*4.2. Aims Fulfillment: Why Improved Instead of Optimized?*

The aims of the testing methodology were fulfilled by designing an energy model for verification of building compliance with the standard. Notably, the principal aim of the proposed model is to verify regulation compliance in this study. The testing method uses improved models and not an optimized model. The reasons for this are as follows.

Mexican social housing differs from the European or American context. The Mexican government does not provide houses directly for the population. Instead, the government provides loans and financial aid for workers. The principal source of housing acquisition for workers and the poor is self-construction. Due to the economic informality and high poverty rates, those requiring social housing experience problems acquiring a loan, mortgage, or financial aids, so the workers save money and build their own houses [11]. Considering the social housing situation, the proposed model prioritizes energy certification with affordable construction plans. An optimized model that complies with the net-zero carbon buildings 2030 target is a distant and inapplicable aim for Mexican social housing. There is no local suppliers for the required equipment, like thermal-break profiles or high-tech materials, so they need to be imported at high prices. Another problem is the lack of public support for self-construction improvements. To increase economic savings during the construction

process, self-constructors prefer to use traditional techniques, and avoid investing in specialized studies, like structural or energy performance analyses. This situation provoked an increase in informal social housing and urban planning problems.

So, to adapt the proposed model for application to the self-construction reality, we compared the energy performance results between the three most-used traditional construction systems. The simulation showed promising results, like the good efficiency of the adobe system for thermal envelope heat gains. The adobe system is well-built by the national labor force and works for the majority of the climatic zones. Adobe is a good material choice for implementing thermal mass strategy, and is more affordable than the reinforced concrete system.

The reason for preferring improved models over an optimized model is for testing the proposed model on a more accurate social housing situation. It is preferable to test and verify compliance with the regulation using affordable and simple bio-climatic strategies (for achieving the energy standard compliance and obtaining an energy efficiency label), rather than implementing complex strategies, high-tech materials, and specialized procedures for achieving optimized results. This does not mean that an NZEB housing model is impossible: the implementation should be step by step. First, the improved models should be promoted for increasing the awareness of the Mexican population about the benefits of energy efficiency strategies. If the market and the authorities increase the application of the Mexican energy standard, the demand for better techniques and materials will increase too. Mexico's authorities are beginning to implement sustainable practices for construction, though there is still a long way to go to achieving the same level of energy efficiency awareness and legislation as in the European Union.

How does the research is aligned with the vision set by Mexico Green Building Council? The Mexico Green Building Council recognizes the NOM\_020\_ENER\_2011 as a mandatory normative, although its applicability has not been strictly monitored by authorities. The research helps the realization of their vision, by focusing on make energy saving building strategies available for a larger segment of population. The Green Council works for bringing educational tools for sustainable building practices, and the proposed model will help as a tool for testing and certifying the norm compliance with social housing models [51].

The proposed model implements technical data from the traditional construction systems available in Mexico. With the climatic zoning designed with Mexican meteorologic information, the model served for testing the building systems energetic performance, their compliance with the national normative, and the possible energy savings by applying several strategies. The model covers several energy requirements for EDGE and LEED certifications. Not all requirements, but is a good starting point for implementing Green Building Council principles of energy performance for self-construction and Mexican social housing. the Mexico Green Building Council encourages the NOM\_020\_ENER\_2011 learning and knowledge for building professionals because of its mandatory use not only in building energy performance, but also because of its utility for materials and equipment certification (home appliances, insulation materials, electric materials, etc.) [52].

How does the proposed model help the AEC (Architecture, Engineering and Construction) Industry for achieving savings for energy consumption? The model design strategies for improvement are oriented for energy savings in operation phase. It did not consider other life cycle stages, like materials extraction or building. But it is possible to make a comparative for energy consumption reduction with an Energy plus report. The normative applied on temperate climatic zones is not functional.

As shown in Figure 15, the normative applied on temperate climatic zones is not functional. The improved model that complied with the energy normative, had higher energy consumption rate than the basic model, resulting on a 1% increment on energy consumption, and a 10% increment of primary energy. But considering that only 10 of 31 Mexican states are classified as tempered climates, the proposed model is applicable and functional for 60% of national territory.

For cold climatic zones (Figure 15), the proposed model showed more efficiency than temperate climates. The improved model that complied with the energy normative, reported lower energy consumption rate, resulting on energy savings of 19% compared to basic model results. For primary energy, the improved model reported energy savings of 21% compared to basic model results. A 20% of energy savings tendency for heating demand cases is a competitive value considering that 10 of 31 Mexican states are classified as cold climates.




**Figure 15.** Comparative Results of Energy Consumption and Primary Energy for the three most representative climatic zones, with their correspondent energy savings percentage.

Remembering the statistics published by INEGI census of 2018, 40% of the northern states' families use air conditioning, and their principal energy consumption waste is electricity (used for HVAC equipment operation). With this context, the results listed in Figure 15 are promising. The improved model that complied with the energy normative, reported lower energy consumption rate, resulted on energy saving of 54% compared to basic model results. For primary energy, the improved model reported energy savings of 55% compared to basic model results. For Warm climatic zones, the proposed model reduces by half the building total energy consumption. A 50% energy saving rate tendency, applicable for 11 of 31 Mexican states with warm climatic classification, is enough for implementing the proposed model at least for this type of climatic zone.

In conclusion, the proposed model reported acceptable energy savings for 21 of 31 Mexican states. In other words, the model is effective and applicable for at least 60% of states, and a 60% of total national territory. It has enough potential market for promoting its application and development, with a national mean energy saving rate of 24% for energy consumption and 21% for primary energy.
