Deep Energy Retrofit of Residential Buildings in the Mediterranean Area: The MedZEB Approach

The methodology adopted is described in the amending EPBD (Directive 844/EU 2018). Global costs have been based on life cycle costs (LCC), and the primary energy consumption (PEC) has been calculated dynamically on an hourly basis by using a software complying with the BESTEST of the IEA. The same methodology has been used also in other references, like BPIE (2010), Brandao et al. (2016), Becchio et al. (2015). An extensive abacus of renovation measures has been produced, by gathering technical solutions country per country. A common climatic zoning for the EU area has also been developed, as well as a common abacus of reference buildings for the Med countries. This led to the calculation of 546 cost-optimal packages of solutions (42 reference buildings × 13 reference climates) in total (Fig. 1).

The research was aimed at developing a new financial solution able to flexibly assist the deep retrofitting process according to a step-by-step approach, thus enabling taking into account unpredictable events occurring to the homeowners in the long run of a reimbursement plan (e.g., asset sale or inheritance, technological updates, fluctuation of energy costs, etc.). The research resulted in the development of the versatile energy loan (VEL) solution, which consists of a single mortgage arrangement (30-year basis) with multiple steps of disbursement, each one corresponding to the cost of the renovation steps. This feature makes possible a reduction of the initial mortgage (see Fig. 2), to the benefit of low-income or low-resources families, as well as for a full flexibility of the solutions, since the plan can be updated or interrupted after each step. Furthermore, the VEL solution is based on a fixed interest rate for the whole duration of the plan, which would enable taking advantage of the actual situation in the money market. Finally, the reimbursement plan would be shaped to be funded by the economies generated at each step by the energy savings achieved, thus allowing for the full financial sustainability of the interventions.

The MedZEB protocol was designed and developed with the aim of incentivizing clients to invest in building retrofitting, by offering them a guarantee that the retrofitting process will be carried out properly along the whole value chain. Furthermore, the protocol contains the quality requirements necessary for accessing the HAPPEN financial solution (see Sect. 2.2), as well as specific KPIs addressing comfort, behavioral and well-being aspects (Fabbri 2016; Antonucci 2019).

The protocol includes also the following main documents:

The VCS will be issued at the end of each renovation step, after a positive assessment of the achievement of energy saving targets. For this reason, the MedZEB VCS entails a “relative,” and not an “absolute,” certification of the energy performance (see Fig. 3).

To this end, a monitoring process will be implemented after each renovation step, based on a dedicated monitoring protocol. In case, the assessment is not fully positive, the guarantee framework of the protocol will be activated, leading to the definition of a contingency plan, the execution of which will be mandatory for the activation of the next step. The development of the MedZEB protocol was based on extensive literature research, including building environmental assessment methods (Triple E 2014; EnerPhit 2015; Kudryashova, Genkov and Mo 2015; Hamelman 2016; Asdrubali 2017; Mattoni 2018; Sesana and Salvalai 2018) and Building Passports running experiences (Sesana and Salvalai 2018; Fabbri 2016). The protocol was designed not only as a detailed, standardized and transparent tool, but also as a simple and cheap one to be used throughout the renovation process.

The outputs described above have been included into the “HAPPEN program”, which is a comprehensive framework of actions, tools and services aimed at boosting the uptake of the MedZEB approach. The program is composed of three main stages:

The HAPPEN platform is conceived as the main vehicle for the market uptake of the HAPPEN program. To this extent, it has been structured in order to support the program main stages with dedicated digital services, by providing different final user types (owners, makers and influencers) with a differentiated access to the HAPPEN outputs, according to their specific needs:

All groups will access digital forums where they will be enabled to interact among each other and to provide feedbacks on the MedZEB approach. In this way, the platform will act as an assisted marketplace, as an e-learning and services provider, and as a digital community for defragmenting the retrofitting supply and value chain, and it will aim to become the reference portal at EU level for the DRM in the Med area. To this extent, the platform has been co-designed with potential end-users thanks to their deep engagement in the HAPPEN Living Laboratories.

