an der Fakultät VI – Planen Bauen Umwelt

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Energy Efficiency Improvement of Residential Building Fenestration

Case studies: Tehran and Berlin

vorgelegt von M. Sc.

Mohammad Reza Razavi

an der Fakultät VI – Planen Bauen Umwelt der Technischen Universität Berlin zur Erlangung des akademischen Grades

Doktor der Ingenieurwissenschaften - Dr.-Ing. –

genehmigte Dissertation

Promotionsausschuss:

Vorsitzender: Prof. Claus Steffan Gutachter: Prof. Dr.-Ing. Klaus Rückert Gutachter: Prof. Dr.-Ing. Jürgen Ruth

Tag der wissenschaftlichen Aussprache: 27. November 2019

Berlin 2021

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Energy Efficiency Improvement of Residential Building Fenestration

Case studies: Tehran and Berlin

PhD student: Mohammad Reza Razavi Supervisor: Prof. Dr.-Ing. Klaus Rückert

Thesis submitted for the degree of Doctor of Philosophy

Department of TEK Institute of Architecture Technical University of Berlin

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Acknowledgment

I would like to thank my respectable supervisor, Professor Dr.-Ing. Klaus Rückert, for his effective advice and patient guidance that he provided throughout my research.

I would like to thank my dear wife Chonour Pejouli, for her love and constant support.

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Table of Contents:

Abstract, English ... IX Abstract, German ... X

1. Chapter one: Introduction ... 01

1.1. Introduction ... 02

1.2. Statement of the Problem ... 02

1.3. Research Objectives ... 03

1.4. Significance of the Research ... 03

1.5. Research structure ... 04

2. Chapter two: Literature Review ... 05

2.2. Window technology ... 06

2.2.1. Glazing ... 06

2.2.1.1. Multilayer glazing ... 06

2.2.1.2. Suspended films ... 07

2.2.1.3. Vacuum glazing ... 07

2.2.1.4. Low-emissivity coatings ... 07

2.2.1.5. Smart windows ... 08

2.2.1.6. Solar cell glazing ... 08

2.2.1.7. Self-cleaning glazing ... 08

2.2.1.8. Aerogels ... 08

2.2.1.9. Glazing cavity gas fills ... 09

2.2.2. Spacers ... 09

2.2.2.1. Foam spacers ... 09

2.2.2.2. Thermoplastic spacers ... 09

2.2.2.3. Metal-based spacers ... 09

2.2.3. Frames ... 10

2.3. New technologies of fenestration ... 10

2.3.1. Water-flow window ... 10

2.3.2. Switchable triple glazing exhaust air window ... 10

2.3.3. Cooling pipes embedded in venetian blinds ... 11

2.3.4. Future of aerogel glazing in energy efficient buildings ... 11

2.3.5. Super insulated aerogel windows ... 12

2.3.6. Thermochromic fenestration with VO2-based materials ... 12

2.3.7. Vacuum glazing for highly insulating windows ... 13

2.4. Window’s energy parameters ... 13

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IV

2.5. Basic concepts of windows energy efficiency ... 14

2.5.1. Insulating Value ... 14

2.5.2. Solar Control ... 16

2.6. Energy codes ... 18

2.6.1. Building energy codes ... 18

2.6.2. Benefits and development of Building Energy Codes ... 19

2.6.3. Building energy codes in Germany ... 19

2.6.4. Building energy codes in the United States ... 20

2.6.5. Building energy codes in Iran ... 21

2.6.5.1. Young Cities Project ... 22

2.7. Influence of Fenestration dimension on energy consumption ... 23

2.8. Conclusion ... 29

2.9. References……….…….30

3. Chapter three: Research Methodology ... 33

3.2. Climatic condition ... 34

3.2.1. Tehran ... 34

3.2.2. Berlin ... 35

3.3. Model description ... 36

3.3.1. Geometry ... 36

3.3.1.1.1. Construction ... 36

3.3.1.2. Iran construction ... 37

3.3.1.3. Germany construction ... 37

3.3.2. Direction ... 38

3.4. Window parameters ... 38

3.4.1. Size ... 38

3.4.2. Window type (energy properties) ... 39

3.4.3. U-Factor ... 39

3.4.4. Solar Heat Gain Coefficient ... 39

3.5. Research case studies ... 39

3.5.1. Case1: Tehran-Code ... 40

3.5.2. Case2: Tehran-Existence ... 40

3.5.3. Case3: Berlin-(Code+Existence) ... 41

3.6. Software ... 41

3.6.1. DesignBuilder ... 42

3.6.2. EnergyPlus ... 43

3.7. Conclusion ... 43

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3.7.1. Simulation Parameters of three sets (Cases) ... 44

3.7.2. Precise description of the simulation models and parameters….…….45

3.8. References………..………46

4. Chapter four: Simulation Results, Tehran, US Code (IEEC+FNRC) ... 48

4.2. Simulation results and analysis for fixed SHGC ... 50

4.2.1. Cooling energy consumption simulation results ... 50

4.2.2. Cooling energy consumption simulation analysis ... 51

4.2.3. Heating energy consumption simulation results ... 52

4.2.4. Heating energy consumption simulation analysis ... 53

4.2.5. Total energy consumption simulation results ... 54

4.2.6. Total energy consumption simulation analysis ... 55

4.3. Simulation results and analysis for fixed U-Value... 56

4.4. Conclusion ... 63

4.4.1. SHGC: fixed and UV: variable ... 63

4.4.2. SHGC: variable and UV: fixed ... 63

4.4.3. Reference Table T01: U-Factor selection (0.4 - 1.2) ... 64

4.4.4. Reference Table Tehran 02: SHGC selection (0.4 - 0.8) ... 65

5. Chapter five: Simulation Results, Tehran, Existence ... 66

5.3. Conclusion ... 74

5.3.2. Reference Table Tehran 03: U-Factor selection (1.4 - 4.0) ... 75

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6. Chapter six: Simulation Results, Berlin, ENEV + Existence ... 76

6.3. Simulation results and analysis for fixed U-Value... 85

6.4. Conclusion ... 92

6.4.2. SHGC: variable and UV: fixed ... 92

6.4.3. Reference Table Berlin 01: U-Factor selection (1.3 – 4.0) ... 93

6.4.4. Reference Table Berlin 02: SHGC selection (0.6 – 0.8) ... 94

7. Research Conclusion ... 95

7.1.1. Tehran International Standard buildings ... 96

7.1.2. Tehran National Standard buildings ... 96

7.1.3. Berlin National Standard buildings ... 97

7.2. Future research development ... 97

References ... 98

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VII

List of Figures:

