blocks in Vienna; one passive and the other one low-energy. These blocks were constructed simultaneously in the same location and with comparable building construction features and floor plans. The main difference between the two blocks (other than the higher thermal insulation level in the passive building) lies in the ventilation system: passive buildings deploy controlled ventilation, whereas the low-energy buildings rely mostly on user-operated natural (window) ventilation. We measured indoor environmental conditions (indoor air temperature, relative humidity, and CO₂ concentration) in two units of each block over a period of five months. Additionally, the buildings were compared in view of operation and embodied energy use, CO₂ emissions, and construction costs.     

An energy impact assessment of ventilation for indoor airborne bacteria exposure risk in air-conditioned offices

Treatment of fresh air in ventilation systems for air-conditioned offices consumes a significant amount of energy and affects the indoor air quality (IAQ). In this study, energy impact on the ventilation systems was examined against certain IAQ objectives for indoor airborne bacteria exposure risk in air-conditioned offices of Hong Kong. The relationship between thermal energy consumptions and indoor airborne bacteria exposure levels based on regional surveys was investigated. The thermal energy consumptions of ventilation systems operating for carbon dioxide (CO₂) exposure concentrations between 800 and 1200 ppmv for typical office buildings and the corresponding failure probability against some target bacteria exposure levels were evaluated. The results showed that, for a reference indoor environment at a CO₂ exposure concentration of 1000 ppmv, the predicted average thermal energy saving of ventilation system for a unit increment of the expected risk of unsatisfactory IAQ of 1% was 55 MJ m⁻² yr⁻¹ and for a unit decrement of 1%, the predicted additional thermal energy consumption was 58 MJ m⁻² yr⁻¹ respectively. This study would be a useful source of reference in evaluation of the energy performance of ventilation strategies in air-conditioned offices at a quantified exposure risk of airborne bacteria.     

Evaluation of four control strategies for building VAV air-conditioning systems

It is necessary to adopt appropriate control strategies to save energy and improve the indoor air quality (IAQ). On the validated TRNSYS simulation platform, four different control strategies are investigated to examine the indoor air temperature, energy consumption, CO₂ concentration and predicted mean vote (PMV) for the variable air volume (VAV) systems in an office building in Shanghai. As an original scheme, Strategy A using constant outdoor air intake fraction shows high energy consumption, low CO₂ concentration and acceptable thermal comfort. By using minimum outdoor air ventilation based on dynamic occupancy detection, Strategy B can provide more than 15% energy saving, acceptable PMV value but high CO₂ concentration in breathing zone. By using indoor air temperature reset, Strategy C presents the most energy savings beyond 20% reduction, low CO₂ concentration but poor thermal comfort. In mild seasons, combining enthalpy-based outdoor airflow economizer cycle with supply air temperature reset, Strategy D can achieve 9.4% energy savings and the lowest CO₂ concentration. Taken together, each strategy covers some strengths as well as some weaknesses. How to comprehensively assess a control strategy for all specific objectives should be considered in future studies.     

A novel methodology for estimating space air change rates and occupant CO2 generation rates from measurements in mechanically-ventilated buildings

It is useful to know ventilation rates and carbon dioxide (CO₂) generation rates for evaluating indoor air quality and ventilation efficiency in mechanically-ventilated buildings. A strong limitation of the current models is either they focus solely on a whole building or they are too complicated for practical use in studies of individual spaces. This paper develops a new method for accurately quantifying ventilation rates (i.e. space air change rate) and CO₂ generation rates from measured CO₂ concentrations for individual spaces. The proposed method firstly determined space air change rate using Maximum Likelihood Estimation (MLE). Additionally, a novel coupled-method was initiated for further estimating CO₂ generation rates. Both simulated and experimental data were used to validate the model. Experiments were conducted in a school office by measuring indoor CO₂ concentrations and pressure differences between the return air vent and space. Excellent agreement was obtained. At least 0.998 R² values were obtained for fitting measured CO₂ concentrations when conducting MLE for estimating space air change rate, and the corresponding residual plots showed no pattern and trend. The estimated numbers of occupants were same as the actual ones. Furthermore, the predicted space air change rates showed great consistencies with those from CO₂ equilibrium analysis. The model is simple, handy and effective for practical use. Moreover, the model is also capable for dealing with time-varying space air change rates.     

