1. Introduction
In the European Union (EU) the building sector is responsible for around 40% of energy consumption and 36% of CO
2 emissions [
1]. In order to address the energy problem, in recent years numerous EU directives have been issued and targeted incentives have been introduced. In particular, the Energy Performance of Building Directive (EPBD), starting from 2002 [
2], has promoted a series of measures to enhance the energy performance of buildings. The last recent amendment of the EPBD (2018/844/EU) [
3] integrated and modified the previous versions, introducing some new objectives: (
i) promoting sustainable mobility [
4,
5]; (
ii) encouraging the use of smart technologies for new and existing buildings [
6,
7]; (
iii) raising end-users’ awareness in energy use [
8,
9,
10]; (
iv) incentivizing decarbonization through the development of a nearly zero energy building (nZEB) and zeroing of greenhouse gas emissions by 2050 [
11,
12]. In particular, increasing importance is being given to buildings that not only meet stringent energy performance requirements (i.e., nZEB) but also associate this feature with the ability to interact actively with both end-users and energy grids. In this sense, the smart building concept presents a series of improvement factors with respect to an nZEB [
13] such as: (
i) the possibility for occupants and operators to interact with the building easily [
14]; (
ii) the collection of useful information from and for the occupants; (
iii) integration with the electricity network [
15]; (
iv) the applicability of load control systems on the electricity network [
16]; (
v) a greater security [
17,
18]; (
vi) a greater comfort [
14,
19]; (
vii) the reduction of CO
2 emissions [
20]; (
viii) the reduction of operating costs of heating, cooling, and lighting [
21].
In this context, the smart readiness indicator (SRI) has been introduced, aiming at providing a framework for assessing and promoting the smartness of buildings in Europe. In particular, SRI aims to measure the building’s ability to adapt its operation to the needs of both the occupants and the network and to improve its efficiency and overall energy performance To this aim, the European Commission has issued a delegated regulation [
22] and an implementing regulation [
23] which define, respectively, a methodological framework for calculating the SRI and provide various possible implementation pathways for the member states that will decide to implement the common European scheme. To provide support for the definition of the SRI calculation methodology, DG ENERGY of the European Commission has promoted two technical studies conducted by a research consortium [
24,
25], which led to the definition of a catalogue of “smart ready services” and to the development of a methodology for calculating the indicator. Thus, for the estimation of the SRI, nine evaluation domains are considered, each with different functionality levels [
26]. In the context of the above-mentioned technical studies, a first beta-testing of the proposed methodology was initiated and two specific automated spreadsheets were also made available to stakeholders to support a uniform SRI calculation process among EU member states. Stakeholders from 21 member states participated to the beta testing, with 112 buildings evaluated (of which 57 were residential and 65 non-residential, most of them built after 2010) [
27]. Italy participated to the public beta testing phase of the second technical study by performing over fifteen SRI assessments in real case studies buildings (e.g., residential buildings, schools, offices, hospitals) [
24,
25].
Few studies are available in the literature that analyze the SRI in detail, with reference to both the calculation methodology and the application to different case study buildings. Marzinger et al. [
26] proposed a simplified methodology for the quantitative assessment of the load shifting potential of buildings with the aim of providing a numerical approach that allows to classify the buildings basing on their energy storage capacity, load and their network interaction. The same authors have further developed their approach based on numerical models on the evaluation of entire districts [
28]. Janhunen et al. [
29] applied the calculation of the SRI in some buildings in northern Europe showing that, in its current form, the SRI is unable to recognize the peculiarities of cold climate buildings, particularly those employing advanced district heating systems. Another implication of [
29] is that the applicability of SRI in all Member States of the EU could be problematic due to the subjective nature of the proposed process for the selection of relevant services. Vigna et al. [
30] assessed the impact of subjective nature of the SRI methodology, adopting a two-step assessment with the involvement of two teams of experts. The authors also present a series of recommendations for an effective and broad implementation of the SRI for increasing the relevance of its assessment and effectiveness, as well as for improving the comparability of smart building readiness. Fokaides et al. [
31] highlighted SRI values are particularly penalizing in small buildings where there are no BMS (building management systems), concluding that although the indicator is promising, there are several aspects that need to be improved. In [
32] the SRI methodology is applied in two service buildings located in the Mediterranean climate, and possible effects of retrofit actions and smart functionalities on energy performance and indoor environment quality were evaluated. The results showed that the defined weighting factors are not able to capture the energy performance of the service buildings and need a revision. Becchio et al. [
33] performed a dynamic simulation of the Energy Center building of Turin in different scenarios (current state and increased level of management and control), and evaluated the influence of these actions on the overall SRI assessment. The results allowed them to link the SRI with the energy needs of the building.
