Risk factors in heating, ventilating, and air-conditioning systems for occupant symptoms in US office buildings: the US EPA BASE study

Building-related symptoms in office workers worldwide are common, but of uncertain etiology. One cause may be contaminants related to characteristics of heating, ventilating, and air-conditioning (HVAC) systems. We analyzed data from 97 representative air-conditioned US office buildings in the Building Assessment and Survey Evaluation (BASE) study. Using logistic regression models with generalized estimating equations, we estimated odds ratios (OR) and 95% confidence intervals for associations between building-related symptom outcomes and HVAC characteristics. Outdoor air intakes less than 60 m above ground level were associated with significant increases in most symptoms: e.g. for upper respiratory symptoms, OR for intake heights 30 to 60 m, 0 to <30 m, and below ground level were 2.7, 2.0, and 2.1. Humidification systems with poor condition/maintenance were associated with significantly increased upper respiratory symptoms, eye symptoms, fatigue/difficulty concentrating, and skin symptoms, with OR = 1.5, 1.5, 1.7, and 1.6. Less frequent cleaning of cooling coils and drain pans was associated with significantly increased eye symptoms and headache, with OR = 1.7 and 1.6. Symptoms may be due to microbial exposures from poorly maintained ventilation systems and to greater levels of vehicular pollutants at air intakes nearer the ground level. Replication and explanation of these findings is needed. PRACTICAL IMPLICATIONS: These findings support current beliefs that moisture-related HVAC components such as cooling coils and humidification systems, when poorly maintained, may be sources of contaminants that cause adverse health effects in occupants, even if we cannot yet identify or measure the causal exposures. While finding substantially elevated risks for poorly maintained humidification systems, relative to no humidification systems, the findings do not identify important (symptom) benefits from well-maintained humidification systems. Findings also provide an initial suggestion, needing corroboration, that outdoor air intakes lower than 18 stories in office buildings may be associated with substantial increases in many symptoms. If this is corroborated and linked to ground-level vehicle emissions, urban ventilation air intakes may need to be located as far above ground level as possible or to incorporate air cleaners that remove gaseous pollutants.     

Association of air-conditioning with respiratory symptoms in office workers in tropical climate

To evaluate the association of heating, ventilation and air-conditioning systems (HVAC) and respiratory symptoms in a tropical city, self-administered questionnaires were given to 2000 individuals working in air-conditioned office buildings and to 500 control workers in naturally ventilated buildings. Reported symptoms from the two populations were analyzed using chi-square tests, univariate and multiple logistic regressions models. Symptoms were the outcome variable and the odds ratios were adjusted by gender, age, accumulated work time, smoking habits and atopic background. There was a 79.8% response rate and there was a positive association of nasal symptoms (odds ratio, OR = 1.59, 95% confidence interval, CI = 1.11-2.28), naso-ocular symptoms (OR = 1.58, 95% CI = 1.05-2.38), persistent cough (OR = 3.04, 95% CI = 2.00-4.63) sinusitis symptoms (OR = 1.85, 95% CI = 1.27-2.71) and building-related worsening of the symptoms (OR = 4.92, 95% CI = 2.93-8.27) with working in air-conditioned buildings. In conclusion, our study suggests that artificial air-conditioning is a matter of concern for respiratory symptoms in cities with hot and humid climate. PRACTICAL IMPLICATIONS: This study suggests that indoor air-related respiratory symptoms are a matter of concern in places with hot and humid climate. The regression models were adjusted by confounders that could be used in further reanalysis of indoor air quality related symptoms and ventilation systems with expanded variety of climatic conditions.     

