As suggested in the above-mentioned document and anticipated in the Introduction section, the design phase has to be faced after a deep acknowledgement of the context, both from architectural and cultural point of view. To that end, the first step of the method is an architectural survey on the project site in order to notice, together with the analysis of the conservation state, the traditional elements and materials characterizing the cultural good. The architectural survey allows also the verification of the acquired dimensional data in order to develop the geometric model for the energy assessment of the buildings involved.

In addition to the regulatory framework and to the architectural survey, in the preliminary analysis, energy simulation of the building before retrofit (baseline) can be accomplished and, if data about energy consumptions are available, calibrated.

According to the information acquired by the architectural survey and taking into account the main criticalities of the buildings involved in the retrofit process, in order to build a simulation model for the energy assessment, the main architectural features of the buildings have to be defined, in such a way as to consider the main traditional elements.

Since there are no ready-to-use solutions in the mentioned Guideline, for finding the best solution, able at the same time to preserve the historical and cultural value of the construction and to ensure the lowest energy consumption, it is appropriate to propose a set of different solutions with increasing levels of energy performance and/or compliance with historical and architectural constraints.

In order to assess the effects of proposed retrofit scenarios, especially in terms of energy saving potential with respect to the pre-retrofit situation, an energy model describing the considered buildings has to be developed. According to the available information derived from the preliminary retrofit project, the model has to be designed through the definition of the buildings shape and construction characteristics, the partition of the thermal zones having different occupational profiles and internal gains, which is even more important in case of multifunctional end use of the buildings [36]. In order to assess the energy behaviour of the buildings, several tools can be adopted with different levels of detail. Among the tools available for properly assessing the dynamic behaviour of buildings, the software IESVE^† can be adopted, as done for the present application (Result section). IESVE has been validated by Building Energy Simulation Test (BESTEST) based on ASHRAE Standard 140 and its capabilities have been recently compared with the EnergyPlus ones, with regard to different operation states of an educational building in Canada, obtaining slightest discrepancies [37]. The use of this software in energy simulation is gaining attention within research framework. Indeed, it has been used in several studies to assess, for instance, the energy consumption of a market building in New Taipei [38], the energy saving potential of an air handling unit within an office building in Singapore [39], the overheating risks and daylighting levels in high-rise residential buildings placed in London [40], and also the building energy demand at community level [41].

The definition of the functions assigned to the thermal zones have to be carried out matching the possible new end use foreseen by the project, based on the needs of the partners involved in it. Once the preliminary functions have been set, the next step regards the definition of the most proper occupational profiles, i.e., the time schedules modulating the heat gains associated to people, appliances and artificial lights. Among the other available and in force in the different contexts, the technical book SIA 2024 [42] offers an exhaustive characterization of many thermal zones, divided by function. Moreover, the parametrization adopted is accurate and well suitable for the integration as input in a dynamic simulation of a building energy model.

The first step, towards the definition of the energy model and its simulation, concerns the development of the geometric model of the buildings involved. Then the model has to be imported into the energy simulation tool detailing constructions, thermal loads and occupancy schedules of each thermal zone. The climatic conditions have to be selected in order to perform the calculation of the energy needs, importing the proper climatic file. Different outputs can be calculated by the energy simulation in order to explore the effects of the different retrofit strategies on thermal comfort, levels of indoor temperature and energy needs. Systems devoted to heating and cooling are usually assumed to be operating according to the occupancy schedule of each thermal zone.

Once the energy simulation has been run, accounting the building envelope retrofit measures, and the cooling and heating needs for each thermal zone have been evaluated, hypotheses and evaluations on the energy supply and use of different energy sources, including renewable ones, have to be given. Further, if the obtained results are not satisfying, according to a recursive approach, the method can be repeated from the beginning, changing the original energy retrofit hypothesis with the aim to improve the design process. The results obtained by different scenarios and approaches can be compared towards the optimal one.

The comparison of different energy retrofit solutions is useful in particular dealing with protected buildings, because the obtained results can influence the Superintendence judgement, in order to approve the most effective and compatible solution.

The different methodological steps are described in Figure 1 where, for the sake of generality, the possibility to compare the results obtained by the same mentioned method or by an energy audit, before and after the retrofit for the energy improvements evaluation, is also represented.

Figure 1.

