In order to solve the problem under the exterior wall of a building, the author proposes a thermodynamic model for HVAC. Scientific and technological progress has promoted social development, under the new development situation, people have higher requirements for living environment. In architectural design, residential environment design is the key content, especially the design of indoor temperature control system. With the continuous promotion of the national sustainable development strategy, the current architectural design pays more at­tention the green design concept, and the HVAC design is the key design content in realizing the green architectural design. In order to make HVAC design more scientific and reasonable, the author studied the concept that HVAC design needs to follow from the perspective of green buildings, and analyzed the specific ap­plication methods of HVAC design technology. The experimental results indicate that the building envelope parameters have a great impact on the building thermodynamic performance, and the annual cooling and heating loads of buildings should be comprehensively considered, reasonably determine the building envelope parameters. The building load has a low support value, so only low quality energy can meet the building load demand, when selecting the HVAC system, consider the matching of energy quality, try to introduce low grade energy, and improve energy utilization efficiency.