Comparison among Detailed and Simpliﬁed Calculation Methods for Thermal and Energy Assessment of the Building Envelope and the Shadings of a New Wooden nZEB House

: This paper deals with research carried out by the University of Florence on the thermal and energy performances of a recently built nZEB in Mediterranean Italian area. Heterogeneous component and thermal bridges performances have been analysed and critically evaluated with different calculation methods, and the results in terms of energy consumptions for heating and cooling have been compared. Some solar shading devices have been evaluated to reduce the building energy need for cooling. Main results of the research are presented for the components and thermal bridges properties and for the energy balance of the building implemented with different solar shadings.


Introduction
The Energy Performance of Buildings Directive (EPBD) recast 2010 [1] introduces the concept and the definition of the "nearly zero-energy building" (nZEB). In the Directive, "nearly zero-energy building" means "a building that has a very high energy performance. The nearly zero or very low amount of energy required should be covered to a very significant extent by energy from renewable sources, including energy from renewable sources produced on-site or nearby" [1]. Since the Commission does not give minimum or maximum harmonized requirements, it will be up to the Member States to define what for them exactly constitutes a "very high energy performance" based on the cost optimal performance level. The cost optimal level could represent "the energy performance that leads to the lowest cost during the estimated economic lifecycle" (the latter determined by Member States). In the definition, local conditions can be obviously considered, but the uniform methodology should be used in all Member States.
EPBD recast requires that after 31 December 2018, public authorities that occupy and own a new building shall ensure that the building will be a nearly zero energy building, and, by 31 December 2020, all new buildings will be nearly zero energy buildings.
According to the EPBD recast, the Italian Decree of 26 June 2015 [2] defines the requirements of the nZEB, whether new or existing construction. In particular, the following parameters should be lower than the values calculated for the reference building (a virtual building geometrically equivalent to the design building, but offering the minimum current energy parameters and thermal characteristics): • the transmission heat transfer global coefficient averaged over envelope dispersing surface (H' T ); • the summer solar equivalent area of glazed elements per unit floor area (A sol,est /A sup utile ); • the specific energy need for space heating (EP H ) and cooling (EP C ); • the specific global primary energy need both total (EP gl,tot ) and non-renewable(EP gl,nren ); and • the efficiency of the heating (η H ), cooling (η C ), and domestic hot water systems (η W ).
Moreover, renewable sources should be present in compliance with the minimum standards set out in the Italian Legislative Decree 3 March 2011, n. 28 [3].
In cold climates, the windows properties, thermal insulation, window-to-wall ratio and shading devices are analysed in [4]. Passive techniques, energy efficient mechanical systems and renewable energy sources are strategic elements to obtain a nZEB [5][6][7][8]. The ZEBRA project [9] individuates the nZEB distribution in Europe. In Italy, there are 100 buildings constructed in accordance with nZEB concept (15 residential buildings and 85 non-residential buildings).
In Southern Europe, the energy performance of residential buildings is strongly penalized in summer [10] and the cooling demand is going to rise due to increasing comfort requirements; in fact, cooling systems are thus becoming standard systems for new or refurbished buildings, as well as heating systems. The Italian legislation introduced only in 2009 the necessity to calculate the summer performance index for buildings and compare it with the legal limits; furthermore, it must be noted that the common design strategies have not been completely adapted to these requirements. Since Southern Europe buildings have to perform effectively both in heating and in cooling mode, some strategies should be taken to match the nZEB requirements in this climatic area [11], such as: • the optimization of the building envelope for the whole year and not only for heating season to reduce the energy need as much as possible (insulation, increased use of daylight, thermal activation of the mass, night natural ventilation, shading devices, etc.); and • the increase of the heating and cooling technical systems energy efficiencies, by using the best available technology (heat recovery, increase the efficiency of air conditioning systems, etc.) and by enhancing the production of heat and electricity from on-site renewable sources (solar thermal, PV, heat pumps, district heating powered by renewable fuels, etc.).
The design of wooden high insulated buildings, currently widely used in Southern Europe to reach the nZEB target, can present some critical issues mainly due to the discontinuity of the thermal insulation layer, the correct envelope heterogeneous components thermal evaluation, the thermal bridge assessment, the summer overheating and the consequent high cooling needs due to the lack of proper solar shading strategies.
To assess the thermal and energy performances of a platform frame nZEB residential building in Central Italy, the University of Florence is carrying out a research dealing both with building envelope performances evaluation and a monitoring campaign. Within this framework this paper analyses heterogeneous components and thermal bridges performances by means of finite elements calculation code. To reduce the building energy need for cooling, the effectiveness of some solar shading devices is carefully evaluated not only with a steady state calculation code but also with dynamic software.
The results of this paper show that all these elements are of fundamental importance to achieve a better design and a correct construction of these kind of buildings when a nZEB target is aimed.

