sustainability
Article
Early-Stage Design Considerations for the
Energy-Efficiency of High-Rise Office Buildings
Babak Raji *, Martin J. Tenpierik and Andy van den Dobbelsteen
Department of Architectural Engineering + Technology, Faculty of Architecture and the Built Environment,
Delft University of Technology, P.O. Box 5043, 2600 GA Delft, The Netherlands; [email protected] (M.J.T.);
[email protected] (A.v.d.D.)
* Correspondence: [email protected]; Tel.: +1-778-681-1615
Academic Editor: Avi Friedman
Received: 10 March 2017; Accepted: 12 April 2017; Published: 17 April 2017
Abstract: Decisions made at early stages of the design are of the utmost importance for the
energy-efficiency of buildings. Wrong decisions and design failures related to a building’s general
layout, shape, façade transparency or orientation can increase the operational energy tremendously.
These failures can be avoided in advance through simple changes in the design. Using extensive
parametric energy simulations by DesignBuilder, this paper investigates the impact of geometric
factors for the energy-efficiency of high-rise office buildings in three climates contexts: Amsterdam
(Temperate), Sydney (Sub-tropical) and Singapore (Tropical). The investigation is carried out on
12 plan shapes, 7 plan depths, 4 building orientations and discrete values for window-to-wall ratio.
Among selected options, each sub-section determines the most efficient solution for different design
measures and climates. The optimal design solution is the one that minimises, on an annual basis,
the sum of the energy use for heating, cooling, electric lighting and fans. The results indicate that the
general building design is an important issue to consider for high-rise buildings: they can influence
the energy use up to 32%. For most of the geometric factors, the greatest difference between the
optimal and the worst solution occurs in the sub-tropical climate, while the tropical climate is the
one that shows the smallest difference. In case of the plan depth, special attention should be paid
in the case of a temperate climate, as the total energy use can increase more than in other climates.
Regarding energy performance, the following building geometry factors have the highest to lowest
influence: building orientation, plan shape, plan depth, and window-to-wall ratio.
Keywords: energy-efficiency; geometric factors; early-stage design; high-rise office building; plan
shape; orientation; window-to-wall ratio; compactness; energy modelling
1. Introduction
In the early phases of the design process, the design of a building may be influenced by
several factors such as site limitations, client demands (e.g., maximum space efficiency for return of
investment), functional and aesthetic quality, costs, building codes, urban regulations, and last but
not least the desire of the designer/client to reduce the environmental impact resulting from energy
consumption and CO2 emissions.
During the early design phases, the decisions made by the designer can have a significant
influence on the building’s energy performance [1]. The general building layout is of great importance
for minimising the energy loads and for enabling passive design strategies. There is a growing
awareness to use building performance simulation tools during the design process [2]. According to a
survey conducted by Athienitis and Attia [3], about 60% of energy models are created for the early
stage design. Building shape and orientation together with the general design of the envelope are the
main areas of focus for energy modelling during the early design phase.
Sustainability 2017, 9, 623; doi:10.3390/su9040623
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2. Overview of Previous Studies
The impact of building shape on energy performance has been investigated widely since the
development of building performance simulation tools. Several studies have shown that a correlation
exists between a building’s compactness and its energy consumption [4–8]. Compactness of a building
is defined as the ratio of the area of the external envelope (A) to the volume (V). Findings showed that
compact shapes can result in lower energy consumption, especially in hot and cold climates [9].
A number of studies researched the application of the relative compactness (RC) coefficient for
creating predictive equations [4–6]. Relative compactness shows the deviation of the compactness
of a building from the most compact shape. An example is the study done by Pessenlehner and
Mahdavi [4]. They examined the reliability of the relative compactness indicator for the evaluation
and prediction of annual heating loads and the total number of overheating hours by running several
thermal simulations on hypothetical buildings with residential use in Vienna. A total number of
720 combinations were generated from 12 shapes, 4 orientations, 3 glazing ratios (10%, 25% and
40%) and 5 alternatives for the distribution of glazing across the external walls. 18 modular cells
(3.5 × 3.5 × 3.5 m) were integrated in different ways to create various building forms at a given volume.
Using the cube as a reference shape, the relative compactness of the different hypothetical buildings
was in a range between 0.98 and 0.62. They found that the respective correlation between heating load
and relative compactness (RC) is reasonably high (R2 = 0.88). Furthermore, they explored the accuracy
of the proposed regression equation to predict the heating load of five distinct shapes with the same
RC value (0.86). The simulated results deviated from the predicted values in a range between −15%
and +10%, which indicates the reliability of RC for assessing heating loads in buildings. However, the
predictions showed a large deviation (−80% to +130%) in case of overheating predictions.
Depecker, Menezo, Virgone and Lepers [5] investigated the relationship between shape (shape
coefficient) and the energy consumption for heating of buildings in a cold, and a mild climate at the
northern hemisphere. For the evaluation of the building’s thermal behaviour a calculation method
based on weighting factors was applied. In their study, 16 cubic elements (5.4 × 5.4 × 5.4 m) were
aggregated under two main categories of single- and multi-blocks to create 14 building morphologies.
For all buildings, the largest façade was facing along north-south and the proportional percentage of
glazed area to external walls was the same in all cases (south: 58%, east and west: 17% and north: 8%).
The correlation between the energy consumption for heating and the shape coefficient was investigated
for the studied shapes. The results showed that a good linear correlation (R2 = 0.91) existed in the
cold climate and that the shape coefficient turned out to be a good indicator to assess the energy
use for heating. In contrast, a weak correlation was found in case of the mild climate. Due to long
periods of sunshine, the incident solar energy flux through glazing is high; hence, heat losses from the
building skin have a smaller impact on the energy balance. As a result, the correlation between the
shape coefficient and energy consumption was weak. Furthermore, the results showed that building
shapes with higher total area of glazing (mostly non-monolithic forms) had less deviation from the
regression line.
Ourghi, Al-Anzi and Krarti [6] developed a calculation method that can predict the annual total
energy use of different building forms using the energy results obtained from a reference shape with
a square floor plan. For all building configurations, the total building volume of conditioned space
remained constant. Using the DOE-2 simulation tool, they came up with a correlation equation that
can predict accurately the relative annual total building energy use as a function of three parameters,
including relative compactness, glazing area and the solar heat gain coefficient (SHGC) of the glazing.
Furthermore, they found the impact of the insulation level of the building envelope to be insignificant.
However, this equation is only applicable for cities with cooling-dominated climates and the result is
only valid for buildings that have the same floor area and the volume of the reference building.
AlAnzi, Seo and Krarti [7] conducted an investigation on several plan shapes with different
geometric dimensions, window-to-wall ratios (WWRs) and orientations for the hot and arid climate of
Kuwait. They found that the annual total building energy use for all building shapes decreases as the
Sustainability 2017, 9, 623
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relative compactness increases. A change of the glazing area from 50% to 0% (no glazing) resulted in
the same trend; an increase of RC leads to a reduction of energy use. Additionally, they found that
orientation has an impact on building energy use, its effect however being almost independent of
the building’s shape, especially for lower values of the window-to-wall ratio. It should be noted that
their approach for the selection of building shapes can be subject of debate since a large number of the
analysed plan configurations were not appropriate for the architectural design of office buildings (e.g.,
2 m plan depth or no glazing for all directions).
Few studies took real case buildings to identify the impact of building shapes on energy
consumption. A comparative case-study was conducted by Choi, Cho and Kim [8] on tall residential
complexes in Korea in order to find the relation between building shape and energy consumption. They
compared two plan forms: a Y-shaped and an I-shaped floor plan. For the purpose of comparison, the
total electricity and gas consumption of households and common areas were calculated as a fraction of
the total floor area in each case. They found that a linear I-shaped floor plan performed better in terms
of total electricity consumption but consumed 10% more gas than the Y-shaped building. Furthermore,
they mentioned that the architectural arrangement of units can influence the energy consumption.
The Y-shaped building has three units around a central core while the two units of the I-shape building
have just one shared wall and therefore a larger ratio of external wall surface area to their volume.
In this study the insulation performance and the geographical location of both buildings were selected
in a way to be almost identical. However, the influence of other design parameters such as WWR or
building orientation was not discussed adequately where it may impact energy consumption.
Multiple studies have explored the optimal building shape by using numerical calculations [10]
or evolutionary algorithms such as the genetic algorithm (GA) [10–13]. There are some arguments for
and against the application of multi-objective optimisation methods in comparison with conventional
trial-and-error methods. New methods of optimisation by using GA allow the user to explore
site-specific complex building geometries without being restricted to a simple form [14]. On the
contrary, the simulations require a long time to run, the utilised method is complex and requires
specialised expertise and is therefore not easy to be used by designers [15]. Due to these constraints,
designers are still relying on conventional trial-and-error methods for decision making at early-stage
design despite the improvements that have been made in integrating optimisation methods into
simulation tools.
From the overview of previous studies, it can be highlighted that compactness is not the only
building layout measure influencing energy consumption, although it might be the most influential
parameter in climates that have a high demand for heating or cooling. Compactness does not reflect
the three-dimensional massing of a building’s shape (e.g., self-shading), the transparency of the
building enclosure (e.g., amount and distribution of windows), and the orientation of a building;
hence, corresponding gains and losses are not being accounted for, even if they might have impact
on energy consumption. In addition, most studies are on low-rises or a combination of building
heights (dependent on the shape to be compared). As a result, this study aims to investigate the impact
of building geometry of high-rise office buildings (40-storey) on the total energy use (and different
energy end-uses), by investigating different combinations of plan shapes, plan aspect ratios, windows
(percentage and distribution) and building orientations.
3. Methodology
The overall methodological scheme of this research is summarised in Figure 1. The main objective
of this study is to investigate the impact of geometry factors on energy-efficiency of high-rise office
buildings in three climates. The geometry factors that have been investigated in this research are
plan shape, plan depth, building orientation, window-to-wall ratio and window orientation. While
comparing the climate and population density maps, it shows that the most densely populated cities
around the world are mainly located in temperate, sub-tropical and tropical climates. These are the
Sustainability 2017, 9, 623
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places where the majority of tall buildings are being constructed. As a result, this study aimed
to
answer the following questions in the context of the three climates:
What is the most energy-efficient building shape for high-rise office buildings?
What is the most energy-efficient building shape for high-rise office buildings?
Which aspect ratio of the floor plan performs best when considering the total energy use for
Which aspect ratio of the floor plan performs best when considering the total energy use for
heating, cooling, lighting and fans?
heating, cooling, lighting and fans?
To what extent can floor plan orientation influence the energy performance?
To what extent can floor plan orientation influence the energy performance?
What is the optimal range of glazed area for the different facades of high-rise office buildings?
What is the optimal range of glazed area for the different facades of high-rise office buildings?
Figure 1.
1. Methodological
Methodological scheme
scheme of
of research.
research.
Figure
Building Model
3.1. Building
To investigate the effect of geometry factors, DesignBuilder version 4.7 (DesignBuilder Software
Ltd.,
London,UK)
UK)was
was used.
used. DesignBuilder
DesignBuilderisis aa powerful
powerful interface
interface that
that incorporates
incorporates the EnergyPlus
Ltd, London,
simulation engine (version 8.3) to calculate building energy performance data. Building performance
indicators that were used to express the simulation results are the annual total energy consumption
indicators
and the breakdown of the total energy consumption
consumption into
into heating,
heating, cooling,
cooling, electric
electric lighting
lighting and
and fans.
fans.
2
inin
kWh/m
Site
energy
is
The energy
energy figures
figurespresented
presentedininthis
thispaper
paperare
are‘site
‘siteenergy’
energy’
kWh/m2ofofnet
netfloor
floorarea.
area.
Site
energy
the
amount
of
heat
and/or
electricity
consumed
by
a
building
as
shown
on
a
utility
bill.
Since
each
floor
is the amount of heat and/or electricity consumed by a building as shown on a utility bill. Since each
level has
single
zone, the
net floor
areafloor
is equal
areato
of the
the climatically
floor
levelone
has
one thermal
single thermal
zone,
the net
areatoisthe
equal
area of the conditioned
climatically
space. The number
time
steps per
hoursteps
was set
6 for was
the heat
balance
calculation
in this
conditioned
space. of
The
number
of time
perathour
set at
6 for model
the heat
balance model
study.
Increasing
the
number
of
time
steps
improves
accuracy
but
increases
the
time
it
takes
to
run
calculation in this study. Increasing the number of time steps improves accuracy but increases
thea
simulation.
value of 6 A
is the
value
forvalue
simulations
with HVAC
time
it takesAtotime
runstep
a simulation.
timesuggested
step value
of 6by
is EnergyPlus
the suggested
by EnergyPlus
for
system (andwith
4 forHVAC
non-HVAC
simulations).
simulations
system
(and 4 for non-HVAC simulations).
The high-rise
have
a total
floor
areaarea
of 60,000
m2 that
distributed
over 40over
storeys
high-risebuilding
buildingmodels
models
have
a total
floor
of 60,000
m2isthat
is distributed
40
with identical
floor plans.
buildingbuilding
shapes and
floorand
plan
aspect
ratios
areratios
created
using
storeys
with identical
floorDifferent
plans. Different
shapes
floor
plan
aspect
areby
created
2 . Building
an using
open an
plan
office
layout
a given
1500
models
are are
simplified
by
by
open
plan
officewith
layout
with a floor
givenarea
floorofarea
of m
1500
m2. Building
models
simplified
defining
oneone
zone
(activity)
forfor
thethe
entire
floor
area.
by
defining
zone
(activity)
entire
floor
area.Each
Eachfacade
facadehas
hasaaWWR
WWRof
of 50%
50% that
that is to all
building
models
havehave
a variable-air-volume
(VAV) (VAV)
dual-duct
system
façade elevations.
elevations.The
Theproposed
proposed
building
models
a variable-air-volume
dual-duct
to
provide
comfort.
Since
each
storey
has
the
same
height
and
floor
area,
all
models
have
an
equal
system to provide comfort. Since each storey has the same height and floor area, all models have
an
volume.
However,
the external
surface
area differs
among
the models;
hencehence
the extent
of losses
and
equal
volume.
However,
the external
surface
area differs
among
the models;
the extent
of losses
gains
through
the the
envelope
of the
building.
The
inputs
and
gains
through
envelope
of the
building.
The
inputsofofthe
thesimulation
simulationfor
forthe
the properties
properties of the
building and the operation details are described in Table
1.
