2024 Volume 12 Issue 1 Pages 1-20
The external environmental conditions in tropical cities are hot due to high temperatures and humidity. Strategic planning and design of exterior spaces can reduce energy consumption for building cooling by reducing various negative effects of tropical climate factors. The desired interior conditions of the building should be similar to the exterior microclimatic conditions. If the microclimate deviates significantly from this, large amounts of cooling energy may be required to create a comfortable interior environment. In this study, single-family houses were randomly selected in two well-planned cities in Malaysia, with 30% of the houses located in Putrajaya and 70% in Shah Alam. Most of the houses used a modern tropical building style to adapt to the challenging tropical climate with high temperatures, high humidity, and heavy downpours. Since air conditioning is the only ideal active system, 90% of the houses in the study areas were operated with this system to create and maintain a comfortable interior temperature. On average, the annual energy cost for cooling was about 36.7% per house. Several comparisons of energy use were made with minimal to moderate landscaping to determine the effectiveness of greening around the houses to reduce energy use in a tropical climate. Annual cooling energy savings reached up to 7%, equivalent to 948kWh (MYR233.00) per house. The results showed that landscaping had a significant impact on the cooling energy of the houses.
Energy costs and environmental concerns have made finding solutions to decrease energy consumption even more vital. Raising the built environment’s energy efficiency is critical as human energy consumption rises. This can benefit the environment, building owners, and building users. There are numerous techniques to increase the built environment’s energy efficiency. Envelope technologies that include wall, floor, roof, and insulation, as well as high-performance windows and doors, and air infiltration, are critical in creating a pleasant interior. To maintain environmental control, buildings in hot, humid areas rely on energy to run cooling and ventilation systems (Misni, 2012; Misni, Baird et al., 2013; Nordin and Misni, 2018; Sun, 2017). Climate, surrounding vegetation, a building’s orientation, as well as the structure and materials used in constructing the building envelope, all influence how much energy is required. Climate conditions have the most significant impact on the balance of energy usage in buildings. By managing the microclimate, it is feasible to limit the energy consumed to cool buildings (McClenon, 1983).
In tropical microclimates, tropical cities’ urban heat island phenomenon is particularly pronounced. The issue also increased the house’s cooling load. Akbari, Taha et al. (1986) state that houses are susceptible to the heat island effect since they are envelope-dominated structures. The heat gained by individual buildings spreads throughout the microclimate. The air temperatures in densely populated urban areas have increased. These structures and surfaces absorb solar energy, re-radiating it to the surrounding area while increasing the ambient temperatures of an urban microclimate by 5.5–10°C (Akbari, Davis et al., 1992).
The role of landscaping in regulating microclimates has been extensively studied in recent years worldwide. Landscaping is an ecological approach to alleviating the difficulties associated with densely populated metropolitan areas (Wong and Yu, 2005). By reducing energy consumption in individual buildings and boosting the community’s energy efficiency, vegetation can potentially increase environmental value. Using the proper species and forms of shade trees strategically planted around a structure could change its microclimate and energy use. They can minimise the radiant energy absorbed and stored by the building and other constructed surfaces by providing shading and evapotranspiration, including encouraging wind flows.
Thus, this study aimed to estimate plants’ outdoor temperature-lowering and energy-saving potential for tropical residences by examining landscape patterns and structures connected to tropical domestic building orientation.
Vegetation can directly affect urban microclimate by using cooling energy on buildings through tree canopy shading, reduction of wind speed, and wind flow channelling. It also indirectly changes the thermal interaction between the structures and their environment through the evapotranspiration of water (Akbari, Davis et al., 1992; DOE, 1993; Misni, 2015) . In the tropics, trees with flat growth rates should be selected from medium to large and located between 4.5m and 6.0m from the buildings’ sidewalls (Mrema, Gumbe et al., 2012). At the same time, the selection of tree species and forms of shade is also essential. The high density of foliage and shade should be selected to provide relief from sunlight and enhance their aesthetic appearance. Subsequently, strategically planted trees can channel airflow in the desired location and create proper cross-ventilation in the buildings’ interior spaces (Misni, Baird et al., 2013; Nordin and Misni, 2018). In tropical climates, shrubs shade buildings’ walls and windows in the morning and afternoon when the sunlight is at a low angle in the sky. They may also be planted between paved areas and the buildings. Moreover, fast-growing vines need a little climbing space to provide shade.
The use of air conditioners for interior spaces is due to solar heat that penetrates the buildings through the building envelope, like glass windows, and is absorbed through the roof and walls. Therefore, adopting natural shading on the building envelope is the most effective method to reduce air conditioning’s rising cost. The reduction of solar heat absorption can achieve this. Field measurements in Sacramento, California by Simpson and McPherson (1996) have proven that the shade created by shrubs and shady trees planted near buildings can directly lessen the daily cooling load. They stressed that the most significant impact on cooling energy savings for all climate zones and the level of insulation of building envelopes is the placement of trees that provide shade from the afternoon and early evening sun in the west.
