Master of Science Thesis KTH School of Industrial Engineering and Management Energy Technology EGI-2012-70MSC Division of xxx SE-100 44 STOCKHOLM Analysis of Building Envelops to Optimize Energy Efficiency as per Code of Practice for Energy Efficient Buildings in Sri Lanka -2008 Epa Arachchillage Ushani Chamikala Epa Kumari
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Master of Science Thesis
KTH School of Industrial Engineering and Management
Energy Technology EGI-2012-70MSC
Division of xxx
SE-100 44 STOCKHOLM
Analysis of Building Envelops to
Optimize Energy Efficiency as per
Code of Practice for Energy Efficient
Buildings in Sri Lanka -2008
Epa Arachchillage Ushani Chamikala Epa
Kumari
i
Master of Science Thesis EGI-2012-70MSC
Analysis of Building Envelops to Optimize Energy
Efficiency as per Code of Practice for Energy
Efficient Buildings in Sri Lanka -2008
Epa Arachchillage Ushani Chamikala Epa Kumari
Approved
Examiner
Dr. Jaime Arias
Supervisor
KTH: Dr. Jaime Arias
OUSL: Prof. Rahula
Attalage
Commissioner
Contact person
Abstract
Residential and commercial buildings consume approximately 20% of the global energy generation. This
value is continuously growing and the governments across the globe have realized the importance of
regulating the building construction to optimize the energy utilization. Energy efficient building codes
have been developed to optimize the energy efficiency in buildings. OTTV (Overall Thermal Transfer
Value) is a key parameter for evaluating energy efficiency of building envelops in the present building code
of Sri Lanka. In this research, the prescriptive requirements mentioned in the building code for the
building envelops to optimize the energy efficiency of five (05) commercial buildings has been analyzed.
The indoor climate was modeled and the annual cooling energy variation with Overall Thermal Transfer
Value was studied using “DesignBuilder” software. A cost benefit analysis was carried out for enhanced
energy efficiency building envelops applications. It was attempted to develop a general relationship
between the OTTV and annual cooling energy requirement for each building. It has been observed that a
second order polynomial relationship with R2 of 0.861 exists for RDA building, linear relationship with R2
of 0.838 exists for AirMech building. However a specific relationship could not be observed for BMICH,
SLSI and WTC buildings. The impact on cooling energy requirement from envelop parameter
modification is unique for each building. In some instances the reduction of OTTV has not resulted in
any reduction of the cooling energy requirement. There is a combined effect from each building
component which affects the final cooling energy requirement. A simulation based technique to be used
1.2 Problem statement ...................................................................................................................................... 2
2 Literature Review ....................................................................................................................... 4
2.1 History of building codes in the world .................................................................................................... 4
2.2 Types of regulations.................................................................................................................................... 4
2.2.1 Prescriptive type regulations ............................................................................................................ 4
2.2.2 Trade-off type regulations ................................................................................................................ 5
2.2.3 Model building type regulations ...................................................................................................... 5
2.2.4 Energy frame type regulations ......................................................................................................... 5
2.2.5 Performance type regulations .......................................................................................................... 5
2.3 Code of Practice for Energy Efficient Buildings in Sri Lanka – 2008 ................................................ 6
3.1 Identification of five (05) office buildings in Colombo, Sri Lanka ...................................................18
3.2 Collection of data for calculation of the building envelop properties ..............................................19
3.3 Modeling of indoor climate .....................................................................................................................19
3.3.1 Building 1: Project Office of Greater Colombo Urban Transport Development Project ...21
3.3.2 Building 2: Wing 4 G of Bandaranayke Memorial International Conference Hall ...............24
3.3.3 Building 3: Air- Mech Engineering Office ...................................................................................27
3.3.4 Building 4: Sri Lanka Standards Institute (SLSI) ........................................................................30
3.3.5 Building 5: World Trade Centre (WTC) .......................................................................................34
iii
4 Analysis of Results ................................................................................................................... 37
4.1 Analysis of Simulation Results ................................................................................................................37
4.2 Cost benefit analysis for enhanced energy efficiency building envelops applications ...................38
4.2.1 Building 1 (RDA) .............................................................................................................................39
4.2.2 Building 2 (BMICH) ........................................................................................................................40
4.2.3 Building 3 (Air-Mech) .....................................................................................................................41
4.2.4 Building 4 (SLSI) ..............................................................................................................................42
4.2.5 Building 5 (WTC) .............................................................................................................................43
4.3 Summary of the optimum building envelops models .........................................................................43
5 Discussion and Conclusion ..................................................................................................... 45
ANNEXURE 1: Calculation of OTTV and annual cooling energy of buildings………………………...51
ANNEXURE 2: Cost of Building Materials …………………………………………………………..106
iv
Index of Tables
Table 2-1: Maximum U-values for facades with or without fenestration ............................................................................13 Table 2-2: Maximum U-Factor values for roofs ...............................................................................................................14 Table 3-1: Assumptions and data used for buildings simulation .......................................................................................20 Table 3-2: Absolute and percentage reduction of OTTV and annual cooling energy with modifications of building 1 .........23 Table 3-3: Absolute and percentage reduction of OTTV and annual cooling energy with modifications of building 2 .........26 Table 3-4: Absolute and percentage reduction of OTTV and annual cooling energy with modifications of building 3 .........29 Table 3-5: Absolute and percentage reduction of OTTV and annual cooling energy with modifications of building 4 .........32 Table 3-6: Absolute and percentage reduction of OTTV and annual cooling energy with modification of building 5 ...........35 Table 4-1: Building modifications resulted to increase of annual cooling energy ...................................................................37 Table 4-2: Relationship between OTTV and annual cooling energy ..................................................................................37 Table 4-3: LCC for different modifications of building 1 ..................................................................................................39 Table 4-4: LCC for different modifications of building 2 ..................................................................................................40 Table 4-5: LCC for different modifications of building 3 ..................................................................................................41 Table 4-6: LCC for different modifications of building 4 ..................................................................................................42 Table 4-7: LCC for different modifications of building 5 ..................................................................................................43 Table 4-8: Recommended modification for buildings ..........................................................................................................43 Table 5-1: Variation of OTTV and specific annual cooling energy requirement with modification for buildings .................45
