ASSESSMENT OF WINDOW SYSTEMS CONSIDERING SOLAR AND THERMAL PERFORMANCE

ASSESSMENT OF WINDOW SYSTEMS CONSIDERING SOLAR AND THERMAL PERFORMANCE Frank Gergaud & Evangelos Marios Liaros Master Thesis in Energy-efficient and Environmental Buildings Faculty of Engineering Lund University

Lund University Lund University, with eight faculties and a number of research centers and specialized institutes, is the largest establishment for research and higher education in Scandinavia. The main part of the University is situated in the small city of Lund which has about 112 000 inhabitants. A number of departments for research and education are, however, located in Malmö and Helsingborg. Lund University was founded in 1666 and has today a total staff of 6 000 employees and 47 000 students attending 280 degree programmes and 2 300 subject courses offered by 63 departments. Master Programme in Energy-efficient and Environmental Building Design This international programme provides knowledge, skills and competencies within the area of energy-efficient and environmental building design in cold climates. The goal is to train highly skilled professionals, who will significantly contribute to and influence the design, building or renovation of energy-efficient buildings, taking into consideration the architecture and environment, the inhabitants behavior and needs, their health and comfort as well as the overall economy. The degree project is the final part of the master programme leading to a Master of Science (120 credits) in Energy-efficient and Environmental Buildings. Examiner: Henrik Davidsson (Energy and Building Design) Supervisor: Niko Gentile (Energy and Building Design), Harris Poirazis (Inform Design) Keywords: Window systems, solar energy, thermal transmittance, Dynamic Thermal Modelling tools Thesis: EEBD 18/05

Abstract The solar and thermal performance of window is subject to a wide range of parameters. To simulate the energy performance is therefore difficult, and limitations might occur depending on the complexity of each case. This study presents some of the current limitations related to the assessment of window considering solar and thermal performance into the policy framework (standards, regulations and certifications) and two dynamic thermal modelling (DTM) tools. It is observed that the regulations and certifications referred to various standards regarding the assessment of solar and thermal performance that could affect the results. The study concluded that for more complex constructions, the difference between the software resulted in bigger deviation among the simulation outputs. By investigating some of the limitations in the DTM tools, this study also provides possible warnings for the assessment of window. Preface The present document represents the final project of the master s degree, promotion 2018, in the field of Energy-efficient and Environmental Building Design from Lund University. We would like to take this opportunity to express our sincere thanks to our supervisor, Dr. Niko Gentile from Lund University and the company Inform Design AB. They supported us in every stage of the thesis. Secondly, we would like to thank Medina Deliahmedova for her help and precious advices during the learning process of the software (WIS 3 and IDA ICE). Finally, yet importantly, a special thanks to Dr. Bengt Hellström for his technical support regarding the equation used in IDA ICE. Moreover, our gratitude goes to Scheldebouw B.V. for giving us further details about the manufacturing process of glazing systems (Scheldebouw Middelburg, Netherlands). Evangelos Marios Liaros & Frank Gergaud 2018 3

Glossary of terms and definitions Actual building ASHRAE BER BRE DGU DTM EVC g-value HVAC IB Iterative method Low-E MRT NCM Nonlinear equation Notional building SBEM SC (Solar Control) TGU Time step U-value Symbols and units The examined building being simulated as-built with the relevant information about size, shape, orientation, shading, activities, zoning, building fabric, fittings and services. American Society of Heating, Refrigerating and Air-Conditioning Engineers BER (actual Building CO2 Emission Rate) is the actual energy performance of the building examined (HM Government, 2016) Building Research Establishment Double Glazed Unit Dynamic Thermal Modelling External Ventilated Cavity Solar transmittance through the glazed construction at specific boundary conditions set by the standard. g-value is unitless. Heating, Ventilation and Air-Conditioning Integrated Blind An iteration procedure or iterative method is a mathematical procedure that is used to solve nonlinear system equations based on initial guess. Low emissivity coatings are used on glass panes to reduce the shortwave infrared transmitted by the pane. Mean Radiant Temperature National Calculation Methodology Equation wheren the output change without proportionality with the input A hypothetical building of the same size and shape as the actual building, but with pre-defined specified properties for the building fabric, fittings and services.. (BRE Global Ltd., 2017) Software tool which provides simplified energy calculations for buildings to comply with UK regulations Solar control coatings are selective coatings used on glass panes to reduce significantly the shortwave infrared transmitted by the pane, while allowing for the biggest portion of light to pass through. Triple Glazed Unit It is the set accuracy of the dynamic simulation. Thermal transmittance through the construction at specific boundary conditions set by the standard and without solar radiation. The unit is in W/(m²K) h cv,ex External convective heat transfer coefficient W/(m² K) h e /h i Surface coefficient of heat transfer (h e = external; h i = internal) W/(m² K) I s Incident solar radiation W/m² J i Radiative heat flow W/m² Q total heat transfer through the window W/m² T int Internal temperature C T op Operative room temperature C T out External Temperature C U f U-value of the frame area W/(m² K) U gv U-value of the glazed area W/(m² K) U t Total U-value W/(m² K) 4