Materials and Methods
This paper deals with the study of a new nZEB detached house in central Italy and includes two main phases:

•
First phase: The main thermal characteristics of the building envelope are calculated and critically evaluated; and the building components (heterogeneous components and thermal bridges) and solar shading systems are analysed with both simplified (commonly used by energy performance certifiers) and detailed calculation methods (2D finite elements and dynamic codes. • Second phase: An energy simulation of the building is carried out with dedicated steady state software; building envelope energy requirements in the heating and cooling mode are assessed and critically analysed. This phase is articulated in three steps: − energy analysis of the nZEB building using the thermal performance of building components analysed with simplified methods (from first phase); − energy analysis of the nZEB building using the thermal performance of building components analysed with detailed calculation methods (from first phase); and − energy analysis of the nZEB building using the thermal performance of building components and the energy performance of solar shading systems analysed with detailed calculation methods (from first phase).
In the present paper, results related to the first and second phase are fully described and discussed.

Description of the Building
The analysed building is a detached house (one-story building) in Tuscany (Figures 1-3); it is built with a platform frame wooden technology combined with a reinforced concrete slab for the floors. The building technology is based on a wooden frame made of studs and joists suitably spaced (0.625 m), plugged by timber boards and filled with large layers of insulating materials. This technology is affected by materials heterogeneity and consequently presents many thermal bridges that are widespread all over the building envelope.
Climatic and building data are reported in Table 1. Table 1. Data refereed to the location and the building.

•
Second phase: An energy simulation of the building is carried out with dedicated steady state software; building envelope energy requirements in the heating and cooling mode are assessed and critically analysed. This phase is articulated in three steps: − energy analysis of the nZEB building using the thermal performance of building components analysed with simplified methods (from first phase); − energy analysis of the nZEB building using the thermal performance of building components analysed with detailed calculation methods (from first phase); and − energy analysis of the nZEB building using the thermal performance of building components and the energy performance of solar shading systems analysed with detailed calculation methods (from first phase).
In the present paper, results related to the first and second phase are fully described and discussed.

Description of the Building
The analysed building is a detached house (one-story building) in Tuscany (Figures 1-3); it is built with a platform frame wooden technology combined with a reinforced concrete slab for the floors. The building technology is based on a wooden frame made of studs and joists suitably spaced (0.625 m), plugged by timber boards and filled with large layers of insulating materials. This technology is affected by materials heterogeneity and consequently presents many thermal bridges that are widespread all over the building envelope.
Climatic and building data are reported in Table 1.    The garage and the cellar, with a reinforced concrete structure, are placed in the unheated basement.
The aim of this building is to reach the nZEB target as defined in Italian Decree of 26 June 2015 [2]. In the building, PV panels are integrated in the roof to produce about 5000 kWh per year. Two heat pumps are installed: the first for heating and cooling is placed outside, while the second for hot water production is placed in the basement. A mechanical ventilation system (VMC) creates a 24 h air flow in every room varying from 1 vol/h to 1.5 vol/h; nominal heat recovery efficiency of the VMC is 84%.     The garage and the cellar, with a reinforced concrete structure, are placed in the unheated basement.
The aim of this building is to reach the nZEB target as defined in Italian Decree of 26 June 2015 [2]. In the building, PV panels are integrated in the roof to produce about 5000 kWh per year. Two heat pumps are installed: the first for heating and cooling is placed outside, while the second for hot water production is placed in the basement. A mechanical ventilation system (VMC) creates a 24 h air flow in every room varying from 1 vol/h to 1.5 vol/h; nominal heat recovery efficiency of the VMC is 84%.   The garage and the cellar, with a reinforced concrete structure, are placed in the unheated basement. The aim of this building is to reach the nZEB target as defined in Italian Decree of 26 June 2015 [2]. In the building, PV panels are integrated in the roof to produce about 5000 kWh per year. Two heat pumps are installed: the first for heating and cooling is placed outside, while the second for hot water production is placed in the basement. A mechanical ventilation system (VMC) creates a 24 h air flow in every room varying from 1 vol/h to 1.5 vol/h; nominal heat recovery efficiency of the VMC is 84%.   The garage and the cellar, with a reinforced concrete structure, are placed in the unheated basement.
The aim of this building is to reach the nZEB target as defined in Italian Decree of 26 June 2015 [2]. In the building, PV panels are integrated in the roof to produce about 5000 kWh per year. Two heat pumps are installed: the first for heating and cooling is placed outside, while the second for hot water production is placed in the basement. A mechanical ventilation system (VMC) creates a 24 h air flow in every room varying from 1 vol/h to 1.5 vol/h; nominal heat recovery efficiency of the VMC is 84%.

