Comparison of Indoor Thermal Environment of an Office with Three Operational Modes of Chilled Panel and Displacement Ventilation System

摘要

Displacement ventilation (DV), chilled panel (CP) and their combination are all energy efficient air-conditioning modes. However, whether displacement ventilation and chilled panel operates individually or jointly can produce more comfortable environment and be more energy efficient is not very clear. Therefore, CFD simulations are conducted to reveal the difference between three modes: DV or CP operates individually, DV and CP jointly works.Indoor zero-equation turbulent model is adopted. Two sets of wall boundary conditions, adiabatic and isothermal conditions, axe specified to represent those of the transitional season and of hot summer season. Two joint operational modes are studied: (1) improving supply air temperature and chilled panel surface temperature, while keeping supply air velocity unchanged;(2) enhancing chilled panel surface temperature and lowering supply air velocity but keeping supply air temperature unchanged. Indoor temperature and velocity distributions are obtained for 8 cases.Results show that DV and CP system can be operated individually to meet the needs of thermal comfort in office room under adiabatic wall conditions. However, DV and CP jointly works, the vertical temperature gradient reduces. Indoor air velocity becomes weaker in combined work mode 2. Also the enhancing of the CP surface temperature offers the possibility of utilizing natural cooling source to chilled panel in transitional season.Results also indicate in hot summer conditions, if the cooling load of the room is high, DV system operated individually may lead to large vertical temperature gradient, exceeding 3℃/m in occupied zone. CP system work independently may not bring about obvious vertical temperature gradient, but condensation on the panel surface may occur if the indoor humidity increases. In comparison, displacement ventilation system operates with chilled panel may reduce vertical temperature gradient. And relatively lower indoor air velocity can be achieved by the combined mode 2, and the possibility of condensation also decreases.