Thermal Energy Performance Simulation of a Residential Building Retroﬁtted with Passive Design Strategies: A Case Study in Mexico

: High energy consumption as a result of an inefﬁcient design has both economic and environmental repercussions throughout the life cycle of a building. In Mexico, the residential sector is the third-largest ﬁnal energy consumer, therefore improving the performance of existing buildings is considered an effective method in achieving energy savings. Moreover, in Mexico warm climate regions predominate, which impacts energy consumption. This article examines a linked, single-family house located in the hot-humid climate city of Villahermosa, Tabasco (M é xico). DesignBuilder software was used to conduct the thermal energy performance simulation of the existing building (base case) and to evaluate the energy-saving potentials by implementing different passive design strategies. As a result, the annual electricity consumption of the base case decreased a maximum of 2.0% with the passive design strategy in exterior windows, 4.9% in walls and, 13.7% reduction in roofs, the latter being the enclosure with the greatest reduction achieved. Nevertheless, a ﬁnal adaptation proposal with the passive design strategies, whose results represented the highest energy savings, accomplished a total reduction of 23.5% with a payback period of 5.8 years.


Introduction
In the last decade, society has increased energy consumption to carry out its daily activities, and the proper operation of its production processes, both of which are essential to enhance the social and economic well-being of a country [1]. The International Energy Agency (IEA) reports that the global primary energy demand increased by 2.3% in 2018, the largest annual increase since 2010, and well above those in 2015 and 2016. Moreover, similarly to primary energy demand, final energy demand also increased in 2018, by 2.2% [2]. The countries that registered the highest energy consumption were: China (20.71%), the United States (16.04%), India (6.10%), Russia (5.18%), and Japan (2.85%) [1].
The residential sector contributes a substantial portion of global energy consumption and greenhouse gas (GHG) emissions in every country. This sector is responsible for more than 40% of global energy used and for as much as 33% of global GHG emissions [3,4]. According to the Energy Information Administration (EIA), it is projected that the energy consumed in this sector will increase by 65% between 2018 and 2050 [5].
In Mexico, the residential sector is the third-largest final energy consumer [1,6,7], representing 14% of total final energy consumption, while in terms of electrical energy consumption, it accounts for 23% of the national total, and represents 17% of total National GHG emissions [1,8]. Therefore, the implementation of energy efficiency actions and GHG mitigation is of great importance and should be studied in detail for this country. Although there have been significant improvements in the energy efficiency for the residential sector; these efforts have achieved a greater impact in temperate climate regions than in by building energy modelling, to improve the usage of energy and conseq reduction of electricity consumption. This may establish a replicability criter residential sector with similar climatic regions within the country.

Methods
A thermal energy performance simulation of a case study building in Vil Tabasco (Mexico) was conducted using DesignBuilder software [36]. This ana to stand for the effect that the passive design strategy has on the energy cons the building studied in this case.

The Case Study
The residential building studied (base case) is a linked, single-family ho in the city of Villahermosa, Tabasco (México). The total building surface area is consists of a total of 3 floors with 4 bedrooms, a study room, a living-dini kitchen, an office, and 4 bathrooms. As shown in Figure 1, the main façade of t is orientated to the west. The weather data of Villahermosa, Tabasco was extracted from Meteonor [37] and added to Designbuilder software. These site-specific weather data we to perform an accurate energy-consumption assessment of the residential buil The annual weather data is a critical input for building energy modeling in order to corroborate that the EPW (EnergyPlus Weather Data) file introd software was accurate, the National Meteorological Service (SMN, by its ac Spanish) weather files [38] and the NASA Langley Research Center (LaRC Project funded through the NASA Earth Science/Applied Science Program file consulted. Table 1 shows the main climatic parameters of Villahermosa including the temperature, relative humidity, precipitation, and wind speed.

Weather Data
The weather data of Villahermosa, Tabasco was extracted from Meteonorm software [37] and added to Designbuilder software. These site-specific weather data were required to perform an accurate energy-consumption assessment of the residential building.
The annual weather data is a critical input for building energy modeling. Therefore, in order to corroborate that the EPW (EnergyPlus Weather Data) file introduced in the software was accurate, the National Meteorological Service (SMN, by its acronyms in Spanish) weather files [38] and the NASA Langley Research Center (LaRC) POWER Project funded through the NASA Earth Science/Applied Science Program files [39] were consulted. Table 1 shows the main climatic parameters of Villahermosa, Tabasco, including the temperature, relative humidity, precipitation, and wind speed.

Building Data
A field study was carried out to investigate the building's data (construction materials, occupancy, lighting loads, HVAC controls, plug loads, and operation schedules). The surface mass, the U-value, and solar factors (of the fenestration only) of the residential building (base case) are shown in Tables 2 and 3. It is worth mentioning that the structural elements of the thermal envelope and interior partitions were typical for this type of buildings in Mexico [40].

