Deep regeneration vs shallow renovation to achieve nearly Zero Energy in existing buildings

Accepted Manuscript Title: Deep regeneration vs shallow renovation to achieve nearly Zero Energy in existing buildings Authors: Giovanni Semprini, Riccardo Gulli, Annarita Ferrante PII: DOI: Reference:

S0378-7788(17)33120-1 http://dx.doi.org/10.1016/j.enbuild.2017.09.044 ENB 7963

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Received date: Revised date: Accepted date:

31-10-2016 6-8-2017 15-9-2017

Please cite this article as: Giovanni Semprini, Riccardo Gulli, Annarita Ferrante, Deep regeneration vs shallow renovation to achieve nearly Zero Energy in existing buildings, Energy and Buildingshttp://dx.doi.org/10.1016/j.enbuild.2017.09.044 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Deep regeneration vs shallow renovation to achieve nearly Zero Energy in existing buildings Energy saving and economic impact of design solutions in the housing stock of Bologna

Giovanni Semprinia, Riccardo Gullib, Annarita Ferranteb a

DIN, Department of Industrial Engineering, School of Engineering and Architecture, University of Bologna DA, Department of Architecture, School of Engineering and Architecture, University of Bologna

b

* Corresponding author. Tel.: +39 051 2093286; E-mail address: [email protected]

Abstract Whilst new nearly Zero Energy (nZE) concepts have been the first priority in the previous decade, in more recent years it has become widely acknowledged that renovating dwellings will have a large impact on the energy use in buildings. Using a simplified calculation method, this paper illustrates the high-energy consumption in several building types within the housing stock in Bologna. Among these, a specific building has been selected as the worst-case for an in-depth investigation. For this building the paper analyses a large set of possible scenarios for renovation -from the more standard operations up to higher levels of façade components’ transformation- as technically feasible solutions to achieve a nearly Zero Energy Building (nZEB). By discussing the economic/energy impact of each scenario, this paper aims at contributing to the debate on deep-versus-shallow renovation in existing buildings. In particular, it attempts at answering the following important research issues: whether the technical feasibility is associated to the economic feasibility in the retrofitting towards nZEBs; to what extent deep renovation and high transformation of buildings is competitive with respect to shallow retrofit; whether non-energy related factors can be considered to properly assess the economic competitiveness. Energy and economic benefits are the main renovation’s objectives in building renovation; nonetheless, non-energy related aspects are also helpful to expand the feasibility of nZEBs retrofit in the current building practises. Contents

DEEP REGENERATION VS SHALLOW RENOVATION TO ACHIEVE NEARLY ZERO ENERGY IN EXISTING BUILDINGS .................................................................................................... 1 Abstract ....................................................................................................................................................... 1 1. Introduction ............................................................................................................................................ 2 2. The existing building stock .................................................................................................................... 4 2.1 The existing building stock in the urban context of Bologna ......................................................... 4 3. Energy analysis of the representative buildings ................................................................................... 5 3.1 Building type .................................................................................................................................. 6 3.2 Opaque envelope ............................................................................................................................ 6 1

3.3 Windows ......................................................................................................................................... 7 4. Energy retrofitting procedure in the “Popolarissime” ........................................................................ 8 4.1 Energy behaviour in the as-built case ............................................................................................. 9 4.2 Thermal insulation of envelope structures ...................................................................................... 9 4.3 Volumetric addition: the greenhouse system ................................................................................ 10 4.4 The generation system: Heat pump system .................................................................................. 10 4.5 Photovoltaic system ...................................................................................................................... 11 5. Economic analysis of design solutions of social housing ”Popolarissime” ....................................... 12 6. Discussion and conclusions .................................................................................................................. 14 7. Further research ................................................................................................................................... 16 Acknowledgements ................................................................................................................................... 16 References ................................................................................................................................................. 18 Keywords: nZEBs – nearly Zero Energy Buildings; Deep renovation; Energy retrofitting; Urban Environment; Social Housing.

1. Introduction The first prototype solar building and the initial attempts to achieve zero-heating demand date back to 1950s [1]; therefore, in some ways, today we may state that the concept of energy conscious building belongs to the “history of architecture” [2]. Over the past three decades, energy oriented innovations in building technology have emerged in many areas of the building construction sector [3], till the latest experiences aiming at zero carbon emission of new urban areas, like the village BedZED, the Beddington Zero Emission Development [4] or even of a whole city [5]. Furthermore, simulation-based decision support tool [6], methodologies for economic efficient design [7] and cost-effective design solutions [8] have been developed to integrate energy design tools and economic efficiency into early design of nearly zero energy buildings (nZEBs). Efforts and discussion to achieve a common and standardized definition of nZEB can be found in [9], [10], [11], [12], and [13]. Whilst new nZEB concepts and experiments might have been the first priority in the previous decade (the majority of pilot models and constructions cited so far refers to newly conceived buildings and development plans), in more recent years it has become widely acknowledged that renovating dwellings is the most significant opportunity to reduce global energy consumption and green house emissions [2], [13], and [14]. This is especially factual in the EU, due to the following geo-political concurrent factors: the historically consolidated continent of the EU, where refurbishment represents the major need;  the most challenging economic crisis that EU is facing, with the construction and real estate sector representing the worst affected market area; 

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the current uncertainties on energy imports (since buildings account for 30% of total energy consumption in the EU, the consequent reduction of gas and oil in this sector could contribute to bring back the EU dependency on imports).

Thus, energy efficient (EE) refurbishment is often suggested as one of the potential solutions for the real estate/building construction crisis [15], as well as a potential leverage towards energy zero targets. The current challenge is to widen technical nZEB knowledge in existing built environments, shifting the methodological and technical achievements on energy-efficiency from newly conceived buildings towards the rehabilitation of existing building stock especially in fragile sectors like the social residential areas and housing [16] and [17]. Systematic approach to retrofit activities have been reported and discussed in [18] and [19], and specific set of tools for energy retrofit including economic cost-benefit models have been developed [20] [21]. Furthermore, studies, design proposals [22] and measurements [23] on building energy retrofitting have discussed and investigated to achieve energy saving tools and techniques towards nZEBs in existing buildings. Despite the recent attention received by this topic from researchers and building market actors and notwithstanding the stress on the goal of reaching nZEBs within 2020, the individual buildings still face a number of obstacles to the retrofit market uptake: i) the long pay-back times of retrofitting interventions (economical barrier); ii) the lack of access to available and affordable finance (financial barrier); iii) the insufficient incentives and the rigidity of current regulations neither allowing significant improvements in existing buildings nor giving priority to deep energy renovation (legislative barriers); iv) the delay of States and Regions in producing strategies for building energy renovation as foreseen by article 4 of the Directive 29/2012/EU (Member State-dependent legislative barrier). Although a large set of economic and financial studies and documents have been produced to overcome these barriers [24-25], in order to reach marketable zero-energy buildings within 2020 it is necessary to understand the technical and economic feasibility of possible design solutions integrating retrofit options and renewable energy systems. In this framework, an inter-sectoral debate is occurring among researchers and practitioners from the different disciplines of the building construction market on whether it is necessary that these buildings be renovated “deeply” or not. Definitions of deep renovation (or deep retrofit/deep refurbishment) are discussed by [26] and [27]. Deep renovation or deep energy renovation is a term for a renovation that captures the full economic energy efficiency potential of improvement works, with a main focus on the building envelope of existing buildings that leads to a very high-energy performance. Some threshold values for Deep Renovation in residential buildings are outlined in [26] and [27] and discussed in [2]; according to these references the energy reduction of the renovated buildings should be at least between the 65% and the 75% compared to the status of the same buildings before the renovation. Against such a backdrop, this work aims at contributing to the current debate on deep-versusshallow renovation in existing buildings, showing potential achievement of deep renovation not discussed so far. First of all, using simplified calculation tools in the context of several buildings of the housing stock in Bologna, this research study defines and assesses a set of main key indicators to describe and compare the energy performance in 10 different construction and building’s types and to help the selection and the prior options and actions to be undertaken in the process of energy retrofitting. Secondly, simplified calculations have been validated with the actual energy consumption trough a bill survey conducted in a specific yet representative case study: the social housing buildings “Popolarissime”. As detailed in part 4., Popolarissime has been selected because they represent the worstcase building in terms of thermal and geometrical properties; furthermore this building type is very frequent in the urban context of the peripheral areas in the European cities. 3

