The paper mainly discusses the key elements of green building HVAC design, in order to improve the energy efficiency of buildings, reduce energy consumption, and reduce the burden on the environment, while improving indoor comfort and improving the quality of living and work. This article analyzes the design of HVAC systems in public buildings under the low-carbon background, and uses literature review methods to analyze the improvement effect of green buildings on energy consumption and indoor comfort. The research results indicate that the design of public building HVAC systems based on the concept of green buildings adopts a series of energy-saving and environmental protection measures, including effective utilization of natural lighting and ventilation, adoption of efficient HVAC equipment and systems, optimization of thermal insulation performance of building exterior walls and windows, etc., significantly reducing energy consumption, and improving indoor air quality and comfort.