In a single-family house, direct control of heat flow to walls and roofs can save energy consumption in some capacities. A study in Los Angeles by (Akbari, Taha et al., 1986) proved that 34% of dwelling cooling demand savings during a hot summer season were achieved by planting shady trees around buildings. They measured that the net effect of shade in hot climates was valuable. Shade from the trees saved annual energy expenditure by US $$60 compared to the no-tree surroundings for the conventional dwelling area in Palm Springs, California. In comparison, Buffington’s study found that the effect of uniformed shading on the building envelope of walls and roofs of a concrete block dwelling in central Florida reduced annual cooling consumption by as much as US$108 (14%) (McPherson, Herrington et al., 1988).
Vegetation cools indirectly through evapotranspiration, through which plants release water vapour. In general, the indirect effects accrue throughout the microclimate. Evapotranspiration is the primary mechanism by which trees contribute to lowering the temperature through the natural process. It releases water into the atmosphere by combining soil evaporation and plant transpiration (Buyadi, Mohd et al., 2014; Santamouris, 2001). This evapotranspiration process can naturally reduce the surrounding hot air temperature. Heisler added that trees could absorb 70–85% of the sun’s heat via transpiration. He also added that trees effectively cool the environment (Akbari, Davis et al., 1992). The foliage in the tree canopy is generally dark and coarse, making it an ideal absorbent and controlling agent of solar radiation while reflecting relatively little light. The tree foliage has the highest sunlight absorption. According to Taiz and Zeiger (2006), these dense leaves can absorb almost 50% of total solar energy. Therefore, through their study’s primary findings, DOE (1995); Foster (1994) suggested that planting at least three shade trees in each house in urban areas can reduce heat accumulation and the effects of urban heat islands. Their evapotranspiration process can lower air temperature to 5°C, while trees provide shade and channel wind.
Moderate wind flows in tropical climates are significant assets that can supply natural wind flow and convection cooling to the building envelope. It has been emphasised by Olgyay (1963) that for an area with temperatures above 29°C and relative humidity above 50%, the wind is essential for the surroundings’ freshness and comfort. In this case, the cooling requirement is high, and the building vegetation should be designed to channel cold air while minimising humidity and temperature near the buildings (Misni, 2012). During droughts and summer seasons, the building envelope should be sheltered from direct solar radiation. Strategic plant placement of the correct shape to provide shade is essential. The airflow around the buildings can be improved by combining strategic plant arrangements between shrubs or hedges, tree branches, and foliage.
In contrast, tree planting can also slow wind velocity by 4.3% in the 0.9-1.0 m/s value range (Aini and Shen, 2019). McPherson, Herrington et al. (1988) suggested that in tropical climates, species with lofty trunks and broad branches of tree canopies combined with low shrubs should be used to provide shading and channel wind to the right path. Thus, the most effective planting designs are trees with tall stems and a canopy spread in medium-dense foliage, shrubs, low flower beds, and ground cover grass. Careful landscaping around the building can shade the building envelope and encourage wind flow. Simultaneously, generating evapotranspiration from trees can reduce heat gain while preventing reflected sunlight from entering buildings.
Yin (2003) suggested that at least three principles can be used according to research appropriateness. In this study, two primary methods were chosen for collecting primary data, as shown in Stage Two, Figure 1. There are six possible sources of documented evidence for collecting primary data. Physical measurements are taken, as well as direct interviews with the house owners. Simultaneously, physical measurements are divided into three parts; physical artefacts, evidence of the building (including the building envelope and surrounding vegetation), and weather data.
Figure 1 illustrates the method used to collect primary data in this study. Two methods of primary data collection (via measurement, observation, and interview) were stated in Stage Two (Figure 1): measurement (M) using physical artefacts/structures of the building and surrounding vegetation; observation (O) of the orientation of the house and landscaping; and survey (S) interview with the house owners regarding their cooling energy usage (electricity used for air-conditioning).
The first phase of collecting data was observing and recording data on each building's envelope materials and structure. It was followed by data on surrounding vegetation that has been planted. Other physical features included hard landscape elements, which were accounted for in on-site measurements using an appropriate scale. Weather data were recorded by digital equipment installed in the interior and exterior parts of the houses. Data for temperature, relative humidity, and wind speeds were measured in exterior spaces, while the interior data concentrated on temperature and relative humidity. All data were validated with data from the Meteorology Department of Malaysia.
The next phase evaluated the effect of exterior vegetation on lowering the amount of internal cooling energy used. All primary data on the surrounding vegetation, building envelope, and cooling energy use, as well as the actual number of occupants in each house, were calculated. The data on cooling energy use were calculated using the average proportion of cooling energy use.