Table of content Assessment of window systems considering solar and thermal performance 1 Introduction... 6 1.1 Background information 6 1.2 Goals 6 1.3 Problem statement 6 1.4 Research questions 6 1.5 Work structure 7 1.6 Software tools 8 1.7 Limitations 8 2 Methodology... 9 2.1 Policy framework 10 2.1.1 Standards 10 2.1.1.1 ISO 15099 10 2.1.1.2 EN 13363-2 11 2.2 Regulation and certification systems 12 2.2.1.1 The Building Regulation - Part L 12 2.2.1.2 BREEAM 13 2.2.1.3 Miljöbyggnad 13 2.3 Description of the cases 13 2.4 Phase 1 - Steady state calculations 16 2.5 Phase 2 - Dynamic thermal modelling 17 2.6 Phase 3 Annual heating and cooling need 21 3 Results... 22 3.1 Preliminary phase 22 3.1.1 Standard comparison (ISO 15099 and EN 13363-2) 22 3.2 Phase 1 Steady state calculations 23 3.3 Phase 2 - Dynamic thermal modelling 25 3.4 Phase 3 Annual heating and cooling need 30 4 Discussion... 33 5 Conclusion... 36 6 References... 37 Appendix A... 38 Appendix B... 39 Appendix C... 40 Appendix D... 41 Appendix E... 52 5

1 Introduction Assessment of window systems considering solar and thermal performance 1.1 Background information Window systems play a primary role on the solar and thermal performance of the buildings. During the last few decades, the growing popularity of transparent constructions in office buildings worldwide propelled a rapid and fascinating development of this type of constructions. With the increasing complexity of window constructions, the performance becomes difficult to assess with simulation software. Not surprisingly, the current scientific literature shows that there is a discrepancy between the empirically collected data and the simulations performed (Kalyanova et al., 2009). 1.2 Goals The M.Sc. thesis makes an investigation of the solar and thermal performance of exemplary type of windows used in office buildings. The performance is calculated by means of different tools, namely standards and Dynamic Thermal Modelling tools (DTM). The M.Sc. thesis identifies the relationships and differences between the results and aims to explain the underlying reasons of divergences. By explaining the reasons of divergences, this thesis fulfills its main goal, which is to raise awareness about possible limitations in this field. 1.3 Problem statement How the solar and thermal performance of window systems is currently assessed in the policy framework and software? 1.4 Research questions The thesis followed three research questions complementary to the problem statement. Which are the current limitations related to the solar and thermal performance of glazing systems in the DTM tools and policy framework? How could those limitations affect the solar and thermal simulation of buildings with such constructions? What could be proposed to enhance the current assessment of solar and thermal performance of window? 6

1.5 Work structure Assessment of window systems considering solar and thermal performance The standards ISO 15099 and EN 13363-2 were used as fundamental reference for describing the physics and the calculation process for the solar and thermal performance of the window. An investigation regarding the difference between those standards was carried out and the results can be observed in the section 3.1 Preliminary phase. Later, an overview analysis of national building regulations of United Kingdom, as well as of two voluntary energy certification systems used in Sweden and in UK, was carried out. The study aimed to investigate differences in the current way of examining window performance (indices used, categorization and thresholds). In the next stage, the solar and thermal performance of several exemplary window cases were simulated with one well-defined software for assessment of window systems in steady-state: WIS 3 and two widespread DTM software: IDA ICE and IES VE. Finally, in order to highlight possible divergences in the results and their causes, an investigation of the software structure some equations used, assumptions made, limitations of the inputs or outputs - was carried out. More specifically, the work was divided as follow. Defining the field of action, consisting of a. Preliminary phase, which included an in-depth study of selected standards, certifications and regulations concerning the solar and thermal performance of windows. Moreover, the preliminary phase included the selection of the five exemplary cases. Modelling, calculating, and understanding, consisting of three phases for the five cases. a. Phase 1 comprised the steady state U-value and g-value calculations. b. Phase 2 consisted of the DTM simulations. c. Phase 3 focused on the analysis of a single room, examining the findings from Phase 2 in terms of energy need. 7

1.6 Software tools Assessment of window systems considering solar and thermal performance Three different software tools were used in this thesis: WIS 3 (Window Information System), IDA ICE (IDA Indoor Climate and Energy) and IES VE (Integrated Environmental Solutions Virtual Environment), where WIS 3 was used for Phase 1 only. The software was selected because it is validated, well established in the industry and commonly used in Europe. WIS 3 WIS 3 is a software tool, developed under the Thematic Network WinDat (2001-2004). It uses the methodology and the formulas described in ISO 15099 to assess the solar and thermal characteristics of window systems and components in steady-state. The version used for this study was WIS 3.0.1 SP2 (windat Thematic Network, 2006). IDA ICE IDA ICE is a DTM tool developed by EQUA, and it is widely used in Sweden, among other countries. The mathematical model used in IDA ICE is traceable. The software provides a wide range of variables that can be logged and analyzed. IDA ICE was used in Phases 1, 2 and 3. The version of IDA ICE used in this study was the 4.7.1 in expert mode (EQUA, 2018). IES VE Integrated Environmental Solutions Virtual Environment (IES VE) is a software suite that unifies several specialized modules related to the energy analysis and performance of the buildings. Integrated Environmental Solutions Limited develops this tool, which is widely used in the UK among other countries. IES VE was used in Phases 1, 2 and 3. The version used for this study was VE 2017.3.0.0. 1.7 Limitations The study was limited to the solar and thermal performance of only the glazed part of the window. Therefore, the effect of the frames or the thermal bridges on the solar gains and the heat transfer was excluded from the analysis. Newly built office was the building type selected for this study, as it is among the building types with the highest applicability for glazing systems. Therefore, the study considered the national regulations and the most common certifications in Sweden and in UK related to this typology of building. In addition, the conclusions are drawn based on the five examined cases that cover a variety of window solutions. The shading device was simulated as a pane in order to follow the standard procedure from ISO 15099 and to be able to compare the results between the software. Indeed, it was noticed that IDA ICE and IES VE had different options for the settings of the shading devices and the comparison was therefore not possible if the shading device was not simulated as a pane. The characteristic properties of them were calculated accordingly and were assigned as properties of the panes. Consequently, there was no ventilation between the pane with the shading device properties and the rest layers of the window system for each case. Finally, windows performance was not compared against measured values in, for example, experimental testbeds. Therefore, the findings refer to the difference between software and the conclusions are drawn considering the standard as benchmark. 8