Analysis of Building Components
The analysis of the thermal performances of the opaque building envelope comprehend the calculation of different indicators in accordance with the Italian standards: • thermal transmittance (U) in accordance to UNI EN ISO 6946:2008 [13];

Analysis of Building Components
The analysis of the thermal performances of the opaque building envelope comprehend the calculation of different indicators in accordance with the Italian standards: • thermal transmittance (U) in accordance to UNI EN ISO 6946:2008 [13];

Analysis of Building Components
The analysis of the thermal performances of the opaque building envelope comprehend the calculation of different indicators in accordance with the Italian standards:  [15]; and • vapour condensation risk assessment (internal surface temperature and interstitial condensation) in accordance to UNI EN ISO 13788:2013 [16].
Calculated values of thermal transmittance have been compared with the reference nZEB ones reported in the Italian Decree of 26 June 2015 [2] for the climatic zone E (Arezzo).
Moreover, to evaluate the inertial performances of the components the Y IE indicator has been assessed even if the local thermal irradiation is less than the reference value (I m,s = 290 W/m 2 ). Table 2 reports the description of the envelope with the layers of the components while the main results of thermal analysis are collected in Table 3.  Table 3. Thermal performances of the opaque envelope.

Vapour Condensation Risk U nZEB Reference Values [W/(m 2 K)]
External As a result of the thermal analysis carried out in accordance to UNI EN ISO 6946:2008, all the opaque components present very low transmittance values compared with the reference ones of the nZEB target and good inertial performances. No condensation risk has been highlighted.
Nevertheless, the platform frame technology requires a more detailed analysis for the heterogeneous components (walls and roof) that present a wooden structure with a 0.625 m distance between studs.
For this reason, all heterogeneous components have been assessed both with the calculation method reported in UNI EN ISO 6946:2008 and with a 2D numeric evaluation method in accordance to UNI EN ISO 10211:2008 [17] by using a finite element analysis tool (Bisco ® ) [18].
The specific requirements of the two-dimensional model refereed to the technology nodes have been defined together with the boundary conditions to calculate thermal fluxes and the internal surface temperatures.
From the thermal balance of the analysed components, heat fluxes and isothermal curves have been deduced for the heterogeneous external wall and the roof. The specific requirements of the two-dimensional model refereed to the technology nodes have been defined together with the boundary conditions to calculate thermal fluxes and the internal surface temperatures.
From the thermal balance of the analysed components, heat fluxes and isothermal curves have been deduced for the heterogeneous external wall and the roof.    From the analysis carried out with Bisco ® , surface temperatures in the different layers have also been calculated and are reported in Table 4 (external wall) and Table 5 (roof). From the analysis carried out with Bisco ® , surface temperatures in the different layers have also been calculated and are reported in Table 4 (external wall) and Table 5 (roof).  In Table 6, thermal transmittance values for the external wall and the roof calculated with Bisco ® software are reported.   In Table 6, thermal transmittance values for the external wall and the roof calculated with Bisco ® software are reported.  Table 7: • connection between external wall and ground floor; • connection between external wall and roof; • connection between wall and window frame;   In Table 6, thermal transmittance values for the external wall and the roof calculated with Bisco ® software are reported. • connection between external wall and ground floor; • connection between external wall and roof; • connection between wall and window frame; • connection between external wall and basement floor; and • convex angle of the external wall.
In Figures 9-13, calculation results from Bisco ® are reported. Moreover, temperature trends and heat fluxes lines are highlighted. In Figures 9-13, calculation results from Bisco ® are reported. Moreover, temperature trends and heat fluxes lines are highlighted.

