In order to achieve a sustainable energy future, advanced control paradigms will be critical at both building and grid levels to achieve harmonious integration of energy resources. This research explores the potential for synergistic effects that may exist through communal coordination of commercial building operations. A framework is presented for diurnal planning of multi-building thermal mass and HVAC system operational strategies in consideration of real-time energy prices, peak demand charges, and ancillary service revenues. Optimizing buildings as a portfolio achieved up to seven additional percentage points of cost savings over individually optimized cases, depending on the simulation case study. The magnitude and nature of synergistic effect was ultimately dependent upon the portfolio construction, grid market design, and the conditions faced by buildings when optimized individually. Enhanced energy and cost savings opportunities were observed by taking the novel perspective of optimizing building portfolios in multiple grid markets, motivating the pursuit of future smart grid advancements that take a holistic and communal vantage point. (C) 2015 Elsevier Ltd. All rights reserved.