2 Methodology Assessment of window systems considering solar and thermal performance The work consisted of a preparatory review of the policy framework, followed by software simulation and data analysis. The overall workflow is presented in Figure 1. Workflow Legend Subject of thesis Research field Monitored output ASSESSMENT OF WINDOW CONSIDERING SOLAR AND THERMAL PERFORMANCE INPUTS (Policy framework) SELECTION OF CASES 1# DGU clear 2# DGU LowE 3# TGU LowE + IB 4# TGU 2LowE 5# TGU LowE + SC OUTPUTS WIS IDA-ICE IES VE - PHASE 1 - Steady-state calculation - PHASE 2 - DTM simulation - PHASE 3 - Energy simulation U-value g-value Inner surface temperature Total solar gain Heat transfer Heating energy needs Cooling energy needs Figure 1: Workflow summary Although part of the work itself, the outcomes of the review are rather presented in this section, as they shaped the following methodology used for simulation and data analysis. In particular, the review helped in finding the possible criticalities of software, and, therefore, suggested the choice of the specific cases. 9

2.1 Policy framework 2.1.1 Standards Assessment of window systems considering solar and thermal performance The theoretical framework of the study was based on the current international and European standards used to assess the solar and thermal performance of windows. Specifically, ISO 15099 and EN 13363-2 were studied, as they were the most commonly used at the time of writing. The ISO 15099 was reviewed in 2016 and remained up-to-date, while EN 13363-2 was replaced by EN ISO 52022-3:2017. The main focus of this study was to understand the affecting factors considered and the overall methodology, rather than the mathematical formulas used to describe the physical phenomena taking place. 2.1.1.1 ISO 15099 ISO 15099 is an international standard for the detailed calculation of solar and thermal transmission properties of fenestration systems. ISO 15099 describes a detailed procedure for calculating the thermal performance of windows, doors and shading devices and is the theoretical framework for validated software tools. Specifically, WIS 3 and IDA ICE use this international standard as a base for the solar and thermal performance calculations. ISO 15099 specifies the calculation methodology for: The thermal transmittance of window. The solar energy transmittance of window. In details, the calculation procedure takes into account: Single and multiple glazed unit systems. Coatings (low-e and solar-control). Pane spacing with gas and mix of gases. Four types of gases are included: Air, Argon, Krypton, and Xenon. Shading devices: only screens, curtains, and venetian blinds. For example, overhangs shading systems (e.g. brise-soleil) are excluded from the international standard. According to ISO 15099 the main physics properties that affects the overall performance of windows, are the thermal transmittance, the solar energy transmittance, the effect of shading devices, and the effect of ventilation. The energy balance quantifies the thermal balance through the window regarding any effect of the surrounding environment. 10

Energy balance Assessment of window systems considering solar and thermal performance The energy balance in a window system is summarized in Figure 2. Figure 2:Energy balance on double pane window Three variables affect the performance of glazing systems: Thermal transmittance Solar absorptance, transmittance and reflectance The energy balance equation is calculated with an iterative procedure until a certain accuracy threshold is reached. The four variables are interconnected to each other. 2.1.1.2 EN 13363-2 The European standard EN 13363-2 describes the detailed calculation for the total solar energy transmittance of the glazing system. EN 13363-2 is also used for the assessment of the thermal performance of window systems and the calculation methodology is similar to ISO 15099. This standard refers to EN 673:2011 and EN 410:2011 for U-value and g-value calculations respectively. 11

2.2 Regulation and certification systems The regulation in UK and certification in Sweden and UK were analyzed. This section explained briefly the criteria to comply with the regulation and certification and how the validation process is described. 2.2.1.1 The Building Regulation - Part L Part L is the part of the Building Regulation in UK that guides stakeholders from the building industry to design and construct energy-efficient buildings. Part L2A: Part L2A is one of the four parts from Part L of the Building Regulation in United Kingdom that focuses on the energy issues for new buildings. Therefore, as the study focuses on solar and thermal performance of window used in office buildings, Part L2A must be taken into consideration for UK. Part L2A comply with EN 410 and indirectly to EN 673 which is a normative reference for EN 13363-2. The design standards should comply with five criteria: 1. Achieving the TER (Target CO 2 Emission Rate) 2. Limits on design flexibility 3. Limiting the effects of heat gains in summer 4. Building performance consistent with the BER 5. Provisions for energy-efficient operation of the building Criteria 2 and 3 are the most interesting in this study, as they are linked to solar gains and thermal transmittance respectively. In order to comply with the building regulation and these criteria, the calculation must be done according to the NCM (National Calculation Methodology) with a specific software tool called SBEM. Other software tools, such as IES VE, can be used as well after being approved by BRE (Building Research Establishment). NCM: The National Calculation Method (NCM) comprises the methodology and the data sets for demonstrating compliance with the Building Regulations for buildings other than dwellings. The process is carried out by calculating the annual energy use for a proposed building and comparing it with the energy use of a comparable 'notional' building, which has pre-defined specified properties for the building fabric, fittings and services. ( UK NCM, 2016) In NCM, a real building is defined as to be the building designed with all the information required (construction, location, orientation, systems set up, fabric parameters). The building should only be modelled through accredited simulation programs or Simplified Building Energy Model (SBEM) software tool. Subsequently, an actual building is created with the same information as the real building but with the NCM database instead. This actual building is used for comparison purposes with the notional building. Finally, a notional building is automatically created from the real building and it is determined by the information input to the SBEM calculation (Building fabric, Zones, Air permeability, HVAC system, Lighting, General input data). NCM describes a methodology for the overall energy simulation of an office building and set the threshold that must be respected for compliance. However, no specific guidelines or methodology were provided for the modeling of window except from SBEM. 12