Study LocationPutrajaya and Shah Alam were chosen as sampling locations for single-family houses. According to Samad, Zain et al. (2011), both were well-planned Malaysian cities. The houses were randomly chosen based on the willingness of the homeowners. Both cities were located at latitudes of 2–3° North and longitude of 101° East, at elevations ranging from 24 to 94m. Both cities are about 25 kilometres south and west of the old capital, Kuala Lumpur. The five districts selected for the case study were Precinct 14 in the Federal Territory of Putrajaya and Sections 11, 9, 6, and 3 in Shah Alam, Selangor. All of the selected locales are situated in low-density mixed residential neighbourhood areas. Chen (2020) stated that Putrajaya, which was planned as a city in the garden, used up to 38% of its urban area for green spaces, accentuating and enhancing the natural green reserve. Its local inhabitants usually use and promote their green and open spaces successfully (Bendjedidi, Bada et al., 2018). Meanwhile, Shah Alam is Selangor State’s capital and one of Malaysia's most organised cities (Aziz and Hadi, 2007). About 10% of its developed area is reserved for green space.
Data WeatherTwo-year data were used to obtain an accurate picture of the weather conditions in the study area. The weather data were obtained from the Malaysian Meteorological Department for 2009 and 2008. The data were from two weather stations: Sepang Weather Station for the Putrajaya study area and Subang Weather Station for Shah Alam. Table 1 lists the average yearly weather data, including the highest and lowest air temperatures, relative humidity (RH), precipitation, global solar radiation, cloud cover, and wind velocity. The drought season with the southwest monsoon begins in late May and lasts until September. The northeast monsoon starts the wet season in early November and lasts until March. The two shorter seasonal periods between the monsoon seasons are April and October.
| Weather data | 2009 | 2008 | ||
|---|---|---|---|---|
| Putrajaya | Shah Alam | Putrajaya | Shah Alam | |
| Air temperature (°C): | ||||
| 1. Maximum | 31.8 | 32.7 | 31.3 | 32.1 |
| 2. Minimum | 24.0 | 24.4 | 23.7 | 23.9 |
| Relative humidity (%) | 81.2 | 75.9 | 81.4 | 77.0 |
| Rainfall: | ||||
| 1. Rainfall amount (mm): | 2099 | 2857 | 2092 | 3279 |
| 2. Number of rain days | 168 | 200 | 167 | 203 |
| Solar radiation (MJ.m-2) | 17.0 | 18.3 | 16.3 | 18.1 |
| Cloud cover (Okta) | 06.9 | 07.0 | 06.9 | 07.1 |
| Wind in all directions (m/s): | ||||
| 1. Speeds | 98.5 | 98.3 | 98.5 | 98.3 |
| 2. Calm | 06.9 | 31.0 | 06.9 | 31.7 |
For primary data, fifty single-family houses in Putrajaya and Shah Alam were chosen. Meanwhile, the interviews were conducted at the same time. The houses were randomly selected, with 30% in Putrajaya and 70% in Shah Alam.
All the houses represented conventional tropical architectural styles that could withstand tropical climates with high temperatures and humidity, minimum wind flow, and heavy rainfall. Over the past four decades, the main features of residential planning have mostly remained the same. They are laid out in an organic and grid-iron manner.
The building envelope of the wall construction was infilled with plastered masonry lined with a reinforced concrete structure, as shown in Figure 2. Moreover, their roofs commonly use timber frames in hip-roofed form covered with concrete or clay tiles—the general typology of a single-family house built with medium fenestration.
The location and amount of vegetation around the houses were meticulously plotted and studied. As shown in Figure 3, each vegetation species' location was recorded at five-metre intervals extending out from the buildings for each of the four azimuths.
The tree azimuth classes were established based on the orientation of the building walls. According to Simpson (2002), a wall is cardinally oriented if the average distance to it is within 45°E of a cardinal direction (North, East, South, or West); otherwise, it is inter-cardinal (NE, SE, SW, or NW). Because different forms of landscaping affect shading, evapotranspiration, and wind movement, a specific landscape design was created for each vegetation type.
The domestic electricity tariff, referred to as National Energy Limited (TNB), is the monthly electricity consumption calculated as the cost of electricity in Ringgit Malaysia (MYR). The energy used is in units of kWh. The amount of cooling energy obtained from an individual house should be analysed. The fluctuating power use is closely associated with air temperature and relative humidity during the wet and dry seasons. Slight temperature changes between the two seasons are highly significant, contributing to the increased use of cooling energy (air conditioning) in tropical homes. The total electricity use and cooling cost were calculated using the following equation:
x (costs per horsepower)…………………………………………………… (1)
Where:
1 horsepower = 0.7457kWh
Total kWh = Total MYR/0.2457
Costs for a horsepower per hour = MYR0.20 and increase MYR0.10 for every 0.5 horsepower until a maximum of 3 horsepower equal to MYR0.60.