v
Index of Figures
Figure 1-1: Share of electricity consumption in Sri Lanka .................................................................................................. 1 Figure 2-1: Exterior and semi-exterior building envelop ..................................................................................................... 7 Figure 2-2: Schematic showing three modes of heat transfer of an exterior envelop element .................................................... 7 Figure 2-3: Nomenclature for conduction in plane walls ...................................................................................................... 8 Figure 2-4: Thermal radiation effects of wall .....................................................................................................................10 Figure 2-5: Climatic zones of Sri Lanka .........................................................................................................................12 Figure 2-6: Input/output to the DesignBuilder software ...................................................................................................17 Figure 3-1: Layout diagram of the existing building 1 ......................................................................................................22 Figure 3-2: Variation of the annual cooling energy with the OTTV of the building 1 .......................................................24 Figure 3-3: Layout diagram of the existing building 2 ......................................................................................................25 Figure 3-4: Variation of the annual cooling energy with the OTTV of the building 2 .......................................................27 Figure 3-5: Layout diagram of the existing building 3 ......................................................................................................28 Figure 3-6: Variation of the annual cooling energy with the OTTV of the building 3 .......................................................30 Figure 3-7: Layout diagram of the existing building 4 ......................................................................................................31 Figure 3-8: Variation of the annual cooling energy with the OTTV of the building 4 .......................................................33 Figure 3-9: Variation of the annual cooling energy with the OTTV of the building 4 (after removing two data points) ......33 Figure 3-10: Layout diagram of the existing building 5 ....................................................................................................34 Figure 3-11: Variation of the annual cooling energy with the OTTV of the building 5 .....................................................35 Figure 3-12: Variation of the annual cooling energy with the OTTV of the building 5(after removing two data points) .....36 Figure 5-1: Variation of specific annual energy consumption Vs OTTV for buildings ......................................................46
vi
Nomenclature
OECD Organization for Economic Cooperation and Development SLSEA Sri Lanka Sustainable Energy Authority
U.S United Status
OTTV Overall Thermal Transfer Value W/m2
U Overall heat transfer Coefficient W/m2.0C
R Unit thermal resistance m2.0C/W
CEB Ceylon Electricity Board
EEBC Code of Practice for Energy Efficient Buildings in Sri Lanka 2008
ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers
IHG Internal Heat Gains
DLG Double Layer Glazing
LKR Sri Lankan Rupees
1
1 Introduction
This chapter provides an introduction to the research. There are three subsections to this introduction,
namely; background, problem statement and objectives. The background section describes the global
energy utilization in building sector and importance of the energy efficient building regulations. The
problem statement focuses some issues identified in the “Code of Practice for Energy Efficient Buildings
in Sri Lanka -2008”. The objectives of the research scope are mentioned in the third part.
1.1 Background
According to the International Energy Outlook 2010, residential and commercial buildings consume
about one fifth of the world’s total energy delivered. It is projected that the energy need growth rate
among residential and commercial sector of non-OECD nations from 2007 to 2035 are 1.9 percent per
year and 2.7 percent per year respectively [U.S. Energy Information Administration, 2010]. In both these
sectors energy goes for the building systems of different nature. This includes energy used for controlling
the climate in buildings, energy used for appliances, lighting and other installed equipment.
As far as the national level electricity consumption is concerned, the use of electricity in buildings
accounts for a large share of the total national energy consumption. Commercial sector, under which large
scale buildings are there, contributes to 24% of the consumption, and the consumption of the domestic
sector is 40% .Total annual electricity consumption in 2010 is 9208 GWh [Sri Lanka Sustainable Energy
Authority, 2010].
Figure 1-1: Share of electricity consumption in Sri Lanka (Sri Lanka Sustainable Energy Authority, 2010)
Building materials and technologies, and building practices have evolved through ages. Housing and
building conditions reflect the living standards of the society. People spend significant amount of time of
Domestic40%
Industrial34%
Commercial24%
Religious1%
Street lighting1%
2
their life in indoors and the condition of the built environment mainly affect to the comfort, health and
productivity of occupants.
In a large scale building, air conditioning is the highest share of electricity load and lighting also
contributes to a significant portion. A significant amount of energy wasted due to the inefficient design,
equipments and inappropriate behavior of occupants.
As such, in the light of the current energy crisis, any positive changes in this sector targeting the efficient
use of energy would have a significantly positive impact on the overall energy consumption of the country.
Buildings are designed for many decades and inefficient buildings consume more energy basically for
space conditioning and lighting. It has been realized that the life cycle cost of a building can be drastically
reduced through better planning and designing. Introduction of energy efficient measures during initial
state may involve no or least cost as an example consideration of building orientation, size and orientation
of windows, selection of construction materials, introduction of natural ventilation and passive design
techniques, installation of efficient equipments etc. But it reduces the lighting, ventilation and cooling or
heating energy during operation. Improvement of energy efficiency of a building at the planning stage is
relatively simple and cost effective while improvements after the construction are much more difficult.
Building codes or energy standards introduce minimum energy performance standards for new buildings
and retrofits. Energy efficiency requirements in building codes or energy standards for new buildings are
therefore among the most important single measures towards improving energy efficiency.
1.2 Problem statement
Code of Practice for Energy Efficient Buildings in Sri Lanka – 2008 has introduced by the Sri Lanka
Sustainable Energy Authority (SLSEA) in year 2009. It has defined the minimum energy performance
standards under five elements namely; lighting, ventilation and air conditioning systems, building envelops,
service and water heating and electrical power distribution [Sri Lanka Sustainable Energy Authority, 2009].
At the moment the Code is in implementation phase and it is practiced by professionals and building
constructors in voluntary basis. Although the SLSEA has defined these minimum energy performance
values, those have not been verified yet.
Building envelop refers to the external elements of the building namely roof, wall, floors and fenestration.
External heat gains and losses of the building are occurred through the envelop. Therefore the properties
of the envelop materials directly affect to the thermal and visual comfort of the occupants as well as the
energy consumption of the building. The building envelop is one of the major element which has huge
potential to reduce the life cycle cost by proper design during the design phase. This research is focused in
finding solutions to following problems of building envelop section of the Code.
1. The impact of the minimum energy performance standards (prescribed in the building code for the
building envelops) to the building energy efficiency has not been verified.
