## 1 Introduction  
Zero energy buildings (ZEBs) are buildings that produce and use an amount of energy that is exactly equal to their annual needs [1]. It has been noticed that some related concepts, such as autonomous houses (self-sufficient buildings) and green buildings (buildings that minimize the negative environmental impacts caused by a construction and use), are frequently associated with ZEBs [2, 3]. Buildings account for about 40% of overall energy consumption and 36% of CO\({}_{2}\) emissions in the European Union [4]. Reducing energy demand and extracting a greater proportion of it from renewable sources are crucial steps in assisting the EU in coping with energy imports, lowering greenhouse gas emissions and encouraging the use of green energy [5]. Some reports argue that energy saving programs have led to greater energy efficiency in Member States, while others highlight the fact that they have caused greater inequalities in energy standards [6]. Among these, a study investigated the different circumstances in each European country regarding the implementation and applicability of energy certification in buildings, and an overview of challenges and instruments for improving energy efficiency in European buildings showed significant differences in terms of commitments, financial capability, and market conditions [7, 8]. It also confirmed that each Member State must fully utilize its energy-saving opportunities, such as new design and refurbishment of buildings, to be able to significantly increase the share of savings in current energy consumption [9]. EspeciallyEuropean countries should promote the modernization of existing buildings, the use of renewable energy in the construction sector, and the transition to ZEBs [10]. It is also important to implement the Smart Readiness Indicator (SRI) concept, resulting from the recast of the directive on the energy efficiency of buildings, adopted in 2018 [11]. The set of SRIs is a measure of the intelligence of buildings systems, and its promotion is expected to contribute to the energy savings of the building sector. The first attempt to present and evaluate SRIs was made by [PERSON] et al. [12]. They have identified gaps and perspectives for improvement of this system and developed specific numerical scenarios for the evolution of its implementation in the coming years. They emphasized that a major transition in the way we evaluate the energy behavior of buildings is needed, which should allow for the technological readiness evaluation of a building's ability to adapt to the needs of its users as well as to the energy environment. In general, our climate is thought to be shifting, and people are becoming increasingly worried about the environmental consequences of current energy usage [13]. It is noteworthy that a building's emissions are significant over its life cycle. In addition to the total amount of energy consumed, each building incurs embodied energy from mining, refining, manufacturing, and transportation of its building materials, as well as energy necessary for demolition [14; 15]. This embodied energy, as well as the energy used over the life of a building is included in its life-cycle energy and emissions footprint [16]. Buildings are responsible for around one-third of global greenhouse gas emissions. The arguments for the idea of sustainable development in terms of climate change and energy policy are strengthened by the statement that the modernization of building stock has the greatest potential in terms of reducing the demand [17]. Therefore, in recent years there has been an increase in the interest in ZEBs [16; 17; 18]. The net energy theory has been used in a number of fields since the 1970s, including fossil fuel [19] and nuclear power generation [20; 21], as well as renewable energy generation.