Preliminary Evaluation of Different Shading Systems
This analysis has been carried out to calculate and evaluate the specific energy need for space heating and cooling: • QH,nd: specific energy need for space heating (kWh/m 2 ); and • QC,nd: specific energy need for space cooling (kWh/m 2 ).
To choose the more performing shading systems, to enhance energy building performances, the following strategies have been assessed. All strategies, reported in Table 8, have to be combined with the window glasses (solar factor ggl = 0.4 and a thermal transmittance Ug = 0.6 W/m 2 K).

Preliminary Evaluation of Different Shading Systems
This analysis has been carried out to calculate and evaluate the specific energy need for space heating and cooling: • Q H,nd : specific energy need for space heating (kWh/m 2 ); and • Q C,nd : specific energy need for space cooling (kWh/m 2 ).
To choose the more performing shading systems, to enhance energy building performances, the following strategies have been assessed. All strategies, reported in Table 8, have to be combined with the window glasses (solar factor g gl = 0.4 and a thermal transmittance U g = 0.6 W/m 2 K).

Simulation Results
Energy analysis has been carried out by means of an official calculation code in steady state conditions (Aermec MC11300) and standardized procedures according to Italian Energy Performance Certificate regulations [2].
This simulation analysis is articulated in three steps: •

Energy Analysis of the nZEB Building-First Step
In Figures 14-18, results dealing with the built house are presented. They refer to: • design transmission and ventilation heat loss for heated space (in percentage) ( Figure 14); • design transmission heat loss for heated space analysed according to exposure, such as NE, NW, SE, SW, roof and floor (in percentage) ( Figure 15); • design transmission heat loss for heated space analysed according to different technological component, such as external wooden wall, external wooden wall-stone coated, floor on basement, ground floor, roof, windows and thermal bridges (in percentage) ( Figure 16); • energy analysis of the building envelope (in kWh/m 2 ) subdivided as: heat transfer by transmission for the heating mode (Q H,tr ) and for the cooling mode (Q C,tr ), heat transfer by ventilation for the heating mode (Q H,ve ) and for the cooling mode (Q C,ve ), internal heat gains (Q int ) and solar heat gains through windows (Q sol,w ) (Figures 17 and 18); and • calculation of specific energy need for space heating (Q H,nd ) and cooling (Q C,nd ) (in kWh/m 2 ). and UNI EN ISO 14683:2008); • second step: energy analysis of the built house taking into account the presence of heterogeneous components and thermal bridges assessed with a 2D finite element analysis tool (Bisco ® ); and • third step: energy analysis of the building carried out taking into account different solar shading strategies preliminary described in Section 2.3.