2. The incremental cost benefit of prescriptive parameters vs energy efficiency has not been quantified.
3. There is no general guideline /grading system for building envelops design based on energy efficiency.
3
1.3 Objectives
The objectives of the research are as follows. These objectives were defined with the view of limiting the
scope of the research to achieve specific target within the available time and resources.
1. Analyze the prescriptive requirements mentioned in the building code for the building envelops to
optimize the energy efficiency of commercial buildings.
2. Modeling of indoor climate and study the cooling energy variation with Overall Thermal Transfer
Value, using “DesignBuilder” software.
3. Carry out a cost benefit analysis for enhanced energy efficiency building envelops applications.
4. Provide general guidelines / recommendations for building envelop design which could be useful to
policy makers.
This chapter provided an introduction to the research project including background, problems to be
solved in this research and the objectives.
4
2 Literature Review
This chapter covers the literature review carried out as a part of the research. The objective of the
literature review was to obtain an in depth understanding of the previous studies carried out in this subject
area. This chapter includes history and overview of the building codes in the world, types of regulations
used for improvement of energy efficiency in buildings, introduction of a code of practice for energy
efficient buildings in Sri Lanka, overview of overall thermal transfer value and overview of the
“DesignBuilder” software.
2.1 History of building codes in the world
Building codes or standards are used from several years ago addressing mainly the occupants' health and
safety. First introduction of insulation requirements for U values, R values and specific insulation
materials or multi glazing was in Scandinavian countries in late 1950s. But in many countries energy
efficient building codes has been introduced and used, specially during the oil crisis in 1970s. [Jens
Laustsen, 2008].
Some of the examples for energy codes available in the world;
1. America - ANSI/ASHRAE/IESNA Standard 90.1-2004 “Energy Standard for Buildings Except
Low-Rise Residential Buildings”
2. Malaysia – Code of Practice on Energy Efficiency and Use of Renewable Energy for Non-
Residential Buildings
3. Philippines – The National Building Code of Philippines
4. India – Energy Conservation Building Code
2.2 Types of regulations
There are different types of energy efficiency regulations which are used in the building codes. Each type
use different approach to achieve the ultimate objective of energy conservation. Basic types are as follows;
1. Prescriptive
2. Trade-off
3. Model building
4. Energy frame
5. Performance
2.2.1 Prescriptive type regulations
In this method, energy efficiency requirements are set for each building part and each part of the
equipment system. As an example, it sets thermal transfer value (U values) or thermal resistance value (R
values) for each element of the building envelop, visual transmittance values for fenestrations, the number
and size of windows or window to wall ratio, coefficient of performance of air conditioners, pumps, fans
etc. In the prescriptive method, it is required to meet each and every individual component with its
specific value [Jens Laustsen, 2008].
5
2.2.2 Trade-off type regulations
In trade-off method it is sets energy efficiency requirements for each component of the building as similar
to the prescriptive method. But there is flexibility to trade-off between different components, so some
values are better and some are worse than the requirements [Jens Laustsen, 2008].
2.2.3 Model building type regulations In this method, it sets the energy efficiency values for each building part and each part of the equipment.
According to the clearly defined calculation method, a building model is developed with the same shape
and characteristics of the actual building are calculated with the energy efficiency set values. Then the
characteristic of the actual building is calculated with the actual values for the individual building parts and
systems, following the same calculation method. Finally the results of the calculation of two buildings are
compared and the actual building must perform as well or better than the model building.
This method offer more freedom and flexibility than prescriptive method. It can replace expensive
systems with more cost effective energy efficient techniques [Jens Laustsen, 2008].
2.2.4 Energy frame type regulations
In Energy Frame method, the overall performance of the building is considered rather than the
performance of individual elements. It sets the values for a building’s maximum energy loss. This is
usually set as a value per m² of building area or as a combination. The building energy loss is calculated
using U-values, temperature, surface and heat gains from sunlight etc according to the specified methods
and set of equations. This method offers the freedom to builder to build parts of the buildings that are
less energy efficient when other parts are made better than typical constructions. As long as the overall
value is met, the building is approved [Jens Laustsen, 2008].
2.2.5 Performance type regulations
In energy performance method, a total requirement for the building is set based on a building’s overall
consumption of energy or fossil fuel or the building’s implied emissions of greenhouse gas. This is usually
set as an overall value, consumption per m² of building area or a mixture, for different types of use or
different types of buildings etc.
The calculations are much comprehensive and it is required to use an advanced computer based model,
which integrate all the different parts and installations of the building. In the energy performance, it is
required to consider the installations of renewable energy, solar gains, recovery of energy losses, shading
and efficiency in installations for energy consumption calculation. Consumption of fossil fuel, building’s
implied emission is calculated comparing the use of different energy forms depending on local energy
conditions.
This method gives optimal freedom for constructors or designers to reduce energy consumption within
the frame by using alternatives [Jens Laustsen, 2008].
6
2.3 Code of Practice for Energy Efficient Buildings in Sri
Lanka – 2008
The history of the energy efficient building codes in Sri Lanka runs back to year 2000. Realizing the
pressing need for the revitalization of building design in the country, Ceylon Electricity Board (CEB)
developed an Energy Efficient Building Code (EEBC) way back in 2000. Unfortunately, as the actual
implementation of the code was on voluntary basis, it did not get off the ground.
Given this background, and the need for building codes to be continuously upgraded in the face of
advancing technological innovations, Sri Lanka Sustainable Energy Authority reviewed the Energy
Efficient Building Code and published the document of Code of Practice on Energy Efficient Buildings in
Sri Lanka - 2008.
Code of Practice for Energy Efficient Buildings encourages energy efficient designs and retrofits of
buildings to reduce energy consumption without compromising the function of the building, or the
comfort, health and productivity of occupants. It sets minimum energy performance standards for
buildings and at the same time provides the methods for determining compliance. The Code is applicable
to commercial buildings, industrial facilities and large scale housing complexes that have at least one of the
features namely; four or more floors, a floor area of 500 m2 or more, an electricity demand of 100 kVA or
more and an air conditioning capacity of 350 kW or more. It has been developed to cover the building
elements; building envelops, ventilation and air conditioning systems, lighting, service and water heating
and electrical power distribution [Sri Lanka Sustainable Energy Authority, 2009].
