S.C. Sekhar

Thermal comfort study of an air-conditioned lecture theatre in the tropics

Abstract This paper evaluates the current thermal comfort conditions of an air-conditioned lecture theatre in a tertiary institution using objective measurement, computational fluid dynamics (CFD) modelling and subjective assessment. A CFD tool was used to simulate the indoor comfort parameters, such as temperature, airflow rate and relative humidity. Corroboration between results from the field measurements and predicted values was conducted. It was found that the measured air temperatures, air velocities and relative humidities were within the limits of thermal comfort standards, although temperature and relative humidity were located at the extreme of the limits. The predicted results showed good distributions of airflow characteristics and temperature gradients, and these were in fair agreement with empirical measurements. The overall comfort vote, predicted mean vote and predicted percentage dissatisfied indices found the occupants to be slightly uncomfortable and dissatisfied. Additionally, recommendations were made to improve the thermal comfort condition and reduce the build-up of concentration of carbon dioxide in the lecture theatre.

Measurements and computations of contaminant's distribution in an office environment

Abstract This paper investigates the dispersion of contaminants in an office environment using empirical and modeling techniques. The experiment was conducted in an environmental test facility with the mock-up of two typical office layouts. Layout 1 has two workstations located in the middle of the room and separated by a low-level partition, while Layout 2 has a low level-partition which separates the room into two halves with one workstation at each corner. The test facility, 6.6 m (L)×3.7 m (W)×2.6 m (H) , is served by an air-conditioning and mechanical ventilation (ACMV) system which is capable of controlling the air temperature and airflow rates at the supply diffuser and extract grille. The contaminants emission was generated by a constant injection of tracer gas, sulfur hexafluoride (SF6), via a 280 mm ×200 mm surface to represent the plane source. The concentration of contaminant in the chamber for both the layouts was measured and simulated using a gas analyzer and a computational fluid dynamic (CFD) program with the Re-Normalization Group k–e model, respectively. In general, the predicted concentration of contaminant was in good correlation with the measured concentration. However, the predicted results were always marginally lower than the measured results. The contaminants dispersion pattern was observed to be highly dependent on the velocity flow field. The layout of furniture influenced the airflow pattern and contaminants distribution in the office. On the whole, Layout 1 was better than Layout 2 with a lower level of contaminant at the occupants breathing zones.

Ceiling‐mounted personalized ventilation system integrated with a secondary air distribution system – a human response study in hot and humid climate

UNLABELLED The benefits of thermal comfort and indoor air quality with personalized ventilation (PV) systems have been demonstrated in recent studies. One of the barriers for wide spread acceptance by architects and HVAC designers has been attributed to challenges and constraints faced in the integration of PV systems with the work station. A newly developed ceiling-mounted PV system addresses these challenges and provides a practical solution while retaining much of the apparent benefits of PV systems. Assessments of thermal environment, air movement, and air quality for ceiling-mounted PV system were performed with tropically acclimatized subjects in a Field Environmental Chamber. Thirty-two subjects performed normal office work and could choose to be exposed to four different PV airflow rates (4, 8, 12, and 16 L/s), thus offering themselves a reasonable degree of individual control. Ambient temperatures of 26 and 23.5 degrees C and PV air temperatures of 26, 23.5, and 21 degrees C were employed. The local and whole body thermal sensations were reduced when PV airflow rates were increased. Inhaled air temperature was perceived cooler and perceived air quality and air freshness improved when PV airflow rate was increased or temperature was reduced. PRACTICAL IMPLICATIONS The newly developed ceiling-mounted PV system offers a practical solution to the integration of PV air terminal devices (ATDs) in the vicinity of the workstation. By remotely locating the PV ATDs on the ceiling directly above the occupants and under their control, the conditioned outdoor air is now provided to the occupants through the downward momentum of the air. A secondary air-conditioning and air distribution system offers additional cooling in the room and maintains a higher ambient temperature, thus offering significant benefits in conserving energy. The results of this study provide designers and consultants with needed knowledge for design of PV systems.

Ventilation characteristics of an air-conditioned office building in Singapore

Abstract The primary functions of mechanical ventilation systems include the delivery of outdoor air to the occupants, the removal of indoor contaminants and the maintenance of thermal comfort conditions in the occupied zones. Air exchange effectiveness can be employed to characterise the ventilation air mixing within a room. This paper presents our findings pertaining to air exchange effectiveness values in a seven-storey office building. Tracer gas analysis, based on concentration decay method, is employed to determine these values. The results indicate air flow patterns in the occupied zones which approximate “perfect mixing”. The measured concentration levels of indoor air pollutants are also found to be within reasonable limits.

Energy simulation approach to air-conditioning system evaluation

Abstract This paper deals with the energy simulation approach in evaluating some of the commonly employed air-conditioning systems for high-rise office buildings. These systems are evaluated on the basis of their thermal comfort performance and energy efficiency. It is found that the Two Pipe Induction Unit System (TPIUS) performs the best and is the most energy efficient, followed by the Variable Air Volume System (VAVS). The thermal comfort performance of Packaged Variable Air Volume System (PVAVS) and the Constant Air Volume System (CAVS) is less preferred among all systems studied and they also appear to be the least energy efficient.

