组合 2

Review

Effects of Architectural Space Layouts on Energy Performance: A Review

Tiantian Du *, Sabine Jansen, Michela Turrin and Andy van den Dobbelsteen

Faculty of Architecture and the Built Environment, Delft University of Technology, 2628 BL Delft, The Netherlands; S.C.Jansen@tudelft.nl (S.J.); M.Turrin@tudelft.nl (M.T.); A.A.J.F.vandenDobbelsteen@tudelft.nl (A.v.d.D.)

* Correspondence: T.Du@tudelft.nl

Received: 13 January 2020; Accepted: 23 February 2020; Published: 29 February 2020

Abstract: As one of the most important design tasks of building design, space layout design affects the building energy performance (BEP). In order to investigate the effect, a literature review of relevant papers was performed. Ten relevant articles were found and reviewed in detail. First, a methodology for studying the effects of space layouts on BEP were proposed regarding design variables, energy indicators and BEP calculation methods, and the methodologies used in the 10 articles were reviewed. Then, the effects of space layouts on energy use and occupant comfort were analysed separately. The results show that the energy use for heating, cooling, lighting and ventilation is highly affected by space layouts, as well as thermal and visual comfort. The effects of space layouts on energy use are higher than on occupant comfort. By changing space layouts, the resulting reductions in the annual final energy for heating and cooling demands were up to 14% and 57%, respectively, in an office building in Sweden. The resulting reductions in the lighting demand of peak summer and winter were up to 67% and 43%, respectively, for the case of an office building in the UK, and the resulting reduction in the air volume supplied by natural ventilation was 65%. The influence of other design parameters, i.e., occupancy and window to wall ratio, on the effects of space layouts on BEP was also identified.

Keywords: space layout; building energy performance; energy-efficient design

1. Introduction

Architectural design highly affects the building energy performance (BEP), and energy-efficient design is therefore often studied [1]. Space layout design is one of the most important tasks in architectural design, taking place around the stages of ‘scheme design’ and ‘design development’ in the early design phase [2,3]. In this paper, the architectural space layout is defined as the allocation of different spaces, and it is decided based on the placement of interior partitions as well as exterior walls. The design variables of space layout design include function allocation, space dimension (width, length, height), space form, interior partition and interior opening. Moreover, the layout boundary can also be the design variables of the space layout design with a non-fixed boundary as a consequence of changing interior and exterior walls. These will be explained in more detail in Section 3.1.1.

There are plenty of studies exploring the effects of geometry on BEP, such as the studies on boundary dimensions [4–8], forms [9–12] and orientations [4,5,13]. Most studies have been reviewed in [1]. These studies imply that space layouts affect BEP greatly, as geometry can be a consequence of the space layout design within a non-fixed layout boundary. Moreover, different functions have different comfort requirements such as thermal comfort and lighting levels, which result in different internal gains. Hence, if spaces can be mapped to the proper orientations and locations that have sufficient daylight and natural ventilation within a building, the building is expected to require less energy demand in total.

Sustainability 2020, 12, 1829; doi:10.3390/su12051829 www.mdpi.com/journal/sustainability

Although architectural space layout is expected to highly affect BEP, it is rarely included in the studies on energy-efficient building design. Numerous studies exist on energy-efficient design, and most of them focus on geometry [11,14], envelope [15,16], façade [17,18], material [19,20], atrium [21,22] and shading systems [23,24]. On the other hand, researchers have been working on space layout design for decades [25,26]; however, they mainly focused on other design objectives rather than energy performance. These objectives include safety [27,28], logistics [29,30], efficiency [31,32], finance cost [33,34], occupant health and performance [35,36], view connection [37,38] and acoustics [39,40]. These two research domains, space layout design and energy-efficient building design, are shown in Figure 1. The overlapping area of the two domains, i.e., energy-efficient space layout design, is the focus of this paper. This paper aims at the effects on BEP caused by changing space layouts, without considering the possible influence on the indirect cost of the building, such as space usability and workability.

Figure 1. Relevant research domains

The review was performed by searching in engines of Google Scholar, ScienceDirect, Web of science and the library of the Delft University of Technology. The keywords used to search the relevant references include two types of terms: space layout and energy, as shown in Table 1. Moreover, we limited the discipline to architectural design.

Table 1. Keywords for searching references.

Terms (space layout) Terms (energy)

Space layout Energy use

Space planning Energy consumption

Space allocation Energy performance

Interior layout

and

Energy saving

Floor plan Heating

Cooling Lighting

Ventilation The paper is structured as follows: first, as background, the mechanism for how space layouts

affect BEP is formulated. Second, the methodology for studying the effects of space layouts on BEP is proposed as the guideline to review each relevant article; then, the procedure for reviewing one article is shown as an example and each article is reviewed following the same procedure. Next, the methodologies used in the relevant articles are analysed and compared. Third, the effects of space layouts on energy use and occupant comfort are identified and analysed separately.

1. Mechanism for How Space Layouts Affect BEP

It is important to analyse the mechanism for how space layouts affect BEP before the detailed review. Based on the studies found with the keywords of space layout terms and energy terms, we identify the following factors that determine how space layouts affects BEP below.

Different Occupancy and Comfort Requirements Between Functions

Different layouts accommodate different occupant densities. For instance, an open office has a higher occupant density than a cellular office [41,42]. Space layouts also affect the occupant behaviour, such as attending an activity or changing the location where the activity happens, as shown in [43]. Different occupancy has different internal gains and also different requirements for comfort purpose, such as the total amount of ventilation. Eventually, the different occupancy affects the energy demand. Additionally, different functions have various levels of comfort requirements. For instance, as shown in the Dutch standard of NEN 16798-1 [44], the minimum operative temperature for space heating is 20 ˚C for sedentary activity like in offices, while the value is 16 ˚C for standing-walking activity like in corridors. As recommended in [45], the illuminance set-point is 500 lux for offices and 300 lux for meeting rooms, while the value is 200 lux for canteens and 150 lux for staircases. Thus, different comfort requirements between functions affect the whole energy demand eventually.

• 1. Daylighting

The effect of daylighting can be explained with the following three points. First, different layouts import different levels of daylight into the building. This is proven by the studies on the daylighting performance of the building with atriums [46–48] and courtyards [49]. These studies show that by changing the shape, location and dimension of atriums or courtyards, the daylighting performance of the whole building changes. Secondly, an appropriate space layout combined with the glazing design boosts the application of daylight within a building. For instance, the function with a higher lighting requirement can be located near the south façade for more solar radiation, and the function with a lower lighting requirement can be located in the middle or near the north façade to make a concession for other spaces, in the Northern Hemisphere. Thirdly, the interior partitions also affect the application of daylight, considering the visual comfort of occupants, as shown in [50].

• 1. Natural Ventilation

By combining with openings, an appropriate space layout distributes fresh air to the rooms based on their demands. For instance, the function with higher occupancy can be located near the windward façade and the function with a lower ventilation requirement, like a storage or facility room, can be located near the leeward façade. The study of [51] shows that by changing the shape of interior partitions for corridors, a higher mean flow velocity can be obtained, increasing up to 33%, as well as a steadier airflow within the building. Moreover, by changing the location and dimension of buffer spaces, such as a courtyard [52], solar chimney [53], atrium [54] and light-well [55], the natural ventilation within buildings changes significantly. The study of [56] showed that the building with a better space connection and integration has a higher natural ventilation velocity. For instance, the corridor and dining room have high permeability and accessibility, and the measured data shows that they also have higher ventilation velocities. Another study [57] showed that a vernacular building with courtyards, patios and gardens has a better microclimate than a modern building without buffer spaces, in term of air temperature, relative humidity and wind velocity.

• 1. Control of the Heating, Cooling, Ventilation and Lighting System

Different space layouts are suitable for different types of control for space heating, space cooling, ventilation and lighting systems. For instance, the individual control is more suitable for a cellular office than an open office, as shown in [58,59]. The blind control is more difficult in an open office than in a cellular office, as shown in [60]. Different control types result in different energy performance. Moreover, the indicators relevant to daylighting and natural ventilation can be used as indicator for controlling, for instance, the availability of daylight for lighting system control [61] and air quality and thermal comfort for ventilation system control [62]. Using dynamic control based on the available daylight and natural ventilation, the effects of space layouts on BEP are boosted.

1. Methodology for Studying the Effects of Space Layouts on BEP

There are plenty of studies that only studied the effects of geometry (such as boundary dimensions, building forms and orientations) on BEP without changing interior layouts. They are not included in the detailed review below, and the following detailed review is limited to the studies that also changed interior layouts. Ten articles were found focusing on the intersection of space layouts and energy performance, as shown in Table 2. First, in Section 3.1, a methodology for how to study the effects of space layouts on BEP is proposed, which was used as the guideline for reviewing the 10 articles. Then, the procedure for reviewing one article is shown as an example, and the other articles were reviewed following the same procedure. It is unnecessary to show the procedures for all articles, as similar procedures were used. After that, the 10 articles were reviewed following the same procedure as shown in Section 3.2 and their methodologies are analysed and compared in Section

• 1. Moreover, the resulting effects of space layouts on BEP derived from the 10 articles are analysed and compared in Section 4 and 5.

Following the methodology proposed in Section 3.1 and the example procedure in Section 3.2, the 10 articles were reviewed in terms of climates, building types, floor areas, constant parameters, design variables, energy indicators, BEP calculation method, BEP calculation tools, multi-domain integration and resulted biggest reduction. All this information is shown in Table 2. In order to quantify the effects of space layouts on BEP, the term of reduction (%) was used, referring to the highest value minus the lowest value, and divided by the highest value. The reduction means the percentage of the studied indicator that the best layout reduces compared to the worst layout. The values shown in the column of the resulting biggest reduction in Table 2 are based on the analysis in Section 4 and 5.

Table 2. Collection of the studies focusing on the effects of space layouts on building energy performance (BEP).

Ref.

Aut

Year

Location

Climat

Buildi

Floor

Constant

Design variables

Energy indicators

BEP

BEP calculation

Multi-

Resulted biggest

hor

e

ng type

Area (m2)

parameters

(unit)

calculati on

tools

domain integration

reduction

period

[42]

Mus

2008

Garston,

Cfb

office

144

boundary

function allocation,

heating demand

peak

-lighting:

daylight +

H: 57%

au &

the UK

(1floor)

dimension, form

interior partition,

(kWh/day)

winter

Lightscape

thermal;

C: 11%

Stee

and orientation,

lighting and ventilation

cooling demand

and

-thermal: TAS

natural

L (winter): 43%

mer

heating and

requirements,

(kWh/day)

summer

-natural

ventilation +

L (summer): 67%

[63]

s Mus

2009

Garston,

Cfb

Office

144 (1

cooling set-points, WWR, material, opening for ventilation, occupancy schedule Same as in [42]

occupancy, number and distribution of workstations closed or opened doors,

lighting demand (kWh/day) air volume from

day peak

ventilation: TAS -lighting:

thermal; Same as in

AV: 65%

au & Stee mer s

the UK

floor)

state of opening windows, the others are the same as in [4]

natural ventilation (m3)

winter and summer day

Lightscape -thermal: TAS -natural ventilation: TAS

[42]

[64]

Sou

2012

London,

Cfb

office

658 (1

boundary

function allocation,

heating demand

One

EnergyPlus

No

H: 52%

za & Alsa ada ni

the UK

floor)

dimension, form and orientation, material, WWR

interior partition, air exchange rate, internal gains

(kWh/m2 a) cooling demand (kWh/m2 a)

year

C:24%

[65]

Poir

2008

Gothenb

Dfb

office

6177 (6

boundary

function allocation,

final energy for

One

IDA ICE 3.0 [66]

No

H:14% (30%

azis

urg,

floors)

dimension, form

interior partition,

heating (kWh/m2 a)

year

WWR)

et al.

