In this study, the internal environment such as the air temperature, humidity, and wall temperature of the underground utility tunnel, was analyzed. The current status and problems of the air conditioning system were examined by analyzing the capacity of the exhaust fan and the air velocity inside the utility tunnel. The field experiment showed that the utility tunnel has a relative humidity of 95% or higher for most sections during summer. The deviation of the internal air temperature was about 4 ℃ depending on the section, and the dew condensation occurred. However, most of the exhaust fans has a capacity below the standard minimum air velocity of 2.5m•s -1 . In particular, in the section where dew condensation occurred, the air velocity was 0.26 to 0.97 m•s -1 , indicating the presence of stagnant air inside the facility. Therefore, this study attempted to minimize dew condensation by calculating the proper exhaust fan capacity using computational fluid dynamics and installing circulation fans and duct systems in the section where the dew condensation occurred. As a result, when a circulation fan was installed, it was possible to increase the air velocity inside the utility tunnel, and the relative humidity could be reduced by about 78%. By installing a duct, the direct supply of external air or the discharge of internal humid air was simulated for the section where dew condensation occurred. The result showed that the relative humidity could be reduced by about 78% when the duct system was operated in the intake direction. INDEX TERMSCondensation, CFD, Circulation fan, Duct, Ventilation, Underground utility tunnel I. INTRODUCTION A. THE CONCEPT AND CURRENT STATUS OF THE UNDERGROUND UTILITY TUNNELAn underground utility tunnel is a structure that accommodates and supplies two or more types of urban lifelines such as pipelines for electricity, gas, water supply, telecommunication, and sewage. In addition, it is a facility installed underground to improve the aesthetics, preservation of road structures, and smooth flow of traffic, especially in urban areas [1]. If a single pipeline for each electricity, gas, and water is constructed in underground, the increased cost due to construction work and the formation of a complex underground structure network can cause problems in the This article has been accepted for publication in IEEE Access.

A Venlo-type greenhouse with a continuous roof vent (CR-Venlo greenhouse) was proposed by the Ministry of Agriculture, Food and Rural Affairs, South Korea (2019) for natural ventilation even during summers. It is ventilated through the buoyancy effect of the heated air using the high eave elevation. However, the CR-Venlo greenhouse was not distributed domestically, and its ventilation efficiency was not quantitatively evaluated. We aimed to analyze the natural ventilation efficiency of the greenhouse according to the eave height, using computational-fluid-dynamics. The simulation model was analyzed for hot summer conditions. The target greenhouse is ventilated only through the roof vent with all roof windows open; therefore, the air introduced through the roof window is easily exhausted. To evaluate the efficiency of ventilation, the external air entering through the roof window was calculated and evaluated. The amount of incoming air varied greatly with the location of the span and average temperature of the greenhouse; The temperature of the crop zone decreased lognormally with increasing height of the eave. Moreover, the ventilation efficiency of CR-Venlo greenhouse could be increased by improving the ventilation structure such as a shape, position or combination of roof window.