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 www.mdpi.com/journal/sustainability Sustainability 2017, 9, 623 2 of 28

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 3 of 28 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 Figure1. 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 4 of 28

Sustainabilityplaces where 2017 the, 9, 623 majority of tall buildings are being constructed. As a result, this study aimed4 of to28 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. MethodologicalMethodological scheme of research.

3.1. Building Building Model To investigate the effect of geometry factors, DesignBuilder version 4.7 (DesignBuilder Software Ltd,Ltd., London, London, UK) UK) was was used. used. DesignBuilder DesignBuilder is is a a powe powerfulrful interface interface that that incorporates incorporates the EnergyPlus simulation engine (version 8.3) to calculate buil buildingding energy performance data. Building performance indicators that that were were used to express the simulati simulationon results are the annual total energy consumption and the breakdown of the total energy consumption in intoto heating, heating, cooling, cooling, electric electric lighting lighting and and fans. fans. The energy figuresfigures presentedpresented in in this this paper paper are are ‘site ‘site energy’ energy’ in in kWh/m kWh/m2 2of of net net floor floor area. area. Site Site energy energy is isthe the amount amount of heatof heat and/or and/or electricity electricity consumed consumed by aby building a building as shown as shown on a on utility a utility bill. Sincebill. Since each each floor floorlevel haslevel one has single one thermalsingle thermal zone, the zone, net floorthe net area floor is equal area to is the equal area to of the the climaticallyarea of the conditionedclimatically conditionedspace. The number space. ofThe time number steps perof time hour steps was setper at hour 6 for was the heatset at balance 6 for modelthe heat calculation balance model in this calculationstudy. Increasing in this the study. number Increasing of time the steps number improves of time accuracy steps butimproves increases accuracy the time but it takesincreases to run the a timesimulation. it takes A to time run stepa simulation. value of 6 A is thetime suggested step value value of 6 byis EnergyPlusthe suggested for value simulations by EnergyPlus with HVAC for simulationssystem (and with 4 for HVAC non-HVAC system simulations). (and 4 for non-HVAC simulations). The high-risehigh-rise buildingbuilding models models have have a totala total floor floor area area of 60,000 of 60,000 m2 that m2 is that distributed is distributed over 40 over storeys 40 storeyswith identical with identical floor plans. floor Different plans. Different building building shapes and shapes floor and plan floor aspect plan ratios aspect are ratios created are by created using byan using open an plan open office plan layout office withlayout a givenwith a floorgiven area floor of area 1500 of m15002. Buildingm2. Building models models are are simplified simplified by bydefining defining one one zone zone (activity) (activity) for for the the entire entire floor floor area. area. Each Each facade facade has has a a WWRWWR ofof 50%50% thatthat is to all façade elevations.elevations. TheThe proposed proposed building building models models have have a variable-air-volume a variable-air-volume (VAV) (VAV) dual-duct dual-duct system systemto provide to provide comfort. comfort. Since each Since storey each hasstorey the has same the height same height and floor and area, floor all area, models all models have anhave equal an equalvolume. volume. However, However, the external the external surface surface area differsarea di amongffers among the models; the models; hence hence the extent the extent of losses of losses and andgains gains through through the the envelope envelope of theof the building. building. The The inputs inputs of of the the simulation simulation for for thethe propertiesproperties of the building and the operation details are described in Table1 1..

Table 1. Simulation inputs for building’s properties and operation details.

Building Properties External wall insulation U-Value: 0.35 W/m2-K Roof insulation U-Value: 0.35 W/m2-K Glazing type A 1 Dbl LoE (e2 = 0.1) Clr 6mm/13mm U-Value Arg SHGC 1.50 W/m2-K Light transmission 0.57 Sustainability 2017, 9, 623 5 of 28

Table 1. Simulation inputs for building’s properties and operation details.

Building Properties External wall insulation U-Value: 0.35 W/m2-K Roof insulation U-Value: 0.35 W/m2-K Glazing type A 1 Dbl LoE (e2 = 0.1) Clr 6 mm/13 mm U-Value Arg SHGC 1.50 W/m2-K 0.57 Light transmission 0.74 Glazing type B 2 Dbl LoE Spec Sel Clr 6 mm/13 mm U-Value Arg SHGC 1.34 W/m2-K 0.42 Light transmission 0.68 Window-to-wall ratio 50% Shading Blinds (inside) with high-reflectivity slats Shading control type Glare Maximum allowable glare index 22 Building Operation Details HVAC system type Dual duct VAV Heating Gas-fired condensing boiler Heating set point temperature 20 ◦C Cooling DOE-2 centrifugal/5.50COP Cooling set point temperature 24 ◦C Fan Power 2 W/l-s Fan total efficiency 70% Fresh air supply rate 10 L/s-person Infiltration 0.5 ac/h Lighting target illuminance 400 lux Type of lighting Fluorescent General lighting power density 3.4 W/m2-100 lux Office equipment gain 11.77 W/m2 Occupancy density 0.11 people/m2 Occupancy schedule Weekdays: 7:00–19:00; weekends: closed 1 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 Table2. This analysis Sustainability 2017, 9, 623 6 of 28 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) Temperate A*,max,D min 4.1 Glazing type Sub-tropical A max,B*,min,D 12.6 Tropical A, B *,min,C max,D 21.8 Temperate E min,F max,G* 11.3 Shading system Sub-tropical E, F max, G *, H min 6.7 Tropical E, F max, G *, H min 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 1.50 0.57 0.47 0.74 Type B. Dbl LoE Spec Sel Clr 6 mm/13 mm Arg 1.34 0.42 0.34 0.68 Type C. Dbl Ref-A-H Clr 6 mm/13 mm Arg 2.26 0.22 0.13 0.18 Type D. Trp LoE (e2 = e5 = 0.1) Clr 3 mm/13 mm Arg 0.79 0.47 0.36 0.66 Shading Description Control Type Type E. Blinds outside Solar: (120 W/m2) Type F. Blinds inside Solar: (120 W/m2) Type G. Blinds inside Glare: (glare index: 22) Type H. Integrated shading system: Solar: (120 W/m2) overhang 0.5 m + blinds outside * 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 Table3 and Figure2 respectively. According to Table3, 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 7 of 28

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 withSustainability Sydney2017 (56°), 9, 623 and Amsterdam (38°). 7 of 28

Table 3. Celsius-based heating and cooling degree days for a base temperature of 18 °C◦C for the year 2002 [16]. [16]. City Climate Type HDD CDD City Climate Type HDD CDD Amsterdam 1 Temperate 2759 149 1 AmsterdamSydney 2 Sub-tropicalTemperate 594 2759 896 149 2 SingaporeSydney 3 TropicalSub-tropical 0 594 3657 896 Singapore 3 Tropical 0 3657 1 Amsterdam Schiphol Airport, The Netherlands (4.77E, 52.30N); 2 Sydney Airport, Australia (151.17E, 1 2 Amsterdam3 Schiphol Airport, The Netherlands (4.77E, 52.30N); Sydney Airport, Australia (151.17E, 33.95S); 33.95S);3 Singapore Singapore Changi Airport, Changi Singapore Airport, (103.98E, Singapore 1.37N). (103.98E, 1.37N).

Figure 2. 2. MeanMean monthly monthly values values of ofdry-bulb dry-bulb temperature temperature and and solar solar radiation radiation in: in:(a) Amsterdam; (a) Amsterdam; (b) Sydney;(b) Sydney; and and (c) Singapore (c) Singapore for forthe theyear year 2002 2002 [16]. [16 ].

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 8 of 28 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 sunSustainability altitude 2017 is at, 9, 75 623◦ above the horizon, which is at a higher angle in comparison with Sydney (568 of◦ 28) and Amsterdam (38◦). 4. Results and Discussion 4. Results and Discussion Space heating, cooling, ventilation and lighting account for the largest amount of energy consumptionSpace heating, in buildings. cooling, However, ventilation the and proportional lighting accountenergy use for in the commercial largest amount buildings of energy differs consumptionfrom other building in buildings. usages. However, In an theoffice proportional building, energy occupancy use in is commercial during the buildings day and differs lighting from is otherparamount building therefor. usages. In In anrecent office ye building,ars, the application occupancy isof during new types the day of andequipment lighting in is paramountcommercial therefor.buildings In has recent contributed years, the significantly application to ofthe new increase types of of electricity equipment consumption. in commercial Besides, buildings the type has of contributedair conditioning significantly system to theand increase its efficiency, of electricity a building’s consumption. operation Besides, details, the type and of airits conditioningconstruction systemproperties and have its efficiency, a big impact a building’s on energy operation use patterns. details, and its construction properties have a big impactThe on results energy obtained use patterns. from the simulations have shown that the energy use for cooling could exceedThe that results for obtained heating from for thehigh-rise simulations office have build shownings thatlocated the energyin temperate use for coolingclimates could such exceed as in thatAmsterdam for heating (see for Figure high-rise 3). The office heat buildings accumulation located infrom temperate internal climates gains are such an asimportant in Amsterdam component (see Figureof the3 heat). The balance heat accumulation of an air-tight from office internal building. gains The are internal an important heat gains component resulting of from the heat the balancepresence ofof an occupants, air-tight officeoffice building.equipment The and internal electric heat lighting gains reduces resulting the from demand the presence for heating of occupants, in winter officewhile equipmentincreasing andthe electricdemand lighting for cooling reduces in thesummer. demand In for this heating parametric in winter study, while a increasingsingle activity thedemand (generic foroffice cooling area) in was summer. used for In the this entire parametric floor space. study, Allo a singlecating activity 100% (genericof usable office area area)to perform was used office for work the entirecontributed floor space. to the Allocating increased 100% use ofof usable electricity area toby perform electric officelighting work and contributed equipment to theand increased therefore useresulted of electricity in a higher by electricamount lighting of internal and heat equipment gains than and expected. therefore Furthermore, resulted in a the higher results amount showed of internalthat fans heat account gains for than roughly expected. 15–20 Furthermore,per cent of the the total results energy showed use in a that 40-storey fans account office building for roughly with 15–20a VAV per dual-duct cent of the system. total energy use in a 40-storey office building with a VAV dual-duct system.

FigureFigure 3. 3.Breakdown Breakdown of of the the total total energy energy use use in in a a simulated simulated 40-storey 40-storey office office building building with with rectangular rectangular floorfloor plan plan (3:1) (3:1) in in Amsterdam, Amsterdam, Sydney, Sydney, and and Singapore. Singapore.

InIn the the following following sections sections the the effects effects of of geometry geometry factors factors on on the the building’s building’s energy energy performance performance willwill be be discussed. discussed. Building Building performance performance indicators indicators that that were were used used toexpress to express the simulationthe simulation results results are theare annual the annual total total energy energy consumption consumption and and the breakdownthe breakdown of total of total energy energy into into different different end-uses. end-uses. In thisIn this study, study, the totalthe total energy energy consumption consumption only only includes includes heating, heating, cooling, cooling, electric electric lighting lighting and and fans fans for thesefor these can becan affected be affected by the by design the design of the of building. 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 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). 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 Table4. 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. Sustainability 2017, 9, 623 6 of 28

SustainabilitySustainability2017 20179 , 9, 623 9 of 28 Sustainability 2017, 9, , 623, 623 10 of 2810 of 28 In order to investigate the effect of plan shape on electric lighting loads, a plan depth indicator was defined. Current practiceTable suggests 4. Plan shapesfor ideal isometric daylighting views, windowaccess in distribution, office buildings relative to compactness 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 Plantaken Shape Planto calculate Shape the plan depth Shape indicator. Shape 1 1 This indicator Shape Shape 2 shows 2 the percentage ShapeShape 3 3 of office spaces Shape Shape that 4 4 Shape 5 Shape 5 Shape 6 Shape 6 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:

Share of each façade from (Opening area on each façade/Total opening area) × 100 the total glazingShare of each area façade (%) from the Alltotal the glazing openings 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 42.6 m major axis: 60 38.7 m 67.1 × 22.4 follows: 45–135° as east-facing windows,2 135–225° as south-facing windows, and 225–315° as west- Floor plate dimensions 43.7 m 42.6 m major axis: 60 38.7 m 51.1 m altitude67.1 × 22.4 Floor plate dimensions 43.7 m2 between facades minor axis: 32 between facades51.1 m altitude Length × width facing windows. In the case of shape 5, no window isbetween oriented facades at an angleminor between axis: 32 315–45°;between hence, facades Length × width Relativeshare compactnessRelativeof the compactnessnorth façade from100% the 100% total opening ar103%ea 103% is 0%. While, each 107% of the other three 113% facades113% 128%128% 130% 130% Planwould depthPlan have indicator depth a one-third indicator share47% of the 47% total glazed area.48% 48% 52%52% 52%52% 58%58% 62% 62% Plan ShapePlan Shape Shape Shape 7 7 Shape Shape 8 8 ShapeShape 9 9 Shape Shape 10 10 Shape 11 Shape 11 Shape 12 Shape 12

