One significant challenge in lightweight modular integrated construction (MIC) is to determine the optimal performance of external wall to minimize life-cycle energy consumption, economic costs, and environmental impact (3E). This study compares 3E-objective and single-objective optimization methods for determining the optimal thickness of MIC across five distinct climatic zones in China. Additionally, it analyzes how factors like heating, ventilation, and air conditioning (HVAC) operational duration, climate change, grid emission factors, and building lifespan affect the optimal thickness. Results reveal that the 3E-objective optimization method achieves the highest cost-benefit ratio in carbon reduction, outperforming the energy or environmental method. Lightweight external walls, with low thermal mass, have an optimal thickness deviating from the current nearly zero-energy building standard, with deviations reaching up to 200 mm in optimal thickness. Reduced HVAC operational duration, global warming, decreased grid emission factors, and extended building lifespan contribute to a potential reduction in the optimal wall thickness by up to 140 mm. These deviations in the configuration of these factors, although they may lower life-cycle cost investments compared to the optimal thickness, could potentially be unfavorable or detrimental to reduce life-cycle energy consumption and carbon emissions. The deviation in HVAC operational duration exhibits the most significant impact on life-cycle 3E results, reaching up to 8.4 %. Climate change has a relatively minimal impact on the life-cycle 3E results. This research can advance the cost-benefit ratio in carbon emission reduction of MIC and highlight the need for flexible building standards to accommodate climatic and operational variations.

Ventilative cooling is an energy-saving technology to diminish thermal discomfort and overheating risk of buildings, meanwhile achieving high indoor air quality (IAQ). However, there is still no optimal control strategy in practice, which considerably limits its application. This study developed a typical office building model to evaluate the performance of ventilative cooling systems with different control parameters and strategies for five typical cities in different climatic zones of China. Results showed that, when the control parameter was selected as the upper limit of satisfied comfortable zone by 90% of the occupants, the adaptive thermal comfort (ATC) model, which outperformed the other models in terms of outdoor air utilization, was not necessarily optimal in terms of energy efficiency. The outdoor air utilization potential based on the indoor dry-bulb air temperature (T_d) and indoor operative temperature (T_op) control was similar, but the energy usage varies considerably, especially in the hot climatic zones. When the overheating period controlled based on the thermal comfort models was the same, the energy usage would be underestimated by 16%–38% without considering the effect of radiant temperature. The ATC-based control could have up to 37% of energy-saving compared to thermostatic control, but inappropriately low limits could make it less advantages to achieve energy-saving. The energy-saving potential associated with the PMV and ATC controls showed a completely opposite trend in the different climatic zones. The analysis results indicate that eliminating the drawbacks of the lower limit in the ATC model is an effective way to demonstrate energy-saving effectiveness. The findings of this study will contribute to the effective improvement of the application potential of ventilative cooling in different climatic zones.