**1. Introduction**

The low thermal comfort in social housing is becoming a severe cause of house abandonment in Mexico. The general director of the National Fund for Social Housing of Mexico (INFONAVIT), David Penchyna, declared for the digital news portal El Financiero: "There are 100 abandoned social houses. The causes are diverse, like non-payment, not enough public services, and houses that did not meet the minimum conditions of comfort" [1]. This social housing problem is the result of the lack of a comfort model, with studies only focusing on construction quality and cost. Taking, for example, the situation in another context, like the European Union, we observe that the public regulations for building construction and restoration consider the energy performance. To address the energy demands and the comfort needs for interior spaces, the European standards provide reference values for ensuring the optimal habitat conditions of buildings. Because not all the social housing owners have enough economical sources for implementing a specialized design and optimization for their particular project, it is crucial that the authorities establish a guide for building based on proper studies and customized reference values.

Some studies focused on building residential projects considering energy efficiency optimization. Griego and Krarti highlighted the importance of implementing energy optimization strategies for residential projects in the Mexican context: "The need to reduce

**Citation:** Guízar Dena1, A.J.; Pascual, M.Á.; Fernández Bandera, C. Building Energy Model for Mexican Energy Standard Verification Using Physics-Based Open Studio SGSAVE Software Simulation. *Sustainability* **2021**, *13*, 1521. https://doi.org/ 10.3390/su13031521

Received: 23 November 2020 Accepted: 26 January 2021 Published: 1 February 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

domestic energy consumption is highly urgent, particularly as the number of homes in Mexico continues to increase. The awareness of this need has initiated the development of sustainability and energy efficiency guide-lines in the national residential building code, CEV. Findings from this study indicate that greater emphasis should be placed on implementing the minimum thermal insulation levels" [2].

For the last twelve years, Mexico has made a remarkable efforts to create and implement the principles of sustainability and energy savings in their laws and codes for construction and the commercialization of equipment and household appliances. In 2011, the government of Mexico published in "Diario Oficial de la Federación" (Official Journal of Mexican Federation), the first energy standard of energy efficiency for buildings: NOM-020-ENER-2011 [3]. The objectives of the norm were defined in the document: "In Mexico, the thermal conditioning of buildings has a great impact on the peak demand of the electrical system. It is greater in the northern and coastal areas of the country, where the use of cooling equipment is more common than heating. In this sense, this standard optimizes the design of the thermal behavior of the envelope, obtaining benefits like energy savings due to the reduction of the capacity of the cooling equipment" [3]. The role of building performance simulation (BPS) in electrical grid stability has been widely studied by different authors [4–6], showing the importance of making these models available from building design to operation.

The Mexican energy standards focus the scope of testing on the heat gains of the thermal envelope of the building. However, given the instability due to the constant change in political parties in charge of government leadership, the Mexican energy standard stopped its development and implementation in the regional building codes of the country. The last actualization of the standard was approved on 2013. The only tools available for the verification of the standard are a digital guide for its application and a digital tool (made in Excel) for automatic calculations by entering the numeric data in the corresponding spaces [7]. Although this tool fulfills its purpose of checking if a building satisfies the Mexican energy requirements, it only considers the total surface area and some climatology variables defined inside the documentation of the rules.

The energy standard should be analyzed by understanding the characteristics of the Mexican housing scheme. In the essay Cuantificando la clase media en México en la primera mitad del siglo XXI: un ejercicio exploratorio (Quantifying the middle class in Mexico at the first half of twenty-first century: an exploratory exercise), the authors conducted a study supported by statistics from the National Institute of Statistics and Geography (INEGI) to analyze the composition of economic classes in depth. They concluded that the highest% of the Mexican population is identified as lower class, at 55.1% of the total. The second group is composed of the middle class at 42.4%, with the upper class being 2.5% of the total. Notably, according to the essay, 80% of the Mexican population lives in cities and metropolitan areas. Therefore, 78% of the population is the target market for social housing developers [8]. The construction industry is one of the strongest and most profitable economic activities in Mexico. Residential and mixed-used constructions are some of the most wanted business models for private and government investment (through the national housing fund, INFONAVIT, and other public institutes).

Although NOM-020-ENER-2011 is the only official standard designed for mandatory application, other public tools are available for enhancing energy performance and environmental strategies for sustainable architecture. The NMX-AA-164-SCFI-2013 is a code developed by the Secretariat of Agriculture and Environment (SEMARNAP) and the Mexican Chamber of Construction Industry (CMIC) for promoting environmentally friendly techniques, strategies, and technologies in construction. It is a document with several categories of different ecological aspects (water, soil, energy, materials, landscape, interior comfort, and social responsibility) and a scheme of credit fulfillment [9]. Mexico also offers economical alternatives to implementing sustainable architecture and technologies for energy savings INFONAVIT runs a public program for social housing constructors called Hipoteca Verde (Green Mortgage). With this program, the constructor can obtain a

public loan for real estate projects if they support the application with eco-technologies: design strategies and technology for energy savings, like photovoltaic panels, solar thermal collectors, thermal insulation, and water recycling [10]. As such, there is an interest in and potential market for the implementation of energy simulation and building efficiency models (BEMs). According to the statistics published by INEGI in 2018, the biggest energy expense of the country's households is electricity. In the northern states, 40% of families use air conditioning in their houses, providing a solution to their thermal comfort needs [11]. Due to the need for mechanical air conditioning, the evaluation of the energy performance of buildings and indoor living space quality provides an opportunity reducing electrical consumption and costs while improving the well-being of users.

Given the lack of practical implementation methods for the standard (providing an opportunity to create a different and attractive proposal for the Mexican market), the collaborating enterprise decided to investigate and develop their own model for energy verification using their tools and software. The aim of this investigation was to develop a model for verifying Mexican energy standard compliance for social housing models, and to research the benefits of using the Energy Plus building energy program [12]. Demonstrating the potential for building energy savings by designing an efficient thermal envelope and applying bio-climatic strategies to the design will be a useful tool for national construction.

The first three sections explain the procedures followed and the primary results. Each section describes the principal sources studied. Then, the procedure used for developing each of the method's aims is explained in detail, and the section ends with primary conclusions. The fourth section begins with an explanation of the testing method used. Then, a quick explanation of the developed models is reported. Finally, the results section reports the simulation results with a brief analysis of each one. In the conclusions section, a list of the pending aims and topics is provided, with a final reflection on the research results.
