Embed Size (px)
Citation preview
A Study of Rooftop Gardens in Singapore In Singapore, continuous efforts in making the country a “garden city” have resulted in lush greenery throughout the island. However, the greenery has been kept at the ground level. The rooftops of many buildings have been left untapped as possible areas for rooftop gardens. One of the potential measures to mitigate the Urban Heat Island effect is the use of plants for roof and sky-rise gardens and it has gained popularity around the world. The study of rooftop gardens, which is a collaborative effort of the National Parks Board (NParks) and Centre for Total Building Performance (CTBP), explores rooftop gardens in Singapore through four perspectives: field measurements, energy simulation, life-cycle costing, and perception studies of building professionals and end-users. METHODOLOGY AND FINDINGS Field measurements were conducted on a rooftop garden of a commercial building (Figure 1). The results of the field measurements reveal that the installation of rooftop gardens would significantly provide thermal protection to buildings and improve the surrounding environment. The main thermal benefits of vegetation on the building roof include reduction of temperature and heat gain of the roof, and solar radiation absorbed by the roof. Figure 2 illustrates the comparison of surface temperatures measured with different kinds of plants, only soil, and without plants. The measured thermal improvements due to the presence of rooftop gardens are summarised in Table 1a.
Energy Simulations The simulation results reflect that the installation of plants or soil layer would significantly reduce the energy consumption required in a five-storey commercial building under the Singapore climatic condition. The data on the reduction of energy consumption due to the installation of plants and soil layer on the roof are summarised in Table 1b.
Life-cycle Cost Analysis This study reveals that by incorporating energy savings into the life-cycle cost analysis, it gives a
Figure 1: Field measurements conducted on a rooftop garden of a commercial building. Table 1: Summary of field measurements and energy simulations Table 1a: Measured reductions of thermal parameters caused by the rooftop garden
Thermal Parameter Range of Reduction Surface temperature of roof 0 – 31.0oC
at 300 mm height 0 – 4.2oC Ambient
temperature at 1000 mm height 0 – 1.5oC
Relative humidity - 23.5% – 0% Solar radiation (at 300 mm height) 4.2 – 124.6 W/m2
MRT 0 – 4.6oC Globe temperature 0 – 4.1oC Heat flux transferred through surface 0.6 – 15.4 W/m2
Total heat gain over a day 395.0 – 466.3 KJ/m2 Table 1b: Reductions in energy consumption caused by plants and soil layer on the roof of a five-storey commercial building
Range of Reduction Thermal Parameter Effects of plants
+ soil layer Effects of soil
layer only Annual energy consumption 0.6% – 19.5% 0% – 2.9%
Space cooling load 17.0% – 79.0% 2.2% – 63.8% Peak space cooling load 17.0% – 78.9% 2.2% – 71.4%
Sensible cooling load 17.1% – 80.6% 2.2% – 63.8%
Peak RTTV 17.1% – 80.6% 2.2% – 63.8%
RESEARCH BRIEF 2002/005
Department of Building, School of Design and Environment, National University of Singapore
23.0
28.0
33.0
38.0
43.0
48.0
53.0
58.0
2001
/11/
03
03:0
0:00
06:0
0:00
09:0
0:00
12:0
0:00
15:0
0:00
18:0
0:00
21:0
0:00
2001
/11/
04
03:0
0:00
06:0
0:00
09:0
0:00
12:0
0:00
15:0
0:00
18:0
0:00
21:0
0:00
Local Time
Tem
pera
ture
(ºC
)
turfing shrub tree bare soil hard surface
Figure 2: The comparison of surface temperatures measured with different kinds of plants, only soil, and without plants on 3 and 4 November 2001. better picture of the cost effectiveness of roof gardens. It can be concluded that by considering the energy savings, the extensive green roof costs no more than the conventional flat roof.
Perception Studies of Building Professionals and End-users The perceptions of building professionals on the benefits and barriers of green roof development were investigated. The results suggest the general acceptance of green roof development among professionals in the building industry. Public attitudes towards rooftop garden provision in Singapore were also investigated. The discussions focused mainly on the usage rate of rooftop gardens, perception of the role and importance of rooftop gardens, and facilities and design features desired for rooftop gardens. CONTACT DETAILS Dr WONG Nyuk Hien Department of Building School of Design and Environment National University of Singapore 4 Architecture Drive Fax: (65) 6775 5502 Tel: (65) 6874 3423 E-mail: [email protected]