2.2.1.2 BREEAM Building Research Establishment's Environmental Assessment Method (BREEAM) is a sustainability rating scheme for the built environment, developed and owned by Building Research Establishment (BRE). It focuses on sustainability in building design, construction and use. It assists the measuring and reduction of the environmental impact of buildings and creates higher value and lower risk assets for the clients ( BREEAM International New Construction 2016 - SD233 2.0, 2016). BREEAM certification follows the same methodology described in Part L, meaning that in order to evaluate the performance of the examined building, it compares it to the notional building. BREEAM follows the same standard as part L. BREEAM certification does not explicitly refer to the solar and thermal performance of the window. This type of construction is regarded together with the rest of the building envelope only through the NCM. 2.2.1.3 Miljöbyggnad Miljöbyggnad is a Swedish environmental certification system for buildings (Sweden Green Building Council, 2018). The certification is oriented towards ensuring a safe and energy efficient construction with emphasis on the quality of the indoor environment. The performance of the buildings is ranked (bronze, silver and gold), and the ranking depends upon the satisfaction of specific minimum requirements. The methodology is based on examining the worst case possible (harsh environmental conditions) rather than the realistic annual performance of the building. The certification system does not seem to go into detailed examination of the characteristics of each case or reward an innovative design. The performance of window is not examined, even though, its influence on the overall performance is evident through the considered indices in all the relevant categories. Miljöbyggnad refers to ISO 15099 and EN 13363-2 for solar energy transmittance and ISO 6946 for the thermal transmittance. Noticed that for the standard related to the thermal transmittance, the calculation methodology is for thermal transmittance of windows without the effect of solar radiation. 2.3 Description of the cases For this study, the analysis was limited to five types of window constructions. The selection was based on the categorization of the window by the industry and the common practice (cavity width, properties of the layers), as well as, on the factors affecting the solar and thermal performance (mainly gas type, coatings and shading). The complexity was built up gradually from the first to the last case. All the cases were tested with and without the selected three shading devices, namely, two venetian blinds (reflective and absorptive), and a reflective roller shade. The five cases are illustrated in Table 1. Appendix A provides all the input parameters used for the pane and blinds. 13

Table 1: Description of the constructions Legend: : Blind (Venetian absorptive/reflective blind at 85 ) or Roller Blind : Low-E coating : Solar control coating CASE #1 Double Glazed Unit (DGU) with clear panes and Argon Outside 6 mm clear pane 16mm Argon 6 mm clear pane Inside The first case was the touch base case used to calibrate the software tools. CASE #2 Outside 6 mm clear pane 16mm Argon 6 mm clear pane with Low-E Inside Double Glazed Unit (DGU) with Low-E coating and Argon The second case introduced a Low-E coating, emphasizing on the simulation of long-wave radiation and how it affected the examined outputs. CASE #3 Outside 6 mm clear pane Air Air 6 mm clear pane 16mm Argon 6 mm clear pane with Low-E Inside Triple Glazed Unit (TGU) with Low-E coating and Integrated Blind (IB). Following the cases one and two, the choice was to investigate the integrated blind with Low-E coating. Indeed, the interstitial shading would directly affect the solar gains, stressing more on the secondary transmission and pointing out any subtle differences in the thermal performance of the construction. 14

CASE #4 Outside 6 mm clear pane with Low-E 16mm Argon 6 mm clear pane with Low-E 16mm Argon 6 mm clear pane Inside Triple Glazed Unit (TGU) with two Low- E coatings and Argon The use of two Low-E coatings in a TGU was selected to further investigate the bounce effect on radiation in between the coatings. The temperature, especially in the gap between the coatings, would be highly depended on the way the calculations would be carried out. CASE #5 Outside 6 mm clear pane with Solar Control 16mm Argon 6 mm clear pane with Low-E 16mm Argon Clear 6 mm pane Inside Triple Glazed Unit (TGU) with Solar Control and Low-E coatings and Argon Changing one of the Low-E coatings on the previously examined TGU to a Solar Control (SC) coating, would add the subtle details of selectivity. In that way, the mapping of the solar performance, hence, the overall thermal performance, would be complete. 15

2.4 Phase 1 - Steady state calculations The first phase of the study focused on the steady state calculations. The standard used was ISO 15099, while the boundary conditions were set according to EN 673:2011 and EN 410:2011 for U-value and g-value calculations respectively (Table 2). It is worthwhile noting that the aforementioned indices were also examined and compared both in WIS 3 and the two DTM tools. Table 2: Boundary conditions (steady-state calculation) Description Unit For U-value calculation For g-value calculation Air temperature outdoor C 0 30 Air temperature indoor C 20 25 Radiant temperature outdoor C 0 30 Radiant temperature indoor C 20 25 Direct solar radiation (W/m 2 ) 0 500 Convection coefficient outdoor (W/m 2 K) 20 8 Convection coefficient indoor (W/m 2 K) 3.6 2.5 The comparison aimed mainly at investigating whether, given the same properties in all software tools, there would be any divergences among the U-value and g-value calculations. Those deviations could have a significant effect on the dynamic performance of the constructions, thus they should be monitored from the beginning. 16