. Building Data
A field study was carried out to investigate the building's data (construction materials, occupancy, lighting loads, HVAC controls, plug loads, and operation schedules). The surface mass, the U-value, and solar factors (of the fenestration only) of the residential building (base case) are shown in Tables 2 and 3. It is worth mentioning that the structural elements of the thermal envelope and interior partitions were typical for this type of buildings in Mexico [40]. A field study was carried out to investigate the building's data (construction materials, occupancy, lighting loads, HVAC controls, plug loads, and operation schedules). The surface mass, the U-value, and solar factors (of the fenestration only) of the residential building (base case) are shown in Tables 2 and 3. It is worth mentioning that the structural elements of the thermal envelope and interior partitions were typical for this type of buildings in Mexico [40]. A field study was carried out to investigate the building's data (construction materials, occupancy, lighting loads, HVAC controls, plug loads, and operation schedules). The surface mass, the U-value, and solar factors (of the fenestration only) of the residential building (base case) are shown in Tables 2 and 3. It is worth mentioning that the structural elements of the thermal envelope and interior partitions were typical for this type of buildings in Mexico [40]. Existing publications suggesting thermal properties for concrete materials provide little or no information on the concrete or mortar mixture proportions, limiting the utility for designers desiring to identify inputs for building energy simulation models. However, considering the year of the building construction and specifications of the construction's Mexican standards, the concrete mixture proportion of the base case was established as 1:4:8.

Software Election
The energy simulation models were generated and evaluated using DesignBuilder, which is one the most established and advanced building energy simulation tools using the EnergyPlus engine [42]. Designbuilder provides an easy-to-use interface for modelling simulation and quantifying building performance. EnergyPlus is a very powerful simulation engine for studies of building energy including construction, HVAC systems and controls, lighting, thermal mass, and economic analysis. The software is widely used and validated in building energy modelling either for conventional construction materials, or for more complicated building materials such as building integrated phase change materials [43][44][45][46][47].
Since the main purpose of this study was to evaluate the thermal performance simulation of an existing residential building, and due to the possibility of interoperability issues between building information modeling (BIM)-building energy modeling (BEM) appearing during the importation of the BIM information to a building energy analysis software [48][49][50][51], which can lead to a rework consisting of re-entering the BIM stored information into the energy model [51], BIM was generated through Designbuilder software.

Building Modelling
For the creation of the model geometry, a total of 3 building blocks were used, which helped to define the different levels of the building. The building's accessories (such as pillars, shading devices, and balconies) and the two adjacent houses, located in the north and south façade of the building (see Figure 1), were established using component blocks. The two adjacent houses were included in the modeling since both houses' height represent important solar obstructions in the project.
The different views of the 3D building model located in Villahermosa are shown in Figure 2 where building blocks are represented in dark gray color, the component blocks in purple, and the location and visual dimensions for the openings (fenestrations and doors) in light gray.
Each building block was internally divided into different thermal zones through the creation of internal partitions. The thermal zones generated at each level are listed below:

•
First level: 4 thermal zones were created, consisting of a kitchen, living-dining room, half bathroom, and a study room (see Table 4). • Second Level: 7 thermal zones were established, which correspond to the master bedroom, master bathroom, bedroom 1, bathroom 1, bedroom 2, bathroom 2, and a corridor (see Table 4).

•
Third Level: 2 thermal zones were defined and consist of an office room and utility room (see Table 4). considering the year of the building construction and specifications of the construction's Mexican standards, the concrete mixture proportion of the base case was established as 1:4:8.

Software Election
The energy simulation models were generated and evaluated using DesignBuilder which is one the most established and advanced building energy simulation tools using the EnergyPlus engine [42]. Designbuilder provides an easy-to-use interface for modelling simulation and quantifying building performance. EnergyPlus is a very powerfu simulation engine for studies of building energy including construction, HVAC systems and controls, lighting, thermal mass, and economic analysis. The software is widely used and validated in building energy modelling either for conventional construction materials, or for more complicated building materials such as building integrated phase change materials [43][44][45][46][47].
Since the main purpose of this study was to evaluate the thermal performance simulation of an existing residential building, and due to the possibility of interoperability issues between building information modeling (BIM)-building energy modeling (BEM appearing during the importation of the BIM information to a building energy analysis software [48][49][50][51], which can lead to a rework consisting of re-entering the BIM stored information into the energy model [51], BIM was generated through Designbuilder software.

Building Modelling
For the creation of the model geometry, a total of 3 building blocks were used, which helped to define the different levels of the building. The building's accessories (such as pillars, shading devices, and balconies) and the two adjacent houses, located in the north and south façade of the building (see Figure 1), were established using component blocks The two adjacent houses were included in the modeling since both houses' heigh represent important solar obstructions in the project.
The different views of the 3D building model located in Villahermosa are shown in Figure 2 where building blocks are represented in dark gray color, the component blocks in purple, and the location and visual dimensions for the openings (fenestrations and doors) in light gray. Each building block was internally divided into different thermal zones through the creation of internal partitions. The thermal zones generated at each level are listed below

•
First level: 4 thermal zones were created, consisting of a kitchen, living-dining room, half bathroom, and a study room (see Table 4).

•
Second Level: 7 thermal zones were established, which correspond to the master bedroom, master bathroom, bedroom 1, bathroom 1, bedroom 2, bathroom 2, and a corridor (see Table 4).