Data analysisAs illustrated in Figure 1, each variable on the effect of the building envelope and building construction, surrounding landscape, and cooling energy use was computed and assessed using Origin software statistical analysis.
The cooling energy use in single-family houses was revealed at different ages and constructions. The main results for the cooling energy used were divided into three sections: building construction, landscape, and cooling energy. A comparative analysis of each group of data is presented as follows:
WeatherThe annual weather data for the two cities, which have slightly differing air temperatures and relative humidity levels, are shown in Figure 4 and Figure 5.
Shah Alam and Putrajaya have slightly warmer temperatures of 23.3 to 34.2°C, respectively. The annual RH in both locations was also relatively high, between 77 and 81.4%, respectively. There was a lot of solar radiation. Solar radiation was somewhat greater in Shah Alam, ranging between 18.1 and 18.3MJ.m-2, with 7 Okta of cloud cover, whereas it varied from 16.3 to 17MJ.m-2 in Putrajaya with a cloud cover of 6.9 Okta.
Precipitation was high over the two years, with average annual amounts exceeding 3300mm in Shah Alam and 2100mm in Putrajaya. From monsoon rain until the drought in Putrajaya, winds dominated between 38 and 41% of the time, while calm conditions occurred about 7% of the time. In comparison, at Shah Alam, the consistent wind flow for 26-27% of the time in the calm scenario was relatively high, at approximately 32%.
Generally, the weather data in these two nearby cities are slightly different. A slight fluctuating pattern is typical of a tropical climate. High temperatures and humidity, combined with slow wind speeds in the study area, cause discomfort to the residents and can result in an urban heat island effect. Hence, the strategic location of vegetation with sufficient size and suitable species is one potential solution to reduce the urban heat island effect on the surrounding housing areas.
Building constructionThe building envelope construction is a significant component because it serves as the primary heat conductor for the house. It can have an impact on how much cooling energy is used in the house. So, the physical characteristics of fifty medium-sized single-family homes in various stages of construction were analysed and documented. Measurements of building size and features were essential, including the age of construction, the number of stories, the size of the floor, walls, and roof, and the car porch. 98% of the houses were two-story, and only 2% were three-story in the 20–29-year-old construction group. The building’s age was closely related to the era and style of architecture and construction, as well as the age and style of landscaping.
Table 2 describes that the majority, around 46%, of the building ages were between 20 and 29 years, while 34% were between 0 and 9 years. Meanwhile, 14% and 6% were between the ages of 30 and 40, and 10 and 19-year-old houses, respectively. The primary construction materials used for the 50 houses were much the same. The main structure included columns and beams of reinforced concrete for all the houses. The materials used for the building envelopes were also remarkably identical: the floor was constructed with reinforced concrete, the walls with bricks and cement plaster, and the pitched roof structure was made of preserved hardwoods. The waterproof materials of the roof cover used approximately 74% concrete tiles, while the rest used clay tiles. There were several sizes of total floors, roofs, car porches, and garden areas within the range of medium-sized houses, as can be seen in Table 2.
| Building | Building area (m2) |
Garden sizes (m2) |
||||||
|---|---|---|---|---|---|---|---|---|
| Age | No. | % | Ground floor | Upper floor | Total floor | Roof | Car porch | |
| 00–09 | 17 | 34 | 234 | 220 | 454 | 264 | 28 | 293 |
| 10–19 | 03 | 06 | 245 | 245 | 490 | 283 | 40 | 200 |
| 20–29 | 23 | 46 | 207 | 202 | 412 | 255 | 31 | 254 |
| 30–40 | 07 | 14 | 171 | 171 | 343 | 219 | 30 | 218 |
| All | 50 | 100 | 214 | 206 | 421 | 255 | 30 | 259 |
There are four types of house configurations: east-west, northwest-southeast, north-south, and northeast-southwest. The northwest-southeast layout dominated 38% (19 houses), and 34% (17 houses) were north-south, and finally, the northeast-southeast and east-west arrangements were only around 18% (9 houses) and 10% (5 houses), respectively. However, the house's composition did not influence the number of walls or opening areas. Instead, the opening area and its locations were influenced by the location of the main garden area, interior spaces, and front elevation.