2.5 Phase 2 - Dynamic thermal modelling The second phase focused on the analysis of the used DTM tools. This section describes the methodology followed to perform the assessment of the solar and thermal performance of the five window cases with the two DTM software tools, IDA ICE and IES VE. Location The climate file selected to assess the difference between the two DTM tools was London (GBR - Gatwick Airport) from ASHRAE IWEC 2. The climate data was selected as indicative of the northern European climate from the database of each DTM tool. Individual cases The five examined cases - with and without shading - were analyzed for the most representative days of the year with two orientations (see Table 3). The orientations were chosen according to the sun altitude, which could drastically affect the output analyzed in Phase 2 and 3 of the window. In details, south orientation was mainly accounted for the high sun altitudes, while west orientation for the low ones. East orientation was discarded due to the limited time of the study and west orientation was considered alone as it is the worst-case scenario for overheating. North was discarded, as its contribution to the study would have been minimal. Concerning the date and for the scope of accentuating the possible divergence between the software tools, the days with the highest and lowest beam and diffuse radiation were selected for the assessment of the solar performance. Similarly, the days with the highest and lowest outdoor dry bulb temperature were selected for the assessment of the thermal transmittance. Table 3 summarizes all the individual subcases analyzed for each window constructions. In definitive, each of the five cases were tested for the six subcases, using the three different type of blinds. A total of ninety cases were analysed. Table 3: Details of Subcases SUBCASE ORIENTATION DETAIL DATE SUBCASE#A West Highest beam radiation 24-April SUBCASE#B West Highest diffuse radiation 23-July SUBCASE#C South Highest beam radiation 24-April SUBCASE#D South Highest diffuse radiation 23-July SUBCASE#E South Highest temperature 30-june SUBCASE#F South Lowest temperature 07-december 17

Construction and calibration process The building model used to perform the simulation with IDA ICE and IES VE was a shoebox model with a floor area of 5 m 5 m (25 m²) and a centered window of 3 m 2 m (6 m²). Figure 3 presents the geometry of the model. The goal was to analyze the performance of the glazing system alone. A calibration process was carried out to define the input parameters that could bias the analysis and then discard their effect. The first case without blinds was used for this purpose. The impact of each parameter was analyzed one at a time in both IDA ICE and IES VE. 2.5m 3m 5m Figure 3: Shoebox model 2m 5m Appendix B presents the table which summarizes every input used after the calibration process. o Other specific inputs In IDA ICE, the window type was set to window detailed, as the setting simply window did not fit the thesis purposes. Regarding the climate data, the daylight-saving time was removed from the results in both programs. An investigation about the sky diffuse model was performed as different models could be used. In IDA ICE, the sky diffuse model (Perez or ASHRAE) recalculates the diffuse solar radiation on a window from the horizontal irradiation given by the weather data. IES VE, instead, simulates the solar radiation as isotropic or anisotropic. After several trials before the actual thesis work, it was found that the ASHRAE sky diffuse model in IDA ICE resembled more to the anisotropic solar radiation in IES VE. Therefore, the ASHRAE sky diffuse model and the anisotropic solar radiation model were used in IDA ICE and IES VE respectively. The mathematical models of the zone was set to Climate in IDA ICE as according to the software developer, it is the most detailed physical model that IDA ICE offers (Sahlin, 2018). In IES VE, the model type was unknown. The convection models, external and internal, selected in IES VE were ASHRAE simple and CIBSE fixed values respectively. The sky and ground long-wave radiation model in IES VE was set to Black body at air temperature, while internal air emissivity was set to off and the starting temperature to 21 C. The same inputs were not explicit in IDA ICE. Nonetheless, all the settings were tested during the calibration process of the two software tools. The gas properties in IDA ICE and IES VE were input differently. IDA ICE followed ISO 15099 and considered conduction, dynamic viscosity, density and heat capacity of the gas in different temperatures (see Appendix C), while in IES VE only resistance and convection coefficient were used. In both cases, the values were calculated according to ISO 15099. 18

Output parameters Assessment of window systems considering solar and thermal performance Three output parameters were included in the comparison: inner surface temperature, total solar gains, and heat transfer through the glazed surface. Inner surface temperature. This variable provides information about the temperature on the internal surface of the innermost pane of the construction. The Inner surface temperature is indicative of the thermal performance of the window. In the standards, the glass temperature is affected by the absorption of the incident solar radiation and the heat transfer through the glass. Total solar gains Total solar gains comprise of all the heat gains indoors passing through the window. The heat gains can be either directly transmitted through the glazed part (primary transmittance) or through radiation and convection when the heat is absorbed (secondary transmittance). Heat transfer through the glazed area The heat transfer due to temperature difference between indoors and outdoors could be by conduction, convection and radiation. This output assesses the thermal performance of the windows, thus, a significant index monitoring any possible differences in the study. The inputs used for calculating the heat transfer were according to hourly weather data for each subcase (i.e. hourly dry bulb temperature, hourly solar radiation). Data analysis The output data were analyzed in Excel. The analysis of the results was carried out using dynamic charts in relation to equations. The entire set of numerical output and equations used for the data analysis are reported in Appendix D. o Dynamic chart The dynamic charts were created for every case and updated automatically with the outputs from the simulations in IDA ICE and IES VE. The dynamic charts had, on the first y-axis (left side) the temperature of the inner surface temperature and on the second y-axis (right side) the power per window area (W/m²). The power per window area was used to describe the power from the total solar gains and the heat transfer per square meter of window area (6m²). 19