Table 1.
Table 1. Simulation inputs for building’s properties and operation details.
External wall insulation
Roof insulation
Glazing type A 1
U-Value
SHGC
Light transmission
Building Properties
U-Value: 0.35 W/m2-K
U-Value: 0.35 W/m2-K
Dbl LoE (e2 = 0.1) Clr 6mm/13mm
Arg
1.50 W/m2-K
0.57
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Table 1. Simulation inputs for building’s properties and operation details.
Building Properties
External wall insulation
Roof insulation
Glazing type A 1
U-Value
SHGC
Light transmission
Glazing type B 2
U-Value
SHGC
Light transmission
Window-to-wall ratio
Shading
Shading control type
Maximum allowable glare index
U-Value: 0.35 W/m2 -K
U-Value: 0.35 W/m2 -K
Dbl LoE (e2 = 0.1) Clr 6 mm/13 mm
Arg
1.50 W/m2 -K
0.57
0.74
Dbl LoE Spec Sel Clr 6 mm/13 mm
Arg
1.34 W/m2 -K
0.42
0.68
50%
Blinds (inside) with high-reflectivity slats
Glare
22
Building Operation Details
HVAC system type
Heating
Heating set point temperature
Cooling
Cooling set point temperature
Fan Power
Fan total efficiency
Fresh air supply rate
Infiltration
Lighting target illuminance
Type of lighting
General lighting power density
Office equipment gain
Occupancy density
Occupancy schedule
1
Dual duct VAV
Gas-fired condensing boiler
20 ◦ C
DOE-2 centrifugal/5.50COP
24 ◦ C
2 W/l-s
70%
10 L/s-person
0.5 ac/h
400 lux
Fluorescent
3.4 W/m2 -100 lux
11.77 W/m2
0.11 people/m2
Weekdays: 7:00–19:00; weekends: closed
Glazing type A is selected for temperate climates; 2 Glazing type B is selected for sub-tropical and tropical climates.
3.2. Sensitivity Test
Before the actual detailed simulations took place, first a sensitivity analysis on certain parameters
was done. For the purpose of simplification, almost all the building’s properties and operation details
were kept constant for all building models in the three climates, except for two envelope measures.
For high-rises, the envelope has a higher impact on gains and losses due to higher exposure to solar
radiation and wind; hence it is important to find the appropriate type of glazing and shading system
that suits each climate type best (functionally, economically and energy wise). For temperate climates,
the thermal transmission through a glass pane should be reduced by choosing a low U value glazing
type. On the other hand, passive heat gains and daylight penetration are highly desired for reducing
the heating and electric lighting loads (high SHGC and Light Transmission value). For hot climates,
the glazing type should be able to limit solar heat gains into the interior (low SHGC), while not
obstructing the transmission of light.
In order to have a better understanding of the relative variables, a sensitivity analysis (SA) was set
up. SA is a way of testing a variable in order to find out its effect on the building performance. With
regards to uncertain input parameters, different alternatives of glazing types and shading systems
were simulated and the variation was observed. A rectangle shape was selected for the purpose of
this sensitivity test. The reference building model has a plan aspect ratio of 3:1 and the long sides of
the building are facing south and north. The results of the SA are presented in Table 2. This analysis
Sustainability 2017, 9, 623
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showed that the demand for heating, cooling and lighting is highly responsive to changes in the
glazing type and shading system.
In a temperate climate, using triple-glazed glass has relatively the same effect on the total building
energy consumption as double-glazed glass. However, triple-glazed glass is more expensive and
therefore might not be the ideal choice for climates with low to average heating requirements. As a
result, a double-glazed low-emission clear glass was selected for temperate climates. Furthermore, it
was found that spectrally-selective glazing is most favourable for climates that need high light levels
and have a long cooling season like tropical and sub-tropical climates.
External shading (e.g., outdoor blinds) performed better in terms of energy saving and solar
control in all climates. A south façade (northern hemisphere) needs overhangs or fixed (stable)
blinds, whereas east or west facades require more dynamic shading. However, the vulnerability of
external shading to high wind speeds at high levels in tall buildings is an important barrier to their
implementation. Indoor shading devices are not prone to damage due to wind. However, shading that
covers the entire window surface reduces the view out and increases the need for artificial lighting
and cooling (due to greenhouse effect). Hence, all simulations were carried out by using indoor blinds
to control only glare.
Table 2. Sensitivity analysis of building envelope parameters.
Building Parameter
Climate
Values
Max. Variation (kW h/m2 )
Glazing type
Temperate
Sub-tropical
Tropical
A *,max , D min
A max , B *,min , D
A, B *,min , C max , D
4.1
12.6
21.8
Shading system
Temperate
Sub-tropical
Tropical
E min , F max , G *
E, F max , G *, H min
E, F max , G *, H min
11.3
6.7
18.1
Glazing Description
U-Value
SHGC 1
TSOL 2
TVIS 3
Type A. Dbl LoE (e2 = 0.1) Clr 6 mm/13 mm Arg
Type B. Dbl LoE Spec Sel Clr 6 mm/13 mm Arg
Type C. Dbl Ref-A-H Clr 6 mm/13 mm Arg
Type D. Trp LoE (e2 = e5 = 0.1) Clr 3 mm/13 mm Arg
1.50
1.34
2.26
0.79
0.57
0.42
0.22
0.47
0.47
0.34
0.13
0.36
0.74
0.68
0.18
0.66
Shading Description
Control Type
Type E. Blinds outside
Type F. Blinds inside
Type G. Blinds inside
Type H. Integrated shading system:
overhang 0.5 m + blinds outside
Solar: (120 W/m2 )
Solar: (120 W/m2 )
Glare: (glare index: 22)
Solar: (120 W/m2 )
* The selected glazing type or shading system; min The design alternative that resulted in minimum energy
use; max The design alternative that resulted in maximum energy use; 1 SHGC = solar heat gain coefficient;
2 TSOL = direct solar transmission; 3 TVIS = light transmission
3.3. Location and Climate Type
For each climate type a representative city was selected and the climate data for one year
(2002) was obtained for energy simulations from the website of the US Department of Energy [16].
The representative cities are Amsterdam for the temperate climate, Sydney for the sub-tropical climate,
and Singapore for the tropical climate. A comparison of climatic features including heating degree
days (HDD) and cooling degree days (CDD), along with mean monthly air temperature and solar
radiation values can be seen in Table 3 and Figure 2 respectively. According to Table 3, the number of
HDDs for Amsterdam is 2759, which is five times greater than for Sydney. The number of CDDs for
Singapore is around 3657 which is considerably higher than for Sydney and Amsterdam.
Sustainability 2017, 9, 623
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Singapore, the solar radiation is intense, but to a great extent diffuse due to haze and clouds. The
temperature is high throughout the year and remains relatively constant. At midday, the annual
average values of the sun altitude is at 75° above the horizon, which is at a higher angle in comparison
Sustainability 2017, 9, 623
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with
Sydney (56°) and Amsterdam (38°).
Table
3. Celsius-based
Celsius-based heating
heating and
◦ C for
Table 3.
and cooling
cooling degree
degree days
days for
for aa base
base temperature
temperature of
of 18
18 °C
for the
the year
year
2002
[16].
2002 [16].
City
City 1
Amsterdam
1
Amsterdam
Sydney 2
2
Sydney 3
Singapore
3
Climate Type
Climate Type
Temperate
Temperate
Sub-tropical
Sub-tropical
Tropical
HDD
HDD
2759
2759
594
0 594
CDD
CDD
149
896149
896
3657
Tropical
0
3657
Singapore
2 Sydney Airport, Australia (151.17E,
Amsterdam Schiphol Airport, The Netherlands (4.77E, 52.30N);
2
Amsterdam
Schiphol Airport, The Netherlands (4.77E, 52.30N); Sydney Airport, Australia (151.17E, 33.95S);
3 Singapore Changi Airport, Singapore (103.98E, 1.37N).
33.95S);
3 Singapore
Changi Airport, Singapore (103.98E, 1.37N).
1
1
Figure 2.
temperature
and
solar
radiation
in: in:
(a) Amsterdam;
(b)
2. Mean
Meanmonthly
monthlyvalues
valuesofofdry-bulb
dry-bulb
temperature
and
solar
radiation
(a) Amsterdam;
Sydney;
andand
(c) Singapore
for for
the the
yearyear
2002
[16].[16].
(b) Sydney;
(c) Singapore
2002
Amsterdam is located on the northern hemisphere in a temperate climate with cool summers
and mild winters. The average monthly temperatures vary by 13.4 ◦ C. The ratio of direct to diffuse
radiation is equal in most part of the year. From the total number of daylight hours, 35% is sunny and
65% is cloudy or with haze and low sun intensity. The sun altitude peaks at 61.3◦ above the horizon
Sustainability 2017, 9, 623
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at solar noon around the 21 June, while at the winter solstice (around 21 December) it reaches its
highest angle at 14.5◦ . Sydney is located on the southern hemisphere and has a humid sub-tropical
climate. The mean monthly average temperatures have a low of 12.5 ◦ C in July and a high of 24.3 ◦ C
in January. For Sydney, the ratio of direct to diffuse radiation is the highest among the three cities, and
the majority of that radiation is direct. At lower latitudes close to the Equator, such as in Singapore,
the solar radiation is intense, but to a great extent diffuse due to haze and clouds. The temperature is
high throughout the year and remains relatively constant. At midday, the annual average values of the
◦ above the horizon, which is at a higher angle in comparison with Sydney (56
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623
8 of◦28
sun
altitude2017,
is at9,75
)
◦
and Amsterdam (38 ).
4. Results and Discussion
4. Results and Discussion
Space heating, cooling, ventilation and lighting account for the largest amount of energy
consumption
in buildings.
theand
proportional
energy use
buildings
differs
Space heating,
cooling,However,
ventilation
lighting account
for in
thecommercial
largest amount
of energy
from other building
usages.
In anthe
office
building,energy
occupancy
during the
day anddiffers
lighting
consumption
in buildings.
However,
proportional
use iniscommercial
buildings
fromis
paramount
therefor.
recent
years,
the application
new types
of and
equipment
commercial
other
building
usages. In
In an
office
building,
occupancy isofduring
the day
lighting in
is paramount
buildingsInhas
contributed
significantly
to of
thenew
increase
electricity
consumption.
Besides,
the type
therefor.
recent
years, the
application
typesofof
equipment
in commercial
buildings
hasof
air conditioning
system
andincrease
its efficiency,
a building’s
operation
details,
and
its conditioning
construction
contributed
significantly
to the
of electricity
consumption.
Besides,
the type
of air
properties
a big impact
on energy
use patterns.
system
and have
its efficiency,
a building’s
operation
details, and its construction properties have a big
The
from the simulations have shown that the energy use for cooling could
impact
on results
energy obtained
use patterns.
exceed
forobtained
heatingfrom
for the
high-rise
officehave
buildings
located
in temperate
climates
such
as in
The that
results
simulations
shown that
the energy
use for cooling
could
exceed
Amsterdam
(see
Figure
3).
The
heat
accumulation
from
internal
gains
are
an
important
component
that for heating for high-rise office buildings located in temperate climates such as in Amsterdam (see
of the 3).
heat
balance
of an air-tightfrom
office
building.
The
internal
heat gains
resultingoffrom
the presence
Figure
The
heat accumulation
internal
gains
are
an important
component
the heat
balance
occupants,
officebuilding.
equipment
and
electric
lighting
demand
for heating
in winteroffice
while
ofofan
air-tight office
The
internal
heat
gains reduces
resultingthe
from
the presence
of occupants,
increasingand
the electric
demand
for cooling
inthe
summer.
Infor
this
parametric
study,
a increasing
single activity
(generic
equipment
lighting
reduces
demand
heating
in winter
while
the demand
office
area)inwas
used for
floor space.
100%(generic
of usableoffice
area area)
to perform
office
for
cooling
summer.
In the
thisentire
parametric
study, Allocating
a single activity
was used
forwork
the
contributed
to
the
increased
use
of
electricity
by
electric
lighting
and
equipment
and
therefore
entire floor space. Allocating 100% of usable area to perform office work contributed to the increased
resulted
in a higher
amountlighting
of internal
gains than
results
showed
use
of electricity
by electric
andheat
equipment
andexpected.
therefore Furthermore,
resulted in a the
higher
amount
of
that fansheat
account
roughly
15–20Furthermore,
per cent of thethe
total
energy
use in athat
40-storey
office building
with
internal
gainsfor
than
expected.
results
showed
fans account
for roughly
a VAV
dual-duct
system.
15–20
per
cent of the
total energy use in a 40-storey office building with a VAV dual-duct system.
Figure
Figure3.3.Breakdown
Breakdownofofthe
thetotal
totalenergy
energyuse
useininaasimulated
simulated40-storey
40-storeyoffice
officebuilding
buildingwith
withrectangular
rectangular
floor
floorplan
plan(3:1)
(3:1)ininAmsterdam,
Amsterdam,Sydney,
Sydney,and
andSingapore.
Singapore.
Inthe
thefollowing
followingsections
sectionsthe
theeffects
effectsofofgeometry
geometryfactors
factorson
onthe
thebuilding’s
building’senergy
energyperformance
performance
In
will
be
discussed.
Building
performance
indicators
that
were
used
to
express
the
simulation
results
will be discussed. Building performance indicators that were used to express the simulation results
are
are
the
annual
total
energy
consumption
and
the
breakdown
of
total
energy
into
different
end-uses.
the annual total energy consumption and the breakdown of total energy into different end-uses. In
In this
study,
the total
energy
consumption
includes
heating,
cooling,
electric
lighting
this
study,
the total
energy
consumption
onlyonly
includes
heating,
cooling,
electric
lighting
and and
fans fans
for
for
these
can
be
affected
by
the
design
of
the
building.
these can be affected by the design of the building.
