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DISSERTATION - SUMMARY
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MEERADEVI KATHALIYIL | Msc. CRESTA | SEM 3 | ARCH 721 | 201577234
BACKGROUND
Recently, human-induced climate change has had observable effects on the environment. Experts believe that if the global temperatures are not limited well below 2°C above pre-industrial levels, we will have to face severe consequences of climate change. As per "The Paris Agreement", the UK is committed to reaching net-zero energy by 2050. In the UK, the construction industry is responsible for 49% of carbon emissions; hence, it is necessary to take quick actions to decarbonize this sector. To achieve net-zero by 2050, the UK is attempting to produce a large percentage of energy from renewable sources while simultaneously improving the energy performance of all existing and new buildings to lower the demands of the new decarbonized grid. Therefore, reducing the energy demands of buildings is of great importance. New technologies are developed and introduced to improve building energy consumption. Validating the performance of these technologies in diverse environments is imperative. Only then can the actual energy-saving potential of these technologies be understood. Therefore, assessing these technologies' performance in the early stages is crucial. Electrochromic (EC) window glazing is one such technology that can dynamically control the entry of daylight and solar radiation into buildings. This technology is said to help achieve energy efficiency by letting in and shielding the sun dynamically in reaction to climatic and weather conditions, reducing the energy consumed for heating, cooling, and lighting.
What are Electrochromic Windows?
The electrochromic windows were introduced in the market as an alternative to the traditional windows that require shading devices. It is an electronically tintable glass that can dynamically control glare from direct sun or bright sky while maintaining occupant comfort, maximizing access to daylight and outdoor views, reducing energy costs, and providing architects with more design freedom. These windows are more popular for their energy-saving potential. Electrochromic (EC) devices consist of materials that can change their properties when electric current or voltage is applied.
How do Electrochromic Windows work?
Electrochromic windows consist of unique materials that have ‘electrochromic’ properties. A material that changes color when energized by electricity is called "electrochromic". In these materials, electricity initiates a chemical reaction. This chemical reaction changes the properties of the material. The material can be changed between colored and transparent states in electrochromic windows by applying electricity. Different levels of visibility are available with electrochromic windows, just like suspended particle devices
SageGlass by Saint-Gobain is one of the world's leading manufacturers of electrochromic windows. The properties of SageGlass electrochromic windows have been used in this study to perform simulation. Electrochromic coating of SageGlass consists of five layers of ceramic material, which are less than 1/50th the thickness of a human hair.
Why the UK?
Studies have shown that EC windows are more effective in warmer climates as it helps in dynamic solar control, thereby reducing the cooling loads drastically. Electrochromic (EC) windows have been studied extensively for their energy performance, but a handful are done for cooling-dominated locations. Research on heating-dominated regions is minimal. There has been very little study of these windows' impact in the UK since it is predominantly a heating-dominated region. However, the UK has been warmer due to climate change over the past few years. Future climate predictions show that winters will be warmer, and summers will be hotter and drier. Currently, the summers are much hotter in the UK than in past decades, and many buildings in the cities face overheating issues in the summer. In addition, many office buildings are said to require mechanical cooling in the future. Therefore, assessing the performance of EC windows in this climate is highly relevant as it might become an excellent solution to reduce the cooling loads or sometimes altogether avoid air conditioning that might be needed in the future.
Why study on office buildings?
Large windows and unobstructed exterior views are essential in an office building to ensure the health and well-being of the employees. It is therefore common for office buildings to have larger windows. This also becomes one of the reasons why offices are found in buildings with large, glazed facades. Offices have become one of the most occupied typologies in most high-rise buildings in urban centers. Due to several advantages, glazed facades are becoming the designer's favorite for high-rise buildings and skyscrapers. However, as the glazing area increases, they facilitate heat transfer between the interior and exterior, which increases the cooling and heating loads. Therefore, in these types of buildings, the choice of glazing type becomes extremely important. Hence, office buildings become one of the most appropriate choices of typology for this study.
Why London and Manchester?
According to the list of the most populated urban areas in the United Kingdom, as defined by the Office for National Statistics (ONS), London and Manchester are the largest and the secondlargest urban areas in the UK. Therefore, both these locations have many office buildings. This becomes one of the reasons for the choice of location. The most crucial factor is the differences in the climate of both locations. London falls in the southern part of the UK and experiences a warmer climate than other regions in the UK. In addition, the city has an urban heat island effect. On the other hand, Manchester lies in the central portion of the UK and has a different climate than London. A detailed climatic comparison of both locations can be found in the next section; hence London and Manchester have been chosen as the locations of study. Ideally, other locations in higher latitudes should also be considered in the study to get a complete picture of the performance of EC windows in the UK. However, considering the study's time frame, scope and extent, the number of locations has been limited to two.