Detailed analysis of heat transfer This section aimed to describe the equations used in IDA ICE and IES VE for the heat transfer in order to explain the difference observed in the results section for Phase 2. The equation used in IES VE was unknown, so assumption was necessary and confirmed by the results of this analysis. Hand calculations and values from the software were monitored and analyzed in the Figure 11 and Figure 13. Since the solar gains were quite similar between the two programs and the calculations used were quite advanced, no hand calculations were done for this index. The inner surface temperature as explained in the ISO 15099 depends on the energy balance equations and is related to the heat transfer. Thus, due to the complexity of the calculations for the former (iterative calculations needed), only heat transfer was calculated in detail. The equations for hand calculations in IDA ICE and IES VE are provided below: o IDA ICE Calculation of heat transfer that passes through the glazed area of the window (Q GlassTrans was given by the software as follow: Q GlassTrans =U GlasswoSurfRes a Glass (T ASide -T BSide ) W/m² (1) Where, Q GlassTrans a Glass is the total heat transfer through the window in W/m². is the glazed area in m². T ASide -T BSide is the difference of inner and outer surface temperature in K. o IES VE The equation in IES VE was unknown, therefore, it was assumed that the equation of the heat transfer was derived from IDA ICE as follow: Where, Q GlassTrans =U window a Glass T outside -T operative room W/m² (2) Q GlassTrans a Glass T outside - T operative room U window is the total heat transfer through the window in W/m². is the glazed area in m². is the difference of temperature between the outside environment and operative room temperature in K. The operative temperature is an output from IES VE for the relevant case and subcase. is the U-value of the glazed area of the window in W/(m²K) assuming the external and internal surface heat transfer coefficients are included. 20

2.6 Phase 3 Annual heating and cooling need Framework Phase 3 focused on monitoring the impact of the deviation noticed in Phase 2 on heating and cooling needed to keep the zone conditioned at 21 C, without the use of any active systems other than ideal air conditioning. The constructions comprising the zone were the same as in Phase 2, meaning that only heat gains or losses through the window were considered. The particular difference from Phase 2 was the dynamic use of the shading device throughout a whole year. Specifically, a threshold of 150 W/m² external incident solar radiation was set in order to draw the shading down. By considering the incident instead of the transmitted solar radiation, the impact of the coatings on the frequency of shading use was disregarded. Since the aim of the study was not the evaluation of the different constructions, but rather the assessment of their performance under the same settings, the use of external incident solar radiation threshold seemed to serve it better. 21

3 Results 3.1 Preliminary phase 3.1.1 Standard comparison (ISO 15099 and EN 13363-2) ISO 15099 and EN 13363-2 were both use for the assessment of the solar and thermal performance of windows. Even though regulations and certifications refer to both, a divergence was noticed. EN 13363-2 is a simplified alternative of ISO 15099. This comparison study pointed out these differences between the calculation methodologies of the analyzed parameters as listed below: Absorbed heat by conduction/convection: It is part of the heat flow rate equation and a difference was noticed in the calculation process between the standard when the glazing is in the vertical axis (90 degrees inclination). - ISO 15099 provides specific equations for vertical glazing. - EN 13363-2 provides two constant values that are integrated in a simplified equation. Boundary conditions: Boundary conditions are used to perform the U-value calculation for steady-state calculation. - ISO 15099: The temperature difference used for calculating the U-value under winter condition in ISO 15099 is 20Kand the external convective heat transfer coefficient, i.e. h cv,ex =20 W/(m 2 K). - EN 13363-2: The temperature difference used for calculating the U-value under winter condition in EN 13363-2 is 15K, having an external convective heat transfer coefficient of h cv,ex =18 W/(m 2 K. Gas properties: Gas properties are used to calculate the heat transfer in the glazing cavity. Differences were observed between ISO 15099 and EN 13363-2, an example is shown below: - ISO 15099: Argon gas has a specific heat capacity of 521.928 J/(kgK) at 10 C. - EN 13363-2: Argon gas has a specific heat capacity of 519 J/(kgK) at 10 C. In definitive, the comparison shows that: In regard to thermal transmittance, the two standards follow slightly different procedures especially in terms of input parameters for the convective heat transfer in the glazing cavity, the boundary condition, and the gas properties. In regard to solar energy transmittance, EN 13363-2 follows the same methodology as ISO 15099. ISO 15099 and EN 13363-2 aim to provide detailed calculation methodologies for the assessment of solar and thermal performance of the windows. However, a slight variation between the standards was noticed. This variation in the inputs used in both standards could affect the assessment. 22

3.2 Phase 1 Steady state calculations Phase 1 presents the results from the steady-state calculations in terms of U-value (Figure 4) and g-value (Figure 5). The Appendix E presents the numerical values. The analysis was performed in WIS 3, IDA ICE and IES VE. Figure 4 presents the U-value of the five selected cases and it seems that WIS 3 and IES VE are always very close to each other. A slight deviation was noticed for IDA ICE, the U-value was always higher especially for the case with high U-value and without blind. However, the difference in between the program was negligible in this phase. WIS 3.0 U-value / W/(m²K) 2.5 2.0 1.5 1.0 0.5 0.0 No shading VB - reflective VB - absorptive Roller blind No shading VB - reflective VB - absorptive Roller blind No shading VB - reflective VB - absorptive Roller blind No shading VB - reflective VB - absorptive Roller blind No shading VB - reflective VB - absorptive Roller blind 1. DGU clear 2. DGU LowE 3. TGU LowE + IB 4. TGU 2 LowE 5. TGU 1 LowE + SC Figure 4: U-values for steady-state conditions of the five cases, calculated with three different software. 23