4.1. Plan Shape and Building Energy Performance
Common shapes of floor plans for the design of high-rise office buildings were modelled in
DesignBuilder and their energy performance was investigated to find the most energy-efficient form
in the three climates. The study focused on 12 floor plan geometries including the circle, octagon,
ellipse, square, triangle, rectangle, courtyard (or atrium), H shape, U shape, Z shape, + shape and Y
shape, as can be seen in Table 4. In this table, some useful information regarding the compactness
coefficient, window distribution and plan depth of the selected geometries are summarised. All
Sustainability 2017, 9, 623
9 of 28
4.1. Plan Shape and Building Energy Performance
Common shapes of floor plans for the design of high-rise office buildings were modelled in
DesignBuilder and their energy performance was investigated to find the most energy-efficient form in
the three climates. The study focused on 12 floor plan geometries including the circle, octagon, ellipse,
square, triangle, rectangle, courtyard (or atrium), H shape, U shape, Z shape, + shape and Y shape, as
can be seen in Table 4. In this table, some useful information regarding the compactness coefficient,
window distribution and plan depth of the selected geometries are summarised. All building models
have the same climatically conditioned floor area, but the ratio of surface area to volume differs from
one shape to another. A building with a circular plan (shape 1) has the minimum ratio of surface
area to volume; hence shape 1 is the most compact form. Since the volume of all plan shapes is equal,
the relative compactness of the other 11 geometries can be calculated by dividing the external surface
area of each building shape (Abui ) by the external surface area of the circle shape (Acir ).
In order to investigate the effect of plan shape on electric lighting loads, a plan depth indicator
was defined. Current practice suggests for ideal daylighting access in office buildings to limit the plan
depth to no more than 6–8 m from a window [17]. In this study the minimum range (6 m) was taken
to calculate the plan depth indicator. This indicator shows the percentage of office spaces that can be
accommodated within 6 m from the external façade. The quantity of electric lighting reduces when the
percentage of peripheral offices along the external façade becomes higher.
Furthermore, the share of each façade from the total glazing area was calculated by using the
following equation:
(Opening area on each façade/Total opening area) × 100
All the openings that are at an angle between 315–45◦ were assumed to have a north-facing
orientation. Accordingly, the share of openings on the other three main directions was calculated
as follows: 45–135◦ as east-facing windows, 135–225◦ as south-facing windows, and 225–315◦ as
west-facing windows. In the case of shape 5, no window is oriented at an angle between 315–45◦ ;
hence, share of the north façade from the total opening area is 0%. While, each of the other three
facades would have a one-third share of the total glazed area.
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2017,
9, 623
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2017,
623
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In order to investigate the effect of plan shape on electric lighting loads, a plan depth indicator
Table
4. Plan shapes
isometric
views, window
distribution,
relative to
compactness
was defined. Current practice
suggests
for ideal
daylighting
access in
office buildings
limit the and plan depth indicator.
Table 4. Plan shapes isometric views, window distribution, relative compactness and plan depth indicator.
plan depth to no more than 6–8 m from a window [17]. In this study the minimum range (6 m) was
Plan Shape
Shape 1
Shape 2
Shape 3
Shape 4
Shape 5
taken
to calculate the plan depth
indicator.
This indicator
that 4
Plan
Shape
Shape
1
Shape
2shows the percentage
Shape 3of office spaces
Shape
Shape 5
can be accommodated within 6 m from the external façade. The quantity of electric lighting reduces
when the percentage of peripheral offices along the external façade becomes higher.
Furthermore, the share of each façade from the total glazing area was calculated by using the
following equation:
10 of 2810 of 28
Shape 6
Shape 6
Share of each façade from(Opening area on each façade/Total opening area) × 100
Share of each
façade
the totalAll
glazing
area
(%) from the
openings
totalthe
glazing
area (%) that are at an angle between 315–45° were assumed to have a north-facing
orientation. Accordingly, the share of openings on the other three main directions was calculated as
67.1 × 22.4
m
majorand
axis:
60
38.7 m
follows:
45–135° as east-facing
135–225°42.6
as south-facing
windows,
225–315°
as west51.1 m altitude
Floor
plate dimensions
43.7windows,
m2
67.1 × 22.4
42.6 m
major axis: 60
38.7 m
2
plate dimensions
between
facades
minor
axis: 32
between
facades51.1 m altitude
Length × width
43.7 5,
m no window
facingFloor
windows.
In the case of shape
isbetween
oriented
at an angle
between
hence,
Length × width
facades
minor
axis: 32 315–45°;
between
facades
100%
103%
107%
113%
128%
130%
Relative
compactness
Relative
compactness
100%
103%
107%
113%
128%
130%
share of the north façade from the total opening area is 0%. While, each of the other three facades
Plan
depth
indicator
47%
48%
52%
52%
58%
62%
Plan
depthhave
indicator
48%
52%
52%
58%
62%
would
a one-third share47%
of the total glazed area.
Plan Shape
7
Shape
Shape
Shape
10
Shape 11Shape 11
Shape 12 Shape 12
Plan Shape
ShapeShape
7
Shape
88
Shape9 9
Shape
10
Before the actual detailed simulations took place, first a sensitivity analysis on certain
parameters was done. For the purpose of simplification, almost all the building’s properties and
operation details were kept constant for all building models in the three climates, except for two
envelope measures. For high-rises, the envelope has a higher impact on gains and losses due to higher
Share of each façade from
exposure to solar radiation and wind; hence it is important to find the appropriate type of glazing
Share of each
façade
the total glazing
area
(%) from the
and shading system that suits each climate type best (functionally, economically and energy wise).
total glazing area (%)
For temperate climates, the thermal transmission through a glass pane should be reduced by choosing
46.6 × 42.0 overalla low60.6
× 60.6glazing
overalltype. 54.4
× 40.4
overall
76.1 ×heat
45.1gains
overall
U value
On the
other
hand, passive
and daylight penetration are highly
33.7 m wing lenght
46.6 × 42.0 overall
60.6 × 60.6 overall
54.4 × 40.4 overall
76.1 × 45.1 overall
14.0 m
length × width desired
length
×reducing
width the heating
length ×and
width
length loads
× width
33.7
m wing
lenght
for
electric
lighting
(high
SHGC
and Light Transmission
14.0 m
length × width
length × width
length × width
length × width
14.0 m
Floor plate
dimensions
Floor plate dimensions
14.0 m
from void
14.014.0
mm
14.0
m type should
14.0
mto limit
from void
14.0
mmhot climates,14.0
mglazing
14.0 m be
value).
For
the14.0
able
solar
heat
gains
into the interior (low
between facades
between facades
between
facades
between
facades
between
facades
between
facades
between facades SHGC),
between
between
facades
whilefacades
not obstructing
the transmission
ofbetween
light. facades
Relative compactness
157%
175%
175%
176%each climate type
176%
178%
a representative
city was selected
and the climate data for
For
Relative compactness
157%
175%
175%
176%
176%
In
order
to
have
a
better
understanding
of
the
relative variables,
a 178%
sensitivity analysis (SA) was
Plan depth indicator
86%
87%
87%
87%
87%
87%
was
obtained
for
energy
simulations
from
the
website
of
the
US Department of E
Plan depth indicator
86%
87%
87%
87%a variable in order 87%
87%
set up.
SA is a way of testing
to find out its effect on
the building performance.
representative cities are Amsterdam for the temperate climate, Sydney for the sub-t
With regards to uncertain input parameters, different alternatives of glazing types and shading
and Singapore for the tropical climate. A comparison of climatic features including
systems
were simulated
and
variation was observed. A rectangle shape was selected for the
for energy
efficiency
of
a the
The optimal balance of plan depth and building external surface area
days (HDD)
and cooling degree days (CDD), along with mean monthly air temper
purpose
of equiangular
this sensitivity
test. The reference building model has a plan aspect ratio of 3:1 and the
40-storey office building was investigated by modelling seven aspect ratios
of an
fourradiation
values can be seen in Table 3 and Figure 2 respectively. According to Tabl
long
sides
of
the
building
are
facing south and north. The results of the SA are presented in Table 2.
2
sided shape with 1500 m of office area per floor (Table 8). The aspect ratio is a measure
of thefor
of HDDs
Amsterdam is 2759, which is five times greater than for Sydney. The nu
This
analysis
showed
that
the
for heating, cooling and lighting is highly responsive to
building’s
describes the proportional relationship between
its length and its width
(x:y). demand
Sustainability footprint
2017, 9, 623;that
doi:10.3390/su9040623
www.mdpi.com/journal/sustainability
for Singapore
is around 3657 which is considerably higher than for Sydney and Ams
in
the
glazing
and shading
The rectangle
is the the
second
most
efficient
shapeinafter
thechanges
ellipse.
According
to type
the
results,
the system.
For an equal floor
area, changing
aspect
ratio
will result
different
external
surface
area
and
Amsterdam
is located on the northern hemisphere in a temperate climate with
2 and 32.8 kWh/m
2 afor
In
temperate
climate,
using
glass has relatively the same effect on the total
lowest
cooling
demand
is
around
32.3
kWh/m
the
ellipse
and
rectangle
plan depth. An aspect ratio of 1:1 represents a square plan shape which has the lowest envelope
areawinters.triple-glazed
and mild
The average monthly temperatures vary by 13.4 °C. The ratio of d
building
energy is
consumption
as double-glazed glass. However, triple-glazed glass is more expensive
respectively (see Table 6). As can be seen, reducing the west-facing
exposure
of great importance
Sustainability 2017, 9, 623
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11 of 28
4.1.1. Temperate Climate
4.1.1. Temperate Climate
It is important to know the position of the sun in order to understand how the sun affects heat
is important
know theFor
position
the sun in
order
to understand
sunmore
affects
heat
gains orItheat
losses in to
buildings.
higheroflatitudes,
the
sun path
across thehow
sky the
makes
seasonal
gains
or
heat
losses
in
buildings.
For
higher
latitudes,
the
sun
path
across
the
sky
makes
more
variations. In summer, the sun path begins from north-east in the morning to a peak that is just below
seasonal variations. In summer, the sun path begins from north-east in the morning to a peak that is
directly overhead in the noon, and then sets to the north-west in the evening. In winter, the sun rises
just below directly overhead in the noon, and then sets to the north-west in the evening. In winter,
south-east, paths a low arc across the sky, and sets south-west. Extending the long axis of a building
the sun rises south-east, paths a low arc across the sky, and sets south-west. Extending the long axis
along east-west has three advantages: it allows more daylight to enter a space, it limits overheating
of a building along east-west has three advantages: it allows more daylight to enter a space, it limits
by west-facing exposures during summer afternoons, and it maximises south-facing exposure for
overheating by west-facing exposures during summer afternoons, and it maximises south-facing
capturing
thermal energy
on winter
days.
the
high summer
sunsummer
during sun
mid-day
exposuresolar
for capturing
solar thermal
energy
on Moreover,
winter days.
Moreover,
the high
duringcan
be mid-day
easily blocked
overhangs
without
blocking
diffuse
daylight
anddaylight
view. and view.
can be by
easily
blocked or
by blinds
overhangs
or blinds
without
blocking
diffuse
The
percentile
difference
in
Table
5
indicates
a
deviation
in
the
total
energy
usebetween
between
The percentile difference in Table 5 indicates a deviation in the total energy use
thethe
most
and
least
efficient
byabout
about12.8%
12.8%between
betweenthe
the
most
and
most
and
least
efficientforms.
forms.AAlarge
large percentile
percentile difference
difference by
most
and
least
efficient
forms
(shape
to aa dominant
dominanteffect
effectofofplan
planshape
shape
energy
least
efficient
forms
(shape3 3and
and12
12respectively)
respectively) points
points to
onon
energy
consumption
in temperate
climates.
As As
shown
in Figure
4, to 4,
some
extentextent
there is
a correlation
between
consumption
in temperate
climates.
shown
in Figure
to some
there
is a correlation
thebetween
annual total
energy
useenergy
and the
relative
compactness
in temperate
climates.climates.
Generally,
the larger
the annual
total
use
and the
relative compactness
in temperate
Generally,
larger the
envelope
area,the
theamount
higher of
theheat
amount
heat
gainsthrough
and losses
thethe
envelope
surface
area,surface
the higher
gainsofand
losses
the through
buildingthe
skin.
As a shapes
result, compact
are more
desirable
for energy
On thethe
other
hand,
Asbuilding
a result, skin.
compact
are moreshapes
desirable
for energy
saving.
On thesaving.
other hand,
percentage
percentage
of office
areas
that can be accommodated
along theperimeter
building perimeter
when a
of the
office
areas that
can be
accommodated
along the building
increasesincreases
when having
having
a narrow
plansobuilding,
that less
electric
lighting isDepending
needed. Depending
on theconditions,
climate
narrow
plan
building,
that lessso
electric
lighting
is needed.
on the climate
conditions,
savings
achieved
by
electrical
loads
and
cooling
loads
(reduced
internal
gains
due
to less
savings achieved by electrical loads and cooling loads (reduced internal gains due to less lighting)
may
lighting)
may
compensate
or
outperform
the
increased
fabric
losses
due
to
an
elongated
compensate or outperform the increased fabric losses due to an elongated form (compare shapeform
1 with
(compare
shape 1 for
withbuildings
shape 3). with
However,
for buildings
withofLED
lighting (instead
of fluorescent
or
shape
3). However,
LED lighting
(instead
fluorescent
or incandescent)
the effect
incandescent) the effect of reduced internal gains due to less lighting become negligible.
of reduced internal gains due to less lighting become negligible.
The circle (shape 1) is the most compact form among the others; however, it is not the most
The circle (shape 1) is the most compact form among the others; however, it is not the most energy
energy efficient form in temperate climates. The results showed that a high-rise building model with
efficient form in temperate climates. The results showed that a high-rise 2building model with an oval
an oval form (shape 3) has the lowest total energy use (about 81.6 kWh/m ). The external surface area
form (shape 3) has the lowest total energy use (about 81.6 kWh/m2 ). The external surface area of the
of the ellipse is about 7% larger than that of the circle and this will increase the amount of heat loss
ellipse is about 7% larger than that of the circle and this will increase the amount of heat loss through
through the building envelope in winter. However, the heating demand of the ellipse building is
theslightly
building
envelope
winter.
the
demand
of performance
the ellipse building
is slightly
lower
2). heating
lower
than ofinthe
circleHowever,
(0.2 kWh/m
This slightly
better
of the ellipse
in terms
2 ). This slightly better performance of the ellipse in terms of heating
than
of
the
circle
(0.2
kWh/m
of heating demand is due to a higher percentage of south-facing windows for an ellipse shape plan
demand
is comparison
due to a higher
south-facing
windows
for an and
ellipse
shape
plan
(35%) in
with apercentage
circle shapeofplan
(25%). According
to Straube
Burnett
[18],
the(35%)
south in
comparison
a circle
shape
to Straube
[18],
the south
façade canwith
receive
twice
the plan
heat (25%).
gain ofAccording
east and west
façadesand
in Burnett
winter at
a latitude
of façade
45°.
