KW Tham

National University of Singapore, Department of Building, Faculty Member

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Papers by KW Tham

Effects of outdoor air supply rates on call handling performance in three call centers in the tropics

Evaluating IAQ effects on people

Association Between PM2.5 Exposure in Child Care Centers and Wheeze Among Young Children in Singapore

Epidemiology, 2007

Improving the design process using simulations and multi-criteria decision making

This paper introduces a newly developed multicriteria decision making tool called RR-PARETO and i... more This paper introduces a newly developed multicriteria decision making tool called RR-PARETO and its application to HVAC design. As an illustration, five criteria have been selected, namely, power consumption, thermal comfort, risk of infection of influenza and tuberculosis and effective differential temperature (Δt eq) of body parts, with the objective of selecting the optimal air exchange rate that makes reasonable trade-offs among the criteria. Two scenarios have been studied:(i) an influenza outbreak with the objective to prevent the spread of infection, and (ii) energy prices are high and the primary objective is to reduce mean load.

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The greening of Singapore's national estate

Habitat International, 1997

This paper presents the unique but achievable case of Singapore's concern for its physical enviro... more This paper presents the unique but achievable case of Singapore's concern for its physical environment by adopting an innovation-managing approach to enhance the practice of effective environmental management. The country's built environment is treated as the estate of the nation, largely because of the indirect influence of government in the physical planning regime with an emphasis on carefully integrated urban design, and of the direct influence of government in the provision of physical infrastructure through government agencies. These have facilitated a synergistic response by the local community comprising policy makers, businesses, industries, citizens and residents, in making environmental management a way of life in Singapore.

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Active Control of Indoor Environment Quality

Automation and Robotics in Construction ― Proceedings of the 24th International Symposium on Automation and Robotics in Construction, 2007

This paper presents a methodology for the integrated control of Indoor Environmental Quality. The... more This paper presents a methodology for the integrated control of Indoor Environmental Quality. The most important aspect of the methodology is the treatment of the task as a multi-objective optimization problem. Appropriate control actions that achieve reasonable tradeoffs among conflicting objectives are selected through multi-objective optimization in which predictive models are trained using machine learning techniques. The methodology is currently being implemented and tested in the Field Environmental Chambers (FEC) of the

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Ventilation effectiveness and contaminant distribution in an occupied space conditioned with low exergy ventilation technologies in the tropics

Low exergy concept can be implemented in air conditioning system of the tropical buildings throug... more Low exergy concept can be implemented in air conditioning system of the tropical buildings through a reduction of the difference between operational temperature of cooling system and indoor space whilst meeting thermal comfort requirements. Decentralized dedicated outdoor air system (DDOAS) coupled with radiant cooling system (RCS) are low exergy designs which can potentially reduce exergy destruction in cooling system of buildings while providing adequate air quality for occupants. In this study, ventilation effectiveness of a DDOAS-RCS design with floor supply – ceiling exhaust (FS-CE) and radiant ceiling panel has been investigated in an experimental setup located in Singapore. Air change efficiency (ACE) and contaminant removal effectiveness (CRE) of the designed system have been determined using tracer gas step down test under various ventilation rates. The results showed that ACE of DDOAS-RCS design with FS-CE distribution is close to that of mixing strategy and there is no si...

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Associations of Plasticized Wall and Floor Coverings With Asthma and Allergies Among Tropical Preschool Children

Epidemiology, 2007

On the associations of fungal levels in child care centers with wheeze and rhinitis symptoms among attending preschool children

On the associations of fungal levels in child care centers with wheeze and rhinitis symptoms amon... more

Airflow Dynamics of Coughing in Healthy Human Volunteers by Shadowgraph Imaging: An Aid to Aerosol Infection Control