In tropical climates, direct solar radiation from glazed windows is undesirable. Nonetheless, glazed windows and doors in the walls primarily allow daylight and natural fresh air flow for ventilation. Table 3 displays the average aluminium frame single-layered glass window areas in all directions. The highest glazed area among all building groups with a construction age of 0–9 years was approximately 16.3m2, while 30–40 years had the lowest glazed area, i.e., around 10.9m2. It can be noted that the highest average amount of the glazed areas was in the north direction, approximately 16.4m2 for 0–9-year-old houses.
| Building | Glazed area (m2) | |||||||
|---|---|---|---|---|---|---|---|---|
| Age | North | North-East | East | South-East | South | South-West | West | North-West |
| 00–09 | 16.4 | 15.7 | 17.5 | 14.6 | 13.5 | 14.1 | 22.9 | 15.6 |
| 10–19 | 03.3 | 06.7 | 23.7 | 08.7 | 15.0 | 12.6 | 14.0 | 13.7 |
| 20–29 | 15.5 | 11.6 | 13.4 | 12.8 | 14.2 | 11.6 | 11.9 | 12.2 |
| 30–40 | 14.9 | 09.5 | 11.0 | 09.7 | 15.0 | 06.6 | 06.7 | 14.3 |
| All | 15.1 | 12.4 | 14.6 | 12.6 | 13.9 | 11.8 | 14.3 | 13.5 |
Meanwhile, the lowest amount of glass area was 3.3m2 in the north direction of 10–19-year-old houses. The highest and lowest glazed areas differed by around 60%. The average glazed area for all directions and all ages of construction was 13.5m2. The glazed areas were well-designed in all directions. In comparison to their floor areas, 13% of each house in the study area practised this. It could provide sufficient natural lighting and ventilation for the building. All windows and sliding doors were positioned under the roof projection, which was between 0.75 and 2 metres long. This provided shade between 11.00 and 15.00 hours and during the peak hours of the day.
The surface torque of the fraction of sunlight reflected from the earth on any surface back into space is normally used to measure albedo. In this study, the value of albedo was within the range of 0.1–1.0. The average albedo value for building envelopes in the study areas was 0.22. Hence, the average colour of both envelopes fell into the light-coloured category. The use of light colours for walls and roofs has been widely applied in the last 30 years.
Cooling energy useIn tropical cities, air conditioning systems are a basic necessity for daily comfort. Most (90%) of the houses in the study area utilised an active cooling system. Meanwhile, the remaining 10% of the houses were equipped with a passive system and natural ventilation. The two air-conditioning systems used were the window system and split unit, respectively represented by 67% and 33%. These systems have comparable cooling capabilities. The window system unit is mounted on the room's wall to be cooled while the split-unit system is housed in a box near the walls. A horsepower is a unit used for air-conditioning systems in Malaysia. Currently, one horsepower is equivalent to 0.7457kWh. It was recorded that 279 air conditioning units in the 49 houses were understudied. The air conditioning units were supplied with approximately 379 horsepower (282.62kWh) to serve 240 occupants. The general areas where the air-conditioning units were located included shared and private rooms. Most occupants operated these air conditioning systems for about five hours every night from 23.00 to 6.00. These were intended for sleeping activities. On average, five occupants of each house only used three to four bedrooms.
Electricity bills for cooling were in current currency units (MYR), while the monthly energy consumption (kWh) for two seasons in tropical climates included rain and dry. In the wet season, the air conditioning was at minimum to medium usage. The low temperatures in the rainy season could provide more significant savings. However, during the dry season, the operation of the air-conditioning systems was high, necessitating the use of additional energy. The ambient air's high temperature and humidity would cause an uncomfortable interior environment. Therefore, the air conditioning system was used for a longer duration. The temperature setting was slightly lower and used in practically all interior spaces involving occupant activity, both day and night. The total increment of general energy use during the wet and dry seasons was around MYR18540 (75458kWh) per year, representing 22.3% because of the increase in air conditioning use.
| House | Cooling costs in the dry season | Cooling costs in the wet season | |||||
|---|---|---|---|---|---|---|---|
| Age | No. | kWh | MYR | Cooling (%) | kWh | MYR | Cooling (%) |
| 00–09 | 17 | 14099 | 3464 | 50.5 | 8136 | 1999 | 37.0 |
| 10–19 | 03 | 2227 | 547 | 53.4 | 1718 | 422 | 46.9 |
| 20–29 | 23 | 12803 | 3146 | 44.6 | 8326 | 2046 | 34.4 |
| 30–40 | 07 | 4178 | 1026 | 50.7 | 2550 | 626 | 38.5 |
| Total per month | 50 | 33306 | 8183 | 48.2 | 20729 | 5093 | 36.7 |
Table 4 shows that, on average, 20729kWh (MYR5093) of energy was used for cooling during this wet season, representing about 36.7% of total energy per house per month. Cooling energy is projected to increase by 11.5% per month during the dry season to reach approximately 48.2% per month.