Sweden

and orientation, occupancy schedule, material, infiltration rate

occupancy, lighting power density, illuminance requirement, equipment power density, ventilation rate, WWR

final energy for cooling (kWh/m2 a) final energy for lighting (kWh/m2 a)

C: 57% (30% WWR) L: 4.1 kWh/m2 a (40% WWR)

[67]

Din

2017

Ankara,

BSk

library

7200 (4-8

material, internal

function allocation,

heating demand

four

OpenStudio

No

H: 19%

o &

Turkey

floors)

gains from

interior partition,

(kWh/day)

seasonal

(EnergyPlus)

C: 20%

Ucol uk

equipment, occupancy schedule

WWR, boundary dimension and form

cooling demand (kWh/day) lighting demand (kWh/day) Illuminance set-point

days

L: 10% IS: 27%

satisfaction

[68]

Yi

2016

Seoul,

Dwa

Office

936 (1

boundary

function allocation,

PMV

One

Ecotect (no longer

No

PMV: 13%

South

floor)

dimension, form

interior partition, WWR

Indoor daylighting

year

available)

DL: 11%

Korea

and orientation,

level (daylight

SL: 2%

material,

illuminance, lux)

occupancy

shading level

schedule

[69]

Rod

2014

Coimbra,

Csb

apartm

141-163

Material,

boundary dimension

thermal discomfort

One

EnergyPlus

No

TDP:

rigu

Portugal

ent

(1floor);

schedule,

and form, function

penalty based on air

year

33% (1 floor),

es et

158-189 (2

occupancy,

allocation, interior

temperature (℃)

29% (2 floors)

al.

floors)

internal gains

partition, WWR, type

and size of shading

system

[70] [71]

Dog an et al. Bau

2014 2005

/ /

/ /

/ /

/ 136-214

Boundary dimension, form and orientation, material, internal gains Material,

inter zone heat flows function allocation,

heating demand (/) cooling demand (/) final energy of heating

One year One

No mention Steady state

No Daylight +

/ /

šys & Pan kraš ovai te

(minimal: 119, 1floor)

occupancy, schedule

interior partition, WWR

(/) final energy of lighting (/)

year

calculation

artificial lighting

[33]

Mic

2002

/

/

/

165

boundary

function allocation,

final energy of

One

Steady state

Daylight +

/

hale

(minimal,

dimension, form

interior partition, WWR

lighting (/)

year

calculation

artificial

k et al.

1 floor)

and orientation, material, internal gains

final energy of heating (/) final energy of cooling

(based on recommendation of ASHRAE)

lighting

(/) Note: ‘/’: the information is not shown in the reference. WWR: window to wall ratio; HVAC: heating, ventilation and air conditioning; PMV: predicted mean vote; ASHRAE: American Society of Heating, Refrigerating and Air-Conditioning Engineers; TAS: Thermal Analysis Software; IDA ICE: IDA Indoor Climate and Energy; H: heating demand or final energy; C: cooling demand or final energy; L: lighting demand or final energy; AV: air volume from natural ventilation; IS: illuminance set-point satisfaction; DL: indoor daylight level; SL: shading level; TDP: thermal discomfort penalty.

The tested climates are identified based on the Köppen-Geiger climate classification as shown in [72]. Cfb: Temperate oceanic climate; Dfb: Humid continental climate; BSk: Cold semi-arid climate; Dwa: Humid continental

climate; Csb: Temperate Mediterranean climate.

Proposed Methodology for Studying the Effects of Space layouts

Based on the methodologies used in the 10 articles (Table 2) and also the mechanism for how space layouts affect BEP, a methodology is proposed for systematically studying the effects of space layouts on BEP. It is also used as the guideline to review and analyse the 10 articles.

• • 1. Design Variables

In order to analyse the isolated effects of space layouts, the design variables influencing energy balance are classified, regarding their relationships with space layouts, as shown in Table 3. Firstly, the design variables belonging to space layouts include function allocation, space dimension, space form, interior partition and interior opening [33,42,68,73]. Secondly, if space layouts are designed within a non-fixed layout boundary, the boundary dimension, form and orientation can also be changed consequently [69,74]. Thirdly, the space properties that influence BEP include functional requirements and the use of spaces: functional requirements mean that if different functions are located in different spaces, they have different requirements for heating, cooling, lighting and ventilation; the use of spaces refers to the profiles of internal gains resulting from occupants, lighting, appliances, etc. Lastly, the envelop design of buildings is important for BEP, and it influences the effects of space layouts on BEP. A systematic methodology for studying the effects of space layouts on BEP should first keep the other design variables constant and only change the design variables of space layouts in order to assess the isolated effects of space layouts on BEP, and after this, by adding the other design variables one by one, evaluate their influence on the effects of space layouts.

Table 3. Classification of design variables affecting BEP, regarding their relationship with space layout design.

Design variables of space layouts (with a non-fixed boundary)		Space properties		Envelope design
Space layout design (within a fixed boundary)	Boundary dimension Boundary form Orientation	Functional requirements	Use of spaces	Thermal transmittance Window area Window location Glazing type Shading type and effectiveness Air tightness
Function allocation Space dimension Space form Interior partition Interior opening		Set-point temperature for heating Set-point temperature for cooling Lighting requirements (e.g., illuminance) Ventilation requirement (e.g., air flow rate) Control types	Occupancy, activity and schedule Internal gains from appliances and lighting Opening state of windows and doors

Note: ‘Function allocation’ means allocating different functions to different rooms. ‘Control types’ means the different types of the control for lighting, ventilation, heating and cooling systems. ‘Appliances’ include the used devices, equipment and

machines.

Energy Indicators

Energy indicators differ in three ways: energy end-use, assessment period and system boundary.

They are classified and explained below:

• • • The energy end-use in buildings include space heating, space cooling, water heating, lighting, ventilation, electricity for appliances, etc. [75]. The more energy end-use is included, the more exhaustive the resulted effects of space layouts are.
    • Regarding the assessment period, energy can be calculated on an annual basis or for a shorter time period, like a summer day and a winter day. The assessment period is decided depending on the located climate zone. For instance, if the heating demand is dominant compared to the cooling demand in one climate, the heating period is more representative and the BEP calculation should be calculated at least for the heating period.
    • There are different system boundaries for the BEP assessment, including the conditioned space perimeter of a building or building unit, building site, and outside building site [75]. The

corresponding energy inputs regarding the system boundaries are energy demand (or energy needs), final energy and primary energy, respectively, as shown in Figure 2. The used assessment boundary should be clearly stated.

Figure 2. Different boundaries for BEP assessment, adapted from [76].

• • 1. BEP Calculation Methods

The way in which the space layout affects BEP highly depends on how daylighting and natural ventilation is used in buildings. Thus, in order to assess the effect, the BEP calculation with multi- domain integrations is necessary, like integrating daylighting and natural ventilation with energy assessment. Moreover, the type of BEP calculation methods highly influences the accuracy of BEP results.

• • • Multi-domain integrations for BEP calculations: As mentioned in Section 2, the daylighting and natural ventilation in buildings is highly affected by space layout design. The possible multi- domain integrations include calculating the reduction of artificial lighting as a result of the available daylighting and calculating the reduction of mechanical ventilation as a result of the available natural ventilation. The possibility of integrations depends on whether the located climate zone prefer daylighting or natural ventilation. Integrating multi-domain influences is also needed to accurately predict BEP for building simulations, as shown in [77]. However, no single simulation tool can simulate all physical domains accurately, thus, exchanging information between different simulation software across multi-domains is needed, as shown in [78,79]. Some tools can help to do this, such as a functional mock-up unit in EnergyPlus [79] and a co-simulator for TRNSYS and ESP-r [80].
    • Types of BEP calculation methods: There are mainly two different types of BEP calculation methods: the steady-state calculation and the dynamic simulation. The steady-state calculation, in principle, is based on energy balance without considering dynamic effects for a given moment [81]. It can also be used for a long time, like one month or a whole season, by taking into account the dynamic effects with empirically determined gain and loss utilisation factors. The dynamic simulation calculates energy balance with a short time step, typically 15 minutes or one hour, taking into account the heat stored in and released from the mass of buildings. The steady-state method does not take into account or roughly calculate the dynamic response of the building thermal mass, and its results are less accurate. National norms are usually based on the steady- state method. A large number of tools are available for dynamic simulation nowadays, such as TRNSYS [82], EnergyPlus [83], IDA Indoor Climate and Energy (IDA ICE) [66], ESP-r [84], and Clim2000 [85].
  1. An Example of the Review Procedure for Each Article

The 10 articles in Table 2 are reviewed systematically following the proposed methodology shown in Section 3.1. The methodologies of previous articles analysed in Section 3.3 and the results shown in Section 4 and 5 are fully based on the systematically review of the 10 articles. In order to explain how each article is reviewed, an example of the procedure for reviewing one article is presented in this section. The other articles are reviewed following the same procedure as shown in this example. In order to avoid unnecessary similar content, the review procedures of the other articles are not presented.

The study of Musau and Steemers [42] is taken as an example, as it provided detailed information on energy simulation and clear results. This article investigated the energy demand for

heating, cooling and lighting with five different office layouts in Garston, the UK, in a temperate oceanic climate (Cfb). The five layouts are Hive (open plan), Den, Club, Combi and Cell, as shown in Figure 3. Occupancy differs between layouts. We extract the following information from the original article, following the methodology shown in Section 3.1, in order to identify the isolated effects of space layouts.

Figure 3. Five layouts with a boundary of 12 m × 12 m in [42].

• • 1. Identifying Design Variables

In order to identify the isolated effects of space layouts, each article needs to be analysed and selected for the cases which only changed the design variables of space layout design while keeping the other variables, such as materials and window to wall ratio (WWR), constant. Regarding the design variables influencing BEP as shown in Table 3, the following variables were changed in this article:

• • • Space layout design: function allocation and interior partition.

Functional requirements: lighting and ventilation requirements. The used control types of lighting and ventilation systems were related to the distribution of occupants. For instance, when a room had no occupants, the lighting and ventilation supply was reduced to the lowest level. Different layouts had different distributions of occupants, resulting in different requirements for lighting and ventilation.

• • • Use of spaces: occupancy and number of workstations. Different layouts had different numbers of occupants and workstations.
    1. Identifying Constant Parameters

Except for design variables, it is also necessary to identify the constant parameters used in each article, in order to compare the results from different articles. Regarding the design variables influencing BEP as shown in Table 3, the following design parameters were kept constant in this article:

• • • Layout boundary: boundary dimension, boundary form and orientation.
    • Functional requirements: temperature set-points for heating and cooling.
    • Use of spaces: occupancy schedule.

Envelope design: WWR (30% for the north and south façade, and 0% for the east and west façade), materials (including the reflectance and conductance of roofs, floors and external walls) and size and location of openings for ventilation (800 mm wide door shutters at the bottom of each door).

• • 1. Identifying Energy Indicators and the BEP Calculation Method

Energy indicators need to be identified for each article, in order to classify the resulting effects of space layouts from different articles. The used BEP calculation method in each article influences the accuracy of results. In this article, the used indicators include heating demand, cooling demand and lighting demand in the peak winter (21st of December) and peak summer (12th of July). This study was performed with dynamic simulation, using Thermal Analysis Software (TAS) for energy and natural ventilation simulation and Lightscape for daylighting simulation. The effects of

daylighting and natural ventilation were integrated with energy simulation. The required artificial lighting was reduced based on the daylighting simulation result, and the required mechanical ventilation was reduced based on the natural ventilation simulation result, and these were used as inputs into the energy simulation.

• • 1. Selecting Cases and Analysing Results

Most articles present multiple cases and some of them mixed the design variables of space layouts with other variables. In order to identify the isolated effects of space layouts, the cases in each article should be strictly selected. Among all cases presented in this article, we selected and compared only the cases with the same number of occupants. The results of the cases with the same occupancy are reorganised and shown in Table 4. Table 4 shows the isolated effects of space layouts as well as the influence of occupancy, as follows:

• • • Isolated effects of space layouts: The heating demand differs highly between layouts with low occupancy. The biggest reduction in the heating demand is 57%, which is between the layouts with six occupants. In contrast, the reduction in the cooling demand is relatively small (11%).
    • Influence of occupancy on the effects of space layouts on BEP: With the increase of occupancy, the reductions in heating and cooling demands decrease apparently. The values of the heating and cooling demands are almost the same in different layouts when layouts are highly occupied (12 occupants). This is because when most rooms are highly occupied, the interior partitions that enable different energy requirements in different rooms have less influence.

Table 4. Energy demand comparison between the layouts with same occupancy, adapted from [42].

