# Are Green Buildings an Indicator of Sustainable Development?
## 2 Methodology
### Data Analysis  
The following indicators are used to evaluate if the adoption of GBRS can be used as an indicator of a higher level of sustainability reached within a region:  
* GBRS as an indicator of the adoption of green solutions in the construction sector. * GHG emissions as an indicator of environmental degradation. * GDP as an indicator of economic growth. In addition, two additional indicators are introduced to better understand the behaviour of the three main variables:  
* Share of renewable energy as an indicator of the adoption of advanced power generation technologies since energy production is the first source of GHG emissions [28]. * Heating degree day (HDD) as an indicator of the climate since the energy demand of buildings is directly related to external conditions. Regarding climate conditions, heating degree day (HDD) is adopted as a weather-based technical index used by Eurostat to describe the need for heating energy requirements in buildings based on observations from about 3000 weather stations across Europe [29]. HDD measures the severity of the cold in a specific period taking into consideration the daily mean outdoor air temperature (T\({}_{\rm{m}}\)) and the average room temperature (i.e., the need for heating). HDD is calculated with the following equations:  
\[\text{If T}_{\rm{m}}>15^{\circ}\text{C},\,\text{HDD}=0 \tag{1}\]  
\[\text{If T}_{\rm{m}}\leq 15^{\circ}\text{C},\,\text{HDD}=\sum_{\rm{j}}\left(18 ^{\circ}\text{C}-\text{T}_{\rm{m}}{}^{\rm{i}}\right) \tag{2}\]where T\({}_{\rm m}\) is the mean outdoor air temperature of day i, 15 \({}^{\circ}\)C is the threshold below which heating is typically activated and 18 \({}^{\circ}\)C is the average room temperature used as a set point when heating is activated. Cooling degree days (CDD) have not been considered in the study since they are less relevant compared to the heating degree days (HDD) because:  
* The region analysed is mainly characterised by heating demand rather than cooling demand due to its geographical location. For this reason, cooling accounts for negligible energy use compared to heating. * Cooling power is provided through electric heat pumps that do not directly emit GHGs even if electric power at a regional level is still partially generated by fossil fuels, whose share is decreasing following the recent EU directives. On the other side, heating is one of the main sources of energy consumption and GHG emissions in buildings due to the consistent use of fossil fuel-based energy resources [30]. The trend presented in Figure 2 shows that, in the last decade, yearly HDD has been decreasing significantly, highlighting warmer and warmer winters due to climate change. In particular, 2014 stands out as the hottest year and the lowest HDD (outlier shown in red in the chart). This may affect the trend of the linear regressions since it impacts, respectively, the typical energy demand of buildings (especially during winter), their energy consumption and, in turn, GHG emissions. Therefore, to obtain a more realistic picture, it could be required to remove 2014 from the analysis. Regarding GBRS, their multi-criterion nature based on indicators and benchmarks is intended to reduce the environmental footprint of buildings. These tools go beyond the simple energy benchmarking since they also assess areas such as pollution, water, materials and resources, waste, land use and ecology, health and wellbeing, and transportation that together contribute to GHG emission [2]. The consumption of fossil fuel-based energy resources is commonly recognised as the main driving factor behind GHG emissions, and the first step to reducing buildings' primary energy consumption is to minimise energy demand through the adoption of passive strategies (e.g., insulation, shading devices, etc.) [31]. However, a small portion of the energy is always required (e.g., for process, lighting, etc. ), but it can come from renewable energy technologies. If this happens, we are in front of a Net Zero Energy Building (NZEB).