Energy-efficient retrofitting with exterior shading device in hot and humid climate – case studies from fully glazed multi-storied office buildings in Chennai, India

ABSTRACT Many existing buildings are not sustainable, such as poorly insulated office buildings with large glass window panels that significantly increase the cooling energy use in a hot and humid climate. Energy-efficient retrofitting can substantially reduce energy use through a passive façade design. This paper suggests simulation as a method for selecting a façade retrofit solution at the early design stage. A façade retrofit solution that requires the integration of all three sustainability dimensions: energy efficiency, visual comfort, and economics. Two case studies of fully glazed multi-storied office buildings of different sizes demonstrate the methodology. This research adopted two simulation methods: one for façade retrofit solutions with fixed exterior shading device (ESD) types and the other for a dynamic ESD. The results show that fixed ESD with perforated fabric for 100% of the glazing area was 22.7% energy-saving retrofitting solution than the base case for the small sample and 17% energy-saving for the large sample with a low payback period of 7 years for both the case sample. Building practitioners, stakeholders, and end-users can use this simulation methodology for a successful façade retrofit decision-making at the early design stage.


Introduction
The growing interest in sustainable high-performance buildings and new construction is not enough to solve the problem of sustainable development. First, new high-performance buildings reflect just a tiny percentage of the buildings compared to the large numbers of existing buildings (Nagarajan et al. 2015). Second, new constructions require land, energy, materials, and financial capital. Demolition existing buildings to build new high-performance buildings would waste all the energy already invested and used (Poel, van Cruchten, and Balaras 2007). Retrofitting existing buildings will significantly reduce their energy usage (Zhenjun et al. 2012;Martinez and Carlson 2014), and "work on the outside of the envelope is likely to be sufficient for most existing buildings." (Mara 2010). For multi-storied buildings, the façade retrofit is an effective way to reduce space cooling energy use.
In the early 2000s, multi-storied office buildings in the major cities of India used transparent glass designs influenced by the West and did not account for the local climate and context. These fully glazed façade was the owner's pride, airtight, and quick to construct. However, they were low-performance as the owner tended to underinvest in building a passive envelope design and over-invest in active building systems (Blumenfeld and Thumm 2014). Such fully glazed buildings in a cooling-dominated energy use context must be protected from solar heat gain by infiltration (by using well-insulated opaque facade elements) or conduction (by using shading devices) (High-performance building envelopes: design methods for energy-efficient facades ajla aksamija Aksamija A 2015). In most retrofit projects, energy-efficient retrofit strategies are not used due to a lack of knowledge of the investment required and the efficiency of the potential energy-saving strategies (Basarir B ,Diri B & Diri C 2012). Recent research has focused on energy cost and turned to financial evaluation of building retrofit (Polly et al. 2011).
With a growing magnitude of existing FG office buildings, India needs to be retrofitted at the earliest for energy efficiency. Façade retrofit in India is a relatively new area of practice and research. Due to the unavailability of energy-efficient retrofit data, methods, and unclarity of return on investment of the façade retrofit, this paper aims to improve the energy performance for FGM office buildings in a hot and humid climate at the early stage.
The study aims to identify the best façade retrofit solution that provides the highest energy saving with optimal visual comfort and the least initial cost for FGM office buildings in the hot and humid climate of Chennai, India. We investigate the simulation tools used in the early design stage to find the energyefficient façade retrofit solution with a payback period by changing the glazing or adding fixed ESD. We also use simulation methods to investigate the performance of a dynamic ESD in this climatic context. This research is in two stages; first, for a façade retrofit solution for fixed types by changing or reducing the glazing or adding fixed ESD with payback periods. The second stage uses the best solution material of the first stage for a simple dynamic ESD without paybacks. Two fully glazed office buildings are selected in the experimental study region of Chennai to understand the dynamic parameters involved in the façade retrofit. The base case simulation model of the case samples is created. The retrofit solutions are compared by revising the base case model's façade elements.