PLoS ONE, 2012

Cough airflow dynamics have been previously studied using a variety of experimental methods. In t... more Cough airflow dynamics have been previously studied using a variety of experimental methods. In this study, real-time, noninvasive shadowgraph imaging was applied to obtain additional analyses of cough airflows produced by healthy volunteers. Twenty healthy volunteers (10 women, mean age 32.2612.9 years; 10 men, mean age 25.362.5 years) were asked to cough freely, then into their sleeves (as per current US CDC recommendations) in this study to analyze cough airflow dynamics. For the 10 females (cases 1-10), their maximum detectable cough propagation distances ranged from 0.16-0.55 m, with maximum derived velocities of 2.2-5.0 m/s, and their maximum detectable 2-D projected areas ranged from 0.010-0.11 m 2 , with maximum derived expansion rates of 0.15-0.55 m 2 /s. For the 10 males (cases 11-20), their maximum detectable cough propagation distances ranged from 0.31-0.64 m, with maximum derived velocities of 3.2-14 m/s, and their maximum detectable 2-D projected areas ranged from 0.04-0.14 m 2 , with maximum derived expansion rates of 0.25-1.4 m 2 /s. These peak velocities were measured when the visibility of the exhaled airflows was optimal and compare favorably with those reported previously using other methods, and may be seen as a validation of these previous approaches in a more natural setting. However, the propagation distances can only represent a lower limit due to the inability of the shadowgraph method to visualize these cough airflows once their temperature cools to that of the ambient air, which is an important limitation of this methodology. The qualitative high-speed video footage of these volunteers coughing into their sleeves demonstrates that although this method rarely completely blocks the cough airflow, it decelerates, splits and redirects the airflow, eventually reducing its propagation. The effectiveness of this intervention depends on optimum positioning of the arm over the nose and mouth during coughing, though unsightly stains on sleeves may make it unacceptable to some.

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Single-Coil Twin-Fan Air-Conditioning and Air-Distribution System—Toward Development of a Mathematical Model of the Compartmented Coil

HVAC&R Research, 2006

ABSTRACT A new air-conditioning and air-distribution system, called the single-coil twin-fan syst... more ABSTRACT A new air-conditioning and air-distribution system, called the single-coil twin-fan system, that provides both energy efficiency and good indoor air quality was developed. It employs a unique compartmented cooling and dehumidifying coil that is fundamental in realizing the significant benefits of the system by being able to treat the outdoor air and the recirculated airstreams separately. In view of the distinctly different features of the compartmented coil, the performance prediction of such coils would have to be approached from first principles, which involves the determination of the fundamental heat and mass transfer coefficients. This paper establishes the need for a new mathematical model for the compartmented coil, outlines the underlying assumptions of classical models, and describes the formulation of an improved model. It presents a unique experimental method for determining the complex fin surface temperatures that constitute the major enhancements to the model development. Finally, the newly developed mathematical model is validated with experimental results.

Experimental investigation of the human convective boundary layer in a quiescent indoor environment

Building and Environment, 2014

This study aims to characterize human convective boundary layer (CBL) in a quiescent indoor envir... more This study aims to characterize human convective boundary layer (CBL) in a quiescent indoor environment. The study has two objectives: first, to characterize the velocity field around the thermal manikin under two ambient temperatures and body postures; and secondly, the influence of clothing insulation/ design, chair design, table positioning and seated body inclination on airflow characteristics in the breathing zone of a sitting manikin is examined. The increase of the ambient temperature from 20 to 26 C widens the CBL flow in front of the sitting manikin but do not influence the shape of the CBL in front of the standing manikin. The same temperature increase causes the reduction of the CBL mean peak velocity from 0.24 to 0.16 m/s in front of the sitting manikin. Dressing the nude manikin with thin-tight clothing ensemble reduces the peak velocity in the breathing zone from 0.205 m/s by 17%, and by 40% for thick-loose ensemble. Removing the wig increases the peak velocity from 0.17 to 0.187 m/s. Clothing and chair design have a minor influence on the velocity profile beyond 5 cm distance from the body. Closing the gap between the table and the manikin reduces the peak velocity from 0.17 to 0.111 m/s. Manikin leaned backwards induces the peak velocity of 0.185 m/s, which is 45% above the case when manikin is leaned forward. PIV measurements complemented with Pseudo color visualization (PCV) technique provide a good synergy between quantitative and qualitative airflow characteristics and can be adequately employed for the CBL investigation.