◦ . Considering the
canConsidering
receive twice
the
heat
gain
of
east
and
west
façades
in
winter
at
a
latitude
of
45
the electric lighting demand, the circle has the maximum plan depth and a large part of
electric
lighting
circlelighting
has the during
maximum
plan
depth
a large
part ofconsumption
the floor areafor
may
the floor
area demand,
may needthe
electric
most
of the
dayand
time.
The energy
need
electric
lighting
during
of the 2day
The energy
for electric lighting is 17.2
electric
lighting
is 17.2
and most
17.9 kWh/m
for time.
the ellipse
and theconsumption
circle respectively.
and 17.9 kWh/m2 for the ellipse and the circle respectively.
Figure
Buildingtotal
total energy
energy use
use of
of 12
12 plan
plan shapes
shapes (window-to-wall
50%)
in in
Figure
4. 4.Building
(window-to-wallratio
ratio(WWR)
(WWR)= =
50%)
association
with
theircompactness
compactnessininAmsterdam
Amsterdam (4.77E,
(4.77E, 52.30N).
association
with
their
52.30N).
Sustainability 2017, 9, 623; doi:10.3390/su9040623
www.mdpi.com/journal/sustainability
Sustainability 2017, 9, 623
12 of 28
Table 5. Breakdown of annual energy consumption per conditioned area for 12 plan shapes
(WWR = 50%) in Amsterdam (4.77E, 52.30N).
Breakdown of Annual Total Energy Demand
Annual Total Energy Demand
Plan Shape
Heating/
Conditioned
Area (kW h/m2 )
Cooling/
Conditioned
Area (kW h/m2 )
Lighting/
Conditioned
Area (kW h/m2 )
Fan/
Conditioned
Area (kW h/m2 )
Total/
Conditioned
Area (kW h/m2 )
Percentile
Difference (%)
Shape 1
Shape 2
Shape 3 ®
Shape 4
Shape 5
Shape 6
Shape 7
Shape 8
Shape 9
Shape 10
Shape 11
Shape 12
15.1
15.2
14.9
15.2
15.6
15.5
18.5
19.2
19.7
19.5
18.5
18.9
22.5
22.6
22.5
23.5
24.3
24.2
24.1
24.4
24.6
24.3
25.8
26.0
17.9
17.1
17.2
17.5
16.4
15.8
14.6
15.6
13.9
14.6
14.0
14.4
27.3
27.4
27.0
28.7
29.7
29.4
30.5
31.2
31.4
31.0
32.6
32.9
82.8
82.3
81.6
84.9
86.1
84.9
87.6
90.4
89.6
89.4
90.8
92.1
1.4%
0.9%
4.0%
5.4%
4.0%
7.3%
10.7%
9.7%
9.5%
11.2%
12.8%
®
Reference (the most efficient design option).
According to the simulations, a high-rise building model with a square shape (1:1) and a rectangle
shape (3:1) both resulted in the same total amount of energy consumption in the temperate climate.
The rectangle shape used more energy for heating, cooling and fans than its deep plan equivalent
(square shape) due to additional transmitted heat through the façade. On the other hand, the rectangle
form has higher percentage of peripheral offices along the external façade and therefore a better access
to daylighting. The energy savings by electric lighting compensate for the extra HVAC energy demand.
So, these two forms might be used interchangeably by designers when there are design restrictions to
choose one of them.
The triangle (shape 5) and Y shape (shape 12) forms both showed considerable increased cooling
demand compared to the other forms. East- and west-facing windows are a major factor in overheating
of buildings in temperate climate. These plan shapes, that maximise east- and west-facing exposures,
should therefore be avoided.
Almost 90% of office spaces can be placed within 6 m from the building enclosure when having
an enclosed courtyard form (shape 7). It has less external surface area compared to linear forms.
As a result, it performs better than linear shapes but is less efficient than other forms with higher
compactness. It is worth to mention that the central atrium’s height-to-width ratio is very limited in
this case (11:1), so that it could not contribute efficiently to the reduction of energy demand for electric
lighting. This indicated that atrium geometry has a crucial importance for the penetration of daylight
to adjacent rooms.
Floor plan shapes that resulted in minimum lighting demand are the + shape (shape 9) and Z
shape (shape 11). Shape 9 received the lowest amount of solar gains among the linear shapes during
winter due to self-shading by extended wings. For that reason, it has the highest amount of heating
energy use (about 19.7 kWh/m2 ). This plan geometry may perform better in tropical climates in which
solar gain protection is critical for achieving energy-efficient buildings.
4.1.2. Sub-Tropical Climate
On the southern hemisphere, the geometry of a building should be reversed compared to on
the northern hemisphere. Among the 12 studied building shapes, a 180◦ rotation of plan would
have no impact on the building’s energy performance except for asymmetrical shapes. Therefore, the
orientation of only three shapes, namely shapes 5, 10 and 12, are reversed (180◦ rotation) for optimal
energy results. In summer, building surfaces that receive the most sun are the roof and the east- and
west-facing walls. In winter, the sun paths a lower arc across the sky, and the north-facing wall receives
the most solar radiation while the south wall of a building receives limited solar radiation in summer
(and in winter), only in the morning and evening.
Sustainability 2017, 9, 623
13 of 28
receives the most solar radiation while the south wall of a building receives limited solar radiation in
13 of 28
summer (and in winter), only in the morning and evening.
In Sydney, the solar radiation is intense and to a great extent direct. The number of cooling
degree
are almost
twice
as much
the number
degreedirect.
days. High
internal gains
from
In days
Sydney,
the solar
radiation
is as
intense
and toofaheating
great extent
The number
of cooling
windows,
computers
office
appliances
limit
theHigh
building’s
for
degree
daysoccupants,
are almost lighting,
twice as much
as the and
number
of heating
degree
days.
internaldemand
gains from
heating
drastically.
As
a
result,
the
efficiency
of
plan
shapes
is
mostly
determined
by
the
energy
windows, occupants, lighting, computers and office appliances limit the building’s demand for heating
demand forAs
cooling,
fans
electricof
lighting.
drastically.
a result,
theand
efficiency
plan shapes is mostly determined by the energy demand for
For fans
the sub-tropical
climate of Sydney, the results show that the ellipse (shape 3) has the lowest
cooling,
and electric lighting.
2), while the highest energy use was found for the Y shape (shape 12)
total For
energy
use (72.0 kWh/m
the sub-tropical
climate
of Sydney, the results show that the ellipse (shape 3) has the lowest
2 or 15.7% higher2than shape 3) (see Figure 5). According to the results, the amount of
(83.3 energy
kWh/muse
total
(72.0 kWh/m ), while the highest energy use was found for the Y shape (shape 12)
2 orspace
energy
used for
cooling
fans
is slightly
forms.
Theresults,
energythe
useamount
for fansof
is
(83.3
kWh/m
15.7%
higherand
than
shape
3) (see lower
Figurein5).compact
According
to the
calculated
based
on
the
supply
air
flow
rate,
pressure
drop
and
fan
efficiency.
The
supply
fan
only
energy used for space cooling and fans is slightly lower in compact forms. The energy use for fans is
runs whenbased
either
or heating
to be supplied
the
zone. For
elongated
shapes,
the
calculated
oncooling
the supply
air flow needs
rate, pressure
drop andtofan
efficiency.
The
supply fan
only runs
increased
length
of
ducts
increases
the
energy
use
for
fans
due
to
higher
pressure
drops
(compare
when either cooling or heating needs to be supplied to the zone. For elongated shapes, the increased
shape 1ofand
shape
6). Contrary
to this,
very
like the
circle drops
shape(compare
would demand
length
ducts
increases
the energy
use afor
fansdeep
due plan
to higher
pressure
shape 1more
and
electrical
lighting; tohence
cooling
needed
to compensate
excessive
by
shape
6). Contrary
this, amore
very deep
planislike
the circle
shape wouldthe
demand
more internal
electricalgains
lighting;
lighting
and
more
energy
is
required
for
the
distribution
of
cold
air
by
fans.
hence more cooling is needed to compensate the excessive internal gains by lighting and more energy
Sustainability 2017, 9, 623
is required for the distribution of cold air by fans.
Figure 5.
Building total
total energy
energy use
use of
of 12 plan shapes (WWR = 50%) in association with their
5. Building
their
compactness
compactness in
in Sydney
Sydney (151.17E,
(151.17E, 33.95S).
33.95S).
The rectangle
rectangle is
is the
the second
second most
most efficient
efficient shape
shape after
after the
the ellipse.
ellipse. According
According to
to the
the results,
results, the
the
The
2
2
lowest cooling
cooling demand
demand isis around
around 32.3
32.3kWh/m
kWh/m2 and
32.8 kWh/m
kWh/m 2 for
and rectangle
rectangle
lowest
and 32.8
for the
the ellipse
ellipse and
respectively
(see
Table
6).
As
can
be
seen,
reducing
the
west-facing
exposure
is
of
great
importance
respectively (see Table 6). As can be seen, reducing the west-facing exposure is of great importance to
to limit
overheating
during
afternoon
hours
in summer.
The
compactness
circle
(shape
limit
overheating
during
thethe
hothot
afternoon
hours
in summer.
The
compactness
of of
thethe
circle
(shape
1)
1)
and
the
octagon
(shape
2)
are
almost
equal
and
therefore
the
energy
use
for
cooling
and
fans
are
and the octagon (shape 2) are almost equal and therefore the energy use for cooling and fans are almost
2 lower energy use
almost
theassame
well. Nonetheless,
the 8-sided
polygon
resulted
0.8 kWh/m
2 lower
the
same
well.asNonetheless,
the 8-sided
polygon
resulted
in 0.8in
kWh/m
energy use for
for
electric
lighting,
which
is
closer
to
that
of
the
rectangle
and
the
ellipse.
electric lighting, which is closer to that of the rectangle and the ellipse.
The Z
best
energy
performance
among
the linear
shapes
and even
The
Z shape
shape (shape
(shape11)
11)has
hasthethe
best
energy
performance
among
the linear
shapes
and
outperformed
the
courtyard
and
the
triangle
(that
both
have
higher
relative
compactness).
The
even outperformed the courtyard and the triangle (that both have higher relative compactness).
extended
top-side
wing
of the
Z shape
design
helps
totominimise
The
extended
top-side
wing
of the
Z shape
design
helps
minimiseafternoon
afternoonsolar
solargains
gains by
by providing
providing
self-shading
for
a
part
of
the
northand
west-facing
walls.
The
H
shape
(shape
8)
also
benefits
from
self-shading for a part of the north- and west-facing walls. The H shape (shape 8) also benefits from
self-shading by
by means
means of
of external
external wings,
wings, however
however the
the distribution
distribution of
of windows
windows being
being not
not as
as effective
effective
self-shading
for
daylighting
as
the
U
shape
(shape
10).
for daylighting as the U shape (shape 10).
After the
the circle,
circle, the
the triangle
triangle has
has the
the second
second largest
largest energy
energy use
use for
for electric
electric lighting.
lighting. The
The two
two sides
sides
After
of the
the inverted
of
inverted triangle
triangle shape
shape are
are facing
facing toward
toward morning
morning and
and evening
evening solar
solar radiation
radiation during
during summer.
summer.
Low
sun
angles
in
the
morning
and
evening
are
a
source
of
glare
when
daylighting
is provided
Low sun angles in the morning and evening are a source of glare when daylighting is provided
through
through
and west-facing
windows.
For all building
high reflective
blinds
are adjusted
eastandeastwest-facing
windows.
For all building
models,models,
high reflective
blinds are
adjusted
inside
the building to provide visual comfort for office occupants. Shading is on if the total daylight glare
Sustainability 2017, 9, 623
14 of 28
index exceeds the maximum glare index specified in the daylighting input for an office zone. The high
amount of electric lighting demand for the triangle shape is probably caused by longer shading hours,
so that less daylight can enter the space.
Table 6. Breakdown of annual energy consumption per conditioned area for 12 plan shapes
(WWR= 50%) in Sydney (151.17E, 33.95S).
Breakdown of Annual Total Energy Demand
Annual Total Energy Demand
Plan Shape
Heating/
Conditioned
Area (kW h/m2 )
Cooling/
Conditioned
Area (kW h/m2 )
Lighting/
Conditioned
Area (kW h/m2 )
Fan/
Conditioned
Area (kW h/m2 )
Total/
Conditioned
Area (kW h/m2 )
Percentile
Difference (%)
Shape 1
Shape 2
Shape 3 ®
Shape 4
Shape 5
Shape 6
Shape 7
Shape 8
Shape 9
Shape 10
Shape 11
Shape 12
0.4
0.4
0.3
0.4
0.4
0.3
0.5
0.5
0.6
0.5
0.4
0.4
33.5
33.6
32.3
34.2
35.8
32.8
36.0
36.3
36.9
37.1
35.9
39.1
13.6
12.8
12.7
12.6
13.5
11.7
11.8
11.3
11.4
10.7
10.6
10.3
27.6
27.7
26.5
28.4
30.1
28.0
30.1
30.5
31.1
31.3
30.2
33.5
75.2
74.6
72.0
75.7
79.8
72.8
78.4
78.5
80.0
79.6
77.0
83.3
4.5%
3.7%
5.1%
10.9%
1.2%
9.0%
9.1%
11.1%
10.5%
7.0%
15.7%
®
Reference (the most efficient design option).
4.1.3. Tropical Climate
At latitudes closer to the equator, such as Singapore, the solar radiation is intense and to a great
extent diffuse due to clouds. The sun rises almost directly in the east, peaks out nearly overhead, and
sets in the west. This path does not change much throughout the year and the average air temperature
is almost constant. On the one hand, a major design objective is reducing the heat transfer through the
external surfaces exposed to outside high temperatures. For this purpose, a compact shape has less
surface-to-volume ratio and can save more energy. On the other hand, the shape and orientation of the
building should minimise the solar heat gains to lighten the cooling load. East- and west-facing walls
and windows are a major factor in overheating. Therefore, the best orientation of the building for sun
protection is along the east-west axis. The design objectives above are often contradictory.
In Singapore, cooling is paramount. Three shapes including the octagon, the ellipse and the
circle require a lower amount of cooling energy and perform better than the others. The breakdown
of annual energy consumption results for these three shapes indicates the superior function of the
octagon shape for saving electric lighting which makes the octagon to have a better performance than
the ellipse (+0.4%) and the circle (+0.5%) (see Figure 6 and Table 7).
