A district heating and cooling system (DHC) is a promising energy saving measure for high density business areas. In a DHC plant, high energy efficiency is achieved by introduction of highly efficient equipment and efficient operation by well trained operators. However, the energy efficiency is affected by a number of issues related to the HVAC systems within a building. The main reason for these problems is that the DHC plant and the air conditioning systems of buildings are designed and operated separately. This study proposes a new energy service in which the operator of the DHC plant controls the air conditioning systems in buildings simultaneously. From a simulation result, it is found that energy conservation measures on the demand side would decrease energy consumption by 23.9% when electric driven heat pumps are used as the heat source. In addition, the potential risks for several factors that cause decreases in saved energy were also assessed by the simulation model. (C) 2012 Elsevier B.V. All rights reserved.