Space layouts Heating demand in peak

winter

Lighting demand in peak winter

Cooling demand in peak summer

Lighting demand in peak summer

a) space layouts with 4 occupants (kWh/day)
Hive	4	14	14	3
Combi	5	10.5	13	1
Cell	7	8.5	13	1
Reduction (%)	43%	39%	7%	67%
b) space layouts with 6 occupants (kWh/day)
Den 1	3	14	19	4
Den 2	7	8	17	2
Club	6	12	18	3
Combi	4	12	18	2
Cell	6	10	19	3
Reduction (%)	57%	43%	11%	50%
c) space layouts with 8 occupants (kWh/day)
Hive	3	15	23	3
Combi	3	14	25	2
Cell	3	15	25	4
Reduction (%)	0%	7%	8%	50%
d) space layouts with 12 occupants (kWh/day)
Hive	3	15	32	3
Den	3	15	33	3
Club	3	15	34	2
Reduction (%)	0%	0%	6%	33%
Biggest reduction	57%	43%	11%	67%

• 1. Methodologies Used in Previous Studies

Following the same procedure shown in Section 3.2, the other nine articles were reviewed and the information is shown in Table 2. The methodologies for studying the effects of space layouts on BEP used in the 10 articles are analysed and compared in this section, in terms of design variables, energy indicators and BEP calculation methods.

• • 1. Design Variables

The following design variables of space layouts were used in these articles: function allocation and interior partition. Nevertheless, in most studies, they were mixed with other parameters. It is difficult to identify the isolated effects of space layouts. For instance, occupancy and distribution of workstations, and lighting and ventilation requirements were also changed in [42,63]. Other parameters were also changed, such as WWRs in [33,65,67–69,71], types and sizes of shading systems in [69] and opening states of windows in [63].

• • 1. Energy Indicators

Regarding end uses of energy, most of these articles only simulated the energy use for space heating and space cooling, and half of the studies also included the energy use for lighting [33,42,65,67,71]. The energy use for ventilation has not been included yet, while one study tested the air volume supplied by natural ventilation [63]. In addition to energy use, some studies also calculated the indicators for thermal and visual comfort. These indicators include predicted mean vote (PMV) in [68], daylight autonomy in [67] and daylight illuminance in [68], which can provide extra information about BEP in addition to energy use. Regarding the system boundary of assessment, most of these articles defined their energy indicators unclearly: three articles described the system efficiency [33,65,71], and we assume that they tested the final energy; the others did not show system information, thus, we assume that they tested energy demands. Regarding the calculation period, most studies calculated the energy use for the whole year [33,64,65,68,70,71], and some studies only calculated it for peak days [42,63] or season representative days [67].

• • 1. BEP Calculation Methods

Regarding BEP calculation methods, most studies used the dynamic simulation method for higher accuracy, except for two studies [33,71]. Lightscape in [42], Ecotect in [68] and IDA ICE 3.0 in

[65] were used for daylighting simulation. TAS in [42], EnergyPlus in [64,67,69] and IDA ICE 3.0 in

[65] were used for energy simulation. Although different calculation methods and simulation software were used in different articles, it is impossible to compare the accuracy of the calculation methods and simulation software between articles, as the calculation conditions in different articles are different in terms of materials, climates, WWRs, layouts (floor areas, interior partitions and functions), etc. Regarding the integration of multi-domains, two studies of [42,63] integrated daylighting and natural ventilation with energy simulation, using Excel to exchange data between the simulation tools of Lightscape and TAS. Another two studies of [33,71] considered the effect of daylighting on the reduction of the artificial lighting demand.

1. Effects of Space Layouts on Energy Use

Following the same procedure shown in Section 3.2, the other articles were reviewed. Their results were used for the analysis in Section 4 and 5. As most information has already been shown in Table 2, the articles that were analysed in this section and Section 5 are introduced briefly. Some articles are not used for the analysis in Section 4 and also in Section 5: the studies of [33,71] did not show the results of energy performance, and the study of [70] did not present sufficient information for the on BEP calculation. As the articles in Table 2 mixed the design variables of space layouts with other parameters, the effects of space layouts cannot be identified directly from the results of these articles. Thus, we selected the cases that were usable to exclude the other design parameters, and reorganised their results to identify the isolated effects of space layouts. The effects on energy use are classified into the effects on space heating and cooling, lighting and ventilation as follows.

• 1. Effects on the Energy Use for Space Heating and Cooling

Most articles shown in Table 2 assessed the energy use for space heating and cooling. Yi [68] also tested the energy demands for heating and cooling, but in the results, heating and cooling demands were summed up as the annual energy use intensity, which cannot be used for detailed analysis in

this study, thus, it was not included in this section. The studies of [42,64,65,67] were analysed and compared below.

• • 1. Analysis of the Relevant Articles

Souza and Alsaadani [64] tested three layouts for an office building in London of the UK, in Cfb, and modelled them with different thermal zoning strategies (Figure 4). Detailed information about this article is shown in Table 2. Although this study focused on testing the effect of different thermal zoning strategies, the different zoning models actually represent different layouts. Ventilation rates and internal gains were also changed in some simulations, but we only selected the simulations in which only space layouts were changed. The selected results are shown in Table 5, and the reduction in the annual heating demand between different zoning strategies is 52%, while the value in the annual cooling demand is 24%.

• • • 1. single zone (b)5 zone (c) Office in use

Figure 4. Three layouts modelled with different thermal zoning strategies in [64]. The interior partitions divide the layout into different thermal zones.

Table 5. Annual energy demand comparison between three layouts, adapted from [64].

	heating demand	cooling demand
‘Single zone’ layout	8.47 (kWh/m2)	28.04 (kWh/m2)
‘5-zone’ layout	5.59 (kWh/m2)	37.06 (kWh/m2)
‘Office in use’ layout	11.69 (kWh/m2)	29.72 (kWh/m2)
reduction (%)	52%	24%

Poirazis et al. [65] compared cell and open office layouts in Gothenburg of Sweden, in the humid continental climate (Dfb) as shown in Figure 5, and tested their final energy for space heating, space cooling and lighting. Detailed information about this article is shown in Table 2. In total, 102 simulations were run, and plenty of parameters were changed. We selected the layouts with same WWRs, although they still have different occupancy, lighting power densities, illuminance requirements, equipment power densities and heating, ventilation and air conditioning systems. Although the occupancy is different between the cell and open layouts, this case represents the real situation in practice. The final energy reductions between open and cell layouts are shown in Table

6. The reduction in the final energy for heating between the cell and open layouts is 14%, and the value for cooling is 57%. As shown in Table 6, with the increase of WWRs, the effects of space layouts on the final energy for heating, cooling and lighting decrease, which means that space layouts matter less when there are large windows.

1,4,6,9: corner office; 2,8: double office; 3,7: single

office; 5,10: meeting room; 11: cell; (a)

1,4: corner zone; 8: intermediate zone; 2,5: meeting rooms;

Figure 5. Cell and open layouts in [65]. The interior partitions divide the layout into different thermal zones.

Table 6. Annual final energy comparison between cell and open layouts, adapted from [65].

	reduction in final energy for heating (cell>open)	reduction in final energy for cooling (cell<open)	reduction in final energy for lighting (cell<open)
30% WWR	14%	57%	4 kWh/m2
60% WWR	11%	28%	4.1 kWh/m2
100% WWR	11%	20%	2.7 kWh/m2

Note: only the reductions and differences in kWh/m2 were shown in the original paper.

Dino and Ucoluk [67] simulated the energy demands of a library building in Ankara of Turkey, in a cold semi-arid climate (BSk), with changed space layouts as well as building geometry. Detailed information about this article is shown in Table 2. Each layout has several functions, including reading, book storage, administration, café, working and conference, which vary in occupancy densities and equipment gains, heating and cooling set-points and illuminance set-points. The tested indicators relevant to energy use include heating, cooling and lighting demands. They were tested for 4 days, representing four seasons. As this study changed WWRs in addition to space layouts, we cannot identify the isolated effects of space layouts. Only the results of several layouts were shown in the original paper. We selected four layouts with the same geometry for comparison (Figure 6), which have a similar amount of total energy demand. The resulting energy indicators of the selected layouts are shown and compared in Table 7. According the table, with the change of space layouts and WWRs, the reductions are 19% for heating demand per day and 20% for cooling demand per day. Although with different WWRs, the total energy demands of different layouts are similar (around 3500 kWh/day). This implies that space layouts affect energy demands, although the isolated effects cannot be identified.

Figure 6. Four different layouts with the same geometry in [67]. Different colours represent different thermal zones.

Table 7. Energy demand comparison between the selected four layouts, adapted from [67].

	Heating demand (kWh/day)	Cooling demand (kWh/day)	Lighting demand (kWh/day)	Illuminance set- point satisfaction
layout 1	1013	1154	1343	2285
layout 2	1092	978	1429	1949
layout 3	1249	924	1334	2378
layout 4	1159	1029	1286	2680
reduction (%)	19%	20%	10%	27%

• • 1. Resulted Effects and Comparison

In addition to the results obtained from Section 4.1.1, the results obtained from the analysis of the example article shown in Section 3.2 are also used for the analysis in this section. The isolated

effects of space layouts can be identified from these articles, except for [67]. By changing space layouts, the resulting reductions in the annual heating and cooling demands are up to 52% and 24%, respectively, for the case of an office building in the UK [64]. The resulting reductions in the heating and cooling demands in peak days are up to 57% and 11%, respectively, for the case of an office building in the UK [42]. The resulting reductions in the annual final energy for heating and cooling are up to 14% and 57%, respectively, for the case of an office building in Sweden [65]. The influence of occupancy on the effect of space layouts on BEP can be identified from [42] as well as the influence of WWRs [65], which show that with the increase of occupancy and WWRs, the reductions between layouts in heating and cooling demands decrease apparently.

Regarding the assessment boundary, both energy demand [42,64] and final energy [65] were tested. Regarding the assessment period, one year [64,65], peak days in winter and summer [42] and four season days [67] were tested. Regarding the BEP calculation method, the thermal zone division would highly affect the accuracy of the results, as shown in [64]. A simulation model with the detailed thermal zone division as shown in Figure 4-c is needed for future studies. In total, three climates (Cfb, Dfb, BSk) were tested and the isolated effects of space layouts were only identified for Cfb and Dfb. However, their results cannot be compared as different layouts are used for the two climates, as well as different energy indicators: heating and cooling demand in peak day [42] and annual heating and cooling demand [64] for Cfb, and annual final energy for heating and cooling for Dfb [65]. Although the studies of [42] and [64] tested the same climates, the layouts used in the two articles are different in floor areas, interior partitions and functions, thus, their results also cannot be compared.

• 1. Effects on the Energy Use for Lighting

Three of the articles in Table 2, which are also analysed in Section 4.1, studied the effects of space layouts on the energy use for lighting [42,65,67]. The resulted effects on the energy use for lighting in the three articles are shown Table 4, 6 and 7, respectively. As shown in Table 4, in the study of [42], the biggest reduction in the lighting demand of peak summer is 67%, although the value of the lighting demand is relatively small. The reduction in the lighting demand of peak winter is 43%. Moreover, with the increase of occupancy, the reductions between layouts in the lighting demands of both peak winter and peak summer decrease apparently. The lighting demands of different layouts are almost the same when the layouts are highly occupied with 12 occupants. In the study of [65], the reduction in the final energy for lighting cannot be identified from the original article as only the demand difference in kWh/m2 is given. However, as shown in Table 6, the effect of space layouts on the lighting demand decreases with the increase of WWRs. From the study of [67], the isolated effect of space layouts on the lighting demand cannot be identified, as WWRs were also changed. Regarding the tested climates, three climates (Cfb, Dfb, BSk) were tested and the isolated effects of space layouts were only identified for Cfb and Dfb. However, their results cannot be compared, as different layouts were used for the two climates, as well as different energy indicators: lighting demand in peak days for Cfb [42] and annual final energy for lighting for Dfb [65]. Compared to the energy use for space heating and cooling, the articles on the energy use for lighting are much less.

• 1. Effects on the Energy Use for Ventilation

There is only one article that tested the ventilation performance among the articles shown in Table 2. In their another study, Musau and Steemers [63] tested the effect of space layouts on the ventilation performance for office buildings in Garston of the UK, in Cfb. The basic settings were the same as in [42]. Detailed information about this article is shown in Table 2. One indicator relevant to ventilation was calculated, i.e., fresh air volume (m3) supplied by natural ventilation through background vents, which was tested for the peak winter and summer. The results of the original paper were reorganised to identify the effect of space layouts in Table 8. According to this table, the biggest reduction between layouts in the air volume supplied by vents of peak winter is 65%. By comparing the variants with a different occupancy in Table 8, the following conclusion can also be drawn: the higher the occupancy is, the lower the effect of space layouts on the air volume supplied by natural ventilation in peak winter. Only one climate was tested, i.e., Cfb, and the isolated effect of

space layouts was identified for this climate. More studies are needed for this topic specifically for the energy use for ventilation.

Table 8. Comparison of the fresh air volume supplied by natural ventilation, adapted from [63].

