Impact of Passive Energy Efficiency Measures on Cooling Energy Demand in an Architectural Campus Building in Karachi, Pakistan

Electric appliances for cooling and lighting are responsible for most of the increase in electricity consumption in Karachi, Pakistan. This study aims to investigate the impact of passive energy efficiency measures (PEEMs) on the potential reduction of indoor temperature and cooling energy demand of an architectural campus building (ACB) in Karachi, Pakistan. PEEMs focus on the building envelope’s design and construction, which is a key factor of influence on a building’s cooling energy demand. The existing architectural campus building was modeled using the building information modeling (BIM) software Autodesk Revit. Data related to the electricity consumption for cooling, building masses, occupancy conditions, utility bills, energy use intensity, as well as space types, were collected and analyzed to develop a virtual ACB model. The utility bill data were used to calibrate the DesignBuilder and EnergyPlus base case models of the existing ACB. The cooling energy demand was compared with different alternative building envelope compositions applied as PEEMs in the renovation of the existing exemplary ACB. Finally, cooling energy demand reduction potentials and the related potential electricity demand savings were determined. The quantification of the cooling energy demand facilitates the definition of the building’s electricity consumption benchmarks for cooling with specific technologies.


Introduction
High fossil energy consumption for the heating, cooling, lighting, and ventilation of buildings and related greenhouse gas emissions contributes significantly to climate change and resource depletion [1,2]. Buildings account for one-third of the final global energy consumption [3]. Around 39% of CO 2 emissions and 36% of the global energy consumption are attributed to the building sector [3]. The building sector in Great Britain accounts for around 27% and that in the US for 38% of CO 2 emissions [1]. Buildings are a major contributor to global environmental impact due to their high energy consumption [1,4]. The building sector consumes more energy than any other sector in Pakistan [5]. Pakistan's highest annual increase in electric energy consumption was 8.4% in the domestic sector, followed by 7.5% in the commercial sector, 5.6% in the agriculture sector, and 4.2% in the industrial sector during 2017-2018 [6]. Generally, the major end-use activities in the building sector are space cooling, space heating, cooking, lighting, and refrigeration. However,

Materials and Methods
This research is based on the analysis and optimization of ACB1 due to the following reasons. ACB2 is a listed heritage site [36] and was excluded from the analysis, since the retrofitting strategies for heritage buildings are different from those for other buildings. Therefore, the findings cannot be transferred to other buildings. The construction materials used in ACB2 are also not exemplary.
During the field visit conducted on the architectural campus buildings by the authors, ACB3 was found to be a shared building with the fine arts department. ACB3 has only one hall for the Department of Architecture. ACB3 mostly serves the Departments of Fine Arts and Design. Since this research's scope is the study of an exemplary architectural campus building in Pakistan, the authors focused within this research on ACB1 to investigate the potential of PEEMs. Figure 1 presents the conceptual study framework of this study, which is based on six axes, which are described in the following sections.

Base Case Building Modeling and Description
The base case ACB1 (ACB) is located in Karachi, Pakistan, at 24.90° N, 67.08° E in a residential-commercial area having a courtyard as a central architectural feature. The ACB is surrounded by a mosque and a Montessori school to the north, residential quarters for the military to the south, an empty plot owned by the ACB to the east, and a primary school to the west. The surrounding buildings and vegetation do not cast shadows on the ACB façades. Figure 2 shows the localization and microclimate of the ACB in a 1.5 km radius in Gulshan-e-Iqbal district, Karachi, Pakistan. This ACB was selected as an exemplary case study based on the factors listed in Table 1, which are research findings published previously by the authors [37].