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A preference driven multi-criteria optimization tool for HVAC design and operation

Energy and Buildings, 2012

This paper discusses the issue of selecting the design solution that best accords with an articul... more This paper discusses the issue of selecting the design solution that best accords with an articulated preference of multiple criteria with an acceptable performance band. The application of a newly developed multi-criteria decision-making tool called RR-PARETO2 is presented. An example of HVAC design is used to illustrate how solutions could be selected within a multi-criteria optimization framework. In this example, five criteria have been selected, namely, power consumption, thermal comfort, risk of airborne infection of influenza and tuberculosis and effective differential temperature (t eq) of body parts. The goal is to select the optimal air exchange rate that makes reasonable trade-offs among all the objectives. Two scenarios have been studied. In the first scenario, there is an influenza outbreak and the important objective is to prevent the spread of infection. In the second scenario, energy prices are high and the primary objective is to reduce energy. In both scenarios, RR-PARETO2 algorithm selects solutions that make reasonable trade-offs among conflicting objectives. The example illustrates how objectives such as reduction of airborne disease transmission and maximizing thermal comfort can be incorporated in the design of a practical, full-scale HVAC system.

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Characterizing exhaled aerosol droplets during influenza A and B infections, and viral hemagglutinin phylogenetic analyses in a university cohort

International Journal of Infectious Diseases

negative for Vibrio cholerae, salmonella and shigella. There was also leakage in the public water... more negative for Vibrio cholerae, salmonella and shigella. There was also leakage in the public water pipe line and water specimens showed coliforms. Conclusion: The investigation suggested that this acute gastroenteritis outbreak is due to the consumption of contaminated water from the damaged public water pipeline. The public water pipeline was repaired, chlorinated and residences were educated.

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Assessment of thermal environment using a thermal manikin in a field environment chamber served by displacement ventilation system

Building and Environment, 2006

This paper presents a thermal comfort study using a thermal manikin in a field environment chambe... more This paper presents a thermal comfort study using a thermal manikin in a field environment chamber served by the Displacement Ventilation (DV) system. The manikin has a female body with 26 individually heated and controlled body segments. The manikin together with subjects was exposed to 3 levels of vertical air temperature gradients, nominally 1, 3 & 5 K/m, between 0.1 and 1.1 m heights at 3 room air temperatures of 20, 23 and 26 1C at 0.6 m height. Relative humidity at 0.6 m height and air velocity near the manikin and the subjects were maintained at 50% and less than 0.2 m/s, respectively. The aims of this study are to assess thermally non-uniform environment served by DV system using the manikin and correlate the subjective responses with measurements from the manikin. The main findings indicate that room air temperature had greater influence on overall and local thermal sensations and comfort than temperature gradient. Local thermal discomfort decreased with increase of room air temperature at overall thermally neutral state. The local discomfort was affected by overall thermal sensation and was lower at overall thermally neutral state than at overall cold and cool sensations.

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Call-centre operator performance with new and used filters at two outdoor air supply rates

Lessons from SARS in an age of emerging infections

La Medicina del lavoro, 2006

SARS, the first pandemic of this century, commanded the world's attention and required public... more SARS, the first pandemic of this century, commanded the world's attention and required public health actions at the national and international levels. In an age of emerging infections, the lessons learnt from combating SARS can be used to improve our preparedness capabilities in three key areas to effectively tackle a public health emergency of international concern. The first area is in outbreak alert, which encompasses use of surveillance to detect, assess, notify and report events involving death or disease, and share information widely to enable proper risk assessment. The system must able to build up a comprehensive picture with appropriate warning for zoonotic diseases, environmental health and food safety. The second area is in public health response. In the event of an outbreak alert, the authorities must be able to quickly investigate cases/deaths and institute comprehensive control measures to break the chain of transmission. Protection of healthcare workers and reduci...