Air volume supplied by vents of peak winter with closed window (m3)

	8 occupants	6 occupants	4 occupants	2 occupants
Cell	310	250	170	80
Comb	320	250	170	80
Club	580	490	380	200
Den	620	620	460	230
Hive	620	620	460	230
Reduction (%)	50%	60%	63%	65%
Biggest reduction (%)			65%

1. Effects of Space Layouts on Occupant Comfort

In addition to energy use, the articles in Table 2 also tested the indicators for occupant comfort. Among the articles shown in Table 2, only thermal and visual comfort was tested, and the articles relevant to occupant comfort were analysed in detail and compared below.

• 1. Effects on Thermal Comfort

There are two articles that test the effects of space layouts on thermal comfort [68,69], and they were analysed in detail and compared below.

• • 1. Analysis of the Articles Relevant to Thermal Comfort

Yi [68] simulated an office building in Seoul of South Korea, in the humid continental climate (Dwa), with changed space layouts as well as WWRs. Detailed information about this article is shown in Table 2. We only selected three layouts for comparison (Figure 7), as their WWRs varied from 31.4% to 35%, which is a small variation. The tested indicators relevant to thermal comfort is PMV. The results are reorganised in Table 9, which shows that the reduction in PMV is 13%. The reduction is mainly caused by changing space layouts, as the WWRs have a much smaller variation.

Figure 7. Three layouts with similar WWRs in [68]. The interior partitions divide the layout into different thermal zones.

Table 9. Energy performance comparison between the selected layouts, adapted from [68].

	PMV	Indoor daylight level (lux)	Shading level
Layout 1	−1.60	309.30	90.80
Layout 2	−1.79	348.50	89.20
Layout 3	−1.55	335.70	89.26
Reduction (%)	13%	11%	2%

Rodrigues et al. [69] simulated a residential building in Coimbra of Portugal, in a temperate Mediterranean climate (Csb), with changed space layouts, WWRs, window orientations, shading systems and floor areas. Detailed information about this article is shown in Table 2. The tested indicator is thermal discomfort penalty (℃), which was calculated by multiplying a weight factor with the difference between the calculated hourly interior air temperature and the temperature limit for thermal comfort. Two layout sets were compared: one has one floor and the other one has two floors (Figure 8). The results of the two sets of layouts are shown and compared in Table 10. The biggest reduction in the thermal discomfort is 33% between one-floor layouts and 29% between two- floor layouts. The isolated effect of space layouts on thermal comfort cannot be identified from this study, while it shows the effect of space layouts combined with other parameters, i.e., WWRs, window orientations, shading systems and floor areas.

• • • 1. Layout example with one floor

1st floor 2nd floor

• • • 1. Layout example with two floors

Figure 8. Examples of two layout sets in [69] (left: layout with one floor, right: layout with two floors). The interior partitions divide the layout into different thermal zones.

Table 10. Hourly thermal discomfort comparison between layouts, adapted from [69] (TDP: thermal discomfort penalty. The higher the thermal penalty, the worse the thermal performance).

layouts with one floor

layout	layout	layout	layout	layout	layout	layout	layout	layout	layout	layout	layout
-1	-2	-3	-4	-5	-6	-7	-8	-9	-10	-11	-12
TDP of layouts with 20.5℃	23.0℃	23.3℃	25.3℃	25.7℃	25.8℃	26.4℃	26.6℃	27.4℃	27.9℃	29.6℃	30.5℃

one floor

reduction 33%

layouts with two floors

layout layout	layout	layout	layout	layout	layout	layout	layout	layout	layout	layout
-13 -14	-15	-16	-17	-18	-19	-20	-21	-22	-23	-24
TDP of layouts with 21.5℃ 22.8℃	22.8℃	23.0℃	23.6℃	25.2℃	25.2℃	25.7℃	25.8℃	28.6℃	28.9℃	30.2℃

one floor

reduction 29%

• • 1. Resulted Effects and Comparison

The isolated effects of space layouts cannot be identified in the two studies [68,69], as both studies also changed other parameters, i.e., WWRs in [68], and WWRs, window orientations, shading systems and floor areas in [69]. However, as the variation of WWRs in [68] was small, the reduction in thermal discomfort is mainly caused by changing space layouts. Thus, the reduction in PMV is around 13% by changing the space layouts in South Korea [68]. Two climates were tested (Dwa and Csb), but the isolated effects of space layouts were only identified for Dwa.

5.2. Effects on Visual Comfort

There were two studies that tested the effect of space layouts on visual comfort [67,68]. In the study of Yi [68], the indoor daylight level (illuminance) and shading level (the ratio of shaded floor area at 12 pm, 21th Dec) were tested, in addition to PMV. The resulting reduction was 11% in indoor daylight level and 2% in shading level, as shown in Table 9. The study of Dino and Ucoluk [67], in addition to energy use, tested the illuminance set-point satisfaction, which refers to how close the calculated daylight illuminance is to the user-defined illuminance set-point. The resulting reduction in the illuminance set-point satisfaction is 27%, as shown in Table 7. In both studies, WWRs were also changed in addition to space layouts. However, the variation of WWRs in [68] was small; thus, the reduction is mainly caused by changing space layouts. Two climates were tested (Dwa and BSk), but the isolated effects of space layouts were only identified for Dwa.

1. Conclusions and Recommendations

In this paper, the articles relevant to the effects of space layouts on building energy performance (BEP) were reviewed. A methodology for studying the effects of space layouts on BEP is proposed in Section 3.1, regarding design variables, energy indicators and BEP calculation methods. Among the large number of studies on building energy-efficient design, only 10 articles were found relevant to the specific topic and they were reviewed in detail to identify the isolated effects of space layouts. The review results show that by only changing space layouts, the energy use for space heating, space cooling and lighting can be reduced significantly.

The resulting effects can be categorised into the isolated effects of space layouts on BEP, and the influence of other design parameters on the effects of space layouts on BEP. Moreover, the recommendations were added regarding future research direction, as well as the methodology for studying the effects of space layouts.

• 1. Isolated Effects of Space Layouts on BEP

The isolated effects of space layouts on BEP tested in the 10 articles were classified into the effects on energy use and the effects on occupant comfort. The effects of space layouts on the energy use for space heating and cooling, lighting and ventilation are as follows:

• Energy use for space heating and cooling: The isolated effects were identified, and both energy demand and final energy for one year were tested. The resulting reductions in the annual heating and cooling demands were substantial, and the reductions were up to 52% and 24%, respectively, for the case of an office building in the UK with varied thermal zoning. The resulting reductions in the heating and cooling demands in peak days were up to 57% and 11%, respectively, for the case of an office building in the UK. The resulting reductions in the annual final energy for heating and cooling are up to 14% and 57%, respectively, for the case of an office building in Sweden.
• Energy use for lighting: Only the isolated effects on the lighting demand for peak summer and winter were tested, and the resulting reductions were significant. The reductions were up to 67% and 43%, respectively, for the case of an office building in the UK.
• Energy use for ventilation: Only the air volume supplied by natural ventilation was tested for the peak winter; the resulting reduction was significant, namely, up to 65% for the case of an office building in the UK.

The effects of space layouts on the thermal and visual comfort were as follows:

• Thermal comfort: PMV and the thermal discomfort (difference between air temperature and thermal comfort temperature) were tested. Although the isolated effects cannot be identified, the approximate effect on PMV can be identified, and the resulting reduction was smaller than the ones in energy use; around 13% for the case of an office building in South Korea.
• Visual comfort: Similar to the thermal comfort, only the approximate effect on the illuminance and shading level can be identified, and the resulting reductions are smaller than the ones in energy use; are around 11% and 2%, respectively, for the case of an office building in South Korea.
  1. The Influence of Other Parameters

From the results of the 10 articles, the influence of other design parameters, i.e., occupancy and WWRs, on the effects of space layouts on BEP can also be identified, as follows:

• Influence of occupancy: With the increase of occupancy, the effects of space layouts on the heating demand, cooling demand, lighting demand and air volume from natural ventilation decrease.
• Influence of WWRs: With the increase of WWRs, the effects of space layouts on the heating demand, cooling demand and lighting demand decrease.

Regarding climates, in total, five climates were tested for the effects of space layouts on BEP. Two climates were tested for the isolated effects on the energy use for space heating and cooling, and two climates were tested for the isolated effects on the energy use for lighting. However, the results for space heating, cooling and lighting cannot be compared between the climates, as different energy indicators and layouts were used for these climates. Moreover, only one climate was tested for the isolated effects on the energy use for ventilation, thermal comfort and visual comfort, respectively. In addition, the construction site and the surrounding buildings were not considered in the 10 articles analysed in this paper, and these would highly influence the effect of space layouts on BEP.

• 1. Recommendations

Designers and architects should consider BEP while designing space layouts, as the effects of space layouts on BEP are significant, although the effects have not been fully confirmed. Studies are needed to compare the effects of space layouts between different climates regarding different energy indicators, in order to obtain the influence of climates on the effects of space layouts on BEP. In order to compare the results between different climates, the same layout should be used in each climate with the same conditions, such as interior partitions, dimensions, forms, orientations and functions, while the functional requirements (such as heating and cooling set-points) and envelope design (transmittance, window area) should adapt to the local standards in order to be suitable for practice and the local climate. Moreover, it would be interesting to test the effects of space layouts on BEP considering the influence of the context with surrounding buildings.

More studies are needed to fully explore the effects of space layouts on BEP. The recommendations for future studies regarding the methodology for studying the effects of space layouts on BEP are as follows.

• Design variables: A systematic study on the effects of space layouts on BEP should first only change the design variables of space layouts, while keeping other design parameters constant, in order to identify the isolated effects of space layouts. Then, by adding other design parameters one by one, their influence on the effects of space layouts can be obtained.
• Energy indicators: Regarding energy use, more studies are needed, especially on the energy use for lighting and ventilation for a long assessment period, such as one year. Regarding occupant comfort, more indicators for thermal and visual comfort need to be tested.
• BEP calculation methods: Regarding the BEP calculation method, a calculation tool with high accuracy is needed. The integration of multi-domain simulations is necessary to predict the real situation and better represent the effects of space layouts, such as integrating daylighting simulation and natural ventilation simulation with energy simulation. In addition, a detailed thermal zone division regarding the different requirements of spaces is necessary as shown in Figure 4-c, as it highly affects the results.

Author Contributions: Conceptualization, A. van den Dobbelsteen and M. Turrin; methodology, T. Du and S. Jansen; writing—original draft preparation, T. Du; writing—review and editing, S. Jansen. All authors have read and agreed to the published version of the manuscript.

Funding: This research received no external funding.

Acknowledgments: We want to show our thanks to Peter van den Engel and Martin Tenpierik for their generous help.

Conflicts of Interest: The authors declare no conflict of interest.

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Energy efficient design of building: A review

Contents lists available at SciVerse ScienceDirect

Renewable and Sustainable Energy Reviews

j ournal ho mepage: www.elsevier.com/locate/rser

R. Pacheco, J. Ordón˜ez ∗, G. Martínez

Department of Construction & Project Engineering, University of Granada, Spain

a r t i c l e i n f o a b s t r a c t

Article history:

Received 17 May 2011

Accepted 10 March 2012

Available online 28 April 2012

Keywords: Energy saving Building design

Heating and cooling demand

Energy saving is a high-priority in developed countries. For this reason, energy-efficient measures are being increasingly implemented in all sectors. The residential sector is responsible for an important part of the energy consumption in the world. Most of this energy is used in heating, cooling, and artificial ven- tilation systems.With a view to developing energy-efficient structures, this article provides an overview of building design criteria that can reduce the energy demand for the heating and cooling of residen- tial buildings. These criteria are based on the adoption of suitable parameters for building orientation, shape, envelope system, passive heating and cooling mechanisms, shading, and glazing. An analysis was made of previous studies that evaluated the influence of these parameters on the total energy demand and suggested the best design options. This study is useful for professionals who are responsible for decision-making during the design phase of energy-efficient residential buildings.