Performance evaluation of a novel personalized ventilation–personalized exhaust system for airborne infection control

In the context of airborne infection control, it is critical that the ventilation system is able to extract the contaminated exhaled air within the shortest possible time. To minimize the spread of contaminated air exhaled by occupants efficiently, a novel personalized ventilation (PV)-personalized exhaust (PE) system has been developed, which aims to exhaust the exhaled air as much as possible from around the infected person (IP). The PV-PE system was studied experimentally for a particular healthcare setting based on a typical consultation room geometry and four different medical consultation positions of an IP and a healthy person (HP). Experiments using two types of tracer gases were conducted to evaluate two types of PE: Top-PE and Shoulder-PE under two different background ventilation systems: Mixing Ventilation and Displacement Ventilation. Personalized exposure effectiveness, intake fraction (iF) and exposure reduction (ε) were used as indices to evaluate the PV-PE system. The results show that the combined PV-PE system for the HP achieves the lowest intake fraction; and the use of PE system for the IP alone shows much better performance than using PV system for the HP alone.

Thermal comfort and indoor air quality in rooms with integrated personalized ventilation and under-floor air distribution systems

A comprehensive study comprising physical measurements and human subject experiments was conducted to explore the potential for improving occupants’ thermal comfort and indoor air quality (IAQ) using a personalized ventilation (PV) system combined with an under-floor air distribution(UFAD) system. The integrated PV-UFAD system, when operated at relatively high temperature of the air supplied from the UFAD system, provided comfortable cooling of the facial region, improved inhaled air quality, and decreased the risk of “cold feet,” which is often reported in rooms with UFAD alone. This article explores associations between the physical measurements and human responses in a room served with a PV-UFAD system. The experiments were conducted in a field environmental chamber served by two dedicated systems—a primary air-handling unit (AHU) for 100% outdoor air that is supplied through the PV air terminal devices and a secondary AHU for 100% recirculated air that is supplied through UFAD outlets. Velocity and temperature distribution in the chamber were measured. A breathing thermal manikin was used to measure the heat loss from 26 body segments and to determine the equivalent temperature. The responses of 30 human subjects were collected. The experiments were performed at various combinations of room air and PV air temperatures. The results reveal improved overall thermal sensation and decrease of cold feet complaints, as well as improved inhaled air quality (including perceived air quality) with PV-UFAD in comparison with the reference case of UFAD alone or mixing ventilation with a ceiling supply diffuser. Increase of predicted draft rating with the decrease of the local thermal sensation at the feet was identified. The manikin-based equivalent temperature determined for the face was positively correlated with thermal sensation at the face region. The measured inhaled air quality indices (personalized exposure effectiveness and personalized exposure index) were improved by decreasing PV supply air temperature. The perceived inhaled air freshness increased with the decrease of the inhaled air temperature and increase of facial velocity.

Individual control of a personalized ventilation system integrated with an ambient mixing ventilation system

In this study, a set of experiments were conducted in a hot and humid climate to evaluate subjects’ behavior in operating an individually controlled personalized ventilation system. The system was equipped with individual control of airflow rate. The effect of the control system on thermal comfort and the responses of subjects were studied. Forty-six tropically acclimatized subjects participated in the experiments that were conducted in a field environment chamber served by a desk-mounted personalized ventilation system integrated with an ambient mixing ventilation system. Ambient temperatures of 23°C and 26°C (73.4°F and 78.8°F) and personalized ventilation air temperatures of 20°C, 23°C, and 26°C (68°F, 73.4°F, and 78.8°F) were employed. The results showed that more than 90% of subjects felt the thermal environment was acceptable, irrespective of the ambient temperature and personalized ventilation air temperature. Subjects’ preferred airflow rates showed a large variation from 0 to 16 L/s/person (33.9 cfm/person), which supports the case for individual control. When the ambient temperature was 26°C (78.8°F), subjects’ whole body and body parts thermal sensations were closer to neutral, which indicates that whole body thermal sensation was largely improved.

The effects of ventilation operations in determining contributions of VOCs sources in air-conditioned tropical buildings

Abstract This study analyses the findings of volatile organic compounds (VOCs) levels found in two tropical office buildings (a 1 year old and a 6 year old building) under different conditions of ventilation operations. The geometric concentrations of 11 target VOCs and TVOC have been measured under two scenarios—(1) normal occupancy with ventilation system operating and (2) when the ventilation system has completely shut down. Under the first scenario, the VOCs emission rate determined through mass balanced modeling is due to the buildings, occupants and their activities and ventilation systems. The emission from the second scenario is purely due to the building materials. Majority of the VOCs rose in concentrations after the ventilation system has shut down with exceptions for benzene, benzaldehyde and tridecane that are attributable to outdoor and occupant related activities and ventilation systems. The indoor–outdoor ( I / O ) ratio method of determining source contributions has been found to be a crude method for this case study. Instead, utilizing the ventilation-resolved mass balanced model method to evaluate contributions of sources (SER) from outdoors, building materials, occupants, their activities and ventilation systems have yielded relatively good and accurate results.

Local Discomfort Caused by Draft Perception in a Space Served by Displacement Ventilation System in the Tropics

This paper reports a subjective study in a field environmental chamber (FEC) served by a displacement ventilation (DV) system. Sixty tropically acclimatised subjects, 30 males and 30 females, were engaged in sedentary office work for 3h. The subjects were exposed to three vertical air temperature gradients (nominally 1, 3 and 5K·m 1) between 0.1 and 1.1m heights and three room air temperatures (20, 23 and 26°C) at 0.6m height. The object of this work was to investigate effects of temperature gradient and room air temperature on local discomfort due to air movement at different thermal sensations. The results indicated that vertical temperature gradient had an insignificant impact on draft perception. Draft perceptions at foot, calf, thigh and arm were affected by both overall and local thermal sensations. A cold sensation would increase the risk of draft complaints and a warm sensation would increase the percentage dissatisfied due to insufficient air movement.