Energy Analysis of the nZEB Building-First Step
In Figures 14-18, results dealing with the built house are presented. They refer to: • design transmission and ventilation heat loss for heated space (in percentage) ( Figure 14); • design transmission heat loss for heated space analysed according to exposure, such as NE, NW, SE, SW, roof and floor (in percentage) ( Figure 15); • design transmission heat loss for heated space analysed according to different technological component, such as external wooden wall, external wooden wall-stone coated, floor on basement, ground floor, roof, windows and thermal bridges (in percentage) ( Figure 16); • energy analysis of the building envelope (in kWh/m 2 ) subdivided as: heat transfer by transmission for the heating mode (QH,tr) and for the cooling mode (QC,tr), heat transfer by ventilation for the heating mode (QH,ve) and for the cooling mode (QC,ve), internal heat gains (Qint) and solar heat gains through windows (Qsol,w) (Figures 17 and 18); and • calculation of specific energy need for space heating (QH,nd) and cooling (QC,nd) (in kWh/m 2 ).          Figure 15 shows a substantial homogeneity among the different transmission losses; the higher percentage is for SW orientation due to the presence of large windows.
This result is according to data reported in Figure 16, where a higher percentage of transmission losses due to thermal transmittance of windows (Uw between 0.77 and 1.09 W/m 2 K) is highlighted. The windows thermal transmittances, although very small for these component types, are larger than those of opaque ones (U between 0.119 and 0.153 W/m 2 K). Data reported in Figures 17 and 18 are related to climatic data of the site, Arezzo (climatic zone E [12]), where the conventional heating season goes from 15 October to 15 April (six months) while the conventional cooling season goes from 9 June to 10 September (three months).
The different duration of the heating and cooling seasons amplifies the difference of heat transfer by transmission and solar gains in heating and cooling mode.
Moreover, it is noted that good winter solar gain values are due to a proper design of the SW overhang that does not excessively reduces solar irradiation on the façade.

Energy Analysis of the nZEB Building-Second Step
Based on the new values of the thermal transmittance and of thermal bridge coefficient, assessed with a 2D finite element analysis tool (Bisco ® ), a new analysis of the simulation results has been carried out.
In this step of the analysis, regarding design transmission and ventilation heat loss for heated space (in percentage), no significant differences come out with respect to Figure 14.
From the comparison of Figures 15 and 19, the following differences come out: • thermal transmission losses of the roof slightly increase from 19% to 20% due to the new value of transmittance calculated with Bisco ® ; and • SW wall decreases from 29% to 28% due to the new thermal bridge coefficient value from 0.138 W/mK to 0.061 W/mK. Figures 16 and 20, a different contribution of thermal bridges from 23% to 15% comes out.

From the comparison of
From the new energy analysis (Figures 21 and 22 compared, respectively, with Figures 17 and  18), the following elements come out: • heat transfer by transmission for the heating mode (QH,tr) goes from 55.5 kWh/m 2 to 52.9 kWh/m 2 (a decrease of about 5%); • heat transfer by transmission for the cooling mode (QC,tr) goes from 6.4 kWh/m 2 to 5.6 kWh/m 2  Figure 15 shows a substantial homogeneity among the different transmission losses; the higher percentage is for SW orientation due to the presence of large windows.
This result is according to data reported in Figure 16, where a higher percentage of transmission losses due to thermal transmittance of windows (U w between 0.77 and 1.09 W/m 2 K) is highlighted. The windows thermal transmittances, although very small for these component types, are larger than those of opaque ones (U between 0.119 and 0.153 W/m 2 K).
Data reported in Figures 17 and 18 are related to climatic data of the site, Arezzo (climatic zone E [12]), where the conventional heating season goes from 15 October to 15 April (six months) while the conventional cooling season goes from 9 June to 10 September (three months).
The different duration of the heating and cooling seasons amplifies the difference of heat transfer by transmission and solar gains in heating and cooling mode.
Moreover, it is noted that good winter solar gain values are due to a proper design of the SW overhang that does not excessively reduces solar irradiation on the façade.

Energy Analysis of the nZEB Building-Second Step
Based on the new values of the thermal transmittance and of thermal bridge coefficient, assessed with a 2D finite element analysis tool (Bisco ® ), a new analysis of the simulation results has been carried out.
In this step of the analysis, regarding design transmission and ventilation heat loss for heated space (in percentage), no significant differences come out with respect to Figure 14.
From the comparison of Figures 15 and 19, the following differences come out: • thermal transmission losses of the roof slightly increase from 19% to 20% due to the new value of transmittance calculated with Bisco ® ; and • SW wall decreases from 29% to 28% due to the new thermal bridge coefficient value from 0.138 W/mK to 0.061 W/mK.
From the comparison of Figures 16 and 20, a different contribution of thermal bridges from 23% to 15% comes out.
From the new energy analysis (Figures 21 and 22 compared, respectively, with Figures 17 and 18

Energy Analysis of the nZEB Building-Third
Step This step of energy analysis is composed of two parts: • preliminary evaluation of the different shading systems described in Section 2.3 to choose, among those assessed, the more performing shading strategy to improve the nZEB energy performances; and • assessment of the nZEB building energy performances with selected shading devices.

