Several new technologies can be today implemented in buildings in order to achieve a NZEB. In this paper a novel computer model for predicting the energy demand of buildings integrating phase change materials, photovoltaic-thermal collectors, adjacent sunspaces and innovative daylighting control is presented. Through this tool, written in MatLab and conceived for research aims, the overall energy and economic performance of multi-zone NZEBs can be assessed. Both the active and passive influences of all the above mentioned technologies (even when simultaneously utilised) are taken into account since in the code they are modelled as building integrated. Parametric and sensitivity analyses, with a unique simulation run, can be carried out for research design purposes. A novel relevant case study referred to a non-residential NZEB for Mediterranean climates is developed. For this building a suitable energy optimization analysis, was also carried out. For each use of the indoor space the optimal value of the pivotal design and operating parameters is calculated. Details about the optimal position of building PCMs and thermal insulation layers, also coupled to BIPV and/or BIPV/T systems are provided. For the obtained best configuration very low heating and cooling demands are achieved (1.6 and 2.9 kWh/m3y, respectively). Results about a simplified economic analysis carried out on the investigated energy saving technologies are reported. At last, new NZEB definition details and criteria are provided for non-residential buildings located in the southern European zones (Mediterranean climates).