In this research it is focused on the building envelop section only. According to the building code [Sri
Lanka Sustainable Energy Authority, 2009], “Building envelope refers to the exterior plus the semi-
exterior portions of a building. For the purposes of determining building envelope requirements, the
classifications are defined as follows:
(a) Building envelope, exterior: the elements of a building that separate conditioned spaces from the
exterior
(b) Building envelope, semi-exterior: the elements of a building that separate conditioned space from
unconditioned space or that encloses semi-cooled spaces through which thermal energy may be
transferred to or from the exterior, or to or from unconditioned spaces, or to or from conditioned spaces”
.
7
Figure 2-1: Exterior and semi-exterior building envelop (American Society of Heating, Refrigerating and Air-Conditioning Engineers, 2004)
Building envelope elements play a considerable role on the visual and thermal comfort of the occupants
and energy consumption of the building. By proper design and construction of the building envelop the
load on these systems can be reduced. Heat transmission of a building is occur through the components
of the building envelop. Generally heat is transferred from high temperature to low temperature. The
three-ways of heat transfer namely; conduction, convection and radiation are occurred in simultaneously
in a building. Conduction is the transfer of heat in a solid medium due to the direct contact of particles.
Convection heat transfer occurs due to the movement of a fluid. Radiation heat transfer is the movement
of energy/heat through space without relying on conduction through the air or by the movement of air.
Figures 2.2 indicate these three-modes of heat transfer occurred in external surfaces of a building.
Figure 2-2: Schematic showing three modes of heat transfer of an exterior envelop element (Bureau of Energy Efficiency,2009)
8
The conductive heat transfer of the envelop element depend on the properties such as thermal
conductivity, density and thickness of the construction material.
The steady-state conduction in one dimension is given by Fourier’s Law of Conduction;
dx
dtkAq
.
(2.1)
Where;
.
q = rate of heat transfer [W]
k = thermal conductivity of the material [Wm2.C-1]
A = area normal to heat flow [m2]
dx
dt = temperature gradient [C/m]
Equation 2.1 incorporates a negative sign because q.
flows in the positive direction of x when dx
dt is
negative.
Figure 2-3: Nomenclature for conduction in plane walls (Faye C. McQuiston, Jerald D. Parker and Jeffrey D. Spitler, 2005)
Considering the flat wall of Figures 2.3 (a), where uniform temperature t1 and t2 are assumed to exist on
each surface. If the thermal conductivity, the heat transfer rate, and the area are constant, Equation 2.1
may be integrated to obtain;
Thermal resistance 𝑅′, is proportional to the material thickness and inversely proportional to the material
conductivity.
kA
x
kA
xxR
)(' 21 (2.2)
k1 k3 k2
x2 –x1
k
x
t1 t2
(a)
x
t1 t2
∆x1 ∆x3 ∆x2
(b)
9
The thermal resistance for a unit area is defined by;
k
xR
(2.3)
The thermal resistance 𝑅′, q and (t2-t1) are analogous to electrical resistance, current and potential
difference in Ohm’s law. This analogy can be used to analyze the conduction heat through a wall, roof
and windows made up of two or more layers of dissimilar materials. Figures 2.3 (b) shows a wall
constructed of three different materials. The heat transfer by conduction is given by;
Ak
x
Ak
x
Ak
xRRRR
3
3
2
2
1
1'
3
'
2
'
1
'
(2.4)
Where; the resistances are in series.
Thermal conductance C of the material is given by;
x
k
RC
1 (2.5)
Heat transfer rate due to the thermal convection is given by;
)(.
wtthAq (2.6)
Where;
h = film coefficient, [Wm-2.K-1]
t = bulk temperature, [0C]
tw = wall temperature, [0C]
Equation 2.6 can also be expressed in terms of thermal resistance for convection 𝑅𝑐𝑛𝑣′ ;
'
.
cnv
w
R
ttq
(2.7)
Where hA
Rcnv
1' (2.8)
Therefore convection thermal resistance for unit area, 𝑅𝑐𝑛𝑣
hR cnv
1 (2.9)
The film coefficient h depends on the fluid, the fluid velocity, the flow channel or wall shape or
orientation, and the degree of development of the flow field. There are two types of convection
mechanisms called forced convection and free or natural convection. When the convection heat transfer is
occurred due to the movement of bulk of fluid relative to the heat transfer surface, the mechanism is
10
called forced convection. Usually the motion is caused by a blower, fan or pump. Here the effects of the
buoyancy forces are negligible. The free convection is occurred due to the movement of fluid due to the
buoyancy forces. The surrounding bulk of the fluid is stationary and exerts a viscous drag on the layer of
moving fluid(Faye C. McQuiston, Jerald D. Parker and Jeffrey D. Spitler, 2005).
The direct net transfer of energy by radiation between two surfaces that see only each other and that are
separated by a nonabsorbent medium is given by;
22
2
121
1
11
1
4
2
4
112
.
111
)(
AFAA
TTq
(2.10)
Where;
= Boltzmann constant = 5.673 x 10-8 [W/m2.K4]
T = absolute temperature [K]
= emittance of surface 1 or surface 2
A = surface area [m2]
F = configuration factor, a function of geometry only
(Faye C. McQuiston, Jerald D. Parker and Jeffrey D. Spitler, 2005)
In equation 2.10, it is assumed that emittance ( ) equals to absorptance ( ) in both surfaces.
Figure 2-4: Thermal radiation effects of wall (Faye C. McQuiston, Jerald D. Parker and Jeffrey D. Spitler, 2005)
Considering the wall at Figures 2.4
....
orwi qqqq (2.11)
For the wall being heated by a combination of convection and radiation on each surfaces and having 5
different resistances, the equivalent thermal resistance '
eR
qr
qw
t0
h0
ti
hi k
qi
q0
11
''
3
'
2
'
1
''
oie RRRRRR (2.12)
In terms of fundamental variables;
OOii
eAhAk
x
A
R
Ak
x
AhR
11
33
3
2
2
11
1'
(2.13)
Overall heat-transfer coefficient is given by;
RAR
U11
/ (2.14)
The heat transfer rate in each component is given by;
tUAq .