•
Third Level: 2 thermal zones were defined and consist of an office room and utility room (see Table 4).    Each building block was internally divided into different thermal zones through the creation of internal partitions. The thermal zones generated at each level are listed below:

•
First level: 4 thermal zones were created, consisting of a kitchen, living-dining room, half bathroom, and a study room (see Table 4).

•
Second Level: 7 thermal zones were established, which correspond to the master bedroom, master bathroom, bedroom 1, bathroom 1, bedroom 2, bathroom 2, and a corridor (see Table 4).

•
Third Level: 2 thermal zones were defined and consist of an office room and utility room (see Table 4).  Each building block was internally divided into different thermal zones through the creation of internal partitions. The thermal zones generated at each level are listed below:

•
First level: 4 thermal zones were created, consisting of a kitchen, living-dining room, half bathroom, and a study room (see Table 4).

•
Second Level: 7 thermal zones were established, which correspond to the master bedroom, master bathroom, bedroom 1, bathroom 1, bedroom 2, bathroom 2, and a corridor (see Table 4).

•
Third Level: 2 thermal zones were defined and consist of an office room and utility room (see Table 4).  Each building block was internally divided into different thermal zones through the creation of internal partitions. The thermal zones generated at each level are listed below: • First level: 4 thermal zones were created, consisting of a kitchen, living-dining room, half bathroom, and a study room (see Table 4).

•
Second Level: 7 thermal zones were established, which correspond to the master bedroom, master bathroom, bedroom 1, bathroom 1, bedroom 2, bathroom 2, and a corridor (see Table 4).

•
Third Level: 2 thermal zones were defined and consist of an office room and utility room (see Table 4).  Each building block was internally divided into different thermal zones through the creation of internal partitions. The thermal zones generated at each level are listed below: • First level: 4 thermal zones were created, consisting of a kitchen, living-dining room, half bathroom, and a study room (see Table 4).

•
Second Level: 7 thermal zones were established, which correspond to the master bedroom, master bathroom, bedroom 1, bathroom 1, bedroom 2, bathroom 2, and a corridor (see Table 4).

•
Third Level: 2 thermal zones were defined and consist of an office room and utility room (see Table 4).  Each building block was internally divided into different thermal zones through the creation of internal partitions. The thermal zones generated at each level are listed below: • First level: 4 thermal zones were created, consisting of a kitchen, living-dining room, half bathroom, and a study room (see Table 4).

•
Second Level: 7 thermal zones were established, which correspond to the master bedroom, master bathroom, bedroom 1, bathroom 1, bedroom 2, bathroom 2, and a corridor (see Table 4).

•
Third Level: 2 thermal zones were defined and consist of an office room and utility room (see Table 4).  Each building block was internally divided into different thermal zones through the creation of internal partitions. The thermal zones generated at each level are listed below:

•
First level: 4 thermal zones were created, consisting of a kitchen, living-dining room, half bathroom, and a study room (see Table 4).

•
Second Level: 7 thermal zones were established, which correspond to the master bedroom, master bathroom, bedroom 1, bathroom 1, bedroom 2, bathroom 2, and a corridor (see Table 4).

•
Third Level: 2 thermal zones were defined and consist of an office room and utility room (see Table 4).  Each building block was internally divided into different thermal zones through the creation of internal partitions. The thermal zones generated at each level are listed below:

•
First level: 4 thermal zones were created, consisting of a kitchen, living-dining room, half bathroom, and a study room (see Table 4).

•
Second Level: 7 thermal zones were established, which correspond to the master bedroom, master bathroom, bedroom 1, bathroom 1, bedroom 2, bathroom 2, and a corridor (see Table 4).

•
Third Level: 2 thermal zones were defined and consist of an office room and utility room (see Table 4).  Each building block was internally divided into different thermal zones through the creation of internal partitions. The thermal zones generated at each level are listed below: • First level: 4 thermal zones were created, consisting of a kitchen, living-dining room, half bathroom, and a study room (see Table 4).

•
Second Level: 7 thermal zones were established, which correspond to the master bedroom, master bathroom, bedroom 1, bathroom 1, bedroom 2, bathroom 2, and a corridor (see Table 4).

•
Third Level: 2 thermal zones were defined and consist of an office room and utility room (see Table 4). (c) (d) Each building block was internally divided into different thermal zones through the creation of internal partitions. The thermal zones generated at each level are listed below: • First level: 4 thermal zones were created, consisting of a kitchen, living-dining room, half bathroom, and a study room (see Table 4).

•
Second Level: 7 thermal zones were established, which correspond to the master bedroom, master bathroom, bedroom 1, bathroom 1, bedroom 2, bathroom 2, and a corridor (see Table 4).

•
Third Level: 2 thermal zones were defined and consist of an office room and utility room (see Table 4).  Each building block was internally divided into different thermal zones through the creation of internal partitions. The thermal zones generated at each level are listed below: • First level: 4 thermal zones were created, consisting of a kitchen, living-dining room, half bathroom, and a study room (see Table 4).

•
Second Level: 7 thermal zones were established, which correspond to the master bedroom, master bathroom, bedroom 1, bathroom 1, bedroom 2, bathroom 2, and a corridor (see Table 4).