Base Case Building Modeling and Description
The base case ACB1 (ACB) is located in Karachi, Pakistan, at 24.90 • N, 67.08 • E in a residential-commercial area having a courtyard as a central architectural feature. The ACB is surrounded by a mosque and a Montessori school to the north, residential quarters for the military to the south, an empty plot owned by the ACB to the east, and a primary school to the west. The surrounding buildings and vegetation do not cast shadows on the ACB façades. Figure 2 shows the localization and microclimate of the ACB in a 1.5 km radius in Gulshan-e-Iqbal district, Karachi, Pakistan. This ACB was selected as an exemplary case study based on the factors listed in Table 1, which are research findings published previously by the authors [37].
The footprint of the ACB is a simple "U" shape: the north-south façade is longer than the east-west façade. The surface-area-to-volume ratio (S/V) of ACB is 0.46 m −1 . Three building clusters surround the central courtyard of the ACB. The north and east clusters are four-storey high, while the west cluster is two-storey high; all clusters consist of corridors for circulation. The ground floor works as an administration floor with a computer laboratory; the second and third floors offer educational facilities, including lecture halls and offices. The fourth floor consists of laboratories in the north cluster, while the east cluster includes a display hall; the fourth floor is not in regular use. The north façade is shaded with 0.3 m fixed overhangs over the windows, and seven 0.2 m fixed vertical louvers at 5.75 m center-to-center distance between the louvers. The overhangs and louvers are provided to obstruct solar radiation through the windows. The east façade is provided with 0.3 m fixed overhangs over the windows. The east façade also consists of galleries on the first, second, and third floors with a hollow concrete mesh on external walls. The west façade consists of 0.6 m roof eaves and 0.3 m fixed overhangs over the windows. The west façade also includes a terrace on the first floor. The footprint of the ACB is a simple "U" shape: the north-south façade is lon the east-west façade. The surface-area-to-volume ratio (S/V) of ACB is 0.46 m − building clusters surround the central courtyard of the ACB. The north and east are four-storey high, while the west cluster is two-storey high; all clusters consist dors for circulation. The ground floor works as an administration floor with a co laboratory; the second and third floors offer educational facilities, including lectu and offices. The fourth floor consists of laboratories in the north cluster, while cluster includes a display hall; the fourth floor is not in regular use. The north f shaded with 0.3 m fixed overhangs over the windows, and seven 0.2 m fixed vert vers at 5.75 m center-to-center distance between the louvers. The overhangs and are provided to obstruct solar radiation through the windows. The east façade is p with 0.3 m fixed overhangs over the windows. The east façade also consists of gall the first, second, and third floors with a hollow concrete mesh on external walls. T façade consists of 0.6 m roof eaves and 0.3 m fixed overhangs over the windows. T façade also includes a terrace on the first floor. Table 2 summarizes the general building description. The ACB is a hybrid b with manually operable windows and a majority of rooms dependent on fans fo culation. The opening of doors and windows facilitates free ventilation in the AC two offices and a computer lab are cooled with personalized split air condition EER). The fans function as cooling by creating a wind-chill effect for the users. T contributors to the electricity consumption in the exemplary ACB are the fans a air conditioners for cooling, since the standard lights were replaced with energy-LED lights/energy-saving lights. Figure A8 presents the breakdown of electric sumption of the exemplary ACB. Hence, this study focuses on the reduction of temperature and cooling energy demand.   Table 2 summarizes the general building description. The ACB is a hybrid building with manually operable windows and a majority of rooms dependent on fans for air circulation. The opening of doors and windows facilitates free ventilation in the ACB. Only two offices and a computer lab are cooled with personalized split air conditioners (2.7 EER). The fans function as cooling by creating a wind-chill effect for the users. The main contributors to the electricity consumption in the exemplary ACB are the fans and split air conditioners for cooling, since the standard lights were replaced with energyefficient LED lights/energy-saving lights. Figure A8 presents the breakdown of electricity consumption of the exemplary ACB. Hence, this study focuses on the reduction of indoor temperature and cooling energy demand. The ACB floor plan layout was drawn after conducting a field survey with measurements. The authors also conducted a field survey to collect construction data and determine component and building material specifications. The generated ACB model is a detailed reconstruction of the existing ACB. The virtual BIM reconstruction of the exemplary ACB was executed with the software Autodesk Revit 2020 [38]. Autodesk Revit uses construction component categories, families, types, and instances. Elements are grouped to form a category that uses the model or documents a building design, and families are types of elements in a category. A family categorizes elements with a standard set of parameters, similar graphical representation, and identical use [38][39][40][41]. The BIM analytical model (AM) was generated, and spaces were defined by adding each room and manually assigning the energy analysis properties, since they are significant electricity consumption factors ( Figure 3). The BIM AM method gives a precise transition from the ACB Revit model to the ACB gbXML file [42]. Hence, BIM AM was used to export the ACB gbXML file. The gbXML is an industry-supported scheme used to store and share building properties between different software [43]. The ACB gbXML file was imported into DesignBuilder (DB) version 6.1.6.008 to determine the cooling energy demand. DB is specifically developed to run EnergyPlus simulations, and has been validated for accuracy and consistency [19,44]. After setting the location and weather data, discussed in the authors' previously published research, the ACB zones were specified, and ACB schedules were created for each zone.
