Residential and commercial buildings account for 41% of total energy consumption in the United States. Optimizing the energy consumptions and designing more Energy Efficient Green Buildings is a promising approach to reducing energy consumption. Modelling and simulation play an important role in design, control and operation of building systems. They are particularly valuable in evaluating performance, Indoor Air-Quality (IAQ), comfort, as well as for HVAC control design. In this talk I will discuss computational approaches to tackle problems associated with building syste ms. These include (a) algorithms and methods for optimal sensor placements for IAQ, especially under uncertainties, and (b) approaches for improving the accuracy of buildings energy prediction tools and incorporating microclimatic conditions for performing year-long energy predictions.