## 1 Introduction  
Buildings play an important role in energy consumption in cities, including cities in the European Union (EU). Buildings are responsible for approximately 40% of EU energy consumption and 36% of the energy-related greenhouse gas emissions [1]. Heating, cooling, and domestic hot water account for 80% of the energy that citizens consume [1]. At present, about 35% of the EU's buildings are over 50 years old, and almost 75% of the building stock is energy inefficient. In the US, buildings account for about 40% of all energy consumption and a similar proportion of greenhouse gas emissions [2]. Based on the 2018 Commercial Buildings Energy Consumption Survey (CBECS), the estimated 5.9 million U.S. commercial buildings consumed 6.8 quadrillion British thermal units of energy and spent 141 billion dollars on energy in 2018. These statistics underscore the significant impact that buildings have on energy usage and emphasize the urgent need for energy-saving measures. The Energy Performance of Buildings Directive (EPBD) has been instrumental in drawing attention to the immense potential for energy savings through improvements in building design, construction, and operation. It catalyzes discussions and actions aimed at enhancing energy efficiency. Furthermore, recent geopolitical events have shed more light on the EU's dependence on Russia for energy resources. This geopolitical situation hasprompted increased discussions about energy security and the need for greater self-reliance in the EU. It has also fueled conversations about energy efficiency as a means to reduce dependence on external energy sources and ensure a more sustainable and resilient energy future. The recognition of energy efficiency as a critical aspect of sustainable building design, renovation [3] and operation has gained traction and is driving the demand for effective tools and strategies to optimize energy consumption [4], occupant comfort [5] and minimize the carbon footprint of buildings. In response to the need to enhance energy efficiency in buildings, there has been a notable shift from conventional buildings to smart buildings [6]. To improve the smartness of buildings, it is necessary to incorporate digital components into the pre-existing technological infrastructure within these structures. These additions have a direct impact on the diverse range of services, such as heating, cooling, ventilation, and others, that collaborate to achieve optimal human comfort. In the context of improving building intelligence, the 2018 edition of the EPBD [7] introduced a novel framework called the Smart Readiness Indicator (SRI). This framework was designed to address the requirement of evaluating the degree of intelligence in contemporary buildings and to encourage the adoption of digitalization in the built environment. For improving the energy efficiency of traditional buildings, research has been conducted on both active and passive methods. The idea of using Recommendation Systems (RSs) originated from companies like Amazon, Netflix, etc. with many other applications including products, movies, and content promotion [8]. It soon found its way into the buildings sector as researchers attempted to work on user behavior. RSs have emerged as valuable tools for improving energy efficiency in buildings. These systems leverage advanced technologies and data analysis algorithms to provide personalized suggestions and guidance to building managers and designers. By analyzing data from multiple sources, such as SRIs and Building Information Modeling (BIM), RSs can offer tailored recommendations that align with specific building characteristics and energy-efficiency goals. The current shift from conventional buildings to smart buildings presents a notable research gap that necessitates attention. Specifically, there is a need to develop a robust RS that is tailored to the unique requirements of modern smart buildings.