As demand for the office jobs has been increasing dramatically and employees
spend most of their time in buildings, the minimum environmental comfort conditions
such as solar irradiation, ventilation, thermal conditions should be provided.
However, providing the environmental comfort conditions is decidedly related
to higher energy consumption; therefore, the attempts like sustainable and green
architecture, usage of renewable energy and development of electricity-efficient
heating and cooling system have been made towards satisfaction of lower energy
consumption and comfort levels (Anselm, 2006). In this
regard, recently, most countries have taken a lot of initiatives and standards
for buildings, industries and transportation in reduction of fossil fuels and
increasing the alternative and clean energies instead to avoid the climate changes
and increment of greenhouse gases (Begum et al.,
2011). For instance, according to Malaysian Standard
(MS) 1525 (2007), code of practice for non-residential buildings on energy
efficiency and use of renewable energy, the non-residential building should
comply with an annual energy consumption of less than:
therefore, its important for professionals and architects to reduce annual
energy consumption especially in office buildings to reach the purpose of (MS)
1525:2007, code of practice on energy efficiency and use of renewable energy
(Malaysian Standard (MS) 1525, 2007). Towards these objectives,
there has been intensive research conducted in architect, building construction,
heating and cooling systems and energy management sectors. The comfort temperature
and rooms temperature distribution was evaluated using Computational Fluid
Dynamics (CFD) in order to simulate the optimum temperature level accepted by
80% occupants (Kwong et al., 2009). Bhaskoro
and Gilani (2011) investigated three methods (solution) in reduction of
air-conditioning systems in tropical region (Malaysia). They proposed the energy
reduction methods for cooling load characteristic during peak month (March)
including, external shading devices for wall, double window glazing and adjustable
room temperature set-point which reduce the air-conditioner consumption energy
by 6, 1.7 and 27.4%, respectively. In the first method, energy reduction was
due to minimization of heat gain from building envelope, second method diminishes
direct irradiation to the test room and finally, the energy consumption reduction
was effected by designing the automatic set-point control that set the room
temperature at 28°C in un-occupied period.
Base on literature, architects usually concentrate more on aesthetics values
rather than climate situation in Malaysia and energy saving (Sulaiman
and Hassan, 2011a). They studied the cooling load of highly glazed a non-commercial
building as well as the ways to reduce the energy. In another study, they investigated
the effects of building orientation, wall shades, space overcooling and outdoor
infiltration on air-conditioning systems energy consumption (Sulaiman
and Hassan, 2011b). Window-to-Wall Ratio (WWR), shading coefficient and
U-Value of wall and windows are effective factors for OTTV determination (Lam,
2000). Energy consumption in buildings can be controlled using two approaches
which are OTTV and day lighting (Li et al., 2002).
OTTV is considered a better performance index than thermal transmittance (U-value)
because it takes into account the impact of direct solar energy on the envelope
of mechanically cooled buildings (Saidur et al.,
2009). Capeluto (2003) suggested the self-shading
geometric forms provide the best solution for betterment use of energy in buildings.
Kadiri and Okosun (2006) examine the area of room that
are most uncomfortable in maximum irradiation period (12:00-3:00 pm), discovered
the main heat source in this period and investigated the effect of shading devices
on room thermal comfort level in Ile-Ife, Nigeria. The internal courtyard impact
on thermal performance in tropical buildings was studied (Sadafi
et al., 2008). By simulation, they proved that courtyard reduces
the energy consumption by increasing the natural ventilation; in addition, they
proposed the self-shading devices for courtyard in order to moderate the enlarged
Self-protected form is one of possible ways against the impact of solar radiation
in high rise buildings. Self-shading building envelopes were suggested for solar
prevention (Capeluto, 2003; Chia,
2007) identified optimum self-shading projection ratio for high rise building
in Malaysia. Researcher identified the optimum form for office building in Malaysia
through reducing solar insolation on envelops with self-shades form (Chia,
On the basis of definition, the amount of heat that transfer from outside to
the inside of the buildings through building envelope is considered as Overall
Thermal Transfer Value (OTTV). Since a large amount of solar heat gain transfer
through window, window area is one of effective parameters on the amount of
OTTV (Tzikopoulos et al., 2005). Besides, solar
heat gain through fenestration is considered as the largest provider to building
envelope cooling load and the most important parameter for OTTV determinations
(Lam and Goodsall, 1994).
One way to reduce electricity consumption would be to limit heat gain into
the buildings and hence reduce the demand for air-conditioning during hot summer
months. Key factors affecting heat gain through building envelopes into the
buildings, are building orientation, exterior wall area and its construction
type (i.e. thermal insulation and U-value) and surface finish (wall absorption
coefficient), window area, glass type (U-value and shading coefficient), external
shading and roof area and its construction details (Lam et
OTTV according to Malaysian standard 1525:2007: The solar heat gain through the building envelope constitutes an important part in cooling load in an air conditioned building. Solar heat gain into a building is a very important consideration in the design of an energy efficient building. The purpose of OTTV is to obtain the optimal design of building envelope to reduce external heat gain to reduce the cooling load of the air-conditioning system. In this research, the OTTV of the building envelope for a building, having a total air-conditioned area exceeding 4000 m2 and above, should not exceed 50 W m-2.
