**1. Introduction**

The environmental energy sustainability of universities cannot be separated from the large-scale overarching problem that a ffects the entire world. There is growing evidence that the situation of the global environment has become critical in several aspects. Thus, problems, such as the depletion of natural resources, global warming, or the depletion of the ozone layer, have received considerable media coverage and have significant social repercussions.

It is estimated that over 50% of the population lived in urban settlements, in 2016, which will increase to over 60% by 2030; that is, two out of every three persons in the world will live in cities [1–5]. This problem is magnified if this densification is considered in conjunction with recent assessments that two-thirds of the world's primary energy consumption can be attributed to urban areas, which in turn means that 71% of the world's direct greenhouse gas (GHG) emissions are energy-related [6]. In the European Community, in particular, buildings and the construction sector in general are responsible for 40% of energy consumption and 25% of CO2 emissions. [7–9].

This situation presents a clear demand, both from the public and private sectors, to forecasters and urban planners for greater environmental awareness in project implementation. This new awareness must encompass many interrelated problems [10], such as the consumption of resources, waste production, water consumption, GHG emissions and the protection of biodiversity and air quality. Most of these problems cannot be addressed at the level of a building or a facility. The urban scale is an extremely relevant scale at both the city and university campus levels [11]. The environmental

and energy impacts at the building scale are magnified at the urban scale [12]. For this reason, urban planners are more frequently employing environmental and energy efficiency parameters in the design of new urban development spaces and in the creation of regeneration projects for city districts [13]. Therefore, it is absolutely necessary to use tools in the simulation, measurement and evaluation of parameters that can facilitate the sustainable development of cities [14–19]. It is crucial to include these parameters at the design stage to be able to choose the most sustainable urban proposals among different projects. Different neighbourhood sustainability assessment (NSA) tools are available depending on the objective of an urban development project. Each tool has its own particularities and produces various forms of environmental assessments for different data.

Several studies have analysed different systems [20]. Lee presents an in-depth review of five representative qualitative assessment tools at the building scale: BREEAM, LEED, CASBEE, BEAM Plus, and ESGB [21]. Reith and Orova [22], compare different NSA tools at three levels of detail for different indicators. Sharifi and Murayama [23], analyse seven systems of sustainability assessment, showing a clear difference in focus among the tools. An in-depth case study in Spain is used to demonstrate substantial differences among thirteen assessment tools for sustainability at the urban scale at the international level [24]. Lastly, Xabat et al. conducts a study on different recent development tools for the energy assessment of cities at the district level [25]. Among the available options, the dynamic energy atlas can be used to solve energy problems in a geographical context, with some drawbacks [26]. Another tool analysed in the study is CitySim, which can be used to simulate energy scenarios at an urban scale, although considerable expertise in energy simulations is required [27].

The NEST (neighbourhood evaluation for sustainable territories) tool is used in this study [28,29]. This recently developed and simply managed tool starts with a life cycle analysis at the building level to evaluate of the design of a district of a city and proposes improvement scenarios for a more sustainable evolution of the city [19]. Using NEST, three-dimensional (3D) models are used to evaluate a series of indicators to analyse the main environmental problems affecting sustainable design at an urban scale. This agile tool generates 3D graphical solutions that are very easy to interpret. The environmental energy sustainability of universities can be successfully studied at the university campus scale, and the impact of the university campus can be related to the city where it is located. This tool was initially developed to evaluate different sustainable scenarios for a city. However, present-day universities can be considered to be small cities because of their large size and population and the complexity of multiple campus activities, which directly or indirectly impact the environment [30,31]. These impacts are mainly related to the consumption of energy and materials related to operations and activities related to research, teaching, administration and services, and transportation to users' homes [32]. Thus, there is a growing demand for projects on sustainability in universities [33–37]. That is why the evaluation of the environmental impact of University of the Basque Country (UPV/EHU) has been carried out using the NEST tool [38].

A global evaluation can be performed using NEST at different scales of analysis, where the impacts of the university campus and the city are evaluated in an interrelated manner, and the links between impacts can be analysed. As a result, improvement scenarios can be proposed that do not focus on organisational or local policies but consider the best intentions of municipal policies in relation to university guidelines, thereby combining efforts to achieve common objectives for worldwide energy improvement.