Here, different options have been considered and compared demonstrating that a large set of possible solutions is technically feasible to achieve nZEBs, even in highly energy consuming buildings. These solutions vary from the more standard operations -like insulation of opaque elements, windows’ replacement and plant system renewal- up to higher levels of façade components’ transformation, like volumetric additions. By discussing and comparing the economic and energy impact of different design options, this paper aims at addressing the following important research questions: - Is the technical feasibility associated to the economic feasibility in the retrofitting of existing buildings towards nZEBs? - To what extent deep renovation and high transformation of buildings towards nZEBs is competitive with respect to shallow or conventional retrofit? Which type of non-energy related factors could be considered to properly assess this competitiveness?

2. The existing building stock As a matter of fact, the existing building stock in EU consists in a large percentage (about the 60%) of buildings built after the Second World War (‘60s and ‘80s) [29]. This percentage even increases (up to 70-75%) if we confine the analysis within the boundaries of the Southern Mediterranean European countries (Greece, Cyprus, Spain, Portugal, etc.) and slightly increases for Italy, as well (about 65%) (Fig. 1). Since the majority of those buildings have been built long before the energy saving measures introduced in the ‘90s and mostly by EU Directives of the last decade, as a result the existing building stock across EU present very low energy performances. 2.1 The existing building stock in the urban context of Bologna

Following a similar trend, in the Emilia Romagna Region over two-thirds of the residential buildings have been built before ‘80s, while in the city of Bologna the percentage rise up 90% due to high presence of historical buildings and urban post-war expansions (Fig. 2). The first important regulation on the energy saving in Italy, dated 1977, imposed limits to the heat losses of the building envelope and to the thermal power of boilers, subsequently replaced by the Law n.10 of 1991 (with specific requirements for the construction of energy efficient buildings) and by new regulations, after the national transpose of European EPBD Directive, in 2005. As a consequence, the higher percentage of these buildings presents an energy consumption for heating and domestic hot water (DHW) production greater than 200 kWh/m2year, while from ’80s new buildings have progressively reduced the energy consumption up to 50 kWh/m2year of the last decade [30]. Correspondingly, the analysis performed for the Energy Plan of the Municipality of Bologna [31] has showed wide potential margins of efficiency in energy use in buildings. To investigate the potential of available measures and technologies in EE retrofitting of existing buildings to achieve nZEBs it is necessary to explore their application into demonstrative design scenarios of real urban environments. Thus, for a specific climate, reference buildings have to be defined on the basis of a building stock analysis. Reliable identification, estimation and quantification of the building peculiar features (type, age, geometrical and thermal characteristics of building components, construction techniques and plant systems) by site surveys, energy modelling and/or bills’ reading are essential for: a - estimating the energy performance in existing buildings, b - evaluate the compatibility of possible retrofitting measures with respect to the architectural and constructive types, c - prioritise retrofit measures as a function of a) and b). 4

Thus, the research study has identified representative pilot cases on the basis of the existing building stock consisting of different building and construction types and located in different areas of the urban context of Bologna, from the historical centre, via the first periphery out to the city borders (Fig. 3). Within this extensive urban sector, 10 different buildings have been analysed as reference buildings and energy retrofit scenarios have been designed to evaluate the energy and economic impact [32] (Figg. 4: 4.1- 4.10).

The main construction types for buildings in the different sectors of the urban area of Bologna are schematized in the following fig 5.

These construction types are associated to different types of envelope, as illustrated in the following table 1. While in historical buildings the structure and the envelope are always coextensive (i.e., the type a) shown in Fig. 5 –brick wall as bearing structure- is associated either with 1 or with 2 –single or double layer of bricks- with no other variations), more recent buildings present multiple variants and different possibilities in the association between the internal structure and the external envelopes. Given the experimental nature of some of these structure-envelope systems with respect to the time of construction, some critical gaps consisting in cracks and breaks within the junctions between the structures and the external walls have been observed in some buildings (VRN, TPL, FIL).

3. Energy analysis of the representative buildings Different methods and approaches for the energy analysis in existing buildings can be used: energy assessment based on type and age of the building’s components and plant construction, on-site energy audit and surveys, energy modelling with stationary or dynamic methods, etc.. For the selected buildings a preliminary analysis of the thermal characteristics of building components and of the type and age of heating plant system was carried oud, followed by energy simulation, in order to make identification and assessment of main geometrical and physics key indicators to describe and compare the energy performance in different construction and building’s types. The energy use for space heating of each whole building has been calculated, according to the quasi-steadystate method based on a monthly heat balance, as described in the international standard ISO 13790 [33] considering “standard conditions” used for the asset rating evaluation. Commercial software certified by the Italian Thermo-Technic Committee (CTI) has been used for energy calculations. The following main standard conditions have been considered:  monthly mean values of temperature and solar radiation based on Italian standard UNI 10349 [34];  internal temperature set to 20°C for 24 h/day from 15 October to 15 April;  monthly mean value of the air change rate set to 0.3 h-1;  internal loads as a function of apartment floor area equal to (5,294*A – 0,01557*A2) as defined in Italian standard UNI TS 11300-1 [35];  gain utilization factor for heating calculated according to [35]. Results of main energy performance parameters correlated to geometrical data of the buildings are shown in Table 2., where different energy parameters are correlated to geometrical data of the buildings. This co-relation allows the analysis of the thermal behaviour as a function of the different building construction types. The investigation is essential to the prior identification of the key choices to be selected and adopted for the energy retrofit operations. 5

Values of the primary energy for heating demand EPH are strictly depending on the type of the heating plant system: for the case studies they vary from independent heating boiler for single apartment, to centralised boiler for a whole building, to district heating system. For each case, different values of the global seasonal performance of the heating plant was evaluated using a tabular method where specific efficiencies are defined for each plant subsystems (emission, distribution, control, production), as proposed by the Italian standard UNI 11300-2 [36]: the calculated values vary from 90% (for recent single heating boiler) to 68% (for the district heating system), giving a wide range of EPH values, varying from a minimum of 150 kWh/m2 year to up to 250 kWh/m2 year. Considering only the energy use for space heating, the energy performance index in the heating season for the building envelope EPH,env, presents high values, approximately varying from 100 to 200 kWh/m2year, where major differences are due to the different geometrical shapes of the buildings’ volumes, the construction systems and materials used. The following remarks are related mainly to the buildings’ construction and layout type: i) the building type (S/V), ii) the opaque envelope (UP), and (iii) the windows components (DW). 3.1 Building type

As far as it concerns the volumetric and geometrical characters of the buildings’ type within the reference building stock, the surface/volume ratio (S/V) varies between 0,35 and 0,64, which means rather dense and compact building types, with the exception of the historic building of Via Santa Caterina (STC) and Barca (BAR). In STC building, the surface/volume ratio reaches the value of 0,75, due to the articulated volume of the house, varying from one to three floors above ground, while the BAR, a long and low building, with porticoes towards the ground and consequent large dissipating surfaces, the surface/volume ratio reaches the higher value of 1.05. The specific heat loss coefficient Cd present high values, from 0,76 up to 1,16, with a very poor correlation to S/V ratio due to different structures and materials used, while the energy performance EPH,env also present large spread of values due to different orientation and windows surfaces (fig. 6).

