This document proposes a methodology to investigate the effects of strategic vegetation planting on the thermal performance of housing in a tropical environment. The study aims to quantify the temperature reduction and energy savings potential of vegetation for the average tropical residence. The methodology involves examining different planting patterns and structures, quantifying the relationship between vegetation and building energy use through simulations and field measurements, and developing design guidelines based on the results. The research will be conducted on single-family homes in Kuala Lumpur, Malaysia to analyze the impacts of surrounding vegetation of different ages.

1. A PROPOSED METHODOLOGY FOR INVESTIGATING THE EFFECTS
OF THE STRATEGIC PLANTING OF VEGETATION ON THE THERMAL
PERFORMANCE OF HOUSING IN A TROPICAL ENVIRONMENT
Alamah Misni 1, George Baird 2, Penny Allan 3
1
University of Technology Mara, Malaysia
2&3
Victoria University of Wellington, New Zealand.
alamahmisni@yahoo.com, George.Baird@vuw.ac.nz & Penny.Allan@vuw.ac.nz
ABSTRACT
Global environmental concerns have made it imperative that we increase the
energy efficiency of our built environment. While design team focus has been
conventionally on the architectural and engineering aspects of energy efficiency,
the effect of the surrounding landscape on the thermal performance of buildings
merits increased attention. At the urban level the „urban heat island effect‟
influences most of the major cities around the world. The absorbed heat is
subsequently re-radiated creating an increase in the surface temperature of
urban structures from 5.5–10°C. As the urban surfaces become hotter, the
overall ambient air temperature can increase by as much as 2–8°C. On hot
summer days, this effect contributes significantly to the urban dweller's
discomfort resulting in an increase in energy bills due to the increased
requirements for cooling. The proposed study will determine how much of the
potential for reducing temperature and increasing energy saving could be
realized for the average residence located in a warm and humid tropical
environment, through the strategic planting of vegetation.
Keywords: thermal performance, vegetation, temperature & energy saving.
INTRODUCTION
Energy costs and environmental concerns have made it more important than
ever to find ways to reduce the energy consumption of our buildings. As human
consumption of energy continues to increase, and while our dependence on
energy is not likely to decrease, it is important to improve the energy efficiency of
our built environment. Making our built environment more energy efficient will
bring great benefit to the environment and also to the owners and users of
buildings.
There are many ways to improve the energy efficiency of the built environment.
Envelope technologies such as wall, floor, and roof insulation, high-performance
windows and doors, and air infiltration have a priority role in producing a
comfortable interior place. However, buildings in warm and humid climates still
frequently depend on energy using for heating, cooling and ventilation systems to
control the environment. That energy use is dependent on a number of
variables, such as the climate, the surrounding vegetation, the orientation, the
structure and the materials used in the construction of the building envelopes. In
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2. essence, climatic factors have a significant effect on the balance of energy usage
in buildings. By controlling the microclimate, it is possible to control the energy
usage for heating and cooling in buildings (McClenon 1983).
Architects can create a microclimate boundary by manipulating the building
envelope and exterior environment (Bomberg and Brown 1993). The planning
and development of exterior spaces can reduce the energy consumption of
buildings by reducing the adverse impact of some climate factors. If the
microclimatic condition around the building is very similar to the desired interior
condition, little extra energy is required. Conversely, if the microclimate is
significantly different from the desired interior conditions, large amounts of energy
may be required for heating or cooling. Awareness and knowledge of the
potential of vegetation to modify microclimate could produce a new method to
quantify the energy saving potential of landscaping (Moffat and Schiler 1981).
This paper will describe the potential benefit of the effects of vegetation, on the
thermal performance of housing in a tropical environment. It will present
background information, identify key issues, state the hypothesis, clarify the aim
and objectives, and propose a methodology.
BACKGROUND OF THE STUDY
Generally, the concern of building designers has focused on thermal comfort and
protection from the elements (ASHRAE 2003; Oral, Yener et al. 2003; Nadel
2006). Designers usually rely upon integration of the building envelope and the
building‟s passive systems to improve thermal performance. Designs focus on
integrating building form and fabric, with the passive systems of environmental
control and the mechanical equipment for heating, ventilation and air-conditioning
(HVAC).
A building‟s thermal performance and energy consumption are influenced by the
layout of buildings, external shading devices, the surface colour, and the
insulation of buildings. Highly reflective finishes for walls, openings, and roofs,
which provide a high amount of albedo, can also indirectly improve a building's
thermal performance. However, proper landscaping, water features and other
landscape structures can also be used to improve thermal performance. They
reduce the amount of radiation falling on the building by shading, by moderating
temperatures, by the evapotranspiration processes, and by controlling wind
direction to assist in keeping the building warm or cool. The design of external
spaces needs to be prioritized because conditions there will influence the building
interior.