© 2012 Elsevier Ltd. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3560

2. Influence of shape on the energy optimization of buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3560

2.1. Compactness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3560

2.2. Shape factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3561

2.3. Climate and shape optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3561

2.4. Cost of the life cycle and shape of the building . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3561

3. Orientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3561

3.1. Orientation and solar radiation received. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3562

3.2. Orientation and shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3562

3.3. Orientation and ground plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3562

3.4. Building orientation and energy demand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3562

4. Influence of the building envelope in the energy demand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3563

4.1. Heat transfer formulas: optimization of the limit U value. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3563

4.2. Building insulation and economic analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3564

4.3. Environmental study of the building envelope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3565

5. Shading on buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3565

5.1. Shading coefficient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3565

5.2. Effectiveness of shading devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3565

5.3. Energy benefits of the shading in hot climates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3566

5.3.1. Roller shades and overhang . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3566

5.3.2. Self-shading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3566

5.4. Energy benefits of shading in cold climates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3567

5.4.1. Shading cast by neighboring buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3567

6. Passive systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3568

6.1. Passive cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3568

6.1.1. Natural ventilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3568

6.1.2. Nocturnal convective cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3568

∗ Corresponding author. Tel.: +34 958 249438; fax: +34 958 249441.

E-mail address: javiord@ugr.es (J. Ordón˜ez).

1364-0321/$ – see front matter © 2012 Elsevier Ltd. All rights reserved.

doi:10.1016/j.rser.2012.03.045

6.1.3. Radiant cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3568

6.1.4. Evaporative cooling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3568

6.1.5. Earth-air cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3570

6.2. Passive heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3570

6.2.1. Trombe wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3570

6.2.2. Solar chimney. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3570

6.2.3. Unglazed transpired solar fac¸ ade. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3570

7. Glazing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3570

7.1. Thermal comfort and indoor illumination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3571

7.2. Glazing types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3571

7.3. Film-plating glazing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3571

7.4. Angle-selective glazing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3571

7.5. Glazing that provides spectrum selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3572

7.6. Construction solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3572

7.6.1. Glass rotation in respect to the building . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3572

7.6.2. Double glazing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3572

7.6.3. Advanced daylighting systems .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3572

8. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3572

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3573

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3573

1. Introduction

In recent years, significant efforts have been made to improve energy efficiency and reduce energy consumption. The concept of energy efficiency in buildings is related to the energy supply needed to achieve desirable environmental conditions that mini- mize energy consumption [1].

A suitable heating and cooling design is one of the best methods to reduce energy cost in buildings [2]. To design energy-efficient building, design variables and construction parameters must be optimized [3]. Consequently, it is necessary to identify the design variables that are directly related to heat transfer processes. Ekici and Aksoy [4] summarized the parameters that affect building energy requirements (see Table 1).

The conceptual design phase of a building is the best time to inte- grate sustainable strategies. When these mechanisms are put into action at the very beginning of the construction phase, this reduces implementation costs as compared to when they are installed in subsequent stages of construction [5].

Evidently, energy-efficient design methods are an added value that benefits the end user. A building design based on energy-saving criteria reduces economic costs throughout the useful life of the building because of its lower energy consumption, and this more than compensates for the greater initial investment. Since there are also fewer CO₂ emissions into the atmosphere throughout the building’s life cycle, this benefits society as well.

1. Influence of shape on the energy optimization of buildings

The shape of a building influences the solar energy that it receives as well as its total energy consumption [6]. The radiation hitting a building can increase energy requirements for cooling to

up to 25% [7]. Accordingly, building shape not only determines the total area of the fac¸ ade and roof that receive solar radiation, but also the surface exposed to the outside, and thus to energy losses. When a building is designed, the ratio between its outer surface and the total constructed volume should be as small as possible, tend- ing toward the ideal case of a hemisphere [8]. However, because of design and construction issues, this shape is not attainable in most projects. For this reason, many researchers have begun to study the performance of parallelepiped-shaped buildings and to vary the shape factor in order to find the best model [6,9]. In other cases, they began by defining a hexagonal or octagonal foundation plan [10], a curved or oval foundation plan [11] or one without any spe- cific geometric shape [5] until obtaining the optimal dimensions for the specific geometric context.

The variables that are related to building shape and which influence heating and cooling requirements are the following: (i) compactness index; (ii) shape factor; (iii) climate; and (iv) the influ- ence of shape on the life cycle of the building. The characteristics of the building envelope are crucial variables that should be taken into account because they are relevant to the energy requirements for maintaining the building at a comfortable temperature.

• 1. Compactness

The compactness index is the ratio between the volume and the outer surface of the building fac¸ ade. It is related to the building’s capacity to store heat and avoid heat loss through its fac¸ ade. A very compact building is one that has a high volume/surface ratio, where the surface exposed to possible heat losses or gains is as small as possible. The relative compactness of a building is defined as the ratio between its compactness index and the compactness index of a reference building as shown in Eq. (1).

Table 1

Parameters that determine building energy requirements [4].

RC (V/A_ext)building

(V/A_ext)ref

=

(1)

Physical–environmental parameters

Design parameters

Fig. 1 shows two buildings with the same volume but with dif- ferent compactness indices.

Daily outside temperature (◦C) Shape factor

Solar radiation (W/m2) Transparent surface

Wind direction and speed (m/s) Orientation

Thermal–physical properties of building materials

Distance between buildings

The compactness index is a ratio that provides an idea of how a building can be cooled and heated [12], and which influences energy consumption [13]. The overheating of a building because of a high compactness index can be compensated by the installation of passive cooling systems.

R. Pacheco et al. / Renewable and Sustainable Energy Reviews 16 (2012) 3559–3573 3561

Fig. 1. Buildings with different compactness indices: (i) building with a compact- ness index of 3.45 (left); (ii) building with a compactness index of 5 (right).

• 1. Shape factor

The shape factor is the ratio of building length to building depth. Along with orientation, this factor defines the percentage of the fac¸ ade exposed at each cardinal point. Both factors are gener- ally studied together [4,9,14,15]. By combining the optimization of shape and orientation, it is possible to obtain benefits that can lead to heat energy savings of 36% [9].

Florides et al. [12] quantified the effect of the shape factor on energy requirements for the heating and cooling of a building. Their conclusion was that the best position for a rectangular house is for the longest wall of the building fac¸ ade to face the south. A model with a 1/2 shape factor (less wall surface with a southern orienta- tion) requires almost 8.2% more energy for heating. This percentage increases considerably (26.7%) when there is more roof insulation since the heating gain is prevented by the roof cladding.

Mingfang [6] studied the influence of building length, depth, and width parameters on the solar radiation received by a parallelepiped-shaped building. In his study, the volume was kept constant and Eq. (2) was applied.

a polygonal-shaped building. For both possibilities, the optimal building shape is conditioned by the years of a building’s service life considered in the calculations. For example, in the case of a polygonal shape for short heating periods, building shape approx- imated an octagon. It is necessary to establish a standard criterion for the years of the building’s service life that must be considered when the economic cost of the energy demand is evaluated.

The life cycle of a building is the period from its conception until the end of its service life or demolition. The life cycle includes the phases of design, construction, occupation, use, and maintenance, and dismantling. This process quantifies and evaluates the flow of material and energy in the system [17]. It is possible to ascertain the distribution of the environmental impact throughout the pro- cesses and stages that make up the building’s life. Fig. 2 describes the phases in the life cycle of a building [18].

Between 80% and 85% of the total energy consumption during a building’s life cycle occurs in the use or occupation phase [19]. This includes the energy costs of heating, cooling and ventilating the building, lighting, equipment operation, water supply, water heating, and wastewater treatment [17].

Wang et al. [5] studied the impact of building shape on energy demand. They calculated the life-cycle cost (LCC) and life-cycle environmental impact (LCEI) with Eqs. (3) and (4).

LCC(X) = IC(X) + OC(X) (3)

LCEI(X) = EE(X) + OE(X) (4)

where IC is the initial construction cost; OC is the current worth of life-cycle operating costs that comprise energy consumption cost and peak demand cost; EE is the environmental impact in megajoules (MJ) caused by the building construction; OE is the

Q (q_s + q_N)³／ ˇ + (q_E + q_w) × ／3

Q₀

=

q_s

+ q_N

+ q_E

+ q_w

−2ˇ + q_H × ／3

ˇ−2

environmental impact (MJ) caused by the building operation for

(2)

heating, cooling, and lighting.

The solution with the lowest life-cycle cost has a shape that

where Q/Q₀ is the relative solar radiation received by the external surface of the buildings; q_S, q_N, q_Z, q_W, q_H are the solar radiation on the south-wall, north-wall, east-wall, west-wall and roof per unit area in daytime; is the length/depth ratio of the building; ˇ is the height/depth ratio of the building.

+ q_H

This equation gives the optimal building proportions that min- imize the direct solar radiation received. By this method, the total solar radiation on the building will decrease as much as 4% in com- parison with radiation on a cubic building

• 1. Climate and shape optimization

In very cold climates, more heat escapes through the building envelope than the amount of heat that can be gained by increasing the surface receiving solar radiation. Therefore, the increase in the shape factor (more external building surface for the same volume, lower compactness index) is proportional to the increase in the energy required for heating [16]. In warm climates, this proportion is not direct, and a fixed type of building performance cannot be determined.

• 1. Cost of the life cycle and shape of the building

Marks [10] calculated construction and heating costs, depend- ing on building shape. He considered a curve-shaped building and

is roughly a regular polygon (this coincides with the fact that the most efficient shape is a cube). In contrast, when the environmental impact of the building and thus, its energy demand (i.e. impact of its construction, heating and cooling, and lighting) are minimized, the model with the lowest environmental-impact cost is the one that has the longest section of the fac¸ ade facing south.

Adamski [11] solved the controversy between the most cost- efficient building shape and the most energy-efficient building shape. For this purpose, he formulated seasonal heating and con- struction costs based on building shape variables, such as height, volume, length of the curves defining each fac¸ ade, and orientation angle. The optimal solution obtained was composed of semi- circular boundaries for the northern section of the building and a curve for the southern part. He found that an oval base had a bet- ter thermal performance than a circular or a square base. The more or less oval shape of the base was directly related to the years of the building’s service life being considered. As the number of years increased, the values of the eccentricity axis of the oval became smaller and the result, less circular.

1. Orientation

Among the parameters that intervene in the passive solar design of buildings, orientation is the most important and the one that has been most frequently studied [20]. The level of direct solar radiation

Fig. 2. Building life cycle.

3562 R. Pacheco et al. / Renewable and Sustainable Energy Reviews 16 (2012) 3559–3573

received on the building fac¸ ade depends on the azimuth in the wall, and thus, on the orientation angle of the building [6]. The orientation of the fac¸ ade also influences other parameters of pas- sive design, such as shading [21] or the performance of the solar envelope [20]. Benefits derived from optimal building orientation are the following:

• It is a low-cost measure that is applicable in the initial stages of project design.
• It reduces the energy demand.
• It reduces the use of more sophisticated passive systems.
• It increases the performance of other complex passive tech- niques.
• It increases the quantity of daylight, reduces the energy demand

for artificial light, and contributes less to the internal heating load of the building.

• It improves the performance of solar collectors.

It is generally agreed that a southern orientation is optimal for gaining heat in the winter and for controlling solar radiation in the summer. As a general rule, the longest wall sections should be oriented toward the south [6]. However, orientation can also be studied with a view to optimizing other parameters such as the total solar radiation received, building shape, ground plan surface, and the annual energy demand.

• 1. Orientation and solar radiation received

Gupta and Ralegaonkar [15] optimized the orientation of a building for various shape factors with the objective of minimizing the solar radiation received in summer and maximizing it in the winter. The total energy gained by this radiation was calculated by applying Eq. (5).

ω2

r （ ＼= × × ×

E A (0.834 H) cos i dω (5)

cos e_z

ω1

where A is the surface area; H is the monthly mean daily global radiation on a horizontal surface; i is the incidence angle; dw is the hour angle at sunrise or sunset; e_Z is the zenith angle or polar angle. The authors optimized the value of the solar radiation received during the months of the most extreme climate conditions (June and December). This was done by using different shape values and varying the orientation angle from 0◦ to 180◦. This method can be used to find the optimal orientation angle for the reception of min- imum solar radiation in summer and maximum solar radiation in winter. The authors concluded that the optimal orientation was generally when the longest wall sections were oriented toward the

north and south.

Chwiduk et al. [22] studied the amount of solar radiation received by elements with different slopes and azimuth angles. For this purpose, they used two radiation models: (i) a diffuse isotropic sky model [23]; (ii) an anisotropic sky model [24]. They calculated the most suitable parameters for the same surface (wall or roof) to receive the maximum possible solar radiation in the winter and the minimum possible radiation in the summer. The influence of the tilt and orientation of the surface on the radiation level was most per- ceptible in the summer. They concluded that in order to maximize the solar energy gain during the whole year, the azimuth angle

of the surface should be approximately 15◦ even though angles

between 15◦ and 45◦ also provided good results. This procedure is especially useful for the installation of solar panels. It can be used to calculate the energy that they receive, and consequently, their effectiveness.

