Kok Wai Cheong

Development and application of an indoor air quality audit to an air-conditioned building in Singapore

Abstract Good indoor air quality (IAQ) enhances occupant health, comfort and workplace productivity. This issue has become more critical in a country like Singapore that has no other natural resources except manpower. In addition, Singapore is located in the tropical region with a hot and humid climate and a large number of the buildings are served by air-conditioning and mechanical ventilation (ACMV) systems to maintain a thermally comfortable indoor environment. The provision of a thermally comfortable indoor environment for the occupants is only one aspect in achieving better indoor air quality. Chemical pollutants, dust particles and microbials are other factors that have impact on the quality of indoor air. Pollutant emissions from people, building materials, air handling units, etc. in the form of both living and dead material take place continuously in any type of buildings, i.e., residential, commercial, industrial, institutional, etc. An IAQ audit methodology developed is adopted to establish the IAQ profile of the building. In this paper, a case-study is used to demonstrate the application of the IAQ audit and evaluate its comprehensiveness and usefulness to the building owners or facility managers. This audit was conducted in the administration offices of a hospital building. The audit consists of examination of the air exchange rate, ventilation effectiveness and age of air. Thermal comfort parameters, microbial counts, dust particles and the concentrations of carbon dioxide (CO 2 ), carbon monoxide (CO), formaldehyde (HCHO) and total volatile organic compounds (TVOC) were also monitored. In addition, a questionnaire was completed by the staff in order to provide a subjective assessment of indoor air quality.

Enhancement of natural ventilation in high-rise residential buildings using stack system

This paper describes the feasibility study on the application of passive and active stack systems to enhance natural ventilation in public housing in Singapore. About 86% of the population is staying in high-rise public housing, known as Housing and Development Board (HDB) flats, which is designed for natural ventilation. The primary objective of this work is to assess the status of natural ventilation in a typical four-room HDB flat using scaled model in the wind tunnel, and to develop an effective passive or active stack system to enhance natural ventilation in the flat. Four numbers of stacks with different sizes were tested at two locations in the flat. The study shows that the passive stack, incorporating the principle of airflow due to buoyancy, does not enhance air velocity in the flat. However, the active stack which operates based on the suction effect induced by a fan fixed at the top of the stack leads to substantial increase in the air velocity at the room and thus meeting the human’s thermal comfort condition. It was noted that the velocities increase along with the increase in the stack size.

Development and application of an indoor air quality audit to an air-conditioned tertiary institutional building in the tropics

Abstract Good indoor air quality (IAQ) in schools and tertiary institutions provides a comfortable and healthy environment for the students and staff to learn and work in, respectively. Hence, it is important to ascertain the IAQ status in the learning environment. This paper presents the development and application of an IAQ audit methodology for the tertiary institutional buildings. A staff room and a typical lecture theatre in a tertiary institution were selected for this study to present the IAQ status in premises with different occupancy pattern and internal loads. The IAQ audit consists of monitoring of thermal comfort parameters, microbial counts, dust particles and the concentrations of carbon dioxide (CO 2 ), carbon monoxide (CO), formaldehyde (HCHO) and total volatile organic compounds (TVOCs). Air exchange rate, ventilation effectiveness and age of air were also investigated. In addition, questionnaires were completed by the staff and students in order to provide a subjective assessment of the indoor air quality. The IAQ results collated in this study will be used to develop an IAQ database for institutional buildings in Singapore. This will be beneficial to the development of guidelines for good indoor air quality in institutional buildings.

Deposition of aerosol particles in ductwork

Many ventilating systems do not function properly due to the fouling of ducts and components. There is a need to study a wide range of different duct systems, in order to reduce the deposition rate in absolute terms, thus arriving at a more efficient system. A preliminary study is conducted in the laboratory to determine the flow behaviour of aerosol particles in relation to the airflow for ducts of various aspect ratios. A constant-injection tracer-gas technique is used to determine the airflow rate in the ductwork. SF6 tracer gas and smoke particles were injected at a constant rate into the inlet of each duct and their tracer-gas concentrations in ppm and smoke-particle concentration in mg m-3 were monitored at various points downstream. Algorithms were established for the deposition rate of smoke particles in various ducts. The results showed that the deposition rate of smoke particles was strongly influenced by the airflow rate and size of the duct.

Monitoring hydrofluorocarbon refrigerant leakage from air-conditioning systems in buildings

Hydrofluorocarbons (HFCs) are now widely used in refrigeration and air-conditioning systems. These systems lose refrigerants through leaks and during servicing. This paper discusses the possibility of determining the emission rate of HFCs in buildings by applying tracer-gas techniques. The measurement of the emission rate of an HFC refrigerant (R134a) using the concentration-decay technique was carried out in a single-zone chamber. The results were compared with measurements made using an SF6 tracer and the Pitot-tube traverse method.

Ventilation, indoor environment quality and climate - comparison of European and Singapore office buildings

SYNOPSIS Indoor environment quality audits were performed in six European countries and in Singapore using the same methodology. Five to eight office buildings were audited in each country. The audits included airflow rate measurements, energy audit, indoor air quality (VOC1 CO2, dust concentrations), and questionnaires to occupants. Questions to occupants addressed their health, their comfort and well-being, as well as their perception of their environment. This paper compares the results obtained from these audits, with particular attention to the effects of ventilation or air conditioning systems and climate. The number of building related symptoms is, on the average, significantly smaller in the buildings audited in Singapore than in Europe. One of the reasons may be the non-smoking policy common in Singapore. It is also once more observed that buildings are often over-warmed in cold climates and overcooled in warm climates. Surprising, but not new, is that there are no correlations between specific air flow rates and perceived air quality or health, as long as airflow rates are within accepted standards.

Effects of an ultraviolet coil irradiation system on the airside heat transfer coefficient and low ΔT syndrome in a hot and humid climate

Biological fouling (biofouling) on cooling coil surfaces acts as thermal insulation, impeding heat transfer from air to coil surfaces, decreasing airside heat transfer coefficient and degrading coil cooling capacity. It is also a common cause of low ΔT syndrome in chilled water distribution systems. The effects of a commercially available ultraviolet germicidal irradiation system installed in a variable air volume system on the airside heat transfer coefficient, cooling coil capacity, and its potential to mitigate low ΔT syndrome were investigated via a field test. Energy-related measurements including chilled water supply/return temperature, water-/airflow rate and entering/leaving air temperature/relative humidity commenced 4 months before turning on ultraviolet lamps and continued for 10 months after ultraviolet germicidal irradiation intervention. The effects of the ultraviolet germicidal irradiation system were evaluated via a “before ultraviolet” and “after ultraviolet” comparison. After ultraviolet intervention, within the face velocity range of 1.5–3.0 m/s, the airside heat transfer coefficient increased by 11.8%–20.1%, which translated into 8.8%–10.2% increase in the overall enthalpy-based thermal conductance. The coil total cooling capacity and latent cooling capacity increased by 3.3%–3.8% and 4.5%–5.7%, respectively. The chilled water flow rate required to maintain the leaving air temperature set-point decreased by 8.0%–11.9% and the water-side temperature difference increased by 0.4°C–0.6°C.