Preliminary Evaluation of the Different Shading Systems
Based on the shadings features described in Section 2.3, the specific energy need for heating (QH,nd), cooling (QC,nd) and global (QH,nd + QC,nd) have been calculated with a dynamic code (Design Builder) [21] to choose the better performing shading strategy [22][23][24]. In Figure 23, simulation results are reported for the analysed shading systems and compared with the sole glass (ggl = 0.4).

Energy Analysis of the nZEB Building-Third Step
This step of energy analysis is composed of two parts: • preliminary evaluation of the different shading systems described in Section 2.3 to choose, among those assessed, the more performing shading strategy to improve the nZEB energy performances; and • assessment of the nZEB building energy performances with selected shading devices.

Preliminary Evaluation of the Different Shading Systems
Based on the shadings features described in Section 2.3, the specific energy need for heating (Q H,nd ), cooling (Q C,nd ) and global (Q H,nd + Q C,nd ) have been calculated with a dynamic code (Design Builder) [21] to choose the better performing shading strategy [22][23][24]. In Figure 23, simulation results are reported for the analysed shading systems and compared with the sole glass (g gl = 0.4).

Preliminary Evaluation of the Different Shading Systems
Based on the shadings features described in Section 2.3, the specific energy need for heating (QH,nd), cooling (QC,nd) and global (QH,nd + QC,nd) have been calculated with a dynamic code (Design Builder) [21] to choose the better performing shading strategy [22][23][24]. In Figure 23, simulation results are reported for the analysed shading systems and compared with the sole glass (ggl = 0.4).   Figure 23 shows that an internal white drape determines a slight increase of global energy need of about 6%, reduces winter solar gains and does not produce any significant reduction in term of specific energy need for space cooling.
The external Venetian blind causes a significant increase of the specific energy need for space heating of 30%, a reduction of specific energy need for space cooling of about 46% and a reduction of global energy need of about 6%.
The external fixed shading causes an increase of the specific energy need for space heating of 10%, a reduction of specific energy need for space cooling of about 33% and a reduction of global energy need of about 11%.
The best performances are those of the external Venetian blind and of the external fixed shading. As the external Venetian blind in the living area could reduce visual comfort and restrict the view of the surrounding landscape, the chosen solar shading strategy is the combination of the external fixed shading on SW façade and the external Venetian blind for all the other windows of the nZEB building.
To evaluate the performance of the chosen solar shading strategy in thesteady state software, the reduction factor related to solar gain (g gl /g gl+sh ) has been calculated. This parameter represents the ratio between the solar factor of the sole glass (g gl ) and the solar factor of the glass combined with a specific shading device (g gl+sh ). It has been calculated, by means of Design Builder software, as the ratio of the solar gain (Q sol,w ) due to the sole glass to those due to the combined window and shading systems.

