Passive Energy-Saving and Carbon Reduction Strategies for Substation Buildings in Cold Regions: A Case Study of Shijiazhuang

Cold region indoor substations experience persistent high thermal disturbance from electrical equipment, limiting the direct applicability of conventional residential low-carbon strategies. This study couples hourly DeST simulation with partial life-cycle carbon accounting covering A1–A5, B6, C1–C4, Module D, and the greening carbon sink for an operational 110 kV indoor substation in Shijiazhuang. The baseline annual average emission is 59.8 tCO2/year, comprising 21.3 tCO2/year from B6 operational energy and 38.4 tCO2/year from non-B6 contributions. Reducing the roof heat transfer coefficient from 0.50 to 0.20 W/(m2·K) lowers total emissions by 9.4%, followed by the exterior wall at 3.6%, whereas changes in exterior window U-value have negligible influence. Building height reduction yields a theoretical upper bound of 10.7% in the simplified height scan model, but the estimated reduction is only about 3% within the practical 8.0–9.4 m range constrained by equipment clear height requirements. Enhanced interior wall insulation increases emissions by 2.4% and provides no net carbon reduction benefit. Increasing the window-to-wall ratio (WWR) raises emissions for north-, east-, and west-facing facades, while the south-facing response is non-monotonic; among the tested cases, the minimum occurs at WWR = 0.25. These findings provide case-specific quantitative references for passive low-carbon design of high-internal-gain indoor substations in cold regions.