Investigations On Indoor Thermal Environment In Warm-air Heating Rooms By Impinging Jet Ventilation

Air-conditioning system and mechanical ventilation system are essential ways formaintaining good indoor air quality in most public buildings and residential buildings in urbanareas. When an air conditioning mode is chosen, the most important thing is to ensure thedemands of indoor air temperature, humidity and thermal comfort for occupants. However, inwinter seasons, when large-height spaces exist in buildings, warm supply air will move to theupper part of the spaces by the buoyancy effect, and thus it is difficult to maintain acceptablethermal environments in the lower zones of the rooms for the occupants. Compared withconventional heating systems, impinging jet ventilation (IJV) systems directly introduce the warmair with high velocity downwards onto the floor and spreads over a large area. This way avoids thedisadvantage of the conventional heating modes that the warm air is difficult to reach the occupiedspace. Furthermore, IJV can improve the temperature distribution of large-height spaces andreduce energy consumptions of air conditioning systems.Based on the previous studies, large-height spaces with local heat loss at the sidewalls or theceiling of the room are considered as important factors which affecting indoor thermalenvironment in the present study, and numerical simulation has been used to analyze the flowfields and temperature distributions in the warm-air heating rooms by IJVs in winter seasons. Inaddition, thermal environments under the conditions that the rooms with different supply heightsand floor-heights by the IJV are also studied by using CFD simulations, and indoor thermalenvironments in both CAV and VAV systems are analyzed and discussed.The results show that in a VAV system, the lower air velocity, the more obvious warm air bythe thermal buoyancy effects. With increasing supply air velocity, warm air can reach the centerpart of the bottom of the room. In a CAV system, as the air temperature increases, the supplytemperature difference also increases, and the thermal buoyancy affects become more significant.,The warm air can reach the center position of the room with the decrease of supply air temperaturedifference. When the supply height is low, the warm air staying time in the room at the bottom will be increased, meaning that heating time in this zone will also be increased. When the ceilingis the main position of heat loss, the indoor temperature will distribute uniformly in the wholespace, and downdraft from the ceiling has no effect on the local flow field in the lower zone of theroom.When heat loss is mainly contributed by the sidewalls, although the cold air sinking along thecold surfaces has a significant effect on the trajectory of the warm jet, the warm jet reachingdirectly to the floor can also overcome the adverse effects of the cold air, and eliminate theshortcomings that the lower temperature of the lower part of the large heating room. In addition,the results also show that the ankles have a relative high risk that draught sensation out the rangeof human comfort zone. It is necessary to optimize the air parameters for eliminating or reducingdraught sensation.