(2.15)
Where;
UA = conductance [W/C]
A = Surface area normal to flow [m2]
t = overall temperature difference [C]
The rate of heat transfer proportional to the overall heat transfer coefficient, surface are normal to flow
and overall temperature difference. Therefore the rate of heat transfer of the element can be reduced by
increasing the thermal resistance. In order to increase the resistance it can introduce low conductive
materials and or increase the thickness of the material layers.
The average yearly temperature of Sri Lanka ranges from 280C to 320C. The difference of elevation in Sri
Lanka influences temperature variation in the country. It ranges from hot to cold from the lowland to
upland. According to the Department of Agriculture, Sri Lanka can be divided in to three climate zones
namely wet, intermediate and dry zone and Figures 2.5 indicates the zones.
12
Figure 2-5: Climatic zones of Sri Lanka (http://www.climatechange.lk/maps/climaticzones.jpg)
The thermal properties of the building depend on its outdoor climate conditions as well as the internal
conditions such as type of the activities, time of operation. In the Code, the country is divided in to three
climatic zones, namely warm-humid, warm-dry and uplands based on the outdoor dry bulb and wet bulb
temperatures. These represent the climate zones wet, intermediate and dry in Figures 2.5 respectively. The
specified dry bulb and wet bulb temperatures of different zones are;
Warm-humid – 310C, 270C
Warm-dry – 330C, 260C
Uplands – 280C, 230C
Based on the duration of the operation of the building two typologies are identified as day-time operation
and extended operation. Normal eight (08) hours per day operation buildings such as offices, shops are
considered as day time operation and more than 08 hour operation buildings such as hospitals, hotels, and
supermarkets are considered as extended operation. The materials to be used in the construction are
decided according to the climatic zone as well as building typology.
13
The code specifies the prescriptive requirement limits for physical properties such as Visual Light
Transmittance, U value, solar absorpsivity of materials used for roofs, fenestrations and facades elements
Introduce insulation to walls 43.8 84.4 0.153 7.01 3.54
Introduce insulation to roof 46.7 87.5 0.159 0.85 0.00
Introduce insulations to walls
and roof, in order to achieve
the maximum U values for
facades and roofs specified in
Building Code
12.3 84.4 0.153 73.89 3.54
Reduce WWR 46.4 87.3 0.159 1.46 0.25
Reduce WWR and Introduce 1m Overhangs to windows
41.9 84.7 0.154 11.08 3.18
Reduce WWR , Introduce 1m Overhangs to windows and change the wall materials to brick
41.4 83.2 0.151 12.17 4.89
Reduce WWR , Introduce 1.5 m Overhangs to windows and change the wall materials to brick
41.3 82.7 0.150 12.39 5.45
Reduce WWR , Introduce 1.5 m Overhangs to windows and change the wall and roof materials to brick and clay tiles respectively
36.5 83.2 0.151 22.46 4.97
Table 3-2: Absolute and percentage reduction of OTTV and annual cooling energy with
modifications of building 1
Introduction of double layer glazing has resulted a reduction of OTTV but it has increased the annual cooling energy. Introduction of insulation to roof has no impact on cooling energy. All other modifications have resulted in reduction of both OTTV and annual cooling energy.
Following graph shows the variation of annual cooling energy with the OTTV.
24
Figure 3-2: Variation of the annual cooling energy with the OTTV of the building 1
The data points can be approximately represented by a second order polynomial with R2 value of 0.861.
It can be observed that up to a certain point the cooling energy reduces with the reduction of OTTV. But
afterward the cooling energy increases while the OTTV decrease.
3.3.2 Building 2: Wing 4 G of Bandaranayke Memorial International
Conference Hall
Bandaranayke Memorial International Conference Hall (BMICH) is a building complex with many office
compartments. Only wing 4 G has been considered for this study. It is a three storey building having
approximate area of 1600m2. The building is oriented in North-West and South-East direction. Two sides
of the building have shaded due to the adjacent buildings. Walls of the building are made from 225mm
thick burned brick and 3mm thick single clear glasses are used for widows. A concrete slab is used as the
roof.
3.3.2.1. Layout diagram of the existing building 2
Below diagram shows the existing layout diagram modeled in the software using the measurements
obtained from the actual building. It has been used component blocks in order to incorporate the shading
effect of the surrounding buildings. There are shading effect due to the verandahs in exterior walls in long
axis also. The components blocks in blue and magenta color shows in Figures 3.2 are used to incorporate
the shading effects due to adjacent buildings and external verandah respectively.
Length of the building = 47 m
Width of the building = 11 m
Slab to Slab height = 3.7 m
25
Figure 3-3: Layout diagram of the existing building 2
(Extracted from DesignBuilder)
3.3.2.2. Summary of the results of building 2
U values of the construction materials of walls, window and roof are 1.796 W/m2.K, 6.257 W/m2.K and
1.302 W/m2.K respectively. According to the prescriptive requirements of the building code, the
maximum U values for the wall and roofs of an office building located in Colombo area are 0.45 W/m2.K
and 0.4 W/m2.K respectively. Therefore this building is not met the prescriptive requirements of the
Code. OTTV of the existing building is 25 W/m2. Calculated OTTV of the building for prescriptive
requirements is 19.1 W/m2. In order to comply the building with the code the OTTV should be lesser
than 19.1 W/m2. Therefore this building is not complying with the code. More details on thermal
properties, and lay out diagrams of the construction materials and calculations are provided in section 2 of
annex 1.
Following table shows the absolute and percentage change of OTTV with annual cooling energy with
modifications.
26
Modification
Overall Thermal Transfer
Value (OTTV),
W/m2
Annual cooling energy, MWh
Specific energy consumption,
MWh/m2
Percentage reduction of OTTV, %
Percentage reduction of
annual cooling
energy, %
Existing building 25.1 428.22 0.268 N/A N/A
Introduce double layer glazing
23.0 446.72 0.279 8.37 -4.32
Introduce insulation to walls
23.4 409.34 0.256 6.77 4.41
Introduce insulation to roof
22.8 419.41 0.262 9.16 2.06
Introduce insulations to walls and roof, in order to achieve the maximum U values for facades and roofs specified in Building Code
19.1 427.99 0.267 23.9 0.05
Reduce WWR 22.7 442.55 0.277 9.56 -3.35
Reduce WWR, introduce double layer glazing for windows and introduce insulations to wall
19.1 410.59 0.257 23.75 4.12
Table 3-3: Absolute and percentage reduction of OTTV and annual cooling energy with modifications of building 2
Introduction of double layer glazing and reduction of WWR has resulted a reduction of OTTV but it has
increased the annual cooling energy. All other modifications have resulted in a reduction of annual cooling
energy requirement.
