Effect of the night ventilation rate on the indoor environment and air-conditioning load while considering wall inner surface moisture transfer

• A whole building hygrothermal model is presented and validated.
• The moisture transfer at the wall inner surface is considered in mathematical model.
• The effect of moisture transfer on the internal surface moisture flux is analyzed.
• Effect of ventilation on indoor environment is analyzed when considering moisture transfer.
• Effect of ventilation on air-condition load is analyzed when considering moisture transfer.

Night ventilation may improve the indoor air temperature and reduce the cooling load. However, the effects of different night ventilation rates on the indoor air relative humidity, wall inner surface temperature, inner surface moisture flux, sensible heat load, latent heat load and total load are rarely studied in terms of the inner surface moisture transfer. The present paper aims to investigate the effect of different night ventilation rates on the above items in a hot-humid climate in China. The results show the following: when the moisture absorption–desorption process at the wall inner surface is not considered, the air-conditioning load of the night ventilation at 15ACH is approximately 5% lower than that at 5ACH. When the moisture absorption–desorption process is considered, the night ventilation rate has a smaller impact on the indoor air temperature and has a larger impact on the indoor air relative humidity during the night. The night ventilation rate negatively correlates with the sensible heat load and positively correlates with the latent heat load due to the increased amount of moisture that is absorbed or desorbed at the interior wall surface. The total air-conditioning load of Case B.1, which featured a 15ACH night ventilation rate, was approximately 8% higher than that of Case A.1, which featured a 5ACH night ventilation rate.