Energy consumption analysis of three-layer prefabricated composite wall panels: an integrated forming process and comparative study with cast-in-situ construction

Abstract The construction industry accounts for approximately 36% of global final energy use and 39% of energy-related CO₂ emissions. Prefabricated construction offers potential energy savings during the construction phase, yet limited studies quantify actual on-site energy consumption for multi-layer composite prefabricated wall panels. This study develops an integrated forming process for a three-layer prefabricated composite wall panel (structural concrete—EPS insulation—recycled aggregate concrete outer layer) and compares its construction-phase energy consumption, thermal performance, and mechanical properties against traditional cast-in-situ methods over a 100 m 2 wall area. Experimental results show that the proposed panel achieves a compressive strength of 36.2 MPa for the structural layer and 28.5 MPa for the outer RAC layer, a flexural strength of 4.8 MPa for the full composite panel, and a thermal transmittance (U-value) of 0.38 W/m 2 K at the center-of-panel region, which is 86% lower than conventional 200 mm solid concrete walls (2.8 W/m 2 K) and 85% lower than 150 mm solid prefabricated walls without insulation (2.5 W/m 2 K). It should be noted that these comparisons are made against uninsulated solid walls; when a conventional 200 mm concrete wall is equipped with 80 mm external EPS insulation, its U-value reaches 0.32 W/m 2 K, which is lower than the composite panel's 0.38 W/m 2 K. The U-value of 0.38 W/m 2 K meets the recommended threshold for passive house standards (U ≤ 0.4 W/m 2 K) at the panel center, though it should be emphasized that this applies only to the center-of-panel region and does not account for thermal bridging at panel edges, joints, and connections to structural elements. Construction energy monitoring indicates that prefabricated systems reduce on-site energy consumption by 27.3% (from 46.9 to 34.1 kWh/m 2 ), primarily due to lower machinery energy (59.6% reduction) and curing energy (45.2% reduction). However, a sensitivity analysis reveals that if electric curing blankets were not used in the cast-in-situ wall (i.e., natural curing at ambient temperature), the energy savings would be substantially smaller—approximately 7.3% instead of 27.3%—indicating that the reported savings are partly dependent on the curing method employed. Transportation energy increases by 68.8% (from 3.2 to 5.4 kWh/m 2 ), but the absolute increase (2.2 kWh/m 2 ) is outweighed by on-site savings (13.6 kWh/m 2 ). The integrated forming process eliminates secondary insulation installation, reducing labor time by 40% and avoiding thermal bridging at the panel center. Energy distribution analysis shows that factory production accounts for 42.5% of total prefabricated construction energy, followed by on-site lifting (27.0%), transportation (15.8%), and joint filling and finishing (14.7%). A sensitivity analysis indicates that the break-even transportation distance, at which the on-site energy savings are offset by increased transportation energy, is approximately 320 km round trip. These findings support the adoption of multi-layer composite prefabricated wall panels for low-carbon construction and provide quantitative benchmarks for construction energy assessment.