A numerical study on the effects of natural ventilation on summer nighttime indoor temperatures in an urban area

Abstract

Natural ventilation is a simple and eff cient method for nighttime passive cooling of buildings to improve residents’ comfort and reduce air conditioning. The effectiveness of ventilative cooling depends on the number and arrangement of the openings and local wind and temperature difference between indoor and outdoor. However, natural ventilation works only if cool air is available in the surrounding of a building and when this cool air f nds a way to inf ltrate indoors. In this paper, numerical models are used to simulate the penetration depths of cool air from the rural countryside into a residential area and to estimate the local cooling potential for an indoor environment of buildings. The results demonstrate that the country breeze is an important process to transport cool air during the night, but, due to the limitations in strength and depth, it is only eff cient in the f rst 100–200 m of the outskirts. Based on numerical experiments for a standard room with two windows, an empirical relation was derived to estimate indoor cooling depending on local wind speed and local temperature difference. This relation was used to calculate individual nighttime room temperatures of all buildings in a residential area. It was found that indoor temperature follows the ambient temperature with a delay and cooling is only half as great as outside the building. In addition, the models are used to demonstrate the cooling effect of the country breeze by calculating for a decade the number of days in the summer months when nocturnal minimum room temperatures are below a given threshold.