Digital twins have gained increasing attention as a tool to facilitate decision-making in the cities. However, the current discourse predominantly focuses on technical aspects while overlooking the human aspect in urban digital twins. This work proposes a conceptual framework that addresses the role of humans in relation to the urban environment, therefore highlighting the social value of urban digital twins. The proposed framework is subsequently implemented in a specific case study of outdoor walking comfort at National University of Singapore, validating its feasibility in practice. By incorporating human sensing data, such as participatory data, urban digital twins have the potential to represent the dynamic interaction between people and environments, generating a holistic physical-social-virtual system.