## 3 Discussion and Results
### Comparison of Energy Consumption Based on CTE and ASHRAE Standards
When this same building incorporates less than 30% recycled materials (Figure 6b), a reduction in the impact associated with the embedded GWP is achieved, resulting in a higher percentage of operational emissions during the energy use phase compared to the case in Figure 6a. Following the stricter energy use restrictions set by ASHRAE, it is observed that, in a highly energy-efficient building that also employs a percentage of recycled materials of less than 30% (Figure 6c), the impact is roughly equivalent in the use phase as well as in the raw material extraction and construction phases. By increasing the use of low-carbon materials (Figure 6d), the impact of embedded emissions can be further reduced. However, in the case of an nZEB building, which has already significantly reduced energy consumption through passive building techniques and, in addition, has renewable energy sources, the operational GWP impact is significantly lower (31%) compared to the embedded impact (69%) (Figure 5b). It is in this context that embedded emissions become of considerable relevance. Reducing operational energy use leads to a reduction in operational carbon emissions. As operational emissions are reduced in low-energy buildings, the importance of embodied emissions, which dominate life-cycle emissions, increases. It is estimated that embedded carbon emissions (released before building use) will account for around 80% of the life cycle emissions of an nZEB building without recycled materials (Figure 5d). Embedded  
Figure 6: Percentage of CO\({}_{2}\) embedded and operational for CTE and ASHRAE criteria: (**a**) CTE 0% recycled; (**b**) CTE 24.1% recycled; (**c**) ASHRAE 24.1% recycled; (**d**) ASHRAE 63.8% recycled. emissions will therefore become more prominent or even dominant in the life cycle carbon emissions balance. As it is shown above, an in-depth energy consumption analysis was conducted for three different building scenarios to further examine the implications of energy performance. The three scenarios were as follows: (a) the most unfavorable scenario, based on the mandatory requirements outlined in the Technical Building Code (CTE); (b) an intermediate scenario representing a highly energy-efficient building, based on the criteria for limiting energy use as established by the ASHRAE standard; and (c) the real-world case of the nZEB IndUVa building. This comparative analysis revealed that the IndUVa building achieved significant reductions in energy demand, with a savings of 78.4% compared to the ASHRAE criteria and 85.6% compared to the CTE criteria. These findings further support the conclusion that, in nZEB buildings, where energy demand is extremely low, the greatest environmental impact is concentrated in the embodied emissions. In contrast, conventional buildings or those with less stringent energy standards demonstrate a significantly higher operational environmental impact, as evidenced by their higher GWP values. For the decarbonization of the construction sector to align with the global push towards zero-emission buildings, it is essential that buildings are designed with an emphasis on achieving high energy-efficiency levels and integrating renewable energy sources to meet their energy demand. This approach significantly minimizes environmental impact during the use phase of the building. Additionally, implementing circular economy practices--especially in the construction phase--will be pivotal. Ensuring that at least 70% of materials used in construction are recycled will have a substantial impact on reducing embodied emissions. Although the embedded GWP of the IndUVa building is relatively high at 69%, the low operational GWP allows it to be classified as a Zero-Emission Building (ZEB).