Fig. 01: Schematic diagram of a vacuum glazing ... 07

Fig. 02: Energy flow paths at natural ventilated PV double pane window ... 10

Fig. 03: Configuration of the traditional and novel DGW ... 11

Fig. 04: Schematic view of the aerogel window prototype ... 12

Fig. 05: Schematic diagram of triple vacuum glazing ... 13

Fig 06: The three major types of energy flow that occur through windows ... 14

Fig. 07: Representative U-Factor of some windows ... 15

Fig. 08: NFRC rating label sample ... 17

Fig. 09: Residential building envelope parameters of Germany Energy Code ... 20

Fig. 10: Hashtgerd, new towns residential development in Iran ... 22

Fig. 11: Influence of daylight on heating, cooling and artificial lighting systems .... 24

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VIII

List of Tables:

Tehran, US Code (IEEC+NFRC):

Cooling energy consumption simulation results (variable UV) ... 50

Heating energy consumption simulation results (variable UV) ... 52

Total energy consumption simulation results (variable UV) ... 54

Cooling energy consumption simulation results (variable SHGC) ... 57

Heating energy consumption simulation results (variable SHGC) ... 59

Total energy consumption simulation results (variable SHGC)... 61

Reference Table T01: U-Factor selection (0.4 - 1.2) ... 64

Reference Table Tehran 02: SHGC selection (0.4 - 0.8) ... 65

Tehran, Existence: Cooling energy consumption simulation results (variable UV) ... 68

Reference Table Tehran 03: U-Factor selection (1.4 - 4.0) ... 75

Berlin, ENEV + Existence: Cooling energy consumption simulation results (variable UV) ... 79

Cooling energy consumption simulation results (variable SHGC) ... 86

Heating energy consumption simulation results (variable SHGC) ... 88

Total energy consumption simulation results (variable SHGC)... 90

Reference Table Berlin 01: U-Factor selection (1.3 – 4.0) ... 93

Reference Table Berlin 02: SHGC selection (0.6 – 0.8) ... 94

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IX

Energy Efficiency Improvement of Residential Building Fenestration

Case studies: Tehran and Berlin

PhD student: Mohammad Reza Razavi m.reza.razavi@gmail.com

Supervisor: Prof. Dr.-Ing. Klaus Rückert (TEK, TU Berlin)

Abstract:

The impacts of windows on energy consumption in the buildings are well established and therefore fenestration guidelines have been developed. In the architecture design process, many cases could be proposed regarding various design aspects, but the best choice of fenestration parameters could not be predicted, unless to do many computer simulations, which needs skill and much time.

The four main fenestration parameters that directly affect building energy performance are windows size, direction, U-Value and SHGC. The various combination of these factors get to so many simulations. Studying the annual cooling, heating and total energy consumption of building lead to guidelines, which can be used by architects in early stages of design process for determining the fenestration that have most efficient energy performance.

The places that are selected for case studies of this research are capitals of Iran and Germany. The building's fenestration energy parameters of Tehran are taken from international codes, Iranian code (19) and available common window products. The fenestration energy parameters of Berlin, are taken from Germany code (ENEV), and available windows of old buildings. For both cases, the window to wall ratios are from 10 to 90 percent, facing main four geographical directions. All simulation results have been analyzed, notable points have been explained and practical instructions for each part of the case studies have been extracted as energy efficient fenestration guideline.

Key words:

Energy efficiency, Fenestration, Energy code, Simulation, Residential buildings

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Verbesserung der Energieeffizienz der Fensteranordnung im Wohnbau

Fallstudien: Teheran und Berlin

Doktorand: Mohammad Reza Razavi m.reza.razavi@gmail.com

Doktorvater: Prof. Dr.-Ing. Klaus Rückert (TEK, TU Berlin)

Inhaltsangabe:

Dass Fenster Auswirkungen beim Energieverbrauch in den Gebäuden haben, ist wohl bekannt, weshalb Richtlinien zur Fensteranordnung entwickelt wurden. Im architektonischen Konstruktionsprozess konnten viele Fällen aufgeführt werden bezüglich diverser Gestaltungsprozesse. Jedoch konnte nicht vorhergesagt werden, welche Fensterungsparameter die besten sind, ohne viele Computersimulationen durchzuführen, was viel Geschick und Zeit erfordert .

Die vier hauptsächlichen Fensterparameter, welche direkt die Leistung der Gebäudeenergie betreffen, sind die Fenstergröße, Ausrichtung, der U-Wert sowie SHGC. Die verschiedenartige Kombination dieser Faktoren führt zu wirklichen vielen Simulationen. Untersucht man die Jahreskühlung und –Hitze, sowie den vollständigen Energieverbrauch von Gebäuden, führt das zu Leitlinien, welche von Architekten in frühen Stadien des Gestaltungsprozesses zur Bestimmung des Fensterbaus, welcher die höchste Energieeffizienz hat, genutzt werden können.

Als Orte für diese Forschungsarbeit wurden die Hauptstädte des Iran und Deutschlands ausgewählt. Die Parameter von Fensteranordnungen in Gebäuden in Teheran stammen aus internationalen Codes, dem Iranischen Code (19) und erhältlichen bekannten Fensterprodukten. Die Parameter Berlins wurden dem deutschen Code ENEV entnommen, sowie vorhandenen Fenstern in alten Gebäuden.

In beiden Fällen variierte das Verhältnis von Fenster zu Wand zwischen 10 und 90 Prozent, den vier geographischen Hauptrichtungen zugewandt. Alle Simulationsresultate wurden analysiert, wichtige Punkte geklärt und praktische Instruktionen für jeden Teil der Fallstudien als Fensteranordnungseffizienzrichtlinie extrahiert.

Schlagworte:

Energieeffizienz, Fensteranordnung, Energiecode, Simulation, Wohnbauten

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1 - C h a p t e r 1

Chapter 1 Introduction

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1.1. Introduction

The importance of the built environment from environmental impact and energy use perspective is well established. High energy efficiency of the constructed building envelope is a key strategy in the design and construction of buildings, which limit the use of active space conditioning systems. For achieving optimum energy conservation, we need to design buildings with optimum fenestration, focusing on their size, visible transmittance, U-factor, and solar heat gain coefficient (SHGC). According to many researches, fenestration of buildings has an important role in saving energy and providing efficient daylight.

Although energy and daylight performance of buildings is determined by primary fenestration parameters and building envelope properties, architects do not possess the necessary simplified tools during the early stage of the design process. Moreover, for most architects and designers, the existing energy simulation programs and analysis tools are very difficult to use. Therefore, this research presents a simplified method to evaluate and analyze the energy performance of fenestration variations and properties in residential buildings in Tehran and Berlin that could be developed for other cities.

