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.     

Using the adaptive model of thermal comfort for obtaining indoor neutral temperature: Findings from a field study in Hyderabad,India

There is a dearth of thermal comfort studies in India. It is aimed to investigate into the aspects of thermal comfort in Hyderabad and to identify the neutral temperature in residential environments. This was achieved through a thermal comfort field study in naturally ventilated apartment buildings conducted during summer and monsoon involving over 100 subjects. A total of 3962 datasets were collected covering their thermal responses and the measurement of the thermal environment. The comfort band (voting within –1 and +1), based on the field study, was found to be 26–32.45°C, with the neutral temperature at 29.23°C. This is way above the indoor temperature standards specified in Indian Codes. It was found that the regression neutral temperature and the globe temperature recorded when voting neutral converged when mean thermal sensation of the subjects was close to 0. This happened during the period of moderate temperature when the adaptive measures were adequate. The indoor temperatures recorded in roof-exposed (top floor) flats were higher than the lower floors. The thermal sensation and preference votes of subjects living in top floors were always higher. Consequently, their acceptance vote was also lower. It was found that the subjects living in top floor flats had a higher neutral temperature when the available adaptive opportunities were sufficient. This was due to their continuous exposure to a higher thermal regime due to much higher solar exposure. This study calls for special adaptive measures for roof-exposed flats to achieve neutrality at higher temperature.     

Three dimensional study for evaluating of air flow movements and thermal comfort in a model room: Experimental validation

This paper presents the results of a three dimensional study for evaluating the temperature profiles and air flow movement in a model room with a numerical model based on the Euler equations. Numerical results obtained for two scenarios of ventilation and air conditioning are compared with the predictions of a Navier-Stokes model. These numerical results are validated by experimental results measured in the model room. A comparison of the local thermal comfort indices PMV and PPD obtained experimentally and numerically is also presented. Results show that the Euler model is able to predict adequately total thermal comfort in the model room. Furthermore, the use of Euler equations allows a reduction of computational time in the order of 50% compared to the Navier-Stokes modeling.     

Passive environment control system of Kerala vernacular residential architecture for a comfortable indoor environment: A qualitative and quantitative analyses

The modern day practice does not give due respect to passive and natural environment control measures in buildings. With modern materials and technology, the buildings of present architectural style results in high energy consumption, in an attempt to provide thermal comfort indoors. The vernacular architecture at any place on the other hand has evolved through ages by consistent and continuous effort for more efficient and perfect solutions. The authors have conducted a qualitative analysis of the passive environment control system of vernacular residential architecture of Kerala that is known for ages for its use of natural and passive methods for a comfortable indoor environment. The orientation of building, internal arrangement of spaces, the presence of internal courtyard, use of locally available materials and special methods of construction, etc. have together created the indoor environment. A quantitative analysis was also carried out based on field experiments by recording thermal comfort parameters in a selected building. The study has provided positive results confirming that the passive environment control system employed in Kerala vernacular architecture is highly effective in providing thermal comfort indoors in all seasons.     

Evidence of inadequate ventilation in portable classrooms: results of a pilot study in Los Angeles County

The prevalence of prefabricated, portable classrooms (portables) for United States public schools has increased; in California, approximately one of three students learn inside portables. Limited research has been conducted on indoor air and environmental quality in American schools, and almost none in portables. Available reports and conference proceedings suggest problems from insufficient ventilation due to poor design, operation, and/or maintenance of heating, ventilation and air conditioning (HVAC) systems; most portables have one mechanical, wall-mounted HVAC system. A pilot assessment was conducted in Los Angeles County, including measurements of integrated ventilation rates based on a perfluorocarbon tracer gas technique and continuous monitoring of temperature (T) and relative humidity (RH). Measured ventilation rates were low [mean school day integrated average 0.8 per hour (range: 0.1-2.9 per hour)]. Compared with relevant standards, results suggested adequate ventilation and associated conditioning of indoor air for occupant comfort were not always provided to these classrooms. Future school studies should include integrated and continuous measurements of T, RH, and ventilation with appropriate tracer gas methods, and other airflow measures. PRACTICAL IMPLICATIONS: Adequate ventilation has the potential to mitigate concentrations of chemical pollutants, particles, carbon dioxide, and odors in portable and traditional classrooms, which should lead to a reduction in reported health outcomes, e.g., symptoms of 'sick building syndrome', allergies, asthma. Investigations of school indoor air and environmental quality should include continuous temperature and relative humidity data with inexpensive instrumentation as indicators of thermal comfort, and techniques to measure ventilation rates.     