−

• 1. Orientation and shape

Aksoy and Inalli [9] studied the relation between building orien- tation and heat demand. For this purpose, they used three models with different shape factors (1/1, 1/2 and 2/1), with and without heating insulation on the fac¸ ade. They rotated the buildings 80◦, and obtained data at 10◦ intervals. Fig. 3 shows the heating energy saving rates, depending on the shape factor of the building and the azimuth angle of the north-south axis compared to a building without any insulation.

By combining shape factor, orientation, and heating insulation, a heating energy saving rate of up to 36% was achieved. It was deter- mined that the best orientation for rectangular buildings was when the longest walls were oriented toward the south. In square build- ings, the highest heating demand values were obtained when the

building was rotated at an intermediate angle of 45◦. They become

lower as the values 0 and 90 or multiples of these values were approximated (in other words, when one of the fac¸ ades of the build- ing began to face south). In buildings without insulation and with different building shapes a heating energy saving rate of 1–8% was obtained, depending on the orientation of the building.

Florides et al. [12] studied the relation between building orien- tation and shape. For a square building, they found that the heating demand reached its minimum value when the building fac¸ ade was directly oriented toward the four cardinal points. In a rectangular building, the heating demand was lower when a smaller portion of its surface faced east. According to the authors, the eastern ori- entation of the building surface was what most contributed to an increase in the heating energy demand.

• 1. Orientation and ground plan

Morrissey et al. [20] determined that buildings with a small ground plan were less sensitive to changes in orientation. In other words, they showed better thermal performance even when their orientation was modified in comparison to buildings of larger dimensions (>200 m2). The ground plan surface was found to be the most crucial factor in terms of adaptability to orientation change. They analyzed data pertaining to the heating and cooling energy demand obtained from a modeling experiment that focused on 81 different residential building designs. They obtained the statistical correlation between these energy demand values and the four vari- ables with the greatest repercussion on the thermal performance of the building (i.e. ground plan surface, wall/floor ratio, total external surface, and total window surface). The results showed that it was more difficult for larger residential buildings to perform at accept- able levels of energy efficiency. The most energy-efficient houses were less sensitive to orientation changes.

• 1. Building orientation and energy demand

The study of the optimal orientation of a building evidently increases energy saving [14]. Table 2 shows the energy saving in heating and cooling that resulted when a model of a large building was rotated 30◦, 45◦ and 60◦ in regards to the southern axis. The greatest energy saving was obtained when the longest walls were rotated 30% to the south.

According to Littlefair [25], most of the books, user guides, and manuals on passive solar techniques recommend that buildings should face southwards, although there is a growing consensus that

the best option is to orient buildings 20–30◦ to the south.

Shaviv [26] studied the orientation of the glazing surface of a building, and obtained the results shown in Table 3. She concluded that in order to obtain maximum energy saving, the main glaz- ing surface should face south, especially in countries with a hot

R. Pacheco et al. / Renewable and Sustainable Energy Reviews 16 (2012) 3559–3573 3563

Fig. 3. Heating energy saving, depending on shape factor and orientation [9].

and humid climate. If this is not possible, the building should face southeast.

1. Influence of the building envelope in the energy demand

The building envelope (foundation, roof, walls, doors, and win- dows) and the operation period of the heating system are the factors that have the greatest impact on the total energy consump- tion of the building [27]. The envelope determines interior climate conditions, and thus, the additional energy demand for heating and cooling. Actions on the elements that make up the building

Table 2

Energy saving obtained, based on the orientation of a rectangular building [14]. Energy saving ($/year)

Installation Change in orientation (in reference to

the south)

envelope can have a positive impact on certain energy require- ments and have a negative affect on others. Consequently, it is necessary to evaluate the performance of the building as a whole [28].

• 1. Heat transfer formulas: optimization of the limit U value

Design parameters that affect indoor thermal comfort and energy conservation are orientation and shape, as well as the optical and thermophysical properties of the fac¸ ade or building envelope. The heat transfer coefficient (U) determines heat loss per unit area of the components of the building envelope. It is frequent for authorities to establish a maximum value of U in order to control heat loss in buildings and guarantee the comfort of the occupants.

Table 3

Energy consumption of an office unit at three different orientations [26].

Energy consumption at three orientations (kWh/year)

30◦ 45◦ 60◦

Heating	29	26	36		South	%	East	%	West	%
Cooling	58	15	0	Heating	186	0	231	24	219	18
Heating, ventilation, and	53	38	23	Cooling	281	0	286	2	369	31
air conditioning (HVAC)				Total	467	0	517	11	588	26

Total 140 79 59 Tmax (◦C) 26.4 26.6 27.0

3564 R. Pacheco et al. / Renewable and Sustainable Energy Reviews 16 (2012) 3559–3573

For Oral and Yilmaz [29], the transfer coefficient of the building fac¸ ade should be calculated on the basis of the compactness index (total fac¸ ade area/volume). The maximum heat loss in a reference building can be calculated with Eq. (6).

q = U₀(ti − t_eo)(1 − X) + U_g(t_i − t_eg)X (6)

where q is daily heat loss; U₀ and U_g are heat transfer coefficients of the opaque components and the transparent components, respec-

tively; t_i is the inside temperature; t_eo and t_eg are the mean sol–air temperatures of the opaque and transparent components; X is the

that have been used to perform an economic evaluation of building fac¸ ade insulation.

C¸ omakli and Yüksel [32] used the concept of present worth factor (PWF) to find the optimal thickness of building fac¸ ade insulation. They formulated Eq. (7), which determines the most cost-effective insulation for various economic parameters, insula- tion materials, and climate conditions.

PWF DD C k

x₀ = 293.34

f

− kR_r (7)

C_iH_uµ

C_iH_uµ

transparency ratio.

Using graphical methods, these authors determine the maxi- mum possible U for values with other compactness indexes.

The method, which was developed by Maniog˘lu and Yilmaz [27], obtained the combination of building envelope and heating system operation that provided thermal comfort conditions at minimum

cost during the life cycle of the building. This procedure determined

where DD represents degree days (◦C day); C_f and C_i are the cost of fuel and insulation, respectively; H_u is fuel heating power; R_r is the thermal resistance of the fac¸ ade; µ is the heating system efficiency; k is a numerical constant.

The PWF is formulated by Eq. (8).

1 − (1 + r)^−N

the optimal materials of the envelope, which as a whole, satis-

PWF =

(8)

r

fied the maximum heat coefficient transfer of the building. For this purpose, they took into account the best combination of materials that provided this U value, the total heat loss, and the economic costs of the heat system operation as well as of the life cycle of the components. For each envelope that satisfied this condition, they studied various operation periods until finding the most eco- nomic and energy-efficient solution. It should be underlined that the optimal solution might not coincide with the option producing the lowest heat loss through the building fac¸ ade.

The effectiveness of actions to improve the thermal performance of the envelope depends on building type and use. It has been shown that in residential buildings with a reduced window/wall ratio, the use of an optimal level of insulation in the building fac¸ ade considerably reduced the energy demand, especially for heating [30]. In contrast, this procedure is not effective in buildings whose fac¸ ade is predominantly made of glass, as is the case of many com- mercial office buildings [28]. The improvement in the U value of these buildings does not involve a reduction in outside heating gain, whereas an action affecting the type of glazing can improve thermal performance.

• 1. Building insulation and economic analysis

Jinghua et al. [31] used an eQUEST simulation to study the effect of the thickness and the position of building fac¸ ade insulation on the total energy demand, among other things. By using a combined optimization strategy for insulation, window/wall ratio, glazing and shading system, they achieved a reduction of up to 25.92% in the total heating and cooling demand. However, after a certain insulation thickness threshold was surpassed, the energy reduction continued, but at a significantly lower rate.

The position of the insulation layer (external surface, inter- nal surface, within the wall itself) has little repercussion on the annual electricity consumption although a minimum consumption is obtained when the insulation is located on the inside wall surface. In contrast, if the cooling energy consumption is considered sepa- rately, the insulation placed within the wall was found to consume more electricity than the other options. The minimum electricity

where N is the number of years in the building’s life cycle, and r is the interest rate adjusted for inflation, according to Eq. (9).

r I − g (I > g) (9)

=

1 + g

where I is the interest and g is the inflation.

Optimal insulation thickness was found to be inversely pro- portional to the cost of the insulation material and its thermal conductivity. An overly thick insulation layer resulted in an unnec- essarily high initial cost that was not compensated by the fuel reduction. Furthermore, a very thin insulation layer was more eco- nomical at the beginning, but ultimately generated higher fuel costs. These authors found that the optimal insulation thickness maintained a linear relation with the PWF.

In the study by Lollini et al. [30], the optimization of the insu- lation levels of the opaque components of the building envelope was performed by carrying out a three-level analysis: energy, econ- omy, and environment. The calculations were performed with EC501 simulation software, created to evaluate the energy and cost performance of various thermal insulation combinations for two reference buildings. They also used the PWF of the insulation material, which represents the cost difference between the initial investment in additional insulation in reference to the estimated annual cost savings during the building’s life cycle. They applied formulas created by Augelli [33], and calculated the PWF by apply- ing Eq. (10) with parameters related to the heat transfer value of the insulation and its mean thickness.

NPV = R − Inv = ((U₀ − U) · 24 · DD^∗ · EPC) − (m · s + q) (10)

where DD* is a parameter that depends on the level of insulation and inside gains; U₀ and U are the reference heat transfer and the insulation heat transfer, respectively; R is the annual energy sav- ing; Inv is the initial investment; s is the thickness of the insulation layer; m and q are the fixed costs and the variable costs of the building material.

Based on this equation, the heat transfer value U of the material can be optimized. Eq. (11) expresses the energy present cost (EPC).

P₀ · r · [(r/vN − 1)]

consumption value for cooling was obtained with an insulation layer of 25 mm, where the minimum value for heating was obtained

EPC =

(11)

µ · NVC · (r − v)

with an insulation layer of 100 mm.

These differences mean that an economic analysis is needed to calculate the insulation layer thickness that is most cost-effective and energy-efficient. However the results of such an analysis may indicate that the most economical insulation layer thickness does not correspond to the optimal insulation obtained for each element individually, or to the insulation providing the lowest heat transfer value U in the building [30]. In this regard, there are two methods

where P₀ is the annual cost of city gas; µ is the overall efficiency of the heating system; NVC is the net calorific value of the gas; N rep- resents the life cycle (i.e. 30 years); r and v are financial indicators of inflation and interests, respectively.

These results seem to agree with the previous ones [31]. Effec- tively, once a critical threshold has been reached, a massive increase in the thickness of the insulation layer does not lead to a significant improvement in the heating performance of buildings. Even though

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the heating demand diminishes as the insulation level increases, the dependency relation between these two elements is somewhat less well defined. Consequently, the effectiveness of increasing the insulation (or reducing the heat transfer of the building envelope) as a method for reducing heating demand is effective only up to a certain point, after which a massive increase in insulation contin- ues to produce a reduction in the heating demand, but at a lower rate.

Even so, these authors affirm that this may occur because the addition of insulation takes place in different parts of the build- ing (walls, roofs, floors) that have different weights in the overall external surface, resulting in a discontinuity of the heating load profiles.

The specification of the most cost-effective overall insulation level is not as precise as in the case of separate building compo- nents [30]. As the level of building insulation increases, the PWF also increases until it reaches an optimal level after which for an overly insulated building, there is only a slight increase in the PWF. The optimal insulation level chosen by the authors was the level that produced the highest PWF, which is compatible with the lowest Pay Back Rate (PBR).

• 1. Environmental study of the building envelope

Other studies have opted for performing an environmental anal- ysis instead of a cost analysis. Pulselli et al. [34] carried out a thermal and energy analysis as well as an emergetic evaluation to evaluate the environmental cost and benefits of building fac¸ ades. Emergy was evaluated by means of the procedure created by Odum [35], in which emergy is defined as the amount of solar energy used, directly

1. Shading on buildings

Shading on building fac¸ ade elements controls the amount of solar radiation received by the building. This strategy provides pos- itive results when actions are performed on the building fac¸ ade cavities since these are the elements that transmit the highest level of radiation to the inside of the building.

• 1. Shading coefficient

A suitable shading coefficient saves energy throughout the year [38]. The American Society for Heating, Refrigerating and Air-conditioning Engineering (ASHRAE) includes the shading coef- ficient (SC) among the factors that should be taken into account in the calculation of the heating and cooling demand of a building. This coefficient is defined as the ratio of solar heat gain through a given fenestration system under a specific set of conditions to the solar heat gain through single glazing of standard 3 mm clear glass, as shown in Eq. (12).

