The design of the envelope is useful to use a unique system for all the apartments, in fact, for the winter period, there are low energy consumptions and in summer, when the cooling is needed, the single heat pump is enough. The heat pump is a water-air type that consumes the energy produced by the photovoltaic panels and the heat produced by solar panels, so to have an energy balance that is near to zero. The design choices optimize the winter mode, but also reduces the summer needs in comparison with the old buildings. The heating system is composed by a radiant floor, instead the cooling system is only mechanical ventilation mode, and all of this can be controlled by a home automation system that has also the function of monitoring the energy balances. It is also possible to have a natural ventilation