•
Third Level: 2 thermal zones were defined and consist of an office room and utility room (see Table 4).  Each building block was internally divided into different thermal zones through the creation of internal partitions. The thermal zones generated at each level are listed below: • First level: 4 thermal zones were created, consisting of a kitchen, living-dining room, half bathroom, and a study room (see Table 4).

•
Second Level: 7 thermal zones were established, which correspond to the master bedroom, master bathroom, bedroom 1, bathroom 1, bedroom 2, bathroom 2, and a corridor (see Table 4).

•
Third Level: 2 thermal zones were defined and consist of an office room and utility room (see Table 4).  Each building block was internally divided into different thermal zones through the creation of internal partitions. The thermal zones generated at each level are listed below: • First level: 4 thermal zones were created, consisting of a kitchen, living-dining room, half bathroom, and a study room (see Table 4).

•
Second Level: 7 thermal zones were established, which correspond to the master bedroom, master bathroom, bedroom 1, bathroom 1, bedroom 2, bathroom 2, and a corridor (see Table 4).

•
Third Level: 2 thermal zones were defined and consist of an office room and utility room (see Table 4).  Each building block was internally divided into different thermal zones through the creation of internal partitions. The thermal zones generated at each level are listed below: • First level: 4 thermal zones were created, consisting of a kitchen, living-dining room, half bathroom, and a study room (see Table 4).

•
Second Level: 7 thermal zones were established, which correspond to the master bedroom, master bathroom, bedroom 1, bathroom 1, bedroom 2, bathroom 2, and a corridor (see Table 4).

•
Third Level: 2 thermal zones were defined and consist of an office room and utility room (see Table 4). Based on the collected information, the internal gains of the building were defined in DesignBuilder software: occupancy, lighting loads, HVAC controls, plug loads (such as miscellaneous, office equipment, and computer), and operation schedules. The cooling set point temperature was set at 25 °C and the assigned values for humidification and dehumidification in site were 50% each, in accordance with the thermal comfort established in ANSI/ASHRAE standard 55-2017 thermal environmental conditions for human occupancy. The heating set point was set at 0 °C, because on-site heating is not considered necessary, due to the climatic conditions of the location in this study. Each building block was internally divided into different thermal zones through the creation of internal partitions. The thermal zones generated at each level are listed below: • First level: 4 thermal zones were created, consisting of a kitchen, living-dining room, half bathroom, and a study room (see Table 4).

•
Second Level: 7 thermal zones were established, which correspond to the master bedroom, master bathroom, bedroom 1, bathroom 1, bedroom 2, bathroom 2, and a corridor (see Table 4).

•
Third Level: 2 thermal zones were defined and consist of an office room and utility room (see Table 4). Based on the collected information, the internal gains of the building were defined in DesignBuilder software: occupancy, lighting loads, HVAC controls, plug loads (such as miscellaneous, office equipment, and computer), and operation schedules. The cooling set point temperature was set at 25 °C and the assigned values for humidification and dehumidification in site were 50% each, in accordance with the thermal comfort Based on the collected information, the internal gains of the building were defined in DesignBuilder software: occupancy, lighting loads, HVAC controls, plug loads (such as miscellaneous, office equipment, and computer), and operation schedules. The cooling set point temperature was set at 25 • C and the assigned values for humidification and dehu-Sustainability 2021, 13, 8064 7 of 21 midification in site were 50% each, in accordance with the thermal comfort established in ANSI/ASHRAE standard 55-2017 thermal environmental conditions for human occupancy. The heating set point was set at 0 • C, because on-site heating is not considered necessary, due to the climatic conditions of the location in this study.
The data of occupancy and operational schedules used to simulate in the software are shown in Tables S1-S3 (Supplementary Material).

Validation of the Building Model (Base Case)
To validate the base case model, ASHRAE Guideline 14 was used, which is an established method for measuring a model's accuracy [52][53][54]. ASHRAE Guideline 14 considered accurate if the mean bias error (MBE) of monthly data is −5% ≤ MBE monthly ≥ 5% and CV(RMSE) monthly ≤ 15% [47]. The MBE and CV(RMSE) were calculated using Equations (1) and (2).
where CV (RMSE) is the coefficient of variation (CV) of the root mean square error (RMSE); mean bias error (MBE) is an indication of overall bias in a regression model; M i is the actual monthly energy consumption at instance i; S i is simulated monthly energy consumption at instance i; and N i is the number of values involved in the error calculation.

Performance Analysis
The building's performance was evaluated based on the energy performance and economic analysis. Equations (3) and (4) were used to measure the energy savings in the base case building after retrofit.
Energy saving (kWh) = Energy used (base − case) − Energy used(retrofit) Energy saving (%) = Energy saving (kWh) Energy used (base − case) × 100% Equation (5) is the discounted payback period (DPP) used as a financial parameter for evaluate the economic feasibility of the final proposal. The DPP is the number of years it takes to break even from undertaking the investment cost (i 0 ) by discounting the cumulative net present values to base year, which is developed and applied with a specific discounting cash flow approach to evaluate an investment in renovation to improve building quality, thus increasing energy efficiency [55,56].
where DPP is the discounted payback period; i 0 is the initial investment cost; NPV is the net present value. The Equation (6) measures the net present value (NPV), which is the sum of the incoming and outgoing cash flows (CF), over a defined time horizon (T), discounted at the discount rate (r), less the initial investment (i 0 ) [56].