Indoor air quality and occupant satisfaction in five mechanically and four naturally ventilated open-plan office buildings

Occupant responses and indoor environment characteristics were recorded and compared in five mechanically and four naturally ventilated open-plan office buildings by using a simple approach that enabled us to survey many buildings simultaneously. All occupant responses were obtained during one afternoon. In a pre-experiment, temperature and the concentration of CO₂ were monitored in 2–10 locations/office to evaluate the variation throughout the offices. A representative measurement point was subsequently selected and measurements of the same parameters were made during one week. All offices were monitored during the same week and occupant responses to the indoor environment were collected via the internet on the same day within that week. The temperature and the CO₂ concentration varied more and were in some cases higher in the naturally ventilated buildings, but occupant responses in terms of symptoms and adverse perceptions differed only modestly between the two building types. Although rarely supported by statistical significance, the results indicated a somewhat higher degree of satisfaction with the indoor environment and a lower prevalence/intensity of symptoms among the occupants in the naturally ventilated buildings.     

Association of ventilation rates and CO2 concentrations with health and other responses in commercial and institutional buildings

This paper reviews current literature on the associations of ventilation rates and carbon dioxide concentrations in non-residential and non-industrial buildings (primarily offices) with health and other human outcomes. Twenty studies, with close to 30,000 subjects, investigated the association of ventilation rates with human responses, and 21 studies, with over 30,000 subjects, investigated the association of carbon dioxide concentration with these responses. Almost all studies found that ventilation rates below 10 Ls-1 per person in all building types were associated with statistically significant worsening in one or more health or perceived air quality outcomes. Some studies determined that increases in ventilation rates above 10 Ls-1 per person, up to approximately 20 Ls-1 per person, were associated with further significant decreases in the prevalence of sick building syndrome (SBS) symptoms or with further significant improvements in perceived air quality. The carbon dioxide studies support these findings. About half of the carbon dioxide studies suggest that the risk of sick building syndrome symptoms continued to decrease significantly with decreasing carbon dioxide concentrations below 800 ppm. The ventilation studies reported relative risks of 1.5-2 for respiratory illnesses and 1.1-6 for sick building syndrome symptoms for low compared to high low ventilation rates.     

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.     

Analysis of stack ventilation system effectiveness in an average kindergarten in north-eastern Poland

The present research is concerned with effectiveness of stack ventilation system in an average Polish kindergarten. The research was carried out in June (2010), before the cleaning of the ventilation ducts, and in December (2009), after they had been cleaned. Two aspects of possible improvement of effectiveness of stack ventilation were considered, namely the influence of duct cleaning, and the supportive role of window unsealing. It seems that duct cleaning considerably improves effectiveness of ventilation: minimum growth in effectiveness of stack ventilation equalled 10%, whereas maximum was up to 100%. With unsealed windows, the air change rate grew up to 30%.     

Association between ventilation rates in 390 Swedish homes and allergic symptoms in children

The aim of the study was to test the hypothesis that a low-ventilation rate in homes is associated with an increased prevalence of asthma and allergic symptoms among children. A total of 198 cases (with at least two of three symptoms: wheezing, rhinitis, eczema) and 202 healthy controls, living in 390 homes, were examined by physicians. Ventilation rates were measured by a passive tracer gas method, and inspections were carried out in the homes. About 60% of the multi-family houses and about 80% of the single-family houses did not fulfill the minimum requirement regarding ventilation rate in the Swedish building code (0.5 air changes per hour, ach). Cases had significantly lower ventilation rates than controls and a dose-response relationship was indicated. PRACTICAL IMPLICATIONS: A low-ventilation rate of homes may be a risk factor for allergies among children. Families with allergic children should be given the advice to have good ventilation in the home. In investigations, of associations between environmental factors and allergies, the air change rate in homes has to be considered.     

Changing microbial concentrations are associated with ventilation performance in Taiwan's air-conditioned office buildings

