Analyzing the Energy Flexibility Potential and Carbon-Emission Impacts of Solar–Air-Source Heat Pump Heating Systems for Nearly Zero-Energy Residential Buildings

Against the background of China’s dual carbon goals and the large-scale integration of renewable energy, building-side energy flexibility is of great significance for alleviating peak load pressure on the power grid, improving renewable energy accommodation, and reducing operational carbon emissions. This study investigates a nearly zero-energy residential building in the hot-summer and cold-winter climate zone of China. A TRNSYS-based dynamic model of a solar–air-source heat pump radiant floor heating system was developed to evaluate the effects of solar collector area, rated heat pump heating capacity, thermal storage tank volume, and heat pump start–stop center temperature on energy flexibility potential under the H1 strategy. Identified in the preceding study as having the greatest flexibility potential among the strategies evaluated, H1 switches off the heat pump throughout the peak period from 08:00 to 22:00, while solar heat and thermal energy stored in the tank provide space heating. Acceptable thermal comfort in all heated rooms was demonstrated under the reference configuration. A one-factor-at-a-time analysis and Spearman rank correlation analysis were conducted using two flexibility indicators: reduction in peak-period operating energy consumption and increase in solar heat collection relative to the corresponding baseline scenario. Peak-period carbon emissions were also evaluated. The collector area showed a strong negative association with peak-period electricity reduction (ρ = −0.97) and a strong positive association with increased solar heat collection (ρ = 0.82). The start–stop center temperature showed positive associations with both indicators, whereas the rated heating capacity and tank volume showed weaker associations. This study provides useful guidance for optimizing system configuration, reducing peak loads on the power grid, promoting renewable energy accommodation, and supporting the low-carbon operation of buildings.