1.2. Statement of the Problem

Firstly, there is a need to improvement of integration between the design decision making by architects and the building energy performance analysis in the early stages of the design process. Thus, late modification and past correction of the design would be decreased or eliminated, since architects consider both architecture and performance parameters of the building simultaneously from the beginning stages.

Secondly, most of building simulation tools are extremely complex and difficult to use. Therefore, a simplified model or applicable instructions need to be provided for architects. Many architects are not expert enough in the science of energy and specifications of relevant softwares; they just prefer to follow clear guidelines.

Thirdly, conducting energy performance simulation in the early steps of designing is very time consuming. Architects normally propose various design concepts in the beginning stage due to a wide range of influential parameters and requirements.

Regarding size of fenestration which is one of the important elements of primary building form design, each early design concept has its own fenestration characteristics and would be simulated for evaluating its energy performance, while none of them is still finalized. This many alternative simulations need a lot of time and could be eliminated by applying specified guidelines and directions.

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Fourthly, there is not practical regulation on interrelationship between various parameters of fenestration for improvement of energy performance of buildings in the selected case studies. Building energy codes have specified restrictions on these properties but there are many different building envelope states and variations that incorporate them. These combinations need to be predicted, simulated and analyzed;

then simple applicable guidelines will be introduced.

1.3. Research Objectives

The major objective of this research is to improve energy efficiency of building fenestration through certain design instructions. Therefore, the main study objective is to establish guidelines for architects, designers and for determining most effective design instructions and properties selections for residential building envelope fenestration in Tehran and Berlin.

This study intends to investigate the energy performance of typical residential buildings, with respect to their windows properties. Furthermore, it quantifies different windows parameters and characteristics in regard to building codes and energy conversation requirements. Considering the fact that although windows are of main architectural form design elements, but they are weakest part of the building envelope regarding energy efficiency. In the viewpoint of energy loss in cold climates they mostly waste heat and energy and therefore should be in the smallest possible size; but according the fact they provide daylight and sight, and in some cases they get direct solar radiant energy, they must be exist, but their size and specifications (UV and SHGC) should be investigated and determined.

The next object is to study the interaction between influential parameters of window’s properties regarding energy efficiency in building. The next factor is four main geographical directions, which has a great impact on the results. Furthermore, finding the quantity of each parameter’s impact on the overall energy consumption, which clarifies its importance and influence percentage. This would be very useful in the possible future study for construction life cycle cost I the case studies.

1.4. Significance of the Research

The primary significance of this research is a practical necessity for developing guidelines and regulations for designers that can help them in defining window properties and design factors to increase building performance efficiency. In order to encourage the development of appropriate sustainable design strategies to ensure high

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energy performance of residential buildings design, detailed study on envelope elements, in particular windows, has to be well developed. This research significance could be summarized as follow:

Initial prediction of fenestration energy performance can be used in the early design stages without long term softwares simulation an analysis. Optimum criteria with respect to fenestration properties and design factors should be recommended to increase energy conservation.

Based on the guidelines, architects and designers can predict the energy performance in the schematic design process. During the process of building evaluation, these guidelines and the prediction tool can easily evaluate, find, and optimize architectural parameters to increase building performance. Such a study, changes complicated energy regulations and softwares to a simplified and easy to use instructions for all architects.

1.5. Research structure

Firstly, a related literature review regarding the subject is provided and then research methodology is presented. The main part of study is simulations and their results. For two cities of Tehran and Berlin, a building unit (room) is supposed and its materials and construction layers are determined according to current construction methods and relevant national building codes. This unit is supposed to have fenestration in five case: four geographical directions and one all directions. The window size is a proportion of the wall between 10 and 90 percent. The two window parameter that affect energy, thermal transmittance (U-value) and Solar Heat Gain Coefficient (SHGC), are determined according to international codes, national codes and available products in construction market. The combinations of these factors result in more than 1700 simulations for cooling, heating and total energy consumption of the proposed unit. Study and comparison of the energy consumption graphs led to find best choices and provide applicable schedules as guidelines for building designers.

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5 - C h a p t e r 2

Chapter 2 Literature Review

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2.1. Introduction

In this chapter, an overview of the latest available fenestration technology and window materials with respect to their energy performance have been presented.

Furthermore, Basic concepts of windows energy efficiency, including insulating value and solar control are provided. In addition, a general introduction on building energy codes in related countries has been written. The last part is a comprehensive review of researches about Influence of Fenestration dimension and window parameters on building energy consumption.

The thermal performance of windows is important for energy efficient buildings. Windows typically account for about 30–50 percent of the transmission losses though the building envelope, even if their area fraction of the envelope is far less. The reason for this can be found by comparing the thermal transmittance (U- factor) of windows to the U-factor of their opaque counterparts (wall, roof and floor constructions). (Gustavsen, Grynning et al. 2011)

2.2. Window technology

Currently, saving energy and carbon emissions is a top priority for buildings and constructions. With up to 60% of the total energy loss of a building coming from its windows, fenestration products have a huge potential to provide large energy savings.

Hence, windows with a low thermal transmittance, or U-value, can substantially reduce energy losses and save costs.

2.2.1. Glazing

Glazing can be considered as the most important part of fenestration products.

This is especially true when calculating the U-value of a window as the glazing nearly always has the largest area of the constituent parts, and this greatly affects the overall window U-value. Presented within this section are examples of multilayer and vacuum glazing. Multilayer glazing is the most popular commercially available glazing and therefore constitutes the majority of products reviewed.

2.2.1.1. Multilayer glazing

The most common glazing type that gives a low U-value is triple glazing.

Typically, this is with a gas fill of either argon or krypton, with krypton producing lower U-values with less cavity or fill thickness (and volume). This can help to reduce the weight of the window, as reduced cavity thickness means the frame can be made

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smaller and thinner. Currently krypton is the most common gas fill for the best high- performance glazing, but krypton is considerably more costly than argon.

2.2.1.2. Suspended films

There are some products on the market that have a variation on the more common multilayer glass with gas fill method. These incorporate ‘suspended coated films’ (SCF) or only ‘suspended films’ in between the outer and inner panes, which act as a third or fourth ‘glass pane’. These films can reduce the weight of the window and may also allow a larger gas cavity thickness in the same window cavity as ordinary multilayer glazing due to the films being thinner than a glass pane.

2.2.1.3. Vacuum glazing

Vacuum glazing consists of two sheets of glass separated by a narrow vacuum space with an array of support pillars keeping the two sheets of glass apart. This can be combined with another layer of low-e coated glass to produce windows with competitive U- values to low-e triple glazing.

2.2.1.4. Low-emissivity coatings

Low-emissivity (low-e) coatings are typically metals or metallic oxides and can be categorized into hard and soft coatings. Hard coatings such as pyrolytic

deposited doped metal oxides, are on-line coatings, i.e. they are applied as part of the float line production. They are more durable than soft coatings and can be toughened.

