High density and compact urban morphology are usually considered prerequisites for sustainable development. This paper explores the effect of density on the air-conditioning demand of urban grids in the Mediterranean climate, based on the case study of the Eixample of Barcelona. Representative periods in the district’s history are selected to create four urban energy models. We calculate their annual heating and cooling demands through dynamic thermal simulations in Honeybee. Results show that the denser the block, the lower the total air conditioning demand for cooling and heating. Since the energy demand of the dwellings on the top floors significantly exceeds those of intermediate floors, increased densities achieved with taller buildings allow for reducing the air-conditioning needs at the block scale.