The ACB model was divided into seven zones: naturally ventilated (NV) lecture halls, NV offices, offices having a cooling system, computer lab having a cooling system, NV common room and canteen, NV laboratories, and NV toilets. The air-conditioning system's setpoint was 25 • C, as mentioned in the Building Code of Pakistan (Energy Provisions-2011) [45]. The ACB was physically inspected to obtain information about the occupancy, lighting, and equipment with the ACB administration's cooperation. The equipment used in the ACB were computers, printers, scanners, and microwaves. The lighting power densities and equipment power densities were calculated based on ASHRAE recommendations. The authors counted the total equipment and lighting fixtures in each zone, followed by calculating equipment power densities in compliance with the ASHRAE standard.
The authors also collected electricity billing data for 72 months (January 2014 to December 2019), since the data provide information about historical annual electricity consumption. Analysis of the bills showed that the electricity consumption was low during December and January, high from February to November excluding June and October, and very low during the summer and winter vacation periods (i.e., June and October). Table 3 provides a detailed description of the zones. The thermophysical properties of ACB are based on the literature and characteristics of the most common materials in Karachi. The specification of materials, building details (size, plans, and elevations), construction techniques, and layers and thicknesses of building elements are based on the existing ACB; the data were collected through interviews with faculty members and a physical observation survey conducted by the authors. The authors also reviewed similar buildings in Karachi with the same building age to verify the composition of the building envelope components and the construction of the ACB. To determine the cooling energy demand, specific occupancy schedules were defined, which Appendix A presents. Occupancy schedules determined the presence of users in each zone, and were defined to be consistent with the users' routines. The occupancy determined the presence of users in the ACB during the working hours for students (09:00 to 16:00) and staff, including teachers (07:00 to 18:00) on working days (Monday to Friday). Holidays, other than summer and winter vacations, were defined with the value of 14 days per year, consistent with the annual academic calendar collected from the ACB. During the summers (May to August), the mean outdoor temperature is 30.7 • C with 59.7% relative humidity in Karachi [37], while the comfort range during summers is 26 to 28 • C [37]. June was excluded from the analysis, since that month is a vacation period for the ACB, and the inclusion of June might cause a discrepancy in the analysis due to the unrealistic internal heat gains/losses from nonoccupancy. Table 3 presents the simulated mean indoor temperatures of the north, west, and east clusters during summer's occupied months. Temperature differences of 3.78, 2.47, and 1.45 • C, are observed from the outdoor to the indoor environment in the north, east, and west clusters, respectively. The authors assumed the building infiltration value of 2.5 air change rate (ACH), since the buildings in Pakistan are not airtight. The values are consistent with the previous studies in Pakistan [8,29]. The ventilation profiles were assumed based on physical inspection, and interviews with faculty members and students. Table 3 presents the simulated airflow rate for each cluster. The proposed airflow rate in EN 15251 is 0.007 m 3 /s per person [46]. The airflow rate in ACB is higher than the proposed standards, which is attributed to the poor airtightness of ACB, free passage of air in the ACB through the semi-covered corridors located in all clusters, galleries located in the east cluster, and a terrace situated in the west cluster. Figure 1 presents the detailed conceptual framework. Figure 3 presents the ground floor plan, north elevation, section, 3D model, and the AM of the exemplary ACB. Table 4 illustrates the base case building envelope components. The majority of buildings in Karachi are constructed using the same building materials and construction techniques. The conventional construction materials in Karachi are concrete block walls (high thermal conductivity and low specific heat capacity) with RCC slab (low specific heat capacity) roof [34]. The thermophysical properties of ACB are actual construction compositions based on interviews, the authors' observations, common practice, and literature studies in Karachi. The ACB consists of a medium-weight concrete block wall with plaster of light color on both the inside and the outside, and has a U-value of 2.7 W/m 2 K, which is higher than the maximum U-value proposed by ENERCON of 0.57 W/m 2 K for external walls [45]. The roof consists of an RCC slab, with plaster on both the inside and the outside, and has a U-value of 2.58 W/m 2 K, which is also higher than the maximum value proposed by ENERCON of 0.44 W/m 2 K for roofs [45]. The windows are single-glazed (U-value = 5.7 W/m 2 K) sliding windows with 50% opening, and have an aluminum frame with a U-value of 5.88 W/m 2 K. Both values are higher than the maximum value for windows of 3.5 W/m 2 K proposed by ENERCON [45]. The ACB components have highly comparable U-values. It is expected that modification of the ACB components will significantly impact the indoor environmental comfort, and accordingly facilitate annual electricity savings. Hence, parametric simulation was carried out using EnergyPlus software considering different parameters discussed in the subsequent sections.  The ACB model was divided into seven zones: naturally ventilated (NV) lecture halls, NV offices, offices having a cooling system, computer lab having a cooling system, NV common room and canteen, NV laboratories, and NV toilets. The air-conditioning system's setpoint was 25 °C, as mentioned in the Building Code of Pakistan (Energy Provisions-2011) [45]. The ACB was physically inspected to obtain information about the oc-