Soft coatings usually consist of dielectric–metal– dielectric layers and are most often off-line coatings, i.e. they are applied to individual glass panes after manufacturing.

The best process of applying soft coatings is magnetron sputtering. Soft coatings have higher infrared reflection and are more transparent than hard coatings but require extra protective layers due to their lack of durability.

Fig. 01: Schematic diagram of a vacuum glazing (Jelle, Hynd et al. 2012)

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2.2.1.5. Smart windows

Smart windows can change solar factor (SF) and transmittance properties to adjust to outside and indoor conditions, thus reducing energy costs related to heating and cooling. Smart windows can be divided into three different categories: chromic materials, liquid crystals and suspended particle devices.

2.2.1.6. Solar cell glazing

Recent developments in technology have enabled solar energy collection from transparent glass. The technology involves spraying a coating of silicon nanoparticles on to the window, which work as solar cells. Windows with the capability to produce electricity can be seen as having a lot of potential in the building industry. This highlights the alternative uses of windows as they can function as normal while also producing electricity.

2.2.1.7. Self-cleaning glazing

Self-cleaning glazing works by utilizing photocatalytic reactions within a thin coating on the glass and then as water falls on the glass it carries dirt off in one movement (hydrophilicity). These self-cleaning glazing products have slightly higher U-values than other products. By removing the need for cleaning chemicals, which runoff into water sources, these products can have a positive environmental impact.

It should be noted that the term self-cleaning does not necessarily mean that one does not have to clean the window oneself anymore, but rather that one may have to clean the window less than a normal window.

2.2.1.8. Aerogels

Aerogels, often known as solid air, are the lowest density solid known. The aerogel products are mostly silica aerogels, but they can be made from various materials. These aerogel products are solar light diffusing as translucent aerogel granules are used. The low Tvis (as a result of sufficient large thickness and thus low Ug), together with the high costs, are the major downsides of aerogel glazing at the moment, as the products are more suited to roofing and facades in commercial buildings and sports halls and are not yet in a position to challenge conventional residential windows where transparent (and not translucent) glazing most often will be a requirement. As aerogel is a very light material this represents a dramatic reduction in weight from triple glazed windows.

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2.2.1.9. Glazing cavity gas fills

Between the extremities vacuum and aerogels, there is normally a gas between the glass panes in a window. Naturally, the traditional and cheapest gas has been common air. As air has a rather high thermal conductivity, i.e. about 26 _{𝑚𝑚𝑚𝑚}^𝑤𝑤 at room temperature and atmospheric pressure, the noble gas argon (Ar) with a thermal conductivity around 18 _{𝑚𝑚𝑚𝑚}^𝑤𝑤 has become in widespread use as a gas fill in today’s fenestration products. The noble gases krypton (Kr) and xenon (Xe) offer considerably lower thermal conductivities, i.e. about 9.5 _{𝑚𝑚𝑚𝑚}^𝑤𝑤 and 5.5 _{𝑚𝑚𝑚𝑚}^𝑤𝑤, respectively, offering even lower U-values and thinner glazing units than with argon. However, as the costs of krypton and xenon are very high, especially xenon, these gases are not in widespread use as of today. Optimum glazing cavity thicknesses with respect to the different gases, their costs and the number of panes may be found, where also thickness restrictions or limitations of the glazing unit may play a role.

2.2.2. Spacers

Spacers are the components that are used to separate panes of glass and with a sealant provide a protective seal for the air or gas fill between them. Traditionally, spacers have been made of metals, in particular aluminum, which have a very high thermal conductivity. Currently, spacers are made of less conductive materials to provide a better thermal insulation in windows, as they can greatly influence on how well a window performs.

2.2.2.1. Foam spacers

The leading foam spacer has ‘warm edge technology’ (WET), which means that it has better thermal properties than traditional aluminum spacers. It is made from structural foam and is pre-desiccated to reduce condensation.

2.2.2.2. Thermoplastic spacers

Thermoplastic spacers (TPS) are usually made from polyisobutylene, also known as PIB. They also include desiccant material and have WET.

2.2.2.3. Metal-based spacers

Metal-based spacers include various stainless-steel spacers. Stainless steel has a thermal conductivity of about 17 _{𝑚𝑚𝑚𝑚}^𝑤𝑤, which is considerably lower than the conductivity for aluminum of about 200 _{𝑚𝑚𝑚𝑚}^𝑤𝑤.

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2.2.3. Frames

When determining how efficient a window is the glazing is not the only part that matters. The frame may also have a significant influence on the efficiency.

Window frames can be manufactured from many different materials including wood (incorporating polyurethane (PUR)), wood with insulation filled aluminum cladding, polyvinylchloride (PVC), PVC with insulation filled aluminum cladding, aluminum and fixed wood and aluminum. The connection between the window frame and the building is also important to address with respect to energy efficiency issues, but is not within the scope of this work.(Jelle, Hynd et al. 2012)

2.3. New technologies of fenestration

Along with sustainability development in architecture and advances in green building methods, fenestration technology is currently under rapid progress. These new technologies are suitable to different, climates, building style, types and functions. Here some of them are introduced.

2.3.1. Water-flow window

This innovative solar window is basically for cooling-demand climates. A water-flow window carries a water circuit that allows a stream of clean water to flow upward within the entire space between two glass panes. The results indicate that this new design is able to support hot water supply system, reduce air- conditioning load and enhance thermal and visual comfort. (Chow, Li et al. 2010)

2.3.2. Switchable triple glazing exhaust air window

The window is characterized by two air cavities with one being a ventilation channel for exhausting indoor air to the ambient. The other cavity is enclosed and, together with the adjacent two glass panes, acts as a conventional double-glazing unit.

Fig. 02: Energy flow paths at natural ventilated PV double pane window

(Chow, Li et al. 2010)

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Venetian blinds are imbedded in the ventilation cavity which is located to the outer side in summer and is switched to the inner side in winter. Such a design makes the window able to reduce its heat loss and gain by utilizing the heat and coolth inherent in the exhaust air. Simulation results show that, in comparison with the double and triple glazing windows, the SEA window reduces 73.5% and 71.9% of the heat gain in summer, respectively, and 74% and 46.8% of the heat loss in winter, respectively.