A neuro-fuzzy model for prediction of the indoor temperature in typical Australian residential buildings

The Masonry Research Group at The University of Newcastle, Australia has embarked on an extensive research program to study the thermal performance of common walling systems in Australian residential buildings by studying the thermal behaviour of four representative purpose-built thermal test buildings (referred to as ‘test modules’ or simply ‘modules’ hereafter). The modules are situated on the university campus and are constructed from brick veneer (BV), cavity brick (CB) and lightweight (LW) constructions. The program of study has both experimental and analytical strands, including the use of a neuro-fuzzy approach to predict the thermal behaviour. The latter approach employs an experimental adaptive neuro-fuzzy inference system (ANFIS) which is used in this study to predict the room (indoor) temperatures of the modules under a range of climatic conditions pertinent to Newcastle (NSW, Australia). The study shows that this neuro-fuzzy model is capable of accurately predicting the room temperature of such buildings; thus providing a potential computationally efficient and inexpensive predictive tool for the more effective thermal design of housing.     

Passive control methods of Kerala traditional architecture for a comfortable indoor environment: Comparative investigation during various periods of rainy season

The traditional architecture of Kerala, a state in India lying along its southwest coast, is known for its use of natural and passive methods for a comfortable indoor environment. Although there have been attempts to analyze the traditional architecture of Kerala, they were focused only on qualitative approach. An investigation was thus initiated by the authors to understand the passive environment control system of Kerala traditional architecture in providing better thermal comfort, by continuously monitoring thermal comfort parameters of a typical traditional residential building over a period of time. The inferences of the first phase of the investigation carried out during winter and summer seasons, lasting about half of the year have already been published. This paper illustrates the inferences of the second phase of the investigation that is carried out during the rainy season of the year. A comparative analysis with the results of the winter and summer periods is also incorporated. The investigation has revealed that, when the outside ambient temperature is below normal, the building system tries to maintain the indoor air temperature at a higher but comfortable level and when the outside temperature is above normal, the indoor is kept at a lower but comfortable level. It is found that a continuous gentle wind flow is maintained inside the building irrespective of the wind outside. The required level of thermal comfort is achieved by maintaining a balanced level of temperature and relative humidity along with a continuous and controlled airflow inside the building irrespective of seasons.     

The effects of night ventilation technique on indoor thermal environment for residential buildings in hot-humid climate of Malaysia

This study investigates the effectiveness of night ventilation technique for residential buildings in hot-humid climate of Malaysia. This paper firstly presents the results of a survey on usage patterns of windows and air-conditioners in typical Malaysian residential areas. Secondly, the effects of different natural ventilation strategies on indoor thermal environment for Malaysian terraced houses are evaluated based on the results of a full-scale field experiment. The results show that the majority of occupants tend to apply not night ventilation but daytime ventilation in Malaysian residential areas. It can be seen from the field experiment that night ventilation would provide better thermal comfort for occupants in Malaysian terraced houses compared with the other ventilation strategies in terms of operative temperature. However, when the evaporative heat loss of occupants is taken into account by using SET*, the night ventilation would not be the superior technique to the others in providing daytime thermal comfort mainly due to the high humidity conditions. Therefore, the indoor humidity control during the daytime such as by dehumidification would be needed when the night ventilation technique is applied to Malaysian terraced houses. Otherwise, full-day ventilation would be a better option compared with night ventilation.     