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 the total glazingShare of each area façade (%) 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 U value × 60.6 glazing overall type. 54.4On the × 40.4 other overall hand, passiv76.1e × heat 45.1 gains overall and daylight penetration are highly 46.6 × 42.0 overall 60.6 × 60.6 overall 54.4 × 40.4 overall 76.1 × 45.1 overall 33.7 m wing lenght 14.0 m length × width length × width length × width length × width33.7 m wing lenght 14.0 m length × width desiredlength for× reducingwidth thelength heating× width and electriclength li×ghtingwidth loads (high SHGC and Light Transmission Floor plateFloor dimensions plate dimensions 14.0 m 14.0 m from voidfrom void 14.014.0 m m value).14.014.0 For m m hot climates,14.0 the14.0 m glazing m type should14.0 m be14.0 ab lem to limit solar heat gains into the interior (low between facadesbetween facades betweenbetween facades facades SHGC),between while facades facades not obstructing betweenbetween the facades transmission facadesbetween ofbetween facadeslight. facades Relative compactness 157% 175% 175%For 176% each climate type 176% a representative 178%city was selected and the climate data for one year (2002) Relative compactnessPlan depth indicator 157% 86%175% 87% 87%In175% order to have a better 87%176% understanding 87% of the176% relative variables, 87% a 178%sensitivity analysis (SA) was was obtained for energy simulations from the website of the US Department of Energy [16]. The Plan depth indicator 86% 87% set up.87% SA is a way of testing87% a variable in order 87%to find out its effect on87% the building performance. representative cities are Amsterdam for the temperate climate, Sydney for the sub-tropical climate, 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 heating degree systems were simulated and the variation was observed. A rectangle shape was selected for the The optimal balance of plan depth and building external surface area for energy efficiencydays (HDD) of a and cooling degree days (CDD), along with mean monthly air temperature and solar purpose of 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 equiangularradiation four- values can be seen in Table 3 and Figure 2 respectively. According to Table 3, the number 2 long sides of the building are facing south and north. The results of the SA are presented in Table 2. sided shape with 1500 m of office area per floor (Table 8). The aspect ratio is a measureof HDDs of the for Amsterdam is 2759, which is five times greater than for Sydney. The number of CDDs This analysis showed that the demand for heating, cooling and lighting is highly responsive to building’sSustainability footprint2017, 9, 623; that doi:10.3390/su9040623 describes the proportional relationship between www.mdpi its length.com/journal/sustainability and its widthfor Singapore (x:y). is around 3657 which is considerably higher than for Sydney and Amsterdam. The rectangle is the second most efficient shape after thechanges ellipse. in According the glazing to typethe results, and shading the system. For an equal floor area, changing the aspect ratio will result in different external surface areaAmsterdam and is located on the northern hemisphere in a temperate climate with cool summers lowest cooling demand is around 32.3 kWh/m2 and 32.8 kWh/mIn2 afor temperate the ellipse climate, and rectangleusing triple-glazed glass has relatively the same effect on the total plan depth. An aspect ratio of 1:1 represents a square plan shape which has the lowest envelopeand mild area winters. The average monthly temperatures vary by 13.4 °C. The ratio of direct to diffuse respectively (see Table 6). As can be seen, reducing the west-facingbuilding exposure energy isconsumption of great importance as double-glazed glass. However, triple-glazed glass is more expensive and the largest plan depth (38.7 m) among the rectangular shapes. Other aspect ratios AmsterdamhaveradiationThe been triangle is equalis located (shape in most 5)on and thepart Ynorthern of shape the year. (shape hemisphe From 12) theformsre totalin botha temperatenumber showed of climatedaylightconsiderable with hours, coolincreased 35% summers is sunny cooling and made by toextending limit overheating the length during of the the floor hot plans afternoon along hours the east-west in summer. axis.and The Sotherefore compactnes, the longand might sidesmilds of not thewinters.of be thecircle the The(shapeideal average choice formonthly climates temperatures with low to vary average by 13.4 heating °C. The requirements. ratio of direct to diffuse Ourghi, Al-Anzi and Krarti [6] developed a calculation method that can predictdemand65% the annualis cloudycompared total or with to the haze other and lowforms. sun East-intensity. and Thewest-facing sun altitude windows peaks atare 61.3° a majorabove thefactor horizon in building will1)Ourghiand face the in, A octagonthel-Anzi direction and (shape Krarti of 2)north are[6] developedalmostand south. equal a calculation and therefore method the energythat can use predictradiation for cooling the isannual equal and fanstotalin most are part of the year. From the total number of daylight hours, 35% is sunny and energy use of different building forms using the energy results obtained from a referenceoverheatingat solar shape noon of with buildingsaround the in 21temperate June, while climate. at the These winter plan solstice shapes, (around that maximise 21 December) east- itand reaches west- its 4.1.4.energy SuitabilityalmostThe use e astthe of ofdifferent andsame Plan west-facing as Shape well.building for Nonetheless, facades Architectural forms usingof the the therectangleDesign 8-sided energy polygon (shape results 6) resultedobtained have the in from smallest0.8 kWh/ma65% reference portion is 2cloudy lower shape of energyorglazing with use haze and low sun intensity. The sun altitude peaks at 61.3° above the horizon a squareCommon floor plan.shapes For of all floor building plans configurations,for the design theof high-rise total2 building office volume buildings offacing conditionedwerehighest modelledexposures, angle space atin should 14.5°. Sydneytherefore is belocated avoided. on the southern hemisphere and has a humid sub-tropical aarea squareTablefor (glazing electric 8.floor Plan islighting, plan.aspect only For ratios12% which all andonbuilding eachis the closer results side). configurations, to of thatEnclosing building of the energy rectangle1500the total mperformance of buildingand floor the areainellipse. volume three by climates. a ofrectangle conditioned shape space will DesignBuilderIn this study, andenergy their efficiency energy performance was the main was indicator invest igatedfor investigating to find the themost optimalat energy-efficient solarclimate. plan Almostnoon shape. Thearound 90% form mean of the office monthly 21 June,spaces average while can be at temperatures placed the wi withinnter solsticehave 6 m afrom low(around theof 12.5 building 21 °C December) in enclosureJuly and it areaches when high ofhaving its 24.3 °C increaseremainedThe the constant. building’sZ shape Using (shape external the 11) DOE-2 surface has thesimulation area best to energy130 tool,% of pethey therformance mostcameIn compactup order among with t oforma havecorrelationthe (shapelinear a better 1).shapes equation understandingThe resultsand that even of the relative variables, a sensitivity analysis (SA) was Otherremainedin thefactors three constant. that climates. might Using The play the study aDOE-2 role focused for simulation selecting on 12 floortool, the theyplanplan camegeometries shape up arewith includingspace a correlation highestefficiency, the circle, angleequation natural octagon,at 14.5°. that Sydney is located on the southern hemisphere and has a humid sub-tropical Plan Aspectcan predict Table accurately 1. Simulation the relative inputs annual for building’s total bu propertiesilding energy andset operation up. use SA as ais details.function a way of of antesting threein enclosed January. parameters, a variable courtyard For Sydney,in order form theto (shape find ratio out 7).of directitsIt has effect lessto diffon external theuse buildingradiation surface performance. isarea the compared highest among to linear the forms.three cities, As canshowoutperformed predict an increase accurately1:1 ofthe total thecourtyard energyrelative2:1 use andannual by the3: 3%1 total triangle compared building 4:1(tha to tenergy theboth most haveuse 5:1 efficient as higher a function form relative 8:1climate. of(shape three compactness). The 2). parameters,10:1 mean monthly The average temperatures have a low of 12.5 °C in July and a high of 24.3 °C ventilation,Ratioincludingellipse, square, material Tablerelative triangle,1. use,Simulationcompactness, structure, rectangle, inputs glazing and forcourtyard aesthetic building’s area and (or qualities properties theatrium), solar [19]. and heatHWith shape, Obviously,operation gain regards coefficientU shape,details. for to two uncertain Z (SHGC) shape, plana result,and shapes +ofinput shape the it glazing.majoritythatperformsparameters, and Y of better thatdiffe thanradiationrent linearalternatives is shapesdirect. of butAt glazing loweris less typeslatitudes efficient and closethanshading toother the formsEquator, with such higher as in includingTheextendedThe over Y relative alshape ltop-side methodological compactness,(shape wing 12) of has the schemeglazing the Z shape lowest areaof designthis andenergy research the helps perfsolar toormance. isheat minimise summarised gain In coefficient afternoontropical in Figure climates,(SHGC)in solar January. 1.gains ofcoolingThe the Forby mainglazing. providingSydney, is the the ratio of direct to diffuse radiation is the highest among the three cities, haveFurthermore,shape, almost as thecan samebethey seen energyfound in Table theperformance, 4.impact BuildingIn this oftable, the Propertiesthe pr someiorityinsu lationuseful would systems levelinformation be withof Figurewere the the regarding simulatedbuilding4. one Building thatcompactness. the envelopeand cantotal compactness providethe energy variationto It isusebe worth of was 12 to planob mentionserved. shapes that A(window-to-wall rectangle the central shape atrium’s ratio was (WWR) height-to-widthselected = 50%) for thein ratio is very limited in objectivemainself-shading end-useofDuring this study of for theenergy; a ise part atorly investigateit ofdesign considerably the north- Buildingphases, the and impact increases the Propertieswest-facing decisions of geometryas the walls. madesolar factors The gainsby Hthe on increase.shape energy-efficiencydesigner (shape In cangeneral, 8) havealso of thebenefits ahigh- significantrisk offrom BuildingmultipleFurthermore,coefficient, shape benefits External window theyrather wall found distributioninsulationthan merethe impact energyand plan ofefficien thedepth insucy. ofTherefore,lationU-Value: the selected level 0.35it isof associationgeometriesW/m worththe2 -Kbuilding to withandbriefly are their thesummarised.envelope discuss majoritycompactne theto ofss Allbe inthat Amsterdam radiation (4.77E, is direct. 52.30N). At lower latitudes close to the Equator, such as in overheatinginsignificant.influenceExternal is However,on higherwall the insulation building’sfor this buildings equation energy that is only haveperformance app largerlicableU-Value: east- [1 for].purpose andThecities 0.35 west-facinggeneral withW/m of this 2cooling-dominated-K building sensitivity walls.this Havinglayout casetest. (11:1),The climatesisa windofreference so great that it buildingcould not model contribute has aeffi planciently aspect to the ratio reduction of 3:1 and of energy the demand for electric riseinsignificant. officeself-shading buildingsRoof However, by insulation in means three this of climates. externalequation wings,The is only geometry however applicable factors U-Value:the fordistribution thatcities 0.35 have with W/m of been cooling-dominated2windows-K investigated being not in climatesas this effective suitabilityandbuilding the of result modelsplan is shapes only have valid from the forsame different buildings climatically perspect that have conditionedives thefor samearchitectural floor longfloor area, sidesarea design and butof 2the the of building tallvolumeratio buildings.lighting. of ofaresurface the facing This reference area indicatedsouth to and that nort atriumh. The geometryresults of hasthe aSA crucial are presented importance in Tablefor the 2. penetration of daylight researchturbineforimportance aredaylighting shape, planRoof aboutfor shape,insulation asminimising theone plan U third shape depth, theof (shape theenergy building façade 10). loads isorientation, irandradiatedU-Value: for enabling halfwindow-to-wall4.3. 0.35Sustainability a Plan day: W/mpassive Orientation during-K 2017 design , ratio9 ,the 623; and strategies.morningdoi:10.3390/su904and Building window the ThereEnergy east 0623 is Performance a www.mdpi.com/journal/sustainability Share ofandvolume Ineach theterms result differs ofGlazing space is from only efficiency,type onevalid Ashape for 1 buildingsthe to flooranother. slab that A shape have buildingDbl theis LoEof same with great (e2 floora = importance.circular 0.1) area Clr planand 6mm/13mm Itthe (shape influences volume 1) has of the thethe interior minimumreference façadebuilding.growing isFigure irradiated,Glazing awareness 2. Mean type and monthly Ato during 1 use valuesbuilding the ofafternoon dry-bulb performanceDbl thetemperature LoEwest si (e2mulation façade. This= and 0.1) analysissolar ClrAs tools a6mm/13mmradiation result, duringshowed shadingsin: the (toathat) adjacentAmsterdam;design theare demandrequiredprocess rooms. (b) for[2]. heating, cooling and lighting is highly responsive to façadeorientation.building. from After While the comparing circle, the trianglethe climate has the and second population largest densityenergy usemaps, for electricit shows lighting. that the The most two sides spaceratio planningAlAnzi, of surface andSeo U-Valuearea structuraland to Krartivolume; system. [7] hence conducted Generally, shape an1 is investigation thethe mostplanning compactchanges onandArg severalIn form. furnishiin order the Sinceplan glazing ngto investigate ofshapesthe right typevolume with Floorandangled the of shading differentplan alleffect or plan shapes of system. plan that orientation resulted inon minimumenergy consumption, lighting demand four aspectare the ratios + shape (shape 9) and Z denselyduringofAccording populated the aSydney; invertedlonger toU-Value andcities aperiod triangle survey (c )around Singapore to conductedshape control the for are world the facingthe by year areAthienitisexcessive toward 2002mainly [16]. morningandgllocated are, Attia so in and [3],that temperate,Arg eveningabout less daylight60% solarsub-tropical of energyradiation can enter modelsand during tropicalthe are space.summer. created the totalshapes AlAnzi, is equal, Seo SHGthe and relativeC Krarti compactness [7] conducted of thean investigationother 11 geometries1.50 (1:1,on W/m several 3:1, 2can-K 5:1 be plan and calculated 10:1)shapes from bywith dividing the different previous the section were modelled in four orientations; 0°, 45°, 90° and asymmetricalgeometricfor the dimensions,shapesearly stage are easier design.window-to-wall than Building floor slabs ratiosshape with (WWRs)and sharp orie ntationand corners, orientations togetherIn and a2 temperate curved withfor the orthe hotclimate,irregular shapegeneral and (shape aridusing shapes.design climate 11).triple-glazed of Shape the 9 received glass has the relatively lowest amount the same of solar effect gains on amongthe total the linear shapes during climates.geometricMoreover,Low These sun dimensions, the areangles Y SHG theshape placesinC haswindow-to-wallthe thewheremorning highest the and majority ratio ratios evening of volume (WWRs)of tall are buildings-to-external-surface a and source1. 50orientations W/m areof beingglare-K forwhenco areanstructed. the among daylightinghot4.4. and Window-to-Wall allAs aridplan a result,is climate shapesprovided Ratio and Building Energy Performance glazingFurthermore,external area surface Lightthe plan transmissionarea shape of each can building affect the shape choice (A forbui) bythe the internal external135°. circulation 0.57 surface A zero-degree area pattern; of the henceorientation circle the shape space means (A cir). that the long sides of the building will face in the direction of of Kuwait.envelopeLight They are transmission thefound main that areas the annualof focus total for enbuildingergy modelling energybuilding use 0.57during for energyall the building early consumption design shapeswinter phase. decreases dueas double-glazed to self-shading as glass. by exte However,nded wings. triple-glazed For that glass reason, is more it has expensive the highest amount of heating this(%)of study Kuwait.through aimed They east- to found answerand west-facing that the the following annual windows. questotaltions buildingFor allin thebuild energy contexting usemodels, of for the all threehigh building reflectiveclimates: shapes blinds decreases are adjusted as efficiency. In case of H shape, + shape or Y shape more floorand areanorth therefore is takenand south. mightup by Other notcorridorsenergy be Simulationsorientations the use dueideal (about to choice werewere 19.7 performedfor madekWh/m climates by2). rotating Thison with a plan40-storey lowthe geometry buildingsto average office may building clockwise heating perform to requirements. withinvestigate better respect in tropical the to optimal climates size in of which the Sustainability 2017, 9, 623; doi:10.3390/su9040623 the north. Aswww.mdpi.com/journal/sustainability a result,windowssolar a totalgain in numberprotection temperate, of is14 sub-tropical critical models for were achieving and simulated tropical energy-efficient climates. and their Since energy buildings. plan performancedepth is a major determinant in analysed. A zero-degreefinding orientationthe optimal alwayssolution, resu twolted plan in scenarios the lowest were energy selected: consumption, a deep plan while (1:1) and a narrow plan rotating the building(5:1).4.1.2. 90° Discreteincreased Sub-Tropical window-to-wall the energyClimate use ratioof the variations building towere a large studied, extent starting (Figure with 8). In a thatminimum value of 0% orientation (0°) the andbuilding increase can withmake 10% optimal increments use of solarto a maximum gains on south of 100%. facades For thein colder deep planclimates scenario, the windows On the southern hemisphere, the geometry of a building should be reversed compared to on the in winter and optimallywere keepdistributed out solar evenly radiation among in theall directions.early morning For orthe afternoon narrow planin warm scenario, climates the north- and south- northern hemisphere. Among the 12 studied building shapes, a 180° rotation of plan would have no or in colder climatesfacing in summer. walls (long sides of the building) are the focus of the investigation, while the east- and west- impact on the building’s energy performance except for asymmetrical shapes. Therefore, the facing walls have no glazing. orientation of only three shapes, namely shapes 5, 10 and 12, are reversed (180° rotation) for optimal Results for the optimal window-to-wall ratios are shown in Appendix B. The energy efficiency energy results. In summer, building surfaces that receive the most sun are the roof and the east- and indicator is the annual total energy use for heating, cooling, electric lighting and fans. Although there west-facing walls. In winter, the sun paths a lower arc across the sky, and the north-facing wall is an optimal WWR for each climate, the recommended values can be classified in four categories based on their degree of efficiency as shown in Figure 9. The most ideal WWR can be found in a relatively narrow range in which the total energy use deviates by less than 1% from the optimal results. The energy consumption trend shows that in a temperate climate a window-to-wall ratio between 20% and 30% would result in the highest energy-efficiency for both the narrow and the deep plan due to lower heat transfer through the façade during winter and summer. Through using a Sustainability 2017, 9, 623 11 of 28