The east and west-facing facades of the rectangle (shape 6) have the smallest portion of glazing
area (glazing is only 12% on each side). Enclosing 1500 m2 of floor area by a rectangle shape will
increase the building’s external surface area to 130% of the most compact form (shape 1). The results
show an increase of total energy use by 3% compared to the most efficient form (shape 2).
The Y shape (shape 12) has the lowest energy performance. In tropical climates, cooling is the
main end-use of energy; it considerably increases as the solar gains increase. In general, the risk of
overheating is higher for buildings that have larger east- and west-facing walls. Having a wind turbine
shape, about one third of the façade is irradiated half a day: during the morning the east façade is
irradiated, and during the afternoon the west façade. As a result, shadings are required during a
longer period to control the excessive glare, so that less daylight can enter the space. Moreover, the Y
shape has the highest ratio of volume-to-external-surface area among all plan shapes (178%). Due to
the aforementioned reasons, a high-rise building with a Y shape plan has the lowest performance of
the investigated shapes, showing up to 11% increase in total energy use.
Sustainability 2017, 9, 623
15 of 28
(178%). Due to the aforementioned reasons, a high-rise building with a Y shape plan has the lowest
performance of the investigated shapes, showing up to 11% increase in total energy use.
Sustainability 2017, 9, 623
15 of 28
Figure
Buildingtotal
totalenergy
energyuseuse
plan
shapes
(WWR
= 50%)
in association
with their
Figure 6.6. Building
of of
12 12
plan
shapes
(WWR
= 50%)
in association
with their
compactness in Singapore
compactness
Singapore(103.98E,
(103.98E,1.37N).
1.37N).
Table 7.
7. Breakdown
of annual
energy
consumption
per conditioned
area for 12 plan
Table
Breakdown
of annual
energy
consumption
per conditioned
areashapes
for 12(WWR
plan =shapes
50%)
in
Singapore
(103.98E,
1.37N).
(WWR = 50%) in Singapore (103.98E, 1.37N).
Breakdown of Annual Total Energy Demand
Annual Total Energy Demand
Breakdown
Total Energy DemandFan/
Annual Total Energy Demand
Heating/
Cooling/of AnnualLighting/
Total/
Plan
Conditioned
Conditioned
Conditioned
Conditioned
Percentile
Heating/
Cooling/
Lighting/ Conditioned
Fan/
Total/
Plan
Shape
Percentile
Shape
Conditioned
Conditioned
Conditioned
Conditioned
Conditioned Difference (%)
Area
Area
Area
Area
Area
Difference (%)
2
2
2
2
2
Area (kW2 h/m )
Area (kW
h/m )
Area (kW
h/m )
Area (kW
h/m )
Area (kW
h/m )
2
2
2
2
(kW h/m )
(kW h/m )
(kW h/m )
(kW h/m )
(kW h/m )
Shape
Shape
1 1®
0.0 0.0
75.4 75.4
11.7 11.7
28.4 28.4
115.5 115.5
0.5% 0.5%
0.0
75.5
10.8
28.6
114.9
Shape ®2
Shape
2
0.0
75.5
10.8
28.6
114.9
- 0.4%
Shape 3
0.0
75.5
11.3
28.4
115.3
Shape
34
0.0 0.0
75.5 76.7
11.3 11.3
28.4 29.5
115.3 117.6
0.4% 2.4%
Shape
Shape
Shape
45
0.0 0.0
76.7 79.0
11.3 10.4
29.5 31.6
117.6 121.0
2.4% 5.4%
Shape 6
0.0
77.8
10.2
30.3
118.3
3.0%
Shape 5
0.0
79.0
10.4
31.6
121.0
5.4%
Shape 7
0.0
79.0
10.6
31.4
121.0
5.4%
Shape
68
0.0 0.0
77.8 80.1
10.2 9.7
30.3 32.3
118.3 122.1
3.0% 6.3%
Shape
Shape
Shape
79
0.0 0.0
79.0 79.6
10.6 8.7
31.4 31.9
121.0 120.2
5.4% 4.7%
Shape
Shape
8 10
0.0 0.0
80.1 81.0
9.7 9.2
32.3 33.2
122.1 123.3
6.3% 7.4%
Shape 11
0.0
80.5
8.7
32.2
121.4
5.7%
Shape
9 12
0.0 0.0
79.6 82.9
8.7 9.8
31.9 34.8
120.2 127.4
4.7%11.0%
Shape
Shape 10
0.0
81.0
33.2
123.3
7.4%
® Reference (the9.2
most efficient design option).
Shape 11
0.0
80.5
8.7
32.2
121.4
5.7%
Shape 12
0.0
82.9
9.8
34.8
127.4
11.0%
® Reference
4.1.4. Suitability of Plan Shape
for Architectural
Designdesign option).
(the most efficient
InSuitability
this study,
efficiency
was the main
indicator for investigating the optimal plan shape.
4.1.4.
ofenergy
Plan Shape
for Architectural
Design
Other factors that might play a role for selecting the plan shape are space efficiency, natural ventilation,
In this study, energy efficiency was the main indicator for investigating the optimal plan shape.
material
use, structure, and aesthetic qualities [19]. Obviously, for two plan shapes that have almost
Other factors that might play a role for selecting the plan shape are space efficiency, natural
the same energy performance, the priority would be with the one that can provide multiple benefits
ventilation, material use, structure, and aesthetic qualities [19]. Obviously, for two plan shapes that
rather than mere energy efficiency. Therefore, it is worth to briefly discuss the suitability of plan shapes
have almost the same energy performance, the priority would be with the one that can provide
from
different
perspectives
formere
architectural
design ofTherefore,
tall buildings.
multiple
benefits
rather than
energy efficiency.
it is worth to briefly discuss the
In
terms
of
space
efficiency,
the
floor
slab
shape
is
of
great
importance.
It influences
suitability of plan shapes from different perspectives for architectural
design of tall
buildings. the interior
space In
planning
and
structural
system.
Generally,
the
planning
and
furnishing
right
angled or
terms of space efficiency, the floor slab shape is of great importance. It influencesofthe
interior
asymmetrical
shapes
are
easier
than
floor
slabs
with
sharp
corners,
and
curved
or
irregular
space planning and structural system. Generally, the planning and furnishing of right angled orshapes.
asymmetricalthe
shapes
easier
than
floorthe
slabs
withfor
sharp
curved or
irregular
shapes.
Furthermore,
planare
shape
can
affect
choice
the corners,
internaland
circulation
pattern;
hence
the space
Furthermore,
the of
plan
affect or
theYchoice
the internal
circulation
pattern;
hence thedue
space
efficiency.
In case
H shape
shape,can
+ shape
shapefor
more
floor area
is taken up
by corridors
to longer
efficiency.
In
case
of
H
shape,
+
shape
or
Y
shape
more
floor
area
is
taken
up
by
corridors
due
to
circulation routes in comparison with compact forms with a central service core. This may reduce
the
percentage of usable space.
The application of natural ventilation has a major impact on selecting the plan shape. Narrow
plan depth and aerodynamic building form (e.g., circle or ellipse) can assist in natural ventilation.
The aerodynamic form encourages the flow of wind around the external envelope and into the building
from a wide range of directions [17]. This also reduces turbulence around the building and improves
pedestrian comfort at street level. The narrow plan depth facilitates the flow of air across the space
Sustainability 2017, 9, 623
16 of 28
longer circulation routes in comparison with compact forms with a central service core. This may
reduce the percentage of usable space.
The application of natural ventilation has a major impact on selecting the plan shape. Narrow
plan depth2017,
and9,aerodynamic
building form (e.g., circle or ellipse) can assist in natural ventilation.
Sustainability
623
16 of 28
The aerodynamic form encourages the flow of wind around the external envelope and into the
building from a wide range of directions [17]. This also reduces turbulence around the building and
and
enhances
the effectiveness
of natural
In contrast,
for buildings
with
a deep
improves
pedestrian
comfort at street
level. ventilation.
The narrow plan
depth facilitates
the flow
of air
acrossplan
cross-ventilation
can
hardly
occur,
so
that
buildings
require
vertical
shafts
such
as
an
atrium
or solar
the space and enhances the effectiveness of natural ventilation. In contrast, for buildings with a deep
chimney
to facilitate natural
ventilation.
of large
elements
like
thatascan
minimise
plan cross-ventilation
can hardly
occur, soThe
thatapplication
buildings require
vertical
shafts
such
an atrium
or the
efficient
use of to
floor
spacenatural
[17]. ventilation. The application of large elements like that can minimise
solar chimney
facilitate
the efficient
of floor
space [17].perspective and material use, asymmetrical compact forms, with
Lookinguse
from
the structural
Looking from
the structural
andare
material
use, asymmetrical
forms,
the structural
and functional
coreperspective
in the centre,
more resistant
to lateral compact
loads (e.g.,
due with
to wind
theearthquakes)
structural andand
functional
the centre,
resistant
to lateral
due tohand,
wind the
or
requirecore
lessinmaterial
forare
themore
bracing
structure
[20].loads
On (e.g.,
the other
or earthquakes)
and require
less
material
for the bracing
structure
[20]. On
the other
hand,
the surface
surface
of curvilinear
shapes
(circle
or ellipse)
represents
a smaller
physical
barrier
against
wind as
of
curvilinear
shapes
(circle
or
ellipse)
represents
a
smaller
physical
barrier
against
wind
as
compared
compared to flat surfaces (square or rectangle), so that wind loads significantly reduce. Shape
(size and
to flat surfaces
(square
rectangle),
so that
wind cost
loadsdriver
significantly
reduce. Shape
(sizebuildings.
and
configuration
of the
floor or
plan)
is the most
important
for the construction
of tall
of the
plan)
the net
mostcost
important
driver for impact
the construction
of tall
buildings. and
Itconfiguration
can contribute
upfloor
to 50%
of is
total
due to cost
its profound
on the cost
of structure
It can contribute up to 50% of total net cost due to its profound impact on the cost of structure and
façade [21]. The two key ratios that represent the relationship between shape and cost are: wall-to-floor
façade [21]. The two key ratios that represent the relationship between shape and cost are: wall-toratio and net-to-gross floor area ratio. The latter determining the efficient use of floor space. While
floor ratio and net-to-gross floor area ratio. The latter determining the efficient use of floor space.
the former represents the amount of wall area that is required to enclose a certain area of floor space.
While the former represents the amount of wall area that is required to enclose a certain area of floor
From a cost perspective, the lower wall-to-floor ratio is better, so that a compact shape is the most
space. From a cost perspective, the lower wall-to-floor ratio is better, so that a compact shape is the
economical choice [21].
most economical choice [21].
Elongated
plates that
thathave
havean
anincreased
increasedperimeter
perimeter
area
deep
plan
shapes
Elongated floor
floor plates
area
(or(or
deep
plan
shapes
thatthat
havehave
a a
central
atrium)
are
favouring
shapes
for
daylight
access
and
views
out
in
workplaces
[17].
However,
central atrium) are favouring shapes for daylight access and views out in workplaces [17]. However,
the
should not
notbe
beoriented
orientedtoward
towardeast
east
west;
since
there
a risk
of overheating
theelongated
elongated sides
sides should
oror
west;
since
there
is aisrisk
of overheating
and
glare
discomfort.
Curvilinear
shapes
can
provide
a
panoramic
view
to
outside
and
improve
and glare discomfort. Curvilinear shapes can provide a panoramic view to outside and improve
the the
aesthetic
design. Curvilinear
Curvilinearshapes
shapesmight
might
also
contribute
in building’s
energy
efficiency
aestheticqualities
qualities of design.
also
contribute
in building’s
energy
efficiency
and
solutions[22].
[22].
andprovide
provide more
more sustainable
sustainable solutions
4.2.
Building Energy
EnergyPerformance
Performance
4.2.Plan
Plan Depth
Depth and
and Building
The
balanceof
ofplan
plandepth
depthand
and
building
external
surface
for energy
efficiency
The optimal
optimal balance
building
external
surface
areaarea
for energy
efficiency
of a of
a40-storey
40-storeyoffice
office
building
investigated
by modelling
aspectofratios
of an equiangular
building
waswas
investigated
by modelling
seven seven
aspect ratios
an equiangular
four2 of office
sided shape
withwith
15001500
m2 ofmoffice
area area
per floor
(Table
8). The
aspect
ratioratio
is a is
measure
of the
four-sided
shape
per floor
(Table
8). The
aspect
a measure
of the
building’s
footprint
that
describes
the
proportional
relationship
between
its
length
and
its
width
(x:y).
building’s footprint
describes the proportional relationship between its length and its width (x:y).
Foran
anequal
equalfloor
floorarea,
area,changing
changingthe
theaspect
aspectratio
ratiowill
willresult
resultinindifferent
differentexternal
externalsurface
surfacearea
areaand
andplan
For
plan depth.
An aspect
1:1 represents
a square
plan
shape
which
has
thelowest
lowestenvelope
envelopearea
area and
depth.
An aspect
ratioratio
of 1:1ofrepresents
a square
plan
shape
which
has
the
andlargest
the largest
plan depth
(38.7
m) among
the rectangular
shapes.
the
plan depth
(38.7 m)
among
the rectangular
shapes.
OtherOther
aspectaspect
ratiosratios
have have
been been
made by
made
by
extending
the
length
of
the
floor
plans
along
the
east-west
axis.
So,
the
long
sides
of the will
extending the length of the floor plans along the east-west axis. So, the long sides of the building
building
face in of
thenorth
direction
north and south.
face
in thewill
direction
and of
south.
Table 8.
8. Plan aspect
energy
performance
in three
climates.
Table
aspect ratios
ratiosand
andthe
theresults
resultsofofbuilding
building
energy
performance
in three
climates.