The role of landscaping in moderating microclimate has been explored all over
the world during recent years. Landscaping is actually an ecological measure to
combat the problems of heavy urban built environment (Wong and Yu 2005).
Vegetation has the potential to increase environmental value by reducing energy
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3. consumption in individual buildings and increasing the energy efficiency of the
community as a whole.
Vegetation has a particularly effective influence on microclimate and associated
building thermal performance (McPherson, Herrington et al. 1988). Vegetation is
all the plant life in a particular region such as trees, shrubs, grasses and lawns.
Vegetation can influence solar radiation, air temperature, humidity and air flow.
While there are a number of landscape strategies that can be implemented to
modify the microclimate, the three main functions of vegetation used to do this
are shade, evapotranspiration, and wind control. Strategically placed shade
trees of the right species and form placed around the building can potentially
modify microclimate and building energy use through shading. This shading can
reduce the amount of radiant energy absorbed and stored by buildings and other
built surfaces. Evapotranspiration is the process of transferring moisture from the
earth to the atmosphere by evaporation of water and transpiration from plants,
thereby cooling the air (Simpson 2002). Vegetation can also be used to control
wind as a barrier or windbreaks and provide more effective ventilation and
convective cooling of building surfaces by channelling or directing the flow of air.
However, there is a lack of data on the effects of vegetation on the thermal
performance of buildings and their microclimates, and the methods for predicting
the effect from shade, evapotranspiration, and channelling wind to reduce hot
temperatures and energy used. Computer models are needed to better predict
the impacts of vegetation and other landscape elements on buildings,
microclimate and energy use (McPherson, Herrington et al. 1988). With
quantitative evidence of energy savings, the likelihood of design implementation
could greatly increase. Policy makers will have a basis for implementing new
landscaping requirements. Architects will have alternative methods and ideas for
complying with the energy saving guidelines by integrating the building with its
site. Developers will be able to entice buyers with the future long term energy-
efficient mortgage credits with only a potentially minimal increase in the early
stage cost of construction of landscaping around the building.
This study will focus on two main issues: environmental issues, and energy
conservation issues.
Environmental issues
Global warming is defined as the increase of the average temperature on earth
(Diekmann 2007). Lechner (2000) mentions that, depending on the scenario
(population and economy growth, energy requirements, etc.), the air temperature
near the ground is predicted to increase by a global average of from 1.8–4.0°C
by the year 2100. An increase of 1°C will make the earth warmer now than it has
been for at least a thousand years. Global warming and the resulting climate
change are predicted to have a serious effect on the planet. As the earth is
getting hotter, disasters like hurricanes, droughts, and floods are becoming more
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4. frequent (Lindinger 2007). Carbon dioxide is a major contributor to the
greenhouse effect and global warming. Burning fossil fuels such as natural gas,
coal, oil, and gasoline raises the level of carbon dioxide in the atmosphere and as
more “greenhouse gases” are produced, they trap more of the sun‟s heat.
As humans alter the character of the natural landscape in the city-building
process, the local energy exchanges that take place within the boundary layer
are affected. Therefore, modification of the landscape influences the local
(microscale), mesoscale, and macroscale climate.
At the urban level the urban heat island effect is a phenomenon where air
temperatures in densely built urban areas are higher than the temperatures of the
surrounding rural country. These heat islands influence most of the major cities
around the world (Akbari, Davis et al. 1992). In urban areas, building and paved
surfaces have gradually replaced pre-existing natural landscapes. As a result,
solar energy is absorbed into building structures, roads, and other hard surfaces
during daytime. The absorbed heat is subsequently re-radiated to the
surroundings and increases ambient temperatures at night causing the surface
temperature of urban structure to become 5.5–10°C higher than surrounding
areas (Akbari, Davis et al. 1992). As the surface throughout an entire
community becomes hotter, the overall ambient air temperature increases by 2–
8°C. In warm and humid tropical climates, heat islands contribute significantly to
the urban dweller's summer discomfort and energy bills due to the increased
cooling loads. Taha et al. (1988) state that, houses are particularly sensitive to
this effect since they are envelope-dominated structures.
Urban heat islands are considered as a mild asset in winter and can reduce the
demand for heating. However they can significantly increase the demand for
cooling energy during the summer.
Energy conservation issues
Improved living standards and the increased population in developing countries
are parameters that may contribute to a dramatic increase in building energy
consumption worldwide. An increase of the urban population by 1 percent has
been reported to increase energy consumption by 2.2% (Santamouris 2001), and
an annual energy consumption increase of 30–40% by the year 2010 was
predicted by the International Energy Agency in 1995 (Battle and McCarthy
2001). A study of the tropical city of Singapore shows the anticipated increase in
building energy consumption is mainly for air conditioning (Tso 1994). By
designing houses with energy efficiency in mind, the amount of energy needed to
keep the house comfortable can be reduced dramatically.