Sustainability 2017, 9, 623 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 gains orItheat is important losses in to buildings. know the For position higher of latitudes, the sun in the order sun pathto understand across the how sky the makes sun moreaffects seasonal heat variations.gains or Inheat summer, losses thein buildings. sun path beginsFor higher from latitudes, north-east the in thesun morningpath across to athe peak sky that makes is just more 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 capturingexposure solar for capturing thermal energy solar thermal on winter energy days. on Moreover,winter days. the Moreover, high summer the high sun summer during sun mid-day during can bemid-day easily blocked can be byeasily overhangs blocked orby blindsoverhangs without or blinds blocking without diffuse bloc daylightking diffuse and daylight view. and view. TheThe percentile percentile difference difference inin TableTable5 5indicates indicates aa deviationdeviation in the total energy energy use use between between the the mostmost and and least least efficient efficient forms. forms. AA largelarge percentilepercentile difference by by about about 12.8% 12.8% between between the the most most and and leastleast efficient efficient forms forms (shape (shape 3 3 and and 12 12 respectively) respectively) pointspoints to to a a dominant dominant effect effect of of plan plan shape shape on on energy energy consumptionconsumption in temperatein temperate climates. climates. As As shown shown in Figure in Figure4, to some4, to some extent extent there isthere a correlation is a correlation between thebetween annual totalthe annual energy total use energy and the use relative and the compactness relative compactness in temperate in temperate climates. climates. Generally, Generally, the larger thethe envelope larger the surface envelope area, surface the higher area, the the amount higher ofthe heat amount gains of and heat losses gains through and losses the through building the skin. Asbuilding a result, skin. compact As a shapesresult, compact are more shapes desirable are more for energy desirable saving. for energy On the saving. other hand,On the the other percentage hand, ofthe office percentage areas that of office can beareas accommodated that can be accommo alongdated the building along the perimeter building perimeter increases increases when having when a narrowhaving plan a narrow building, plan so building, that less so electric that less lighting electric is needed.lighting is Depending needed. Depending on the climate on the conditions, climate savingsconditions, achieved savings by electrical achieved loads by electrical and cooling loads loadsand cooling (reduced loads internal (reduced gains internal due to gains less lighting) due to less may compensatelighting) may or outperform compensate the or increased outperform fabric the losses increased due to fabric an elongated losses due form to (compare an elongated shape form 1 with shape(compare 3). However, shape 1 forwith buildings shape 3). withHowever, LED lightingfor buildi (insteadngs with of LED fluorescent lighting (instead or incandescent) of fluorescent the effect or of reducedincandescent) internal the gainseffect of due reduced to less internal lighting gains become duenegligible. 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 building model with an oval an oval form (shape 3) has the lowest total energy use (about 81.6 kWh/m2). 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 lower envelope than of in the winter. circle However,(0.2 kWh/m the2). heatingThis slightly demand better of performance the ellipse building of the ellipse is slightly in terms lower 2 thanof heating of the circle demand (0.2 is kWh/m due to a ).higher This slightlypercentage better of south-facing performance windows of the ellipsefor an ellipse in terms shape of heating plan demand(35%) in is comparison due to a higher with a percentage circle shape of plan south-facing (25%). According windows to Straube for an and ellipse Burnett shape [18], plan the(35%) south in comparisonfaçade can with receive a circle twice shape the planheat (25%).gain of Accordingeast and west to Straube façades and in Burnettwinter at [18 a], latitude the south of façade45°. ◦ canConsidering receive twice the the electric heat lighting gain of eastdemand, and westthe circle façades has inthe winter maximum at a latitudeplan depth of 45and. Consideringa large part of the electricthe floor lighting area demand,may need the electric circle lighting has the during maximum most plan of the depth day and time. a largeThe energy part of consumption the floor area for may needelectric electric lighting lighting is 17.2 during and most17.9 kWh/m of the2 day for time.the ellipse The energyand the consumption circle respectively. for electric lighting is 17.2 and 17.9 kWh/m2 for the ellipse and the circle respectively.

FigureFigure 4. 4.Building Building totaltotal energyenergy useuse ofof 1212 planplan shapesshapes (window-to-wall ratio ratio (WWR) (WWR) = =50%) 50%) in in associationassociation with with their their compactness compactness in in Amsterdam Amsterdam (4.77E,(4.77E, 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 Heating/ Cooling/ Lighting/ Fan/ Total/ Plan Shape Percentile Conditioned Conditioned Conditioned Conditioned Conditioned Difference (%) Area (kW h/m2) Area (kW h/m2) Area (kW h/m2) Area (kW h/m2) Area (kW h/m2) Shape 1 15.1 22.5 17.9 27.3 82.8 1.4% Shape 2 15.2 22.6 17.1 27.4 82.3 0.9% Shape 3 ® 14.9 22.5 17.2 27.0 81.6 - Shape 4 15.2 23.5 17.5 28.7 84.9 4.0% Shape 5 15.6 24.3 16.4 29.7 86.1 5.4% Shape 6 15.5 24.2 15.8 29.4 84.9 4.0% Shape 7 18.5 24.1 14.6 30.5 87.6 7.3% Shape 8 19.2 24.4 15.6 31.2 90.4 10.7% Shape 9 19.7 24.6 13.9 31.4 89.6 9.7% Shape 10 19.5 24.3 14.6 31.0 89.4 9.5% Shape 11 18.5 25.8 14.0 32.6 90.8 11.2% Shape 12 18.9 26.0 14.4 32.9 92.1 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 Sustainabilitysummer (and2017 in, 9, winter), 623 only in the morning and evening. 13 of 28 In Sydney, the solar radiation is intense and to a great extent direct. The number of cooling degreeIn days Sydney, are almost the solar twice radiation as much is as intense the number and to of a heating great extent degree direct. days. High The numberinternal gains of cooling from degreewindows, days occupants, are almost lighting, twice as muchcomputers as the and number office of heatingappliances degree limit days. the Highbuilding’s internal demand gains from for windows,heating drastically. occupants, As lighting, a result, computers the efficiency and office of plan appliances shapes limit is mostly the building’s determined demand by the for heatingenergy drastically.demand for As cooling, a result, fans the and efficiency electric oflighting. plan shapes is mostly determined by the energy demand for cooling,For fansthe sub-tropical and electric lighting.climate of Sydney, the results show that the ellipse (shape 3) has the lowest total Forenergy the sub-tropicaluse (72.0 kWh/m climate2), while of Sydney, the highest the results energy show use that was the found ellipse for (shape the Y 3)shape has the(shape lowest 12) total(83.3 energykWh/m use2 or (72.015.7% kWh/m higher2 than), while shape the 3) highest (see Figure energy 5). use According was found to forthe theresults, Y shape the amount (shape 12) of (83.3energy kWh/m used for2 or space 15.7% cooling higher and than fans shape is slightly 3) (see lower Figure in5). compact According forms. to the The results, energy the use amount for fans of is energycalculated used based for space on the cooling supply and airfans flow is rate, slightly pres lowersure drop in compact and fan forms. efficiency. The energy The supply use for fan fans only is calculatedruns when based either on cooling the supply or heating air flow needs rate, pressure to be supplied drop and to fan the efficiency. zone. For The elongated supply fan shapes, only runs the whenincreased either length cooling of ducts or heating increases needs the to beenergy supplied use for to thefans zone. due Forto higher elongated pressure shapes, drops the increased(compare lengthshape 1 of and ducts shape increases 6). Contrary the energy to this, use a for very fans deep due plan to higher like the pressure circle dropsshape (comparewould demand shape 1more and shapeelectrical 6). Contrarylighting; tohence this, amore very deepcooling plan is like needed the circle to compensate shape would the demand excessive more internal electrical gains lighting; by hencelighting more and cooling more energy is needed is required to compensate for the thedistribution excessive of internal cold air gains by fans. by lighting and more energy is required for the distribution of cold air by fans.