The OTTV of building envelope is given by following formula:
where, Ai is the gross exterior wall area for orientation i; and OTTVi
is the OTTV value for orientation i from below equation.
For a fenestration at a given orientation, the formula is given as below:
where, WWR is the window-to-gross exterior wall area ratio for the orientation
||Uw is the thermal transmittance of opaque wall
||Uf is the thermal transmittance of fenestration system (W/m2
CF is the solar correction factor which is shown in Table 1.
Table 1 specifies CF for the various orientation of the fenestration.
It is recommended to select the nearest predominant orientation for the calculation
of CF. Fenestration system may consist of a glazing material such as glass,
a shading device and a combination of both (Malaysian Standard
(MS) 1525 (2007).
SC is the shading coefficient of the fenestration system. Where, SC is the
effective shading coefficient of the fenestration system; the shading coefficient
of external shading devices can be obtained from Table 2.
R1 in Table 2 is the ratio of width of horizontal projection
per height of fenestration (Malaysian Standard (MS) 1525
The energy commission diamond building: The Energy Commission Malaysia
is an energy efficient office which is located in the commercial and business
district of core Island, Putrajaya, Malaysia. It is considered as a sustainable
building or green building in Malaysia. As it is obviously shown in Fig.
1, the diamond-shaped building is slanted downwards and inwards to provide
self-shading form as a passive design strategy.
|| Energy commission diamond building (Author)
The facade is integrated with internal light shelves to direct natural daylight
deep into the office space at the same time as the glazing is specially coated
with low-energy coating to address the heat. The building energy index is designed
MATERIALS AND METHODS
The OTTV equation is used to compute the amount of reduced OTTV in energy commission
building by applying the self-shading strategy (Nikpour
et al., 2011). In addition, the amount of OTTV is compared with conventional
building which has no shading devices. Some parameters in OTTV equation such
as WWR should be measured physically. Therefore, some parameters and values
are substituted by experimental measurements of building in the OTTV equation,
directly and indirectly. Some parameters in OTTV equation remain in parametric
shape, which are considered the same for both conditions (conventional and self-shaded
buildings); and some of them could be omitted in determination process.
According to Malaysian standard 1525:2007, the amounts of solar Correction
Factors (CF) for each orientation is given in Table 1. Therefore,
CFs for different orientations strategy from the (North, South, East and West)
are 0.9, 0.92, 1.23 and 0.94, respectively.
In order to clarify the effectiveness of self-shading passive strategy on overall thermal transfer value, the amount of OTTV is calculated by subtracting the amount of OTTV when there is no shading strategy from the amount of OTTV when self-shading strategy is applied. In OTTV calculation process, all parameters are considered constant and some of parameters could be omitted in calculation process; therefore some parameters such as area of wall (a), Uw and Uf were remained parametrically. WWR of this building were considered 60% from experimental measurement of energy commission building.
CF for North and south is 0.9 also CFs for east and west orientations are considered 1.23 and 0.94, respectively.
SC (shading coefficient) for conventional building that has no shading device is equal to 1.
OTTV with this assumption that building has no shading devices is as follow:
Suppose that all parameters are equal for the building with no shading strategy
except SC which is related to shading strategy; therefore SC for energy commission
building can be calculated in following section.
As it was mentioned, the ratio R1 in Table 2 that is defined as the ratio of width of horizontal projection per height of fenestration for energy commission building which is 0.8 in this study; therefore, SC is equal to 0.67 for north and south orientation and SC for east and west are 0.6 and 0.65, respectively.
OTTV with this building can be calculated as follow: where, OTTVss is identified
as OTTV self-shading building:
||15xαx(1-0.6)xUw+6x (0.6)xUf+ (194x1.23 x0.6x0.6)
The amount of OTTV reduction can be calculated by subtracting of OTTV in two
Therefore, the amount of OTTV shows 41.37 w m-2 reductions with
applying self shading strategy in this building.
Self-shading strategy has significant impact on preventing direct solar radiation
that caused less heat gain. By applying this strategy, the amount of overall
thermal transfer value of Energy Commission Diamond Building is obviously reduced
with significant amount of 41.37 w m-2 compare to the conventional
building without any shading devices. Therefore, self-shading designs has considerable
affect to reduce solar radiant heat gain to comply the current code of practice
for overall thermal-transfer value OTTV standard. This is a substantial opportunity
for architecture to design energy-efficient and green building using this strategy.
Energy savings mean not only low electric-lighting but also reduced cooling
loads and the potential for smaller Heating, Ventilating and Air-Conditioning
(HVAC) systems. In addition maintenance costs of a building due to lower HVAC
systems can be reduced.
The work is financed by International Doctoral Fellowship (IDF) provided by Universiti Teknologi Malaysia and the Ministry of Higher Education of Malaysia.