A large amount of energy is consumed for buildings around the world, and therefore, energy saving is being studied extensively.
Mixing ventilation system (MVS) is one of the mechanical ventilation systems that makes the entire indoor air mixed completely using the jet flow made from blast air. Displacement ventilation system (DVS) is one of the mechanical ventilation systems, which blows air with lower temperature than indoor air into the lower part of a room and causes upward flow of indoor air by buoyant force to exhaust it at the ceiling.
The basic difference between DVS and MVS is that DVS mainly relies on the buoyancy effect, while MVS uses mechanical ventilation force. As DVS is aimed at only meeting the requirements of the workplace, there is a thermal and concentration stratification between the lower and upper parts. DVS is characterized by good air quality, efficient emission of polluted air and significant energy saving effect. In the design of DVS, the height of thermodynamic stratification has to be set to be higher than the height of the workplace, but not too high, because it might cause waste and increase in the amount of air blast. So, the determination of the height of thermodynamic stratification is one of the vital problems arising in the application of DVS. In DVS, ventilation volume for keeping the temperature below the required level is too much when the cooling load is heavy. For DVS, experiments, experiences and engineering design methods have already been presented and mathematical analysis methods have been studied. However, there is little data about DVS for high-ceiling rooms.
Paek Myong Chol, a section head at the Faculty of Heat Engineering, has investigated the temperature change at the workplace when there is heat source in MVS and HDVS with the vertical supply duct by using CFD and presented its effectiveness. In addition, he has verified the existence of the effective length of the vertical supply duct in HDVS with supply ducts from the view of energy saving.
He has found that under the conditions of providing equal temperature and velocity of air inflow, the temperature of the air in the working zone depends on the length of a vertical supply duct, and that the temperature of the air in the working zone increases when the vertical supply duct is longer than the limited value.
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