Measure Category Input Measures Values/Parameters
Computer lab Occupancy (people) 40 Type of system (cooled, natural ventilation) 1. Natural ventilation. Fans used for air movement.
Energy efficiency ratio (EER) of the cooling system 2.7 Cooling temperature setpoint ( • C) 25 Weekday occupancy schedule Figure

Calibration of the Model
The ASHRAE Guideline 14-2014 [47] was used to validate the ACB model. There are two indices mentioned in the guideline that present the variability of the measured and simulated electricity consumption data. Normalized mean bias error (NMBE) and coefficient of variation of the root mean square error (CVRMSE) are the indices that determine variability by comparing the simulation predicted electricity demand to the electricity consumption from the electricity bills. The simulated electricity demand was compared with the measured (electricity billing) data to calibrate the ACB model. The ACB model was graphically represented to analyze the difference between the simulated and measured electricity consumption. For the ACB model's calibration, some suitable modifications, including occupancy, equipment, and lighting schedule setting, were applied. A linear regression statistical approach was also used after manual calibration to assess the model's correlation and precision. According to the ASHRAE Guideline 14-2014 [47], the model is considered calibrated when the NMBE and CV (RMSE) are not larger than 5 and 15%, respectively, when the monthly data are used [8,48,49]. The mathematical equations are presented below: Normalized Mean Bias Error Coefficient of Variation of Root Square Mean Error In the above equations, Np is the total number of data values, Mi (where i = 1, 2, . . . , Np) represents the measured data, and Si (where i = 1, 2, . . . , Np) represents the simulated data.

Results
The climate of Karachi is hot and humid [37]; hence reducing the heat gains in buildings remains a priority for indoor environmental comfort. Conduction has a large impact on the building's load values [1,4]. The passive gains of ACB were analyzed to provide a graphical representation of contributing factors. Figure 4 indicates the monthly heat balance of the building envelope, and internal and solar gains in the base case building. It is observed that the solar gains are higher than the internal gains. This is mainly due to the conduction of the building envelope and radiation through transparent windows. Adding thermal mass and thermal insulation and improving window glazing in the existing building envelope can improve the building envelope efficiency, which will improve indoor environmental comfort, and accordingly, facilitate annual electricity savings. Low internal gains during June and October are due to the vacations in the ACB.

Calibration of the Model
In order to calibrate the model, NMBE and CV (RMSE) equations were applied in compliance with ASHRAE standard 14-2014, considering allowable limits [47]. The model was calibrated manually, and several modifications, including occupancy, equipment,

Calibration of the Model
In order to calibrate the model, NMBE and CV (RMSE) equations were applied in compliance with ASHRAE standard 14-2014, considering allowable limits [47]. The model was calibrated manually, and several modifications, including occupancy, equipment, and lighting schedule setting, were applied to calibrate the model. The simulated and measured electricity consumption data were compared. Linear regression analysis was also performed to assess the accuracy, precision, and correlation of the calibration. NMBE, CV (RMSE), and the correlation coefficient (R 2 ) values 2.26%, 13.8%, and 0.9921 of the final simulation were found suitable to verify the simulation model's calibration. Figure 5a,b presents the calibration of the simulated model:

Calibration of the Model
In order to calibrate the model, NMBE and CV (RMSE) equations were applied in compliance with ASHRAE standard 14-2014, considering allowable limits [47]. The model was calibrated manually, and several modifications, including occupancy, equipment, and lighting schedule setting, were applied to calibrate the model. The simulated and measured electricity consumption data were compared. Linear regression analysis was also performed to assess the accuracy, precision, and correlation of the calibration. NMBE, CV (RMSE), and the correlation coefficient (R 2 ) values 2.26%, 13.8%, and 0.9921 of the final simulation were found suitable to verify the simulation model's calibration. Figure 5a,b presents the calibration of the simulated model:  7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67

PEEM
After the ACB model calibration, different PEEM cases for external wall, roof, windows, and doors were tested based on previous research [4,10,14,19,34,[50][51][52] in a hot and humid climate. The authors visited local markets to check the availability of the materials in Karachi. Concrete block walls, RCC slab, and single-glazed windows having high Uvalues are common practice in Karachi, without considering the standard U-values defined by ENERCON [45]. Hence, considering the benchmark U-values by ENERCON and the material availability in Karachi, the authors chose the compositions in the following sections from previous studies in a hot and humid climate.
A significant amount of heat conduction in buildings is carried out through external walls [53]. Being an essential component of the building envelope, the external walls play a significant role in providing indoor environmental comfort and energy conservation [53]. The amount of heat conduction through external walls is highly dependent on the

PEEM
After the ACB model calibration, different PEEM cases for external wall, roof, windows, and doors were tested based on previous research [4,10,14,19,34,[50][51][52] in a hot and humid climate. The authors visited local markets to check the availability of the materials in Karachi. Concrete block walls, RCC slab, and single-glazed windows having high U-values are common practice in Karachi, without considering the standard U-values defined by ENERCON [45]. Hence, considering the benchmark U-values by ENERCON and the material availability in Karachi, the authors chose the compositions in the following sections from previous studies in a hot and humid climate.