Surrounding landscapingThe private garden around the single-family houses is landscaped. Each house practises a tropical style of landscaping. The plants around the garden ranged in size, from minimal to moderate. Landscaping encompasses aesthetics, leisure, and environmental cooling. They planted tropic and subtropical native plant species in individuals and groups in a natural-setting image design. The unique identity of native tropical plants, which are fertile and lush, usually has a waxy and thick leaf surface. The quality of tropical landscape design depends on the type of crop choice and arrangement, as well as its strategic location around the house and garden. The most fertile plants in tropical climates are during the rainy season because they receive natural water almost daily while the heat is moderate. The study’s results included the overall size of the garden or open area, as well as the regular collection of data from the five main categories of plant types that cover the entire soil around the house. These include shade trees, shrubs, vines, ground cover, and turf or grass.
The various garden zones around the houses include the access road area, the house entrance, the central garden area, the edible garden in the backyard, and the boundary lines or fences of the properties. Plants are designed and planted naturally around the houses and in the garden, creating networks for other outdoor zones. In this study, trees are essential in moderating soil temperature, providing shade to the building envelope, and producing evapotranspiration, cooling, and shade under their foliage. At peak times of the day, shade trees prevent heat build-up in the buildings.
All tropical trees in the study area were evergreen species consisting of several types of plants, such as flowering plants, conifers, edible fruit trees, palms, and bamboo. The trees were the central garden's primary soft landscape structure. The height of their trunks was higher, while the spreading canopy could provide much more prominent shade. In the study area, about 38% of the soft landscape was from the palm category, i.e., the most popular plants among homeowners. The palm has become a fashionable emblem of luxury and pleasure in the domestic landscape because of its aesthetic merits, unique structures, and leaf forms.
The following types of trees were 25% garden trees and 18% edible fruit trees. Besides, 13% were contributed by roadside trees located around the entrance to the houses understudied. Roadside palm and bamboo were planted less, i.e., about 5% and 1%, respectively. The total of the tree structures was approximately 542, and their distribution was significant, as displayed in Table 5. The size of the trees and the canopy were divided into four groups. The measurement was in the canopy diameter: small (1–2m trunk height and 2–4m diametres), small moderate (2–3m trunk height and 4–7m diametres), medium (2.5m and above trunk height and 8-11m diameter), and large (3m and above trunk height and 12–15m diametres). Most (322) of the trees were small, representing 59% of the total trees in all directions around the houses. Moreover, 176 small and moderate-sized trees accounted for 33% of the entire tree population. There were 42 medium-sized trees (8%), and only two (0.4%) trees were huge in size. There were two significant leaf size and density categories: small and medium.
| Tree size | Distance | Shade tree directions | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| (meter) | N | NE | E | SE | S | SW | W | NW | All | Sum | % | |
| Small | 3–5 | 16 | 14 | 35 | 22 | 25 | 13 | 19 | 26 | 170 | 322 | 59 |
| 6–10 | 23 | 13 | 24 | 4 | 17 | 13 | 27 | 19 | 140 | |||
| 11–15 | 0 | 0 | 1 | 0 | 4 | 1 | 6 | 0 | 12 | |||
| 16–20 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |||
| Small moderate | 3–5 | 4 | 4 | 9 | 10 | 3 | 9 | 5 | 3 | 47 | 176 | 33 |
| 6–10 | 15 | 12 | 22 | 7 | 18 | 16 | 18 | 8 | 116 | |||
| 11–15 | 0 | 0 | 0 | 1 | 3 | 0 | 2 | 0 | 6 | |||
| 16–20 | 0 | 0 | 0 | 0 | 0 | 0 | 7 | 0 | 7 | |||
| Medium | 3–5 | 8 | 2 | 3 | 1 | 1 | 4 | 1 | 0 | 20 | 42 | 8 |
| 6–10 | 6 | 1 | 1 | 2 | 0 | 6 | 3 | 0 | 19 | |||
| 11–15 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 2 | |||
| 16–20 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | |||
| Large | 3–5 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 0 |
| 6–10 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 2 | |||
| 11–15 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |||
| 16–20 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |||
| All sizes/distances | 71 | 47 | 99 | 47 | 78 | 64 | 80 | 56 | 542 | 542 | 100 | |
| Percentage | 13 | 9 | 18 | 9 | 14 | 12 | 15 | 10 | 100 | 100 | 100 | |
The distance between the building structure and the trees was divided into four groups. The ranges of distance were between 0 and 20m. However, 3 metres was the minimum distance for trees. If the trees planted were too close to the buildings, their roots could harm the flooring and foundation structures. Most of the trees, about 51%, were located at a distance of 6–10m, followed by a distance of 0–5m (approximately 44%). Trees planted at distances of 11–15 and 16–20m were fewer, i.e., around 3.5% and 1.5%, respectively.