Plan
Aspect
Plan Aspect
Ratio
Ratio
1:1
1:1
2:1
2:1
3:1
3:1
4:1
4:1
5:1
5:1
8:1
8:1
10:1
10:1
Building
shape
Building shape
Share of each
façade
from
Share of
each
façade from the
the
total
total glazing
area (%)
glazing
area
(%)plate
Floor
dimensions
length × width
Relative
compactness
Plan depth
indicator
38.7 × 38.7 m
54.8 × 27.4 m
67.1 × 22.4 m
77.5 × 19.4 m
86.6 × 17.3 m
109.5 × 13.7 m
122.5 × 12.2 m
100%
120%
130%
140%
150%
180%
197%
52%
56%
62%
68%
74%
89%
98%
The building performance simulation results of the seven plan aspect ratios are provided in
Figure 7 and Appendix A. In temperate climates, the most compact form (1:1) requires the lowest
Plan depth
indicator
52%
56%
62%
68%
74%
89%
98%
The building performance simulation results of the seven plan aspect ratios are provided in
Figure
7 and
Appendix
A. In temperate climates, the most compact form (1:1) requires the lowest
Sustainability
2017,
9, 623
17 of 28
amount of heating and cooling energy. On the other hand, the deeper the plan, the harder it will be
to naturally light the interior space, so that the electric lighting demand would be higher. Therefore,
amount
of heating
and better
cooling
energy.
Onshape
the other
hand,
the deeper
the A
plan,
the
harder itinwill
be
the
2:1 shape
is slightly
than
the 1:1
in the
temperate
climate.
large
deviation
total
to
naturally
light
the
interior
space,
so
that
the
electric
lighting
demand
would
be
higher.
Therefore,
energy use by about 12.8% can be observed between the most efficient (2:1) and least efficient (10:1)
the 2:1
is slightlyclimate.
better than
the 1:1
shape
in the
temperate
climate.
large deviation
total
plan
in shape
the temperate
Having
a plan
aspect
ratio
of 1:1 or
3:1 canAresult
in a minorin0.8%
energy
use
by
about
12.8%
can
be
observed
between
the
most
efficient
(2:1)
and
least
efficient
(10:1)
increase of the total energy use from the most efficient one.
planIninsub-tropical
the temperate
climate.
a plan
ratio
of energy
1:1 or 3:1
result
in a minor
0.8%
climates,
theHaving
impact of
plan aspect
depth on
total
usecan
is less
significant
both
in
increasevalue
of the(6%)
totaland
energy
use fromvalue
the most
relative
in absolute
(4.4 efficient
kWh/m2one.
). A plan aspect ratio between 2:1 and 5:1 is
In the
sub-tropical
climates,
plan depth
on totalthe
energy
useshell
is less
both in
ideal in
sub-tropical
climatethe
of impact
Sydney.ofAlthough
reducing
external
is significant
critical for energy
2
relativeinvalue
(6%) climates,
and in absolute
value
kWh/m
A plan
aspectthe
ratio
between
2:1 and 5:1
saving
tropical
reducing
the(4.4
plan
depth ).can
improve
access
to daylight
andis
ideal
in
the
sub-tropical
climate
of
Sydney.
Although
reducing
the
external
shell
is
critical
for
energy
compensate for the extra cooling energy demand due to solar gains. Consequently, the same as in the
saving in tropical
reducing
planmost
depth
can improve
access
to tropical
daylightclimate,
and compensate
temperate
climate,climates,
a plan ratio
of 2:1the
is the
efficient
aspectthe
ratio
in the
while a
for the plan
extra shape
cooling(1:1)
energy
demand
to solar
gains. for
Consequently,
the same as
in theintemperate
square
could
be thedue
next
alternative
good energy-based
design
tropical
climate, a plan ratio of 2:1 is the most efficient aspect ratio in the tropical climate, while a square plan
climates.
shape (1:1) could be the next alternative for good energy-based design in tropical climates.
Figure7.7.Building
Building
total
energy
of seven
aspect
ratios
(WWR
= 50%)
in association
to
Figure
total
energy
useuse
of seven
planplan
aspect
ratios
(WWR
= 50%)
in association
to their
their compactness.
compactness.
4.3.Plan
PlanOrientation
Orientationand
andBuilding
BuildingEnergy
EnergyPerformance
Performance
4.3.
Inorder
orderto
to investigate
investigatethe
theeffect
effect of
of plan
plan orientation
orientation on
on energy
energy consumption,
consumption,four
fouraspect
aspectratios
ratios
In
◦
◦
(1:1,3:1,
3:1,5:1
5:1and
and 10:1)
10:1) from
from the
the previous
previous section
section were
were modelled
modelled in
in four
four orientations;
orientations; 0°,
0 , 45°,
45 ,90°
90◦ and
and
(1:1,
◦
135 .AAzero-degree
zero-degreeorientation
orientationmeans
means
that
the
long
sides
building
will
face
in the
direction
135°.
that
the
long
sides
of of
thethe
building
will
face
in the
direction
of
of north
south.
Other
orientations
were
made
by rotating
buildings
clockwise
with
respect
north
andand
south.
Other
orientations
were
made
by rotating
the the
buildings
clockwise
with
respect
to
to the
north.
a result,
a total
number
modelswere
weresimulated
simulatedand
andtheir
theirenergy
energy performance
performance
the
north.
As As
a result,
a total
number
ofof
1414models
analysed. A zero-degree
always
resulted
in the
energyenergy
consumption,
while rotating
analysed.
zero-degreeorientation
orientation
always
resulted
in lowest
the lowest
consumption,
while
◦
the building
90 increased
the energy
of theuse
building
a large extent
(Figure
8). (Figure
In that orientation
rotating
the building
90° increased
theuse
energy
of the to
building
to a large
extent
8). In that
(0◦ ) the building
can
make optimal
use optimal
of solar gains
south
facades
in colder
climates
in winter
and
orientation
(0°) the
building
can make
use ofon
solar
gains
on south
facades
in colder
climates
optimally
keep
out solar
radiation
in the
early morning
or afternoon
inafternoon
warm climates
or in
colder
in
winter and
optimally
keep
out solar
radiation
in the early
morning or
in warm
climates
climates
in summer.
or
in colder
climates in summer.
The largest impact of orientation was observed for the sub-tropical climates (up to 32%) when the
building is oriented at 90◦ and for the minimum plan depth (10:1). The effect of changing orientation is
smaller for the temperate and tropical climates when the worst orientation is adopted compared to the
optimal results; showing +15% and +8% increase respectively. Compact forms (deep plan buildings)
are less sensitive to changes in orientation. In all climates, a building oriented 45◦ consumed less
energy for electric lighting than one oriented 0◦ when the building has a deep plan (1:1). However,
the increased overall energy demand caused by extra heating and cooling loads beat the energy saving
in electric lighting. Our results are in good agreement with the findings in Florides, et al. [23]. They
found that the thermal loads of a square-shaped building reached its minimum value when facades
are directly oriented toward the four cardinal directions. Our findings also determined that a 0◦
plan buildings) are less sensitive to changes in orientation. In all climates, a building oriented 45°
consumed less energy for electric lighting than one oriented 0° when the building has a deep plan
(1:1). However, the increased overall energy demand caused by extra heating and cooling loads beat
the energy saving in electric lighting. Our results are in good agreement with the findings in Florides,
Sustainability 2017, 9, 623
of 28
et al. [23]. They found that the thermal loads of a square-shaped building reached its minimum18value
when facades are directly oriented toward the four cardinal directions. Our findings also determined
that a 0°from
rotation
fromisthe
is orientation
the optimal
foringaining
heat in (temperate)
cooler climates
rotation
the north
the north
optimal
fororientation
gaining heat
cooler climates
and
(temperate)
and
for
controlling
solar
radiation
in
warmer
climates
(sub-tropical
and
tropical);
thisthe
is
for controlling solar radiation in warmer climates (sub-tropical and tropical); this is in line with
in line with
the findings
earlier studies [24–26].
findings
of earlier
studiesof[24–26].
Figure
8. The
Theenergy
energyimpact
impactofof
building
orientation
aspect
ratios
(WWR
= 50%)
in
Figure 8.
building
orientation
on on
fourfour
planplan
aspect
ratios
(WWR
= 50%)
in three
three
climates.
climates.
4.4.
Window-to-Wall Ratio
4.4. Window-to-Wall
Ratio and
and Building
Building Energy
Energy Performance
Performance
Simulations
Simulations were
were performed
performed on
on aa 40-storey
40-storey office
office building
building to
to investigate
investigate the
the optimal
optimal size
size of
of the
the
windows
windows in
in temperate,
temperate, sub-tropical
sub-tropical and
and tropical
tropical climates.
climates. Since
Since plan
plan depth
depth is
is aa major
major determinant
determinant in
in
finding
the
optimal
solution,
two
plan
scenarios
were
selected:
a
deep
plan
(1:1)
and
a
narrow
plan
finding the optimal solution, two plan scenarios were selected: a deep plan (1:1) and a narrow plan
(5:1).
were
studied,
starting
with
a minimum
value
of 0%
(5:1). Discrete
Discretewindow-to-wall
window-to-wallratio
ratiovariations
variations
were
studied,
starting
with
a minimum
value
ofand
0%
increase
with
10%
increments
to
a
maximum
of
100%.
For
the
deep
plan
scenario,
the
windows
were
and increase with 10% increments to a maximum of 100%. For the deep plan scenario, the windows
distributed
evenlyevenly
among
all directions.
For the
narrow
plan scenario,
the northand south-facing
were distributed
among
all directions.
For
the narrow
plan scenario,
the northand southwalls
the building)
are theare
focus
the investigation,
while the
eastwest-facing
facing(long
wallssides
(longofsides
of the building)
theof
focus
of the investigation,
while
theand
eastand westwalls
have
no
glazing.
facing walls have no glazing.
Results
ratios are
are shown
Results for
for the
the optimal
optimal window-to-wall
window-to-wall ratios
shown in
in Appendix
Appendix B.
B. The
The energy
energy efficiency
efficiency
indicator
indicator is
is the
the annual
annual total
total energy
energy use
use for
for heating,
heating, cooling,
cooling, electric
electric lighting
lighting and
and fans.
fans. Although
Although there
there
is
an
optimal
WWR
for
each
climate,
the
recommended
values
can
be
classified
in
four
categories
based
is an optimal WWR for each climate, the recommended values can be classified in four categories
on
their
of efficiency
as shown
Figurein9.Figure
The most
ideal
WWR
canWWR
be found
in afound
relatively
based
ondegree
their degree
of efficiency
as in
shown
9. The
most
ideal
can be
in a
narrow
range
in which
energy
use deviates
by less
than 1%
the optimal
results.
relatively
narrow
rangethe
intotal
which
the total
energy use
deviates
by from
less than
1% from
the optimal
The energy consumption trend shows that in a temperate climate a window-to-wall ratio
results.
between
andconsumption
30% would result
the highest
for both
the narrow andratio
the
The 20%
energy
trend in
shows
that inenergy-efficiency
a temperate climate
a window-to-wall
deep
plan
due
to
lower
heat
transfer
through
the
façade
during
winter
and
summer.
Through
using
between 20% and 30% would result in the highest energy-efficiency for both the narrow and the deep
aplan
similar
integrated
thermal
daylighting
simulations
in the temperate
due approach—the
to lower heat transfer
through
theand
façade
during winter
and summer.
Through oceanic
using a
climates—earlier studies obtained the optimal WWR at slightly different ranges. Kheiri [27] found
the optimal value in the range of 20–32% for a building that was featured by a low-performance
façade (U values for windows and walls were 2.4 W/m2 K and 2.6 W/m2 K respectively) and had no
shading system. However, Goia et al. [28] found the optimal value in the range of 35–45% through the
integration of external solar shading devices with a high-performance façade (U values for windows
and walls were 0.7 W/m2 K and 0.15 W/m2 K respectively). Therefore, it can be inferred that the optimal
WWR value depends on the envelope properties employed in the simulations and can influence the
results to some extent. The higher thermal resistance of the envelope, the lower impact of WWR on
total energy use; hence, building can take advantage of larger windows for energy saving. Furthermore,
façade (U values for windows and walls were 2.4 W/m2K and 2.6 W/m2K respectively) and had no
shading system. However, Goia et al. [28] found the optimal value in the range of 35–45% through
the integration of external solar shading devices with a high-performance façade (U values for
windows and walls were 0.7 W/m2K and 0.15 W/m2K respectively). Therefore, it can be inferred that
the optimal WWR value depends on the envelope properties employed in the simulations and can
Sustainability 2017, 9, 623
19 of 28
influence the results to some extent. The higher thermal resistance of the envelope, the lower impact
of WWR on total energy use; hence, building can take advantage of larger windows for energy saving.
our
findings show
for WWR
smaller
20%,smaller
the energy
forthe
electric
lighting
incredibly
Furthermore,
our that
findings
showvalues
that for
WWRthan
values
thanuse
20%,
energy
use for
electric
increases.
In a temperate
climate,
upper limit
of the
is 60%; higherWWR
values
lighting incredibly
increases.
In a the
temperate
climate,
therecommended
upper limit ofWWR
the recommended
is
result
in up tovalues
10% increase
in up
totaltoenergy
consumption
due
to additional
transmission
losses
60%; higher
result in
10% increase
in total
energy
consumption
due to heat
additional
through
the façade.
transmission
heat losses through the façade.
In
In aa sub-tropical
sub-tropical climate,
climate, the
the optimal
optimal WWR
WWR value is 35–45%
35–45% for aa deep
deep plan
plan and
and 30–40%
30–40% for
for aa
narrow
narrow plan
plan building.
building. WWR variations
variations that
that contain
contain average
average performance
performance (1–5%
(1–5% deviation)
deviation) cover
cover aa
relatively
relatively big
big range.
range. For example,
example, in case of the narrow plan scenario, window-to-wall
window-to-wall ratios
ratios between
between
25–30%
have
average
performance,
but in
a temperate
climateclimate
this range
to limits
between
25–30% and
and40–70%
40–70%
have
average
performance,
but
in a temperate
thislimits
range
to
10–20%
30–40%.
the heating
energy
required
is required
not significant
buildingsfor
in buildings
sub-tropical
betweenand
10–20%
andSince
30–40%.
Since the
heating
energy
is notfor
significant
in
climates,
a larger
window
areawindow
can result
in acan
smaller
for electric
lighting;
hence
a betterhence
total
sub-tropical
climates,
a larger
area
resultdemand
in a smaller
demand
for electric
lighting;
energy
However, values
highervalues
than 80%
andthan
90%80%
are not
respectively
a betterperformance.
total energy performance.
However,
higher
andrecommended,
90% are not recommended,
for
a deep plan
narrow
because
thesebecause
have tothese
high solar
gains.
respectively
forand
a deep
planplan
and building
narrow plan
building
have heat
to high
solar heat gains.
