Application of 3d CFD model to analyses thermal comfort of an underground built environment

Abstract

Kotmale underground hydro electric power generating station is the first ever built underground structure (hydro electric power station) in Sri Lanka, which was commissioned in 1988. This hydro power station is situated about 25 km south west of the central hill country main city Kandy, which has a tropical climate ambient temperature ranging from 20 Celsius to 30 Celsius during the dry season. Location of the hydro power station Cavern where the three 70 MW generators, turbines and other accessories are located is 250m below the ground level. The power station cavern is accessed through a 500m long tunnel to the underground. In a structure of this nature, it is important to keep the temperature and the air quantity in an acceptable range for the well being of the occupants. The ventilation to the power station cavern is provided through a forced air ventilation system which pumps air through a 250 m long tunnel from the top. The power station cavern itself consists of three floors, where ventilation air is distributed through a duct system which runs through the floors. But, according to the past experience, it has been noticed that the rate of ventilation or the air refreshing rate is insufficient for the thermal comfort and to maintain the air quality inside of this structure. Traditional methods of evaluating thermal comfort are not capable of analyzing the air flow path of a complex built structure of this nature. Hence, this paper discusses the application of a 3D CFD model to analyze and simulate the ventilation air flow path, in order to analyze the thermal comfort of this underground built environment to find out the issues related to thermal comfort and air quality of the system that affects to its occupants i.e. operators and maintenance staff. CD Adapco star CCM+ software was used for modelling and simulating the ventilation system.