SC solar heat gain factor of fenestration (12) solar heat gain factor of reference glass

=

One of the problems of establishing a fixed shading coefficient is that the angle of incidence of solar rays does not remain constant [39]. Various research studies have been carried out to develop a reliable method or system of calculating this shading coefficient [39,40].

The procedure to calculate optimal shading proposed by Yang et al. [38] transforms the energy saving from shading in sum- mer and solar penetration in winter into energy savings in the equipment. They used Eq. (13) to calculate the total annual energy savings, depending on the value of the shading coefficient:

or indirectly, to obtain a product or final service. Three models were compared:

SEC =

Q_S × (1 − SC + Q_W × SC)

Q_S + Q_W

(13)

• A conventional air cavity wall with insulation.
• A cavity wall with an external cork covering added.
• A ventilated wall with external brick panels fixed on an extruded frame.

The study was performed for cold, warm, and hot climate con- ditions. The authors concluded that the building wall with the additional insulation layer as well as the ventilated wall had a bet- ter thermal, energy, and emergy performance. In terms of natural resources, the emergetic analysis assigned a more important role to regions with a hot and warm climate. This was due to the fact that the reduction in cooling demand provided greater environmental benefits than the reduction in heating demand. Generally speak- ing, air conditioning systems operate with electricity (which has a greater environmental impact), whereas heating systems use other fuels.

Chel and Tiwari [36,37] studied the environmental impact of a mud house by estimating the thermal performance, embodied energy, energy payback time, CO₂ emission mitigation potential and corresponding carbon credits. The adobe house temperatures are temperate throughout the year and it leads to energy sav- ing potential. It was determined an annual heating and cooling energy saving potential as 1481 kW h/year and 1813 kW h/year. The authors estimated that on an average adobe or mud-house can mit- igate 5.2 metric tons/year CO₂ emissions in to the atmosphere. The authors concluded that it must be chosen not only the material with the lower embodied energy but also with the lower environmental impact.

where SEC is the solar radiation synthetic energy savings coeffi- cient; SC is the shading coefficient; Q_s is the summer energy savings gain from shading; Q_w is the winter energy savings gain from solar penetration.

In hot climates, there are greater energy benefits with a high shading coefficient since heating gains are reduced. However, the shading coefficient should not be excessively high [38]. If these energy gains are transformed into economic costs, in terms of the price of fuel used for the heating and cooling systems, the economic balance is not as close to a high shading coefficient as the energy balance.

• 1. Effectiveness of shading devices

In the same way as with other energy-saving devices in the building, the use of shading devices can be beneficial at certain times of the year though they are counter-productive at other times [38]. Control of shading is necessary in order to assure thermal and visual comfort inside the building. Passive shading systems favor a reduction of the heat gained by the building, which means that cooling systems are not operated as frequently. Nonetheless, they have the drawback of reducing daylight availability [41]. Protect- ing buildings from excessive shading increases the hours of daylight and reduces the use of artificial light. This generates energy savings as well as cost savings, and also provides occupants with greater comfort since daylight is more comfortable than artificial light. The reduced use of artificial light also brings with it a reduction in the heat generated in the building [25].

Shading can be provided by neighboring elements or come from systems incorporated in the building itself. As the use of solar energy (e.g. solar panels) becomes more widespread, there will be a

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Fig. 4. Effect of overhang on incident radiation through a window.

greater need to standardize methods for the evaluation of shading on buildings as a consequence of their proximity to other construc- tions. The energy benefits of shading are obviously conditioned by the climate of the building site.

• 1. Energy benefits of the shading in hot climates

The control of shading elements, lighting as well as heating and cooling components could significantly reduce peak cooling load and energy consumption for lighting and cooling, while maintain- ing suitable heating and lighting conditions [41].

• • 1. Roller shades and overhang

One problem with shading devices, such as roller shades and overhang, is that they are often designed to remain in one posi- tion. This evidently favors energy saving in certain situations, while hampering it in others. According to Bouchlaghem [40], shading devices should be designed so that their position can be adapted to the season of the year. The building would thus be shaded in the summer, but not in the winter. This study performed a TRANSYS simulation which showed that by increasing the solar protection provided by overhang, the annual cooling demand decreased as the heating demand increased [12]. This was due to the fact that these devices blocked part of the solar radiation that is so benefi- cial in winter. Both positive and negative effects were accentuated when the windows were more oriented toward the south since they received more annual solar radiation. As a result, it could be advantageous to use long projecting horizontal overhangs that can be folded back or removed in winter.

The use of mobile shading systems is more beneficial in regards to natural illumination and to lower energy consumption. Tzem- pelikos and Athienitis [41] compared the effectiveness of fixed passive shading systems with a simple automatic shading system

(automatic roller shades). They had them operate alternatively and calculated the light transmitted into the room by applying Eq. (14).

D E_b ∗ r_b + E_d ∗ r_d (14)

=

1 − pr_rs ∗ p_w

where D is the transmitted radiation into the room; r_b is the beam window transmittance; r_rs is the roller shade transmittance; p_rs is the roller shade reflectance.

They thus managed to increase the annual daylight availability by 20%. This led to energy savings in artificial light as well as to greater productivity.

Overhangs avoid the entry of direct radiation through the win- dow at certain times of the day. This has the advantage of regulating the entry of excessive heat and daylight as shown in Fig. 4.

Florides et al. [12] quantified the effect of overhang length on energy demand. They found that a longer horizontal overhang reduced the cooling demand and increased the heating demand.

Robert and Jones [42] measured the ratio between overhang dimension and winter solar radiation. This study describes a method to calculate the optimal overhang dimensions for a specific emplacement. When these dimensions were surpassed, the winter heat loss was not compensated by the reduction of solar radiation in the summer.

• • 1. Self-shading

An appropriate building design can cause the building to shade itself without the need of additional elements. This can be benefi- cial especially in the case of isolated buildings that are subject to excessive quantities of direct solar radiation. This idea led to the concept of self-shading. The most widely used building shape for this purpose is the inverted pyramid [21]. Certain architects opt for making all walls slant inwards, such as in the Tempe City Hall. One problem with such a design is that since all windows slant inwards as well, less of the window surface receives solar radiation, and consequently, window size must be increased. This inconvenience

Fig. 5. Self-shading buildings [21].

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can be avoided by using a stepped inverted pyramid design (e.g. the Bank of Israel). In such a building, the window surface is not affected. Fig. 5 shows examples of buildings with this design.

Depending on the degree of inclination of the building fac¸ ade, the shading period is of longer or shorter duration. When the angle is greater, the building will be shaded for a longer time. Because of this, the use of self-shading fac¸ ades is only useful when a limited number of hours of shading are needed since in the opposite case, the walls would be excessively inclined.

• 1. Energy benefits of shading in cold climates

The amount of sunlight that enters a building through the win- dows depends on the latitude, climate, daylight availability at the emplacement, incident angle of solar radiation, obstruction created by other buildings, and the energy reflected by neighboring ele- ments [43]. The procedures used to study sunlight availability at a specific site or location can be classified as follows:

• • • • Graphical methods [44].
      • Analysis of the obstruction angle [25].
      • Solar envelope [45].
      • Computer simulation methods [46].
    1. Shading cast by neighboring buildings

Site layout has the greatest impact on passive solar heating. According to Littlefair [44], the loss of solar light and the heat gain from neighboring constructions are characteristic parameters of any large city. High buildings and other nearby constructions affect the distribution of natural light inside a building and block the entry of sunlight, particularly in the winter. Fig. 6 is an example of an obstruction angle. There is a need for more research on how obstructions can affect the reception of diffuse radiation. As the urban area becomes denser, current methods for the calculation of solar radiation obstructed by the proximity of other buildings become less precise.

The obstruction angle can be calculated by graphical methods, using diagrams of the sun’s path. Fig. 7 depicts a solar diagram for a latitude of 55◦, and shows the impact of obstruction angles of 10◦

and 40◦. As can be observed, an obstruction angle of 10◦ allows the

building fac¸ ade to receive most of the solar radiation, whereas an angle of 40◦ blocks all sunlight from September to March.

Table 4

Light obstruction angles due to nearby elements, depending on emplacement lati- tude [25].

Latitude Climate Obstruction angle (◦C)

35 Mediterranean 40

40 Warm Mediterranean 35

45 Temperate 30

50 Temperate 25

55 Moderately cold 22

60 Sub-arctic 20

It is thus possible to specify the limit values for angles of neigh- boring elements. When these angles are surpassed, the occupants of the building perceive a reduction in daylight with the subse- quent increase in the demand for artificial light. Table 4 shows the maximum value of the obstruction angle for which a building can keep receiving sufficient sunlight, depending on the latitude of its emplacement.

Access to passive solar radiation in buildings is an inalienable right and should be protected by national law or local urban plan- ning [44].

The need to receive solar radiation in winter should not only be taken into account during the project design phase of the building, but also during the design phase of entire neighborhoods including sidewalks and open spaces. This means that each district should be projected as an optimized system which should receive the appropriate amount of sunlight to make it energy efficient and to guarantee the comfort of its occupants. The design guidelines

Fig. 6. Section of a building showing an obstruction angle of 25◦ [25].

Fig. 7. Solar diagram for a latitude of 55◦ with obstruction angles of 10◦ and 40◦ [44].

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Fig. 8. Solar volume as the conjunction of the solar rights envelope (upper plane) and solar collection envelope (lower plane) [45].

proposed by Capeluto and Shaviv [45] are based on obtaining the solar volume of buildings, depending on their location and orien- tation, as shown in Fig. 8.

These authors use such graphical representations to determine building height, street width, and overall building shape orienta- tion in order to obtain the highest possible urban density levels combined optimal solar exposure.

1. Passive systems

Passive techniques of temperature control and inside humidity were first employed in ancient times. With the widespread use of electrical energy, these methods gradually became obsolete [47]. However, in developed countries, especially those with very hot climates, there is currently a growing interest in these low-cost systems for the passive cooling of buildings [48]. These mecha- nisms are based on the natural convective movement caused by the different densities of cold and hot air [49]. However, the term passive does not exclude the use of a fan or pump to enhance sys- tem performance. Even though passive systems highlight the use of natural heating or cooling sources, some type of power is nec- essary to initially start operation. Since the passive heat transfer system is low cost and simple, the ratio of power consumption to the total consumption of the installation is relatively low [48]. The type of passive system chosen will influence different aspects of the design.

• 1. Passive cooling

Passive cooling is defined as the limitation of heat inside buildings by means of natural processes to expel heat into the atmosphere (i.e. convection, evaporation, and radiation), or into the ground beneath buildings (i.e. conduction and convection) [47]. This section follows the classification of passive cooling systems elaborated by Givoni [50] and summarized in Fig. 9.

The efficiency of passive cooling systems is closely related to the nocturnal and diurnal outside temperature gradient with maximum temperature peaks, depending on the location. Certain passive cooling procedures are immediately effective (e.g. natu- ral ventilation and direct evaporative cooling). Other systems store cold energy in the structural mass of the building. The main factor that constrains the efficiency and applicability of such systems is the limited capacity of the structural mass of the building to store thermal energy [48]. The following sections are a summary of the most important types of passive cooling methods listed in Fig. 9.

• • 1. Natural ventilation

Natural ventilation is also known as comfort ventilation, and is based on the positive psychological effect of a suitable air flow throughout the building. In hot humid climates, this effect con- siderably improves the feeling of well-being of the occupants, even when the temperature and humidity conditions of the air from the

outside is the same as those of the inside air. Therefore, daily ven- tilation is necessary to minimize the psychological effect of high humidity and improve the convective loss of body heat [48]. The term advanced naturally ventilated building was coined to designate buildings that use the stack effect (natural movement of air due to differences in temperature and density) to drive an air flow [51]. Fig. 10 shows an example.

• • 1. Nocturnal convective cooling

Nocturnal convective cooling cools the structural mass of the building by means of nocturnal ventilation. Closing the building during the day keeps indoor temperatures from rising. This pro- cedure is especially applicable in arid or desert regions with high daytime temperatures, and where the minimum night temperature in summer is lower than 20 ◦C. It is also effective in non-residential buildings with a high cooling demand and with no night occupa- tion, such as academic buildings or offices. Nocturnal ventilation helps to reduce demand peaks and operation periods of electrical cooling equipment. Research has shown that the mean tempera- ture of a building can be reduced by up to 3 ◦C with this type of ventilation [50].