In
In aa tropical
tropical climate,
climate, the
the optimal
optimal window-to-wall
window-to-wall ratio
ratio is
is higher
higher than
than that
that in
in aa temperate
temperate climate
climate
but
climate. ItItisisin
inaarange
rangeofof30–40%
30–40%for
foraadeep
deepplan
planand
and25–35%
25–35%for
fora
but lower than in a sub-tropical climate.
electric lighting
lighting
anarrow
narrowplan
planbuilding.
building.According
AccordingtotoFigure
Figure3,3,in
inthe
the tropical
tropical climate,
climate, the
the share of electric
loads from
from the
the total
total end-use
end-use of
of energy
energy is
is lower
lower than
than in
in the sub-tropical
sub-tropical climate.
climate. As a result, the energy
loads
savings for
forelectric
electriclighting
lighting(due
(duetotohigher
higherWWR
WWRvalues)
values)inin
the
tropical
climate
cannot
much
as
savings
the
tropical
climate
cannot
be be
as as
much
as in
in sub-tropical
the sub-tropical
climate.
In addition,
the difference
between
the outdoor
indoor air
and
outdoor air
the
climate.
In addition,
the difference
between the
indoor and
temperature
in
temperature
in the tropical
high as inclimate.
the temperate
climate.
So climate,
in the tropical
climate,
the
tropical climate
is not asclimate
high asisinnot
theastemperate
So in the
tropical
buildings
can
buildings
canrange
have of
a wider
WWR values
to that
in temperate
regions;
especially
have
a wider
WWR range
valuesof
compared
to thatcompared
in temperate
regions;
especially
when the
proper
whenofthe
proper
type
glazing
value
and
solar heatand
gainthe
coefficient)
and the shading
systems
type
glazing
(low
Uof
value
and(low
solarUheat
gain
coefficient)
shading systems
are employed
in
are facades
employed
the gain
facades
for solar gain control.
the
forin
solar
control.
Figure 9.9. Recommended
Recommendedwindow-to-wall
window-to-wallratios
ratios
energy
efficiency
a 40-storey
building
Figure
forfor
energy
efficiency
of aof
40-storey
officeoffice
building
with
deep (1:1)
planand
(1:1)aand
a narrow
planin
(5:1)
in temperate,
sub-tropical,
and tropical
climates.
awith
deepa plan
narrow
plan (5:1)
temperate,
sub-tropical,
and tropical
climates.
4.5. Window
Window Orientation
Orientation and
and Building
Building Energy
Energy Performance
Performance
4.5.
In the
the previous
previous sub-section,
sub-section, optimal
optimal WWR
WWR values
values of
of the
the façade,
façade, were
were determined
determined for
for two
two plan
plan
In
scenarios
regardless
of
the
window
orientation.
In
this
part
of
the
paper,
the
effect
of
window
scenarios regardless of the window orientation. In this part of the paper, the effect of window
orientation on
on the
the total
total energy
energy demand
demand of
of the
the building
building will
will be
be investigated.
investigated. Discrete
Discrete window-to-wall
window-to-wall
orientation
ratio
variations
were
tested,
ranging
from
10%
to
90%,
in
incremental
steps
of
10%.
One side
side of
of the
the
ratio variations were tested, ranging from 10% to 90%, in incremental steps of 10%. One
plan was the subject of change on every iteration while the WWR for the other three sides was kept at
the optimal value that was previously determined. The inputs of the simulation for the optimal WWR
are 20% for the temperate climate, 40% for the sub-tropical climate, and 30% for the tropical climate.
The investigation was carried out on the four main orientations of the deep plan scenario and the
two north- and south-facing facades of the narrow plan scenario. For the purpose of readiness, few
graphs containing simulation results for the effect of window orientation on total energy use and energy
end-uses (heating and cooling) are not shown in the text, but they can be found in Appendixs C–E.
Sensitivity of different window orientations to a change in the WWR value was analysed in regards to
climate.
The investigation was carried out on the four main orientations of the deep plan scenario and
the two north- and south-facing facades of the narrow plan scenario. For the purpose of readiness,
few graphs containing simulation results for the effect of window orientation on total energy use and
Sustainability
2017, 9, 623
20 of 28
energy end-uses
(heating and cooling) are not shown in the text, but they can be found in Appendixes
C, D and E. Sensitivity of different window orientations to a change in the WWR value was analysed
in regards
total
energy use
resultsinare
provided
in Table 9.
Accordingly,
the
total
energytouse
variations
andvariations
the resultsand
are the
provided
Table
9. Accordingly,
the
recommended
recommended
values
of
WWR
for
different
orientations
and
climates
are
summarised
in
Figure
10.
values of WWR for different orientations and climates are summarised in Figure 10. The efficiency
The efficiency
indicator
defining the recommended
values
the total
of all energy
end-uses.
indicator
for defining
thefor
recommended
values is the total
of allisenergy
end-uses.
As can
be seen As
in
can
be
seen
in
Table
9,
the
acceptable
window-to-wall
ratio
can
range
from
10%
to
90%
depending
on
Table 9, the acceptable window-to-wall ratio can range from 10% to 90% depending on the effectiveness
thedifferent
effectiveness
of orientations
different window
orientations
forWWR
energy
saving. For
WWR
of less
of
window
for energy
saving. For
increments
of less
thanincrements
10%, the average
than 10%,
the average
performance
WWR valuesvalues
was represent
obtained.
energy
performance
from energy
two consecutive
WWRfrom
valuestwo
wasconsecutive
obtained. Recommended
Recommended
values
represent
a
range
of
WWR
in
which
the
deviation
of
total
energy
use
is
a range of WWR in which the deviation of total energy use is smaller than 1% from the optimalsmaller
value
than
1%
from
the
optimal
value
in
each
orientation.
in each orientation.
Table9.9.Recommended
RecommendedWWR
WWRvalue
valuefor
fordifferent
differentorientations
orientationsand
andclimates
climatesin
inwhich
whichthe
thedeviation
deviationof
of
Table
total energy
energyuse
useisissmaller
smallerthan
than1%
1%from
fromthe
theoptimal
optimalvalue
valuein
ineach
eachorientation.
orientation.
total
Temperate
Climate Type/
Climate Type/Plan Aspect
Plan Aspect
Ratio
Ratio
Recommended
Recommended
WWR
value
WWR
value(%)
(%)
North
North
East
East
South
South
West
West
Temperate
1:1
5:1
5:1
10–90
10–70
10–90
10–70
35–60 NoNo
glazing
35–60
glazing
65–75
25–35
65–75
25–35
10–15
glazing
10–15 NoNo
glazing
1:1
Sub-Tropical
Tropical
Sub-Tropical
1:1
10–15
10–15
10–20
10–20
10–70
10–70
10–20
10–20
1:1
5:1
15–40
15–40
Noglazing
glazing
No
10–40
10–40
No
Noglazing
glazing
5:1
Tropical
1:1
5:1
5:1
10–50
10–35
10–50
10–35
10–20 NoNo
glazing
10–20
glazing
10–80
10–55
10–80
10–55
10–20
glazing
10–20 NoNo
glazing
1:1
Figure 10. Sensitivity of different window orientations to a change in the WWR value (ranging from
Figure
10. Sensitivity
ofmaximum
different window
orientations
to a change
the WWR
value
(ranging
from
10%
to 90%)
in terms of
variations
in total energy
use of ain40-storey
office
building
with
a
10%
to
90%)
in
terms
of
maximum
variations
in
total
energy
use
of
a
40-storey
office
building
with
a
deep plan (a) and a narrow plan (b) in temperate, sub-tropical, and tropical climates.
deep plan (a) and a narrow plan (b) in temperate, sub-tropical, and tropical climates.
In temperate climates, the north-facing façade was found to be the least sensitive orientation,
In temperate climates, the north-facing façade was found to be the least sensitive orientation,
with no significant variation in energy use when relatively high insulation values were included in
with no significant variation in energy use when relatively
high insulation values were included in
2 K) and opaque surfaces (U value: 0.35 W/m2 K),
the simulations for windows (U value: 1.50 W/m
2
the simulations for windows (U value: 1.50 W/m K) and opaque surfaces (U value: 0.35 W/m2K), and
and indoor blinds were adjusted only for glare control. In case of a deep plan, the ideal WWR for
indoor blinds were adjusted only for glare control. In case of a deep plan, the ideal WWR for northnorth-orientated windows can be found in a considerably wide range (10–90%) in which the deviation
orientated windows can be found in a considerably wide range (10–90%) in which the deviation of
of total energy use is less than 1% from the optimal results. For the south-facing façade, the best
total energy use is less than 1% from the optimal results. For the south-facing façade, the best energy
energy performance is achieved with large windows when WWR is in a range of 65–75%. The optimal
performance is achieved with large windows when WWR is in a range of 65–75%. The optimal WWR
WWR for the west-facing façade is the lowest value of the investigated WWR range. According to
for the west-facing façade is the lowest value of the investigated WWR range. According to Figures
Figures A3a and A4a, the heating and cooling energy demand both increased significantly when the
A3(a) and A4(a), the heating and cooling energy demand both increased significantly when the WWR
WWR percentage changed from 10% to 20%. The east-facing façade does not increase the cooling
percentage changed from 10% to 20%. The east-facing façade does not increase the cooling energy
energy demand as much as the west-facing façade and does not contribute to capturing solar thermal
energy on winter days as much as the south-facing exposure; therefore, the optimal range of WWR
is 35–60%. In case of a narrow floor plan, lower values of the optimal WWR are achieved for the
north- and south-facing facades due to a higher impact of the cooling energy use in the total energy
balance. A wrong selection of WWR in the south-facing façade of a narrow floor plan can cause a
greater increase of the cooling energy use (up to 68%) than of a deep plan building (13%).
In sub-tropical climates and for the deep plan scenario, the north-facing façade is the most
sensitive orientation to a change in the WWR value, showing up to 11% deviation in total energy
Sustainability 2017, 9, 623
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use. In order to achieve the highest energy performance (<1% deviation) it is important to reduce the
size of east- and west-facing windows (10–20%) to protect the building against overheating, while for
the south-facing exposure the total energy use is barley influenced by the WWR value. In case of a
narrow plan building, the north- and south-facing facades present relatively similar trends and the
recommended WWR ranges for those exposures are very close too (around 10–40%).
For all orientations in tropical climates, the cooling energy use is the driving force for selecting
the recommended WWR range. The highest increases in cooling energy use are observed when a
high WWR value is adopted for the west and east orientation, respectively. Therefore, the east- and
west-facing walls should particularly avoid high WWR values. In the tropics and during mid-day,
the building surface that receives the most sun is the roof since the sun paths a high arc across the sky.
In case of a deep plan building, a wrong selection of WWR in north- and south-facing facades can
cause a lower increase in the total energy use (+2.1% and +1.1%, respectively). For a building with a
plan aspect ratio of 5:1, the recommended WWR values are found in a relatively narrow range; 10–35%
for north-facing façade and 10–55% for south-facing façade.
4.6. Research Limitations and Recommendations
There are several points that need to be further discussed for the proper use of findings and for
the future development of this research. First of all, single-zone open-plan layout offices were defined
for the entire floor space in all building models. Using one activity template has both advantages and
disadvantages. On the positive side, it reduces the model’s complexity, hence speeds up the simulation.
In contrast, design potentials that some geometries might have in comparison to others, and their
consequent effect on energy consumption cannot be reflected (e.g., usability of space). Furthermore,
an increase of usable space can increase the internal gains due to occupancy, computers and lighting,
which might have impact on the heating and cooling demands.
The optimal design solution depends on the exact set of variables for the properties of the building
and the operation details. A sensitivity analysis was performed to obtain the glazing types and shading
strategies for each of the climates used in this study. It was found that external shading performed
better in terms of energy saving; however, the vulnerability of external shadings to high wind speeds
at high levels in tall buildings is an important barrier for the application of them. Moreover, indoor
shading devices are not prone to damage due to wind. They, however, reduce the view out and
increase the need of artificial lighting and cooling. Hence, all simulations were carried out by using
indoor blinds to control only glare. This means that cooling demands were probably less favourable
than in reality.
Amsterdam, Sydney and Singapore were the representative cities for the investigation of the
impact of geometric factors on energy use in the three main climate categories where the majority
of tall buildings are being constructed. In general, for each latitude, the course of the sun and local
microclimate conditions might influence a building’s performance to some extent, so it is important
to use the specific site location data as input for the simulations when the aim is finding the optimal
results. The main objective of this study was to propose early-stage design considerations for the
energy-efficiency of high-rise office buildings in three specific climates, so that these can be used to
increase the awareness of designers regarding the consequences on energy consumption of decisions
in the early phases of the design process.
Small to significant deviations may exist between the simulated and actual energy consumption
for buildings. According to Wang et al. [29] these deviations can be attributed to uncertainties related to
the accuracy of the underlying models, input parameters, actual weather data and building operation
details. There are some uncertainties related to the accuracy of simulation tool to consider thermal
performance of curved shapes, and the optimal choice of number of timesteps per hour for heat balance
model calculation. Furthermore, high-rise buildings are exposed to variable micro-climate conditions
that changes gradually with the increase in building height. In tall buildings, the top levels are exposed
to higher wind speeds and slightly lower air temperature as compared to the levels that are within the
Sustainability 2017, 9, 623
22 of 28
urban canopy. Additionally, at the higher altitude, the stack effect and wind pressures increase so that
the air leakage through the building envelope and the consequent heat losses and gains might vary
along the height. When using the weather data from a certain height, the impact of changing outdoor
conditions and infiltration rates along the height could not be taken into account.
Finally, the investigation highlights that focusing on just one entry of the total energy balance
is not correct and may lead to wrong conclusions. Therefore, determination of the optimal building
geometry factor requires the analysis of heating, cooling, electric lighting and fans altogether, since
these can be affected by the design of the building.
5. Conclusions
The study presented in this paper investigated the effect of basic geometry factors on energy
efficiency of high-rise office buildings in temperate, sub-tropical and tropical climates. Four geometric
factors were the subject of investigation, which included plan shape, plan aspect ratio, building
orientation and windows (percentage and distribution). A large number of energy simulations
were performed using EnergyPlus as part of DesignBuilder. The results of the total annual energy
consumption were used to define the optimal building geometry for each climate. This study shows
the following:
1.
2.
3.
4.
5.
The effect of plan shape on building energy consumption is the highest in the sub-tropical climate
(15.7%), and is lowest in the temperate climate (12.8%) and tropical climate (11.0%). The ellipse
was found to be the ideal plan shape in all climates. It is the most efficient form in temperate
and sub-tropical climates and the second efficient form in tropical climates after the octagon.