Following graph shows the variation of annual cooling energy with the OTTV.
27
Figure 3-4: Variation of the annual cooling energy with the OTTV of the building 2
A relationship could not be found between the data points. In some cases, totally different annual cooling
energies for approximately same OTTV can be observed.
3.3.3 Building 3: Air- Mech Engineering Office
Air- Mech is a 4 storey office building having approximate floor area 500m2. The building is oriented in
North-South direction. Walls of the building are made from 225mm thick burned brick and 3mm thick
single clear glasses are used for widows. A concrete slab is used as a roof.
Length of the building = 15 m
Width of the building = 10 m
Height of ground floor = 3.5 m
Slab to Slab height of 1st, 2nd and 3rd floors = 3 m
3.3.3.1. Layout diagram of the existing building 3
Below diagram shows the existing layout diagram modeled in the software using the measurements
obtained from the actual building.
405
410
415
420
425
430
435
440
445
450
15 17 19 21 23 25 27
BMICH
BMICH
Annual cooling energy, MWh
OTTV, W/m2
28
Figure 3-5: Layout diagram of the existing building 3
(Extracted from DesignBuilder)
3.3.3.2. Summary of the results of building 3
U values of the construction materials of walls, window and roof are 1.796 W/m2.K, 6.257 W/m2.K and
1.302 W/m2.K respectively. According to the prescriptive requirements of the building code, the
maximum U values for the wall and roofs of an office building located in Colombo area are 0.45 W/m2.K
and 0.4 W/m2.K respectively. Therefore this building has not met the prescriptive requirements of the
Code. OTTV of the existing building is 55 W/m2. Calculated OTTV of the building for prescriptive
requirements is 47.4 W/m2. In order to comply the building with the code the OTTV should be lesser
than 47.4 W/m2. Therefore this building is not complying with the code.
More details on thermal properties, and lay out diagrams of the construction materials and calculations are
provided in section 3 of annex 1.
Following table shows the absolute and percentage change of OTTV and annual cooling energy with
modifications.
29
Modification
Overall Thermal Transfer
Value (OTTV),
W/m2
Annual cooling energy, MWh
Specific energy consumption,
MWh/m2
Percentage reduction of OTTV, %
Percentage reduction of
annual cooling
energy, %
Existing building 55.3 156.93 0.314 N/A N/A
Introduce double layer glazing
52.8 156.25 0.313 4.52 0.43
Introduce insulation to walls
51.3 158.02 0.316 7.31 -0.69
Introduce insulation to roof
46.9 149.87 0.300 15.19 4.50
Introduce insulations to walls and roof, in order to achieve the maximum U values for facades and roofs specified in Building Code
47.4 153.80 0.308 14.29 1.99
Introduce insulation to walls and roof
49.8 142.96 0.286 9.98 8.90
Introduce insulation to walls and roof and reduce WWR
44.0 138.75 0.278 20.47 11.58
Introduce insulation to walls and roof , reduce WWR and introduce 1m Overhangs to windows
29.5 124.04 0.248 46.69 20.96
Table 3-4: Absolute and percentage reduction of OTTV and annual cooling energy with modifications of building 3
Introduction of insulations to wall has resulted a reduction of OTTV but it has increased the annual
cooling energy by 0.7%. All other modifications have resulted in a reduction of both OTTV and annual
cooling energy requirement.
Following graph shows the variation of annual cooling energy with the OTTV.
30
Figure 3-6: Variation of the annual cooling energy with the OTTV of the building 3
The data points can be represented by a linear graph with R2 value of 0.838.
3.3.4 Building 4: Sri Lanka Standards Institute (SLSI)
SLSI is an 8 storey office building having approximate floor area of 6100m2. Walls of the building are
made from 225mm thick burned brick and 3mm thick single clear glasses are used for widows. A concrete
slab is used as a roof. The building is shaded by the buildings and trees in all directions except south.
Building has an open court yard at the middle. This building is surrounded by shady trees and some
buildings from three sides. This factor also has been considered when calculating the OTTV values and
simulations.
3.3.4.1. Layout diagram of the existing building 4
Below diagram shows the existing layout diagram modeled in the software using the measurements
obtained from the actual building. The components blocks in blue and magenta color shows in Figures
3.4 are used to incorporate the shading effects due to adjacent buildings and external verandah
respectively.
31
Figure 3-7: Layout diagram of the existing building 4
(Extracted from DesignBuilder)
3.3.4.2. Summary of the results of building 4.
U values of the construction materials of walls, window and roof are 1.796 W/m2.K, 6.257 W/m2.K and
1.302 W/m2.K respectively. According to the prescriptive requirements of the building code, the
maximum U values for the wall and roofs of an office building located in Colombo area are 0.45 W/m2.K
and 0.4 W/m2.K respectively. Therefore this building is not met the prescriptive requirements of the
Code. OTTV of the existing building is 44 W/m2. Calculated OTTV of the building for prescriptive
requirements is 32 W/m2. In order to comply the building with the code the OTTV should be lesser than
32 W/m2. Therefore this building is not complying with the code.
More details on thermal properties, and lay out diagrams of the construction materials and calculations are
provided in section 4 of annex 1.
Following table shows the absolute and percentage change of OTTV with annual cooling energy with
modifications.
32
Modification
Overall Thermal Transfer
Value (OTTV),
W/m2
Annual cooling energy, MWh
Specific energy consumption,
MWh/m2
Percentage reduction of OTTV, %
Percentage reduction of
annual cooling
energy, %
Existing building 44.2 1,650 0.270 N/A N/A
Introduce double layer glazing
41.0 1,660 0.272 7.24 -0.61
Introduce insulation to walls
39.6 1,510 0.248 10.41 8.48
Introduce insulation to roof
38.7 1,610 0.264 12.44 2.42
Introduce insulations to walls and roof, in order to achieve the maximum U values for facades and roofs specified in Building Code
32.0 1,662 0.272 27.60 -0.73
Reduce WWR 39.7 1,630 0.267 10.18 1.21
Reduce WWR and Introduce insulation to walls
34.6 1,500 0.246 21.72 9.09
Table 3-5: Absolute and percentage reduction of OTTV and annual cooling energy with modifications of building 4
Introduction of double layer glazing has resulted an increase of the annual cooling energy by 0.6%.