Italy, as with other EU member states, is called to decide whether to implement the SRI calculation and, in this case, to define a suitable methodology taking into account the real peculiarities and characteristics of the national building stock. To this end, the EU Implementing Regulation [
23] provides for a non-binding testing phase, after which the member state will be able to decide whether to implement the calculation system. In this sense, testing the application of the general SRI methodology on different buildings (i.e., residential and non-residential, existing and new buildings, retrofitted and not-retrofitted, etc.) will be useful to identify the most significant case-study buildings for the testing phase.
In this context, the aim of this work is to apply the SRI methodology developed during the second European technical study to estimate both the actual and potential smartness of the Italian residential building stock in different scenarios. To this end, eight “smart building typologies” (SBT) representative of the Italian residential building stock were identified by using the information available in the existing national buildings databases [
34,
35,
36]. The analysis of the regulatory and legislative framework regarding the building automation and control systems (BACS) in Italy was also performed to define the following three application scenarios: (
a) a “base scenario” (building stock as it is); (
b) an “energy scenario” (simple energy retrofit); and (
c) a “smart energy scenario” (energy retrofit from a smart perspective).
This study was carried out as part of the national three-year research project “Ricerca di Sistema Elettrico”, whose main aim is to develop a tailored methodology for the SRI calculation in Italy. This project involves several phases: (i) assessing the SRI in the existing building stock; (ii) providing a specific market analysis involving the main players in the BACS market (builders, technicians, designers etc.); (iii) updating the catalog of services proposed by the European study; and (iv) developing a calculation tool for SRI in the national context. The results will be made available to the European working group that is supporting the implementation of the SRI in Europe.
The present paper presents a number of innovative aspects compared to the existing literature: (
i) unlike precedent studies [
29,
30,
31], the focus of this work is on residential buildings which, although expected to have a limited impact on the SRI implementation, in Italy represent the majority on existing buildings (about 84% in 2011 [
34]); (
ii) the proposed approach is not focused on single case studies, but presents a more general framework useful for defining reference building typologies for SRI calculation; (
iii) it provides a quantitative estimate of the SRI potential in a series of statistically representative buildings; and (
iv) it highlights the actions required for the optimal implementation of SRI in the residential sector.
In the following, the SRI methodology calculation employed within this study is described. Then, the characteristics of the SBT are detailed in each scenario. Finally, results of the SRI calculation at a national scale are presented and discussed.
2. Materials and Methods
The methodological framework for calculating the SRI is described in [
24]. A multilevel approach is proposed basing on nine domains (i.e., energy services) and seven impact criteria, as shown in
Figure 1.
For each domain, specific smart ready services are defined according to the system characteristics of the service considered. Different levels of functionality are assigned to each service, with each having its own degree of smartness, on an increasing scale from 0 (i.e., “non-intelligent” service) to a maximum value (which can vary from 2 to 5 depending on the service) for advanced features. Since the maximum scores assigned to the different functionality levels are variable, a direct comparison between the different services is not applicable [
30].