Methodological scheme

The origin of Cascina Nosedo lies around 1600 with the realization of a productive farm. In 2013, after a long period of abusive occupation, the Municipality of Milano regained the site in order to valorise the historic and artistic relevance of this protected cultural heritage. The farmhouse area is composed by 11 buildings arranged in a traditional court scheme. As highlighted in Figure 2, the buildings that will undergo the retrofit are the two on the right (buildings 9 and 10), object of the present study. They have a single floor regular rectangular plan, for an overall floor surface of 337 m² for building 9 (B9) and 554 m² for building 10 (B10).

Through the architectural survey carried out on the project site, all the buildings’ features have been scheduled in a check list, in order to have an overview on the conservation status, and to highlight the traditional elements and materials that should commonly be kept unaltered or re-established to restore the historical value of the site. In particular, consistently with the original features of the buildings of the farmhouse (Figure 3), the following elements should be considered: the visible clay brick pillars within the external walls, the external plaster, the wooden roof framing and the clay tiles roofing.

Figure 2.

Masterplan of Cascina Nosedo and indication of the buildings analysed (B9 and B10)

Figure 3.

Building 10 (left), building 9 (centre) and detail on conservation status (right)

The survey carried out on the project site has been useful to highlight the criticalities related both to the conservation state of the constructions and to the feasibility of the retrofit directives from Municipality of Milano advisors. The buildings 9 and 10, as well as the rest of the farmhouse, show diffuse deterioration signs, mainly related to the complete absence of a planned maintenance during the time. The plasterboard is detaching from the brick walls due to atmospheric corrosion, many clays on the roofs are damaged and the roof of building 10 has been roughly replaced with an asbestos shelter in the past, therefore, in order to restore the safety and serviceability of the two buildings, some preliminary interventions have to be accomplished.

Several criticalities arise also in the development of the energy retrofit simulation, indeed, it concerns the energy performance improvement of buildings mostly abandoned and composed by open and unheated spaces at the actual state. For this reason, the assessment of an energy audit, in order to define a reference case for the energy improvements evaluation, was not possible.

A first retrofit hypothesis concerned, together with the substitution of windows and roofs, the insulation of the opaque envelope from the outer side, a common solution for energy retrofits. However, considering the adverse opinion of the Superintendence on the feasibility of this first proposal, due to the alteration of the external aspect, it was necessary to develop an alternative retrofit solution, providing thermal insulation of the opaque envelope from the inner side.

Nevertheless, both the envelope scenarios have been kept into account for the whole design process, in order to evaluate their potential benefits.

Both solutions studied and proposed foresee an insulation with 10 cm wood fibre panels, provide the same walls thermal transmittance (0.26 W/m²K), in line with the indexes in force [6], while different internal heat capacity (15 and 179 kJ/m²K for internal and external insulation cases, respectively). Hence, the main difference between the two scenarios is represented by the relative position of the insulation layer with the respect of the thermal mass of the wall.

The two buildings have been divided into several new spaces (i.e., thermal zones) arranged in two floors in each building. Consequently, the façades are expected to be equipped with a proper number of windows in order to match the minimum requirements of daylight and natural ventilation. The definition of the functions assigned to the thermal zones has been carried out matching the new end use foreseen by the project, based on the needs of the partners involved in it. Once the preliminary functions have been set, the most proper occupational profiles (i.e., the time schedules modulating the heat gains associated to people, appliances and artificial lights) have been implemented. Since the buildings have been simulated before the publication of ISO 17772-1:2017 [43], that contains the precise weekly time schedules for each typology of space, the national reference in force [44] was compared to other available and more detailed references. Among them, the technical book SIA 2024 [42] according to the considerations reported in the Method sections. Therefore, in order to develop the thermal template of the model, the time schedules and the related internal gains for people, lights, appliances, ventilation rates and DHW referred to five different thermal zone typologies (kitchen, restaurant, laboratory, expo/conference room and office) were extrapolated from SIA 2024. Heating and cooling systems were assumed to be operating according to the occupancy schedule of each thermal zone. The sensible heating and cooling demands are computed by imposing the achievement of a set point temperature, 20 °C and 26 °C for the heating and cooling season^‡, respectively.

Hence, the whole model was finally divided into 8 thermal zones. The main features related to them are briefly described in Table 2, for both ground floor (GF) and first floor (1F).

As example, the appliances profiles assigned to the restaurant and office thermal zones follows (Figure 4), highlighting the different schemes of the time schedules adopted. While, the artificial lights profiles were defined by SIA2024 in a different way, with a constant value of electric consumption associated to a certain number of hours per day that has been adjusted on the occupancy profile of each thermal zone.

Figure 4.