Literature review of façade retrofit in hot and humid climates
High solar radiation and high humidity are the most influential climatic factors in hot, humid climates. Two most common strategies for fully glazed buildings are incorporating interior or exterior shading devices (Balaras et al. 2000) to minimize the heat gain and improve the glazing (Cheung, Fuller, and Luther 2005). In hot and humid regions, the fully glazed commercial buildings have to deal with sun-glare and cooling load energy use; the natural ventilation is insufficient or impossible as these buildings are fully air-conditioned for thermal comfort (Tariq Sheikh and Asghar 2019).
Building envelopes in a hot and humid climate can enormously impact total energy consumption for HVAC (Aurora and Hasibuan 2020). Energy efficiency can be achieved through envelope designs, including shading, WWR, glass selection with a low shading coefficient, and using natural light for indoor lighting (Aurora and Hasibuan 2020;El-Darwish and Gomaa 2017). The most effective is the shading design that can be applied to building a façade retrofit. It can mitigate solar insolation, offer reductions in cooling loads, and improve the distribution of daylight (Carletti, Sciurpi, and Pierangioli 2014). The shading device added to the exterior is more effective than the interior blinds or shades (Saifelnasr 2015). Solar shading has been an essential step in energysaving control of solar radiation before it gets to the inside buildings. Use of shading devices: there are several examples found in the existing literature. Shading systems have been extensively studied by Singh et al. (Singh, Lazarus, and Kishore 2015), which concluded that fixed and dynamic devices save significant energy by reducing cooling loads due to solar gains. The shading devices are primarily classified as fixed and dynamic ESD. The basic types of fixed shading are the horizontal fins, vertical fins, egg crate (both), and solar screen. Research on horizontal fins or overhang of 1 m in a hot and humid climate like that of Calcutta can reduce heat gain by 10-12% in all orientations (Saboor, Kirankumar, and Setty 2016). In Malaysia, egg-crate shading devices can result in higher annual cooling energy savings than vertical shading and horizontal shading (Khin Kiet Lau et al. 2016). Like the traditional Jaali, solar screens are shading devices used in building design as a continuous layer covering transparent areas (Lavin and Fiorito 2017). Solar screens are used in traditional or vernacular buildings such as Jaali to protect the windows from sun rays and reduce glare. A study of a solar screen in a desert climate was carried out to improve daylight, reduce glare and increase thermal comfort by analyzing its perforations (Sherif, Sabry, and Rakha 2012). The solar screen takes the direct, indirect, reflected, transmitted, and absorbed solar radiation (Premier and Dehò 2013). Today solar screens are made of innovative materials such as technical fabrics and composite materials, especially with smart materials and technologies (Premier and Dehò 2013). With the advancement in simulation tools and methods, dynamic shading has been applied to new buildings in hot climates. More specifically, the shading devices of the Al-Bahar facade open like an umbrella as soon as sun rays hit its sensors and close when the sun goes down in the evening (Boake TM2014). This process reduces the building's solar heat gain, cooling load, and optimum daylight.
In the past decade, limited studies on the use of shading as a façade retrofit to hot and humid climates, and most studies for residential retrofit (FacadeRetrofit. org: web reference) or fully glazed buildings in cold climates (Ayodele, Oyinlola, and Subhes 2020). However, the literature review showed an apparent lack of review papers on applying simulation methods for façade retrofit and its financial evaluation, especially for FGM office buildings in a hot and humid climate in developing countries like India. Moreover, there is minimal research on dynamic shading as a retrofit strategy for this climate.

Research context
India faces the issue of a multitude of existing office buildings that need to be retrofitted for energy efficiency. India is still in the nascent stage of energy conservation for new buildings, as existing office buildings' retrofit practices are not yet established. Most countries in Asia are retrofitting their existing government buildings; in India, however, hardly a dozen office buildings in the IT sector have registered for façade retrofit since 2012 (Martinez et al. 2016). In Chennai, India, after 2000, a great demand for IT office spaces increased drastically. The typology of these office building facades was predominantly fully glazed curtain wall system (WWR>70 %) developed by private promoters. It was an adaptation of the Western style of glass box facades. The following sections explain the climatic context, location, selected case samples, and simulation tools used in this research context.

Climatic context
Chennai locates at Lat. 13.0827°N Lon. 80.2707°E has a tropical wet and dry or savanna climate under the Köppen climate classification as Aw or As (Köppen 1936). The city lies on the thermal equator and is also on the coast, which prevents extreme variation in seasonal temperatures. The hottest part of the year is late May to early June, with maximum temperatures around 37-41 °C. The coolest part of the year is January, with minimum temperatures around 19-25 ° C. This climate requires only space cooling energy, as the daytime temperature is more than 23°C throughout the year.