Figure 5.5. BuildingBuilding total total energy energy use use of 12 plan shapes (WWR = 50%) in association with their compactness inin SydneySydney (151.17E,(151.17E, 33.95S).33.95S).

The rectangle is thethe secondsecond mostmost efficientefficient shapeshape afterafter thethe ellipse.ellipse. According to the results,results, thethe 2 2 lowestlowest coolingcooling demanddemand isis aroundaround 32.332.3 kWh/mkWh/m2 and 32.8 kWh/mkWh/m 2 forfor the the ellipse and rectanglerectangle respectively (see(see TableTable6 ).6). As As can can be be seen, seen, reducing reducing the the west-facing west-facing exposure exposure is ofis greatof great importance importance to limitto limit overheating overheating during during the the hot hot afternoon afternoon hours hours in summer.in summer. The The compactness compactnes ofs of the the circle circle (shape (shape 1) and1) and the the octagon octagon (shape (shape 2) are 2) almostare almost equal equal and thereforeand therefore the energy the energy use for use cooling for cooling and fans and are fans almost are 2 thealmost same the as same well. as Nonetheless, well. Nonetheless, the 8-sided the 8-sided polygon polygon resulted resulted in 0.8 in kWh/m 0.8 kWh/m2 lower lower energy energy use use for electricfor electric lighting, lighting, which which is closer is closer to that to that of the of rectanglethe rectangle and and the ellipse.the ellipse. The Z shape shape (shape (shape 11) 11) has has the the best best energy energy performance performance among among the linear the linear shapes shapes and even and evenoutperformed outperformed the courtyard the courtyard and the and triangle the triangle (that (thatboth bothhave havehigher higher relative relative compactness). compactness). The Theextended extended top-side top-side wing wing of the of the Z shape Z shape design design helps helps to to minimise minimise afternoon afternoon solar solar gains gains by by providing self-shading for a part of thethe north-north- andand west-facingwest-facing walls.walls. The H shape (shape 8) also benefitsbenefits from self-shading by means of external wings, however the distribution of windows being not as effective forfor daylightingdaylighting asas thethe UU shapeshape (shape(shape 10).10). After the circle, the triangle has the second largest energyenergy useuse forfor electricelectric lighting.lighting. The two sides of the inverted triangle shape are facing toward morning and and evening evening solar solar radiation radiation during during summer. summer. Low sunsun angles angles in in the the morning morning and and evening evening are aare source a source of glare of whenglare daylightingwhen daylighting is provided is provided through east-through and east- west-facing and west-facing windows. windows. For allbuilding For all build models,ing models, high reflective high reflective blinds areblinds adjusted 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 Heating/ Cooling/ Lighting/ Fan/ Total/ Plan Shape Percentile Conditioned Conditioned Conditioned Conditioned Conditioned Difference (%) Area (kW h/m2) Area (kW h/m2) Area (kW h/m2) Area (kW h/m2) Area (kW h/m2) Shape 1 0.4 33.5 13.6 27.6 75.2 4.5% Shape 2 0.4 33.6 12.8 27.7 74.6 3.7% Shape 3 ® 0.3 32.3 12.7 26.5 72.0 - Shape 4 0.4 34.2 12.6 28.4 75.7 5.1% Shape 5 0.4 35.8 13.5 30.1 79.8 10.9% Shape 6 0.3 32.8 11.7 28.0 72.8 1.2% Shape 7 0.5 36.0 11.8 30.1 78.4 9.0% Shape 8 0.5 36.3 11.3 30.5 78.5 9.1% Shape 9 0.6 36.9 11.4 31.1 80.0 11.1% Shape 10 0.5 37.1 10.7 31.3 79.6 10.5% Shape 11 0.4 35.9 10.6 30.2 77.0 7.0% Shape 12 0.4 39.1 10.3 33.5 83.3 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 Figure6 and Table7). 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

Sustainabilityperformance2017 of, 9 the, 623 investigated shapes, showing up to 11% increase in total energy use. 15 of 28

FigureFigure 6.6. BuildingBuilding total total energy energy use use of of12 12plan plan shapes shapes (WWR (WWR = 50%) = 50%)in association in association with their with their compactnesscompactness in Singapore (103.98E, (103.98E, 1.37N). 1.37N).

TableTable 7.7. BreakdownBreakdown of annual of annual energy energy consumption consumption per conditioned per conditioned area for 12 plan area shapes for 12 (WWR plan = shapes (WWR50%) in = Singapore 50%) in Singapore (103.98E, 1.37N). (103.98E, 1.37N). Breakdown of Annual Total Energy Demand Annual Total Energy Demand Heating/ BreakdownCooling/ of AnnualLighting/ Total Energy DemandFan/ Total/ Annual Total Energy Demand Plan ConditionedHeating/ ConditionedCooling/ ConditionedLighting/ ConditionedFan/ ConditionedTotal/ Percentile Plan Shape Percentile Shape Conditioned Conditioned Conditioned Conditioned Conditioned Area Area Area Area Area DifferenceDifference (%) (%) Area (kW h/m2) Area (kW h/m2) Area (kW h/m2) Area (kW h/m2) Area (kW h/m2) (kW h/m2) (kW h/m2) (kW h/m2) (kW h/m2) (kW h/m2) Shape 1 0.0 75.4 11.7 28.4 115.5 0.5% Shape 1 ® 0.0 75.4 11.7 28.4 115.5 0.5% Shape® 2 0.0 75.5 10.8 28.6 114.9 - ShapeShape 2 30.0 0.0 75.5 75.5 10.8 11.3 28.6 28.4 114.9 115.3 - 0.4% ShapeShape 3 4 0.0 0.0 75.5 76.7 11.3 11.3 28.4 29.5 115.3 117.6 0.4% 2.4% ShapeShape 4 5 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% ShapeShape 6 8 0.0 0.0 77.8 80.1 10.2 9.7 30.3 32.3 118.3 122.1 3.0% 6.3% ShapeShape 7 9 0.0 0.0 79.0 79.6 10.6 8.7 31.4 31.9 121.0 120.2 5.4% 4.7% ShapeShape 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% ShapeShape 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 10 0.0 81.0 9.2 33.2 123.3 7.4% ® Reference (the 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% 4.1.4. Suitability of Plan Shape® Reference for Architectural (the most efficient Design design option).

4.1.4.In Suitability this study, of energyPlan Shape efficiency for Architectural was the main Design indicator for investigating the optimal plan shape. Other factors that might play a role for selecting the plan shape are space efficiency, natural ventilation, materialIn this use, study, structure, energy and efficiency aesthetic was qualities the main [ 19indicator]. Obviously, for investigating for two plan the optimal shapes plan that shape. 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 frommultiple different benefits perspectives rather than for mere architectural energy efficien designcy. of Therefore, tall buildings. it is worth to briefly discuss the suitabilityIn terms of plan of space shapes efficiency, from different the floor perspect slabives shape for is architectural of great importance. design of tall It influencesbuildings. the interior spaceIn planning terms of andspace structural efficiency, system.the floor slab Generally, shape is theof great planning importance. and furnishing It influences of the right interior angled or asymmetricalspace planning shapes and structural are easier system. than floor Generally, slabs withthe planning sharp corners, and furnishi and curvedng of right or irregularangled or shapes. Furthermore,asymmetrical theshapes plan are shape easier can than affect floor the slabs choice with for sharp the corners, internal and circulation curved or pattern; irregular hence shapes. the space efficiency.Furthermore, In case the ofplan H shape shape, can + shape affect orthe Y choice shape for more the internal floor area circulation is taken uppattern; by corridors hence the due space to longer circulationefficiency. routesIn case inof comparisonH shape, + shape with compactor Y shape forms more with floor a area central is taken service up core.by corridors This may due reduce to 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 Sustainabilityplan depth2017 and, 9 ,aerodynamic 623 building form (e.g., circle or ellipse) can assist in natural ventilation.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 andimproves enhances pedestrian the effectiveness comfort at street of natural level. ventilation.The narrow plan In contrast, depth facilitates for buildings the flow with of air a deepacross plan cross-ventilationthe space and enhances can hardly the effectiveness occur, so that of buildingsnatural ventilation. require vertical In contrast, shafts for such buildings as an with atrium a deep or solar chimneyplan cross-ventilation to facilitate natural can hardly ventilation. occur, so The that application buildings require of large vertical elements shafts like such that as can an atrium minimise or the efficientsolar chimney use of to floor facilitate space natural [17]. ventilation. The application of large elements like that can minimise the efficientLooking use from of floor the structuralspace [17]. perspective and material use, asymmetrical compact forms, with the structuralLooking from and functionalthe structural core perspective in the centre, and are mate morerial resistantuse, asymmetrical to lateral compact loads (e.g., forms, due with to wind orthe earthquakes) structural and and functional require core less in material the centre, for are the more bracing resistant structure to lateral [20 ].loads On (e.g., the otherdue to hand, wind the surfaceor earthquakes) of curvilinear and require shapes less (circle material or ellipse) for the br representsacing structure a smaller [20]. On physical the other barrier hand, against the surface wind as comparedof curvilinear to flat shapes surfaces (circle (square or ellipse) or rectangle), represents so a thatsmaller wind physical loads significantlybarrier against reduce. wind as Shape compared (size and configurationto flat surfaces of the(square floor or plan) rectangle), is the most so that important wind costloads driver significantly for the constructionreduce. Shape of tall(size buildings. and Itconfiguration can contribute of the up floor to 50% plan) of is total the netmost cost importan due tot cost its profound driver for impactthe construction on the cost of tall of structurebuildings. and façadeIt can [contribute21]. The two up keyto 50% ratios of total that representnet cost due the to relationship its profound between impact shape on the and cost cost of structure are: wall-to-floor and façade [21]. The two key ratios that represent the relationship between shape and cost are: wall-to- ratio 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]. ElongatedElongated floorfloor plates that that have have an an increased increased pe perimeterrimeter area area (or (or deep deep plan plan shapes shapes that that have have a a centralcentral atrium)atrium) are favouring shapes shapes for for daylight daylight access access and and views views out out in workplaces in workplaces [17]. [ 17However,]. However, thethe elongatedelongated sidessides should not not be be oriented oriented toward toward ea eastst or orwest; west; since since there there is a is risk a risk of overheating of overheating andand glareglare discomfort.discomfort. Curvilinear shapes shapes can can provide provide a panoramic a panoramic view view to outside to outside and and improve improve the the aestheticaesthetic qualitiesqualities of design. Curvi Curvilinearlinear shapes shapes might might also also contribute contribute in building’s in building’s energy energy efficiency efficiency andand provide provide moremore sustainablesustainable solutions solutions [22]. [22].

4.2.4.2. PlanPlan DepthDepth and Building Energy Energy Performance Performance TheThe optimaloptimal balance of of plan plan depth depth and and building building external external surface surface areaarea for energy for energy efficiency efficiency of a of a40-storey 40-storey office office building building was was investigated investigated by modelling by modelling seven sevenaspect ratios aspect of ratios an equiangular of an equiangular four- four-sidedsided shape shape with with1500 1500m2 of m office2 of office area areaper floor per floor (Table (Table 8). The8). The aspect aspect ratio ratio is a ismeasure a measure of the of the building’sbuilding’s footprintfootprint that describes describes the the proportional proportional relationship relationship between between its length its length and and its width its width (x:y). ( x:y). ForFor an an equal equal floor floor area, area, changing changing the the aspect aspect ratio ratio will will result result in in different different external external surface surface area area and and plan depth.plan depth. An aspect An aspect ratio ratio of 1:1 of represents 1:1 represents a square a square plan plan shape shape which which has has the the lowest lowest envelope envelope areaarea and theand largest the largest plan depthplan depth (38.7 m)(38.7 among m) among the rectangular the rectangular shapes. shapes. Other Other aspect aspect ratios ratios have have been been made by extendingmade by extending the length the of thelength floor of plans the floor along plans the east-westalong the axis.east-west So, theaxis. long So, sidesthe long of the sides building of the will facebuilding in the will direction face in ofthe north direction and of south. north and south.