Energy Simulations of the nZEB Building with the Chosen Solar Shading Strategy
In this section, the assessment of the nZEB building energy performances with the chosen solar shading strategy is reported and discussed (Figures 24 and 25).
From the comparison between results of the third step of energy analysis (Figures 24 and 25) and the results of the second step (Figures 21 and 22 and the results of the second step (Figures 21 and 22), the following elements come out: • solar heat gains through windows (Qsol,w) for the heating mode decrease from 35.8 kWh/m 2 to 33.7 kWh/m 2 (about 6%); • solar heat gains through windows (Qsol,w) for the cooling mode decrease from 22.6 kWh/m 2 to 19.3 kWh/m 2 (about 15%); and • other values do not change.  The energy simulation of the chosen shading strategy added to the nZEB building produces the following energy indices: 110.76 kWh/m 2 for the heating mode (QH,nd) and 9.01 kWh/m 2 for the cooling mode (QC,nd).
The results of the simulations carried out in the first, second and third steps are presented in Figures 26 and 27, respectively.  The energy simulation of the chosen shading strategy added to the nZEB building produces the following energy indices: 110.76 kWh/m 2 for the heating mode (Q H,nd ) and 9.01 kWh/m 2 for the cooling mode (Q C,nd ).
The results of the simulations carried out in the first, second and third steps are presented in Figures 26 and 27  The energy simulation of the chosen shading strategy added to the nZEB building produces the following energy indices: 110.76 kWh/m 2 for the heating mode (QH,nd) and 9.01 kWh/m 2 for the cooling mode (QC,nd).
The results of the simulations carried out in the first, second and third steps are presented in Figures 26 and 27, respectively.    As regards the results shown in Figures 26 and 27, it can be noted that, moving from a simplified analysis to a detailed one, the heat transfer by transmission for the heating mode is reduced by 5% and the heat transfer by transmission for the cooling mode is reduced by 12%. Heat transfer by ventilation for the heating mode and for the cooling mode as well as internal heat gains are unchanged. Solar heat gains through windows are reduced of 6% in winter and of 15% in summer.
Since the aim of the paper is to assess the differences between steady state conditions analysis (UNI/TS 11300) and detailed calculations methods (Bisco ® and Design Builder) for the assessment of thermal bridges, heterogeneous components and the effectiveness of complex shading systems, the gap between the results obtained by means of different calculation methodologies is not negligible, in particular when residential highly insulted buildings are involved.

Conclusions
The design process and the construction of nZEB building in Southern Europe is an important challenge for the reduction of energy consumption of civil buildings.
The use of wooden high insulated technologies to reach the nZEB target presents some critical issues regarding the correct envelope heterogeneous components thermal evaluation and the proper control of solar radiation.
The complexity of the design process of this kind of technologies needs to be supported by detailed analysis of the component performances considering also the cooling mode with an accurate evaluation of shading strategies to control indoor overheating.
Calculation methodologies must be adapted to heterogeneous components, as platform frame, and a dynamic evaluation is necessary to verify the effectiveness of shading device systems to achieve a better design process.
In this paper, a methodology to correctly assess the energy performance of a nZEB building is presented and it is applied to a platform frame detached house recently built in central Italy.
This methodology includes two main phases: in the first phase, the building components and solar shading systems are analysed with both simplified and detailed calculation methods; and, in the second phase (articulated in three steps), starting from the results of the first phase, energy simulation of the building are carried out with a dedicated steady state software also assessing the effectiveness of different solar shadings.
In the second phase of the methodology, switching from a simplified analysis of the thermal performance of the building components (first step) to a detailed analysis (second step), a substantial difference in the performance of the building due to more accurate transmittance values arises. Such a methodology is suitable when the presence of heterogeneous components, such as platform frame technology, has to be assessed.
To obtain accurate values to be entered in the steady state calculation code for the energy performance certification, the use of a 2D finite elements calculation code for building components assessment (U and ψ) and a dynamic code for different shading systems evaluation (g gl /g gl+sh ) is of strategic importance.
In the cooling mode, complex shading strategies are properly evaluated and entered into the energy performance certification software, giving useful information about the improvement of the energy performance of the nZEB residential building under analysis. Among different shading systems assessed, the chosen solar shading strategy is the combination of the external fixed shading on SW façade and the external Venetian blind for all the other windows of the building.
In particular, moving from a simplified analysis to a detailed one, the heat transfer by transmission for the heating mode is reduced by 5% and for the cooling mode is reduced by 12%. Solar heat gains through windows are reduced by 6% in winter and 15% in summer. While the specific energy need for heating increases by 1%, the specific energy need for cooling strongly decreases by about 22%.
As a result of the performed evaluation, it comes out that the complexity of the wooden technology nZEB design process in Mediterranean climate must be successfully supported by a detailed analysis of the building performances (components and shadings) aimed at an energy evaluation properly fitted with the real buildings features. All these elements are of fundamental importance to improve a correct design process of these technologies when the nZEB target is aimed.