3.2 Opaque envelope

Typical construction systems of years ‘50 to’70 are reflected in a decisive way on the low thermal performance of the building envelope and, in particular, on the values of the thermal transmittance of the external structures. Also thermal bridges are widely present: joints between external walls and floors, on the external horizontal surfaces (roofs, coverings and floors against the ground), pillars and balconies, joints between opaque and transparent elements. Historical buildings constructed or re-constructed before 1800, although renovated after the second world war, consist in bearing walls without insulation (MIR, STC) and present average thermal transmittance values from 1,5 to 1.8 (W/m2K), and the rate of thermal bridges losses is less than 15÷18% compared to the total dispersion for transmission through the opaque elements. This physical and construction factor, together with the very low compatibility to facades’ modification due to historical preservation, entails the selection of alternative retrofitting choices instead of the external insulation (coatings): windows’ replacements with higher thermal performing glazing and light internal insulation may be the prior interventions in the energy retrofitting process in this type of buildings. Framed buildings with concrete load-bearing structure and single hollow brick wall (PPB) have average thermal transmittance values around 1,37 W/m2K, while solutions with double hollow brick layer and air gap (PBO) present lower values (0,8 ÷ 0.9 W/m2K). Conversely, in these last mentioned building types, the presence of concrete pillars and beams leads to a higher incidence of thermal bridges with 6

values of 23÷24% compared to the total transmission loss; this is a significant amount, considering that those buildings do not present overhangs, balconies, etc. whose presence would have further increased this percentage. Finally, the “Tunnel” construction types, with reinforced concrete baffles perpendicular to front facade (VRN, TCV) present external concrete panels slightly isolated with high thermal transmittance (1,0÷1,3 W/m2K). Also in this case, the incidence of thermal bridges on total transmission loss exceeds 20%. Analysis of different heat losses parameters allows a first assessment of the thermal insulation of each building. The high values of Cd (generally greater than 0,9) are mainly due to high thermal transmittances of building components that are 3÷5 times higher than the actual limits set by recent legislation (according to EPBD standard) for new buildings. The heat losses of opaque lateral envelopes generally represent 40-50% of the total heat losses, while roofs and porticoes floors represent about the 20%. 3.3 Windows

Type and construction system of each building greatly influences the amount of glazed surfaces. Analysing the ratio between transparent and total dissipating surfaces SW/St, relatively low values in the historic building type can be deduced (SW/St less than 10%), compared to building block type and to the buildings built with the "tunnel" single cast structure. In this last case (PBO and VRN) the existing large windows cause respectively 55% and 58% of the total thermal losses in winter period. Heat losses are strictly related to the ratio between windowed and opaque surfaces. In general, we can note that the increase of the SW/St ratio produces a correspondently increase of the heat losses (fig. 7), except for building FIL, due high thermal performance of windows and to presence of solar greenhouses. Heat losses from windows have a big influence on total heat dissipation of buildings (in general more than 30%) and in some cases they reach values up to 50%, like for “Popolarissime” (PBO), Virgolone (VRN) and the “Pilastro” Tower buildings (TPL). In particular, for the VRN building, large window areas are present and in many cases even with single glass, representing the "weak" point for these types of buildings. Also buildings TPL and PBO present high windows winter losses due to the high values of thermal transmittance of the current window glazing and frames. For those buildings, interventions aimed at the replacement of windows with higher thermal performance can lead to significant improvements of the winter energy performance; thus, in the hypothetical scenario of a “step by step” renovation, this option should be prioritized amongst others in the energy retrofitting process. A different consideration can be made for the building TCV, where the typical geometrical shape creates a low SW/St ratio, with higher thermal losses through the opaque surfaces than windows. Furthermore, solar heat gains from glazing surfaces are taken into account. Considering the specific heat solar gains related to internal floor surface, results for different buildings show a wide spread of values depending not only on size of window surfaces, but also on other factors like orientation, shading devices and volumetric obstructions (Fig. 7).

Table 3 summarizes previous considerations and displays how the correlation between construction type and associated envelopes (alongside with historical or legislative constraints and the analysis of the thermal behaviour as a function of the different building construction types) can be very useful to the prior identification of the options to be selected and adopted in the energy retrofitting operations. In this context, the main possible options for energy retrofitting of the building’s envelope are: 7

A) Opaque envelope’s insulation including horizontal external floors and coverings; B) Opaque envelope’s substitution (re-moving of existing and mounting of new envelopes); C) Windows’ replacement. These solutions may have some limitations. Historical and legislative constraints reduce the possibility of a standard insulation of the opaque envelopes (A). In such cases, the only options left are windows’ replacement (C) (MIR, STC, T2M). Other non-energy related factors, like the presence of structural gaps in the joints between structure and envelopes encountered in particular kind of prefabricated building constructions (FIL, VRN, TPL) might disrupt the effectiveness of opaque envelope’s insulation (A); in these cases, the substitution of the envelope (B) represents a preferable option.

4. Energy retrofitting procedure in the “Popolarissime” Among the 10 different buildings (Fig. 4 and table 3), the two buildings “Popolarissime” have been selected for an in-depth investigation to test and compare different energy retrofit options, considering the consequent impact of each solution. The selection of the buildings has been made according the following criteria: (i) Suitability to transformation by means of both standard and deep renovation methods; (ii) Presence of the building type and consequent impact in the specific and wider context of the EU cities; (iii) Worst-case building in terms of thermal and geometrical properties. In fact (i), as shown in table 3, in Popolarissime, standard insulation (A) and substitution (B) are both possible options, as well as windows’ replacement C). Secondly (ii), as block stand-alone buildings, they represent the most frequent building type in the selected case of Bologna and in the periphery of the majority of the EU and western-world cities as well. Finally (iii), Popolarissime represent the worst case in terms of thermal properties of the building envelopes. The buildings have an high surface/volume ratio (S/V=0,64 m2/m3), because of the specific geometry: a very limited width (7 m), long façades (42 m) and the height of the building up to 7 floors. This aspect determines the most unfavourable conditions in terms of thermal performance of the building. Thus, the adaptability to be transformed, the reiterated presence of this building type, together with the thermal/geometrical properties has driven to the selection of these buildings as the most representative amongst others. Between the two identical buildings Popolarissime, the southern one has been selected for further investigation (Fig. 8). A detailed survey has been conducted on the household building (dated 1937) to determine the construction methods, the used materials and the typology and main characteristics of the plant system. The energy model of the building (monthly method as described in par. 3) was validated comparing the outputs with measured consumption bills in winter season; furthermore, the energy performances of the building-plant system have been evaluated for different scenarios. The external envelope of the building consists of hollow brick walls (Up=1,37 W/m2K) and single/double glass windows with a metal frame (average value of Uw= 4,5 W/m2K). Floors of building roof and underground cellars have been recently insulated (average value of Uf= 0,6 W/m2K). The existing centralized heating system consists of two new condensing gas boilers with a vertical water pipe distribution (partially insulated) and radiators (located in each room on the external 8

walls) with thermostatic valves and climatic control system for the thermal power plant. According to [36], the following mean subsystem plant performances are considered:  radiator emission efficiency: 93%  distribution efficiency: 95%  control system efficiency: 95%  gas boiler efficiency: 95% Under these assumptions, the resulting global mean seasonal efficiency of thermal plant system is 80%. The rehabilitation procedure research has set this reference building against alternative design scenarios, starting from the more standard retrofitting options (the provision of thermal insulation and the replacement of the glazed components) up to the introduction of volumetric additions in the façade creating buffer zones between the inside and the outside of the building, designed to reduce the energy losses through the building envelope and improve overall energy performance. Different levels of plants’ upgrading are considered, from a centralized system with heat pumps to photovoltaic energy production.