Case samples
Two sample buildings of different sizes were selected, representing the typical typology of FGM office buildings developed in the early 2000s in Chennai.
Criteria for case sample selection: (1) Multi-storied: more than 18 m in height or 6-16 floors.
(2) Multi-tenant: office spaces with multiple tenants on the same floor or building. (3) Fully glazed façade with similar curtain wall system of 1 × 1.5 m panel size with single reflective glass on 150 × 75 mm aluminum frames. (4) On a floor, the glazing area is more than 25% of the office area, as the solar heat gain increases due to the significant % of glazing (Chandrasekaran 2020).
The selected samples are (A) Lancor Westminster as a small office, which is a "small glass box," and (B) Raheja Towers as a large office, which is "cruciform. " From the field survey, the data for the case samples are compiled in categories such as, building level and envelope level as in Table 1 and Figure 1.

Lancor Westminster (A)
It is built in a small plot of 1530 m 2 with a total built-up area of 6000 m 2 and DOF of 18 m. It has a rectangular plan with the longer sides oriented east-west as in Figure 1. Its HVAC equipment is more than 18 years old. The core and utilities, which are 60% of the façade area on the unfavorable west side, are the only passive solar façade design in this building. With EUI of 546 kWh/m 2 and SCEUI of 336 kWh/m 2

Raheja towers (B)
It is built in a plot area of 13,377 m 2 with a total builtup area of 42,123 m 2 in a cruciform shape with DOF of 23 m with the core in the center as in Figure 1. The more extended wing of the cross faces north. Its HVAC equipment is less than 5 years old. With EUI of 207 kWh/m 2 and SCEUI of 130 kWh/m 2 .

Simulation tools
The data compiled using a field survey is presented in Table 1. The data could not be compared since the age of HVAC equipment, type of lighting, occupancy rate, and type vary in both samples. Hence, both samples used a simulation method for a base case model with the same building elements, HVAC equipment, fixed occupancy rate, and office space planning type. With standardized inputs, the validation error between simulation and reality could be minimized (Aboulnaga and Moustafa et al. 2016). Only the geometry is taken from field survey data to create base case models with standardized inputs in this research. Façade retrofit design case by revising the base case model's façade elements and comparing results with the base case. The tools used in this study for testing the energy use in E-Quest and daylighting performance in Insight, a plugin for Revit. Dynamo is a visual programming tool that works with Revit and is used to create the dynamic ESD. The following section explains the simulation software used in the research with its assumptions and limitations.

Energy analysis in E-Quest
Among the significant energy simulation software, E-Quest gives dynamic heat characteristics for every hour, which is applicable for building envelope dynamic heat transfer. A graphically reporting energy model with a simulation "engine" is derived from DOE-2, which is used as both schematic and detailed creation wizard. The Energy efficiency measure (EEM) in E-Quest is a sub-simulation of the base case model's elements. It is an essential and valuable tool to improve energy efficiency by changing the building envelope, internal loads, HVAC equipment, or other mechanical systems. E-Quest is a sophisticated yet easy-to-use building energy analysis tool that provides professional-level results with minimal effort (Thumann and Younger 2008). Moreover, it is approved by green building regulations, including ECBC 17 and GrihaV19 in India (ECBC 2017). The limitation of E-Quest in this research is that it cannot change the fin's angle, the solar heat transfer through the device, and the thermal properties of the device material.
The following fixed data input assumptions were assigned for the energy simulation:

Daylight analysis in Revit-insight
Autodesk Revit Architecture is a robust architectural design and documentation software application that supports BIM. It has more accurate building component design and construction information which is helpful for façade designing. Insight is a cloud-based environmental performance analysis program that integrates lighting and solar analysis for a holistic approach to building design and performance evaluation and is combined with Revit. The analysis options are simple, fast, and professional. In this research, the following daylighting metrics are used: • SDA%: Spatial Daylight Autonomy (SDA) assesses whether a space receives sufficient daylight on a work plane during standard operating hours on an annual basis. The target is 300 lux for 50% of the occupied period. Annual analysis as per LEED v4.  • LEED Eqv4 opt2: The two days in equinox, i.e., March 21 st and September 22 nd . Luminance levels between 300 and 3,000 lux from 9 am and 3 pm. One day within 15 days of September 21 and one day within 15 days of March 21st represent the clearest sky condition (Illuminance calculation LEED v4EQ opt2 2020).
Simulation is based on the following input assumptions: • Blinds, shades, or internal partitions are excluded from the model. • Default surface reflectance of 80% for ceilings, 20% for floors, and 50% for walls. • The analysis plane is 0.8 meters.
• Analysis grid is 0.6 × 0.6 m • 8 am to 6 pm -a total of 3650 hours. • Sky Component: as per Annual weather data for Chennai.