Shrubs, vines, groundcovers, turf, and trees are essential in landscape design. Shrubs have multiple stems and are relatively shorter in height. They are typically planted in garden areas and on walls. Conversely, vines are planted on walls and garden structures, such as a pergola, to provide shade. Groundcovers and turf were grown to cover earth surfaces. These four types of plants could offer shades in and under their foliage to the buildings’ walls, and windows, as well as underground and garden surfaces. They provide moderate ground temperatures by producing evapotranspiration to cool the surrounding environment. Most tropical shrubs come from flowering plants, edible palms, and bamboo. Figure 6 exhibits the distribution of shrubs, vines, and groundcovers around the houses to create tropical landscape styles of balance and harmony. There were 1903 individuals and groups of shrubs with varying sizes and heights, 67 places of vines, and 44 groups of groundcovers. The rest of the garden surfaces were planted with turf, giving the garden areas a soft and lush appearance.
Givoni (1994) asserted that the relative importance of natural lighting and ventilation problems significantly influences the building facade and opening. Most houses’ main facade orientations were in north-south and northwest-southeast directions. These orientations faced indirect sunlight and had the potential to minimise the heat gain from the buildings. Minimal solar penetration into the interior spaces and encouraging natural cross-ventilation during the day and night are also influenced by the strategic location of glass openings along walls. Each wall direction in the study had an average vertical glass opening of 13.3m2 per side. At the same time, most of the sliding doors faced the central garden of each house. Shading devices were installed on all windows to protect them from direct solar radiation during the day’s peak.
The primary function of shrubs and vines is to provide shading along the walls and windows of buildings in the morning and late afternoon. Simultaneously, other low plants helped cover the soil surface around the houses and gardens, keeping them at a moderate temperature. Although the opening in each house had been built with an adequate shading device, sunlight would still be able to penetrate the buildings’ interior without the help of shrubs of the appropriate size and height. The sunlight could directly touch the east and west directions of the buildings on the walls that did not have shrubs. Moreover, having windows and doors that were more open could encourage natural cross-ventilation flow, especially when the surrounding air was cold. Cold air would increase interior comfort while also indirectly lowering energy costs for air conditioning cooling systematically.
In the tropics, the ratios of solar reflections to wall and roof surfaces were critical, as expressed by the albedo value. The value of albedo was influenced by the reflective ability of solar radiation on building envelopes. The surface colour of the outer envelope had a significant sunlight effect on the buildings and the internal temperature. Hence, the average home albedo value was 0.22 for light-coloured paint on walls mixed with light and dark roofing. However, this value was sufficient to reflect sunlight on the buildings’ envelope. The insulated roof was well-used for all houses. The material covered under the roof tiles was a layer of aluminium foil, equivalent to a height of 2.9m from the precise ceiling construction. The material served as an insulator for the roof. The insulating layer is designed to reflect and prevent heat rise from the roof surface, resulting in a cool and comfortable interior environment.
According to Hariri (2010), an Assistant Manager of Customer Relations and Marketing for TNB Shah Alam, the energy consumption increment was influenced by the two seasons’ varied air temperatures. The air temperature in the dry season could reach as high as 2.5ºC compared to the wet season. This has an indirect effect on the high use of air conditioning during the dry season, significantly raising residential buildings’ electricity bills. 90% of the houses in the study areas operated air-conditioning systems as active systems to achieve thermal comfort in their homes. On average, the total energy used for cooling during the wet season reached approximately 36.7% for each house per month. However, the cooling energy is predicted to increase by 11.5% to 48.2% per month during the dry season. The energy consumption for air conditioning will increase annually due to the current global climate change phenomenon. Therefore, landscaping around the houses could influence air conditioning. This is because the cooler outdoor ambient air directly affected the indoor spaces of the houses.
An ordinary tropical landscape design had been widely practised in the study areas. Native tropical and sub-tropical evergreen plant species were chosen for a lively and harmonic garden design. A sufficient number of plants of adequate sizes could provide pleasant and comfortable ambient air around the garden. During the wet season, most plants were in fertile, green, and lush conditions, which had an impact on the surrounding area. In the study areas, trees were dominant and promoted as usable shades for buildings and garden surfaces, while shrubs, vines, groundcovers, and turf also provided shading on a lesser scale. Each of them generated evapotranspiration, cooling the surrounding garden.
Most small and moderate-sized trees had been planted in all houses with sufficient trunk heights to allow wind to flow into the garden and building surfaces. These sizes were suitable for low-density residential areas. They were proportional to the heights of the buildings and safe according to their physical strength. The building’s eastern and western parts were the most critical facades, which received high temperatures and heat gain in the morning and afternoon. Trees outnumbered them at approximately 18% and 15%, effectively promoting shades. However, the north and south sides also planted vast trees at around 13% and 14%, respectively. The direct sunlight, almost in the middle, required shades at every angle to keep the houses cool and comfortable. Besides, most trees in the study areas were 6–10m (51%) and 0–5m (44%) from the buildings. These distances were closed and strategically positioned for cooling purposes by providing full shade and cool effects to the buildings and surrounding gardens.