Base Case Simulation
The thermal energy performance simulation was made to analyze the internal and external heat gains/losses of the building. The actual and simulated monthly electricity consumption of the residential building studied (base case) is shown in Table 5. The results showed that the MBE electricity consumption is −4.1% and the CV (RMSE) is 14.1%. Thus, the values are within the acceptable limits to be considered as accurate according to the ASHRAE Guideline 14. The monthly heat gains result by the base case throughout the year can be seen in Figure 3, caused by walls, ceilings, floors, ground floors, partitions, roof, lighting, miscellaneous, catering, computers and equipment, occupancy, solar gains, and zonesensible cooling. In this figure, we can see that the greater heat gain is due to the increase in solar gains by exterior windows, followed by the roof, occupancy, and lastly, by the walls. On the other hand, it can be observed that the primary heat loss of the building is due to the interior floors and through the ground floor, which is responsible for reducing the sensible cooling zone of the building.

Passive Design Strategies Proposed
Once the results of the thermal energy performance simulation of the base cas analyzed, different passive design strategies were proposed, which were based on enclosures and/or openings that had greater contributions of heat gains in the bas exterior windows, roofs, and walls. Regarding the occupancy, which represents th

Passive Design Strategies Proposed
Once the results of the thermal energy performance simulation of the base case were analyzed, different passive design strategies were proposed, which were based on those enclosures and/or openings that had greater contributions of heat gains in the base case: exterior windows, roofs, and walls. Regarding the occupancy, which represents the third position of the heat gains in the base case, it is not feasible to be modified, since it would signify changes in the occupancy hours, the number of occupants, or the current metabolic conditions. The passive design strategies proposed for the residential building are described hereafter: • Exterior windows: To reduce the solar gains, which represent the greatest heat gain, it was proposed to add another glass with a thickness of 13 mm in all the windows placing air in between them (see Figure 4). In the same way, since the frames influence the thermal behavior of the window, it was proposed to change the aluminum frames to wooden frames and place wooden frames on exterior windows with "no frames", to improve their thermal properties. Table 6 describes the thermal properties of the exterior windows, both base case and with the proposed passive design strategy. • Roof: To reduce the heat gains in this enclosure and maintain the interior thermal comfort, a passive design strategy was proposed on roofs through the installation of expanded polystyrene (EPS) insulation panels. A total of 4 different thicknesses of the insulation material was proposed, to achieve compliance with the U-values established in two different Mexican standards: the official Mexican standard NOM-020-ENER-2011 [26], whose adoption is mandatory, and the Mexican standard NMX-C-460-ONNCCE-2009 [27], which is voluntary. Both standards focus on limiting the heat gains through the building envelope. Regarding the NMX-C-460, the Mexican standard suggests specifications for R-values in three categories: "minimum", "habitability", and "energy-saving" [27]. The construction layers and the thermal properties of the roofs in the base case building and the building with the proposed passive design strategy are shown in Table 8, in which scenario 1 corresponds to the base case building (without thermal insulation), scenario 2 represents the three categories of the NMX-C-460, and scenario 3 corresponds to the compliance with the NOM-020. • Walls: As in roofs, the installation of expanded polystyrene (EPS) insulation panels inside the building was proposed as a passive design strategy to reduce the thermal load (heat-cold) on the walls. A total of 4 different thicknesses of the insulation were proposed to achieve compliance with the U-values of two different Mexican standards: The official Mexican standard NOM-020 [26], and the voluntary Mexican standard NMX-C-460 [27]. Table 7 describes the construction layers and thermal properties on walls of the different simulated scenarios: the scenario 1 corresponds to the base case building, which has no thermal insulation on walls, scenario 2 describes the three categories of the NMX-C-460, and scenario 3 corresponds to the compliance with the NOM-020.  • Roof: To reduce the heat gains in this enclosure and maintain the interior ther comfort, a passive design strategy was proposed on roofs through the installatio expanded polystyrene (EPS) insulation panels. A total of 4 different thicknesse the insulation material was proposed, to achieve compliance with the U-va  • Walls: As in roofs, the installation of expanded polystyrene (EPS) insulation panels inside the building was proposed as a passive design strategy to reduce the thermal load (heat-cold) on the walls. A total of 4 different thicknesses of the insulation were proposed to achieve compliance with the U-values of two different Mexican standards: The official Mexican standard NOM-020 [26], and the voluntary Mexican standard NMX-C-460 [27]. Table 8 describes the construction layers and thermal properties on walls of the different simulated scenarios: the scenario 1 corresponds to the base case building, which has no thermal insulation on walls, scenario 2 describes the three categories of the NMX-C-460, and scenario 3 corresponds to the compliance with the NOM-020.

