The building sector is one of the three major energy consumption areas and one of the main areas responsible for carbon emissions. In 2019, carbon emissions related to construction and building operations in China accounted for 38% of the total social carbon emissions, of which construction accounted for 16% and operations accounted for 22%. Due to its large volume and high energy consumption per unit area, public buildings account for 38% of the operating energy consumption of all buildings, that is, 8% of the total national energy consumption. At this time, the building industry must take decarbonization actions to avoid a delay in realizing carbon neutrality and an emission peak. We need to form a unified process for the implementation boundary, implementation path, and index system to build a zero-carbon implementation plan for China’s public building sector. Based on bottom-up practical cases, this paper proposes the KAYA model, which is applicable to different scales and different types of public buildings/communities, and proposes specific and feasible plans. Through the implementation of demand reduction, energy efficiency improvement, and the fully-use of renewable energy in all five clear steps, this paper promotes the implementation of decarbonization in China’s building industry.

This study analyzes the configurations and control strategies of hybrid heating systems of air-source heat pumps (ASHPs) and gas boilers for space heating in different climatic regions in China, with the aim of improving the comprehensive energy efficiency. Parallel and series hybrid modes were proposed, and simulation analysis was conducted to analyze the energy performance, energy costs, and CO₂ emissions of different hybrid systems. The results show that the supply water temperatures of ASHPs in series mode are lower than that of ASHPs in parallel mode; thus, the COP of ASHPs in series mode reached 2.73 and was higher than the COP of ASHPs in parallel mode with a value of 2.65. Then, the optimal intermediate temperatures of hybrid system in series mode were analyzed, so as to guide the system control. The results show that compared with series mode with a fixed 50% load distribution, the operational costs and CO₂ emissions were reduced by 10.0% and 10.4% in Harbin, reduced by 6.4% and 8.3% in Beijing, and reduced by 10.0% and 15.1% in Wuhan. Additionally, the optimal intermediate temperature was affected by the building load ratio, supply water temperature, ambient air temperature, and the electricity–gas price ratio. The series-hybrid ASHP and gas boiler system achieves remarkable energy and cost savings across different climatic conditions, providing a scientific basis for promoting low-carbon heating solutions.

Mid-deep geothermal heat pump systems (MD-GHPs) feature high energy efficiency and low energy consumption, yet their promotion is restricted by high initial investment. While the initial investment of air-source heat pumps (ASHPs) is obviously lower, it also has a larger energy consumption. To address the complementary strengths and weaknesses of single-source heat pump systems, this paper puts forward an integrated system combining MD-GHPs and ASHPs, and the series mode was determined as the optimal integration approach for the hybrid system through comparative analysis. Simulation analysis was conducted to explore the adaptability of series mode, and numbers of mid-deep ground heat exchangers in nine cities across various climate regions were studied. The MD-GHP system is suitable for space heating in Xining and Xi’an, while ASHPs are suitable for space heating in Nanjing and Hangzhou. For intermediate resource areas like Urumqi and Tsingdao, the series mode achieves the best economic benefits during the 24th year of operation.

Mid-deep geothermal heat pump systems (MD-GHPs) use mid-deep borehole heat exchangers (MDBHEs) to extract heat from the geothermal energy at a depth of 2–3 km, and have been used for space heating in China over the last decade. This paper proposes a comprehensive and multilevel evaluation-index system to analyze and evaluate the energy performance of MD-GHPs. The multilevel evaluation index system consists of a target layer, a criterion layer, and an index layer, where the criterion layer is subdivided into six aspects and the index layer includes 26 specific indices, reflecting the geothermal resources, heat transfer performance of the MDBHEs, energy efficiency of the heat pump systems, building space heating demand, grid dynamic response capability, and energy-saving and economic benefits. Then, based on both expert survey results and case study data, the entropy weight method and the analytic hierarchy process are integrated to determine indicator weight coefficients among the multilevel evaluation indices, comprehensively considering both subjective and objective analyses. Furthermore, a fuzzy comprehensive evaluation model is conducted to integrate these weighted indices into a multi-criteria evaluation of MD-GHP performance. Finally, the proposed method was applied to evaluate the practical performance of four projects, returning scores of 61.56, 58.33, 72.73, and 78.41. These evaluations enable an overall assessment of the energy performance of MD-GHPs, reflecting the technical weaknesses and offering optimization guidance for system design and operation.