Annual evolution of the natural ventilation in an underground construction: Influence of the access tunnel and the ventilation chimney

Abstract

The knowledge of natural ventilation in underground constructions can help to optimize the design of their ventilation systems, reduce their energy consumption, and avoid the risk of accumulation of gases or toxics agents. This paper studies the natural ventilation in an underground construction throughout the year. The results show that natural ventilation is strongly conditioned by the existing gradient between the exterior and the interior temperature. The temperature of the interior walls evolves differently depending on the area and depth of construction. The access tunnel and the ventilation chimney, that is, the transition areas, are those which experience the highest changes in temperature, and play a key-role in the regulation of natural ventilation. For this reason, natural ventilation has large variations throughout the year. When the outdoor temperature is several degrees below the temperature of the transition areas, occurs a permanent entry of heavier cold air coming from the outside, which enter the cave through the lower area of the access tunnel. Simultaneously at the entrance of outside cold air in the underground construction, occurs the exit of the hottest air of the cave, via the highest area of the access tunnel, and the ventilation chimney. This phenomenon causes a homogenization of the temperature in the entire construction, despite the large distance that covers and the difference in depth of the different areas, which affect the ventilation in subsequent periods. On the contrary, when the outside temperature is higher than the inside temperature, the gradients of temperature along the access tunnel and the chimney hinder the entry of outside air. This causes a stagnation of the indoor air, heavier than the outside, which makes the indoor air to acclimate to the temperature of the walls at each point. In transition periods, during the day it is produced a similar behavior to the hot period and during the night it occurs a similar behavior to the cold period. However, there are differences in the period after the summer and in the period after the winter, due to differences in the temperature of the interior walls in each period. © 2015 Elsevier Ltd.