RESEARCH AIMS, OBJECTIVES AND HYPOTHESIS
Research Aims and Objectives
This research aims at evaluating the annual energy performance of office buildings with EC windows in the climate of the UK. The energy performance of EC windows will be compared with clear, LoE Argon-filled double and tripleglazed units. The study will focus on the effect of various design parameters and each case's total, heating, cooling, and lighting energy consumption. The evaluations will be done for both current and future weather files to assess the long-term effect. The UK is in a cold temperate zone, and very few studies have been conducted on the effect of electrochromic windows. So, the main questions this research aims to answer are: � Are EC windows effective in reducing energy consumption in the climate of the UK? � In which location (London/Manchester) do these windows perform better, and what are the energy-saving potentials? � In which orientations do these windows perform best? � In which window-to-wall area ratios do these windows perform best? � Which is the most influential design parameter? � Compared to the base scenario, how much do these windows reduce or increase energy consumption? The actual performance of any system is not limited to the factors discussed above and is dependent on several other local factors. Hence a complete decision cannot be made based on this study. However, this research can act as an initial reference for energy assessors and sustainable architects before considering electrochromic windows in buildings.
Hypothesis
The hypothesis was that, compared to base scenarios, � EC windows effectively reduce total annual energy consumption in the climate of the UK. � Due to London's higher temperatures than Manchester, EC windows save more energy in London. � Energy savings of EC windows are more in southern orientations. � EC windows help in reducing cooling energy. � EC windows make significant savings in lighting energy.
Research Gaps
Following are the identified gaps in the research: � It was found that several studies have been done on EC windows, and their energy-saving potentials have been calculated, but most of them were done in cooling-dominated regions. � Very few studies have been done in heating-dominated regions. For example, the UK is a heatingdominated region, and very few researchers have tried to evaluate the EC window's effectiveness in this climate. � None of the studies done in the UK context has deeply analyzed EC windows' total energy saving potential. � The parameters considered in the studies are also less. For example, in the case of WWR and orientations, many research papers referred highlighted the importance of these parameters. However, the studies have considered only one or three WWRs in specific orientations, which may not give a complete picture of the performance of EC windows. Only a detailed analysis of different WWRs and orientations can give a complete picture of the effectiveness of these windows. � It was also observed that most of the research papers had compared the performance of EC windows with single pane windows. This will show a larger percentage of energy saving. In a real scenario, designers need to know how far they perform better than efficient standard double-glazed or triple-glazed units available in the market. � The studies that used sensitivity analysis to identify the most influential design parameter have considered overall building construction parameters. Window parameters just become some among them. No studies have done a sensitivity analysis exclusively for window design parameters and studied its relative importance.
Most of the research papers referred had similar aims to the research questions of this study. The difference lies in the location, climate and the parameters considered. This study aims to bridge this gap and contribute to the knowledge about the performance of EC windows in the climate of the UK, which can become a valuable reference during the early stages of the design.
LOCATIONS
London and Manchester are the two locations chosen for this research. Diversity in their climates is one of the reasons for the choice of these two locations. As per the 4.5 SRES scenario, the current and future weather files of both locations are compared and shown in the following figures. Values from the .epw files of the locations generated using Meteonorm software are used to create the graphs below.
Temperature graphs clearly show that London is warmer than Manchester. As per the temperature records of 2022, the temperature in London has gone as high as 40 degrees. However, future weather files also show that the temperatures will rise. Graphs show that Manchester is more humid than London. In the future, for summer months, humidity slightly reduces by 2050 and then again increase by 2080.
The predominant wind directions in both locations remain the same in current and future climates. Manchester experiences cooler and stronger winds. In London, the wind direction is mainly from the west and southwest; in Manchester, the wind direction is predominantly southwest. There is no significant change in wind speed in future weather conditions. Manchester experiences stronger winds than London on an average daily basis. However, on observing the graph of recorded high and low wind speeds, it can be observed that the recorded high wind speeds in London are higher.