Dynamo for dynamic ESD
Dynamo extends the power of Revit by providing access to the Revit API in a more accessible manner (). We need not type code, as Dynamo creates programs by manipulating graphic elements called "nodes" and using a computational process to encode the workflow design. Each step with specific parameters becomes a series of instructions that can be useful for design, evaluation, revision, and improvisation. The following are the essential nodes used in this research for dynamic shading: • Sun vector: Sun vector is the vector drawn from the sun to the plane for a given location, time, and direction as in Figure 2.
• Plane normal: The perpendicular line from the façade plane for each of the curtain wall panels as in Figure 2. • The incidental angle (α) is the angle between the sun directional vector and the normal plane vector (line drawn perpendicular to the curtain glass panel) as in Figure 2. The α for each orientation is generated using Dynamo for a given hour and location.

Methodology
Two simulation methods are adopted in this research in two stages. One is for a façade retrofit solution for a fixed type with a payback period, and the other for a dynamic ESD without paybacks. The second method is to find the performance of a dynamic ESD using the best shading material from the fixed ESD.
Methodology flow chart as shown in Figure 3 for fixed types and Figure 4 for dynamic type. The second method does not include payback as the cost of a dynamic system is complex to calculate. For fixed options, the energy and daylighting performance evaluation are annual compared to dynamic shading, which is only for four seasonal days; hence, the results among the methods cannot be compared.

Analysis
Façade retrofit solutions are generated by changing or adding to the existing glazed curtain wall components of the base case models in two types: Type 1: Achieved by changing glazing type or varying WWR percentage by replacing the existing glazing with opaque panels.
Type 2: Exterior shading device by adding fixed solar fins or fixed solar screen.  The solutions that passed the SDA threshold of a percentage of 40 are selected for payback analysis.
• Results: Payback period has been used as an effective tool to analyze the economic viability of available solutions (Malatji, Zhang, and Xia 2013;Chidiac et al. 2011). The payback period is the time required for an activity to recover its initial costs through the expected savings it brings. In this study, only SCUIC is better than the base case, and the initial façade retrofit investment cost is considered to calculate the payback period based on data available from the case study using Equation 1. Cost categories such as maintenance costs, operation costs, interests, inflation, and tax could be considered more accurate results.
where P = payback period, IIC = initial investment cost per sqmt of office floor area for the retrofit options, AES = annual energy saving per sqmt of office floor area for space cooling.

Façade retrofits by dynamic ESD
Dynamo is used to generate for each façade plane the hourly incidental angle from the sun vector that changes hourly for the designed dynamic ESD. Hourly incidental angle would be the panel opening angle for the dynamic ESD. The methodology flow chart is presented in Figure 4. . The hourly space-cooling energy use these days was compared with the base case for the same analysis period. • Daylight analysis: As a dynamic ESD response to the hourly sun direction, generating annual daylight results was impossible. Hence results for only 2 days as per LEED v4EQ opt 2 (Illuminance calculation LEED v4EQ opt2 2020). The two days in equinox, i.e., March 21 st and September 22 nd at 9 am and 3 pm. The hourly WWR percentage was derived from the directional sun angle generated through Dynamo for 9 am and 3 pm for these 2 days. The results are compared to the base case results for the same analysis period.

Façade retrofits for the case samples
The façade retrofit solution was applied only on the south, east, and West. The thermal load on the north façade is low in Chennai (Lat. 13.0827°N Lon. 80.2707° E) as it is in the northern hemisphere. Two existing FG multi-storied buildings of different geometry, shape, and size are taken as case samples. The retrofitting glazed area of a typical floor for sample A is 144 m 2, and for sample B of 496 m 2 with an office area of 496 m 2 and 2410 m 2 , respectively.

Façade retrofits for the case samples by fixed types
We evaluated two types of retrofit solutions by changing the glazing type or replacing the existing glazing with opaque panels as type 1 and by exterior shading with fins, overhangs, or both and solar screen as type 2. The options as in Figure 6. These options are revised and analyzed to the base case model for daylighting and space cooling energy use and compared to the base case results. Fixed retrofit solutions no 1 to 18, its annual daylighting and space cooling energy saving better than the base case for samples A and B as in Table 3. Base case: Using field survey data of the context, geometry, and building materials, a base case model for daylighting is created in Revit BIM. The 6 th floor is a typical floor for simulation since it would have minimum or no impact on trees and surrounding buildings. The annual daylight performance index, such as SDA and ASE percentages stipulated by green building regulations, are considered for the base case model ( Table 2). The same BIM model is created as the base case model for energy analysis in E-Quest by floor multiplier to get annual, monthly, daily, and hourly results for EUI and SCEUI as in Table 2. The base case simulation results as in Figure 5 for both the case samples.

