Indoor Thermal Environment And Transient Characteristics Of An Office With Hybrid System Of Chilled Ceiling Panel And Displacement Ventilation

Along with the development of economy and the enhancement of people's living standard, energy consumption of air-conditioning systems increases unceasingly. Though air-conditioning system has already been used very widely, more and more attention is paid to indoor thermal comfort and indoor quality it can produce and its energy consumption problems.Hybrid system of radiant cooling and displacement ventilation becomes adopted gradually in practical project and arouses wide research interest for it can provide better thermal environment more energy efficiently.Firstly, comfort indoor indexes were summarized. CFD simulation results based on indoor zero-equation turbulence model were validated using experimental data. Then, the effect of the number of grids on simulation result was investigated. And then a steady state mathematic model of a chilled panel was established and the effect of the structural parameters on surface temperatue distribution and cooling capacity of chilled panel was analyzed. The influence of panel temperature evenness on indoor thermal environment simulation result was also discussed. It is found that it has little infulence on thermal comfort in occupied zone.Choosing proper combined cooling parameters is an important step in designing hybrid air-conditioning systems of chilled ceiling panel and displacement ventilation. Different combination may bring about different indoor thermal comfort as well as different operational cost. A set of optimal combined cooling parameters were proposed by conducting 5 factors, 5 levels simulation experiments arranged by.orthogonal test design method. Under the optimal condition, the PMV value reaches zero with 5% PPD and ventilation efficiency obtain relatively high value. The individual influence of such cooling parameters as supply air flow rate, temperature and relative humidity of DV, the surface temperature of CP and the area ratio of CP to the ceiling on PMV value were studied by analysis range method and analysis of variance method. Results indicate that hybrid air-conditioning pattern can achieve the best indoor thermal environment in one among all simulation experiments. And the dynamic responses of room air to the change in supply air flow rate, which has the strongest influence on PMV, were simulated. It is analyzed how the air average temeperature and relative humidity in the occupied zone and non-occupied zone change along with time after the change in supply air flow rate was exerted. It reveals it will take about 20 minutes for the indoor air temperature to approach another steady value. And the air layer temperature just below the celing panel was higher than that of occupied zone. The dew point of the air layer is higher than the surface temperature of the chilled ceiling panel. It indicates that the possiblity of dew occur on the chilled ceiling panel is very less.Finally, the boundary condition of the external wall was specified using hourly outdoor air temperature in a typical day of Xian and using thermal properties of two types of wall structure normally used. When the optimal combination of supply air temperature, flowrate and surface temperature of the chilled panel was adopted, the best area ratio of the chilled ceiling panel to that of the ceiling was selected through simulations. The best values of the hourly area ratio of chilled panel were determined for a typical office from 8:00 A.M. to 6:00 P.M. With these cooling parameters, PMV values of the occupied zone can remain within the accepted range, -0.5 to o.5. The influence of the external wall structure and the area ratio of the chilled ceiling panel on internal surface temperature of the exterior wall and indoor PMV values were also analyzed.