The climate of Milan corresponds to the W2S2 HAPPEN climate scale (for more details see Appendix §5.1). The building corresponds to the multi-family reference building typology “Italy 1980–2000.” Costs for the renovation measures have been evaluated using the Milano Municipality price-list for public works. The POS identified for this case study, expressed in terms of minimizing the life cycle cost, is briefly described as follows (for more details see Appendix §5.2).Because the whole intervention cost would be very high to be sustained in one step, also provided the large number of owners, a step-by-step approach has been defined. The inner constraints assumed for the definition of the steps are the following: Façades and thermal bridges related to façades are improved simultaneously; air-tightness and façades are improved together; windows and outside glass-doors are changed together; window renewal is associated with the improvement of thermal bridges on the windows contour; limited investment per step: max. 144,000 € (120 €/m² of useful surface). Basing on this, the POS has been divided into three steps (Fig. 5), the characteristics of which are the following (for more details see Appendix §5.3):

The simulations have been carried out by assuming an interest rate at 3%, and by introducing an excess approximation of the costs, as well as an efficiency decrease of the installation/envelope system, to test the robustness of the solution under stress conditions. The fiscal incentives available in Italy according to actual laws have also been considered (tax credit mechanism with 70% of reimbursement in ten years), but only for the first step, to cope with uncertainties on their future confirmation. Starting data and results of the simulation are the following (for more details see Appendix §5.4);

The plan is largely sustainable in 18 years, with wide margins of guarantee. According to this simulation, the objective of supporting the 100% costs of energy renovation with the savings obtained seems to be fully achieved. A feasibility assessment in the absence of the tax credit has also been performed to test the financial solution in other EU countries without incentives schemes. The plan proves to be largely sustainable in 27 years, with the following reimbursement plan: the first step as long as 22 years, the second step lasting ten years from the tenth year of the first step and the third step lasting seven years from the end of the second step. An analogous test (no incentives) was then carried out in the case of a single-stage intervention, resulting in a plan largely sustainable in 15 years (see Appendix §5.4), decreasing to eleven years if incentivized according to the actual Italian system.

The winter severity climatic index is 1.24; the summer severity climatic index is 0.62 according to the methodology proposed by Salmeron et al. (2013). Total useful surface is 1198.7 sq.m. Compactness, defined as volume to area ratio, is 2.96 m because the two lateral walls—east and south oriented—are party-wall in contact with other blocks. The north façade is glazed 6% while the south façade is 12% glazed. The global thermal transmittance (U-value) of the façades is 1.81 W/m²K, the U-value of the roof is 2.25 W/m²K, the U-value of the slab-on-grade is 1.75 W/m²K and the U-value of the windows is 5.7 W/m²K, giving an average U-value for the whole building envelope weighted by the surface of each element of 2.54 W/m²K. The heating needs of the building are 139.31 kWh per sq.m. of useful surface (u.s.) and the cooling needs are 3.46 kWh/m² of u.s. The heating and domestic hot-water system is a mixed gas boiler with a seasonal performance of 0.89. The cooling system consists of a centralized heat pump per dwelling, with a seasonal energy efficiency ratio (SEER) of 2.0.

Building envelope:Building systems:

Building surroundings: Basing on the Solene project outputs, for this typology of intervention, glazing ratio and level of insulation, the optimum solution is to plant trees in the street (Morille et al. 2015).

Step-by-step approach, with Italian incentives applied only on the first step:

Step-by-step approach, without incentives:

Starting parameters: loan of €270,000.00 for eleven years, with a fixed rate 3%; maximum financial commitment: €14,322.00/year (about 57% of the prudentially estimated savings of €25,000.00/year).

Starting parameters: loan of €27,000.00 for 15 years, with a fixed rate 3%; 180 monthly payments of €1865.00, equal to €22,380.00/year (about 89% of the prudentially estimated savings of €25,000.00/year).