*3.2. Testing Results 2: Comparison between Different Construction Systems*

The previous results only apply to the traditional reinforced concrete structure fabric walls system. New simulations were run to test the other two proposed construction systems: wood and adobe–metal sheet. Because the goal of this second testing was to quickly compare the systems, the most extreme climatic zones were chosen: V3, Toluca de Lerdo, for the coolest climate zone; Z2, Mexicali, for the warmest climate zone; and V1, Mexico City, for the temperate climate zone. Before running the simulations, there was a problem of units that needed to be addressed. The Mexican energy standard NOM-020-ENER-2011 reports the heat gains of the thermal envelope in Watts. The Energy Plus engine reports the heat gains of the thermal envelope in kilowatts hour per square meter (kWh/m2). For precise comparison, the results of both methods, the complementary simulation report was modified to obtain a wider range of results. For this comparison, two indicators were taken: window total heat loss rate (for radiation heat gains) and surface inside face conduction heat transfer rate (for conductive heat gains). Both indicators are expressed in Watts. The results obtained from the simulations are depicted in Figure 14.

Energy Plus considers other heat sources and heat gains for the projected building. The internal gains, for example, are an important source of heat for building interiors. In accordance with the conclusions of Turley et al., occupancy heating plays an important role in internal heating and energy performance: "Occupancy-aware heating, ventilation, and air conditioning (HVAC) control offers the opportunity to reduce energy use without sacrificing thermal comfort. Residential HVAC systems often use manually-adjusted or constant set-point temperatures, which heat and cool the house regardless of whether it is needed. By incorporating occupancy-awareness into HVAC control, heating and cooling can be used for only those time periods it is needed" [41]. Turley et al. found that occupancy-aware control of HVAC equipment produces important energy savings due to the contribution of internal gains and no-waste-energy intervals.

This sensitive control theory of HVAC equipment for the proposed new building is supported by Jonghoon's findings about achieving an equilibrium between thermal comfort and the energy use of a building: "Despite the improvement of mechanical thermal models associated with advanced statistical tools have been performed, there is a necessity of the investigation of sensitive control models for supply heating and cooling energy into a single space scale which can be closely related to users' workability and productivity" [42]. Constructing a simulation of HVAC equipment with sensitive control of set-point temperature could be achieved using Energy Plus with a detailed model and advance parameters definition.

The behaviors of the three systems were similar for the three representative climatic zones. The construction system with the lowest heat gains was the traditional system of reinforced concrete and fabric walls. The construction system with the worst performance and the highest heat gains in the three climatic zones was the wood system.This phenomenon occurs because of wood high insulation properties. Wood restricts heat transfer from inside to outside, promoting heat accumulation for interior spaces. For cold climatic zones, this phenomenon helps for lowering heating demand. But for warm climatic zones, the effects are different. In summer, wood does not dissipate heat properly, and the interior spaces have unwanted heat accumulation. The same effect occurs for arid warm and desertic climatic zones. The heat accumulation increases building cooling demands. And for Mexican normative, by absorbing and not dissipating heat gains, wood reported high heat gains balance. In contrast with concrete and adobe systems, because of the breath-ability characteristics of their principal materials.

Notably, the aim of this second testing exercise was to perform a quick comparison between the different systems. For detailed results and exact behaviors, we strongly recommend additional, separate research. Some important findings to highlight from the previous graphs include: The adobe-metal sheet construction system showed remarkable performance in the three climatic zones, although it did not have the best performance.

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**Conduction Heat Gains Radiation Heat Gains**

**Figure 14.** Comparison of the heat gains of the thermal envelope for the three construction systems chosen for testing: traditional reinforced concrete and fabric walls, wood, and adobe with metal sheet. The two graphs with the NOM-020-ENER-2011 label show the calculated heat gains results using the standard method. The two graphs with the Energy Plus label show the heat gains results using the simulation tool software.

It provides a good staring point for new inquiries because this construction system is most environmentally friendly. It produces less waste and has lower primary energy needs for its construction than the traditional reinforced concrete system. The results showed that the three construction systems perform their best in V1, Mexico City, having low heat gains.

This results proved the viability of using vernacular construction techniques for improving the energy efficiency of housing projects. A similar study was developed by Zhai and Previtali. They selected a variety of vernacular techniques (in accordance with climatic zones) and followed a similar methodology to ours. They creates a construction techniques and materials catalogue, and split them into categories by roof, wall, and floor. After comparing and cataloguing the materials and systems, several simulation were run with BEopt software (developed by the U.S. Department of Energy). The computer optimization tool was able to find a combination of vernacular construction techniques that exceeded both the IECC (International Energy Conservation Code) reference case and the observed vernacular case, revealing the potential room for improvement in building codes and vernacular architecture [43].

The simulation also helped to prove the efficiency of the proposed bio-climatic strategies. This helps the architects and energy managers of a project by proving the viability of these design strategies with data. The ventilated air gaps in the warmest climatic zones help to increase the energy savings.This finding agrees with Oropeza-Perez et al. who stated, "Through a sensitivity analysis, it is found that the efficiency of natural ventilation under warm conditions is affected by the following inputs in this order: climate conditions, windows opening schedule, materials of construction, built area, and number of occupants. The potential for saving energy by using natural ventilation is more when the dwelling materials of construction have high heat capacity and the dwelling is located in a hot-dry climate. In a hot-humid climate, low heat capacity materials and natural ventilation help to lower the indoor temperature" [44].

We highlight the differences between the NOM-020-ENER-2011 and Energy Plus results. The Mexican standard results are similar, with very little difference between climatic zones. Conversely, the Energy Plus results have a larger difference between them. This shows how the Mexican standard only considered reference values and standardized coefficients for climate and thermal envelope characteristics, whereas Energy Plus considers more specific variables, like internal gains, shadow elements, and location. In other words, Energy Plus results provide precise information about a project, with its particular characteristics; however, the building must have limited complexity, and the results are basic. As concluded by the authors of the Science Direct article Optimization Tools for Building Energy Model Calibration: "On the one hand, parametric analysis results are exhaustive and show the entire spectrum of results for a given problem, providing a complete picture of the possibilities to consider. On the other, this straightforward 'brute force' approach proved to be quite resource-demanding both regarding calculation time and computational capacity, preventing its implementation when a complex building simulation model is analyzed" [45].