4.1 Energy behaviour in the as-built case

The heating demand of the building has been evaluated by collecting the data of the gas consumption during three winter seasons (2011/12÷2013/14): table 4 illustrates the heating primary energy demands calculated from the annual gas volume consumptions and the mean lower calorific value (LCV). Gas consumptions during the three years (and consequently the primary energy for heating demands) are proportional to the external climatic conditions, as illustrated in table 4 by the substantial equivalence of the specific gas consumptions normalized to Heating Degree Days (HDD) for the three winter periods (117-114 m3/°C). This result is the logical consequence of the introduction of thermostatic valves (occurred in 2011). Considering an average seasonal performance of the heating plant of 80%, the primary energy demand for continuous heating in standard conditions (HDD = 2259 °C) is calculated as 260296 kWh according to [33, 34]: this value is very close to the actual consumption of winter season 2011-12 with similar HDD (table 4). Thus, the primary energy demand for heating in standard conditions, in the current situation, gives an EPH index equal to 188 kWh/m2year. Domestic hot water (DHW) is independently produced in each apartment and it is not monitored. Standard consumption for DHW production is calculated according to national directive [36] which provides normalized consumption values depending on apartment dimensions: a mean value of EPDHW = 18 kWh/m2year is considered, giving a total value of EPTOT = 206,39 kWh/m2year: thus, Popolarissime is undoubtedly a very energy-intensive consuming building. 4.2 Thermal insulation of envelope structures

As the energy performance of a building is mainly related to the building envelope’s type and elements, these components represent the most significant parts to be analysed, re-designed and transformed through energy efficient (EE) solutions in the retrofitting process. Different solutions have been suggested to increase the insulation and thermal performance of envelope components. The first retrofitting scenario consists of thermal insulation of opaque walls, roofs and porticoes by using 10 cm thick layer of EPS placed on the outer surfaces (Fig. 9); this solution reduce thermal bridges, avoids the risk of interstitial water vapour condensation and increase the energy performance of the building bringing the EP H index down to = 64,31 kWh/m2year (EPTOT = 82,31 kWh/m2year); with the only replacement of window components (low emitting double glass and PVC frame), the energy performances are reduced to EPH = 151,26 kWh/m2year (EPTOT = 169,26 9

kWh/m2year). Combining the two above-mentioned options, EPTOT =50,47 kWh/m2year. This solution would allow a saving equal to 82,6% than the current energy consumption of the building.

4.3 Volumetric addition: the greenhouse system

A higher transformation of the building’s shell has been hypothesized and a buffer zone consisting of a sunspace between the building and the outdoor environment has been designed. The main role of this solution is to provide an effective zone to reduce thermal losses in the cold winter season. Nonetheless, many significant advantages can be identified within this solution: i) Increasing of the internal volume and creation of additional spaces; ii) New architectural façade with higher level of maintainability, iii) Higher commercial value, iv) Solar gains for better performances and indoor comfort in winter and summer periods, v) Cross ventilation with the addition of a stack ventilation through vertical chimneys, vi) Possibility of inserting new pipe network for heating and DHW plant, centralised mechanical ventilation, vii) Flexibility in the internal rearrangement of the single apartments. Furthermore, the structural feasibility of this solution is given by an external grid supporting the additional spaces in order to avoid the risk of exceeding the load bearing of the existing building, which was not conceived for these additional volumes. In fact, the application of sunspace and additional volumes with respect to the existing building envelope is technically feasible thanks to the hypothesis of structural external grids appropriately fixed to the existing buildings (Figures 10, 11, 12). This structure, if specifically designed and properly anchored in the structural joints with the existing structure, could even provide the opportunity to improve the seismic performance of the building. The energy potential and overheating problems of sunspace structures connected to the building has been comprehensively investigated; in this specific context, these added spaces are considered open during the hot summer season (thus providing balconies and shading on the building envelope) and closed in winter period, when the spaces interposed between the filter and the outside may greatly reduce the transmission losses through the building envelope. If this solution is combined to the external thermal insulation, the building envelope can satisfy the values of transmittance required by actual standards and, simultaneously, the building as a whole may achieve the minimum criteria required for the building energy performance index. This additional building envelope is a powerful technological solution combining the improved energy performance of the buildings with a new aesthetic/formal quality. In fact, it could represent the possible resolution of critical aspects in the existing context, by providing more socially inclusive and attractive urban environments (Fig. 11).

4.4 The generation system: Heat pump system

A significant improvement in the energy performance of the building can be achieved through the substitution of gas boilers with a central heating heat pump system and the replacement of current old radiators with new elements working at lower temperature (or radiating systems in case of internal restructuration). The more efficient solution for the heating generation system is a geothermal heat pump system (GHP) powered by a photovoltaic plant (PV). 10

Energy calculations for this case study were carried out by the “bin method” [37] where the energy delivered and the energy performance of the heat pump was calculated considering the hourly distribution of thermal loads, also taking in account consumption of all auxiliary equipment. Results are reported in Fig.13. In order to optimise the energy performance of the GHP, an integration system with a simple electric resistance is planned due to a large production from PV system. Alternatively, a gas boiler may be provided, with higher values of primary energy; however the choice should be assessed as a function of PV system’s size. The total energy delivered from the heat pump is 29500 kWh, while those delivered from the integrating system is 4700 kWh. The calculated electric energy demand for the heating HP system and auxiliary system is still about 5700 (4400+1300) kWhe/year.

4.5 Photovoltaic system

The criterion to define the amount of photovoltaic (PV) panels is strongly dependent to national energy policies and feed-in tariffs. In the current context the best financial criterion for PV sizing is related to direct use of the building for electric and thermal needs. Because of the favourable solar orientation of the reference building, the integration with technologies for the energy production from renewable sources have been further explored, thus extending the possibility of transformation to the plant systems. Coloured photovoltaic panels in red and grey, made up by monocrystalline silicon and semi-transparent panels in single-crystal silicon (with level transparency 10-15% as they are used a partial replacement of the window glass components) are supposed to be used in the south-oriented façade. Figure 14 shows the energy production from PV modules located in different position of building: existing pitched roof, added canopy on the last floor of the façade addition (shed in Figures 13 and 14), façade. For the case of insulated building with heat pump system, only roof and shed PV mono-crystalline modules (P= 195 W/m2) are needed for heating needs, corresponding to about 105 m2 of PV surface installed. In the financial analysis a larger installation of PV system has been hypothesised, involving also the existing façades corresponding to 370 m2 of coloured amorphous modules (P= 122÷143 W/m2). This global solution (Fig. 15) may provide a total PV production of about 65.000 kWhe/year, thus producing a surplus of energy to be used in the urban context or to be sold back to the Energy Management Service. In figure 14 the electric energy needs for the GHP system are compared to PV production from roof. The high-efficiency mono-crystalline photovoltaic panels on the roof address both the energy required by the heat pump and the energy demand for residential users for domestic purposes, thus bringing the building to zero energy balance. Considering a conversion factor of 0,4 to transform thermal to electric energy, the options 3 and 6 would have had the following electric energy demand in standard conditions: (1)

0,4 x 50 kWh/m2y x 1.380 m2 = 27.000 kWhe

Thus, as 1 kW peak (1 kWp) of PV produces a mean year value of 1300 kWhe , the total peak power required will be: (2)

11

27.000 kWhe / 1300 kWhe = 20,77 kWp

To produce 1 kWp net, 5 m2 of PV surface are needed, thus the total PV surface necessary for achieving nZEB could be only 103,85 m2.

