**4. Discussion**

Based on the obtained results, some clues can be found to outline alternatives for reducing greenhouse emissions. The contribution of electricity to emissions is noteworthy, being the highest negative contributor and coinciding with other results of other reviewed studies [23]. This source represents a difficult optimization; today, education is strongly linked to technological progress and the use of tools that require considerable electrical expenditure, and electrical devices (PCs, lighting, air conditioning) are already of maximum efficiency. As regards air conditioning, the insulation of the enclosure has recently been improved; a ventilated façade covers the entire surface and enclosures have double-glass windows with air chambers. The replacement of the aluminum carpentry by a more efficient one with thermal break could be assumed, but this option would represent an important investment. However, a better solution is within reach: the availability of certified renewable energy in Spain means that the best option is to replace the supplier with one with certified green energy. Taking into account this option, the purchased electricity will have no GHG emissions, reducing the total to 183,078 kg CO2-e (Scenario 2).

In this case, the GHG emissions of Scenario 2, compared with the initial situation (Scenario 1), represents a saving of 28% (Figure 1). This is the easiest and most immediate way to reduce the CF of ESNE, and can be reached with noninvestments, probably even with discounts from suppliers, since electricity from renewable sources in Spain usually has a lower annual cost than the regular mix.

01. Direct emissions and removals 02. Indirect energy emissions 03. Other indirect emissions

**Figure 1.** Electricity supply carbon footprint distribution scopes (kg CO2-e).

The change between scenarios can be reflected by means of the indexes described in Section 2.1. Table 6 shows the activity rates in both scenarios (255,548 kg CO2-e for Scenario 1, and 183,078 for Scenario 2), considering 1500 students enrolled and a total of 900,000 h/year, as indicated in Section 2.2:


**Table 6.** Activity rates of Scenarios 1 and 2.

The emission ratio per person decreases from 0.28 to 0.20 kg CO2-e/student·hour, and the hourly emission is 420 to 300 kg CO2-e/hour for the total number of students. Each student enrolled in a full academic year of 600 teaching hours per year, meaning a total emission of 170 kg CO2-e in the present situation, and 120 kg CO2-e for Scenario 2. This figure should be updated annually, taking into account the improvements made to correct the resulting carbon footprint. Educational centers could inform students and future students of these data in an exercise of transparency or even promotion.

The next option in importance to decrease GHG emissions may be found in the 31,548 kg CO2-e from the combustion of heating oil. To maintain the current water radiator system, this fuel could be replaced by natural gas, but this solution is expensive, since it requires the replacement of the current low efficiency boiler, unfeasible to adapt for use with natural gas. However, replacing direct combustion heating with heat pump air conditioners powered by green electricity would be a better solution. By means of a quick calculation, the additional electricity consumption needed can be estimated considering: a boiler combustion efficiency of 80%, a lower calorific value of 1028 kWh/L for Diesel C [42] and an efficiency of 60% for Split heating equipment [43]. This would result in an approximate electricity consumption of 90,000 kWh. This would increase annual electricity consumption to 331,000 kWh, 37% higher, but would eliminate the consumption of 11,000 L of a fossil fuel, its GHG emissions and highly polluting smoke. The result would be a decrease in CF to 155,500 kg CO2-e, 60% of the initial amount.

In order to further CF improve, the next option should be to decrease GHG emissions from transportation. Employees produce 28,290 kg CO2-e a year to go to work every with private fuel vehicles. According to the results obtained in the survey conducted using 116 employees, 37 use this mode of transport. This represents about 0.79 kg CO2-e/km·person (or 764 kg CO2-e/year per person). In comparison, about 80 people using public transport produce 17,190 kg CO2-e, a ratio of about 0.05 kg CO2-e/km·person (183 kg CO2-e/year per person), only 6% in terms of km·person (24% in a year·person basis). It should be noted that several electric (six in the present day) and hybrid cars are continuously being incorporated into the workforce. Measures such as time optimization, including the reduction in attendance days, could significantly improve this balance.

Business and field trips give another perspective. While there are significant improvements to be made, long-distance air travel has few solutions. In this account, there are 73 person flights in Europe and long trips, 18 person traveling to Beijin and 10 to Miami (USA). It should be noted that international flights cause a significant amount of 409 kg CO2-e/year, but, taking in account the distance (kg CO2-e/km·person), the emission ratio is as low as intercity bus transportation. Once again, the lower emissions are due to high-speed railway transportation, less than 5% of private diesel cars (Table 7).


**Table 7.** Carbon Footprint (CF) ratios per year of business and field trips (Scenario 1).

## **5. Conclusions**

The results obtained and literature review make it possible to draw conclusions based on a proposal for reducing carbon footprints.

If the calculation of the student-hour activity rate is applied, accompanied by calculation rules agreed by the sector, a register could be developed to allow comparability and to help mitigate global warming caused by educational activities and infrastructure.

The impact of Scope 2 is the highest of the factors studied, referring to the University's electricity expenditure. This incidence could be eliminated if the production of electrical energy was supplied by a company with a 100% renewable energy source, where the contribution of kg CO2-e emissions disappears, in addition to replacing old and inefficient installations with systems that use less energy.

Another action to be taken is the rehabilitation of old buildings in order to improve energy efficiency. In this study, the emission of greenhouse gases due to heating is 31,548 kg CO2-e. The insulation of the building envelope is an action to be taken into account to reduce the thermal transmittance and the heating energy consumption by around 90% if it is combined with adequate ventilation and a more efficient heating system, reaching values of 3155 kg CO2-e [44].

On the other hand, the carbon footprint produced by ESNE could be mitigated with the contribution of green spaces responsible for absorbing carbon, with an annual action of extending the trees in an institution, as was considered by Diponegoro University on its university campus [22] or Trisakti University in Jakarta [45], and studied at Suranaree University of Technology in Thailand, where the green area captured 40% of the total emissions produced by the university [46]. In the event that no land is available on campus, one option to consider would be the creation of green façades or vertical gardens, which also contribute to the insulation of the building's façade envelope [47].

University education should include sustainability and sustainable development in training actions [48], instructing students in sustainable development in all areas, as well as informing them of the impact that their way of life has on the planet, efficiency in the use of electricity and water, reduction in the use of paper (10), and contribute to raising awareness of the three Rs method "reduce, reuse and recycle", in addition to the alternatives presented, in order to improve the impact of kg CO2-e [49].

Another point to be dealt with would be the study of the optimization of working time in attendance, trying to reduce attendance as much as possible, to avoid trips that are not essential, even considering the possibility of limiting working days to four.

**Author Contributions:** Conceptualization, G.F.; Formal analysis, S.L.; Investigation, R.S.; Writing–original draft, G.F. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding

**Institutional Review Board Statement:** Not applicable

**Informed Consent Statement:** Not applicable

**Data Availability Statement:** The data described in the research are made public in this document, based on the research carried out by the authors.

**Conflicts of Interest:** The authors declare no conflict of interest.