Bayesian estimation of occupancy distribution in a multi-room office building based on CO<Subscript>2</Subscript> concentrations

Occupancy information in an office building is an important asset for determining energy-efficient operations and emergency evacuation of a building. In this study, we developed a method to estimate the occupancy distribution in a multi-room office building using Bayesian inference. The Markov chain Monte Carlo algorithm was used to estimate the real-time occupancy in individual rooms based on indoor carbon dioxide concentrations. The office building was made-up of five rooms with different physical configurations and dimensions, and the rooms were air-conditioned and ventilated by a central air handling unit. The carbon dioxide concentration data were generated by the simulation software CONTAMW according to a given schedule of occupancy and the supply airflow rates in each room. The objective of the present paper is to investigate the effects of various parameters of Bayesian inference on the accuracy of estimation results. The parameters include the probability of prior information, the uncertainty level of CO₂ data, and the time interval for monitoring CO₂.     

Particulate Matter Intervention Study: A Causal Factor of Building-Related Symptoms in an Older Building

Abstract Five floors of a 20-year old 6-story office building were investigated using an integrated step-by-step investigation strategy. This involved a walkthrough inspection, an occupant questionnaire, and targeted environmental monitoring of indoor air quality and comfort parameters. The initial questionnaire survey revealed a high occurrence of building-related symptoms. The walkthrough inspection and environmental monitoring identified deposits of surface dust (indoor surface pollution – ISP) on carpets and hard surfaces, and elevated levels of carbon dioxide and respirable suspended particulate matter (RSP) throughout the building. An intervention study (blinded to the occupants) was targeted at reducing ISP levels by replacing normal carpet cleaning practices with higher performance vacuum cleaners and improved cleaning practices. The intervention reduced ISP levels and significantly lowered RSP concentrations by approx. 80% from initial values and against control floors. A follow-up SBS questionnaire revealed significant reductions in all but two of the symptoms. The most significant reductions occurred with symptoms of eye irritation, throat irritation, dry unproductive cough, and nose irritation. The study showed that in older buildings with poor ventilation, a build-up of ISP, and elevated RSP levels, using higher performance carpet cleaning practices can reduce RSP to acceptable levels and can reduce SBS symptoms.     

An integrated modeling tool for simultaneous analysis of thermal performance and indoor air quality in buildings

To analyze the thermal performance and indoor air quality (IAQ) in building simultaneously and quickly, we have developed an integrated modeling tool to simulate the dynamic indoor multi-parameters distributions and concentrations. The tool can take the parameters including indoor temperature, indoor humidity, and pollutant concentrations (e.g., volatile organic compounds (VOC) CO₂, particulate matter (PM)), as well as the heating/cooling load of heating, ventilating, and air-conditioning (HVAC) system into account. It couples a new zonal approach based on room air age. This paper presents the basic concept and flow chart in developing the modeling tool, and demonstrates the tool's application in a hypothetical health care building. The tool could be used for design of HVAC system with IAQ control devices and for the simultaneous analysis of thermal performance and IAQ in buildings.     

An investigation into the thermal performance of office buildings in Ghana

This paper comprises the outcome of a long-term monitoring of the thermal conditions in a selected number of office buildings in Kumasi, Ghana. The observed data was not only used to assess indoor environmental conditions in these offices, but also to calibrate a number of thermal simulation models of the buildings. Thus, a simulation-based exploration of thermal retrofit options towards a general reduction of cooling requirements could be conducted. Moreover, the impact of thermal retrofit measures towards reducing carbon dioxide (CO₂) emissions was assessed and the amortization times for investments in such retrofit measures were estimated. The results suggest that improvements in building fabric and controls (with payback times of 3–12 years) can reduce buildings’ cooling loads by around 20–35% and CO₂ emissions around 27%. Additionally, the outcome of interviews conducted showed that 45% and 70% of occupants in mixed-mode and naturally ventilated buildings were uncomfortable with the air quality during the dry season. The highest dissatisfaction with indoor environment was reported by 85% of the occupants in the naturally ventilated building. The importance attached to the operation of windows and shades was relatively high, 55–80%, depending on building type.     