Table 5 highlights (yellow) the possible solutions to set the building energy requirements within the current regulatory limits for heating and domestic hot water (primary energy demand lower than EPlim = 64,69 kWh/m2year). As showed, also the simple insulation of opaque envelope components and the substitution of existing windows (option 3) allow the building to reach the minimum performances. The highest transformations given by combining sunspaces and insulation present very high energy performance (green). Furthermore, the combination of GHP and PV systems would drastically reduce the energy performance index of the building (option 7 and 8). The energy price where evaluated by Eurostat [38] and by the Natural gas price statistics and the National Energy Authority [39] considering prudential values for natural gas prices referred to the period 20132014 for household consumers. It can be affirmed that there is a high level of technical feasibility to set to zero the energy balance of existing buildings by using solutions where energy saving can be reached by the search of an integrated design combining constructive passive tools with existing technologies, like heat pumps using RES,. Furthermore, from the obtained results it can be observed that: -

The preliminary analysis of geometrical and constructive constraints of the different building types is essential to individuate the possible retrofitting options and the degree of transformability in the existing building stock. In fact, compared with the limited possibilities of energy adaptation in historic buildings, on the contrary, the energy and environmental adaptation of the dwellings from the Modernism to date, show higher levels of transformability: the technological and constructive characteristics of the buildings, alongside the critical issues and the potential values of the urban spaces they are located in, concur to the formulation of proposals for energy retrofitting not necessarily limited to the standard retrofitting, but more extensively intertwined with the overall buildings transformation, positively incising at the urban scale, as well.

-

The “standard retrofitting” option consisting in the insulation of opaque elements and windows replacement is the minimum scenario to reach the energy performance limit (EPH about 65 kWm2year) according to the current national legislation.

5. Economic analysis of design solutions of social housing ”Popolarissime” To identify the economical feasibility of the energy retrofit options, a cost-benefit analysis was conducted by means of market surveys and techno-economical estimation [26], determining, for each different design option, the evaluation in terms of energy performance improvement, the related cost estimations and the consequent cost-benefit analysis. To achieve a direct comparison of the different hypotheses presented so far, the table 6 is reported, where the various design assumptions are correlated with their relative costs consisting in the construction costs, the possible deductions, the savings costs derived from the building's primary energy reduction for heating and hot water production. 12

Construction and refurbishment costs vary throughout European countries, building types, geographical location and context. Specific costs were derived by applying the official regional list [40] in the Emilia Romagna. The maximum tax deduction in Table 6 refers to a year discount over 10 years. Considering the tax deduction as distributed in 10 years, the payback time values, for options 2 to 8, do not change, since for these types of intervention the payback time is far longer than 10 years. The only variation in this context could be the payback time related to the option 1: here its value changes from 8,5 to 8,89 when considering the year discount. As shown in Tab. 6, pay-back time (PBT) of standard retrofitting operations (option 3) with and without public incentives varies from 11 years to 26 years, respectively. The deep renovation by high transformation scenario (option 8) does not appear to be economically competitive with respect to the complete building retrofitting (option 7): the PBT of this solution, with and without public incentives, varies from 18 years to 40 years, respectively, while for the deep renovation including volumetric additions (option 8) varies from 41 years to 92 years. The above data shows that the high transformation (option 8) are in no way comparable, in terms of up-front costs, with the standard retrofitting solution (insulation and replacement of window components - option 3). Nonetheless, this more radical transformation hypothesis drastically reduces the energy performance indices of the buildings up to the target of a passive house, which can easily achieve the target of nZEB by using technologies fed up by renewable energy sources (RES) like photovoltaic panels. The different Energy Performance indices of the retrofitting options have been compared to the corresponding costs in Fig. 16 where results of table 5 and table 6 are combined: as expected, the lower is the energy required by the building, the higher is the building’s transformation, the higher are the up-front costs. The same methodology of this case-study has been applied in buildings with similar conditions in order to obtain more generally applicable results. All of the 10 reference buildings in Bologna have been investigated with similar simulations quantifying different variants in retrofitting actions [32]; results showed that it is always possible to reach an average Energy Performance index (EP) varying from 35 to 70 to kWh/m2year by the insulation of opaque surfaces (internal insulation in the case of protected buildings) and the replacement of existing windows. However, similarly to the case of the Popolarissime, the cost-benefit assessments of standard retrofitting have always showed excessive payback times, with very similar results with respect to the case illustrated in this paper. To verify the possibility to counterbalance the economic investments, a more detailed financial analysis has been performed, by a financial calculation consisting in the analysis of profitability of the investment by using the Net Present Value (NPV) index. This analysis includes the differential cash flows by which the NPV - as the index of the ability of the investment to provide some economic benefit- is calculated. To calculate this value, it is necessary to know the annual cash flow, both incoming and outgoing, and the rate of return costs. The annual cash flows are calculated as a difference between gains and costs (Euro): (3)

Fk = Rk + Ck

where: Fk is the annual cash flow; Rk are the annual gains and savings; Ck are the annual maintenance costs. 13

Thus, the NPV has been calculated by applying the following formula: NPV = ∑nk=1

(4)

Fk (1+i)k

where: n is the life cycle of the retrofitted components and plant (years); i is the rate of return.

The graphs drawn in Fig. 17 show that for none of the hypothesised interventions present a financial profitability within the lifetime considered (30 years). In particular, for the retrofitting options not including the installation of photovoltaic systems and replacement of heating and DHW plants, there will never be return of investment (descending curve in the option 3 and 6). Thus, the economic analysis of design solutions and the mutual comparison among data show that the shallow renovation consisting in the standard solution of thermal wall insulation and insulated glazed components is the one requiring lower initial costs but will never reach a return of investment in financial terms. Conversely, the solution providing plant retrofitting combined to the energy production requires a higher initial investment (ascending curve in option 7); thus, even if it is economically unfavourable in the short-term period, it will produce a partial capital return. This financial performance also depends on the Italian national feed-in tariffs. In particular, the option 7 (standard retrofitting including new plant and PV systems) is able to match the option 3 in 25 years. The full regeneration of the building, through the increase of building transformation’s levels by the introduction of the bioclimatic double skin (the greenhouse system) and the integration of photovoltaic panels (option 8) represents undoubtedly the most expensive solution, but it will produce a capital return in percentage higher than in option 7 (the curve in 8 is more ascending than in 7).

6. Discussion and conclusions This paper presented and discussed selected energy saving design solutions up to the nZEBs target in a selected residential building representative of the housing stock of Bologna. It demonstrates that deep energy renovation of existing building stock, especially if combined with the overall enhancement of the building involving also not-energy related aspects, is one of the major opportunities to decrease energy consumption while improving the quality of life for residents. In particular, with respect to the main research questions, the paper shows that: 

14

Considering the simple pay back time (PBT), the technical feasibility is weakly and inadequately associated to the economic feasibility in the retrofitting of existing buildings, being the design solutions’ life cycle comparable to the pay back time of design solutions (30 years). Albeit this is especially true considering the case of deep retrofitting scenarios, the costs of investment show high pay back times, even in the case of more standard retrofitting options (PBT varies from 11 to 25 years for the standard retrofitting scenario and from 40 to 90 years in the deep regeneration scenario, with or without incentives, respectively).