Example of time schedule profiles (restaurant aboveand office below) for appliances’ internal heat gains [43]

According to the Method section, the geometric 3D model of the two buildings has been implemented by using SketchUp^**. The model includes the 8 thermal zones and the surrounding shading context. Once imported into IESVE, the construction templates, the thermal loads templates and the occupancy time schedules of each thermal zone have been defined. Then, the climatic data have been assigned by selecting the climatic file of Milano_Linate_TMW^††. The output obtained quantifies the thermal energy needs for heating, cooling and DHW, and the electricity demands for appliances and artificial lights for each thermal zone and grouped for building 9 and building 10.

A preliminary evaluation on the availability of local renewable potential, and the possibility of implementation of it for the building energy supply, has been carried out.

In order to explore solar energy conversion, an assessment about PV potential has been carried out, because Building Integrated Photovoltaics (BIPV) on roofs are suggested also in case of renovation of historic buildings in de Santoli [35]. Solar simulations have been performed on a 3D model of the area using the tool DIVA for Rhino^‡‡ adopting the validated Radiance/Daysim engine, over geometrical objects in Rhinoceros^§§. The first step is a preliminary assessment of the surfaces, within the buildings in the model that better fit for a solar panels’ installation, adopting the total annual solar radiation as benchmark. The results indicate good availability of solar potential. The implementation of BIPV has been envisioned only on the south-western roof’s pitch of building 10 (1,130 kWh/m² per year of average total irradiation) since the actual roof has to be disposed anyway (asbestos).

Moreover, even if insufficient information was available for a predesign of the heating/cooling systems and plants, a hypothesis about the exploitation of the renewable local sources devoted to it was provided. The presence of a water treatment plant of Nosedo in the vicinity and of a sewer collector behind the area of Cascina Nosedo have been considered for the operation of HPs. The wastewater collected is characterized by interesting temperature profiles, between 10 and 20 °C around the year, giving the possibility to extract the heat from it through reversible HPs, connected to the wastewater collector by heat exchangers, and exploit it in the heating/cooling and DHW systems.

For what concerns the energy performance of the two buildings in terms of heating and cooling needs, the results of the simulations have been schematized as reported in Table 3, highlighting the comparison between the two envelope scenarios, according to the results obtained by the energy simulations.

As main results, the internal insulation implies a decrease of 18% of heating energy need (and a decrease of 9% in the hours of heating system activation) but an increase of 16% in related peak, affecting the size of the heating system. Cooling side, internal insulation implies an increase of 8% of energy need, maintaining the same pick and the same number of hours of system activation.

It is possible to note that, due to the destination of the buildings (non-residential) and to the assumed profile of use that is rather intermittent, there are not significant differences in terms of energy needs on yearly basis in the two scenarios (internal and external insulation).

For a better understanding of the energy behaviour of the buildings depending on the two envelopes configurations, the internal temperatures in free floating during the year have been plotted and compared to external and set point temperature. As example, Figure 5 and Figure 6 show the result for a winter week and a summer week, respectively, of an office thermal zone (TZ08, administrative office). Since external insulation implies a slower response to the temperature variation than the internal insulation, the representation underlines the light benefits of external insulation on temperature profiles.

Figure 5.

Temperatures profiles for internal and external insulation scenarios of thermal zone TZ08 (office) during a winter week

Figure 6.

Temperature profiles for internal and external insulation scenarios of thermal zone TZ08 (office) during a summer week

It is well known that buildings energy needs simulated in different studies, even in the similar field of investigation, are inevitably diverse. This is due to obvious reasons, such as different climatic conditions, buildings envelope dimensions, shapes and features, use categories, etc. Other less evident reasons can be referred to the adoption of different calculation methods or different simulation tools and different assumptions in defining the building energy simulation models. Concerning the latter, for instance, the outcomes of the tests for the comparison of different users of the standard [46] attested that diverse energy modellers may obtain results, differing by as much as 20% for the same building in the same climate, as reported in the standard itself.

Aware of these criticalities, based on the literature review reported in the Introduction section, a selection of Italian case studies has been considered for comparing at least the order of magnitude of the results obtained in the present case study. The selection of the case studies, summarized below mentioning the main envelope retrofit features, is based on the ones that reveal similar climatic conditions of Cascina Nosedo (i.e., related to locations falling within the range of Heating Degree Days [47] 2,100-3,000, which correspond to the national climatic classification “Zone E”) and for which data of estimated energy needs are available.

