# From Nearly Zero Energy to Carbon-Neutral: Case Study of a Hospitality Building
## 3 Methodology
No embodied carbon due to user-related activities is (yet) considered in the calculations since they are heavily dependent on the users and their aleatory lifestyle choices, and neither have carbon emissions related to the B1-3 stages that cover the release of greenhouse gases from products and materials (e.g., paints, carpets, etc.) during the normal operation of the building, the carbon emissions of all ordinary maintenance activities (e.g., cleaning), and of the repair of the relevant building components before the end of their service life. Biogenic carbon should not be included in the calculation until scientific literature and standards can provide a shared methodology to assess it. Any residual carbon emissions at the end of the building's service life should be offset. Offsetting criteria can include the financing of local or delocalized vegetation and renewable energy projects, the purchase of certified green energy and carbon credits, and the local contribution of renewable energy on site. The standard service life for a residential building may be assumed as 50 years, unless properly argued (e.g., offices and retails may report a shorter service life), whereas the service lives of the building components and materials should be as declared by the producer. Operational energy-related emissions must derive from dynamic energy simulations, including all the main building services (heating, cooling, ventilation, hot water, lighting, and appliances), and the nomenclature must be compliant with the ISO 52000-1 standard [47]\". In the paper, the new definition of CNB is tested via a case study. In order to assess the practical consequences of the definition on the design, a real lot in an urban environment has been selected, choosing a final use that might provide actual, though challenging, conditions to the carbon neutrality objective. If a countryside single family house, with large envelope surfaces and a relatively small volume, may easily offset its emissions through large active surfaces producing renewable energy, and via the planting of a few trees, an urban building, because of urban laws, including front alignment and limitations in the use of active renewable technologies because of low irradiance values, may experience more  
Figure 1: The overall approach to carbon neutrality considered in the study. challenging conditions. The selected case study is, thus, a hostel located on an urban lot in Milan, Italy. The calculations are developed both for the CNB objective and for a reference, or state-of-the-art, scenario, which, according to national and regional legislations [48; 49; 50], requires reaching the nZEB standard. This will allow for understanding if an nZEB building may also reach carbon neutrality, or how far it might be from it. According to the new CNB definition, the evaluation of the carbon emissions related to the use stage (B6), the operational energy use in both the nZEB and CNB scenarios, is performed by means of numerical simulations under dynamic conditions, using the calculation suite TRNsys 17 [51], in order to achieve the yearly energy need. The energy use for all of the main building services (heating, cooling, ventilation, hot water, lighting, and appliances) was considered in the calculations. The carbon emissions were assessed via LCA according to ISO 14040:2006, ISO 14044:2006, and to EN 15804+A1:2019 and EN 15978:2011. A comparison of the results between the CNB and nZEB leads to general considerations about the feasibility of the carbon neutrality objective for urban buildings, either new constructions or renovations, posing important questions to the pledges of cities and businesses.