上海市办公楼室内空气品质的测试和分析

本文利用上海市六幢大楼的实测数据对上海市办公楼室内空气品质环境作了客观和主观两方面的评价,经分析可知,上海市办公楼内室内空气品质环境在客观评价中未达标的情况比较严重,而主观调研的结果也显示,上海市办公楼室内空气品质的可接受率远远低于ASHRAE62-1989所提出的可接受室内空气品质应满足80％的可接受率,实测说明,上海办公楼内仍然存在建筑病综合症(SBS)。同时本文强调基于“可感受的可接受的室内空气品质”这一指标,主观评价良好应是建筑物的设计人员、建造者及管理人员不懈追求的目标。     

Impact of psycho-social factors on perception of the indoor air environment studies in 12 office buildings

The main function of a mechanically ventilated office building is to provide a healthy and comfortable working environment for occupants, while maintaining minimum energy consumption. Twelve mechanically ventilated buildings were selected. They varied greatly in surface area, number of floors, occupant density, and building use. The indoor air quality, thermal comfort, energy consumption, and perception of occupants were investigated in these buildings. A total of 877 subjects participated in the questionnaire survey during the hot summer months of June, July, and August, and during the cold winter months of January, February, and March. The questions included in the questionnaire dealt with health, environmental sensitivity, work area satisfaction, personal control of the workstations environment, and job satisfaction. Measured parameters concerning the quality of indoor air included ventilation rate, concentration of TVOC, CO₂, CO, RH, and formaldehyde. The thermal comfort parameters included room air, mean radiant, plane radiant asymmetry, and dew point temperatures, as well as air velocity and turbulence intensity. Monthly energy consumption data was also gathered for each building. Ventilation performance, in terms of air flow rate and indoor air quality, was compared with the ASHRAE Standard 62-89R (Ventilation for Acceptable Indoor Air Quality. Atlanta: American Society of Heating, Refrigerating, and Air Conditioning Engineers, Inc. U.S.A. [1]). The measured and calculated thermal environmental results were also compared with the ASHRAE Standard 55-92 (Thermal Environmental Conditions for Human Occupancy. Atlanta: American Society of Heating, Refrigerating, and Air Conditioning Engineers, Inc. U.S.A. [2]). CO₂ and CO levels satisfied the recommended limits. The outdoor airflow rate was half that recommended in only one building. The formaldehyde and TVOC levels were moderately higher than suggested comfort levels. However, more than 56% of the occupants rated dissatisfaction with the indoor air quality. Only 63% of the indoor climatic observations fell within the ASHRAE Standard 55-92 summer comfort zone; 27% in the winter. However, only 69% of those surveyed agreed with the comfort zones. More symptoms were reported by workers who perceived IAQ to be poor. Positive relationships were observed between the job satisfaction and satisfaction with office air quality, ventilation, work area temperature, and ratings of work area environment. However, job dissatisfaction did not correlate with symptom reports. The occupants were more dissatisfied with IAQ when they preferred more air movement. In other words, the higher the perceived air movement, the greater the satisfaction with IAQ.     

The Indoor Air Quality Programme of the WHO Regional Office for Europe

The indoor air quality (IAQ) programme of the World Health Organization Regional office for Europe was initiated in the mid-seventies when it was realized that over 70% of the general population spends its time indoors in homes, office buildings, schools, hospitals, transportation means, etc. The first meting of experts on health aspects related to IAQ was convened in 1979, being probably the first international meeting on IAQ with participation from eastern and western Europe as well as from North America. Seven meetings followed between 1982 and 1990, at which the “sick building” syndrome, IAQ research, formaldehyde and radon, organic pollutants, biological contaminants, combustion products, and mineral fibres were discussed. A ninth meeting on sources, control and mitigation is planned for 1991.     