For the retrofit of the historical school building, having a load-bearing masonry made of full clay bricks, located in Milan and analysed in Ferrari and Romeo [3], a space heating need of 37 kWh/m² per year and a space cooling need of 28 kWh/m² per year were estimated after the assessed retrofit scenario (insulation of external walls from inside, of basement ceiling and ground floors, and installation of additional internal double-glazed windows). While, for the retrofit of a hotel building in Turin assessed in Buso et al. [25] (i.e., external insulation of vertical and horizontal opaque envelope and installation of new windows), a space heating need of 20 kWh/m² per year and a space cooling need of 38 kWh/m² per year were estimated. A set of retrofit solutions (i.e., the installation of double-glazing windows and the insulation of both vertical stones walls and horizontal floor of the unconditioned loft below the pitched roof) was assessed for an aged typical farmhouse located in Perugia, Central Italy, in Menconi et al. [27]. In this case, the optimal solution results in a space heating energy need of 56 kWh/m² per year, while no cooling system is foreseen.

In Becchio et al. [24], two refurbishment options (implying high and low investment costs, based on different thermal performances, original or new use category and conditioned volume) for a traditional rural building located in Livorno Ferraris (a small town in Northern Italy) were analysed. Both scenarios foresee the insulation of the external walls and roof, the realization of insulated and ventilated floor over the ground, and the replacement of windows with new ones having different performances based on different targets. Space heating and cooling needs around 35 kWh/m² per year and 8 kWh/m² per year, respectively, are reported for the low investment scenario, while around 20 kWh/m² per year and 8 kWh/m² per year for the high investment scenario.

Figure 7 shows the energy needs of the mentioned case of studies together with the ones evaluated for Cascina Nosedo. Results obtained for the two energy retrofit scenarios of this last are in the ranges obtained for the mentioned selected case of studies, i.e., 20 ÷ 37 kWh/m² for heating and 8 ÷ 28 kWh/m² for cooling, demonstrating the global consistency of method adopted and presented here.

Figure 7.

Selected case studies’ energy needs and the Cascina Nosedo ones

In order to explore the effects on comfort, among the several thermal zones simulated, a focus has been done on the one that revealed the larger thermal energy needs difference in relation to the two insulation scenarios: the so-calledTZ05 (Greenhouse Lab).

To that end, the operative temperature, able to combine the effect of air temperature and mean radiant temperature, was taken into account because it represents more accurately the performance of the building envelope in contributing to overall thermal comfort sensation. In fact, operative temperature is a fundamental parameter for defining indoor environmental conditions based on the human body heat balance according to Fanger [48]. The Fanger equation is used to determine (according to conventional seasonal clothing level and standard air humidity and velocity) reference operative temperature ranges related to the building use, which corresponds to defined activity levels. The operative temperature limits for the building uses connected to moderate activity level are a minimum 20 °C in winter and a maximum 26 °C in summer. Despite the influence of operative temperature on the real building energy need, it is commonly neglected in simplified building energy assessment, which considers only the air temperature. As a matter of fact, in case of unfavourable radiant temperatures, the air temperature set-point is usually corrected by the users in order to adjust the indoor condition to compensate the radiative component, and the consequent overuse of the active climatization systems causes an unpredicted increase of building energy consumption.

In order to explore this issue, a comparison of the operative temperatures, together with air temperatures, related to the two insulation scenarios for the selected thermal zone is reported in Figure 8 and Figure 9, for a winter and a summer week.

Figure 8.

Operative and air temperatures profiles for internal and external insulation scenarios of thermal zone TZ05 (Greenhouse Lab) during a summer week

Figure 9.

Operative and air temperatures profiles for internal and external insulation scenarios of thermal zone TZ05 (Greenhouse Lab) during a winter week

Looking at the two plotted charts, it can be noted that the operative temperatures are quite similar in the two cases (internal and external insulation), likely due to the same very low thermal transmittance of the walls, in line with the strictest indexes in force, that affect similar values of surfaces temperatures. Moreover, during the occupancy hours, driven by the air temperature set points, the operative temperatures of the two cases reach values similar to the imposed air temperature, having the maximum differences less than 1 °C, therefore, both the cases satisfy similar thermal comfort conditions.

Additionally, the adaptive comfort approach has also been taken into account. This approach considers the social and psychological aspects of thermal perception and assumes that the users’ thermal expectations are actually connected with the outside climatic conditions on a variable base [49]. More in detail, it considers the ability of human beings to adapt themselves to the environmental conditions through conscious or unconscious changes in their metabolic rate or clothing level, and to interact with the environment in order to adapt it to their needs through available environmental controls, such as openable windows, thermostats, fans switches, etc.

