Nyuk Hien Wong

Investigation of thermal benefits of rooftop garden in the tropical environment

Vegetation strategically placed on roofs and walls can be considered as a complement of urban greens. It is actually an ecological solution to the concrete jungle in cities. The benefits of green roofs are unquestionable from the thermal point of view. But some quantitative data on this subject are still needed in the context of tropical climate. Therefore, a field measurement was conducted in Singapore to investigate the thermal impacts of rooftop garden. From the derived data, it has been confirmed that rooftop gardens contribute thermal benefits to both buildings and their surrounding environments.

The effects of rooftop garden on energy consumption of a commercial building in Singapore

Abstract DOE-2 energy simulation program was used to determine the effects of rooftop garden on the annual energy consumption, cooling load and roof thermal transfer value (RTTV) of a five-story hypothetical commercial building in Singapore. The thermal resistances (R-values) of turfing, shrubs and trees were estimated using data from site measurements, and the effects on the building energy consumption of a rooftop garden with these three types of plants were simulated. Two soil types with different soil thickness on the building roof were also simulated. The results showed that the installation of rooftop garden on the five-story commercial building can result in a saving of 0.6–14.5% in the annual energy consumption, and shrubs was found to be most effective in reducing building energy consumption. The results also revealed that the increase of soil thickness would further reduce the building energy consumption and the moisture content of soil can affect the outcome quite substantially.

Thermal comfort in classrooms in the tropics

Abstract A field study was conducted in classrooms in Singapore, which were mechanically ventilated by fans, to assess their thermal conditions during the students’ lesson hours. Thermal comfort variables were measured at the same time when students and teachers answered a survey on their perception/sensation of the indoor climate. Objective data analysis showed that none of the classes had thermal conditions falling within the comfort zone of ASHRAE standard 55. Occupants found temperature range beyond the comfort zone acceptable. This suggests that the standard is not applicable in free-running buildings in the local climate. A new PMV model, which incorporates two common forms of adaptation-reducing activity pace and expectation, still showed discrepancy in predicting actual thermal sensations, especially at lower temperatures. Comparison of the various methods of assessing thermal acceptability showed that they produce widely disparate results, with the Bedford scale giving the highest level of acceptability. Classroom occupants generally accepted cool thermal sensations more readily than warm thermal sensations.

Life cycle cost analysis of rooftop gardens in Singapore

Abstract Since the 1960s green movement, green roofs have ‘re-emerged’ as a viable solution to address pressing environmental issues like increased storm water runoff, the urban heat island effect, deterioration of air and water quality, and loss of habitat and biodiversity facing urban centres. Increasingly becoming popular worldwide, green roofs are still not an area local builders are keen to take on. Despite the availability of materials and suitability of climate here, they are held back partly by concerns pertaining to costs. The objectives of this study are to highlight the economic benefits of green roofs that can offset the initial costs; to examine the initial cost implications of having a green roof as compared to a conventional flat roof; to compute and compare the life cycle costs of roof gardens and average flat roofs; and to incorporate economic benefits by incorporating energy costs into life cycle costs. It is observed that life cycle costs of extensive green roofs with or without consideration for energy costs, are lower than that of exposed flat roofs, despite its higher initial costs. However, for accessible rooftops, even life cycle (energy) costs of intensive system are not less than the normal build-up flat roof.

Thermal comfort evaluation of naturally ventilated public housing in Singapore

Abstract Field survey was conducted to evaluate thermal comfort perception of the occupants in naturally ventilated public housing in Singapore. Thermal acceptability assessment was performed to find out whether the naturally ventilated indoor environment meets the ASHRAE Standard-55s 80% acceptability criteria. The study investigated whether thermal perception was influenced by different sessions of the day, building height, and flat types. Comparative analysis of thermal sensation and thermal comfort votes revealed that a high proportion of people experiencing sensations of +2,+3 still found the conditions to be comfortable. The survey also examined the adaptive behavior of the occupants in the usage of climatic control such as windows, fans and air-conditioning to modify the indoor environment.

Local climate change and urban heat island mitigation techniques – the state of the art

AbstractIncrease of the ambient air temperature in cities caused by the urban heat island phenomenon has a seri- ous impact on the economic and social system of cities. to counterbalance the consequences of the increased urban temperatures important research has been carried out resulting in the development of efficient mitigation technologies. the present paper aims to present the state of the art in terms of local climate change and urban heat island mitigation techniques. In particular, developments in the field on highly reflective materials, cool and green roofs, cool pavements, urban green and of other mitigation technologies are presented in detail, while examples of implemented projects are given.

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.

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.

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.

Perception Studies of Vertical Greenery Systems in Singapore

The objective is to discover the current perception of vertical greenery systems and barriers to their widespread adoption in Singapore. It can be concluded that the energy saving property of vertical greenery systems make them suitable for the local conditions as Singapore depends heavily on air conditioning. In addition, vertical greenery systems will also enhance the aesthetic of a building. Moreover, the installation of vertical greenery system is part of the effort to reduce the increasing serious air and noise pollution. Lastly, vertical greenery system is able to bring nature closer to humans. As with all greenery, constant clearing of the residue of dead leaves as well as periodical replacement and trimming cannot be avoided. These may become a barrier in convincing building owners to adopt vertical greenery systems. Furthermore, there is a lack of technical information, maintenance instructions, and information on plants suitable for vertical greenery systems locally. Lastly, there is lack of awareness of the benefits and performance of vertical greenery systems as well as a lack of grants and subsidies for implementation of vertical greenery systems.