PEEM Alternative #1 (Wall)
A significant amount of heat conduction in buildings is carried out through external walls [53]. Being an essential component of the building envelope, the external walls play a significant role in providing indoor environmental comfort and energy conservation [53]. The amount of heat conduction through external walls is highly dependent on the thermal mass and thermal insulation [54]. The existing wall component, medium-weight concrete block of the building, was replaced by alternative materials, such as aerated concrete block, and added thermal insulation to identify materials and insulation with better energy performance while retaining the building's existing structure.
Different thermal insulation materials were considered for the study depending on their availability in Karachi. Insulation was also applied on the outside to include thermal mass in the analysis, since in a hot and humid climate, thermal mass and night ventilation substantially impact electricity consumption [54,55]. Table 5 and Figure A9 present the alternative wall compositions. Figure 6 and Table 6 indicate that case-W7 provides the most significant reduction in cooling demand of 13.56%, while case-W1 offers no reduction in cooling demand. The thermal conductivity and specific heat capacity of thermal insulation material exert a strong influence on the energy performance; low thermal conductivity and a high specific heat capacity of external walls are favorable for energy efficiency in buildings [2,56]. Case-W7 insulation material (EPS) has the lowest thermal conductivity and the highest specific heat capacity among the investigated insulation materials and is therefore found to be the most effective insulating material in renovation systems with similar thickness. Case-W4 (glass mineral wool) and case-W5 (rock mineral wool) have similar conductivity values as EPS, but low comparative specific heat capacity. Therefore, they are less effective insulating materials as compared to EPS for energy efficiency in the ACB. Case-W1 (aerated concrete block) is the common practice in renovation strategies; however, consideration of the standard U-values presented by ENERCON is neglected in Karachi. It is observed that using insulation in wall composition will improve indoor environmental conditions, and accordingly will reduce cooling energy demand. Moreover, the results show that expanded polystyrene (EPS) is the most effective insulating material in lowering cooling energy demand, which is attributed to its thermophysical properties. The results are consistent with the previous study [4].  The roof is the primary source of heat gains in the ACB, because of the high U-value in the base case. By insulating the existing roof with different materials (Table 7 and Figure A10), i.e., bitumen, EPS, and polyurethane, reductions in cooling demand of 2.3, 5.5, and 5.1%, respectively, were achieved. The roof was insulated to minimize the heat gains in the building. Case-R1 is not recommended, since the insulating layer "bitumen" has a high conductivity value compared to EPS and polyurethane and is mainly used for waterproofing. Case-R3 (polyurethane) and case-R4 (EPS) have similar construction and thickness; however, case-R4 (EPS) has a lower U-value and is found to be the most effective insulating material in the renovation system. Hence, case-R4 was further modified, and a significant reduction in cooling energy demand of 8.8% was achieved by using case-R5 ( Figure 7, Table 8).        The glazing type and layers directly impact the amount of heat transmission through the windows by either solar radiation or conduction heat transfer mechanisms [17]. Glazing plays a crucial role in the heat balance of a building. The existing single-glazed window is the dominant type of window glazing in Karachi, with a high U-value (5.7 W/m 2 K) and solar heat gain coefficient (SHGC) (0.81), high heat gain, and heat transmittance. The replacement of an existing single-glazed window with other materials (Table 9), such as a double clear glass window, clear triple glass, double tinted glass, and double low-E clear glass, gave up to 8.6% reduction in cooling energy demand. Case-WW3 has the lowest SHGC, which makes this glazing type most suitable. However, case-WW3 also has a low light transmittance value (0.50), which is not desired in educational buildings. Case-WW1 has the highest light transmittance value (0.81) with a high SHGC (0.76). Hence this glazing is also unsuitable. Use of double low-E clear glass in case-WW6 provides the maximum reduction in cooling energy demand of 8.6% with SHGC (0.56) and light transmittance (0.74), and is attributed to the thermal properties of this glazing type, which prevents direct heat gain in the building (Figure 8, Table 10). Hence, case-WW6 provides a good compromise between thermal loss/gain and natural light quality [46,57]. It is found that the glazing type is the main factor that determines the energy performance of the window. Shading was also provided, keeping all other parameters as in the base case to investigate