Furthermore, the Y shape is the least efficient form in all climates.
The effect of plan depth on total energy consumption is more dominant in the temperate climate
(12.8%) than in the tropical (8.8%) and sub-tropical climate (6.0%). The optimal range of plan
aspect ratio are 1:1 to 3:1 in Amsterdam, 3:1 to 4:1 in Sydney, and 1:1 to 3:1 in Singapore.
In all climates, a rotation 0◦ from the north was found to be the ideal orientation for energy
efficiency. In addition, a 90◦ rotation from the north is the least efficient orientation in all climates
and for all plan aspect ratios (1:1 to 10:1) with an equiangular four-sided plan shape.
Assuming that windows are equally distributed across building orientations, for a deep plan
design, the optimal range of the window-to-wall ratio is 20–30% in the temperate climate, 35–45%
in the sub-tropical climate, and 30–40% in the tropical climate. For a narrow plan design (with
no glazing for the east- and west-facing walls), the optimal range is 5% lower, except for the
temperate climate, which has the same values as for the deep plan design.
The investigation also highlights the most sensitive orientations that potentially increase the total
energy use (relative value) to a large extent for a wrong selection of WWR in different climates;
those include the west-facing exposure in temperate climates (+4.5%), the north-facing exposure
in sub-tropical climates (+11.3%), and the two facades facing east and west in tropical climates (up
to 3.3%). Furthermore, the recommended WWR values are pointed out for different orientations
and climates (see Table 9).
The impact of geometric factors on energy-efficiency of high-rise office buildings in the three
climates is summarised in Table 10. The recommended design options are classified according to
their degree of energy performance under three categories: remarkable energy saving, average energy
saving, and low energy saving. If the deviation of total energy use is greater than 10% from the
optimal solution, the design alternative will be considered as not recommended. The results could be
of assistance to make energy-wise decisions in the early phases of the design process.
Sustainability 2017, 9, 623
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Sustainability 2017, 9, 623
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optimal solution, the design alternative will be considered as not recommended. The results could be
of assistance to make energy-wise decisions in the early phases of the design process.
Table 10. Early stage design considerations for energy efficiency of high-rise office buildings.
Table 10. Early stage design considerations for energy efficiency of high-rise office buildings.
Temperate
A B C D
Ellipse
+
+
Octagon
+
+
Plan shape
<1%
Circle
Square
Rectangle
Triangle
Atrium
U shape
+ shape
1–5%
5–10%
+
+
+
+
H shape
Z shape
Y shape
>10%
+
+
+
+
Rectangle
Octagon
Circle
Square
Z shape
Courtyard
H shape
+
+
+
MD (%)
12.8
<1%
1–5%
5–10%
>10%
MD (%)
1:1, 2:1, 3:1
4:1, 5:1
8:1
10:1
12.4
1:1
3:1
5:1
10:1
<1%
0°
0°
0°
0°
1–5%
45°
135°
45°
135°
5–10%
---
90°
45°
90°
>10%
---
---
---
MD (%)
1.2
5.6
8.4
<1%
N
10–90
1–5%
---
5–10%
>10%
MD (%)
----0.5
E
35–60
10–35
60–90
----2.8
S
65–75
10–65
75–90
----1.8
<1%
N
10–70
E
---
1–5%
70–90
---
5–10%
----3.0
-------
S
25–35
10–25
35–55
55–85
85–90
10.3
>10%
stainability
2017,Sustainability
9, 623 2017, 9,2017,
Sustainability
623 9, 623
MD (%)
Sub-Tropical
A B C D
Ellipse
+
+
135°
+
+
+
+
+
+
+
+
+
+
U shape
Triangle
+ shape
Y shape
+
Tropical
A B C
Octagon
+
Ellipse
+
Circle
+
Square
+
Rectangle
+
+ shape
+
Triangle
Courtyard
+
Z shape
+
H shape
+
U shape
+
Y shape
+
D
+
+
+
+
+
+
15.7
Plan aspect ratio
3:1, 4:1
1:1, 2:1, 5:1, 8:1
10:1
--6.0
Plan orientation
1:1
3:1
5:1
11.0
1:1, 2:1, 3:1
4:1, 5:1
8:1, 10:1
--8.8
10:1
1:1
0°
45°
3:1
0°
45°
5:1
10:1
0°
0°
0°
0°
0°
0°
45°
---
---
---
---
135°
45°
45°
135°
90°
45°
---
45°
135°
---
---
---
---
---
135°
90°
45°
135°
90°
15.1
2.1
12.3
20.4
WWR (%): deep plan (1:1)
W
N
E
S
10–15 10–15 10–20 10–70
45°
135°
90°
32.0
---
---
---
---
0.7
2.8
4.7
7.9
W
10–20
N
10–50
E
10–20
S
10–80
W
10–20
15–90
20–90
50–90
20–90
80–90
20–90
----3.1
----2.9
----3.3
----1.1
----3.0
W
---
N
10–35
E
---
S
10–55
W
---
---
35–70
---
55–90
---
-------
70–90Sustainability
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--2017,
---24 of 28--- 24 of---28
--24 of 28
8.6
--3.2
--Energy efficiency of design options:
45°
90°
---
15–50
90°
20–90
70–90
--50–80
------80–90
----4.5
11.3
2.9
1.1
WWR (%): narrow plan (5:1)
W
N
E
S
--15–40
--10–40
10–15
----40–90
40–75
--75–90
--------------6.8
--5.2
<
Energy efficiency
of design
options:
<1% options:
(remarkable
energy
saving);
1–5%
(average
energy
Energy
efficiency
of
design
<1% (remarkable
energy
saving);
1–5%(average
(average
energy
Energy
efficiency
of design
<1%
(remarkable
energy
saving);
1–5%
(average
energy 5–10%
saving);
5–10% (low energy saving);
Energy
efficiency
of options:
design
options:
<1%
(remarkable
energy
saving);
1–5%
energy
saving);
(low
energy
saving);
>10%
(not
recommended).
A: High
B:High
Aerodynamic
form;
C: Narrow
saving); saving);
5–10%
(low
energy
saving);
>10%saving);
(not
recommended).
A: space
Highefficiency;
space
efficiency;
B: efficiency;
5–10%
(low
energy
saving);
>10%
(not recommended).
A: High
space
efficiency;
B:
Aerodynamic
form; C: Narrow plan (N
saving);
5–10%
(low energy
>10%
(not
recommended).
A:
space
B: plan
(NV
&
daylight
access);
D:
Less
material
use
for
external
envelope;
MD:
Maximum
deviation;
N:
North
orientation;
Aerodynamic
form;
C: Narrow
& daylight
access);
D:access);
Lessaccess);
material
external
Aerodynamic
form; form;
C:plan
Narrow
plan
(NV
daylight
D: Less
material
use for
Aerodynamic
C:(NV
Narrow
plan &
(NV
& daylight
D: use
Lessformaterial
useexternal
forenvelope;
external MD: Maximum deviation; N: N
E: East orientation; S: South orientation; W: West orientation.
envelope; envelope;
MD: Maximum
deviation;
N: North
orientation;
E: East
orientation;
S: South
orientation;
MD: Maximum
deviation;
N: North
orientation;
E: East
S: South
orientation;
envelope;
MD:
Maximum
deviation;
N: North
orientation;
E:orientation;
East
orientation;
S: South
orientation;
W: West orientation.
W: West orientation.
W: West
W: orientation.
West orientation.
Appendix A
ppendixAppendix
A Appendix
A A
Table A1. Breakdown of annual energy co
Table A1. Breakdown
of
energy
perconsumption
conditioned
areaconditioned
for seven
aspect
ratios
TableTable
A1. Breakdown
of annual
energy
consumption
per conditioned
areaplan
for
seven
plan
aspect
ratios
A1.annual
Breakdown
ofconsumption
annual
energy
per
area
for seven
plan aspect
ratios
(WWR=
50%) in: (a) Amsterdam, (b) Sydn
(WWR= 50%)
in:(WWR=
(a)50%)
Amsterdam,
(b)Amsterdam,
Sydney,
(c) Sydney,
Singapore.
(WWR=
in:
(a)in:
Amsterdam,
(b)and
Sydney,
and (c)
Singapore.
50%)
(a)
(b)
and
(c) Singapore.
Sustainability 2017, 9, 623
24 of 28
Acknowledgments: The authors would like to thank the anonymous reviewers for their helpful and constructive
comments that greatly contributed to improving the final version of the paper. They would also like to thank the
Editors for their support during the review process.
Author Contributions: All authors contributed extensively to the work presented in this paper. Babak Raji
carried out simulations, collected data and prepared drafts. Martin J. Tenpierik and Andy van den Dobbelsteen
supervised data analysis and edited the manuscript. All authors discussed the results and implications and
commented on the manuscript at all stages.
Conflicts of Interest: The authors declare no conflict of interest.
Appendix A
Table A1. Breakdown of annual energy consumption per conditioned area for seven plan aspect ratios
(WWR= 50%) in: (a) Amsterdam, (b) Sydney, and (c) Singapore.
(a) Amsterdam
Breakdown of Annual Total Energy Demand
Annual Total Energy Demand
Plan Aspect
Ratio
Heating/
Conditioned
Area
(kW h/m2 )
Cooling/
Conditioned
Area
(kW h/m2 )
Lighting/
Conditioned
Area
(kW h/m2 )
Fan/
Conditioned
Area
(kW h/m2 )
Total/
Conditioned
Area
(kW h/m2 )
Percentile
Difference
(%)
1:1
2:1 ®
3:1
4:1
5:1
8:1
10:1
15.2
15.3
15.5
15.6
15.9
16.7
17.2
23.5
23.6
24.2
24.9
25.8
27.8
29.0
17.5
16.7
15.8
15.0
14.4
13.0
12.4
28.7
28.6
29.4
30.4
31.4
34.3
36.0
84.9
84.2
84.9
85.9
87.5
91.8
94.7
0.8%
0.8%
2.1%
3.9%
9.0%
12.4%
(b) Sydney
Breakdown of Annual Total Energy Demand
Annual Total Energy Demand
Plan Aspect
Ratio
Heating/
conditioned
Area
(kW h/m2 )
Cooling/
Conditioned
Area
(kW h/m2 )
Lighting/
Conditioned
Area
(kW h/m2 )
Fan/
Conditioned
Area
(kW h/m2 )
Total/
Conditioned
Area
(kW h/m2 )
Percentile
Difference
(%)
1:1
2:1
3:1 ®
4:1
5:1
8:1
10:1
0.4
0.3
0.3
0.2
0.2
0.2
0.2
34.2
33.3
32.8
33.5
34.0
35.3
36.1
12.6
12.3
11.7
11.3
10.9
10.2
10.0
28.4
27.6
28.0
28.0
28.5
30.0
30.9
75.7
73.5
72.8
73.0
73.6
75.7
77.2
4.0%
1.0%
0.3%
1.1%
4.0%
6.0%
(c) Singapore
Breakdown of Annual Total Energy Demand
Annual Total Energy Demand
Plan Aspect
Ratio
Heating/
Conditioned
Area
(kW h/m2 )
Cooling/
Conditioned
Area
(kW h/m2 )
Lighting/
Conditioned
Area
(kW h/m2 )
Fan/
Conditioned
Area
(kW h/m2 )
Total/
Conditioned
Area
(kW h/m2 )
Percentile
Difference
(%)
1:1
2:1 ®
3:1
4:1
5:1
8:1
10:1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
76.5
76.7
77.8
78.7
79.7
82.6
84.2
11.3
10.8
10.2
9.5
9.0
8.1
7.7
29.5
29.7
30.3
31.2
32.1
34.3
35.7
117.6
117.2
118.3
119.4
120.8
125.0
127.5
0.3%
0.9%
1.9%
3.0%
6.6%
8.8%
®
Reference (the most efficient design option).
Sustainability 2017, 9, 623
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Appendix
25 of 28
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Appendix B
B
Appendix
Figure
A1.
Theoptimal
optimalpercentage
percentage
window-to-wall
ratio
fortwo
twoplan
plantypes
types
(1:15:1)
and
5:1)inin
FigureA1.
A1. The
The
optimal
ofofof
window-to-wall
ratio
for for
two
plan
types
(1:1 and
in5:1)
Figure
percentage
window-to-wall
ratio
(1:1
and
Temperate,
Sub-tropical,
andTropical
Tropicalclimates.
climates.
Temperate,Sub-tropical,
Sub-tropical, and
Temperate,
and
Tropical
climates.
Appendix C
C
Appendix
Appendix
C
Figure A2. Cont.
Sustainability
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2626ofof2828
26 of 28
Figure A2. The optimal percentage of window-to-wall ratio in different orientations for two plan
Figure
A2. The
The narrow)
optimal percentage
ofofwindow-to-wall
ratio
in different
orientations
for two
types
Figure
A2.
optimal
percentage
window-to-wall
ratio
in different
orientations
for plan
two plan
types
(deep
and
in three climates.
(deep
and
narrow)
in
three
climates.
types (deep and narrow) in three climates.
Appendix D
AppendixDD
Appendix
Figure A3. Relationship between energy use for heating and window-to-wall ratio in different
Figure A3.
A3. Relationship
Relationship
between
energy
usefor
for
heating
and
window-to-wall
ratioand
different
Figure
energy
heating
window-to-wall
ratio
inin different
orientations
for
two planbetween
scenarios
(deepuse
and
narrow)
inand
temperate,
sub-tropical,
tropical
orientations
for
two
plan
scenarios
(deep
and
narrow)
in
temperate,
sub-tropical,
and
tropical
orientations for two plan scenarios (deep and narrow) in temperate, sub-tropical, and climates.
tropical
climates.
climates.
AppendixEE
Appendix
Appendix E
Figure A4. Cont.
Sustainability 2017, 9, 623
Sustainability 2017, 9, 623
27 of 28
27 of 28
Figure A4.
A4. Relationship
Relationshipbetween
betweenenergy
energyuse
usefor
forcooling
coolingand
and window-to-wall
window-to-wallratio
ratio inin different
different
Figure
orientations
for
two
plan
scenarios
(deep
and
narrow)
in
temperate,
sub-tropical,
and
tropical
orientations for two plan scenarios (deep and narrow) in temperate, sub-tropical, and climates.
tropical
climates.
Acknowledgments:
The authors would like to thank the anonymous reviewers for their helpful and constructive
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