Optimum configuration of internal walls in intermittently conditioned rooms with different ventilation-behavior during off-periods and air conditioner operation durations

Investigations focus on optimizing insulation placement and thickness within internal walls of rooms equipped with intermittently operated air conditioners (AC), specifically targeting buildings located in China's Hot Summer and Cold Winter region. To achieve this objective, cooling and heating transmission loads for internal walls with varying insulation thicknesses, both internally and externally insulated, are calculated using EnergyPlus. Calculations are repeated across different air change rate (ACH) during AC off-periods and for varying AC operation durations. Subsequently, these transmission loads facilitate the determination of the optimal insulation position and thickness. The findings demonstrate that the internal walls with inside insulation (Wall-2) achieves an energy-saving rate of approximately 16–20 % during the cooling season and 30–60 % throughout the heating season when compared to that with outside insulation (Wall-1). Moreover, Wall-2's energy-saving advantage over Wall-1 is further accentuated with heightened ACH during off-periods and reduced durations of AC operation. Additionally, the optimal insulation thickness for Wall-2 was determined to be 0.06 m, 0.08 m, and 0.098 m for AC operation durations of 4 h, 7 h, and 10 h, respectively, with ACH having no impact on this optimal thickness. Life cycle savings varied between 254.56 and 552.31 ¥/m2/year, while payback periods varied between 1.76 and 2.33 years. These two indexes are both influenced by AC operation durations and ACH. Finally, the total energy consumption for cooling and heating is reduced by 40–50 %, when the internal wall is insulated to the optimal thickness internally.