To address the issues of unreasonable air distribution design and poor thermal comfort in heating systems for large spaces in severe cold and cold zones, this paper conducts on-site measurements and analyses of temperature, air volume, and heat demand in the lobby of a building in Beijing, and also investigates similar typical large-space projects. Based on the original heating and air conditioning system scheme, a renovation scheme that adds a floor radiant heating system is proposed. By using CFD simulation software, a comparative analysis of air distribution in the indoor thermal environment before and after the renovation is carried out. The results indicate that after adopting the floor radiant heating system renovation scheme, the thermal comfort in the lobby during winter can be significantly improved. The research findings can provide references for the design and optimization retrofit of heating and air conditioning systems for large spaces in severe cold and cold zones during winter.