A Study Of The Heat Transfer And Energy Performance Of Exhaust Air Insulation Window For Building Application

Window plays important roles in buildings.It may tend to result in adverse effect to building energy efficiency since the window is the weakest insulation of building envelope components.The advanced windows can significantly reduce the building energy consumption and also provide a suitable indoor environment with a satisfactory thermal and visual comfort.This study proposes a concept of exhaust air insulation window.The window consists of three glass panes,two air cavities,and built-in Venetian blinds.It allows the exhaust air from conditioned room to be ventilated through the cavity between the glass panes to ambient.Part of the heat/coolth of the exhaust air is recovered and utilized to remove the heat loss/gain through the window,and then the temperature of the indoor side surface of the glass pane will be made close to that of indoor air,resulting in reduction of the cooling/heating load through window.Such a window system can be regarded as an exhaust air heat recovery device in buildings.The heat transfer characteristic and energy performance of the exhaust air insulation window are investigated with theoretical analysis,numerical simulation and experimental measurement.The main contents of this paper are as follows:(1)A two-dimensional zonal model is developed to analyze the insulation mechanism and thermal behavior of the exhaust air insulation window in this study.The optical properties of the entire exhaust air insulation window are obtained by using dynamic optical method,which is based on the energy balance of each component.In addition,the experimental tests are carried out in a full-scale test cell.The two-dimensional zonal model is validated by comparing the simulation results with the experimental measurements.Further,the applicability of the proposed model in mechanically ventilated double skin facade is also analyzed.The model simulates the facade in both steady-state and unsteady-state conditions and is validated by comparison with the measured data reported in a published literature.(2)Numerical simulations are carried out to compare the thermal performance of the exhaust air insulation window with that of the blinds window and low-emissivity(low-e)window in hot summer and cold window zone in China.Simulation results show that,in comparison with the blinds window and low-e window,the exhaust air insulation window can effectively reduce the temperature difference between the interior surface of window and the indoor air,resulting in the reduction of heat gain in summer and heat loss in winter.(3)The parametric analysis is also conducted to optimaze the window design.The effects of air flow velocity,width of air cavity,slat angle,and slat reflectance on thermal performance of the window are investigated.Moreover,to study the possibility of condensation on window surface in winter condition,the impact of indoor temperature and indoor humidity are tracked.The results indicate that the air flow velocity has a great effect on the thermal performance of the window,and the effect of cavity width is not significant.The slat angle and slat reflectance have great impact on the optical properties of the window.Adjusting the slat angle may be an effective approach to control the indoor solar heat gain.(4)The proposed model is applied to calculate the temperatures of glass layers for evaluating the hourly thermal performance of the window.The annual energy performances of the exhaust air insulation window,blinds window,and low-e window are calculated and compared.The investigation is carried out for different climate zones in China in order to generalize the window applications.Simulation results show that the exhaust air insulation window can achieve dramatically low annual energy consumption compared to the blinds window and low-e window.The advantageous performance of the exhaust air insulation window pertains to different climate zones.(5)Comparison of heat recovery performance between the exhaust air insulation window and traditional heat recovery ventilators is presents.The impact of fresh air rate on heat recovery performance of the window is discussed.Different climate zones are covered.The results demonstrate that the exhaust air insulation window performs much better than traditional heat recovery ventilator in cooling season,but its performance is inferior to the traditional heat recovery ventilators in heating season.Such a window may provide alternative solution for recovering the low-grade energy from air-conditioning exhaust air.(6)The effects of solar radiation and window performance on thermal comfort are investigated.A mathematical model is developed to calculate the mean radiant temperature of people in the presence of solar radiation.The predicted mean vote and predicted percentage of dissatisfied are chosen as the thermal comfort index.Considering the non-uniforn distribution of irradiated zone inside a room,the distribution of thermal comfort level at different locations in the room is analyzed.Results shows that the exhaust air insulation window can reduce the effects of long-wave radiative and solar raidition on thermal comfort and enhance the indoor thermal environment.A comprehensive study of the heat transfer and energy performance of exhaust air insulation window is conducted in this dissertation.Above studies have shown the advantageous energy performance and thermal comfort of the exhaust air insulation window.The study will provide fundamental theory and analysis tool for the novel window.Basic data will also be suppled for possible engineering application.