*2.5. Testing Methodology*

For the fourth aim of the methodology, the testing of the proposed verification model of the Mexican standard, we followed two fundamental steps. First, we needed to learn and understand the digital software SGSAVE provided by EFINOVATIC [21]. Next, we designed a personalized testing methodology for the verification of the model to achieve the desired results. The digital tool used for the testing methodology was the energy simulation software Open Studio, using the complementary software called SGSAVE.

For understating how SGSAVE works, we reviewed the energy performance simulation process in Open Studio [31]. Open Studio is software contained inside the Google Sketch-up interface. The energy simulation process is composed of four principal phases: modeling, definition, simulation, and reporting. For the first phase, the 3D modeling of the evaluated building project, the user works in the Google Sketch-up interface. In this phase, the user establishes the physical values of the building (height, length, width, opening geometry, etc.). For the second phase, the user establishes the parameters and reference values for the modeled building project (materials, construction systems, schedules and calendars, HVAC definitions, space types, etc.). For the third phase, the user defines the simulation parameters before running the simulation engine (run period, desired report results, etc.). The final phase is the report, where the user analyzes the generated simulation report with the corresponding results (verification of the standard, energy demands, etc.). Open Studio functions are delimited from the first to the last phase.

SGSAVE is software that offers a direct verification of the Spanish energy standard and generates a complete report of all energy simulation results, including the European Union energy label designed by the EU Directive 92/75/EC [32]. SGSAVE introduces the reference values, parameters, and directives of Spanish energy standards (CTE) into Open Studio interface by: (1) entering Spanish/European reference values and parameters and (2) generating the Spanish/European verification certification report of compliance. The parameters and reference values are introduced by the user using a SGSAVE tool panel in the Google Sketch-up interface. With this panel, the user can introduce values, like thermal bridges, U-value limit verification, thermal space configuration for reference occupation schedules, window and door configurations, etc. It also includes tools to clean and refine the three-dimensional model, HVAC installation design, and location customization tools. For the report final phase, SGSAVE generates a certification report that declares whether the building project complies with the standard. The report also includes a graphic of detail heat gains, projected energy demands for ideal loads, and physical characteristics of the model (square meters per thermal zone, for example). Figure 7 describes the workflow.

**Figure 7.** Open Studio and SGSAVE workflow diagram explaining the work process for entering the building project in the software interface and using the digital model for energy simulation.

By understanding how SGSAVE works in refining and adapting the European/Spanish standard requirements for Open Studio parameters, our aim was to adapt the software for the Mexican standard. As the standard's development in Mexican is in its infancy, the technical data were insufficient for fulfilling all SGSAVE data requirements. For the testing exercise, the data provided by the Mexican standard was used, and the Spanish/European values were used for the remaining fields to enable testing the Mexican data's adaptability to the software.

For each component (roof, openings, walls, doors, and shading elements), the software allows the user to assign values, entering the data corresponding to each requested variable, and then the user assigns a construction system for each element. Each construction system was entered into the software, determining the width of each of its composition layers and their respective conductivity coefficients and characteristics, like density and measurement unit. For the last arrangements of the thermal envelope's geometrical model, the user enters the remaining data needed, like occupation calendar, zone uses (kitchen or bedroom, for example), external shading components, and immediate context elements (trees, roads, location, or other adjacent buildings) [31]. A base model was introduced and configured with Openstudio tools, following the geometry of a typical social housing model, replicated on different Mexican cities (Figure 8).

**Figure 8.** The basic model of the economic housing type. Geometry modeled in the Open Studio interface.

Before launching the simulation, the user must enter the weather file EPW of the city's project location and choose the desired simulation period. For the next step in the fourth aim, we determined the application of the following testing methodology. First, the most representative climatic cities of Mexico were chosen in accordance with summer severities (V, W, X, Y, and Z, returning to Figure 4) and those with the most extreme weather: Toluca de Lerdo for the coolest city and Mexicali for the warmest city. In the next step, the housing models were used and different simulations were performed by changing the weather file. Before running simulation processes for the testing method, a Building Component Library (BCL) report-generation add-on for Mexican standard verification was installed in the software. This add-on was developed by the Mexican agency ITÖM. It is a public-access complement provided at no cost. The add-on takes the geometry and the simulation parameters of the tested model and generates a report with the verdict (if the project complies with the standards) [33].

Using the verification complement of NOM-020-ENER-2011 for Open Studio, we tested if the building complied with the standards. If not, changes and bio-climatic design strategies for the optimization of the economic housing thermal envelope were applied to increase the energy savings (improving the score) of each housing model. After verifying the improved models for economic housing with personalized content for each tested climatic zone, new simulations were run for the improved models to verify if the model complied with the norm standards. With the analysis of the results of radiative and conductive heat gains, we compared the simulated energy savings between the normal case and the improved case. Finally, new simulations were run, but with the Open Studio report manager, for evaluating the differences between both reports.

Although these test simulations provided results for improving building energy performance, remember that the simulation needed other factors that are strictly related to the potential user. David Bienvenido Huertas stated: "Energy consumption simulations are directly related to six factors: three technical and physical factors (climate, building envelope, and building equipment) and three social factors (operation and maintenance, occupant behavior, and indoor environment conditions). So, the energy performance of a building depends not just on technical characteristics (e.g., the thermal performance of the facade) but also on users' behavior" [34]. For the simulation, the Mexican user operation, occupant behavior, and indoor environment conditions characteristics were needed. Some information was provided by NOM-020-ENER-2011 guide, but, for the remaining variables, the CTE (Spanish Building Technical Code) calendars and reference values [35] provided by SGSAVE were used. The reference values used from CTE were: occupation calendars, thermal bridges, average consumption rates, etc. The simulations were run with an HVAC configuration for ideal loads.