Introduction of insulations to walls and roof, as specified in Building Code also has resulted an increase of
the annual cooling energy by 0.73%. All other modifications have resulted a reduction of the annual
cooling energy.
Following graph shows the variation of annual cooling energy with the OTTV.
33
Figure 3-8: Variation of the annual cooling energy with the OTTV of the building 4
A clear relationship could not be found between the data points. This could have been due to extreme
data points. Therefore a further analysis was carried out by eliminating extreme data points. When the
data points (39.6, 1510) and (32.0, 1662) were removed, following graph could be obtained.
Figure 3-9: Variation of the annual cooling energy with the OTTV of the building 4 (after
removing two data points)
Above data set displays a linear relationship with R2 of 0.799.
1,480
1,500
1,520
1,540
1,560
1,580
1,600
1,620
1,640
1,660
1,680
30 35 40 45 50 55 60
SLSI
SLSI
Annual cooling energy, MWh
OTTV, W/m2
y = 16.47x + 957.0R² = 0.799
1,450
1,500
1,550
1,600
1,650
1,700
30 35 40 45
SLSI
SLSI
Linear (SLSI)
Annual cooling energy, MWh
OTTV, W/m2
34
3.3.5 Building 5: World Trade Centre (WTC)
WTC is high rise building having 37 storeys. It has twin towers. There are several offices building in this
space and floor area is around 81,500m2. The building is shaded by the buildings located in east and west
directions. Unconditioned car park is attached to the Southside wall of the ground floor. Therefore it is
assumed that there is no solar heat gains through that wall and do not consider it for OTTV calculation.
3.3.5.1. Layout diagram of the existing building 5
Below diagram shows the existing layout diagram modeled in the software using the measurements
obtained from the actual building.
Figure 3-10: Layout diagram of the existing building 5
(Extracted from DesignBuilder)
3.3.5.2. Summary of the results of building 5.
U values of the construction materials of walls, window and roof are 2.37W/m2.K, 6.121 W/m2.K and
1.302 W/m2.K respectively. According to the prescriptive requirements of the building code, the
maximum U values for the wall and roofs of an office building located in Colombo area are 0.45 W/m2.K
and 0.4 W/m2.K respectively. Therefore this building is not met the prescriptive requirements of the
Code. OTTV of the existing building is 87.6 W/m2. Calculated OTTV of the building for prescriptive
requirements is 84.4 W/m2. In order to comply the building with the code the OTTV should be lesser 50
W/m2. Therefore this building is not complying with the code. More details on thermal properties, and lay
out diagrams of the construction materials and calculations are provided in section 5 of annex 1.
In order to reduce the OTTV, following parameters were changed. Following table shows the absolute
and percentage change of OTTV with annual cooling energy for modifications done.
35
Modification
Overall Thermal Transfer
Value (OTTV),
W/m2
Annual cooling energy, MWh
Specific energy consumption,
MWh/m2
Percentage reduction of OTTV, %
Percentage reduction of
annual cooling
energy, %
Existing building 87.8 33,200 0.407 N/A N/A
Introduce double layer glazing
81.8 33,091 0.406 6.1 0.3
Introduce insulation to walls
84.8 32,962 0.404 2.9 0.7
Introduce insulation to roof
85.1 33,175 0.407 1.1 0.1
Introduce insulations to walls and roof, in order to achieve the maximum U values for facades and roofs specified in Building Code
82.8 33,107 0.406 3.7 0.3
Table 3-6: Absolute and percentage reduction of OTTV and annual cooling energy with modification of building 5
In this building all the modifications have resulted reduction of both OTTV and annual cooling energy.
Following graph shows the variation of annual cooling energy with the OTTV.
Figure 3-11: Variation of the annual cooling energy with the OTTV of the building 5
36
A clear relationship could not be found between the data points. This could have been due to extreme
data points. Therefore, a further analysis was carried out by eliminating extreme data points. When the
data points (84.8, 32962) were removed, following graph could be obtained.
Figure 3-12: Variation of the annual cooling energy with the OTTV of the building 5(after
removing two data points)
Above data set displays a linear relationship with R2 of 0.946.
y = 19.06x + 31534R² = 0.946
32,800
32,850
32,900
32,950
33,000
33,050
33,100
33,150
33,200
33,250
81.0 82.0 83.0 84.0 85.0 86.0 87.0 88.0 89.0
WTCAnnual cooling energy, MWh
OTTV, W/m2
37
4 Analysis of Results
This chapter provides a detailed analysis of the simulation results. There are 3 sections namely; analysis of
simulation results, cost benefit analysis for enhanced energy efficiency building and identification of the
optimum building models. In the cost benefit analysis the LCC was calculated using the incremental cost
of modifications to the existing building. Finally optimum building envelop models were identified based
on the cost benefit analysis.
4.1 Analysis of Simulation Results
The main objective of specifying the maximum U values and OTTV for the building envelop is to reduce
the cooling energy requirement of the building. A proportional relationship between the OTTV and the
annual cooling energy was expected. But in some cases this has not happened. Table 4.1 and Table 4.2
summarize the situations where unexpected increase of annual cooling energy with the reduction of
OTTV and observed relationship between OTTV and annual cooling energy respectively.
Building Modifications resulted in an increase of annual cooling energy
requirement with compared to existing building
Building 1 (RDA) Introduction of double layer glazing
Building 2 (BMICH) 1. Introduce insulations to walls
2. Reduction of WWR
Building 3 (Air Mech) Introduction of insulations to walls
Building 4 (SLSI) 1. Introduction of double layer glazing
2. Introduce insulations to walls and roof, in order to achieve the
maximum U values for facades and roofs specified in Building
Code
Table 4-1: Building modifications resulted to increase of annual cooling energy
It can be observed that even for the same modification, there are different behaviors in different
buildings. Which means that the required envelop properties to optimize cooling energy requirement of a
building is unique for each building.