(Zhang, Wang et al. 2016)

2.3.3. Cooling pipes embedded in venetian blinds Cooling pipes embedded in the

venetian blinds of a double-skin envelope are a system for reducing the heat transfer of the glass envelope in summer. Solar radiation is taken away directly by pipes through which cooling water is circulated, and the water can be produced from natural cooling. The cooling pipes can significantly reduce the temperature of the venetian blinds and air cavity, which will in turn lower heat transfer and improve thermal comfort. With pipe embedded,

cooling water averagely takes away about 60% of the solar radiation directly and the average solar energy transmittance is only 13%. In addition, cheap glass can be employed to the pipe-embedded DGW with only small negative influence. (Shen and Li 2016)

2.3.4. Future of aerogel glazing in energy efficient buildings

By incorporating aerogel granules into the air cavity of corresponding double- glazing units, a prototype aerogel glazing unit have been assembled, which an experimental investigation on their physical properties and a subsequent numerical simulation on their energy performance have been conducted. The results showed that, compared to the double glazing counterparts, aerogel glazing can contribute to about 21% reduction in energy consumptions related to heating, cooling, and lighting;

payback time calculations indicate that the return on investment of aerogel glazing is about 4.4 years in a cold climates. (Gao, Ihara et al. 2016)

Fig. 03: Configuration of the traditional and novel DGW. (a) Traditional DGW; (b) Pipe-

embedded DGW (Shen and Li 2016)

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2.3.5. Super insulated aerogel windows

Windows in buildings enable the penetration of natural light. However, selecting a window glazing is complicated when considering daylighting, thermal comfort and energy saving aspects concurrently due to their conflicting contribution towards energy use. Comparing the newly developed aerogel window against the more traditional Argon-filled, coated double-glazing, the aerogel window provided an extremely low heat- loss index of 0.3 _{𝑚𝑚2𝑚𝑚}^𝑤𝑤 , the latter usually offered a centre-glazing U-value of 1.4 _{𝑚𝑚2𝑚𝑚}^𝑤𝑤 . On a like-with- like basis the daylight transmission of the aerogel window was significantly lower than double- glazing. However, in view of low thermal loss larger areas of the former can be deployed. (Garnier, Muneer et al. 2015)

2.3.6. Thermochromic fenestration with VO2-based materials

Thermochromics windows don’t have a huge savings potential, but thermochromic devices can be based on a single thin layer and are hence simpler than electrochromic devices which typically embody five superimposed layers. It should also be noticed that thermochromic and electrochromic devices might be combined with optimized thermal insulation in future “super fenestration”. VO2 has interesting thermochromic properties as a consequence of its reversible structural transformation and associated metal–insulator transition at a “critical” temperature not too far from a comfort temperature of about 25 °C. The material is monoclinic, semiconducting and fairly infrared transparent. (Li, Niklasson et al. 2012)

Fig. 04: Schematic view of the aerogel window prototype (Garnier,

Muneer et al. 2015)

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2. 3. 7 . V ac u u m gl azi n g f or hi g hl y i ns ul ati n g wi n d o ws

V ac u u m gl azi n g is a u ni q u e a n d hi g h - p erf or m a nc e f e n estr ati o n t ec h n ol o g y w hic h e n a bl es mi ni m u m h e at l oss a n d hi g h visi bl e tr a ns mitt a nc e i n a sli m wi n d o w pr o d uct. V ac u u m gl azi n g t ec h n ol o g y d o es n ot h a v e c o m pl ex f a bric ati o n d et ails. A c o n v e nti o n al v ac u u m gl azi n g c o nsists of t w o s h e ets of gl ass s e p ar at e d b y a v ac u u m m e di u m wit h a n arr a y of s u p p ort pill ars k e e pi n g t h e t w o s h e ets of gl ass a p art. T h e s u p p ort pill ars ar e m ostl y i m p erc e pti bl e fr o m a dist a nc e of a b o ut 2– 3 m, h e nc e t h eir i nfl u e nc e o n visi o n is n e gli gi bl e.

T h e k e y r ol e of t h e v ac u u m g a p b et w e e n t h e gl ass s h e ets is t o eli mi n at e t h e

c o n d ucti o n a n d c o n v ecti o n w hic h pl a y a si g nific a nt r ol e i n t h e U -v al u e of f e n estr ati o n pr o d ucts. It c a n b e c o ncl u d e d t h at o v er all h e at tr a nsf er c o effici e nt of a v ac u u m gl azi n g c a n b e r e d uc e d u p t o 0. 2 0 _{𝑚𝑚 2 𝑚𝑚}^𝑤𝑤 t hr o u g h o ptimiz e d i nt e gr ati o ns wit h l o w -e c o ati n gs. ^{(C uc e}

a n d C uc e 2 0 1 6 )

2. 4 . Wi n d o w’s e n er g y p ar a m et ers

Wi n d o ws c o nstr ucti o n m a y v ar y i n a gr e at ext e nt, as a r es ult b uil di n g e n er g y d e m a n d m a y b e i nfl u e nc e d d u e t o c h a n g es of h e at l oss, s ol ar h e at g ai ns as w ell as e n er g y d e m a n d f or artifici al li g hti n g. I n or d er t o esti m at e a n act u al i m p act of wi n d o ws o n a b uil di n g e n er g y d e m a n d f o ur m ai n p ar a m et ers s h o ul d b e t a k e n i nt o acc o u nt as f oll o ws:

-T h er m al e n er g y tr a ns mitt a nc e – U w, -Air p er m e a bilit y – Q 1 0 0,

- S ol ar e n er g y tr a ns mitt a nc e – G w, - D a yli g ht tr a ns mitt a nc e – T w.

T h es e f o ur p ar a m et ers all o w t o t a k e i nt o acc o u nt all as p ects of t h e e n er g y i m p act of wi n d o ws o n t h e e n er g y p erf or m a nc e of b uil di n gs ( h e at tr a nsf er, s ol ar h e at g ai ns a n d d a yli g hti n g). H o w e v er act u al di m e nsi o ns of wi n d o ws h a v e a si g nific a nt i m p act o n t h e p ar a m et ers of a wi n d o w as a w h ol e. D u e t o a fix e d fr a m e c o nstr ucti o n t h e

Fi g. 0 5: Sc h e m atic di a gr a m a n d t hr e e st a g e c o m p osit e e d g e s e ali n g d esi g n pr oc ess f or t h e f a bric ati o n of tri pl e v ac u u m gl azi n g (C uc e a n d C uc e 2 0 1 6 )

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glazing/window area and the influence of thermal bridges may vary in a great extent for different heights and widths. Therefore actual Uw, Gw and Tw for a particular window may differ significantly from the values estimated for the product certificate.

(Trząski and Rucińska 2015)

2.5. Basic concepts of windows energy efficiency

An understanding of some basic energy concepts is essential to choosing appropriate windows and skylights. Three major types of energy flow occur through windows: (1) non-solar heat losses and gains in the form of conduction, convection, and radiation; (2) solar heat gains in the form of radiation; and (3) airflow, both intentional (ventilation) and unintentional (infiltration).