Simulation of the Different Passive Design Strategies
For the present model, the thermal energy performance simulation of the building with the different passive design strategies described in the previous section was carried out. The aim was to evaluate the thermal energy performance and observe the impact that each passive design strategy represents in the reduction of the heat gains. The results obtained for each of the passive design strategies are described below: • Exterior windows: The output energy performance of the building by replacing the fenestration type was analyzed and compared with the base case. A reduction in energy consumption of 2% was observed, going from energy consumption of 14,416.76 kWh to 14,129.09 kWh, described in Table 9.
Concrete, reinforced (with 2% steel) 62.1 Plaster, dense 10.0 Expanded polystyrene (EPS) 54.8 Table 8. Construction layers and thermal properties of the roofs in the base case building and the building with the proposed passive design strategy.

Passive Design Strategy on Roofs: Thermal Insulation Material Thickness (mm) U-Value (W/(m 2 ·K)) Construction Image [41]
Scenario 1 Ceramic/porcelain 20.  • Roof: To reduce the heat gains in this enclosure and maintain the interior thermal comfort, a passive design strategy was proposed on roofs through the installation of expanded polystyrene (EPS) insulation panels. A total of 4 different thicknesses of the insulation material was proposed, to achieve compliance with the U-values established in two different Mexican standards: the official Mexican standard NOM-020-ENER-2011 [26], whose adoption is mandatory, and the Mexican standard NMX-C-460-ONNCCE-2009 [27], which is voluntary. Both standards focus on limiting the heat gains through the building envelope. Regarding the NMX-C-460, the Mexican standard suggests specifications for R-values in three categories: "minimum", "habitability", and "energy-saving" [27]. The construction layers and the thermal properties of the roofs in the base case building and the building with the proposed passive design strategy are shown in Table 7, in which scenario 1 corresponds to the base case building (without thermal insulation), scenario 2 represents the three categories of the NMX-C-460, and scenario 3 corresponds to the compliance with the NOM-020.  • Roof: To reduce the heat gains in this enclosure and maintain the interior thermal comfort, a passive design strategy was proposed on roofs through the installation of expanded polystyrene (EPS) insulation panels. A total of 4 different thicknesses of the insulation material was proposed, to achieve compliance with the U-values established in two different Mexican standards: the official Mexican standard NOM-020-ENER-2011 [26], whose adoption is mandatory, and the Mexican standard NMX-C-460-ONNCCE-2009 [27], which is voluntary. Both standards focus on limiting the heat gains through the building envelope. Regarding the NMX-C-460, the Mexican standard suggests specifications for R-values in three categories: "minimum", "habitability", and "energy-saving" [27]. The construction layers and the thermal properties of the roofs in the base case building and the building with the proposed passive design strategy are shown in Table 7, in which scenario 1 corresponds to the base case building (without thermal insulation), scenario 2 represents the three categories of the NMX-C-460, and scenario 3 corresponds to the compliance with the NOM-020.  • Walls: As in roofs, the installation of expanded polystyrene (EPS) insulation panels inside the building was proposed as a passive design strategy to reduce the thermal load (heat-cold) on the walls. A total of 4 different thicknesses of the insulation were proposed to achieve compliance with the U-values of two different Mexican standards: The official Mexican standard NOM-020 [26], and the voluntary Mexican standard NMX-C-460 [27]. Table 8 describes the construction layers and thermal properties on walls of the different simulated scenarios: the scenario 1 corresponds to the base case building, which has no thermal insulation on walls, scenario 2 describes the three categories of the NMX-C-460, and scenario 3 corresponds to the compliance with the NOM-020.

Simulation of the Different Passive Design Strategies
For the present model, the thermal energy performance simulation of the building with the different passive design strategies described in the previous section was carried out. The aim was to evaluate the thermal energy performance and observe the impact that each passive design strategy represents in the reduction of the heat gains. The results obtained for each of the passive design strategies are described below: • Exterior windows: The output energy performance of the building by replacing the fenestration type was analyzed and compared with the base case. A reduction in energy consumption of 2% was observed, going from energy consumption of 14,416.76 kWh to 14,129.09 kWh, described in Table 9. The results of the heat balance with the implementation of the proposed passive design strategy in exterior windows are shown in Figure 5. The solar gains from exterior windows decreased in comparison with the base case ( Figure 3) and, therefore, the sensible cooling of the zone. In general, the average reduction percentage obtained from solar gains in exterior windows was 22.81%, with March, May, and June being the months with the highest external heat gains with 487 kWh and, on the contrary, the month with the lowest heat gains was February with 420 kWh. Regarding the sensible cooling zone, it was reduced by 1.96% compared to the base case.
• Roofs: Table 10 shows the energy performance results and Figure 6 shows the heat gains/ losses as a result of the thermal energy performance simulation of each passive design strategy on roofs. As expected, the lower energy consumption compared to the base case (see Figure 6), corresponded to the building that complies with the NMX-C-460-ONNCCE-2009 [27] in the range of "energy saving" (Figure 6c) since it is the one with the best thermal properties. On the other hand, the lowest savings in energy consumption presented was the one that complies with the same standard, but for the "minimum" range ( Figure 6a). • Walls: Regarding the energy performance of the building with passive design strategy on walls, as shown in Table 11 and Figure 7d, the proposal that had the greatest energy savings compared to the base case corresponded to the building that complies with the NOM-020 [26] standard, since it is the one with the best thermal properties. On the other hand, the one with the minimum energy savings was the one that complies with the NMX-C-460 [27] standard for the "minimum" range ( Figure 7a).