TableTable 8.8. Plan aspect ratios ratios and and the the results results of of bu buildingilding energy energy performance performance in three in three climates. climates. Plan Aspect Plan Aspect 1:11:1 2:12:1 3:13:1 4:1 4:1 5:1 5:1 8:1 8:1 10:1 10:1 RatioRatio

Building shape Building shape Share of each façadeShare offrom each façade from the thetotal total glazing glazingarea (%)area Floor(%) plate dimensions 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 length × width Relative 100% 120% 130% 140% 150% 180% 197% compactness Plan depth 52% 56% 62% 68% 74% 89% 98% indicator

The building performance simulation results of the seven plan aspect ratios are provided in Figure7 and AppendixA. In temperate climates, the most compact form (1:1) requires the lowest

Figure 7. Building total energy use of seven plan aspect ratios (WWR = 50%) in association to their compactness. almost the same as well. Nonetheless, the 8-sided polygon resulted in 0.8 kWh/m2 lower energy use 4.3. Plan Orientation and Buildingfor Energy electric Performance lighting, which is closer to that of the rectangle and the ellipse. The Z shape (shape 11) has the best energy performance among the linear shapes and even In this study, energy efficiencyIn order was to the investigate main indicator the effect for investigatingof plan orientation the optimal on energy plan consumption,shape. four aspect ratios outperformed the courtyard and the triangle (that both have higher relative compactness). The Other factors that might(1:1, play 3:1, a 5:1role and for 10:1) selecting from thethe previous plan shape section are werespace modelled efficiency, in fournatural orientations; 0°, 45°, 90° and extended top-side wing of the Z shape design helps to minimise afternoon solar gains by providing ventilation, material use, 135°.structure, A zero-degree and aesthetic orientation qualities means [19]. Obviously,that the long for sides two ofplan the shapes building that will face in the direction of self-shadingResults for for a partthe optimalof the north- window-to-w and west-facingall ratios walls. are shown The H in shape Appendix (shape B. 8) The also energy benefits efficiency from have almost the same energynorth performance,and south. Other the orientationspriority would were be made with bythe rotating one that the can buildings provide clockwise with respect to Table 8. Plan aspect ratios and the self-shadingresultsindicator of building is by the means energy annual of performance totalexternal energy wings, in use three howeverfor climates. heating, the cooling, distribution electric of windowslighting and being fans. not Although as effective there multiple benefits rather thanthe north. mere Asenergy a result, efficien a totalcy. Therefore,number of it14 is mo worthdels wereto briefly simulated discuss and the their energy performance foris daylighting an optimal as WWR the U for shape each (shape climate, 10). the recommended values can be classified in four categories suitability of planPlan shapes Aspect analysed.from different A zero-degree perspectives orientation for architectural always design resulted of tall in buildings. the lowest energy consumption, while 1:1 2:1 based3:After1 on the their circle, 4:1degree the triangle of efficiency 5:1 has the as second shown 8:1 largest in Figure10:1 energy 9. The use mostfor electric ideal WWRlighting. can The be two found sides in a CommonIn shapesterms of of space flooRatior efficiency, plans rotating for the thethe floor designbuilding slab of shape90° high-rise increased is of officegreat the importance. buildingsenergy use were ofIt influencesthe modelled building the in to interior a large extent (Figure 8). In that of relativelythe inverted narrow triangle range shape in arewhich facing the toward total energy morning use and deviates evening by solar less radiation than 1% during from the summer. optimal DesignBuilderspace planning and their andenergy structural performanceorientation system. (0°) was Generally, the invest buildingigated the can toplanning find make the optimal andmost furnishi energy-efficient use ofng solar of gainsright form angledon south or facades in colder climates Building shape Lowresults. sun angles in the morning and evening are a source of glare when daylighting is provided in the threeasymmetrical climates. shapesThe study are infocusedeasier winter than on and floor12 optimally floor slabs plan with keep geometries sharp out solar corners, including radiation and curvedthe in thecircle, earlyor irregularoctagon, morning shapes. or afternoon in warm climates throughThe east- energy and west-facing consumption windows. trend showsFor all buildthat ining a models, temperate high climate reflective a window-to-wallblinds are adjusted ratio ellipse, square,Furthermore, triangle,Figure the 2. rectangle, planMean shape monthlyor courtyard in can colder values affect climates (orof the dry-bulbatrium), choice in summer. temperature forH shape,the internal U and shape, circulationsolar Z radiation shape, pattern; + in: shape (a) henceAmsterdam; and Ythe space (b) Share of each between 20% and 30% would result in the highest energy-efficiency for both the narrow and the deep shape,The asefficiency. Y can sh apebe Sydney; seen(shape In case in and Table12) of ( hascH) Singapore 4.shape, the In thislowest + forshapetable, theenergy yearsomeor Y 2002perf shapeuseful ormance.[16]. more information floorIn tropical area regarding is climates, taken the up cooling compactness by corridors is the due to façade from plan due to lower heat transfer through the façade during winter and summer. Through using a maincoefficient, end-use window of energy; distribution it considerably and plan increases depth asof thethe solarselected gains geometries increase. Inare general, summarised. the risk All of the total overheatingbuilding models is higher have forthe buildingssame climatically that have conditioned larger east- floor and area, west-facing but the ratiowalls. of Having surface aarea wind to glazing area turbinevolume shape,differs fromabout one one shape third to of another. the façade A building is irradiated with ahalf circular a day: plan during (shape the 1) morninghas the minimum the east (%) façaderatio of is surface irradiated, area toand volume; during hence the afternoon shape 1 is thethe westmost façade.compact As form. a result, Since shadings the volume are of required all plan duringshapes isa equal,longer the period relative to compactnesscontrol the excessive of the other glare, 11 geometries so that less can daylight be calculated can enter by dividing the space. the Moreover,external surface the Y areashape of has each the building highest shape ratio of (A volumebui) by the-to-external-surface external surface area area of among the circle all planshape shapes (Acir).

Figure 9. Recommended window-to-wall ratios for energy efficiency of a 40-storey office building with a deep plan (1:1) and a narrow plan (5:1) in temperate, sub-tropical, and tropical climates.

4.5. Window Orientation and Building Energy Performance In the previous sub-section, optimal WWR values of the façade, were determined for two plan scenarios regardless of the window orientation. In this part of the paper, the effect of window orientation on the total energy demand of the building will be investigated. Discrete window-to-wall ratio variations were tested, ranging from 10% to 90%, in incremental steps of 10%. One side of the Sustainability 2017, 9, 623 17 of 28

Floor plate 38.7 × 54.8 × 67.1 × 77.5 × 86.6 × 109.5 × 122.5 × dimensions 38.7 m 27.4 m 22.4 m 19.4 m 17.3 m 13.7 m 12.2 m length × width Relative 100% 120% 130% 140% 150% 180% 197% compactness Plan depth 52% 56% 62% 68% 74% 89% 98% indicator

The building performance simulation results of the seven plan aspect ratios are provided in FigureSustainability 7 and2017 Appendix, 9, 623 A. In temperate climates, the most compact form (1:1) requires the lowest17 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, theamount 2:1 shape of heating is slightly and better cooling than energy. the 1:1 On shape the other in the hand, temperate the deeper climate. the A plan, large the deviation harder it in will total be energyto naturally use by light about the 12.8% interior can space, be observed so that thebetween electric the lighting most efficient demand (2:1) would and beleast higher. efficient Therefore, (10:1) planthe 2:1in shapethe temperate is slightly climate. better thanHaving the 1:1a plan shape aspect in the ratio temperate of 1:1 or climate. 3:1 can A result large deviationin a minor in 0.8% total increaseenergy useof the by total about energy 12.8% use can from be observed the most between efficient theone. most efficient (2:1) and least efficient (10:1) planIn in sub-tropical the temperate climates, climate. the Havingimpact of a planplan aspectdepth on ratio total of energy 1:1 or 3:1 use can is less result significant in a minor both 0.8% in increase of the total energy use from the most efficient one. relative value (6%) and in absolute value (4.4 kWh/m2). A plan aspect ratio between 2:1 and 5:1 is ideal inIn the sub-tropical sub-tropical climates, climate the of impactSydney. of Although plan depth reducing on total the energy external use shell is less is significantcritical for energy both in 2 savingrelative in value tropical (6%) climates, and in absolute reducing value the (4.4 plan kWh/m depth ).can A planimprove aspect the ratio access between to daylight 2:1 and 5:1and is compensateideal in the sub-tropicalfor the extra climatecooling ofenergy Sydney. demand Although due to reducing solar gains. the externalConsequently, shell is the critical same for as energyin the temperatesaving in tropicalclimate, climates, a plan ratio reducing of 2:1 the is the plan most depth efficient can improve aspect theratio access in the to tropical daylight climate, and compensate while a squarefor the plan extra shape cooling (1:1) energy could demand be the due next to solaraltern gains.ative for Consequently, good energy-based the same asdesign in the in temperate tropical climates.climate, a plan ratio of 2:1 is the most efficient aspect ratio in the tropical climate, while a square plan shape (1:1) could be the next alternative for good energy-based design in tropical climates.

FigureFigure 7. 7. BuildingBuilding total total energy energy use use of seven of seven plan plan aspect aspect ratios ratios (WWR (WWR = 50%) = 50%)in association in association to their to compactness.their compactness.

4.3.4.3. Plan Plan Orientation Orientation and and Building Building Energy Energy Performance Performance InIn order order to to investigate investigate the the effect effect of of plan plan orientation orientation on on energy energy consumption, consumption, four four aspect aspect ratios ratios (1:1,(1:1, 3:1, 3:1, 5:1 5:1 and 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◦ andand 135°.135◦ .A A zero-degree zero-degree orientation orientation means means that that the the long long sides sides of ofthe the building building will will face face in the in thedirection direction of northof north and and south. south. Other Other orientations orientations were were made made by rotating by rotating the thebuildings buildings clockwise clockwise with with respect respect to theto thenorth. north. As Asa result, a result, a total a total number number of of14 14 mo modelsdels were were simulated simulated and and their their energy energy performance performance analysed.analysed. A zero-degreezero-degree orientation orientation always always resulted resulted inthe in lowestthe lowest energy energy consumption, consumption, while rotating while rotatingthe building the building 90◦ increased 90° increased the energy the use energy of the use building of the tobuilding a large extentto a large (Figure extent8). In(Figure that orientation 8). In that orientation(0◦) the building (0°) the can building make optimal can make use optimal of solar gainsuse of on solar south gains facades on south in colder facades climates in colder in winter climates and inoptimally winter and keep optimally out solar keep radiation out solar in theradiation early morningin the early or afternoonmorning or in afternoon warm climates in warm or inclimates colder orclimates in colder in summer.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◦ Sustainability 2017, 9, 623 18 of 28

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, Sustainabilityet al. [23]. They2017, 9found, 623 that the thermal loads of a square-shaped building reached its minimum18 value of 28 when facades are directly oriented toward the four cardinal directions. Our findings also determined rotationthat a 0° from rotation the north from is the the north optimal is orientationthe optimal for orientation gaining heat for in gaining cooler climatesheat in (temperate)cooler climates and for(temperate) controlling and solar for controlling radiation in solar warmer radiation climates in warmer (sub-tropical climates and (sub-tropical tropical); this and is intropical); line with this the is findingsin line with ofearlier the findings studies of [ 24earlier–26]. studies [24–26].

Figure 8. TheThe energy energy impact impact of ofbuilding building orientation orientation on onfour four plan plan aspect aspect ratios ratios (WWR (WWR = 50%) = 50%)in three in threeclimates. climates.