2.5.1. Insulating Value

The non-solar heat flow through a window is a result of the temperature difference between the indoors and outdoors. Windows lose heat to the outside during the heating season and gain heat from the outside during the cooling season, adding to the energy needs in a home. The effects of non-solar heat flow are generally greater on heating needs than on cooling needs because indoor-outdoor temperature differences are greater during the heating season than during the cooling season in most regions of the United States. For any window product, the greater the temperature difference from inside to out, the greater the rate of heat flow.

U-factor is a measure of the rate of non-solar heat flow through a window or skylight. R-value is a measure of the resistance of a window or skylight to heat flow and is the reciprocal of a U-factor. Lower U-factors (or higher R-values), thus indicate reduced heat flow. U-factors allow consumers to compare the insulating properties of different windows and skylights.

Fig 06: The three major types of energy flow that occur through windows: (1) non-solar heat losses and gains in the form of conduction, convection, and radiation; (2) solar heat gains in the form of radiation; and (3) airflow, both intentional (ventilation) and unintentional (infiltration). (Selecting Windows for Energy Efficiency, 2014)

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The insulating value of a single pane window is due mainly to the thin films of still air on the interior and moving air on the exterior glazing surfaces. The glazing itself does not offer much resistance to heat flow. Additional panes markedly reduce the U- factor by creating still air spaces, which increase insulating value. In addition to conventional double-pane windows, many manufacturers offer windows that incorporate relatively new technologies aimed at decreasing U-factors.

These technologies include low-emittance (low-E) coatings and gas fills. A low- E coating is a microscopically thin, virtually invisible, metal or metallic oxide coating deposited on a glazing surface. The coating may be applied to one or more of the glazing surfaces facing an air space in a multiple-pane window or to a thin plastic film inserted between panes. The coating limits radiative heat flow between panes by reflecting heat back into the home during cold weather and back to the outdoors during warm weather. This effect increases the insulating value of the window. Most window manufacturers now offer windows and skylights with low-E coatings.

The spaces between windowpanes can be filled with gases that insulate better than air. Argon, krypton, sulfur hexafluoride, and carbon dioxide are among the gases used for this purpose. Gas fills add only a few dollars to the prices of most windows and skylights. They are most effective when used in conjunction with low-E coatings.

For these reasons, some manufacturers have made gas fills standard in their low-E windows and skylights.

Fig. 07: Representative U-Factor of some windows (Selecting Windows for Energy Efficiency, 2014)

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The insulating value of an entire window can be very different from that of the glazing alone. The whole-window U-factor includes the effects of the glazing, the frame, and the insulating glass spacer. The spacer is the component in a window that separates glazing panes. It often reduces the insulating value at the glazing edges.

Since a single-pane window with a metal frame has about the same overall U- factor as a single glass pane alone, frame and glazing edge effects were not of great concern before multiple-pane, low-E, and gas-filled windows and skylights were widely used. With the recent expansion of thermally improved glazing options offered by manufacturers, frame and spacer properties now can have a more pronounced influence on the U-factors of windows and skylights. As a result, frame and spacer options have also multiplied as manufacturers offer improved designs.

Window frames can be made of aluminum, steel, wood, vinyl, fiberglass, or composites of these materials. Wood, fiberglass, and vinyl frames are better insulators than metal. Some aluminum frames are designed with internal thermal breaks, non- metal components that reduce heat flow through the frame. These thermally broken aluminum frames can resist heat flow considerably better than aluminum frames without thermal breaks.

Composite frames may use two or more materials (e.g. aluminum-clad wood, vinyl-clad wood) to optimize their design and performance, and typically have insulating values intermediate between those of the materials comprising them.

Frame geometry, as well as material type, also strongly influences thermal performance properties. Spacers can be made of aluminum, steel, fiberglass, foam, or combinations of these materials. Spacer thermal performance is as much a function of geometry as of composition. For example, some well-designed metal spacers insulate almost as well as foam.

2.5.2. Solar Control

Solar transmission through windows and skylights can provide free heating during the heating season, but it can cause a home to overheat during the cooling season. Depending upon orientation, shading and climate, solar-induced cooling costs can be greater than heating benefits in many regions of the United States. In fact, solar transmission through windows and skylights may account for 30% or more of the cooling requirements in a residence in some climates.

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Because the sun’s position in the sky changes throughout the day and from one season to another, window orientation has a strong bearing on solar heat gain. South- facing windows allow the greatest and potentially most beneficial solar heat gain during the heating season, while admitting relatively little of the solar heat that contributes to cooling requirements during the cooling season. The reverse is true for skylights and east and west-facing windows. North exposures transmit only minimal solar heat at any time. The ultimate importance of these climatic and orientation effects will depend on the type of glazing under consideration.

The Solar Heat Gain Coefficient (SHGC) is a measure of the rate of solar heat flowing through a window or skylight. Shading Coefficient (SC) is the previous standard indicator of a window’s shading ability and for simple glazing is approximately equal to the solar heat gain coefficient multiplied by 1.15.

Solar heat gain coefficients allow consumers to compare the solar heat gain properties of different windows and skylights. The solar heat gain coefficient accounts for both the transmissive glazing element, as well as the opaque frame and sash.

Additional glazing layers provide more

barriers to solar radiation, thus reducing the solar heat gain coefficient of a window.

Tinted glazing, such as bronze and green, provide lower solar heat gain coefficients than does clear glass. Low-E coatings can be engineered to reduce window solar heat gain coefficients by rejecting more of the incident solar radiation. Spectrally selective glazings, including some low-E coated glazings with low solar heat gain coefficients and new light blue and light blue-green tinted glazings, block out much of the sun’s heat while maintaining higher visible transmittances and more neutral colors than more heavily tinted bronze and grey glazings. High-transmittance, low-E coatings, used in conjunction with a tinted outer glass layer, also reduce solar heat gain by preventing the absorbed heat from reaching the interior space. Mirror-like reflective glazings are commonly used in office buildings, but only occasionally chosen for residences. While they may have very low solar heat gain coefficients, they block so much of the light and view that they are not normally desirable in homes. (Windows and Glazing 2016)

Fig. 08: NFRC rating label sample

(Energy performance rating, 2014)

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2.6. Energy codes

Creating a more energy efficient world is one of the most formidable environmental and economic challenges facing us today. According to the U.S.

Department of Energy (DOE), buildings consume 40 percent of all the energy used nationwide. Achieving optimal energy efficiency in buildings can drastically reduce overall energy consumption, and you can play a key role in achieving improved performance by supporting the adoption, implementation, and enforcement of the latest building energy codes.

