# From Nearly Zero Energy to Carbon-Neutral: Case Study of a Hospitality Building
## 4 Case Study
### CNB Scenario  
Because of the characteristics of the urban lot and regulations, with a bonded orientation and shape, and limited access to solar energy (see Figure 2), the building envelope and systems cannot be conventional ones to achieve the CNB objective, but they must outperform the nzEB approach. Therefore, the CNB scenario is characterized by wooden structures for the floors above ground, and by reinforced concrete structures with a high level of recycled materials for the basement, whereas the limitation of the building's thermal energy need for space heating and cooling was based on a careful design of the building envelope components, and their integration within the system infrastructure. As far as the opaque vertical envelope is concerned, the breathing wall (BW) technology was adopted [52; 53; 54; 55; 56]; the overall layer sequence of this technology consists of an external cladding, a ventilated air gap, a multilayer porous core based on air-permeable materials, a second air gap, and an internal cladding. Through a small indoor-outdoor pressure difference, it is possible to generate a low velocity airflow (around 0.001 m/s) driven across the wall, which is integrated into the mechanical ventilation system [57; 58] as a heat recovery component and a filter. The BW technology operates in two modes, according to the direction of the heat flux and the airflow [58]: pro-flux and contra-flux. In the first configuration, the heat flux and the airflow go in the same direction, while they are opposite in the second one. Through the selection of the working regime and airflow velocity, it is possible to: (i) Affect the temperature distribution across the wall [55; 56; 58]; (ii) Preheat the ventilation air [53], which reaches the same temperature as the interior ventilated air cavity; (iii) Drop the effective thermal transmittance, as shown in the literature [59], and mitigate heat losses due to transmission in winter; (iv) Maximize the heat dissipation through the envelope in summer and exploit night-free cooling (pro-flux); (v) Modulate the effective wall heat capacity [52] and the indoor-outdoor thermal coupling; (vi) Filrate the incoming ventilation air. BW technology is considered, in the CNB scenario, as a tool to further reduce the energy need with respect to the nzEB scenario, consequently mitigating the CO\({}_{2}\)-eq emissions related to the B6 stage of the LCA analysis. The horizontal structures (roof and terrace) are made, in the CNB scenario, of CLT (cross-laminated timber) slabs, wood-based insulation panels (16 cm), waterproofing and breathable membranes and a gravel drainage layer, and outdoor wood flooring, or a green roof, according to the zone of the building. Table 2 reports the thermal transmittance values (U-values) of the chosen external horizontal and vertical envelope structures. All of the insulating materials of the internal partitions and the external envelope are wood-based, except for the external layer of the BW that, to comply with fire regulations, is made of mineral wool. High-performance low-emissivity double-glazed windows with wooden frames were considered for the transparent envelope. The high envelope performance is complemented by the local production of renewable electric energy by means of 72 PV panels, of 300 W\({}_{\rm p}\) each, installed on the roof, for a totalpeak power of 21.6 kW\({}_{\rm P}\), overcoming the minimum nZEB requirements. The size of the PV plant, as declared previously, is, nevertheless, limited by the small roof area available and by the urban context (i.e., shadows projected by adjacent buildings). To further increase the local production, electric energy, as well as thermal energy, are also generated by 9 micro-combined heat and power (CHP) systems, based on fuel-cell technology, able to produce 0.9 kW\({}_{\rm TH}\), used for DHW, and 1.5 kW\({}_{\rm EL}\) each, with an hourly natural gas consumption of 0.25 m\({}^{3}\)/h.