Type 1: changing the glazing or WWR %
The base model glazing SHGC is revised in the glazing type of the building envelope. The base case model's glazing is revised in E-Quest EEM for energy analysis. The visual material properties of the glass VTL are revised in the Revit base case model for daylighting analysis.       • Option no 16: with 60% of the glazing area with perforated fabric.

Changing the existing glazing in
• Option no 17: with 80% of the glazing area with perforated fabric. • Option no 18: with 100% of the glazing area with perforated fabric.
All the 18 options performance results are compared with the base case for daylighting and space cooling energy for both case samples, as shown in Table 3, Figures 7, and 8.

Payback
For the initial investment, the material and labor costs façade options were based on Indian national average best trade prices and from building practitioners in Chennai. The façade retrofit cost per m 2 of the façade area as in Table 4 for the selected solutions is converted to an annual conversion of $1 = ₹ 74.13(Average exchange rate in 2020 for Indian Rupee to US $). This cost is multiplied by the façade area for a typical floor and divided by a typical floor office area to get the IIC for each sample. The cost per kWh from TNEB for commercial use is Rs. 8 (Statement on tariff rates as in the TNERC order no: TP), converted to the USD and calculated as the annual space cooling energy saving per m 2 of the office area to get AES for each solution.
The payback period for each solution is calculated using Equation 1.  The selected solution for payback analysis is when the SDA percentage results pass the threshold of 40% as per LEED v4.1 (Table 1. Points forday lit floor area:-Spatial daylight autonomy). The results of the payback period as in Table 4 and Figure 9. The selected solutions are no 1 and 3 of type 1 and no 7, 8, 10, 16, 17, and 18 of type 2.

Observations
(1) Energy-saving by sample A is more than sample B.

Façade retrofits for the case samples by dynamic ESD
Dynamo is used to generate for each façade plane the hourly incidental angle from the sun vector that changes hourly for the designed dynamic ESD and interacts dynamically with the Revit BIM model for simulation. The dynamic ESD over the existing glazing was created with a simple type of dynamic shading. This research considers the simplest that fold and slide on the vertical plane like an eye-lid type (Kim, Asl, and Yan 2015) as in Figure 11 and is automatically controlled. The perforated fabric screen as the best-fixed method solution is used as the dynamic shading material. In this research, phase-changing materials or electrochromic glazing is not considered. The WWR percentage was derived for the incidental angle of the sun and assigned to the opening angle for the dynamic ESD. The methodology flow chart is presented in Figure 5.

Base case model, daylighting and energy analysis
Using the same base case as the fixed option, but data is taken only for 4 seasonal days for energy analysis. For daylighting analysis, a base case was created per LEED v4EQ opt2 in Insight. The data is presented in Table 5 and Figure 10. The daylighting analysis as per LEED v4EQ opt2 and energy analysis for 4 seasonal days. The data were compared with the base case for the same analysis period as in Table 5 and Figure 11. A Dynamo script as in Figure 2 created gives the incidental angel for each panel which is the panel opening angles. Through the process, each panel can have different opening ratios, automatically updated based on the change in time (Ji, Hwang, and Lee 2014;Gugliermetti and Bisegna 2004). From the incidental angle result for each hour and orientation, the complementary angle is the panel opening angle and its equivalent WWR percentage derived from Figure 12. The hourly comparative results by dynamic shading as in Figures 13  and 4 analysis days comparative results as in Figure 14

Observations as in Table 5, Figs 13 and 14
(1) Daylighting performance for dynamic shading is >15 percent lower than the base case performance for both samples.
(2) From the daylighting results, the glare is reduced in both the samples, as in Figure 10.
(3) Energy-saving better than base case by dynamic shading is 24% for sample A and 18% for sample B, as Sample A is small and has more glazing area on east and west orientation. (4) Space cooling energy saving by dynamic shading was better in the summer than winter for both the samples, as in Figure 14. (5) For Sample A, the dynamic shading performed better in the morning than in the afternoon as sample A had a less glazed façade office area in the West than in the east, as in Figure 13. (6) The difference in energy saving between the samples is almost equal in summer (June 21 st ) and more than 50% in winter (December 21 st ), as in Figure 14.