PEEM Alternative #3 (Windows)
The glazing type and layers directly impact the amount of heat transmission through the windows by either solar radiation or conduction heat transfer mechanisms [17]. Glazing plays a crucial role in the heat balance of a building. The existing single-glazed window is the dominant type of window glazing in Karachi, with a high U-value (5.7 W/m 2 K) and solar heat gain coefficient (SHGC) (0.81), high heat gain, and heat transmittance. The replacement of an existing single-glazed window with other materials (Table 9), such as a double clear glass window, clear triple glass, double tinted glass, and double low-E clear glass, gave up to 8.6% reduction in cooling energy demand. Case-WW3 has the lowest SHGC, which makes this glazing type most suitable. However, case-WW3 also has a low light transmittance value (0.50), which is not desired in educational buildings. Case-WW1 has the highest light transmittance value (0.81) with a high SHGC (0.76). Hence this glazing is also unsuitable. Use of double low-E clear glass in case-WW6 provides the maximum reduction in cooling energy demand of 8.6% with SHGC (0.56) and light transmittance (0.74), and is attributed to the thermal properties of this glazing type, which prevents direct heat gain in the building (Figure 8, Table 10). Hence, case-WW6 provides a good compromise between thermal loss/gain and natural light quality [46,57]. It is found that the glazing type is the main factor that determines the energy performance of the window. Shading was also provided, keeping all other parameters as in the base case to investigate the effect of shading on the reduction of cooling energy demand. The results indicated that the longer the shading, the greater the savings. The maximum energy demand reduction of 2.5% was achieved with 1.0 m overhangs, but this is not recommended, because the effectiveness of the extended shading length starts to level off ( Figure 8, Table 10). The results are in agreement with previous studies [19,20].  The optimum window-to-wall ratio (WWR) at different façades was also calculated. The WWR in three façades: north, east, and west, was investigated from 0 to 100%, in steps of 5%. First, the WWR of all three façades was changed to 5%, then 10%, and so on. With 25% WWR on the north façade, the maximum cooling demand reduction of 0.1% was observed. The WWR value of 15% on the west and east façades gave a cooling demand reduction of 0.3%. The results show 5% discrepancy in the east and west façades, and no disparity in the north and south façades to the results of previous studies in the hot and humid climates of Asia [58,59]. The discrepancy is because of the different sun angles of different cities. The WWR modification is not included in the final recommendations, since the existing WWR (north façade = 27%, east and west façades = 14%) of all façades have optimum results in terms of cooling energy reduction. The existing WWR has also been proved to be effective in reducing the energy demand from previous studies in a hot and humid climate [58,59]. The optimum window-to-wall ratio (WWR) at different façades was also calculated. The WWR in three façades: north, east, and west, was investigated from 0 to 100%, in steps of 5%. First, the WWR of all three façades was changed to 5%, then 10%, and so on. With 25% WWR on the north façade, the maximum cooling demand reduction of 0.1% was observed. The WWR value of 15% on the west and east façades gave a cooling demand reduction of 0.3%. The results show 5% discrepancy in the east and west façades, and no disparity in the north and south façades to the results of previous studies in the hot and humid climates of Asia [58,59]. The discrepancy is because of the different sun angles of different cities. The WWR modification is not included in the final recommendations, since the existing WWR (north façade = 27%, east and west façades = 14%) of all façades have optimum results in terms of cooling energy reduction. The existing WWR has also been proved to be effective in reducing the energy demand from previous studies in a hot and humid climate [58,59]. Two different alternatives based on common practice in Karachi were considered substitutes for hollow core plywood doors (Table 11). Figure 9 indicates the cooling energy demand reductions achieved by using alternative doors. There is a slight reduction in cooling energy demand, and case-D2 provides a 0.2% reduction (Figure 9, Table 12).