Notwithstanding very high PBT in deep regeneration and high transformation of buildings towards nZEBs, the NPV analysis has shown how potential margins of profitability are achievable by coupling the retrofitting scenarios with the RES systems. In fact, an economic and financial viability of the deep renovation scenario is achieved when it is coupled with the complete plant retrofitting associated with RES (geothermal heat pump, PV panels and solar panels). But, high initial costs undeniably represent high-factor risks under economic uncertainty. These very high initial costs and the potential trend of profitability lead future research works in searching for new strategies and applications to increase the economical competitiveness of deep renovation options in energy retrofitting towards nZEBs.



The reflection on economical quantifiable values, whether they are energetic, economic, or technical, remains to be intersected with other aspects, not quantified here. More holistic perspectives are needed to properly assess the competitiveness of deep energy regeneration with respect to shallow renovation. In particular, a set of non-energy related factors should be considered; they consist in the overall retrofit of the building addressing other physical, social and environmental characteristics, as listed in the following points.

i)

The possibility of achieve additional and new spaces with volumetric additions without exceeding the loading of the buildings and the possible contribution of external structures to the seismic retrofitting of the building; as a matter of fact, the larger majority of existing building stock in EU consists of buildings built well before standardization of regulatory requirements for structural reliability in seismic areas. In many urban areas, especially in the Mediterranean, it is becoming imperative to restructure and retrofit existing building to improve their seismic reliability and safety. As a result, in the retrofitting of the built environment the adoption of seismic provisions like energy dissipation through external structures and other safety protection devices could be more easily provided by using external structures (exoskeletons) and high transformation scenarios. The influence of the new external structure as a buffer zone protecting the building from atmospheric agents, thus contributing to the improved maintenance of the existing buildings’ envelopes and to a longer life-time of the building as a whole. The possibility of using the external addition for stack ventilation through vertical chimneys and new pipe network for heating and DHW plant, centralised mechanical ventilation and, generally, for plant systems’ retrofitting with lower impact on existing residential units and dwellers during retrofitting and construction works. This may imply a consequent enhanced social inclusiveness for dwellers (often low-income tenants/owners) not forced to abandon their dwellings and the flexibility in the internal restructuring of each apartment. In a market perspective, the Real Estate incremented value produced by the volumetric addition, alongside with new building envelope and the achievement of highly energy performing buildings are all-important parameters in estimating the commercial value of the buildings. In environmental terms, it is crucial to highlight the lower environmental impact of the retrofitting option with respect to the demolition and reconstruction. The extraction of raw materials for construction, production, processing of materials and their transport, as well as the demolition and removal of the buildings would require high energy and would consequently produce high carbon emissions. These factors will be assessed and combined with the economical analysis considering the retrofitting scenario by deep regeneration strategy versus the option of new building re-construction including demolition as these options cannot be assessed based only on the variable price of reconstruction and market value.

ii)

iii)

iv)

v)

15

In the search for answer the research issues related to the technical feasibility and economic feasibility in the retrofitting towards nZEBs, the paper highlights the importance of considering nonenergy related factors to properly and holistically assess the economic competitiveness of the energy and architectural retrofit. In fact, deep energy and architectural regeneration, by incorporating non-energy related benefits, might use them to increase motivations and willingness of main stakeholders (inhabitants, home-owners, public bodies, real estate agencies, ESCOs) in the energy retrofit market uptake. In other terms, it can be concluded that retrofit is a multi-objective optimisation problem and the energy and economical benefit are indeed the main objectives but cannot be the only criteria for the selection of retrofit and renovation options; non-energy related aspects could increase the feasibility of deep regeneration towards nZEBs in the building current practise.

7. Further research In the present work, which is essentially based on the economic evaluation based on a context specific case, many externalities having a major impact on aggregate gain or loss of the society as a whole have been disregarded in this paper. For these reasons, the authors are currently performing wider and in-depth studies in residential buildings located in other climatic areas and under different economic conditions, developing a sensitivity analysis of the results for different costs and contexts. While generic conclusions cannot be drawn from one single case study, this particular case presents a remarkable series of repeatable factors in the larger scale of the European and west-world urban contexts. Firstly, considering the case study’s significance, it should be considered that Modernism in architecture has conceived buildings to be universal; thus, similar buildings in the different contexts of the Western civilization and EU as well, were produced, starting from the ‘50s. As a consequence, the relative recent European building stock presents similar energy and non-energy problems and main common solutions can be identified, with a potential large impact. Amongst others, one common solution can be identified in the proposed external structure, representing a powerful tool incorporating other aspects of building performance improvement as safety and seismic reliability and market attractiveness. In fact, the volumetric addition here presented is a design answer with high level of technical feasibility, whose novelty relies in the original integration of the main requirements of a building (energy, safety, comfort, attractiveness, etc.) in a single technological solution. To successfully implement this kind of energy solution in the deep renovation of buildings, further research works are under development. They are mainly focussed on the following aspects: i) the evaluation and assessment of the seismic performance given by the external structures as designed; ii) the life cycle analysis and assessment of the environmental benefit due construction activities in the different design options; iii) the search for strategies and applications to increase the economical competitiveness of the volumetric additions, using them as a firmer leverage to reach marketable zero-energy buildings within 2020.

Acknowledgements The present paper contains data and images firstly elaborated during the Master Thesis for Degree in Construction Engineering and Architecture, 2009-10; 2010-11 by Stefano Romito and Chiara Margini. The data have been elaborated under the supervision of the authors and in collaboration with Eng. M. Monacelli. In both cases, the supervisor was A. Ferrante and co-supervisor G. Semprini. Recently, calculations have been assessed, revised and updated by the authors. The authors acknowledge Stefano Romito and Chiara Margini for their helpful production of materials and data. The authors also 16

acknowledge ACER Bologna for the kind help in achieving original data and drawings of the social housing stock.

