Evaluation of ventilation loads in buildings energy modelling at urban scale

Generally, the models for evaluating the energy performance of buildings have a ventilation thermal load that depends on the type of building and its occupancy rate. The models apply a constant rate of air changes and therefore the ventilation load depends on this value and on the temperature gradient between internal and external environments. In this work, a single zone air flow model is presented to modify monthly the air changes according to the climatic data, the air permeability, shape and orientation of the building and the urban morphology. The results of this work, show how the air change rates vary with the building floor and with the wind direction and velocity. For both case studies, the air changes per hours vary monthly with minimum values in wintertime and with monthly differences of 41%. Of course, if the building is not well exposed and there is no wind, the air infiltrations are not sufficient to ensure good air quality conditions and it will be necessary to open the windows. In these first two case-studies, a very simple single zone evaluation of air flow rate by natural ventilation improved the existing energy performance placebased model. The results of this work encourage the application of this model at district-urban scale, taking into account the characteristics of each single building and its surroundings.