Energy–Indoor Air Quality–Health Nexus in Rural Residential Retrofits: A Field-Calibrated Coupled Simulation and Multi-Criteria Evaluation for the Central Plains Transitional Climate of China

Rural residential buildings in China’s Central Plains transitional climate zone face intertwined challenges of high heating/cooling energy consumption, severe indoor air pollution from solid-fuel combustion, and associated public health burdens. While envelope energy retrofits are widely promoted for carbon reduction, their integrated impacts on energy performance, indoor air quality (IAQ), and health outcomes remain insufficiently quantified. This study develops a field-calibrated coupled simulation framework to evaluate four retrofit scenarios for typical brick-concrete rural residences in Anyang, Henan Province. A paired before–after field measurement campaign was conducted over 72 h in both winter and summer, monitoring five priority pollutants (PM2.5, PM10, CO2, formaldehyde, and TVOC) alongside thermal parameters. A two-way EnergyPlus–CONTAM co-simulation model was established and calibrated following ASHRAE Guideline 14, achieving NMBE of −2.1% and CV(RMSE) of 6.7% for indoor temperature, with independent out-of-sample validation for, CO2 and summer operation. Four scenarios were compared: baseline (S0), basic envelope retrofit (S1), envelope retrofit plus schedule-optimized natural ventilation (S2), and envelope retrofit plus heat-recovery ventilation (S3). The results show that S1 reduces the annual thermal loads by 52.2% but increases the winter average PM2.5 by 25.8% and formaldehyde by 32.4% owing to a 62.3% reduction in air infiltration. S2 preserves 95.6% of energy savings while reducing the PM2.5 non-carcinogenic hazard quotient by 20.3% and the formaldehyde carcinogenic risk by 14.9% relative to the baseline. S3 achieves the best IAQ and health outcomes but extends the payback period to 8.9 years. A TOPSIS multi-criteria analysis identifies S2 as the optimal cost-balanced strategy for large-scale rural promotion. This study demonstrates that unilaterally pursuing envelope airtightness may exacerbate indoor pollution exposure, and that coordinated ventilation optimization can simultaneously achieve energy conservation, IAQ compliance, and net health benefits. The findings provide evidence-based technical parameters for rural building upgrading programs in transitional climate zones. To our knowledge, this is the first study to integrate a field-calibrated EnergyPlus–CONTAM two-way coupling, an auditable health-risk assessment, and an entropy-weighted TOPSIS ranking specifically for solid-fuel-dependent brick-concrete rural housing in the Central Plains transitional climate; the novelty lies in this context-specific integrated application rather than in a new coupling or ranking algorithm (payback quoted on a standardized-comfort basis; on the actual-use basis with no mechanical cooling, the corresponding S1 payback is ≈6.8 years).