Distributed direct current (DC) power distribution system in buildings are gaining popularity. In this paper, a real world DC building distribution system is presented. Both the steady state and transient state models are developed. In the steady-state state model, the optimal location of DC converters is designed to enhance the energy efficiency of the buildings. In the transient state model, the safety operation of the DC building grids is achieved by the coordination of distributed energy resources. Furthermore, different operation scenarios are conducted, and the results indicate that the DC building achieves safe operation under the proposed coordination mechanism.