The scores assigned to the individual services are summed up for each of the domains and divided by the maximum individual scores so as to obtain a “domain impact score”. For each impact criterion, the total score is calculated as a weighted sum of the domain impact scores. The SRI is then obtained as a weighted sum of the total impact scores. The SRI evaluator is free to choose the predefined weighting system or to assign different weighting factors based on the specific characteristics of the buildings being evaluated (climatic conditions, characteristics of the national or regional building stock, etc.). In the present study, the predefined weighting system has been applied as suggested in [
25]. It is possible to calculate the total building SRI, the SRI per impact criterion, the SRI related to EPBD key capabilities, and the SRI per domain.
Figure 2 shows the main steps of the SRI methodology.
Three methods have been proposed for the assessment of the SRI:
Method A (simplified): intended for residential buildings or small non-residential buildings. It allows both third-party and self-evaluations;
Method B (detailed): consists of a more detailed assessment including by default on-field verification by an independent expert;
Method C (advanced): consists of a more advanced assessment based on direct monitoring on-field (for example through self-reporting from BACS systems).
The application of method A includes a small number of intelligent services (27 services), while the implementation of methods B allows for the evaluation of more complex buildings and services (54 services). Method C is currently considered to be a potential future evolution of a certification approach for a commissioned building. The analysis carried out in this paper has been performed using method B [
24].
In the preliminary phase, it is essential to define the domains present in the building being evaluated, through an initial evaluation process called “triage process” [
24]. In this phase, an inventory of the intelligent services present in the analyzed building is made through a simple check-list. In a subsequent phase, the levels of functionality are assigned to each of the smart ready services identified, allowing, eventually, the assessment the total SRI, the domain, and impact SRIs, as shown in the flow chart in
Figure 3 [
31,
37].
2.1. SBT Definition in the Base Scenario
Aimed at obtaining a rough estimation of the SRI of the Italian residential building stock, the authors first analyzed the following data: (
i) statistical data on buildings and housing derived from the last ISTAT census [
34], (
ii) statistical data on heating, cooling and domestic hot water systems as well as results of the TABULA project for the characterization of building/heating systems typologies [
35,
36], (
iii) the regulatory evolution regarding the performance obligations and regulation requirements of the technical systems of buildings belonging to the residential sector in Italy [
38,
39,
40,
41]. It is believed that the estimate of the SRI of the Italian building stock is substantially determined by the characteristics of heating and domestic hot water systems. In addition, in the residential sector one can highlight: (
i) the scarce diffusion of controlled mechanical ventilation systems and, generally, the scarce application of HVAC systems [
34]; (
ii) the absence of obligations to install centralized automation systems (i.e., BACS systems, mandatory starting from 2015 only for non-residential buildings and for new residential constructions only in few Italian regions); (
iii) the lack of a regulatory framework establishing the minimum smartness requirements of residential buildings (i.e., the lack of obligations for the automated and intelligent management of the building systems).
Table 1 shows the main legislative references that were useful for associating the related heating system to each SBT.
Based on the findings of the above-mentioned analysis, eight SBTs were identified based on the following main criteria:
As a final step, following the above-described analyses, a real building was associated to each defined SBT and fully characterized in terms of services and functionality. The information necessary for the characterization was collected through on-site inspections and interviews with users. The details about applicable domains and main systems characteristics resulting from this analysis have been reported in
Table 2 and
Table 3.
In particular, the active domains, construction period, and type of heating system of the SBTs obtained from the preliminary analysis are highlighted in
Table 2, while in
Table 3 the main systems characteristics of the SBTs are highlighted for each domain. For the sake of clearness, in
Table 3, the “Lighting”, “Dynamic Envelope” and “Electricity: renewables and storage” domains have been omitted. The reader should note that, for the “Lighting” domain, the hypothesis of an on/off manual control system has been applied to all cases of the base scenario. The “Dynamic Envelope” and “Electricity: renewables and storage” domains were activated only for SBTs “G” and “H” where, respectively, motorized mobile screens with manual control and PV system without storage have been considered. The remaining domains “Controlled Ventilation”, “Electric vehicle charge” and “Monitoring and control” were considered active in none of the SBTs since the analysis of the literature highlighted a scarce diffusion of these systems in the residential sector in Italy.