Results and discussion
This new approach to energy retrofits provides excellent opportunities for reducing energy consumption in buildings with façades designed and built when the energy cost was not an issue. This research's main contribution is applying a performance framework to a specific retrofit type, the fully glazed façade. This type of retrofit is a complex problem that could significantly impact the overall valuation of the building. In contrast to other studies, this research attempts to fill a gap in the approach to façade retrofit decision by quantifying uncertainties in three dimensions of performance, energy-saving for space cooling, optimal daylighting, and cost-effectiveness. Two case study is conducted through simulation to evaluate the feasibility of the façade retrofit performance framework. Three retrofit types are examined. The performance indicators are quantified: retrofit cost or IIC annual energy savings or AES, the present energy value, and the payback period for types 1 and 2.

Type 1
The firt printed double glazing has the maximum energy saving and good daylighting; however, the IIC has a more extended payback period, but the retrofitting would interrupt the building occupant's workflow as the existing glazed panels have to be replaced. Reducing the existing glazing or WWR percentage solution no 4, 5 and 6 also have maximum energy saving but requires strategies to improve its daylighting performance.

Type 2
A fixed exterior shading is added to the existing glazing. The shading fins of 0.6 m can reduce up to 10% of the space cooling energy, and more depth could increase the energy saving. As in the case samples, the depth could not be increased as it was added to the existing curtain framework. The retrofit solutions by adding fins would not interrupt the building occupant's workflow. It has a low IIC and payback period but is outdated and difficult to maintain. The solar shading screen shows high energy saving with better daylighting performance. As the perforated fabric is lightweight and fixed away from the glazing, it reduces the direct radiation and acts as a second layer to block the diffused radiation. Moreover, it reduces glare and improves daylighting and view. Low IIC and high AES make it the best facade retrofit solution for energy saving, optimal daylighting, and a low payback period. It is an innovative material with more design patterns and color options. It can improve the building identity and is easy to install without interrupting the occupant workflow.

Dynamic ESD
With advancements in computer applications to design and fabricate façade systems, this research is an attempt at a Dynamic ESD as a façade retrofit   solution. Dynamic ESD combines shading fins and solar screen solutions responsive to sun rays, reducing the direct and diffused radiation. The energy-saving for sample A is 24%, and 18% for sample B better than the base case. While the methodology is helpful for an early design, it is imprecise as the performance analysis is not annually simulated. It reveals the differences in energy performance for every hour, glazing orientation, and season between the case samples. Dynamic ESD is a complex system to test and derive the cost of ICC. Future research could create prototypes and test them in a façade lab for precise results.

Conclusion
By retrofitting with a perforated solar screen, we can reduce the space cooling energy use by 20% for a multi-storied fully glazed office building in Chennai. Dynamic ESD with the same perforated solar screen could save space cooling energy by up to 24%. The novelty of the research is to use advanced and innovative materials such as perforated solar fabric screens for both fixed and dynamic ESD. Furthermore, compare new materials with the know fixed types of façade retrofitting in the same simulation methods. The dynamic ESD with perforated solar fabric screen as a retrofit solution is new to this climate and context. This approach of context-based retrofit strategy provides a clear understanding at the early stages of the retrofitting decision-making to all the stakeholders as most office buildings in this context are multi-tenant. A deeper analysis of the recent literature on the energy retrofit processes revealed a comprehensive integration between energy efficiency and comfort, and mainly fails through the façade retrofit practices and studies. This research contributes to façade retrofit for this climatic context of a developing nation like India, with many existing fully glazed office buildings that need to be retrofitted for energy efficiency, visual comfort, and a low payback period. It also contributes a method for performance evaluation of dynamic ESD as a retrofit strategy. The study was limited to glazing type, fixed and dynamic ESD. This research does not combine multiple solutions. Moreover, the dynamic ESD was generated as the advancement of simulation tools, and the cost could not be derived to compare with the fixed ESD.
However, relying only on passive strategies might not be feasible, and combined strategies must be considered in future studies. Furthermore, the results from this research could be applied to one floor to make an accurate evaluation and real case validation. Finally, it is beneficial to simulate and evaluate the measures through simulation tools for decision-making at the early design stage. This energy-efficient retrofit simulation approach could be used in any climatic context.

Disclosure statement
No potential conflict of interest was reported by the author (s).