2.6.1. Building energy codes

Building energy codes provide a target for achieving recognized and acceptable levels of energy efficiency. They establish minimum performance standards for residential and commercial buildings. From the National Fenestration Rating Council's (NFRC) perspective, one of the most important aspects of building energy codes is specifying requirements for how much heat is lost or gained by windows. This is important because installing the appropriate windows facilitates integrated, efficient construction practices in the design stage, where the greatest, long-term cost savings can be built in for building occupants and realized throughout the life of the building.

These codes address the energy-efficiency requirements for the design, materials, and equipment used in nearly all new construction, additions, renovations, and construction techniques. Their requirements affect the overall energy efficiency of any structure and can reduce the energy needed to maintain a healthy, comfortable, and fully functioning indoor environment. Quite comprehensive in nature, codes apply to:

-Wall, floor, and ceiling -Doors and windows

-Heating, ventilating, and cooling systems and equipment -Lighting systems and equipment

-Water-heating systems and equipment.

2.6.2. Benefits and development of Building Energy Codes

By supporting the latest building energy codes when installing new or replacement windows, consumers contribute to meeting the energy efficiency challenge. Adhering to codes makes their homes more energy efficient, which in turn helps to reduce peak energy demand and thereby reduce utility bills. Additionally, supporting energy codes leads to fewer power plants being constructed and less natural resources being used to provide electricity and natural gas. This in turn results

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in fewer emissions to the atmosphere and emissions from power plants are a primary contributor to global warming.

Building energy codes are minimum requirements for energy efficient design and construction for new and renovated residential and commercial buildings. A component of a complete set of building regulations that govern all aspects of the design and construction of buildings, building energy codes set an energy-efficiency baseline for the building envelope, systems, and equipment. Improving these minimum requirements or broadening the scope of energy codes softens the environmental impact of buildings as well as generates additional energy and cost savings over the decades-long, or even centuries-long, life cycle of a building. (Building Energy Codes Program 2016)

2.6.3. Building energy codes in Germany

The Energy Saving Ordinance (EnEV) is part of the German economic administrative law. In it by the legislature on the legal basis of the authorization granted by the Energy Saving Act (Energy Conservation Code) Building structural standard requirements for efficient operation required energy consumption of your building or construction project. It applies to residential buildings, office buildings and some farm buildings. EnEV stipulates:

-Energy performance certificates for buildings.

-Minimum energy requirements for new buildings.

-Minimum energy requirements for modernization, reconstructions and extensions of existing buildings.

-Minimum requirements for heating, cooling and air-conditioning systems as well as hot-water systems.

-Energy inspection of air-conditioning systems.

EnEV is applicable for:

-All heated and cooled buildings and/or parts of buildings.

-Special stipulations apply for buildings which are not heated, cooled or used regularly (such as holiday homes), which are erected only for a short period of time (such as tents and air halls) or which are used for special purposes, such as stables and greenhouses.

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-Small buildings with a floor space of less than 50 m2 and historic monuments protected by German land law are not obliged to produce energy performance certificates. (Rose 2015)

2.6.4. Building energy codes in the United States

In the United States, two primary baseline building energy codes may be adopted by states and local jurisdictions to regulate the design and construction of new buildings: the International Energy Conservation Code (IECC), and the ANSI/ASHRAE/IESNA Standard 90.1 Energy Standard for Buildings except Low-Rise Residential Buildings. The IECC addresses all residential and commercial buildings.

ASHRAE 90.1 covers commercial buildings, defined as buildings other than single- family dwellings and multi-family buildings three stories or less above grade. The IECC adopted, by reference, ASHRAE 90.1; that is, compliance with ASHRAE 90.1 qualifies as compliance with IECC for commercial buildings.

The IECC is developed under the auspices of the ICC using a government consensus process. Per this process, all interested parties may participate, but the final vote on the content of the codes is made by individuals associated with federal, state, or local governments who are also members of the ICC. The IECC is one of 14 model codes developed under the auspices of the ICC that combined provide the foundation for a complete set of building construction regulations. The ICC codes are updated

Fig. 09: residential building envelope parameters of Germany Energy Code EnEV (Goschenhofer 2018)

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every three years, providing a model the jurisdiction can adopt as is, or modify.

Because the IECC is written in mandatory, enforceable language, state and local jurisdictions can easily adopt, implement, and enforce the IECC as their energy code.

Before adopting the IECC, state and local governments often make changes to reflect regional building practices, or state-specific energy-efficiency goals.

ASHRAE 90.1 is developed under the auspices of the American Society of Heating, Refrigerating and Air Conditioning Engineers using the ANSI consensus process, which requires a balance of interests. All interested parties can participate by addressing the committee during deliberations, participating in subcommittees, or commenting during the public review process. The final vote of the project committee includes members from a balance of all interests, not limited to government representatives. Revisions in the development and maintenance of the standard occur on an ongoing basis and are not approved without achieving this balanced consensus, or substantial agreement reached by directly and materially affected interest categories. Before adopting ASHRAE 90.1, state and local governments often make changes to reflect regional building practices, or state-specific energy-efficiency goals.

(Building Energy Codes 101, 2010)

2.6.5. Building energy codes in Iran

The first national building code on energy conservation, Code No. 19, was approved in 1991 by the Ministry of Housing and Urbanism. It was revised several times, in 2001 finalized, and imposed on construction and building organizations. In the Code 19, two methods for calculation were introduced, mandatory and system performance. In the mandatory method which is used for small buildings, R m2 K/W values for each building component are assigned and designers should calculate the thickness of thermal insulation according to the construction layers of the component.

In the performance method, total heat loss of the building H W/K is calculated and compared with total heat loss of the same building when its U W/m2 K values meet the requirements of the code. The result should always be less than that of the reference building. Only in regions with HDD values more than 2600 K day, designers can use a correction factor c with regard to thermal inertia of the building, area of the fenestration, type of the glass, amount of the shade on windows from outside obstructions to consider free solar gains in the calculations. This allows a reduction of thermal resistances. In Code 19, buildings are divided into four groups which are ordered in terms of their energy conservation requirements. Three climatic zones are defined for the country. The group affiliation of each building is specified by the type of the climatic zone where the city is located, building’s usage, its heated floor area,

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building’s location (small or large city). In this code, U values for the building components of buildings which use electrical energy are about 20% less than that of the buildings using fossil fuels. In addition, there are recommendations for mechanical and lighting equipment. Actually, it is the building envelope which is mostly under consideration. (Fayaz and Kari 2009)

2.6.5.1. Young Cities Project

The Young Cities Project was an applied German-Iranian research project aimed at elaborating solutions and strategies for a sustainable, energy-efficient development of new urban developments in Iran as a contribution to a significant CO2 reduction.