This issue is particularly important in tropical climates due to high temperatures
and humidity all year round. These climates and the increase in the purchasing
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5. power of the population lead to greater use of air-conditioners. Air conditioning is
often seen as the only means of achieving thermal comfort during the hot season
but unfortunately it consumes a high amount of energy. In warm and humid
tropical climates designers should provide a microclimate in any built
environment such that people would have an energy balance of “near zero”(not
overheated or underheated) (Bakar 2002).
RESEARCH HYPOTHESIS
This research argues for the following hypothesis: well designed landscaping
around tropical domestic buildings contributes significantly to cooling the
surroundings and saving energy.
The hypothesis will focus on two main research questions. The questions are:
(1) how much can temperature be decreased by well-designed landscaping
around tropical domestic building? (2) How much energy can be saved through
well-designed landscaping around the tropical domestic buildings and their
immediate neighbourhood?
AIM AND OBJECTIVES
The aim of this study is to examine and quantify the relationship between
surrounding vegetation, and the thermal performance of housing in a warm and
humid tropical environment The primary objective is to determine, for the
average tropical residence, the reduction in temperature and energy savings
potential of vegetation. The literature (see for example Akbari, Parker,
McPherson, Simpson, and Taha) is fairly consistent in its recommendations for
where trees should be placed for optimal energy benefits. In reality, houses vary
considerably in orientation, and homeowners generally make landscaping
decisions based upon aesthetics.
There are three specific research objectives to achieve the primary objective:
examine planting patterns and structures, quantify and validate the results, and
develop design guidelines.
Examine planting patterns and structures
Examine planting patterns and structures in relation to the specific orientation of
tropical domestic buildings and to determine the magnitude of benefit from
vegetation. Tree-shade alters building cooling loads by reducing incident solar
radiation (Simpson 2002). A related question is whether the shading benefits of
vegetation are of primary importance or whether the transpiration cooling plays
an important role in the building energy balance equation. In other words, is
there a measurable benefit from shrubs and grass or it is only trees that can
effectively provide the cooling benefit? And does the leaf size and structure of
vegetation play a role? It is also important to determine the relationship between
the quantity of vegetation and energy consumption of the adjacent building.
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6. Quantify and validate the results
Quantify the relationship between vegetation, building construction and human
factors on thermal performance, and validating those results. What is the impact
of vegetation on a house, and how much can that benefit increase if the quantity,
type or configuration of vegetation is increased? The strategy for this study is to
obtain a large enough sample of existing homes such that the vagaries of the
occupants‟ energy-use habits and building design could be effectively averaged
over the data set. In doing so, the computer simulation and analysis should
reveal the relative importance of each of these human and building construction
variables along with the vegetation variables for a comprehensive picture of
residential cooling loads.
Design guidelines
Translate the validated results of the relationship between vegetation, building
construction and human factors on thermal performance into design guidelines.
Finally, the results of this study will be interpreted for those who could benefit
from the information. Homeowners, energy companies, housing departments,
policy makers, and the members of the construction industry need to understand
the implications of landscaping around housing areas, and other buildings. The
intent is to use the results of the analysis to generate design guidelines for
effectively integrating vegetation with housing in a warm and humid tropical
environment.
RESEARCH METHODOLOGY
The area of this study is in the tropical city of Kuala Lumpur and in other cities
nearby. Kuala Lumpur is located at 3° North latitude and 101° East longitude. It
is in the warm and humid tropical climate region with abundant solar radiation
and averages six hours of sunshine per day (Zakaria, Mokhtar et al. 2008). In
Malaysia, single family houses with a surrounding garden are presently the most
common type of house typology for the middle and upper classes. Medium sized
single-family houses (190–380 square metre) in the context of the tropical city of
Malaysia will be chosen in these studies based on its unique characteristics.
Most conventional single-family houses are built on land lots with open space
around the building. The area surrounding the house is commonly called a
garden. The garden includes the entire space around the building and is private
to the owner and family. This research will be undertaken in at least two different
phases of single-family housing development; the first development of housing
with surrounding vegetation aged more from 20–30 years and the second
development, less than 5 years. The reason for choosing a different age of
housing estate is because of the different of age and maturity of landscaping
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7. around the house as this influences the energy used and thermal comfort and
performance for the home resident.