Figure 5 presents the results for the g-value of the five cases. The same trend was observed as for the U-value, IDA ICE was slightly different than WIS 3 and IES VE especially in the case of no blind where the g-value is usually higher. The case 3 is much more affected by the shading device. WIS g-value / 1 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 No shading VB - reflective VB - absorptive Roller blind No shading VB - reflective VB - absorptive Roller blind No shading VB - reflective VB - absorptive Roller blind No shading VB - reflective VB - absorptive Roller blind No shading VB - reflective VB - absorptive Roller blind 1. DGU clear 2. DGU LowE 3. TGU LowE + IB 4. TGU 2 LowE 5. TGU 1 LowE + SC Figure 5: g-values - for steady-state conditions of the five cases, calculated with three different software. To conclude with Phase 1, the steady-state calculation does not differ significantly between WIS 3, IDA ICE and IES VE. 24

3.3 Phase 2 - Dynamic thermal modelling Phase 2, based on IDA ICE and IES VE, generated a number of results for the cases analyzed. Some of those were interesting to highlight divergences between the two DTM software. Those cases are reported below, while Appendix D presents the data analyzed of every simulated cases. The same trend of results as CASE#1 were observed in CASE#2,3,4 and 5, it was decided not to show the graphs. The legend for all the graphs is shown only in Figure 6. It is noteworthy that in the cases where internal shading is used, the inner surface temperature referred to the temperature on the surface of the internal shading device. CASE #1 - DGU with clear panes and Argon Figure 6 presents the DGU with clear panes and Argon without shading. Subcase#C (south orientation and highest beam radiation) showed that in case of without blind, IDA ICE and IES VE performs the same. Similar results were observed between IDA ICE and IES VE. The other cases analyzed did not present different results either when there is no blind. Temperature / C 60 50 40 30 20 10 IDA Solar Gain IDA Heat transfer IDA Inner surface temperature 0 00:00 06:00 12:00 18:00 Figure 6: Case#1 / Subcase#C / Without blind 24-Apr Figure 7, Figure 8, and Figure 9 show the results for inner surface temperature, heat transfer and solar gains in the case of blinds for a DGU clear filled with Argon. It was noticed, that the results differed between IDA ICE and IES VE especially for the heat transfer and inner surface temperature. Indeed, IDA ICE had higher heat transfer but lower inner surface temperature than IES VE. This difference became significant when the absorptive venetian blind was applied. Regarding, the solar gains, it was found out that the slight variation observed was due to weather data interpolation in IDA ICE. Figure 10 shows that the solar gain is the same in IDA ICE and IES VE when smaller time step was used. The solar gains were considered to be the same. 25 IES Solar Gain IES Heat transfer IES Inner surface temperature 500 400 300 200 100 0-100 Power per window area / (W/m²)

Temperature / C 60 50 40 30 20 10 0 500 400 300 200 100 0-100 Power per window area / (W/m²) 00:00 02:00 04:00 06:00 08:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 24-Apr Figure 7: Case#1 / Subcase#C / With reflective venetian blind at slat inclination of 85 Temperature / C 60 50 40 30 20 10 0 500 400 300 200 100 0-100 00:00 02:00 04:00 06:00 08:00 10:00 12:00 14:00 Power per window area / (W/m²) 16:00 18:00 20:00 22:00 24-Apr Figure 8: Case#1 / Subcase#C / With absorptive venetian blind at slat inclination of 85 Temperature / C 60 50 40 30 20 10 0 500 400 300 200 100 0-100 Power per window area / (W/m²) 00:00 02:00 04:00 06:00 08:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 24-Apr Figure 9: Figure 5: Case#1 / Subcase#C / With roller blind 26

Weather data interpolation In all the cases, a slight deviation was noticed between the programs for the solar gains. This deviation was due to interpolation of the weather data in IDA ICE which were calculated according to the used time step. In IES VE, the values were not interpolated, as the data were taken directly from the weather file. A time step of less than 0.05 hours in the simulation increased the accuracy of the interpolation and the results were closer between IDA ICE and IES VE. Nevertheless, the results of this thesis were calculated with 1.5 hour time-step, to maximize the speed of the calculations, as the difference in the results was minor for the examined cases. Figure 10 shows that with a lower time step (i.e. larger amount of data) the interpolation of data was not significant and the difference between IDA ICE and IES VE regarding the solar gains was the same. The results from the heat transfer and the inner surface temperature were slightly affected but this difference was neglected. The time step in IDA ICE used was set to 0.01h. This explains the difference observed in Figure 6 regarding the solar gains. Temperature / C IDA Solar Gain IES Solar Gain IDA Heat transfer IES Heat transfer IDA Inner surface temperature IES Inner surface temperature 60 50 40 30 20 10 0 00:00 06:00 12:00 18:00 24 Apr Figure 10: Case#1 / Subcase#C / Without blind / Time step set to 0.01h 500 400 300 200 100 0 100 Power per window area / (W/m²) 27