2.2. “Energy” and “Smart Energy” Scenarios for Retrofit Interventions
In order to evaluate the potential improvement of the overall SRI score of the national building stock, the impacts of various retrofit interventions applied to the selected building typologies were evaluated. In particular, the retrofit interventions were identified keeping in mind the most widespread domains and respective services in the residential sector (i.e., heating, lighting, DHW production, dynamic envelope, and installation of production systems from RES). For the definition of the retrofit scenarios, a preliminary statistical analysis of the retrofit interventions carried out in the 2014–2019 period [
42] based on the type of intervention and the potential “smartness” was performed. To this aim, two efficiency scenarios [
43] were defined (“energy” and “smart-energy”) with increasing level of smartness. The “energy” scenario is based on the hypothesis of retrofitting the building stock accordingly to the 2014–2019 trends, whose main results are described in [
42]. The minimum smart functionalities of the new installation/replacement systems for the “energy” scenario are shown in
Table 4. In the case of pre-existing system already meeting the minimum established requirements, no replacement/requalification has been considered.
For the “smart energy” scenario, a series of smart energy efficiency retrofit interventions have been hypothesized, basing also on the results of [
43], by acting on individual services and domains with installations not involving substantial changes to the systems. Therefore, the interventions already hypothesized for the “energy” scenario have been revised from a “smart” perspective, thus assuming for the newly installed/replacement systems the minimum additional functions including: WLAN/Wireless connectivity, remote management and control systems, connected sensors for management, control and monitoring purposes. The minimum smart functionalities of the newly installed/replaced systems for the “smart energy” scenario are shown in
Table 5.
5. Conclusions
In this paper, aiming at providing a first estimation of the potential of SRI implementation in the Italian building stock, the authors applied the SRI methodology in different scenarios. To this end, the authors developed: (i) a preliminary analysis of statistical data of the residential building stock, and (ii) an analysis of the regulatory context regarding management and control systems in residential buildings. Eight “smart building typologies” typical of the national building stock were identified and fully characterized in terms of domains and of smart functionalities. The SRI of each single smart building typology has been found to vary from 0% to 23% in absence of any retrofit. This allowed us to estimate the SRI of the entire building stock in the base scenario approximately equal to 5.0%. Moreover, considering two simulated retrofitting scenarios, the potential SRI of the Italian building stock has been estimated to be equal to 15.7% in the case of a simple energy requalification and to 27.5% in the case of a smart energy requalification.
From the results obtained, the following actions may be adopted for the integration and further development of the SRI methodology: (i) performing a specific statistical analysis regarding the automation systems commonly present in existing buildings and the smart functionalities of the devices available on the market; (ii) defining reference buildings both for residential and non-residential sectors with the consequent update of domains, technical services and functionality levels; (iii) developing a catalog of reference services and functionality levels for different construction types; and (iv) defining supplementary measures to favor the spread of the SRI taking into account minimum system requirements (e.g., BACS). This would allow a better matching between the smart ready services and the real functionalities of the devices actually available on market.
The results of this work can provide useful information to evaluate the best opportunities for implementing the current SRI methodology at a national level. Indeed, the main contribution of this study is to provide a comprehensive picture of the application of the SRI methodology, defined by the European technical study, to a wide range of residential buildings representative of the Italian building stock. In this sense, this study is preparatory to the testing phase of the SRI envisaged by the European Union not only in Italy, but also in other EU Member States having building stocks with similar characteristics, peculiarities, and climatic conditions. Besides, this study identifies, among the most widespread, the energy retrofit interventions with the greatest impact on the SRI in existing residential buildings, thus being particularly useful for builders, installers and designers active in the smart buildings sector. Further development of this research will concern a specific technical-economic feasibility study aiming at estimating the potential of different smart refurbishment interventions under real application constraints.