Temperature Relative Humidity
Wind
London Manchester
LOCATIONS
The sun shading chart of London signifies the necessity of shading devices for current climates, whereas in Manchester, though shading may not be significant in the current scenario, it can have a considerable effect in future climates. The graphs also show that considerably deep overhangs can only effectively control the summer sun in London.
In London, the regular comfort hours rise from 12.6% in the current climate to 15% in 2080. As the temperature rises, more hours below the comfort zone fall into the comfort zone. The effectiveness of window shading also increases. The heating load decreases by 2050 and rises by 2080, whereas the cooling load increases by 2050 and slightly reduce by 2080. The effectiveness of passive techniques like direct evaporative cooling, natural ventilation, fanforced ventilation, etc., are slightly reducing over the years. Internal heat again and heating play a significant role in bringing comfortable conditions. Passive solar heat gains also help in bringing many hours into comfortable conditions. Though EC windows in clear state help in passive solar heat gain, it is possible that EC windows perform well in terms of energy savings in these climates. In Manchester, the percentage of regular comfort hours rises from 5.6% in the current climate to 6.9% in 2080. In London, heating could bring 38% of hours into the comfort zone, whereas in Manchester, heating is required to bring 49.2% of hours into comfort conditions. This shows the difference in temperatures in both locations. The heating load reduces over the years; however, in this region, cooling is required for a few hours in the future, though it is not required in the current condition.
All the graphs analyzed so far show the differences in the climatic conditions of both locations. In addition, the temperature, relative humidity, sun shading, psychrometric charts and future climatic conditions show that the temperatures are rising and will continue to rise, which makes the evaluation of energy-saving technologies like Electrochromic windows highly significant. In addition, performance evaluation of EC windows in these climates can give a picture of how far they are effective in the climate of the UK.
Psychrometric chart London
Manchester
BUILDING MODEL AND PARAMETERS STUDIED
Building Model Parameters studied
Building Geometry
A square shaped, six-sided representative office building of length 12m, width 12m and height 3m was modelled in design builder. One of the façades consisted of a window. The glazing templates, window-to-wall area ratios and orientations of this window were varied during simulations. As a rule of thumb, daylight penetrates a room for most latitudes, roughly 2.5 times the height of the top of the window (Ibrahim and Hayman 2005). The standard height of the test cell was 3m. The daylight zone may vary slightly for different orientations. Hence, to ensure that the effect of natural daylight and artificial light is quantified correctly, 4 times the window's height (12m) was chosen as the dimension of the sides of the room. A square shape was chosen to ensure that the gains/losses remained identical from all sides
Building Construction
Default state-of-the-art medium-weight construction templates available in Design Builder were used for the roof, walls, and ground floor. The U-values were modified to 0.1 W/m2-K. The LETI standard has been followed here. LETI suggests a U-value between 0.13-0.15 W/m2-K for walls, 0.08-0.10 W/m2-K for floor, and 0.10-0.12 W/m2-K for Roof. Table 1 shows the test cell’s fabric U-values. As per the LETI standard, the airtightness needs to be less than 1 m3/h-m2 @50 Pa. However, this test cell has been made airtight as per the Passivhaus standard (<0.6 m3/h-m2 a@50 Pa). Four major parameters were studied and analyzed in this research.
Location
To understand the effect of location on the performance of Electrochromic windows, 2 locations were chosen for the study. Considering the time frame and extensive number of simulations involved in this study, the number of locations chosen was limited to 2. In addition to current weather files, future weather files for 2050 and 2080 as per 4.5 SRES scenario was also obtained for both locations and used in the simulations.
Glazing type
Detailed descriptions of all the glazing types used in the study are described in the following sections. The study aims to analyze if electrochromic windows are effective in the UK climate and compare their performance with standard double and triple-glazed units. So, the base case is a clear LoE Argon-filled glazing type. In a real-life scenario, the glazing units may have internal shading devices to control excessive heat and light from the sun. The energy performance of the transparent state windows will differ from those with internal blinds. Hence, EC windows are also compared with clear LoE Argon-filled windows with internal blinds.
Window to Wall area Ratio (WWR)
One of the variables considered was the window-to-wall area ratio. Though several studies have emphasized the importance of WWR, very few studies have observed the energy consumption of EC windows in different WWRs. So, this research tried to analyze how the energy consumption changes for each glazing type for different WWRs. The choice of 10 ratios in equal intervals helps identify how energy varies as the ratios gradually increase.
Orientation
Simulation results were obtained for all major 8 orientations. This helps identify the orientation where EC windows are most effective and least effective.