Our study conducted serial environmental measurements in 12 large office buildings with two different ventilation designs to obtain airborne microbial concentrations in typical office buildings, and to examine the effects of occupant density, ventilation type and air exchange efficiency on indoor microbial concentrations. Duplicate samples of airborne fungi and bacteria, a total of 2477 measurements, were collected based on a scheme of conducting sampling three times a day for at least seven consecutive days at every study building. Air change rates (ACHs) were also estimated by tracer gas concentration decay method, and measured by continuous Multi-Gas monitor for each building. Most sampling sites were with total fungal and bacteria concentrations higher than 1000 CFU/m(3), an often-quoted guideline in earlier research. Significantly higher concentrations of fungi and bacteria, as well as higher indoor/outdoor (I/O) ratios across most groups of airborne microbes, were identified in buildings with fan coil unit (FCU) system than those with air-handling unit (AHU) system (Student's t test, P < 0.0001). Older buildings and higher air exchange rates were statistically associated with greater indoor bacteria levels in FCU ventilated buildings (R(2) = 0.452); a pattern not found in AHU buildings. Increasing ACH seemed to be the determinant factor for rising indoor fungal and Cladosporium concentrations in those FCU buildings (R(2) = 0.346; 0.518). Our data indicated that FCU ventilated buildings might have provided more outdoor matters into indoor environments through direct penetration of outdoor air. Results also demonstrated a quantitative association between rising numbers of occupants and increasing indoor levels of yeast in both FCU and AHU ventilated buildings. The regression model identified in this study may be considered a reference value for proposing an optimal ACH, while with adequate filtration of fresh air, as an effective strategy in lowering indoor microbial concentrations in air-conditioned buildings. PRACTICAL IMPLICATIONS: As control of indoor microbial contamination has become an increasing concern around the world, feasibility and effectiveness of adopting ventilation approach has attracted a significant interest. This field investigation demonstrated, quantitatively, critical variables to be taken into consideration while applying such a measure, including the kinds of microbes to be removed and the types of ventilation system already in place.     

Evaluation of buoyancy-driven ventilation in respect of exergy utilization

Our work aimed to analyze and evaluate the buoyancy-driven ventilation based on the exergy analysis. We took the exergy load as a desired output for this consumer system and used the functional exergy efficiency to evaluate the ventilation performance. Through the numerical case studies for a high-rise building with a tall atrium, we found that the results from the energy and exergy analysis are quite different from each other, but the latter reveals the real essence of energy utilization in ventilation systems. The results showed that the exergy efficiency of the buoyancy-driven ventilation system is very poor, only 16.9% of the exergy input is effectively utilized and the exergy destruction counts for 83.1% of the total input. However, the exergy efficiency of the mechanical ventilation system is 100% because the input shaft work is entirely utilized to undertake the exergy load; no extra exergy losses are produced. We also analyzed the relationships between the temperature difference and the exergy efficiency. Furthermore, we found that the total radiation-to-exergy efficiency is 3.5 and 15% for ventilation systems equipped with solar collectors and solar cells respectively, it is concluded preliminarily that the latter is more efficient to utilize solar energy to create ventilation.     

Determination of particle concentration in the breathing zone for four different types of office ventilation systems

Many factors affect the airflow patterns, thermal comfort, contaminant removal efficiency and indoor air quality at individual workstations in office buildings. In this study, four ventilation systems were used in a test chamber designed to represent an area of a typical office building floor and reproduce the real characteristics of a modern office space. Measurements of particle concentration and thermal parameters (temperature and velocity) were carried out for each of the following types of ventilation systems: (a) conventional air distribution system with ceiling supply and return; (b) conventional air distribution system with ceiling supply and return near the floor; (c) underfloor air distribution system; and (d) split system. The measurements aimed to analyse the particle removal efficiency in the breathing zone and the impact of particle concentration on an individual at the workstation. The efficiency of the ventilation system was analysed by measuring particle size and concentration, ventilation effectiveness and the indoor/outdoor ratio. Each ventilation system showed different airflow patterns and the efficiency of each ventilation system in the removal of the particles in the breathing zone showed no correlation with particle size and the various methods of analyses used.     