17

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[23] M. Morelli, L. Rønby, S.E. Mikkelsen, M. G. Minzari, T. Kildemoes, H. M. Tommerup, Energy retrofitting of a typical old Danish multi-family building to a “nearly-zero” energy building based on experiences from a test apartment, Energy and Buildings 54 (2012) 395–406. [24] JWG: Towards assisting EU Member States on developing long term strategies for mobilising investment in building energy renovation (per EU Energy Efficiency Directive Article 4), Composite Document of the Joint Working Group of CA EED, CA EPBD and CA RES, November 2013 (http://www.ca-eed.eu/reports/art-4-guidance-document/eed-article-4-assistancedocument). [25] Delivering Article 4 of the Energy Efficiency Directive, BPIE, Published in February 2013 by Buildings Performance Institute Europe (BPIE). [26] Shnapp. S., Sitjà, R., Laustsen, J., 2013. What Is a Deep Renovation Definition? Global Buildings Performance Network, Technical Report, Feb. 2013, [email protected], www.gbpn. org, @GBPNetwork. [27] Bettgenhäuser, K., de Vos, R., Grözinger, J., Boermans, T., 2014. Deep renovation of buildings. An effective way to decrease Europe’s energy import dependency, Project number: BUIDE14901 © Ecofys 2014. [28] Assistant documents by the Joint Working Group of CA EED, CA EPBD and CA RES, 2013. [29] EU Report, Housing Statistics in the European Union (2010). [30] K. Fabbri, Building and fuel poverty, an index to measure fuel poverty: An Italian case study, Energy 89 (2015) 244–258. [31] Piano d’azione per l’energia sostenibile, Action plan for sustainable energy, http://www.comune.bologna.it/media/files/paes_12maggio2012_approvato_1.pdf, accessed March 2015. [32] A. Ferrante, A.A.A. Adeguamento, Adattabilità, Architettura, teorie e metodi per la riqualificazione architettonica, energetica ed ambientale del patrimonio edilizio esistente, Bruno Mondadori Editore, Milano, 2012, 9788861598560. [33] ISO 13790 (2008): Energy performance of buildings - Calculation of energy use for space heating and cooling, International Organization for Standardization, Switzerland [34] UNI 10349 (1994): Riscaldamento e raffrescamento degli edifici – Dati climatici, Ente Nazionale Italiano di Unificazione , Milano [35] UNI 11300-1 (2008): Prestazioni energetiche degli edifici – Parte 1: Determinazione del fabbisogno di energia termica dell’edificio per la climatizzazione estiva ed invernale, Ente Nazionale Italiano di Unificazione , Milano [36] UNI 11300-2 (2008): Prestazioni energetiche degli edifici – Parte 2: Determinazione del fabbisogno di energia primaria e dei rendimenti per la climatizzazione invernale e per la produzione di acqua calda sanitaria, Ente Nazionale Italiano di Unificazione, Milano [37] EN 15316-4-2 (2008): Heating systems and water based cooling systems in buildings - Method for calculation of system energy requirements and system efficiencies - Part 4-2: Space heating generation systems, heat pump systems, European Committee for Standardization, Brussels. [38] Eurostat. Natural gas price statistics, site: http://ec.europa.eu/eurostat/statisticsexplained/index.php/Natural_gas_price_statistics#Natural_gas_prices_for_household_consumers; december 2016. [39] Autorità per l’energia elettrica, il gas e il sistema idrico http://www.autorita.energia.it/it/dati/gp27new.htm, december 2016. [40] Elenco Regionale dei prezzi delle opera pubbliche –Regione Emilia-Romagna – Ed. 2012, January 2015.

19

FIGURE CAPTIONS Error! Reference source not found. Error! Reference source not found. Fig. 4. Location of the reference residential buildings in the urban context of Bologna

Error! Reference source not found. Fig. 5. Main constructive and structural types encountered in the selected buildings

Error! Reference source not found. Error! Reference source not found. Fig. 8. Location of the social houses “Popolari” (two block buildings on right side of the map N-NE and S-SE oriented) and “Popolarissime”, on the left side, S-SW. The reference building - on the far left side - is framed by the red rectangle. Fig. 1. Sketch of the building with external wall insulated with 10 cm of EPS (U=0.27 W/m 2K). On the right, diagram of water vapour pressure (blu line) is lower than saturation pressure (red line) calculate in January with internal conditions of T= 20°C and UR= 65%.

Error! Reference source not found. Error! Reference source not found. Error! Reference source not found. Error! Reference source not found. Error! Reference source not found. Error! Reference source not found. Error! Reference source not found. Fig. 17. The financial analysis of profitability using the method of differential cash flows to calculate the Net Present Value (NPV) and evaluate the investment profitability (Options 3, 6, 7, 8)

20

35%

300

30%

250

25%

200

20% 150 15% 100

10%

EPTOT (kWh/m2)

Building rate (%)

Fig. 2. The age distribution of EU existing building stock shows that the larger majority of buildings (about the 60%) have been constructed after the Second World War (‘60s and ’80s). Source: EU Report, Housing Statistics in the European Union, 2010

50

5% 0%

0 < 1918

1919-45

1946-60

1961-70

Emilia Romagna

1971-80 Bologna

1981-90

1991-00

2001-05

2006-11

Energy Performance

Fig. 3. Percentage of residential buildings in Emilia Romagna and in the city of Bologna (source: ISTAT 2011) and global energy performances for Heating and DHW (source K. Fabbri [30]) as a function of the years of construction

21

Fig. 4. Location of the reference residential buildings in the urban context of Bologna

1_MIR_ Mirasole, Historical centre (HC)

22

2_STC_ Santa Caterina, (HC)

3_PPB_ Popolarissime, Via Vezza, 1934-1935

4_PBO_ Popolari, Via Vezza, 1935-1937

7_FIL_ Blocks in Filanda, 1968-1974

5_T2M_Towers, 2 Madonne, 1955-1958

8_TCV_ Towers,

9_VRN_ “Virgolone”, Pilastro,

Cavedone, 1974-77

1975-1986

6_BAR_ “Treno”, Barca, 1957-1962

10_TPL_ Towers, Pilastro, 1975-1986

Fig. 5. 4.1-10.Ten selected reference buildings

a) Brick walls

b) Reinforced concrete pillar-beams frame structure

c) Coffrage tunnel = Formwork

Fig. 6. Main constructive and structural types for the selected buildings

23

d) Precast reinforced concrete slabs

e) Reinforced concrete structure for stairs – elevators

Fig. 7. Comparison of specific heat losses Cd and energy performance EPH,env with respect to S/V ratio

Fig. 8. Comparison of window heat losses (DW) and specific solar heat gains (QG/Su) to Sw/St ratio

Fig. 9. Location of the social houses “Popolari” (two block buildings on right side of the map N-NE and S-SE oriented) and “Popolarissime”, on the left side, S-SW. The reference building - on the far left side - is framed by the red rectangle.

24

Fig. 10. Sketch of the building with external wall insulated with 10 cm of EPS (U=0.27 W/m2K). On the right, diagram of water vapour pressure (blu line) is lower than saturation pressure (red line) calculate in January with internal conditions of T= 20°C and UR= 65%.

Fig. 10. From left to right: the structural grid of the existing buildings; the addition of external grids; the top connection; finally, the building-grid integration

Fig. 11. The buildings Popolarissime as built (on the left) and in the deep-regeneration scenario including volumetric additions

25

Fig. 12. Technical feasibility assessment via the detailed study of the structural connections between the new extension and the existing building

Fig. 13. Building thermal energy need and supplied by heat pump and the integrated system

26

Fig. 14. Energy produced from different PV modules

Fig. 15. Electric energy need for HP system compared to PV production from roof

27

Fig. 16. Different Energy performance indexes in the various options and relative costs. The dashed line represents the EP limit value

Fig. 17. The financial analysis of profitability using the method of differential cash flows to calculate the Net Present Value (NPV) and evaluate the investment Profitability (Options 3, 6, 7, 8)

28

Table 1. Main envelope type and thermal transmittance in the selected buildings Table 2. Main geometrical features and correlated energy performance parameters of the building envelope Error! Reference source not found.