In order to establish the effectiveness of using landscaping to reduce the energy consumed in buildings in a hot and humid tropical climate, several comparisons were made with the energy consumed by houses that were minimally to moderately landscaped. Figure 7 shows the fluctuating pattern of cooling energy (%) use compared to the houses’ landscaping amounts. The essential tool for this measurement of cooling was closely related to the number of trees, which was also well supported by shrubs, vines, and groundcovers. The linear data for cooling energy usage gradually increased when fewer trees were planted around the houses.
Similarly, less cooling energy will be generated if more trees are planted around the houses. Hence, the result revealed that landscaping had a considerable impact on the cooling energy of the houses. Figure 7 compares the number of trees in the garden to their average cooling energy use. The polynomial data for cooling energy used gradually declined as the number of trees rose. The first group of below-five trees planted around the houses (18% of houses) needed up to 43% of the cooling energy. For twenty and more trees (10% of houses) planted around the houses, they provided a significant advantage, with cooling energy generated as low as 36%. The cooling energy savings between five and 20 small to small-moderate trees was 7%. These energy-savings were equal to MYR233 (948kWh) per house per year.
In this study, most houses applied a moderate landscape style. They were planted in groups of six to ten trees (34% of houses) and 11–19 trees (30% of houses) around the houses. These houses saved 2% and 4% on cooling energy, respectively. Their cooling energy could be saved as much as MYR68 (271kWh) and MYR133 (541kWh) per house per year. Studies have stressed that significant cooling energy savings could be gained by strategically planting several trees on the west and east sides of the houses to stimulate maximum wind flow and provide ample shade (Figure 8,Figure 9,Figure 10,Figure 11). These tree clusters could also offer beneficial shade and increase wind to flow into the house (Figure 8 and Figure 11). Evapotranspiration cooling, along with shrubs and other soft landscape elements around the houses, had been produced and provided a cool, comfortable, and pleasant environment.
This study indicates that both housing areas in Shah Alam and Putrajaya had slightly different weather; however, most houses had similar results in energy-savings. Landscaping is one of the most effective tools for reducing the energy consumed in tropical residential space cooling. Strategic positioning and sufficient amounts of trees, supported by shrubs, vines, and groundcover, can optimise energy-savings, particularly during peak load of the day, by decreasing air conditioning consumption and enhancing comfort levels for house occupants. The tropical building construction and its attributes were similarly designed. The building envelopes were likewise comparable, with medium amounts of single-layered glass windows and sliding doors installed on either side of the houses, along with adequate roof projection and shading devices. They also possessed a similar albedo value of 0.22. The data obtained from the cooling energy use was compared to soft landscape elements around the houses to ensure the data's comparability with minimum and moderate landscaping. Most small-sized trees were located 3–10m from buildings, while small moderate trees were located 6–10m from buildings on the east and west sides. These provided effective shading for the buildings and surrounding gardens. Their average trunk heights of up to 2 metres would effectively allow the breeze to flow into the houses and gardens. More trees, supported by shrubs, vines, groundcovers, and turf cover, could provide more evaporated cooling. Therefore, the most extensive cooling energy savings were 7%, equal to 948kWh (MYR233) per house per year.
Limitations and future studiesHowever, this study area is limited to the tropical climate of Malaysia and a specific type of residence: medium-sized single-family houses with gardens planted with new or mature landscaping. The construction of the houses chosen was similar, using concrete and brick materials to find a similar response to the surrounding evergreen landscaping. The house’s location was also limited to the Klang Valley of Malaysia, with a moderate number of houses and participants interviewed. If more occupants from more housing estates participated in the survey, the increase in data regarding diverse building constructions, landscaping techniques, and the living habits of the occupants would improve the results. Future studies will source more data but still focus on modest-sized houses with diverse landscaping and occupants so that the validity of the results on the effect of various stratifications of landscaping representing a large number of different social backgrounds and lifestyles of users can be obtained from a more diversified preferred solution for energy savings.This study’s data were only recorded during the day. This was because the residents preferred not to have their privacy invaded as they secured their property carefully at this time. However, most nights during the rainy season contain light rainfall for a few hours, so information about these times should be gathered.
Housing estates in the tropical city centre contribute to the urban heat island phenomenon. The heat gain in individual houses spreads to entire neighbourhoods. Each neighbourhood collaborates with those adjacent to it to form the city’s microclimate. In the future study, these climate data for the whole neighbourhood will be produced by the Geographic Information System (GIS). An Urban Climate Analysis Map (GIS) is needed to manage multiple data layers in the specific neighbourhood area. Three options can be used to alter the urban heat island effect: land cover alteration, anthropogenic heat reduction, and wind utilisation. Other benefits include improving the aesthetics of the area, increasing property value, and improving the absorption of CO2.
The author has read and agreed to the published version of the manuscript.
The authors declare that they have no conflicts of interest regarding the publication of the paper.