Performance characteristics of a fan filter unit (FFU) in mitigating particulate matter levels in a naturally ventilated classroom during haze conditions

Indoor Air

The performance of a low cost Fan Filter Unit (FFU) in mitigating hazardous Particulate Matter (P... more The performance of a low cost Fan Filter Unit (FFU) in mitigating hazardous Particulate Matter (PM) levels in a naturally ventilated school classroom is presented. The FFU can be considered as a simplified Mechanical Ventilation and Air-conditioning system without heating and cooling functions. The FFU improves indoor air quality through introduction of cleaned outdoor air to flush out internally generated heat and moisture and reducing infiltration by maintaining indoor pressurization. Indoor Particle number concentrations was reduced between 85 to 95%. The particle removal performance (PRFFFU ) of the FFU is determined and incorporated into the augmented façade penetration factor (Paug ). A case specific recursive dynamic mass balance model is used to characterise the infiltration factor (FINF ), deposition rate (K) and the penetration efficiency (Paug ) from continuously monitored indoor and outdoor mass concentration levels. Computed 'Paug ' (0.07, 0.09 and 0.13) 'FINF ' (0.06, 0.08 and 0.11) respectively for PM10, PM2.5 and PM1 suggest that exposure to PM was significantly reduced indoors. The effectiveness of the FFU for reduced 'FINF ' and 'Paug ' may be attributed to its superior filtration, dilution and exfiltration mechanisms. In comparison with alternative PM mitigation solutions, the FFU is effective, affordable and sustainable.

PROBER—a design system based on design prototypes

A knowledge-based design system for routine design, acronymed PROBER, is described. PROBER assist... more A knowledge-based design system for routine design, acronymed PROBER, is described. PROBER assists routine design by drawing on design prototypes which have recently been proposed as schemas for capturing design knowledge integrally and comprehensively. By appealing to design prototypes, PROBER supports design commencement, continuation and exploration. Underlying PROBER is a process model of design which focuses on reasoning among function, behaviour and structure. The architecture of PROBER and its implementation are presented in detail.

Home air‐conditioning, traffic exposure, and asthma and allergic symptoms among preschool children

Pediatric Allergy and …, 2011

Epidemiological data suggest that traffic exposures can influence asthma and allergic symptoms am... more Epidemiological data suggest that traffic exposures can influence asthma and allergic symptoms among preschool children; however, there is no information on risk reduction via home airconditioning (AC). The aim of this study is to evaluate the associations of self-reported traffic densities with asthma and allergic symptoms among preschool children and determine whether AC is an effect modifier. A crosssectional study adopting an expanded and modified ISAAC-International Study of Asthma and Allergies in Childhood conducted on randomly selected 2994 children living in homes without any indoor risk factors. Specific information on demographics, indoor home risk factors, and traffic variables were obtained. Adjusted prevalence ratios (PR) and 95% confidence interval (CI) were determined by Cox proportional hazard regression model with assumption of a constant risk period controlled for covariates. We found dose-response significant relationships between validated self-reported traffic densities and asthma and rhinitis symptoms. Among children sleeping in non-air-conditioned homes, there were stronger associations between asthma and rhinitis symptoms studied. PRs for heavy traffic density were 2.06 for wheeze (95% CI 0.97-4.38), 2.89 for asthma (1.14-7.32), 1.73 for rhinitis (1.00-2.99), and 3.39 for rhinoconjunctivitis (1.24-9.27). There were no associations found for children sleeping in air-conditioned homes. Our results suggest that AC in the bedroom modifies the health effects of traffic among preschool children. This finding suggests that attention should also be paid to ventilation characteristics of the homes to remediate health-related traffic pollution problems.

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