Local thermal sensation and comfort study in a field environment chamber served by displacement ventilation system in the tropics

This paper presents a study of local thermal sensation (LTS) and comfort in a field environmental chamber (FEC) served by displacement ventilation (DV) system. The FEC, 11.12 m (L)×7.53 m (W)×2.60 m (H), simulates a typical office layout. A total of 60 tropically acclimatized subjects, 30 male and 30 female, were engaged in sedentary office work for 3 h. Subjects were exposed to three vertical air temperature gradients, nominally 1, 3 and 5 K/m, between 0.1 and 1.1 m heights and three room air temperatures of 20, 23 and 26 °C at 0.6 m height. The objective of this study is to investigate the mutual effect of local and overall thermal sensation (OTS) and comfort in DV environment. The results show that in a space served by DV system, at OTS close to neutral, local thermal discomfort decreased with the increase of room air temperature. The OTS of occupants was mainly affected by LTS at the arm, calf, foot, back and hand. Local thermal discomfort was affected by both LTS and OTS. At overall cold thermal sensation, all body segments prefer slightly warm sensation. At overall slightly warm thermal sensation, all body segments prefer slightly cool sensation.     

A field study of the thermal comfort in residential buildings in Harbin

This field study was performed during the winter of 2000–2001 in order to investigate the thermal environment and thermal comfort in residential buildings in Harbin, northeast of China. A total of 120 participants provided 120 sets of physical data and subjective questionnaires. An indoor climate analyzer and a thermal comfort meter made in Denmark were used to collect the measured parameters of the indoor environment, the predicted mean vote (PMV), and predicted percentage of dissatisfied (PPD). The conclusions are as follows: males are less sensitive to temperature variations than females; the neutral operative temperature of males is 1 °C lower than that of females; Harbin subjects are as sensitive to temperature variations as the Beijing and Tianjin subjects; the minimum value of PPD (7.5%) is similar to the Tianjin occupants; both the sensitivity and the minimum value of PPD are lower than those of the foreign field studies.     

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.     

居住建筑室内热环境低能耗营造的多目标设计方法

人居环境改善涉及重大民生问题,节能减排是国家重大战略。因此,有必要寻求合理的居住建筑设计方法,使设计方案既满足居民的室内热舒适需求又能降低建筑能耗。基于多目标遗传优化算法,建立能够对建筑设计方案进行优化、实现增加室内热舒适时间比例的同时降低建筑全年冷热负荷的居住建筑设计双目标优化模型。最后,以重庆典型户型为实例进行优化,优化后的设计方案建筑全年冷热负荷降低了47.74%,室内热舒适时间比例提高了3.94%,验证了模型的可行性和准确性。     

Assessment of the microclimatic and human comfort conditions in a complex urban environment: Modelling and measurements

Several complex thermal indices (e.g. Predicted Mean Vote and Physiological Equivalent Temperature) were developed in the last decades to describe and quantify the thermal environment of humans and the energy fluxes between body and environment. Compared to open spaces/landscapes the complex surface structure of urban areas creates an environment with special microclimatic characteristics, which have a dominant effect on the energy balance of the human body. In this study, outdoor thermal comfort conditions are examined through two field-surveys in Szeged, a South-Hungarian city (population 160,000). The intensity of radiation fluxes is dependent on several factors, such as surface structure and housing density. Since our sample area is located in a heavily built-up city centre, radiation fluxes are mainly influenced by narrow streets and several 20–30-year-old (20–30 m tall) trees. Special emphasis is given to the human-biometeorological assessment of the microclimate of complex urban environments through the application of the thermal index PET. The analysis is carried out by the utilization of the RayMan model. Firstly, bioclimatic conditions of sites located close to each other but shaded differently by buildings and plants are compared. The results show that differences in the PET index amongst these places can be as high as 15–20 ^°C${}^{°}\mathrm{C}$ due to the different irradiation. Secondly, the investigation of different modelled environments by RayMan (only buildings, buildings+trees$\mathrm{buildings}+\mathrm{trees}$ and only trees) shows significant alterations in the human comfort sensation between the situations.     