Table 4. Gas consumption and Primary Energy demand of the building. Lower Calorific Values (LCV) are evaluated from declared Gross Calorific Values of the local Energy Supply and distribution Company. The last column reports the Gas consumption normalised to Heating Degree Days. Table 5. A comparison among the different energy retrofitting actions in the reference building and the corresponding energy saving Table 6. Investment costs (simple pay back time) for the different energy retrofitting options in the reference building Popolarissime

29

Table 1. Main envelope type and thermal transmittance in the selected buildings 1) Single layer of brick (15 cm)

2) Double layer of brick (30 cm)

3) Single layer of hollow brick

U= 1,80

U= 1,55

U= 1,37

4) Double layer of hollow brick with air gap U= 0,76

5) Precast reinforced coatings (20 cm) with light insulation U= 0,98-1,15

Table 2. Main geometrical features and correlated energy performance parameters of the building envelope

Buildings

SU m2

S m2

V m3

SW/St m2/m2

2.787

S/V m2/ m3 0,35

Cd W/ m3K 0,76

QH,nd kWh

0,07

UP W/ m2K 1,80

QG kWh

DO %

DF %

Dw %

DTB %

34.681

EPH,env kWh/ m2 123,9

1_MIR

769

983

2_STC

720

2.013

2.710

0,74

0,04

1,55

0,91

14.220

52%

20%

28%

12%

80.310

111,5

29.510

45%

26%

29%

3_PPB

1.380

2.542

3.956

0,64

0,18

1,37

18%

0,97

208.237

150,8

82.295

42%

14%

44%

4_PBO

2.179

3.280

7.841

0,42

0,18

24%

0,76

1,01

302.275

138,7

116.300

33%

12%

55%

5_T2M

826

1.239

3.221

0,38

23%

0,15

1,30

1,49

166.415

201,5

66.566

41%

19%

40%

6_BAR

10.496

33.152

31.616

23%

1,05

0,10

1,15

0,98

2.080.768

198,2

832.307

39%

21%

40%

7_FIL

7.200

10.344

22%

21.600

0,48

0,25

1,15

1,16

1.152.600

143,5

413.040

51%

17%

32%

8_TCV

5.350

24%

7.834

19.115

0,41

0,07

1,36

0,80

561.450

104,9

185.000

48%

13%

39%

9_VRN

25%

15.400

28.767

57.807

0,50

0,37

0,98

1,01

2.379.741

154,5

1.045.680

25%

17%

58%

10_TPL

17%

8.347

12.888

32.544

0,39

0,11

1,15

0,88

1.168.994

140,1

467.597

33%

17%

50%

18%

Where: SU = S= V= S/V = UP = SW/St = Cd = D= T = QH,nd = EPH,env = QG = DO = DF = DW= DTB =

Net internal surface of the whole building block (m2) Total dissipating surface of the building envelope (m2) Gross heated volume (m3) Ratio of dissipating surface to heated volume (m2/m3) Average thermal transmittance of the external opaque envelope including thermal bridges (W/m2K) Ratio of the windowed surface to the total dissipating surface Specific heat loss coefficient = D/(V*T) (W/m3K) Total heat loss calculated with a reference T = 25 K for Bologna difference of internal and external temperature (K) Building energy need for continuous heating (kWh) Energy performance index in the heating season for the building envelope (kWh/m2 year) Solar heat gains in the winter season (kWh) Ratio of opaque envelope heat loss to total heat loss including thermal bridges (%) Ratio of floor heat loss to total heat loss (%) Ratio of window heat loss to total heat loss (%) Ratio of thermal bridge heat loss to total opaque heat loss (%)

Table 3. Correlations between buildings’ type and prior identification of the energy retrofitting options. The buildings selected for in-depth energy investigation are highlighted with a dotted (red) line

Buildings’ Data inputs Buildings

1_MIR

30

Construction type (letter - Fig.5) and associated envelope (number - table 1) a1-a2

Options for energy retrofit on the buildings’ envelope Presence of age/Historical Constraints

Opaque envelope’s insulation (A)

yes

YES (Limited to internal insulation and

Opaque envelope’s substitution (B)

Windows’ replacement (C)

(only admitted

2_STC

a1-a2

yes

3_PPB

b3

-

4_PBO

b4

-

5_T2M

b4

partial

6_BAR

b4

-

7_FIL

d5

-

8_TCV

d5

-

9_VRN

c5

-

10_TPL

c5-d5

-

minor facades)

option)

YES (Limited to internal insulation and minor facades) YES (External coatings to eliminate high thermal bridges) YES (External coatings to eliminate high thermal bridges) YES (Partial external coatings to eliminate high thermal bridges) YES

(only admitted option) YES

possible

YES (only admitted option)

YES (limited for gaps between structure and envelope) YES

YES

YES (limited for gaps between structure and envelope) YES (limited for gaps between structure and envelope)

YES

possible

YES

possible

YES

Table 4. Gas consumption and Primary Energy demand of the building. Lower Calorific Values (LCV) are evaluated from declared Gross Calorific Values of the local Energy Supply and distribution Company. The last column reports the Gas consumption normalised to Heating Degree Days.

Gas Consumption m

3

LCV Gas MJ/Sm

3

Primary Energy

HDD

GC/HDD

kWh

°C

m3/°C

2011/12

25633

35,29

261508

2232

117

2012/13

24920

34,95

251825

2311

109

2013/14

20320

34,86

204762

1797

114

260296

2259

model

115

Table 5. A comparison among the different energy retrofitting actions in the reference building and the corresponding energy saving Different scenarios 0 – As built 1 – External Insulation 2 – Insulated windows 3 – 1+2 4 – Sunspaces (4-12-4) 31

Qht

QH

QP

EPH

EPDHWEPTOT

EPlim

€/kWh €

Saving €/year

%

234.062,19 208.237,19

260.296,49 188,39

18,00 206,39 64,69

0,086

22.385,50 \

110.579,12 72.297,20

90.371,50

18,00 82,31

64,69

0,086

7.771,95

196.265,34 166.637,64

208.297,05 151,26

18,00 169,26

64,69

0,086

17.913,55 4.471,95 -20,0

74.970,01

36.270,68

45.338,34

32,47

18,00 50,47

64,69

0,086

3.899,10

18.486,40 -82,6

87.256,40

49.256,83

61.571,04

48,65

18,00 66,65

65,35

0,086

5.295,11

17.090,39 -76,3

64,31

\

14.613,55 -65,3

5 – Sunspaces (4-12-4-12-4)

81.574,70

40.452,64

50.565,80

39,98

18,00 57,98

65,35

0,086

4.348,66

18.036,84 -80,6

6 – 1+4 64.800,50 7 – 3 + PV + Plant retrofitting 74.970,01 8 – 6+PV + Plant retrofitting 64.800,50

33.110,17

41.387,72

32,75

18,00 50,75

65,35

0,086

3.559,34

18.826,15 -84,1

36.270,68

15.633,94

5,67

5,18

10,70

64,69

0,086

1.344,52

21.040,98 -94,0

33.110,17

13.866,86

4,67

5,72

10,39

65,35

0,086

1.192,55

21.192,95 -94,7

Table 6. Investment costs (simple pay back time) for the different energy retrofitting options in the reference building Popolarissime Retrofitting Option (1-8) 1 – Insulation (10 cm polystyrene)

Construction Costs €

Max tax deduction (55%) €

Costs with tax deductions €

Saving

PBT

PBT

€/year

(years)

(years)

254.006

139.703

114.303

14.614

8,89

17,38

2 – Windows replacement

187.495

103.122

84.373

4.472

18,87

41,93

3 – 1+2

441.500

242.825

198.675

18.486

10,75

23,88

4 – Sunspace (4-12-4)

1.039.268

571.597

467.671

17.090

27,37

60,81

5 – Sunspace (4-12-4-12-4) 1.105.732

608.153

497.579

18.037

27,59

61,30

6 – 1+4

1.274.704

701.087

573.617

18.826

30,47

67,71

7 – 3 + PV+ new Plant

842.719

463.495

379.224

21.041

18,02

40,05

8 – 6 + PV+ new Plant

1.955.552

1.075.554

879.998

21.193

41,52

92,27

32