The impacts of ventilation strategies and facade on indoor thermal environment for naturally ventilated residential buildings in Singapore

The impacts of various ventilation strategies and facade designs on indoor thermal environment for naturally ventilated residential buildings in Singapore are investigated in this study based on thermal comfort index. Four ventilation strategies, nighttime-only ventilation, daytime-only ventilation, full-day ventilation and no ventilation were evaluated for hot-humid climate according to the number of thermal discomfort hours in the whole typical year on the basis of a series of TAS simulations. Parametric studies of facade designs on orientations, window to wall ratios and shading devices were performed for two typical weeks by coupled simulations between building simulation ESP-r and CFD (FLUENT). The results indicate that full-day ventilation for indoor thermal comfort is better than the other three ventilation strategies. With various facade design studies, it was found that north- and south-facing facades can provide much comfortable indoor environment than east- and west-facing facades in Singapore. It is recommended that optimum window to wall ratio 0.24 can improve indoor thermal comfort for full-day ventilation and 600 mm horizontal shading devices are needed for each orientation in order to improve thermal comfort in further.     

重庆市嘉华隧道通风系统设计

结合工程实际情况,对目前重庆主城区最大隧道嘉华隧道的通风方式选择、需风量计算、风机组合设计等具体过程以及火灾时的通风控制进行了介绍,以满足车辆正常行驶条件下的隧道需风量。     

Effects of pollution from personal computers on perceived air quality, SBS symptoms and productivity in offices

In groups of six, 30 female subjects were exposed for 4.8 h in a low-polluting office to each of two conditions--the presence or absence of 3-month-old personal computers (PCs). These PCs were placed behind a screen so that they were not visible to the subjects. Throughout the exposure the outdoor air supply was maintained at 10 l/s per person. Under each of the two conditions the subjects performed simulated office work using old low-polluting PCs. They also evaluated the air quality and reported Sick Building Syndrome (SBS) symptoms. The PCs were found to be strong indoor pollution sources, even after they had been in service for 3 months. The sensory pollution load of each PC was 3.4 olf, more than three times the pollution of a standard person. The presence of PCs increased the percentage of people dissatisfied with the perceived air quality from 13 to 41% and increased by 9% the time required for text processing. Chemical analyses were performed to determine the pollutants emitted by the PCs. The most significant chemicals detected included phenol, toluene, 2-ethylhexanol, formaldehyde, and styrene. The identified compounds were, however, insufficient in concentration and kind to explain the observed adverse effects. This suggests that chemicals other than those detected, so-called 'stealth chemicals', may contribute to the negative effects. PRACTICAL IMPLICATIONS: PCs are an important, but hitherto overlooked, source of pollution indoors. They can decrease the perceived air quality, increase SBS symptoms and decrease office productivity. The ventilation rate in an office with a 3-month-old PC would need to be increased several times to achieve the same perceived air quality as in a low-polluting office with the PC absent. Pollution from PCs has an important negative impact on the air quality, not only in offices but also in many other spaces, including homes. PCs may have played a role in previously published studies on SBS and perceived air quality, where PCs were overlooked as a possible pollution source in the indoor environment. The fact that the chemicals identified in the office air and in the chamber experiments were insufficient to explain the adverse effects observed during human exposures illustrates the inadequacy of the analytical chemical methods commonly used in indoor air quality investigations. For certain chemicals the human senses are much more sensitive than the chemical methods routinely used in indoor air quality investigations. The adverse effects of PC-generated air pollutants could be reduced by modifications in the manufacturing process, increased ventilation, localized PC exhaust, or personalized ventilation systems.     

Effects of the solid curtains on natural ventilation performance in a subway tunnel

Solid curtains can be installed in subway tunnels for the promotion of air ventilation in ventilation ducts in association with the piston effect caused by a running train. With an aim to analyze the effects of solid curtains on duct ventilation performance in a subway tunnel, the current study adopts the tunnel and subway train geometries which are exactly the same as those in a previous model tunnel experiment, but newly incorporates two ventilation ducts connected vertically to the tunnel ceiling and two solid curtains placed at an upstream position of a duct near the tunnel inlet and at a downstream position of another duct near the tunnel outlet, respectively. A three-dimensional CFD model adopting the dynamic layering method for tracking the motion of a train, which was validated against the reported model tunnel experiment in a previous study, is employed to predict the train-induced unsteady airflows in the subway tunnel and in the ducts. The numerical results reveal that the duct ventilation performance in a subway tunnel strongly depends on the operation of the solid curtains. The suction mass flow of the air through the duct near the tunnel inlet and the exhaust mass flow of the air through the duct near the tunnel outlet are increased considerably in the case with the solid curtains in comparison with those in the case without the solid curtains.     