Hence, based on the adaptive formulation considered in Ferrari and Zanotto [50], the adaptive comfort range referred to “very good” indoor conditions (i.e., 90% of acceptability) has been calculated. The comfort band together with the temperatures simulated in free floating of the two cases are shown in Figure 10.

Figure 10.

Adaptive comfort band and free-floating annual temperatures profiles for internal (left) and external (right) insulation scenarios of thermal zone TZ05 (Greenhouse Lab)

Analysing the annual performance of the two cases simulated in free floating, the Discomfort Degree Hours (DDH), i.e., the number of hours in which indoor conditions are outside the comfort limits and in which heating or cooling loads are required, have been calculated according to Blázquez et al. [28] .

For the selected thermal zones, Table 4 reports the heating and cooling energy needs, assessed by simulating the conventional set points 20 ÷ 26 °C, and the adaptive DDH^***, underlining the same trend (during winter internal insulation is better, while during summer external insulation is better).

Tuning to BIPV, for the roof integration on the South-western pitch of building 10, the suitable area for the panels is 328 m² wide. This configuration has been simulated through the tool PVSyst^††† obtaining the annual yields of different PV technologies (mono-crystalline, poly-crystalline, thin film), reported in Table 5.

As already mentioned, the design of the plant configuration is under definition, because of the several obstacles encountered during the project development. Nevertheless, some considerations, based on the results discussed in this section, can be carried out. A good solution could be to satisfy the energy needs of the buildings with a reversible HP both for cooling, heating and DHW. It was assumed to integrate the sewer collector as the heat source in order to optimise the performance of the HP thank to the proper level of temperature. A preliminary estimation of the total electric demand needed by the HP to satisfy the buildings’ energy needs has been accomplished and compared to the yearly PV potential, as reported in Table 6. As Hepbasli et al. [51] suggest, the performance indexes of a Waste Water Heat Pump (WWHP) depend on the boundary and application conditions (inlet and outlet temperatures of the heat exchanger, system typology, etc.) and can vary in a wide range. In our case, without the needed details, a range of COP was adopted [51] in first analysis, and results are reported in Table 6.

As concerns the evaluation of the best envelope scenario for the case study retrofit, beyond the results obtained in terms of energy needs, the features of the envelope to be evaluated regard the dynamic building behaviour and architectural integration. For what concerns the architectural aspects, a sensitive topic dealing with the retrofit of a historical building, the external insulation involves a modification of the exterior aspect, while the case with insulation from inside results in a slightly reduced net internal space. Concerning the thermal inertia of the envelope, comparing the two different configurations, it was observed that the external insulation implies a slower response and adaptation to the temperature variation than the internal insulation. This is a consequence of the insulation strategy that includes, with external insulation, or excludes, with internal insulation, the brick layer in the computation of the effective thermal mass of the envelope.

In terms of total needs (heating and cooling), the simulations accomplished show negligible difference between the two alternatives, while, in terms of thermal power, the external insulation scenario provides a slightly lower peak. Concluding, given the previous considerations, it can be stated that, having an intermitting control system regime, serving many adjacent zones thermally independent and considering the constrains involved in protected building retrofit, the internal insulation scenario could be the optimal solution in terms of energy behaviour, architectural integration and feasibility in this particular case of study. As mentioned, since the buildings are currently mostly abandoned and composed by open and unheated spaces, the definition of a reference case towards comparison of the related energy performances and evaluation of the energy improvement is not possible, additionally, in this stage, monitoring data are not available.

Of course, the results obtained are strongly affected by the software calculation method and by the assumptions carried out on the thermal zones functions that could slightly change in the definitive version of the project.

Conversely, on the supply side, although there are no defined rules to prevent BIPV in protected buildings and rather the national guidelines for energy retrofit in historical buildings (i.e., [34], [35]) contemplate BIPV on the roofs, the official opinion of the Superintendence made us lose the benefit of PV generation. The opportunity of PV integration is even more significant if it is considered as supply system, in a preliminary hypothesis, an electrically-powered HP, through which all the energy demand is translated in electricity consumption. Fortunately, the possibility of adopting wastewater as heat source for the HP was not discarded. Nonetheless, the definition and the design of the system configuration is still in progress, because of the several obstacles encountered during the development of the project, such as economic, managerial and infrastructural issues.

After our elaborations, the renovation of Cascina Nosedo complex has been designed and the executive project foresees some differences in relation to heating and cooling systems, Renewable Energy Sources (RES) integration and buildings to be retrofitted. Therefore, further development of our work will regard the energy simulations once the executive project is completed and a monitoring activity once building 10 is completed and in operation.