Final Proposal for Adaptation of Passive Design Strategies
Once the energy performance of the building was analyzed with the simulation of the different adaptation proposals with passive design strategies in exterior windows, roofs, and walls, a final adaptation proposal was established, selecting those passive design strategies whose results represented the highest energy savings in the building, in order to evaluate its final energy performance and to ascertain the total energy savings that the implementation of these strategies presents in comparison with the base case. Table 12 shows the passive design strategies chosen and the results in total energy savings.
As shown in Figure 8, the heat gains and losses of the building with the final adaptation proposal described in Table 12 decreased significantly in comparison to the base case ( Figure 3). Regarding heat gains, specifically, we can see that the walls were the enclosure with the highest average reduction percentage, with 79.38%, going from 157.30 kWh to 32.43 kWh; followed by the roofs with 40.85% (from 520.11 kWh to 307.66 kWh); and, thirdly, exterior windows with a 23.55% reduction (from 601.58 kWh to 459.91 kWh), since the proposed strategies are mainly focused on reducing the heat gains of these enclosures and openings. Regarding the heat losses of the building, we see that a reduction was also obtained and the sensible cooling of the area presented a decrease of 33.28% (from −561.72 kWh to −374.77 kWh).
On the other hand, we can corroborate that the behavior of sensible cooling zone is related to the average temperatures of the state of Tabasco, since the higher the outside temperature, the greater the sensible cooling required by the building. The months of May and July are the months with the highest sensible cooling in the area, with −583.78 kWh. Moreover, the percentage of energy savings in consumption from the base case shows that the more sensible cooling zone is required in the building, the higher the percentage of energy saving is achieved. However, January and December showed an increase in energy consumption needed to achieve thermal comfort (see Figure 9). windows decreased in comparison with the base case ( Figure 3) and, therefore sensible cooling of the zone. In general, the average reduction percentage obtained f solar gains in exterior windows was 22.81%, with March, May, and June being the mo with the highest external heat gains with 487 kWh and, on the contrary, the month the lowest heat gains was February with 420 kWh. Regarding the sensible cooling zon was reduced by 1.96% compared to the base case. • Roofs: Table 10 shows the energy performance results and Figure 6 shows the gains/ losses as a result of the thermal energy performance simulation of each pas design strategy on roofs. As expected, the lower energy consumption compare the base case (see Figure 6), corresponded to the building that complies with NMX-C-460-ONNCCE-2009 [27] in the range of "energy saving" (Figure 6c) sin is the one with the best thermal properties. On the other hand, the lowest savin energy consumption presented was the one that complies with the same stand but for the "minimum" range ( Figure 6a).  • Walls: Regarding the energy performance of the building with passive desig strategy on walls, as shown in Table 11 and Figure 7d, the proposal that had t greatest energy savings compared to the base case corresponded to the building th complies with the NOM-020 [26] standard, since it is the one with the best therm properties. On the other hand, the one with the minimum energy savings was t one that complies with the NMX-C-460 [27] standard for the "minimum" ran ( Figure 7a).  • Walls: Regarding the energy performance of the building with passive design strategy on walls, as shown in Table 11 and Figure 7d, the proposal that had the greatest energy savings compared to the base case corresponded to the building that complies with the NOM-020 [26] standard, since it is the one with the best thermal properties. On the other hand, the one with the minimum energy savings was the one that complies with the NMX-C-460 [27] standard for the "minimum" range ( Figure 7a).

Final Proposal for Adaptation of Passive Design Strategies
Once the energy performance of the building was analyzed with the simulation of the different adaptation proposals with passive design strategies in exterior windows, roofs, and walls, a final adaptation proposal was established, selecting those passive design strategies whose results represented the highest energy savings in the building, in order to evaluate its final energy performance and to ascertain the total energy savings that the implementation of these strategies presents in comparison with the base case. Table 12 shows the passive design strategies chosen and the results in total energy savings. kWh to 32.43 kWh; followed by the roofs with 40.85% (from 520.11 kWh to 307.66 kW and, thirdly, exterior windows with a 23.55% reduction (from 601.58 kWh to 459.91 kW since the proposed strategies are mainly focused on reducing the heat gains of the enclosures and openings. Regarding the heat losses of the building, we see that reduction was also obtained and the sensible cooling of the area presented a decrease 33.28% (from −561.72 kWh to −374.77 kWh). On the other hand, we can corroborate that the behavior of sensible cooling zone related to the average temperatures of the state of Tabasco, since the higher the outsi temperature, the greater the sensible cooling required by the building. The months of M and July are the months with the highest sensible cooling in the area, with −583.78 kW Moreover, the percentage of energy savings in consumption from the base case shows th the more sensible cooling zone is required in the building, the higher the percentage energy saving is achieved. However, January and December showed an increase in ener consumption needed to achieve thermal comfort (see Figure 9).