Cases
Energy Demand (kWh) Reduction in Energy Demand (%) Figure 9. Alternative door modifications presenting simulated energy demand as compared to the base case. After investigating the modification strategies for each element of the ACB, the combined effect of all these modification strategies in reducing cooling energy demand and comfort temperature of the ACB was studied. Table 13 presents a combination of the modifications: airtightness, airflow, indoor temperature, and cooling energy demand reduction achieved by modifying the existing building envelope. The combination can reduce the cooling energy demand by 31.96% annually. Cases A and B illustrate a cooling energy demand reduction of 31.96% each, but case A is recommended, since case B includes an O4 (1 m overhangs) modification strategy, which is not recommended, as discussed in Section 3.2.3. Figure 10 represents the temperature curve for the outdoor and indoor temperatures with a comfortable temperature range in Karachi of 26-28 • C. In Karachi, there is a need for frequent and balanced airflow and air change [60]; however, high airflow was observed in the base case ACB. Natural ventilation rooms are dependent on outdoor temperatures and the existence of openings allowing airflow between the rooms and adjacent environments [61]. Case A is suitable for ACB modification, since it gives the highest reduction in energy demand and is the closest to the comfortable temperatures, and the airtightness standard of 0.6 ACH [62,63] and the airflow standard of 0.35 m 3 /s [46] in Karachi. Figure 11 presents the heat transmission in the modified building envelope. The modified building envelope minimizes the heat transfer through walls by 51%, windows by 50%, and roof by 30%. Solar gains are also minimized by 57% (Figure 10). Table 13. Effect of modification strategies on the indoor temperature, airtightness, airflow, and total reduction of energy demand (%). Legend: N, north cluster; E, east cluster; W, west cluster.

Key Findings and Recommendations
The study selected an exemplary ACB, which was simulated, and then calibrated using electricity billing data. PEEMs were applied to identify the best case for reducing indoor temperature and energy demand for cooling. Modification measures of walls, roof, windows, and doors were considered with better energy performance while retaining the building's existing structure. The results showed that thermal insulation in the wall is the best modification measure for reducing energy demand for cooling. It was found that PEEM plays a crucial role in reducing energy demand for cooling in the exemplary ACB.
The study proved that PEEM is significantly effective in improving indoor environmental comfort, and accordingly, minimizing electricity demand in ACB. The results showed that using insulation in the building envelope positively impacts indoor environmental comfort, and reduces the energy demand for cooling. Moreover, the results revealed that among the investigated insulation materials, EPS had the lowest thermal conductivity and the highest specific heat capacity, and was therefore the most effective in-

Key Findings and Recommendations
The study selected an exemplary ACB, which was simulated, and then calibrated using electricity billing data. PEEMs were applied to identify the best case for reducing indoor temperature and energy demand for cooling. Modification measures of walls, roof, windows, and doors were considered with better energy performance while retaining the building's existing structure. The results showed that thermal insulation in the wall is the best modification measure for reducing energy demand for cooling. It was found that PEEM plays a crucial role in reducing energy demand for cooling in the exemplary ACB.
The study proved that PEEM is significantly effective in improving indoor environmental comfort, and accordingly, minimizing electricity demand in ACB. The results showed that using insulation in the building envelope positively impacts indoor environmental comfort, and reduces the energy demand for cooling. Moreover, the results revealed that among the investigated insulation materials, EPS had the lowest thermal conductivity and the highest specific heat capacity, and was therefore the most effective insulating material in renovation systems with similar thickness for reducing the indoor temperature and the related energy demand for cooling.
The following recommendations are given based on the significant findings as resources to help architects in setting out the design plan for existing educational buildings using PEEMs in a hot and humid climate: • Building users consume a major proportion of electricity for thermal comfort, such as cooling in Karachi. This consumption can be reduced by using PEEMs. Building envelope modification is a crucial PEEM for thermal comfort and reduction in energy demand for cooling. By using PEEMs, a 31.96% reduction in energy demand for cooling can be achieved. • Thermal insulation of 100 mm outside the thermal mass (200 mm) in the wall plays a significant role in reducing the maximum indoor temperature in hybrid buildings, and accordingly, reducing the electricity demand of a building.

•
The common practice in Karachi is the use of single-glazed windows with high Uvalues (5.7 W/m 2 K). By replacing the single-glazed windows with double-glazed low-E reflective glass windows, the cooling energy demand can be reduced by 8.6%. • Awnings (overhangs) above the windows are provided to reduce heat gains in the building. This study showed that the longer the overhangs, the greater the reduction in energy demand for cooling. However, long fixed overhangs are not practical, because they limit the solar heat gain in winter, as well as natural light. Hence, adjustable shading devices can be useful, since adjustable shading devices allow greater flexibility to make adjustments in response to changing weather conditions. • Pakistan's urban population experiences 12-15 h of electricity blackout (load shedding) per day. Hence, reliance on active systems is not possible, and PEEMs are recommended. Retrofitting existing buildings to improve building energy efficiency is a better solution to such problems, since the existing buildings in Pakistan are energy inefficient.