Detailed analysis of heat transfer The analysis of heat transfer was performed for the CASE#1.C with absorptive venetian blind where the biggest difference was observed in order to explain the difference noticed in the Figure 8 for the heat transfer in IDA ICE and IES VE. o Heat transfer in IDA ICE Figure 11 presents the results for the U-value used in IDA ICE (U glasswosurfres ) combined with the total solar gains. The period analyzed is the same as the CASE#1.C with absorptive venetian blind in the Figure 8. The U-value of the window was logged from IDA ICE. The U-value varied from 2.4 W/m²K to 3.2 W/m²K. U-value / W/(m²K) 2.5 3 1.5 2 0.5 1 0 00:00 06:00 12:00 IDA Solar gain 18:00 00:00 06:00 Figure 11: Combined U-value of the window and solar gain in IDA ICE The logged U-value seems to be affected by the solar gains. The heat transfer of the window was calculated with the U-value of the window as can be seen in Equation 1. Therefore, this analysis shows that the thermal transmittance in IDA ICE is affected by the solar gains as U- value is affected by solar gains. o Heat transfer in IES VE 12:00 Figure 12 presents the results for the U-value of the window in IES VE combined with the total solar gains for the same three days in April as in IDA ICE. The U-value of the window was logged from IES VE and seems to be steady-state (no change during the day). 18:00 U-value "transient" IDA 00:00 06:00 12:00 23-Apr 24-Apr 25-Apr 18:00 300 250 200 150 100 50 0 Solar gain / (W/m²) IES Solar gain U-value IES U-value / W/(m²K) 2.5 3 1.5 2 0.5 1 0 00:00 06:00 12:00 18:00 00:00 06:00 12:00 18:00 00:00 06:00 12:00 18:00 300 250 200 150 100 50 0 Solar gain / (W/m²) 23-Apr 24-Apr 25-Apr Figure 12: Combined U-value and solar gain in IES VE 28

According to the results of the detailed analysis of heat transfer, it seems that IDA ICE considers a heat transfer that is affected by the solar radiation while the heat transfer in IES VE does not seem to vary. This could be the reason of the difference observed for the heat transfer in the Figure 8. The assumption made regarding the equation used in IES VE was proved with Figure 13. The figure compared the results from IES VE and the hand calculation made with assumed equation for IES VE. IES hand calculation with inner surface temperature show the hand calculation values when instead of operative room temperature, the inner surface temperature is considered in the equation. The assumed equation for IES VE with room operative temperature ( IES hand calculation ) seemed to be close to the results given by IES VE ( IES monitored value from software ). 0 00:00 12:00 00:00 12:00 00:00 12:00 23-Apr 24-Apr 25-Apr IES hand calculation with operative room temperature IES monitored value from software IES hand calculation with inner surface temperature -10-20 -30-40 -50-60 -70-80 Heat transfer / W/m² Figure 13: Comparison between heat transfer from monitored value and hand calculated value. 29

3.4 Phase 3 Annual heating and cooling need The results showing the impact of each construction on heating and cooling need for both programs are presented in Figure 14. The diagram shows that the differences between software increase as the complexity of the constructions increases. Indeed, the differences in cases #4 and #5 were higher than the other, respectively 15% and 11%. The relative difference in the total energy needs between the two software tools was examined, as can be seen on the upper part of Figure 14 with the percentage of difference. 120 100 80 60 40 20 43.5 41.2 61.5 57.7 32.3 30.6 37.7 36.5 37.7 36.5 37.7 36.5 64.6 60.4 22.8 20.5 50.6 43.6 25.5 23.3 11.7 0 15.4 15.2 12.8 11.9 8.4 6.8 8.5 7.0 13.1 IES - VB Reflective IDA - VB Reflective IES - VB Absorptive IDA - VB Absorptive IES - Roller blind Energy need per floor area / (kwh/m²) IDA - Roller blind IES - VB Absorptive IDA - VB Absorptive IES - VB Absorptive IDA - VB Absorptive IES - VB Absorptive IDA - VB Absorptive IES - VB Absorptive IDA - VB Absorptive IDA - VB Absorptive CASE#1 CASE#2 CASE#3 CASE#4 CASE#5 DSF Heating (kwh/m²) Cooling (kwh/m²) Figure 14: Energy need comparison between IDA ICE and IES VE 30

Even though an overall increase of the difference was noticed, as the construction had gradually lower U-value and g-value (cases #1 to #5), further investigation was carried out to examine the results in cases #4 and #5. Subcase#C with venetian absorptive blind was examined for both cases, as the effect of solar radiation was more obvious. Figure 15 illustrates the difference between heat transfer for IDA ICE and IES VE. The latter seemed to have a very similar performance between cases #4 and #5, while IDA ICE differed significantly. As noticed in Phase 2, the heat transfer in IDA ICE was affected by the solar gains, while in IES VE did not. IDA #4 IES #4 IDA #5 IES #5 Heat transmission / W/m² 0-2 -4-6 -8-10 -12 00:00 06:00 12:00 18:00 00:00 06:00 12:00 18:00 00:00 06:00 12:00 18:00 00:00 23-Apr 24-Apr 25-Apr Figure 15: Heat transfer for case #4 and 5 in IDA ICE and IES VE To highlight the impact, that the consideration of solar radiation could have in the energy calculations (difference noticed between IDA ICE and IES VE), Figure 16, presented below, illustrates the difference between the thermal balance (solar gains - heat transfer) in IDA ICE and IES VE for three days related to Subcase C. It was shown that the difference between the results was taking place during the day, when there were solar gains. Case #4 was always higher than case #5, explaining the relative difference between those cases shown in Figure 14 (15% and 11% respectively). Absolute difference between thermal balance (solar gain - heat transfer) / (W/m²) CASE #4 (IDA ICE - IES VE) 30 25 20 15 10 5 0 00:00 06:00 12:00 18:00 00:00 06:00 CASE #5 (IDA ICE - IES VE) 12:00 18:00 00:00 06:00 12:00 23-Apr 24-Apr 25-Apr 18:00 00:00 Figure 16: Absolute difference between thermal balance (solar gain - heat transfer) in IDA ICE and IES VE 31