Economic Analysis
The annual economic savings that could be achieved if the proposed strategies we implemented were calculated through a discounted payback period. To carry out t above, the estimated initial investment cost was calculated through the average mark prices of Villahermosa, Tabasco as shown in Table 13. As a result, the initial investme cost of the passive design strategy proposed is $39,364.30 MXN in total.  base case (Figure 3). Regarding heat gains, specifically, we can see that the walls wer enclosure with the highest average reduction percentage, with 79.38%, going from 1 kWh to 32.43 kWh; followed by the roofs with 40.85% (from 520.11 kWh to 307.66 k and, thirdly, exterior windows with a 23.55% reduction (from 601.58 kWh to 459.91 k since the proposed strategies are mainly focused on reducing the heat gains of enclosures and openings. Regarding the heat losses of the building, we see th reduction was also obtained and the sensible cooling of the area presented a decrea 33.28% (from −561.72 kWh to −374.77 kWh). On the other hand, we can corroborate that the behavior of sensible cooling zo related to the average temperatures of the state of Tabasco, since the higher the ou temperature, the greater the sensible cooling required by the building. The months of and July are the months with the highest sensible cooling in the area, with −583.78 k Moreover, the percentage of energy savings in consumption from the base case show the more sensible cooling zone is required in the building, the higher the percenta energy saving is achieved. However, January and December showed an increase in en consumption needed to achieve thermal comfort (see Figure 9). igure 9. Mean temperature (°C) of Tabasco vs sensible cooling zone (kWh) and monthly energy savings of the building ith the final proposed of passive design strategy.

Economic Analysis
The annual economic savings that could be achieved if the proposed strategies implemented were calculated through a discounted payback period. To carry ou above, the estimated initial investment cost was calculated through the average m prices of Villahermosa, Tabasco as shown in Table 13. As a result, the initial invest cost of the passive design strategy proposed is $39,364.30 MXN in total.

Economic Analysis
The annual economic savings that could be achieved if the proposed strategies were implemented were calculated through a discounted payback period. To carry out the above, the estimated initial investment cost was calculated through the average market prices of Villahermosa, Tabasco as shown in Table 13. As a result, the initial investment cost of the passive design strategy proposed is $39,364.30 MXN in total.
As shown in Table 12, the total energy saving of the retrofitted building with the final proposal for adaptation of passive design strategies is 3386.32 kWh, which represents a total energy saving of 23.50%. The electricity price in this region according to the building electricity bills is $2.28/kWh, therefore, the cost of saved electricity is $7720.82 per year.
The discounted payback period was calculated using Equation (5), resulting in 5.8 years based on a discount rate of 4.02% [57]. Moreover, in accordance with the guide to estimated useful life and depreciation percentages [58], the useful life of a residential building is approximately 50 years. The residential building studied (base case) has been occupied for 18 years since 2003 and considering that the retrofitting project will last for a month, the owner could start to turn a profit in 2027 and continue to benefit for the remaining 26 years.

Conclusions
Through building energy modeling (BEM), it is feasible to evaluate the energy performance of the building studied, which will depend on both external and internal heat gains of the building; the modeling can also be used as a base tool to determine the impact that passive design strategies will entail for improve the energy-efficiency of the building. The simulation results show that the envelope of a building has an enormous impact on the amount of energy necessary to maintain the interior temperature within a comfortable range: a consequence of the hot-humid climate region of the location. Thus, by improving the thermal properties of these enclosures, we can reduce the amount of heat that enters the building, therefore reducing the amount of energy needed for cooling. Moreover, the annual electricity consumption of the residential building (base case) decreased when simulating each of the strategies proposed for the enclosures, reaching a maximum reduction of 2.0% in exterior windows, up to 4.9% in walls and a 13.7% reduction in roofs, the latter being the enclosure with the greatest reduction achieved. On the other hand, the results of the final adaptation proposal showed the greatest energy savings by improving the energy efficiency of the building, reducing electricity consumption by up to 23.5% compared to the base case. Moreover, the economic analysis showed that the payback period for the final proposal with the passive design strategies was 5.8 years, therefore the owner can be benefited in the remaining lifetime of the building.
The results of this study are of particular interest given since the structural elements of the thermal envelope and interior partitions of the simulated base case building are typical for the residential buildings in Mexico. Therefore, this study can be replicable not only in Villahermosa, Tabasco but in those federal entities whose climatic regions are similar to the one studied. On the other hand, it is imperative to highlight the importance of the implementation of current efficiency policies in Mexico for both new and existing residential buildings, since the results shown a great reduction in the annual electricity consumption through the improvement of the thermal envelope.
Although there are several passive design strategies, this study evaluated the reduction of energy consumption through the implementation of passive design strategies in the walls, roofs, and exterior windows, which had greater contributions of heat gains in the base case. Therefore, this study aims to be a guideline for evaluating the impact that different passive strategies entail in different climates and their adaptation to existing residential buildings. However, future work should be conducted with the use of different passive design by means of thermal energy performance simulation, to accomplish a greater reduction of electricity consumption with the consideration of the thermal balance of the building.
Supplementary Materials: The following are available online at https://www.mdpi.com/article/ 10.3390/su13148064/s1. Table S1. Data of the internal gains (occupancy) used to simulate in the software. Table S2. Base-case building operation schedules per room for weekdays. Table S3. Base-case building operation schedules per room for weekends.