Indoor air quality in energy‐efficient dwellings: Levels and sources of pollutants

Worldwide, public policies are promoting energy‐efficient buildings and accelerating the thermal renovation of existing buildings. The effects of these changes on the indoor air quality (IAQ) in these buildings remain insufficiently understood. In this context, a field study was conducted in 72 energy‐efficient dwellings to describe the pollutants known to be associated with health concerns. Measured parameters included the concentrations of 19 volatile organic compounds and aldehydes, nitrogen dioxide, particulate matter (PM_2.5), radon, temperature, and relative humidity. The air stuffiness index and night‐time air exchange rate were calculated from the monitored carbon dioxide (CO₂) concentrations. Indoor and outdoor measurements were performed at each dwelling during 1 week in each of the two following seasons: heating and non‐heating. Moreover, questionnaires were completed by the occupants to characterize the building, equipment, household, and occupants’ habits. Perspective on our results was provided by previous measurements made in low‐energy European dwellings. Statistical comparisons with the French housing stock and a pilot study showed higher concentrations of terpenes, that is, alpha‐pinene and limonene, and hexaldehyde in our study than in previous studies. Alpha‐pinene and hexaldehyde are emitted by wood or wood‐based products used for the construction, insulation, decoration, and furnishings of the dwellings, whereas limonene is more associated with discontinuous sources related to human activities.     

Evaluation of professional choice of sampling locations for indoor air quality assessment

The uncertainties of professional choice of ‘representative’ sampling locations for general indoor air quality (IAQ) assessment are reported from the perspective of probable errors deviated from the sample-spatial average pollutant concentration of an indoor environment. In this study, associations between the professional choices of the sampling locations and attributes of the assessors were examined to quantify the uncertainties of the IAQ assessment results for a typical air-conditioned office in Hong Kong. In particular, a long-term (one-year) measurement result of the spatial indoor carbon dioxide (CO₂) concentrations in this office was used as a basis to investigate the probable errors due to the choices of sampling locations. Comparing with the random choices, the assessment accuracy with the expert choices would be significantly improved for coarse sampling point densities at certain engineering acceptable error limits. It was reported that the location choices and assessment accuracy would be significantly influenced by the academic background of the assessors. An assessor group with higher academic level would make a choice leaning towards more accurate assessment results. To avoid an inappropriate level of reliance on the assessment results, uncertainties must be quantified for IAQ assessment. This study provided a template for further investigations into the uncertainties of IAQ assessment results involving professional choice of ‘representative’ sampling locations and the results might be a useful reference for assessing indoor environment elsewhere.     

Effects of ventilation rate per person and per floor area on perceived air quality,sick building syndrome symptoms,and decision‐making

Ventilation rates (VRs) in buildings must adequately control indoor levels of pollutants; however, VRs are constrained by the energy costs. Experiments in a simulated office assessed the effects of VR per occupant on perceived air quality (PAQ), Sick Building Syndrome (SBS) symptoms, and decision‐making performance. A parallel set of experiments assessed the effects of VR per unit floor area on the same outcomes. Sixteen blinded healthy young adult subjects participated in each study. Each exposure lasted four hours and each subject experienced two conditions in a within‐subject study design. The order of presentation of test conditions, day of testing, and gender were balanced. Temperature, relative humidity, VRs, and concentrations of pollutants were monitored. Online surveys assessed PAQ and SBS symptoms and a validated computer‐based tool measured decision‐making performance. Neither changing the VR per person nor changing the VR per floor area, had consistent statistically significant effects on PAQ or SBS symptoms. However, reductions in either occupant‐based VR or floor‐area‐based VR had a significant and independent negative impact on most decision‐making measures. These results indicate that the changes in VR employed in the study influence performance of healthy young adults even when PAQ and SBS symptoms are unaffected.     

Carbon dioxide generation rates for building occupants

Indoor carbon dioxide (CO₂) concentrations have been used for decades to characterize building ventilation and indoor air quality. Many of these applications require rates of CO₂ generation from the building occupants, which are currently based on approaches and data that are several decades old. However, CO₂ generation rates can be derived from well‐established concepts within the fields of human metabolism and exercise physiology, which relate these rates to body size and composition, diet, and level of physical activity. This paper reviews how CO₂ generation rates have been estimated in the past and discusses how they can be characterized more accurately. Based on this information, a new approach to estimating CO₂ generation rates is presented, which is based on the described concepts from the fields of human metabolism and exercise physiology. Using this approach and more recent data on body mass and physical activity, values of CO₂ generation rates from building occupants are presented along with the variability that may occur based on body mass and activity data.