4.4. Window-to-Wall Ratio and Building Energy PerformancePerformance Simulations were performed on a 40-storey officeoffice building to investigate the optimal size of the windows inin temperate,temperate, sub-tropicalsub-tropical andand tropicaltropical climates.climates. Since plan depth is a major determinant in findingfinding the optimal solution, two plan scenarios were selected: a deep plan (1:1) and a narrow plan (5:1).(5:1). DiscreteDiscrete window-to-wallwindow-to-wall ratio ratio variations variations were were studied, studied, starting starting with with a minimum a minimum value value of 0% of and0% increaseand increase with with 10% increments10% increments to a maximumto a maximum of 100%. of 100%. For the For deep the deep plan scenario,plan scenario, the windows the windows were distributedwere distributed evenly evenly among among all directions. all directions. For the Fo narrowr the narrow planscenario, plan scenario, the north- the north- and south-facing and south- wallsfacing (long walls sides (long of sides the building)of the building) are the are focus the offo thecus investigation,of the investigation, while thewhile east- the and east- west-facing and west- wallsfacing have walls no have glazing. no glazing. Results for the optimal window-to-wall ratios ar aree shown in Appendix BB.. TheThe energyenergy efficiencyefficiency indicator isis the annual total energy useuse for heating, cooling, electric lighting and fans. Although there is anan optimaloptimal WWR WWR for for each each climate, climate, the the recommended recommended values values can becan classified be classified in four in categories four categories based onbased their on degree their degree of efficiency of efficiency as shown as inshown Figure in9 .Figure The most 9. The ideal most WWR ideal can WWR be found can inbe a found relatively in a narrowrelatively range narrow in which range the in totalwhich energy the total use deviatesenergy use by lessdeviates than 1%by fromless than the optimal 1% from results. the optimal results.The energy consumption trend shows that in a temperate climate a window-to-wall ratio betweenThe 20%energy and consumption 30% would resulttrend inshows the highest that in energy-efficiency a temperate climate for both a window-to-wall the narrow and ratio the deepbetween plan 20% due and to lower30% would heat transfer result in through the highest the façadeenergy-efficiency during winter for both and summer.the narrow Through and the using deep aplan similar due approach—theto lower heat transfer integrated through thermal theand façade daylighting during wint simulationser and summer. in the temperate Through oceanicusing 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/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 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, Sustainability 2017, 9, 623 19 of 28

similar approach—the integrated thermal and daylighting simulations in the temperate oceanic 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/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. ourFurthermore, findings show our thatfindings for WWR show values that for smaller WWR than valu 20%,es smaller the energy than use 20%, for the electric energy lighting use for incredibly electric increases.lighting incredibly In a temperate increases. climate, In a thetemperate upper limitclimate, of the the recommended upper limit of WWR the recommended is 60%; higher WWR values is result60%; higher in up to values 10% increase result in in up total to energy 10% increase consumption in total due energy to additional consumption transmission due to heatadditional losses throughtransmission the façade. heat losses through the façade. InIn aa sub-tropicalsub-tropical climate,climate, thethe optimaloptimal WWRWWR valuevalue isis 35–45%35–45% forfor aa deepdeep planplan andand 30–40%30–40% forfor aa narrownarrow planplan building.building. WWR variationsvariations thatthat containcontain averageaverage performanceperformance (1–5%(1–5% deviation)deviation) covercover aa relativelyrelatively bigbig range.range. For example, in case of the narrow plan scenario, window-to-wall ratios between 25–30%25–30% andand 40–70% 40–70% have have average average performance, performance, but inbut a temperatein a temperate climate climate this range this limits range to limits between to 10–20%between and 10–20% 30–40%. and Since 30–40%. the heatingSince the energy heating required energy is required not significant is not for significant buildings for in buildings sub-tropical in climates,sub-tropical a larger climates, window a larger area window can result area in acan smaller result demand in a smaller for electric demand lighting; for electric hence lighting; a better hence total energya better performance. total energy performance. However, values However, higher values than 80% higher and than 90% 80% are notandrecommended, 90% are not recommended, respectively forrespectively a deep plan for and a deep narrow plan planand buildingnarrow plan because buildi theseng because have to these high solarhave heatto high gains. solar heat gains. InIn aa tropicaltropical climate,climate, thethe optimaloptimal window-to-wallwindow-to-wall ratioratio isis higherhigher thanthan thatthat inin aa temperatetemperate climateclimate butbut lower than in a sub-tropical climate. It It is is in in a a range range of of 30–40% 30–40% for for a adeep deep plan plan and and 25–35% 25–35% for for a anarrow narrow plan plan building. building. According According to to Figure Figure 3,3, in the tropical climate,climate, thethe shareshare ofof electricelectric lightinglighting loadsloads fromfrom thethe totaltotal end-useend-use ofof energyenergy isis lowerlower thanthan inin the sub-tropical climate.climate. AsAs a result, the energy savingssavings forfor electricelectric lightinglighting (due (due to to higher higher WWR WWR values) values) in in the the tropical tropical climate climate cannot cannot be be as as much much as inas thein sub-tropicalthe sub-tropical climate. climate. In addition, In addition, the difference the difference between the between indoor andthe outdoorindoor airand temperature outdoor air in thetemperature tropical climate in the tropical is not as climate high as is in not the as temperate high as in climate.the temperate So in the climate. tropical So climate,in the tropical buildings climate, can havebuildings a wider can range have ofa wider WWR range values of compared WWR values to that comp in temperateared to that regions; in temperate especially regions; when theespecially proper typewhen of the glazing proper (low type U of value glazing and (low solar U heat value gain and coefficient) solar heat andgain the coefficient) shading systemsand the shading are employed systems in theare facadesemployed for in solar the gainfacade control.s for solar gain control.

FigureFigure 9.9. RecommendedRecommended window-to-wall window-to-wall ratios ratios for for energy energy efficiency efficiency of a of 40-storey a 40-storey office office building building with awith deep a plandeep (1:1)plan and(1:1) a and narrow a narrow plan (5:1)plan in(5:1) temperate, in temperate, sub-tropical, sub-tropical, and tropical and tropical climates. climates.

4.5.4.5. Window Orientation andand BuildingBuilding EnergyEnergy PerformancePerformance InIn thethe previousprevious sub-section,sub-section, optimaloptimal WWRWWR valuesvalues ofof thethe façade,façade, werewere determineddetermined forfor twotwo planplan scenariosscenarios regardlessregardless ofof thethe windowwindow orientation.orientation. In In this this part part of the paper, the effect ofof windowwindow orientationorientation onon thethe totaltotal energyenergy demanddemand ofof thethe buildingbuilding willwill be investigated. Discrete window-to-wall ratioratio variationsvariations werewere tested,tested, rangingranging fromfrom 10%10% toto 90%,90%, inin incrementalincremental stepssteps ofof 10%.10%. OneOne sideside ofof thethe 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 AppendixsC–E. Sensitivity of different window orientations to a change in the WWR value was analysed in regards to Sustainability 2017, 9, 623 20 of 28

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 Sustainabilityenergy end-uses2017, 9, 623(heating and cooling) are not shown in the text, but they can be found in Appendixes20 of 28 C, D and E. Sensitivity of different window orientations to a change in the WWR value was analysed totalin regards energy to use total variations energy use and variations the results and are the provided results in are Table provided9. Accordingly, in Table the9. Accordingly, recommended the valuesrecommended of WWR values for different of WWR orientations for different and orientations climates are and summarised climates are in summarised Figure 10. The in efficiencyFigure 10. indicatorThe efficiency for defining indicator the for recommended defining the recommended values is the total values of all is energythe total end-uses. of all energy As can end-uses. be seen As in Tablecan be9, seen the acceptable in Table 9, window-to-wall the acceptable window-to- ratio can rangewall from ratio 10% can torange 90% from depending 10% to on 90% the depending effectiveness on ofthe different effectiveness window of orientationsdifferent wi forndow energy orientations saving. For for WWR energy increments saving. For of lessWWR than increments 10%, the average of less energythan 10%, performance the average from energy two consecutive performance WWR from values two was consecutive obtained. Recommended WWR values values was representobtained. aRecommended range of WWR values in which represent the deviation a range of of total WWR energy in which use isthe smaller deviation than of 1% total from energy the optimal use is smaller value inthan each 1% orientation. from the optimal value in each orientation.

TableTable 9.9.Recommended Recommended WWRWWR valuevalue forfor differentdifferent orientationsorientations andand climatesclimates inin whichwhich thethe deviationdeviation ofof totaltotal energyenergy useuse isis smallersmaller thanthan 1%1% fromfrom thethe optimaloptimal valuevalue in in each each orientation. orientation.

Climate Type/ Temperate Sub-Tropical Tropical Climate Type/Plan Aspect Temperate Sub-Tropical Tropical Plan Aspect Ratio Ratio 1:11:1 5:15:1 1:1 1:1 5:1 5:1 1:1 1:1 5:15:1 North 10–90 10–70 10–15 15–40 10–50 10–35 North 10–90 10–70 10–15 15–40 10–50 10–35 RecommendedRecommended EastEast 35–60 35–60 No No glazing glazing 10–20 10–20 No No glazing glazing 10–20 10–20 No No glazing glazing WWRWWR value value (%) (%) SouthSouth 65–7565–75 25–3525–35 10–7010–70 10–4010–40 10–8010–80 10–5510–55 WestWest 10–15 10–15 No No glazing glazing 10–20 10–20 No No glazing glazing 10–20 10–20 No No glazing glazing

Figure 10. Sensitivity of different window orientations to a change in the WWR value (ranging from 10%Figure to 90%)10. Sensitivity in terms ofof maximumdifferent window variations orientations in total energy to a change use of ain 40-storey the WWR office value building (ranging with from a deep10% to plan 90%) (a) in and terms a narrow of maximum plan (b) variations in temperate, in total sub-tropical, energy use and of tropicala 40-storey climates. office building with a 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 the simulations for windows (U value: 1.50 W/m2K) and opaque surfaces (U value: 0.35 W/m2K), the simulations for windows (U value: 1.50 W/m2K) 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 north- north-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 21 of 28 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. 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. 2. 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. 3. 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. 4. 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. 5. 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 Table9).