Air flow behavior and gas dispersion in the recirculation ventilation system of a twin-tunnel construction

Forced ventilation and recirculation systems are usually used in the construction of long twin tunnels as they offer large amounts of fresh air economically. However, because of the confluence near the cross-aisle, the fluid behavior and gas concentration are very different than in traditional forced ventilation for a single tunnel. A three-dimensional numerical model was built to study the air flow behavior and hazardous gas dispersion near the cross-aisle of a twin-tunnel construction. Field measurements were also carried out to validate the numerical model. The results show that there is a “dead zone” ahead of the cross-aisle which has a much lower air velocity than in other parts of the twin tunnels and where hazardous gases are more concentrated and uniformly distributed. In the cross-aisle and confluence zone of the air flow-out tunnel, methane tends to gather at the top and hydrogen sulfide tends to gather at the bottom. Increasing the recirculation velocity does not eliminate the “dead zone” near the cross-aisle although it consumes a huge amount of energy. Increasing the air velocity of the duct is an effective method to improve the air quality, but it is also expensive, especially when the air duct is long. When a jet fan was placed ahead of the cross-aisle in this study, the “dead zone” was eliminated completely. With respect to the recirculation ventilation system of twin tunnels, local jet fans offer an effective and economical way to eliminate the “dead zone”.     

Impact of adaptive thermal comfort on climatic suitability of natural ventilation in office buildings

In earlier work [1], NIST developed a climate suitability analysis method to evaluate the potential of a given location for direct ventilative cooling and nighttime ventilative cooling. The direct ventilative cooling may be provided by either a natural ventilation system or a fan-powered economizer system. The climate suitability analysis is based on a general single-zone thermal model of a building configured to make optimal use of direct and/or nighttime ventilative cooling. This paper describes a new tool implementing this climate suitability methodology and its capability to consider an adaptive thermal comfort option and presents results from its application to analyze a variety of U.S. climates. The adaptive thermal comfort option has the potential to substantially increase the effectiveness of natural ventilation cooling for many U.S. cities. However, this impact is very dependent on the acceptable humidity range. If a dewpoint limit is used, the increase is significant for a dry climate such as Phoenix but much smaller for humid climates such as Miami. While ASHRAE Standard 55 does not impose a limit on humidity when using the adaptive thermal comfort option, the necessity of limiting humidity for other reasons needs to be considered.     

Effects of double skin envelopes on natural ventilation and heating loads in office buildings

The influence of natural ventilation on heating load and energy savings in a building with a double skinned envelope (DSE) was examined in this study. Field measurements and computer simulations were performed under various weather conditions. The DSE was effective for saving energy and creating natural ventilation rates under clear and partly cloudy skies. Due to insufficient irradiance, the DSE was not effective for reducing the heating load under overcast sky conditions. When natural airflow rates from the cavity space between internal and external skin to the indoor space were controlled, the southwest-facing DSE effectively reduced heating loads due to the accumulation of solar irradiance.Regression models showed that outdoor air temperature was the most significant factor governing variations in cavity temperature under all sky conditions. Computer simulations indicated that natural ventilation was practical at an appropriate supply temperature only when the sky ratio was less than 0.7. The airspace in cavity of the DSE provided additional natural ventilation rates to the indoor space and effectively reduced heating loads. Natural ventilation was available for 135 h during three winter months without consuming additional energy to heat the outdoor air. The heating load was reduced by the DSE ranged from 17.98% to 18.7% depending on the airflow control options for the cavity space.     

浅议工业厂房通风空调设计中的几个问题

分析了现代工业建筑的基本形式与特点,阐述了工业厂房通风空调系统设计中常见的几个问题,重点探讨了如何既节能又有效地改善高大空调厂房的室内空气品质以及防爆空调厂房通风空调系统的设计方法。