Building Relationship between OTTV
and annual cooling energy
R2 Value
Building 1 (RDA) Second order polynomial 0.836
Building 2 (BMICH) None N/A
Building 3 (Air Mech) Linear 0.838
Building 4 (SLSI) None N/A
Building 5 (WTC) None N/A
Table 4-2: Relationship between OTTV and annual cooling energy
As per above table, only building 1(RDA) and building 3 (Airmech) shows a positive relationship between
the OTTV and cooling energy requirement. Any of the other buildings do not show any relationship.
Therefore further analysis is required to assess the other factors which have not been considered for
above analysis.
38
4.2 Cost benefit analysis for enhanced energy efficiency
building envelops applications
Ultimate objective of the Energy Efficient Building Code is to optimize the energy usage and related
energy cost. A cost benefit analysis was carried out to assess the optimum building envelop model.
Average incremental cost was calculated using market rates for each modification done. This cost is
compared against the long term cost saving due to reduction of annual cooling energy. Life Cycle Cost
was calculated for each option by assuming electricity tariff of LKR.20 and percentage cost of capital 12%
to be constant for 20 year period. The option with the minimum Life Cycle Cost (LCC) is considered as
the preferred option.
Tables 4.3 to 4.7 summarize the Life Cycle Cost calculation for each building element change. Preference
is given for the option with lesser Life Cycle Cost.
39
4.2.1 Building 1 (RDA)
Modification
OTTV, W/m2
Annual cooling energy, MWh
Incremental Cost, LKR
Annual cost for
energy, LKR
Million
Present value of 20 year energy cost, LKR
Million
Total Life
Cycle cost, LKR
Million
Preference
Existing building 47.1 87.5 N/A 0.963 7.19 7.19 6
Introduce double layer glazing
46.5 87.7 103,400 0.965 7.21 7.31 8
Introduce insulation to walls
43.8 84.4 834,328 0.928 6.93 7.77 9
Introduce insulation to roof
46.7 87.5 85,006 0.963 7.19 7.27 7
Introduce insulations to walls and roof, in order to achieve the maximum U values for facades and roofs specified in Code
12.3 84.4 1,274,146 0.928 6.93 8.21 10
Reduce WWR 46.4 87.3 -73 0.960 7.17 7.17 5
Reduce WWR and Introduce 1m Overhangs to windows
41.9 84.7 88,117 0.932 6.96 7.05 1
Reduce WWR , Introduce 1m Overhangs to windows and change the wall materials to brick
41.4 83.2 231,341 0.915 6.84 7.07 3
Reduce WWR , Introduce 1.5 m Overhangs to windows and change the wall materials to brick
41.3 82.7 274,412 0.910 6.80 7.07 4
Reduce WWR , Introduce 1.5 m Overhangs to windows and change the wall and roof materials to brick and clay tiles respectively
36.5 83.2 231,269 0.915 6.83 7.06 2
Table 4-3: LCC for different modifications of building 1
Based on the minimum LCC, Reduce WWR and introduce 1m overhangs to windows can be considered
as the preferred option for the building 1 from the options considered.
40
4.2.2 Building 2 (BMICH)
Modification OTTV, W/m2
Annual cooling energy, MWh
Incremental Cost, LKR
Annual cost for
energy, LKR
Million
Present value of 20 year energy cost, LKR
Million
Total Life
Cycle cost, LKR
Million
Preference
Existing building 25.1 428.22 N/A 4.71 35.18 35.18 1
Introduce double layer glazing
23.0 446.72 833,250 4.91 36.70 37.54 6
Introduce insulation to walls
23.4 409.34 1,989,010 4.50 33.63 35.62 2
Introduce insulation to roof
22.8 419.41 2,720,490 4.61 34.46 37.18 5
Introduce insulations to walls and roof, in order to achieve the maximum U values for facades and roofs specified in Code
19.1 427.99 3,539,181 4.71 35.16 38.70 7
Reduce WWR 22.7 442.55 -9,293 4.87 36.36 36.35 3
Reduce WWR and Introduce double layer glazing and introduce insulations to wall
19.1 410.59 2,778,900 4.52 33.73 36.51 4
Table 4-4: LCC for different modifications of building 2
Based on the minimum LCC, the existing building envelop is the preferred option for the building 2 from
the options considered.
41
4.2.3 Building 3 (Air-Mech)
Modification OTTV, W/m2
Annual cooling energy, MWh
Incremental Cost, LKR
Annual cost for
energy, LKR
Million
Present value of 20 year energy cost, LKR
Million
Total Life
Cycle cost, LKR
Million
Preference
Existing building 55.3 151.3 N/A 1.66 12.43 12.43 1
Introduce double layer glazing
52.8 151.1 448,800 1.66 12.41 12.86 2
Introduce insulation to walls
52.7 152.2 1,395,183 1.67 12.50 13.90 6
Introduce insulation to roof
52.5 151.1 592,137 1.66 12.41 13.01 3
Introduce insulations to walls and roof, in order to achieve the maximum U values for facades and roofs specified in Code
47.4 153.8 1,684,045 1.69 12.64 14.32 7
Introduce insulation to walls and roof
49.78 142.96 1,987,320 1.57 11.75 13.73 5
Introduce insulation to walls and roof and reduce WWR
43.98 138.75 2,027,607 1.53 11.40 13.43 4
Introduce insulation to walls and roof , reduce WWR and introduce 1m overhangs to windows
29.48 124.04 4,901,422 1.36 10.19 15.09 8
Table 4-5: LCC for different modifications of building 3
Based on the minimum LCC, the existing building envelop is the preferred option for the building 3 from
the options considered.
42
4.2.4 Building 4 (SLSI)
Modification OTTV, W/m2
Annual cooling energy, MWh
Incremental Cost, LKR
Annual cost for
energy, LKR
Million
Present value of 20 year energy cost, LKR
Million
Total Life Cycle cost,
LKR Million
Preference
Existing building
44.2 1,650 N/A 18.15 135.56 135.56 3
Introduce double layer glazing
41.0 1,660 3,707,000 18.26 136.38 140.09 6
Introduce insulation to walls
39.6 1,510 6,380,036 16.61 124.06 130.44 1
Introduce insulation to roof
38.7 1,610 3,886,848 17.71 132.28 136.16 4
Introduce insulations to walls and roof, in order to achieve the maximum U values for facades and roofs specified in Code