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 23 of 28 Sustainability 2017, 9, 623 23 of 28 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 Sub-Tropical Tropical Plan shape A B C D A B C D A B C D Ellipse + + Ellipse + + Octagon + + <1% Octagon + + Ellipse + + Circle + + Circle + + Rectangle + Square + + 1–5% Square + + Octagon + + Rectangle + Rectangle + Circle + + + shape + Triangle Square + + Triangle Atrium + Z shape + Courtyard + 5–10% U shape + Courtyard + Z shape + + shape + H shape + H shape + U shape + H shape + U shape + Y shape + Z shape + Triangle >10% Y shape + + shape + Y shape + MD (%) 12.8 15.7 11.0 Plan aspect ratio <1% 1:1, 2:1, 3:1 3:1, 4:1 1:1, 2:1, 3:1 1–5% 4:1, 5:1 1:1, 2:1, 5:1, 8:1 4:1, 5:1 5–10% 8:1 10:1 8:1, 10:1 >10% 10:1 ------MD (%) 12.4 6.0 8.8 Plan orientation 1:1 3:1 5:1 10:1 1:1 3:1 5:1 10:1 1:1 3:1 5:1 10:1 0° 0° <1% 0° 0° 0° 0° 0° 0° 0° 0° 0° 0° 45° 45° 45° 135° 135° 1–5% 45° 135° 45° ------135° 45° 45° 45° 90° 45° 45° 135° 5–10% --- 90° 135° ------90° 135° 90° 45° 45° 45° >10% ------90° 135° 135° ------90° 90° 90° MD (%) 1.2 5.6 8.4 15.1 2.1 12.3 20.4 32.0 0.7 2.8 4.7 7.9 WWR (%): deep plan (1:1) N E S W N E S W N E S W <1% 10–90 35–60 65–75 10–15 10–15 10–20 10–70 10–20 10–50 10–20 10–80 10–20 10–35 10–65 1–5% --- 15–90 15–50 20–90 70–90 20–90 50–90 20–90 80–90 20–90 60–90 75–90 5–10% ------50–80 ------>10% ------80–90 ------MD (%) 0.5 2.8 1.8 4.5 11.3 2.9 1.1 3.1 2.9 3.3 1.1 3.0 WWR (%): narrow plan (5:1) N E S W N E S W N E S W <1% 10–70 --- 25–35 --- 15–40 --- 10–40 --- 10–35 --- 10–55 --- 10–25 10–15 1–5% 70–90 ------40–90 --- 35–70 --- 55–90 --- 35–55 40–75 5–10% ------55–85 --- 75–90 ------70–90Sustainability --- 2017--- , 9, 623--- 24 of 28 SustainabilitySustainability 2017Sustainability, 9, 623 2017 , 9 2017, >10%623, 9 , 623 ------85–90 ------24 of 28--- 24 of--- 2824 of 28--- MD (%) 3.0 --- 10.3 --- 6.8 --- 5.2 --- 8.6 ---Energy 3.2 efficiency --- of design options: <1% (remarkable energy saving); 1–5% (average energy Energy efficiencyEnergyEnergy efficiencyof designEnergy efficiency efficiencyofoptions: design of design of options: design <1% options:(rem options: arkable<1% (rem<1% energy (remarkablearkable(rem arkablesaving); energy energy energy saving); 1–5% saving); saving); (average 1–5% (average energy1–5%(average (average energy energysaving); saving); energy 5–10%5–10% (low energy saving); >10% (not recommended). A: High space efficiency; B: saving); saving); 5–10%saving); (low 5–10%(low energy energy5–10% (low saving); saving); energy(low energy saving); >10%>10% saving);(not (not recommended). >10% recommended). >10%(not recommended).(not A:High recommended).A: spaceHighefficiency; spaceA: High A:efficiency; B: Highspace Aerodynamic space efficiency;B: efficiency; form;Aerodynamic B: C: Narrow B: plan form; C: Narrow plan (NV & daylight access); D: Less material use for external (NV & daylight access); D: Less material use for external envelope; MD: Maximum deviation; N: North orientation; AerodynamicAerodynamic form;Aerodynamic C: Narrowform; form;C: plan Narrow C: (NV Narrow plan& daylight (NVplan &(NV access);daylight & daylight D: access); Less access); material D: Less D: usematerialLess for material external use for use external forenvelope; external MD: Maximum deviation; N: North orientation; E: East orientation; S: South orientation; E: East orientation; S: South orientation; W: West orientation. envelope; envelope;MD: Maximumenvelope; MD: Maximum MD:deviation; Maximum deviation;N: North deviation; orientation;N: North N: North orientation; E: East orientation; orientation; E: East E: orientation;East S: South orientation; orientation; S: South S: South orientation; orientation;W: West orientation. W: West orientation.W: WestW: orientation.West orientation. Appendix A AppendixAppendix A Appendix A A Table A1. Breakdown of annual energy consumption per conditioned area for seven plan aspect ratios Table A1. BreakdownTableTable A1. Breakdown ofA1. annual Breakdown energy of annual of consumption annual energy energy consumption per consumption conditioned per co perareanditioned co fornditioned seve arean plan for area seve aspect forn seve plan ratiosn aspect plan aspect ratios(WWR= ratios 50%) in: (a) Amsterdam, (b) Sydney, and (c) Singapore. (WWR= 50%)(WWR= in:(WWR= (a 50%)) Amsterdam, in:50%) (a) in: Amsterdam, ((ab)) Amsterdam, Sydney, (b and) Sydney, ((bc)) Sydney,Singapore. and ( cand) Singapore. (c) Singapore. (a) Amsterdam (a) Amsterdam(a) Amsterdam(a) Amsterdam Annual Total Energy Breakdown of Annual Total Energy Demand Annual TotalAnnual EnergyAnnual Total TotalEnergy Energy Demand BreakdownBreakdown of AnnualBreakdown of Total Annual of Energy Annual Total Demand TotalEnergy Energy Demand Demand Plan Demand DemandDemand Heating/ Cooling/ Lighting/ Fan/ Total/ Plan Plan Plan Aspect Percentile Heating/ Heating/Heating/Cooling/ Cooling/Cooling/Lighting/ Lighting/Lighting/Fan/ Fan/ Fan/Total/ Total/Total/ Conditioned Conditioned Conditioned Conditioned Conditioned Aspect AspectAspect PercentilePercentile RatioPercentile Difference ConditionedConditioned ConditionedConditioned Conditioned ConditionedConditioned Conditioned ConditionedConditioned Conditioned ConditionedConditioned Conditioned Conditioned Area Area Area Area Area Ratio Ratio Ratio DifferenceDifference Difference (%) Area Area AreaArea Area AreaArea Area AreaArea Area AreaArea Area Area (kW h/m2) (kW h/m2) (kW h/m2) (kW h/m2) (kW h/m2) (%) (%) (%) (kW h/m2)(kW h/m(kW(kW2) h/mh/m22)) (kW h/m(kW(kW2) h/m h/m2)2 )(kW h/m(kW(kW2) h/m h/m2)2 )(kW h/m(kW(kW2) h/m h/m2)2 )(kW h/m(kW2) h/m2) 1:1 15.2 23.5 17.5 28.7 84.9 0.8% 1:1 1:1 15.21:1 15.2 15.2 23.5 23.5 23.5 17.5 17.5 17.5 28.7 28.7 28.7 84.9 84.9 0.8% 84.9 2:10.8% ® 0.8% 15.3 23.6 16.7 28.6 84.2 - 2:1 ® 2:1 ® 15.32:1 ® 15.3 15.3 23.6 23.6 23.6 16.7 16.7 16.7 28.6 28.6 28.6 84.2 84.2 84.2 - 3:1 - - 15.5 24.2 15.8 29.4 84.9 0.8% 3:1 3:1 15.53:1 15.5 15.5 24.2 24.2 24.2 15.8 15.8 15.8 29.4 29.4 29.4 84.9 84.9 0.8% 84.9 4:10.8% 0.8% 15.6 24.9 15.0 30.4 85.9 2.1% 4:1 4:1 15.64:1 15.6 15.6 24.9 24.9 24.9 15.0 15.0 15.0 30.4 30.4 30.4 85.9 85.9 2.1% 85.9 5:12.1% 2.1% 15.9 25.8 14.4 31.4 87.5 3.9% 5:1 5:1 15.95:1 15.9 15.9 25.8 25.8 25.8 14.4 14.4 14.4 31.4 31.4 31.4 87.5 87.5 3.9% 87.5 8:13.9% 3.9% 16.7 27.8 13.0 34.3 91.8 9.0% 8:1 8:1 16.78:1 16.7 16.7 27.8 27.8 27.8 13.0 13.0 13.0 34.3 34.3 34.3 91.8 91.8 9.0% 91.8 10:19.0% 9.0% 17.2 29.0 12.4 36.0 94.7 12.4% 10:1 10:1 17.210:1 17.2 17.2 29.0 29.0 29.0 12.4 12.4 12.4 36.0 36.0 36.0 94.7 94.7 12.4% 94.7 12.4%12.4% (b) Sydney (b) Sydney(b) Sydney(b) Sydney Annual Total Energy Breakdown of Annual Total Energy Demand Annual TotalAnnual EnergyAnnual Total TotalEnergy Energy Demand BreakdownBreakdown of AnnualBreakdown of Total Annual of Energy Annual Total Demand TotalEnergy Energy Demand Demand Plan Demand DemandDemand Heating/ Cooling/ Lighting/ Fan/ Total/ Plan Plan Plan Aspect Percentile Heating/ Heating/Heating/Cooling/ Cooling/Cooling/Lighting/ Lighting/Lighting/Fan/ Fan/ Fan/Total/ Total/Total/ conditioned Conditioned Conditioned Conditioned Conditioned Aspect AspectAspect PercentilePercentile RatioPercentile Difference conditionedconditioned conditionedConditioned Conditioned ConditionedConditionedConditioned ConditionedConditioned Conditioned ConditionedConditioned Conditioned Conditioned Area Area Area Area Area Ratio Ratio Ratio DifferenceDifference Difference (%) Area Area AreaArea Area AreaArea Area AreaArea Area AreaArea Area Area (kW h/m2) (kW h/m2) (kW h/m2) (kW h/m2) (kW h/m2) (%) (%) (%) (kW h/m2)(kW h/m(kW(kW2) h/mh/m22)) (kW h/m(kW(kW2) h/m h/m2)2 )(kW h/m(kW(kW2) h/m h/m2)2 )(kW h/m(kW(kW2) h/m h/m2)2 )(kW h/m(kW2) h/m2) 1:1 0.4 34.2 12.6 28.4 75.7 4.0% 1:1 1:1 0.41:1 0.4 34.20.4 34.2 34.2 12.6 12.6 12.6 28.4 28.4 28.4 75.7 75.7 4.0% 75.7 2:14.0% 4.0% 0.3 33.3 12.3 27.6 73.5 1.0% 2:1 2:1 0.32:1 0.3 33.30.3 33.3 33.3 12.3 12.3 12.3 27.6 27.6 27.6 73.5 73.5 1.0% 73.5 3:11.0% ® 1.0% 0.3 32.8 11.7 28.0 72.8 - 3:1 ® 3:1 ® 0.33:1 ® 0.3 32.80.3 32.8 32.8 11.7 11.7 11.7 28.0 28.0 28.0 72.8 72.8 72.8 - 4:1 - - 0.2 33.5 11.3 28.0 73.0 0.3% 4:1 4:1 0.24:1 0.2 33.50.2 33.5 33.5 11.3 11.3 11.3 28.0 28.0 28.0 73.0 73.0 0.3% 73.0 5:10.3% 0.3% 0.2 34.0 10.9 28.5 73.6 1.1% 5:1 5:1 0.25:1 0.2 34.00.2 34.0 34.0 10.9 10.9 10.9 28.5 28.5 28.5 73.6 73.6 1.1% 73.6 8:11.1% 1.1% 0.2 35.3 10.2 30.0 75.7 4.0% 8:1 8:1 0.28:1 0.2 35.30.2 35.3 35.3 10.2 10.2 10.2 30.0 30.0 30.0 75.7 75.7 4.0% 75.7 10:14.0% 4.0% 0.2 36.1 10.0 30.9 77.2 6.0% 10:1 10:1 0.210:1 0.2 36.10.2 36.1 36.1 10.0 10.0 10.0 30.9 30.9 30.9 77.2 77.2 6.0% 77.2 6.0% 6.0% (c) Singapore (c) Singapore(c) Singapore(c) Singapore Annual Total Energy Breakdown of Annual Total Energy Demand Annual TotalAnnual EnergyAnnual Total TotalEnergy Energy Demand BreakdownBreakdown of AnnualBreakdown of Total Annual of Energy Annual Total Demand TotalEnergy Energy Demand Demand Plan Demand DemandDemand Heating/ Cooling/ Lighting/ Fan/ Total/ Plan Plan Plan Aspect Percentile Heating/ Heating/Heating/Cooling/ Cooling/Cooling/Lighting/ Lighting/Lighting/Fan/ Fan/ Fan/Total/ Total/Total/ Conditioned Conditioned Conditioned Conditioned Conditioned Aspect AspectAspect PercentilePercentile RatioPercentile Difference ConditionedConditioned ConditionedConditioned Conditioned ConditionedConditionedConditioned ConditionedConditioned Conditioned ConditionedConditioned Conditioned Conditioned Area Area Area Area Area Ratio Ratio Ratio DifferenceDifference Difference (%) Area Area AreaArea Area AreaArea Area AreaArea Area AreaArea Area Area (kW h/m2) (kW h/m2) (kW h/m2) (kW h/m2) (kW h/m2) (%) (%) (%) (kW h/m2)(kW h/m(kW(kW2) h/mh/m22)) (kW h/m(kW(kW2) h/m h/m2)2 )(kW h/m(kW(kW2) h/m h/m2)2 )(kW h/m(kW(kW2) h/m h/m2)2 )(kW h/m(kW2) h/m2) 1:1 0.0 76.5 11.3 29.5 117.6 0.3% 1:1 1:1 0.01:1 0.0 76.50.0 76.5 76.5 11.3 11.3 11.3 29.5 29.5 29.5117.6 117.6 0.3%117.6 2:10.3% ® 0.3% 0.0 76.7 10.8 29.7 117.2 - 2:1 ® 2:1 ® 0.02:1 ® 0.0 76.70.0 76.7 76.7 10.8 10.8 10.8 29.7 29.7 29.7 117.2 117.2 117.2 - 3:1 - - 0.0 77.8 10.2 30.3 118.3 0.9% 3:1 3:1 0.03:1 0.0 77.80.0 77.8 77.8 10.2 10.2 10.2 30.3 30.3 30.3118.3 118.3 0.9%118.3 4:10.9% 0.9% 0.0 78.7 9.5 31.2 119.4 1.9% 4:1 4:1 0.04:1 0.0 78.70.0 78.7 78.7 9.5 9.5 9.5 31.2 31.2 31.2119.4 119.4 1.9%119.4 5:11.9% 1.9% 0.0 79.7 9.0 32.1 120.8 3.0% 5:1 5:1 0.05:1 0.0 79.70.0 79.7 79.7 9.0 9.0 9.0 32.1 32.1 32.1120.8 120.8 3.0%120.8 8:13.0% 3.0% 0.0 82.6 8.1 34.3 125.0 6.6% 8:1 8:1 0.08:1 0.0 82.60.0 82.6 82.6 8.1 8.1 8.1 34.3 34.3 34.3125.0 125.0 6.6%125.0 10:16.6% 6.6% 0.0 84.2 7.7 35.7 127.5 8.8% 10:1 10:1 0.010:1 0.0 84.20.0 84.2 84.2 7.7 7.7 7.7 35.7 35.7 35.7 127.5 127.5 8.8% 127.5 8.8% 8.8% ® Reference (the most efficient design option). ® Reference® Reference(the ®most Reference efficient(the most (the design efficientmost option).efficient design design option). option).

