A concept of 'cooperative' optimization of building energy systems is proposed in this paper. A cooperative optimization framework for a group of buildings connected to heat pumps in the context of economic model predictive control is formulated. Two optimization scenarios have been considered for analysis - a 'selfish' optimization of an individual building and a cooperative optimization of agroup of buildings. The impact of cooperative optimization on the energy usage patterns and cost of electricity for operating the heat pumps have been investigated. The proposed cooperative optimization approach is able to achieve up to 15% reduction in energy demand cost in comparison with selfish optimization. The benefits arising out of the cooperative optimization concept may be a major drive for the future smart cities and will play a significant role in advancing the concept of smart energy systems. (C) 2016 Elsevier B.V. All rights reserved.