Effect of age, gender, economic group and tenure on thermal comfort: A field study in residential buildings in hot and dry climate with seasonal variations

Energy consumption in Indian residential buildings is one of the highest and is increasing phenomenally. Indian standards specify comfort temperatures between 23 and 26 °C for all types of buildings across the nation. However, thermal comfort research in India is very limited. A field study in naturally ventilated apartments was done in 2008, during the summer and monsoon seasons in Hyderabad in composite climate. This survey involved over 100 subjects, giving 3962 datasets. They were analysed under different groups: age, gender, economic group and tenure. Age, gender and tenure correlated weakly with thermal comfort. However, thermal acceptance of women, older subjects and owner-subjects was higher. Economic level of the subjects showed significant effect on the thermal sensation, preference, acceptance and neutrality. The comfort band for lowest economic group was found to be 27.3-33.1 °C with the neutral temperature at 30.2 °C. This is way above the standard. This finding has far reaching energy implications on building and HVAC systems design and practice. Occupants’ responses for other environmental parameters often depended on their thermal sensation, often resulting in a near normal distribution. The subjects displayed acoustic and olfactory obliviousness due to habituation, resulting in higher satisfaction and acceptance.     

Perception of the thermal environment in high school and university classrooms: Subjective preferences and thermal comfort

This work shows some of the results of a field study about environmental comfort investigations in classrooms. In this project thermal, acoustic, visual and air quality aspects were analysed in a number of classrooms—13 classrooms at four different high schools of the Provincia di Torino and four typical medium-sized university classrooms of the Politecnico di Torino, Italy. The investigations were carried out during the heating period. Both field measurements and subjective surveys were performed at the same time during the regular lesson periods.     

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.     

Application of computational fluid dynamics in building performance simulation for the outdoor environment: an overview

This article provides an overview of the application of computational fluid dynamics (CFD) in building performance simulation for the outdoor environment, focused on four topics: (1) pedestrian wind environment around buildings, (2) wind-driven rain on building facades, (3) convective heat transfer coefficients at exterior building surfaces and (4) air pollutant dispersion around buildings. For each topic, its background, the need for CFD, an overview of some past CFD studies, a discussion about accuracy and some perspectives for practical application are provided. This article indicates that for all four topics, CFD offers considerable advantages compared with wind tunnel modelling or (semi-)empirical formulae because it can provide detailed whole-flow field data under fully controlled conditions and without similarity constraints. The main limitations are the deficiencies of steady Reynolds-averaged Navier–Stokes modelling, the increased complexity and computational expense of large eddy simulation and the requirement of systematic and time-consuming CFD solution verification and validation studies.     

An internal assessment of the thermal comfort and daylighting conditions of a naturally ventilated building with an active glazed facade in a temperate climate

An active facade is often used to promote the flow of air through a building, however in order to ensure that this process is effective the facade should face a southerly orientation. This means that not only solar energy is transferred across the glazing but in sunny periods shading is needed to prevent excess brightness levels occurring on the working areas where it may result in the luminance distributions not complying with current lighting requirements. The building investigated is located in Sheffield, England and is one of the University of Sheffield's recently built green buildings. It has a high thermal mass which is used to promote the use of night cooling. This paper reports the initial findings of an internal assessment of the thermal comfort and daylighting conditions in such a building. The results have indicated that such designs are to be commended for their passive use of solar energy and can provide a high quality working environment.     

A study of perceived air quality and sick building syndrome in a field environment chamber served by displacement ventilation system in the tropics

This paper presents a study of Perceived Air Quality (PAQ) and Sick Building Syndrome (SBS) using tropically acclimatized subjects in a Field Environmental Chamber (FEC) served by Displacement Ventilation (DV) system. The FEC, 11.12 m (L)×7.53 m (W)×2.60 m (H), simulates a typical office layout. A total of 60 subjects, 30 males and 30 females, were engaged in sedentary office work for 3 h. Air velocity in the space near the subjects was kept at below 0.2 m/s. Relative Humidity (RH) at 0.6 m height and outdoor air provision were maintained at 50% and 10 l/s/p, respectively. Subjects were exposed to three vertical air temperature gradients, nominally 1, 3 and 5 K/m, between 0.1 and 1.1 m heights and three room air temperatures 20, 23 and 26 °C at 0.6 m height. The main objective of this study is to evaluate the influence of temperature gradient and room air temperature (at 0.6 m height) on PAQ and SBS in DV environment. It was found that temperature gradient had insignificant impact on PAQ and SBS. Dry air sensation, irritations and air freshness decreased with increase of room air temperature.