A total of five pilot projects were implemented in 35 ha area of Hashtgerd New Town in order to examine different strategies and solutions for energy efficient urban planning and building design. The knowledge gained from these practical experiences were introduced into the work process in order to increase their effectiveness. The following pilot projects are elaborated at different spatial levels:

• The 35-hectare housing area

• The New Quality residential building

• Three New Generation buildings for residential, office and educational uses The following supportive project dimensions complement the technical approach of the pilot projects:

• Vocational training for construction workers in order to achieve a higher quality of construction and hence a lower energy demand of the buildings

• Awareness-raising activities with multipliers and inhabitants, in order to promote sustainable lifestyles

• Development of local and regional energy concepts. (K. Rueckert 2011)

Fig. 10: Hashtgerd, new towns residential development in Iran (K.

Rueckert 2011)

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2.7. Influence of Fenestration dimension on energy consumption

A generally accepted way of energy efficient building fenestration has been to have small windows facing north and large windows to the south. This is to minimize losses on the north side while gaining as much solar heat as possible on the south. But there are other factors which affect the area of windows in all buildings sides which should to be studied and then define optimum window size. Over the past decade, many studies has been conducted to estimate the energy-saving potential of windows for various climates. Furthermore, using computational analysis the optimum window size and type for minimizing building energy consumption have also been explored. All the researches have proven that considerable energy can be conserved when windows are designed properly. (Ko 2009)

Iqbal and Al-Homoud conducted an evaluation of various energy conversation measures by using the Visual DOE-4 energy simulation program. For one of the energy conservation methods, a 7% reduction in energy consumption was achieved in summer by using an efficient glazing system. It is recommended that low-e double- glazed windows be employed for energy efficiency, particularly in large, glazed buildings in hot climates. They concluded that using more energy-efficient windows (high R-value and low-e) can be beneficial for reducing energy consumption and improving indoor comfort levels. (Iqbal and Al-Homoud 2007)

Mehlica et al. analyzed how to minimize heating and cooling loads by means of optimum window size and building aspect ratio. Based on a computer simulation in five different climate regions in Turkey, it was concluded that a window size of 25%

facing the south was the optimum for hot climates. (Inanici and Demirbilek 2000)

Mari-Louise Persson et al. investigated how decreasing the window size facing south and increasing the window size facing north in low energy houses would influence the energy consumption. The results show that the size of the energy efficient windows does not have a major influence on the heating demand in the winter, but is relevant for the cooling need in the summer. This indicates that instead of the traditional way of building passive houses it is possible to enlarge the window area facing north and get better lighting conditions. To decrease the risk of excessive temperatures or energy needed for cooling, there is an optimal window size facing south that is smaller than the original size of the investigated buildings. (Persson, Roos et al. 2006)

K. Hassouneh and others, conducted an evaluation of Influence of windows on the energy balance of apartment buildings in Amman. It has been found that choosing a larger area facing south, east and west can save more energy and decrease heating

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costs in winter using certain types of glazing, while decreasing the glazing area facing north can save money and energy. However, it has been found that the energy can be saved in the north direction if certain types of glazing has been used. In the apartment building, it is found that certain combination of glazing is energy efficient than others.

This combination consists of using large area of certain types of glass in the east, west and south direction, and certain types of glass in the north direction or reducing glazing area as possible in the north direction. (Hassouneh, Alshboul et al. 2010)

Carlos E. Ochoa et al. have done a consideration on design optimization criteria for windows providing low energy consumption and high visual comfort. The results were classified using a graphical optimization method, obtaining a solution space satisfying both energy and visual requirements. Most project expectations can be met within the range of sizes. However, unprotected windows barely meet acceptance criteria, needing additional control devices. Applying various related criteria with adequate values increases the diversity of acceptable solutions but too many limits it.

Clear objectives and acceptance ranges have to be conceptualized in order to translate them into decisions. (Ochoa, Aries et al. 2012)

Vesna ˇZegarac Leskovar et al. has done a research on the approach in architectural design of energy-efficient timber buildings with a focus on the optimal glazing size in the south-oriented facade. A parametric analysis is performed on the variation of the glazing-to-wall area ratio (AGAW) from 0% to 80% for six different exterior wall elements with different thermal properties. Modifications are performed for the main cardinal directions, while a detailed analysis is carried out only for the south facade. It is evident from the results that the increase of the south-oriented glazing surfaces installed in the single-panel wall elements with higher U-values acts positively on the sum total of energy demand for heating and cooling. The research

Fig. 11: Influence of daylight on heating, cooling and artificial lighting systems

(Ochoa, Aries et al.

2012)

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main objective was to demonstrate an approach which could be used by architects to define the optimal glazing surface for a specific direction in order to obtain the optimal model of an energy-efficient house, depending on a single independent variable (Uwall-value). But the results showed that it is difficult to establish what a realistic optimal model is since most of the buildings are unique and trends also vary over time.

However, by applying the research presented approach to each individual timber- frame house, the optimal glazing surface is determinable with reference to the lowest energy demand for heating and cooling. Such application would still allow the houses to keep their uniqueness. (Leskovar and Premrov 2012)

John A. Tinker et al. studied an Ideal Window Area concept for energy efficient integration of daylight and artificial light in buildings. He presents a methodology to predict the potential for energy savings on lighting using an Ideal Window Area concept when there is effective daylight integration with the artificial lighting system.

The energy analysis work was performed using the Visual DOE program for the climatic conditions of Leeds, in the UK, and Florianopolis, in Brazil. Following this, the potential for lighting energy savings was assessed for each room using a method based on Daylight Factors. It was observed that the potential for energy savings on lighting in Leeds ranged from 10.8% to 44.0% over all room sizes and room ratios for an external illuminate of 5000 lux; and in Florianopolis, the potential ranged between 20.6% and 86.2% for an external illuminate of 10000 lux. (Ghisi and Tinker 2005)

Andrea Gasparella et al. has done an analysis and modeling of window and glazing systems energy performance for a well-insulated residential building. This work evaluates the impact of different kinds of glazing systems (two double and two triple glazing), window size (from 16% to 41% of window to floor area ratio), orientation of the main windowed facade and internal gains on winter and summer energy need and peak loads of a well-insulated residential building. The climatic data of four localities of central and southern Europe have been considered: Paris, Milan, Nice and Rome. A statistical analysis has been performed on the results in order to identify the most influencing parameters. It is possible to summarize the results as follows:

- The use of large glazings enhances winter performance but worsens slightly the peak of winter loads (the adoption of shutters for night hours could limit this problem);

- There is an improved effect for the south orientation, which is the best performing in winter;

- In winter, the use of windows with low thermal transmittance is useful if accompanied by high solar transmittance;

- However higher solar transmittance considerably worsens summer performance;