Strengths and Limitations
In this study, the possibility and capability of BIM and building performance simulation (BPS) to virtually model and assess building energy demand against modification strategies, such as PEEMs, offer the opportunity to explore alternatives for an existing ACB. This provides an excellent opportunity to avoid mistakes that might arise when the building is being assessed using manual or traditional techniques. Furthermore, when such errors occur, it is difficult to correct them when the building has already been modified. The study used a virtual model based on physical observations and surveys, which was calibrated using actual data by validated calibration methods. Using advanced building performance simulation provided reliable results to understand the electricity demand and potential reduction in electricity demand for cooling by applying PEEMs.
The strength of this study is associated with the selection of the base case ACB. Furthermore, the novelty of this study lies in the context, climate, and building type. The findings not only investigate the potential of PEEMs in reducing energy demand for cooling, but can set live (good-practice) examples for students (future architects) who are studying ACB to design the buildings considering PEEMs.
Although this research focused on one ACB in Karachi, the implications made would be helpful in creating the general performance of energy efficiency in architecture campus buildings in a hot and humid climate, which would assist architects while designing architecture campus buildings in comparable climates. However, there are limitations to the generalizability of the results, since the building use, microclimate, and design of each building is different. Consequently, it will not be advisable to develop design strategies based on the investigation of only one building. However, the method used in this research can be considered for developing design strategies in a similar climate and for similar building use. Secondly, this research focused on construction materials and thermal properties, and other associated building properties; lighting issues may be investigated for more detailed insights. Thirdly, the degree of the building's airtightness may be investigated using airtightness testing to identify air infiltration through the building envelope.

Study Implications and Future Research
Karachi is a metropolitan city, and is the most populous city of Pakistan, where most buildings are not designed considering energy efficiency. As in many other cities of Pakistan [31], the building users rely on active measures, such as personalized split air conditioners. This results in high electricity bills, which create a financial burden on the building users. These active measures do not perform during the electricity blackout hours, which decrease building users' thermal comfort. For this reason, the renovation of existing buildings through PEEMs is a more suitable solution to such problems. However, these building owners do not undertake the necessary building renovations due to upfront cost and high hurdle rates, lack of information and awareness, absence of incentives, financing difficulties, mispricing, and lack of attention and materiality [64]. The government of Pakistan should encourage energy-efficient renovations, which are uncommon in Pakistan. Future research on ACB will focus on (i) earth-to-air heat exchangers as a PEEM to improve thermal comfort and reduce energy demand in the exemplary ACB; (ii) sensitivity analysis of the impact of passive design strategies on thermal comfort and energy efficiency in the hot and humid climate of Karachi; and (iii) combining active and passive measures to achieve optimal thermal comfort in the ACB.

Conclusions
This research focused on PEEMs to investigate various building components with different materials to mitigate heat transmission from/into the ACB, and improve the building performance in reducing indoor temperature and energy demand for cooling with the aid of BIM and parametric analysis using building performance simulation. This research also analyzed various building envelope compositions for the reduction in energy demand for the cooling perspective. Modifications of building envelope components are generally referred to as PEEMs. The investigated ACB showed significant potential in reducing indoor temperature and energy demand for cooling by adding thermal insulation outside of the opaque building envelope. The reduction in energy demand for cooling can be achieved by replacing the clear single-glazed windows (with high U-value) to double low-E electro reflective glass windows (with low U-value). A broader conclusion can be derived that a high-thermal-mass building with thermal insulation outside of the opaque building envelope performs well in a hot and humid climate. This conclusion is in agreement with the results of previous studies conducted in a hot and humid climate [55,65,66].
Based on this research, the following conclusions are made: 1. Thermal insulation of walls is found to be the best modification measure to reduce cooling energy demand.

2.
Replacing single-glazed windows with double low-E electro reflective glass gave 8.6% reduction in cooling energy demand.

3.
Thermal insulation with the lowest thermal conductivity and the highest specific heat capacity with similar thickness among the investigated insulation materials is the most effective insulating material for lowering the cooling energy demand.

4.
The indoor temperature of the base case ACB was 34.3 • C. The modification strategies applied in case A reduced the indoor temperature to 29.4 • C. Case B, case C, and case D reduced the indoor temperature to 29.5, 31, and 31.5 • C, respectively.

5.
An architect and designer can use building thermal modeling to design an energyefficient building by analyzing the effectiveness of various construction and material alternatives. Hence, it is recommended to use BIM and building performance simulation to investigate energy-efficient measures. 6.
In Pakistan, building owners lack the knowledge, interest, expertise, and awareness in the retrofitting of buildings for energy efficiency. Therefore, the government should provide incentives to facilitate the retrofitting of buildings to achieve energy efficiency.