The current practice of domestic buildings construction and material used in the
context of Malaysia will be applied in this study. Buildings are usually
constructed using reinforced concrete as a main structure, walls of brickwork laid
in cement mortar, hardwood construction timber and roof coverings of tiles. Roof
insulation is generally used as a barrier to prevent hot air from radiating down
into the house‟s habitable space. Shading includes roof eaves (overhang) and
window eaves (awning) that may reduce direct sunlight penetration into the wall.
The tropical and subtropical plants from different types of foliage, ranging from
ground cover vegetation, through to different kinds of shrubs, grasses, to trees of
various sizes and types will be applied in this study. The length and patterns of
shade varies with the time of day.
Research methodology is divided into two stages:
Stage 1
In Malaysia, the air conditioning of almost every house is proving to be a
successful way of dealing with the extremes of an uncomfortably hot summer
day. Air conditioners account for about 30% of total electricity consumption for
residential buildings (Saidur, Hasanuzzaman et al. 2009).
This research will quantify the vegetation effects on a large number of buildings
in neighbourhood areas. Field measurements and computer simulation will be
used to measure and evaluate thermal performance. The fieldwork
measurements structure is divided into four categories: weather data, building
construction, landscaping, and human factors. Simulation models that account for
plant type and configurations (species, age and location), building characteristics
(building surfaces, window area, building orientation, level of insulation), human
factors, and weather conditions can be used to estimate the effect of vegetation
on cooling energy use (Simpson 2002). This survey and field measurement will
also evaluate the amount of energy consumption for every house in monthly to
yearly figures manually. It will use the amount of electricity consumption for two
types of single-family dwelling: dwellings with mature surrounding vegetation,
and dwellings with immature surrounding vegetation. The scale will be larger: the
target respondents are about 150 houses.
Weather data will be validated from „Meteorology Department‟ for year 2008–
2009. Key plan, layout plan, building plan, and detailing including landscape,
buildings and its neighbourhood from local authority, housing department, and
aerial photographs from „Google earth‟. However, direct observation will be
essential. Electricity or energy consumption data will be validated from „Energy
Department‟ for each house in 2008–2009 and household data from „Economic
Planning Unit‟.
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8. The energy savings will be calculated by taking the difference between estimated
annual air conditioning costs for a given house with and without vegetation. The
energy saving will also be potentially influenced by vegetation species and their
configuration. The results of the effects of vegetation, building construction and
human factors on the thermal performance of housing in a warm and humid
tropical environment will be analysed to determine the amount of energy used
and energy saving for the two different types of single-family housing
development.
Stage 2
The data will be produced by computer simulation models which will be used in
this study to test, evaluate, and analyse the impact of vegetation on building
thermal performance for two different of single-family dwelling. The houses will
be chosen from stage 1 to be similar in size, building construction, and household
but different in landscaping. Two different types of single family dwelling with and
without air-conditioning will be chosen by strategic location: dwellings with
mature surrounding vegetation, and dwellings with immature surrounding
vegetation. The scale will be smaller: the target respondents are about 10
houses. The landscape design will be divided into at least three designs for
comparison and one design without landscape. The landscape design will use
different amount, species, and configurations of vegetation. Choice of vegetation
will be based on their shade, evapotranspiration, and wind channelling
characteristics. Different colours of building envelope also will be included in this
fieldwork.
This experiment will use quantitative measurements to document savings in the
energy used for air conditioning through every type of vegetation include trees,
shrubs, lawn, and grasses. The data will be obtained from internal condition and
during days of similar climate conditions to ensure the comparability of the data
for house with and without landscaping. The weather data will be stated in every
hourly inside and outside of the house. The energy consumption by air
conditioning also will be given hourly. The albedo data for every type of building
envelop will be stated during day time. Landscape elements and house
configurations will be drawn to scale and detail. Infrared thermography will be
used to explain the current situation of thermal performance of the houses.
An analysis of the reduction of ambient temperature and in air conditioning
consumption during the day and the hottest afternoons or night will reveal the
savings potentially associated with the corresponding landscaping.
CONCLUSION
In this study the direct and indirect thermal impacts of vegetation around single
family dwellings and their neighbourhood under warm humid tropical climatic
conditions will be investigated through field measurements. Data on the effects of
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9. vegetation on the thermal performance of buildings and their microclimates, and
the methods for predicting the effects of shade, evapotranspiration and
channelling wind to reduce the temperature and energy used will be used to
analyse the results. Computer models will be used to quantify produce the
quantitative result on the impacts of vegetation and other landscape elements on
thermal performance of the buildings, microclimate and energy use. With this
quantitative evidence of energy savings and thermal performance design
guidelines will be developed to assist the construction team and industries, and
the owner of the building and their communities, to increase the energy efficiency
and thermal performance of dwellings in warm and humid tropical climates.
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