• • 1. Radiant cooling

Radiant cooling requires the construction of roofs made of heavy and highly conductive material (e.g. concrete) as well as insulation material. During the day, the external insulation on the roof mini- mizes the heat gain from solar radiation. The cooled roof mass can then act as a heat sink, and absorb, through the ceiling, the heat penetrating into and generated inside the building during the day- time hours. This system is effective and related to radiant heat loss during the night [48].

• • 1. Evaporative cooling

Evaporative cooling takes advantage of fresh air currents to cool buildings by means of the direct or indirect evaporation of the water in the air. One example of direct evaporation is the placement of wetted pads made of fibers in the windows. A drawback of this system, however, is that the pads block the view through the win- dows [48]. In indirect evaporation systems, the moisture content of indoor air does not increase. The air from the outside enters the roof, which is at a lower temperature. From there, the cool air is distributed throughout the building by means of convection. Exam- ples of indirect evaporation are: (i) thatched rooftops that absorb moisture during the night, which then evaporates during the day;

(ii) a pond on the roof [47]. This method conceived by Raman [49] (see Fig. 11) is one of the most effective and achieves the greatest reduction in indoor temperatures [47].

This system involves the installation of sack-cloth gunny bags or other dampened material to cool the air that enters the roof through the upper ventilation cavities. This is combined with a solar chim- ney to maintain the convective movement in the building, such that when the cool air comes into contact with this partition, it warms

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Fig. 9. Classification of passive cooling systems [50].

Fig. 10. Operation of a natural ventilation system.

Fig. 11. Evaporative cooling system [49].

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Fig. 12. Trombe wall models.

up, becomes less dense, goes up the wall, and leaves through its upper cavities. In winter, it can be beneficial to remove the wet bags, and thus modify the place where the air enters. This system maintains indoor temperatures 10 ◦C lower in summer and 15 ◦C higher in winter in relation to the outside temperature [49].

• • 1. Earth-air cooling

Earth-air cooling takes advantage of the thermal inertia of earth to cool the building. In this type of system, buildings can be either totally or partially underground. Alternatively, underground air conducts can also be installed. In temperate climates, the natural temperature of the earth in summer at a depth of 2–3 m can be sufficiently low so that the earth can be used as a cooling source. In warmer climates, the natural temperature of the earth in summer is generally too high for this [48].

• 1. Passive heating

Passive heating options, based on thermo-physical properties as well as on the configuration of building envelopes can eliminate up to 2/3 of thermal discomfort [52]. The passive use of solar energy uses certain building elements (walls, roof, glazing) to store heat. The degree of effectiveness of these systems depends on climate conditions, construction materials, and the direct or indirect use of solar energy [8].

Enclosed spaces with direct solar gains, such as solariums, pro- vide extra surface for the absorption of solar radiation as well as additional mass for its storage. They are the most effective systems for heating and daytime lighting in the building [52]. More research has been done on passive heating methods than on passive cooling methods [49]. Generally speaking, passive mechanisms work better when they operate in combination with each other [53]. The follow- ing sections describe the most important passive heating methods for buildings.

• • 1. Trombe wall

A Trombe wall is a wall separated from the outdoors by glaz- ing and an air cavity. It also has vents at the top and bottom of the interior wall, to control air flow. Solar energy is stored in the wall, and subsequently conveyed to the inside of the building by conduction. Hot air is released through upper air vents. Cold air

enters the space between the wall and the glazing through the lower air vents, and comes in contact with the wall, which makes its temperature rise. Afterwards, the cycle begins again [53]. Many researchers have tried to improve the basic design. Fig. 12 shows various examples [53,54]: (a) a conventional Trombe wall design;

(b) a Trombe-Michel wall with an insulation wall between the glaz- ing and the wall; (c) a design in which the massive wall is replaced by a lattice wall).

The lattice wall improves thermal efficiency by almost 18% (obtaining an efficiency of up to 30.2%). It also has the advantage of using 35% less concrete in its construction [54].

• • 1. Solar chimney

The solar chimney is based on natural convective air movement stemming from the variation in density of indoor air currents. In those cases in which the chimney is attached to the building wall, it operates similarly to the Trombe wall, and also provides benefits in the summer. Despite its positive results, the use of a solar chimney is not always feasible for aesthetic reasons [53]. Depending on the distribution and opening of air vents, the solar chimney can act as a natural ventilation system, passive heating method, or thermal insulation device, as shown in Fig. 13.

• • 1. Unglazed transpired solar fac¸ ade

This solar fac¸ ade is composed of metal sheet with holes, as shown in Fig. 14. The outside metal cladding receives solar radi- ation, and the air that enters (with the help of a fan) through the holes to the inside of the building is thus heated. The heated air is then ducted into the building via a connection to the heating system. Experimental results show that this system can provide savings in energy consumption of up to 1 MWh/m2 year, with an effectiveness of up to 63–68% [53]. It is also more economical to build than the Trombe wall.

1. Glazing

Window glazing is one of the weakest thermal control points in building interiors. In a standard family residence, 10–20% of all heat loss occurs through the windows [55].

Fig. 13. Solar chimney models.

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Fig. 15. Light transmission through angle-selective glazing.

7.3. Film-plating glazing

Fig. 14. Operation of solar fac¸ ade.

• 1. Thermal comfort and indoor illumination

In glazing design, it is necessary to consider performance in terms of heat transfer, thermal comfort, light transmission, and appearance [56]. Window glazing that reduces the entry of solar radiation is most effective in summer and reduces the cooling demand. In contrast, in winter, this type of glazing increases the need for heating because it hinders the use of solar energy for passive heating. The development of glazing that reduces the quan- tity of solar radiation should not affect the possibility of seeing through windows, especially when a large amount of natural light is required, such as in office buildings. A reduction in natural day- light causes a corresponding increase in artificial light. This signifies higher energy costs and as well as an increase in indoor tempera- ture [57]. Furthermore, design solutions that improve the amount of daylight entering windows are often associated with a potential risk of inside overheating [39,57] and an increase in the cooling demand in hot seasons when temperatures are high.

• 1. Glazing types

Glazing that provides energy savings can be classified in the following types [38]:

• Heat-absorbing glass: this glazing transforms solar radiation in heat energy (i.e. increasing its temperature), and distributing heat throughout the room by means of convection and radiation to reduce the direct radiation through the glass.
• Heat-reflecting glass: this glazing has a coating or film that blocks

the entry of solar radiation into the building.

• Low radiation glass: this glazing also has a coating or film which reduces the heat transfer coefficient. It can also facilitate energy saving in winter.

Film-plating glazing is treated with layers of another material to improve its thermal performance. The most common coating is done with metals (Cr, Ti, Ag and stainless steel), metal nitrides (CrN, TiN, ZrN), or metal oxides (SnO₂, TiO₂, ZnO). The coating layers can be low-emissivity films, reflective films, tinted films or spec- trally selective coating. Generally, most of them involve a high-cost process [58].

The thermal performance of this glazing depends on its spectral properties. To evaluate its effectiveness in terms of thermal comfort and heat transmission, the total transmission properties and total absorption of the glass should be evaluated simultaneously [56].

The coating or film applied to the glazing reduces its transfer level and at the same time increases its absorption level. A high heat transfer intensifies the risk of overheating within the building. Moreover, a high absorption increases the temperature on the glaz- ing surface. When the coating is applied to the glazing, this reduces the negative effect of the solar radiation on the building. However, the temperature of the glass surface reaches undesired levels and the level of natural illumination inside the building is reduced. Glaz- ing with an additional coating (except for heat reflecting glass), which has a high heat transfer value, causes greater discomfort to the occupants [56].

Gijón-Rivera et al. [58] found a solution for this problem. They developed glazing with an internal coating that blocked the exces- sive heating of the glass. They evaluated the effectiveness of glazing coated with a combination of chemicals (SnS and Cu_xS) which lim- ited the access of light and heat to the building. They found that the energy saving from the use of optimal glazing was influenced by the climate where the building is located.

• 1. Angle-selective glazing

The intensity of solar radiation depends on its angle of incidence. Solar rays with a larger angle (at noon and in the summer) provide more radiation. A system that selects the angle of the rays that enter the building can effectively control heat.

For this purpose, angle-selective devices can be embedded in the glazing, incorporated in new objects placed between the panes, or be part of elements attached to the inside or outside win- dow frames. There are a wide variety of elements of this type, such as roller blinds, screens, fixed or mobile louvers, and even glass-enclosed surfaces for the redirection of sunlight entering the building [59].

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Fig. 16. Architectural solutions for glass rotation [60].

Reppel and Edmonds [57] developed glazing that was able to select the rays entering the building, depending on their incidence angle. This did not negatively affect the transparency of the glass. In this system, horizontal laser-cut panels were placed inside the glazing. When the sun rays came in contact with these panels, they underwent a series of reflections, which deflected them from their initial path. Based on the distance between the laser-cut panels as well as their width, these authors calculated the path of each sun- ray. They managed to deflect or reflect those rays with the largest incidence angle so that only those rays with a smaller angle could penetrate the building. They formulated the fraction of sunrays reflected as an equation based on the incidence angle. Fig. 15 shows how solar rays are transmitted through angle-selective glazing.

• 1. Glazing that provides spectrum selection

Still another option is to install glazing with spectrum selection, and thus control radiation according to wavelength [55,59].

• 1. Construction solutions
     1. Glass rotation in respect to the building

Glass rotation effectively modifies the amount of heat entering the building through the windows. The modification of the angle between the glazing and the building fac¸ ade involves changes in the intensity of the solar radiation received and thus in heat gains [60]. Construction solutions that amplify the rotation angle of the win- dowpane can considerably increase the area that receives sunlight, and thus, the solar heat gain. Saleh et al. used a computer simula- tion model to study the advantages of glass rotation. They found that, thanks to horizontal glass rotation, solar heat gains increased by a total of 63% in comparison to a simulation in which there was no glass rotation [60]. The main drawback of this system was that heat gains also increased in summer since this system is perma- nent and cannot be moved. The cooling was thus increased. Fig. 16 shows various solutions of this type.

• • 1. Double glazing

Another way of optimizing window performance is through the use of double glazing. This is an effective method for both hot and cold climate conditions [58]. In hot climates, the best option is dou- ble clear glazing, and in cold climates, double glazing with a film coating that limits the heating of the window surface.

• • 1. Advanced daylighting systems

The objective of advanced daylighting systems is for daylight to reach the center of the building spaces. The components of these systems are sunlight duct systems or solar tubes, solar pan- els located on the roof, optical collection systems, and special

collection systems on the walls [59]. However, the performance of these systems is difficult to evaluate because of the complex nature of the angle-selection mechanisms.

1. Conclusions
2. The importance of energy consumption in the residential build- ing sector makes it necessary not only to carry out basic research on the thermodynamic operation of the various sys- tems designed to save energy. However, it is also necessary to formulate project criteria linked to the sustainability of these buildings. Based on the overview of recent research provided in this article, the following conclusions can be derived.
3. The sustainable design of buildings reduces the energy demand for heating and cooling.
4. The implementation of these measures in the project design phase reduces the final cost of the building.
5. The benefits of an energy-efficient building design should be evaluated for the entire life cycle of the building.
6. Factors with the greatest repercussion on the final energy demand are building orientation, shape, and the ratio between the external building surface and building volume.
7. Building design measures that are beneficial for one season of the year are not necessarily beneficial for the other seasons. Insulation systems should be developed that are capable of changing their configuration or performance as outside climate conditions vary.
8. A more energy-efficient building design does not necessar- ily coincide with more economical or more environmentally friendly designs.
9. Mobile shading devices offer greater benefits than fixed shading devices.
10. Conventional methods of estimating solar radiation lose their effectiveness as the urban area increases in density. More research is thus needed to determine the level of sunlight or diffuse radiation received in such areas.
11. More research should also be carried out on the influence of urban texture on the energy efficiency of city buildings.
12. The use of glazing that limits the access of radiation to a building should not affect the quality of inside illumination or bright- ness.
13. The study of optimal orientation and tilt improve the perfor- mance of solar panels. The angle of inclination depends on the

operation of the installation. In this regard, panels should be tilted 10–25◦ if they only operate during months with high

temperatures; 50–65% if they operate during months with low temperatures; and 30◦ if they operate all year around.

R. Pacheco et al. / Renewable and Sustainable Energy Reviews 16 (2012) 3559–3573 3573

Acknowledgments

This study was funded by research contract No. C-3513 between Ferrovial Agromán S.A. and the Fundación General UGR-Empresa of the University of Granada.

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