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MEASURED EFFECTS OF COOLING BY VEGETATION

Kang Kim Huat School of Housing, Building and Planning

Universiti Sains Malaysia 11 800 USM, Penang, Malaysia E-mail:kimhuat84@yahoo.com

Syarifah Fairuz Syed Fadzil School of Housing, Building and Planning

Universiti Sains Malaysia 11 800 USM, Penang, Malaysia

E-mail:sfsf@usm.my

Nor A'zam Shuib School of Housing, Building and Planning

Universiti Sains Malaysia 1 1800 USM, Penang, Malaysia

E-mail:norazam@usm.my

ABSTRACT

This paper investigates the role of vegetation with regard to its ability to cool the hot outdoor urban spaces. The effect of vegetation as a mean of controlling the ambient temperature is studied. Investigations are carried out on d~fferent tree species including d~rerent kinds of ground covers and their eflciency in controlling ambient temperature in the surrounding. Surface temperature data are collected beneath the crowns of trees in green areas and this is to be compared to open hard adiacent surface areas. Ambient temperature data are collected under the trees in relation to the measured values in the open (without vegetation). Other environmental parameters are analyzed by their relative values in the shade as compared to the correspondent ones in the open. Study concluded that the vegetation in the tropics can contribute significantly to cooling in the tropics by a range of Z'C to 5 ' ~ .

Key words: cooling vegetation, ambient temperature.

1.0 INTRODUCTION

In general, the word landscape has given the image of agriculture and beautification factors of cities. Urban planners and developers tend to ignore the importance of landscape; they perceive landscaping as one of the side products of any development. Urban planners usually always ignored the impact of landscape on the equilibrium of the environment which can lead to undesirable consequences: flash flood, landslide, urban heat island which reduce the thermal comfort and increase the potential of health impairment of urban populations.

However, a number of researches have shown that landscape plays an important role in balancing the capacity of nature to adapt the human activities. Trees will absorb the rainwater when it is raining thus prevents the occurrence of flood. The roots of the trees will also get hold and grip the soil reducing the chances of landslide. Vegetation release oxygen and absorb carbon dioxide while the process of photosynthesis carried on with the existence of sunlight, which reduce the impact of green house effects consequently from carbon dioxide.

Studies of urban climate have shown that vegetation modifies both mesoscale and microscale climates by changing the surface energy balance (Myrup, 1969; Outcalt, 1972). These modifications can affect human comfort in both indoor and outdoor spaces (Mayer and Hoppe, - - - 2 4 5 I P a g c

1987; Heisler, 1974; Heisler, 1977) and potentially reduce requirements for air conditioning in hot climates. A number of publications, summarized by Hutchison and Taylor (1983), describe how to use vegetation to design landscapes for energy conservation.

Mechanisms by which vegetation affects building energy balance include shading, alteration of wind speed and direction, and evaporative cooling of vegetation and air temperature (Hutchison and Taylor, 1983). Shade and wind alteration operate at the microscale, and their effects on building indoor air and surface temperatures and cooling costs have been well-documented peering, 1956; Buffington, 1978; Thayer and Maeda, 1985; Huang et al., 1987; McPherson et al., 1988).

Evaporative cooling of air was found to be a mesoscale process and have little impact at the microscale level (Hutchison and Taylor, 1983). Huang et al. (1987) used computer simulation to evaluate the potential of vegetation for reducing building cooling loads in Los Angeles, Sacramento, Phoenix and Lake Charles. They found that evapotranspiration (ET) from vegetation was more effective than shading in reducing energy consumption.

2.0 OBJECTIVES AND METHODOLOGY

In this research, quantitative and comparison method has been used, which is more focused on the collection and analysis of numerical data and statistics.

The objectives of this research are to identify the role of vegetation in terms of its ability to lower ambient temperature to a specific site and to compare with the adjacent open hard landscape area without vegetation. This study also determines the environmental factors that will affect the microclimate of the selected site. For example, air temperature, surface temperature, and relative humidity. All these environmental factors are taken at 15 minutes interval variables, air temperature (OC), humidity (%), and surface temperature (OC). These include using individual probes like digital Thermohygrometer and Temtestr fro surface temperature. In addition, the thermal imager (infrared camera) called Fluke, which were used to capture surface temperature profile of the vegetated surface temperature area and its adjacent hard and open non-vegetated area.

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The methodology chart is given below:

I THREE SELECTED SITE AT USM CAMPUS I

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I VEGETATED AREA UNDER TREE SHADE EXPOSED NON-VEGETATED AREA

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SUMMARY AND CONCLUSION

I

DATA COLLECTION 9 RELATIVEHUMIDITY

AIR TEMPERATURE SURFACE TEMPERATURE

USM I

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Figure 1: Methodology Chart

COMPARISON I ANALYSIS MEAN MAX AVERAGE DIFFERENCES IN PERCENTAGE

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I FINDINGS AND OUTCOME

3.0 METHODOLOGY

Diagrams and pictures below indicate the surface temperature profile of unpaved grass vegetated area and hard open non-vegetated area of Site A, Site B, and Site C taken at selected times and days:

Table 2 : Thermal Profile of Site A, Site B, and Site C.

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Results

Table 1 below indicates the minimum, maximum and average temperature of the field work on Site A, Site B, and Site C.

From the Table, the data are the average of three days. For example, there are 21 readings per day for air temperature taken in one site from I Oam to 3pm every 15 minutes, summarized fiom the data; the minimum, maximum, average and the differences for each site are derived.

4.0 ANALYSIS AND DISCUSSION

The highest air temperature of Site A on red clay block area is 43.70'~; Site B Tarmac area, 35.4o0c, and Site C concrete area 43.30'~. Relative humidity in vegetated area is the highest, 52.15%, 58.15%, 62.15% adjacent to Site A on red clay block area, Site B on tarmac area and Site C on concrete area. The lowest relative humidity is Site A on red clay block, 48.50%. The highest surface temperature is Site B on tarmac surface, 4 5 . 0 0 ' ~ ~ while the adjacent vegetated surface is the 34.25'~. On the other hand, highest air temperature at vegetated area occurs at 35 .6 '~ at Site A, 36.00'~ at Site B, and 35.9 '~ at Site C. This is lower by compared to average 2 - 5 ' ~ with the adjacent open hard surface.

This research signifies the role of vegetation in lowering the air temperature and surface temperature. Relative humidity on the other hand is not significant because relative humidity in Malaysia climate is quite high regardless the location. The choice of construction materials is also significant as it will release heat to the atmosphere causes the air temperature to rise.

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5.0 CONCLUSION

From the research, the conclusions below can be derived:

Air temperature can differ significantly even though at site which is just adjacent to each other as material, shading and vegetation affect the ambient air temperature. Vegetation and softscape is proven to have cooling effect by up to 50C compared to the adjacent open hard surface area without vegetation and shading. In tropics, hard surface open area should be minimized or avoided totally as heat built up and increase in both air and surface temperature will create discomfort zones and contribute to global warming. The choice of hard landscape with large vegetation for example canopy trees maybe a better alternative if totally a softscape design cannot be achieved. Hard landscape may also be considered with man made structures (pergola, etc) that provide shading if large shading trees are not a viable option.

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