Building space heating and cooling system built-in the town's infrastructure is an important factors for building energy consumption and carbon emission source. In order to understand the roles of building energy system in the global warming, this paper established a mathematical model of energy consumption and carbon emission for the building energy system. Two district heating systems for residential buildings and nine space heating and cooling systems for public buildings were selected to analyze their energy consumption, carbon emission and economy based on a calculating model. The results showed that the two residential building cases B-01 and B-02 of life-cycle carbon emissions are 743.60 kg/m(2) and 620.98 kg/m(2), the public building cases B-03 similar to b(l1) of life-cycle carbon emissions are 800.15-1377.85 kg/m(2). Equipment materials production, installation and maintenance phase embodied energy and carbon emissions proportion reached up to 6%similar to 14%, energy conservation and emissions reduction potential should not be neglected. The application of some renewable energy reaches a certain effect of energy conservation and emissions reduction in building, but the life cycle cost of emission reduction is much higher than carbon tax in China. (C) 2015 Elsevier Ltd. All rights reserved.