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 Heating/ Cooling/ Lighting/ Fan/ Total/ Plan Aspect Percentile Conditioned Conditioned Conditioned Conditioned Conditioned Ratio Difference Area Area Area Area Area (%) (kW h/m2) (kW h/m2) (kW h/m2) (kW h/m2) (kW h/m2) 1:1 15.2 23.5 17.5 28.7 84.9 0.8% 2:1 ® 15.3 23.6 16.7 28.6 84.2 - 3:1 15.5 24.2 15.8 29.4 84.9 0.8% 4:1 15.6 24.9 15.0 30.4 85.9 2.1% 5:1 15.9 25.8 14.4 31.4 87.5 3.9% 8:1 16.7 27.8 13.0 34.3 91.8 9.0% 10:1 17.2 29.0 12.4 36.0 94.7 12.4% (b) Sydney Breakdown of Annual Total Energy Demand Annual Total Energy Demand Heating/ Cooling/ Lighting/ Fan/ Total/ Plan Aspect Percentile conditioned Conditioned Conditioned Conditioned Conditioned Ratio Difference Area Area Area Area Area (%) (kW h/m2) (kW h/m2) (kW h/m2) (kW h/m2) (kW h/m2) 1:1 0.4 34.2 12.6 28.4 75.7 4.0% 2:1 0.3 33.3 12.3 27.6 73.5 1.0% 3:1 ® 0.3 32.8 11.7 28.0 72.8 - 4:1 0.2 33.5 11.3 28.0 73.0 0.3% 5:1 0.2 34.0 10.9 28.5 73.6 1.1% 8:1 0.2 35.3 10.2 30.0 75.7 4.0% 10:1 0.2 36.1 10.0 30.9 77.2 6.0% (c) Singapore Breakdown of Annual Total Energy Demand Annual Total Energy Demand Heating/ Cooling/ Lighting/ Fan/ Total/ Plan Aspect Percentile Conditioned Conditioned Conditioned Conditioned Conditioned Ratio Difference Area Area Area Area Area (%) (kW h/m2) (kW h/m2) (kW h/m2) (kW h/m2) (kW h/m2) 1:1 0.0 76.5 11.3 29.5 117.6 0.3% 2:1 ® 0.0 76.7 10.8 29.7 117.2 - 3:1 0.0 77.8 10.2 30.3 118.3 0.9% 4:1 0.0 78.7 9.5 31.2 119.4 1.9% 5:1 0.0 79.7 9.0 32.1 120.8 3.0% 8:1 0.0 82.6 8.1 34.3 125.0 6.6% 10:1 0.0 84.2 7.7 35.7 127.5 8.8% ® Reference (the most efficient design option). Sustainability 2017, 9, 623 25 of 28

AppendixSustainability B2017 , 9, 623 25 of 28 Sustainability 2017, 9, 623 25 of 28

AppendixAppendix BB

FigureFigureFigure A1. A1.A1. TheTheThe optimaloptimal optimal percentagepercentage percentage of of ofwindow-to-wall window-to-wall window-to-wall ratio ra ratiotiofor fortwo for twoplan two plan types plan types types(1:1 and(1:1 (1:1 5:1)and and in 5:1) 5:1) in in Temperate,Temperate,Temperate, Sub-tropical, Sub-tropical, andand and Tropical Tropical Tropical climates. climates. climates.

Appendix C AppendixAppendix C C

Figure A2. Cont. SustainabilitySustainability 20172017, ,99, ,623 623 2626 of of 28 28 Sustainability 2017,, 9,, 623623 26 of 28

Figure A2. The optimal percentage of window-to-wall ratio in different orientations for two plan typesFigureFigure (deep A2. A2. TheandThe narrow)optimal percentagepercentagein three climates. of of window-to-wall window-to-wall ratio ratio in differentin different orientations orientations for twofor plantwo plan types types(deep (deep and narrow) and narrow) in three in three climates. climates. Appendix D AppendixAppendix D D

Figure A3. Relationship between energy use for heating and window-to-wall ratio in different orientationsFigureFigure A3. A3. RelationshipforRelationship two plan between betweenscenarios energy energy(deep use and use for forna heatingrrow) heating in and andtemperate, window-to-wall window-to-wall sub-tropical, ratio ratio andin in different differenttropical climates.orientationsorientations for twotwo planplan scenarios scenarios (deep (deep and and narrow) narrow) in temperate, in temperate, sub-tropical, sub-tropical, and tropical and climates.tropical climates. AppendixAppendix E E Appendix E

Figure A4. Cont. Sustainability 2017, 9, 623 27 of 28 Sustainability 2017, 9, 623 27 of 28

FigureFigure A4. A4. RelationshipRelationship between between energy energy use use for for coolin coolingg and and window-to-wall window-to-wall ratio ratio in in different different orientationsorientations for twotwo planplan scenarios scenarios (deep (deep and and narrow) narrow) in temperate, in temperate, sub-tropical, sub-tropical, and tropical and climates.tropical climates.

Acknowledgments:References 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 1. Bragança, L.; Vieira, S.M.; Andrade, J.B. Early stage design decisions: The way to achieve sustainable Editors for their support during the review process. buildings at lower costs. Sci. World J. 2014. Available online: http://www.hindawi.com/journals/tswj/ Author2014/365364/abs/ Contributions: All (accessed authors on contributed 22 December extensively 2016.). to the work presented in this paper. Babak Raji carried2. Attia, out simulations, S.; De Herde, collected A. Design data decision and prepared tools for zerodrafts. energy Martin buildings. J. Tenpierik In Proceedings and Andy van of the den 27th Dobbelsteen Conference supervisedon Passive data analysis and Low and Energy edited Architecture, the manuscript. Louvain-la-Neuve, All authors discusse Belgium,d 13–15the results July 2011; and pp.implications 77–82. and commented on the manuscript at all stages. 3. Athienitis, A.; Attia, S. Strategic design, optimization, and modelling issues of net-zero energy solar buildings. ConflictsIn Proceedings of Interest: ofThe the authors Eurosun declare 2010, no Graz, conflict Austria, of interest. 28 September–1 October 2010. 4. Pessenlehner, W.; Mahdavi, A. Building morphology, transparence, and energy performance. In Proceedings Referenceof the Eighth International IBPSA Conference, Eindhoven, The Netherlands, 2003; pp. 1025–1032. 5. Depecker, P.; Menezo, C.; Virgone, J.; Lepers, S. Design of buildings shape and energetic consumption. 1. Bragança, L.; Vieira, S.M.; Andrade, J.B. Early stage design decisions: The way to achieve sustainable Build. Environ. 2001, 36, 627–635. [CrossRef] buildings at lower costs. Sci. World J. 2014. Available online: 6. Ourghi, R.; Al-Anzi, A.; Krarti, M. A simplified analysis method to predict the impact of shape on annual http://www.hindawi.com/journals/tswj/2014/365364/abs/ (accessed on 22 December 2016.) energy use for office buildings. Energy Convers. Manag. 2007, 48, 300–305. [CrossRef] 2. Attia, S.; De Herde, A. Design decision tools for zero energy buildings. In Proceedings of the 27th 7. AlAnzi, A.; Seo, D.; Krarti, M. Impact of building shape on thermal performance of office buildings in kuwait. Conference on Passive and Low Energy Architecture, Louvain-la-Neuve, Belgium, 13–15 July 2011; pp. 77– Energy Convers. Manag. 2009, 50, 822–828. [CrossRef] 82. 8. Choi, I.Y.; Cho, S.H.; Kim, J.T. Energy consumption characteristics of high-rise apartment buildings according 3. Athienitis, A.; Attia, S. Strategic design, optimization, and modelling issues of net-zero energy solar to building shape and mixed-use development. Energy Build. 2012, 46, 123–131. [CrossRef] buildings. In Proceedings of the Eurosun 2010, Graz, Austria, 28 September–1 October 2010. 9. Susorova, I.; Tabibzadeh, M.; Rahman, A.; Clack, H.L.; Elnimeiri, M. The effect of geometry factors on 4. Pessenlehner, W.; Mahdavi, A. Building morphology, transparence, and energy performance. In fenestration energy performance and energy savings in office buildings. Energy Build. 2013, 57, 6–13. Proceedings of the Eighth International IBPSA Conference, Eindhoven, The Netherlands, 2003; pp. 1025– [CrossRef] 1032. 10. Kämpf, J.H.; Robinson, D. Optimisation of building form for solar energy utilisation using constrained 5. Depecker, P.; Menezo, C.; Virgone, J.; Lepers, S. Design of buildings shape and energetic consumption. evolutionary algorithms. Energy Build. 2010, 42, 807–814. [CrossRef] Build. Environ. 2001, 36, 627–635. 11. Yi, Y.K.; Malkawi, A.M. Site-specific optimal energy form generation based on hierarchical geometry relation. 6. Ourghi, R.; Al-Anzi, A.; Krarti, M. A simplified analysis method to predict the impact of shape on annual Autom. Constr. 2012, 26, 77–91. [CrossRef] energy use for office buildings. Energy Convers. Manag. 2007, 48, 300–305. 12. Wang, W.; Rivard, H.; Zmeureanu, R. An object-oriented framework for simulation-based green building 7. AlAnzi, A.; Seo, D.; Krarti, M. Impact of building shape on thermal performance of office buildings in design optimization with genetic algorithms. Adv. Eng. Inform. 2005, 19, 5–23. [CrossRef] kuwait. Energy Convers. Manag. 2009, 50, 822–828. 13. Magnier, L.; Haghighat, F. Multiobjective optimization of building design using trnsys simulations, genetic 8. Choi, I.Y.; Cho, S.H.; Kim, J.T. Energy consumption characteristics of high-rise apartment buildings algorithm, and artificial neural network. Build. Environ. 2010, 45, 739–746. [CrossRef] according to building shape and mixed-use development. Energy Build. 2012, 46, 123–131. 9. Susorova, I.; Tabibzadeh, M.; Rahman, A.; Clack, H.L.; Elnimeiri, M. The effect of geometry factors on fenestration energy performance and energy savings in office buildings. Energy Build. 2013, 57, 6–13. Sustainability 2017, 9, 623 28 of 28

14. Yi, Y.K.; Malkawi, A.M. Optimizing building form for energy performance based on hierarchical geometry relation. Autom. Constr. 2009, 18, 825–833. [CrossRef] 15. Malkawi, A.M. Developments in environmental performance simulation. Autom. Constr. 2004, 13, 437–445. [CrossRef] 16. US Department of Energy. Weather Data. Available online: https://energyplus.net/weather (accessed on 20 September 2016). 17. Wood, A.; Salib, R. Natural Ventilation in High-Rise Office Buildings, Ctbuh Technical Guides; Routledge: New York, NY, USA, 2013. 18. Straube, J.F.; Burnett, E.F.P. Building Science for Building Enclosures; Building Science Press: Westford, MA, USA, 2005. 19. Raji, B.; Tenpierik, M.J.; van den Dobbelsteen, A. A comparative study: Design strategies for energy-efficiency of high-rise office buildings. J. Green Build. 2016, 11, 134–158. [CrossRef] 20. Van den Dobbelsteen, A.; Thijssen, S.; Colaleo, V.; Metz, T. Ecology of the building geometry-environmental performance of different building shapes. In Proceedings of the CIB World Building Congress 2007; CIB/CSIR. Cape Town, South Africa, 14–17 May 2007; pp. 178–188. 21. Watts, S. Tall building economics. In The Tall Buildings Reference Book; Parker, D., Wood, A., Eds.; Routledge: New York, NY, USA, 2013; pp. 49–70. 22. Wilkinson, C. Aesthetics, symbolism and status in the twenty-first century. In The Tall Buildings Reference Book; Parker, D., Wood, A., Eds.; Routledge: New York, NY, USA, 2013; pp. 33–40. 23. Florides, G.A.; Tassou, S.A.; Kalogirou, S.A.; Wrobel, L.C. Measures used to lower building energy consumption and their cost effectiveness. Appl. Energy 2002, 73, 299–328. [CrossRef] 24. Pacheco, R.; Ordóñez, J.; Martínez, G. Energy efficient design of building: A review. Renew. Sustain. Energy Rev. 2012, 16, 3559–3573. [CrossRef] 25. Mingfang, T. Solar control for buildings. Build. Environ. 2002, 37, 659–664. [CrossRef] 26. Abanda, F.H.; Byers, L. An investigation of the impact of building orientation on energy consumption in a domestic building using emerging bim (building information modelling). Energy 2016, 97, 517–527. [CrossRef] 27. Kheiri, F. The relation of orientation and dimensional specifications of window with building energy consumption in four different climates of koppen classification. Researcher 2013, 5, 107–115. 28. Goia, F.; Haase, M.; Perino, M. Optimizing the configuration of a façade module for office buildings by means of integrated thermal and lighting simulations in a total energy perspective. Appl. Energy 2013, 108, 515–527. [CrossRef] 29. Wang, L.; Mathew, P.; Pang, X. Uncertainties in energy consumption introduced by building operations and weather for a medium-size office building. Energy Build. 2012, 53, 152–158. [CrossRef]

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