Investigations Of Dynamic Modeling And Energy Performance For Double Skin Facade In Hot Summer And Cold Winter Zone In China

Double skin facade(DSF)is one of the most popular building envelops widely used in the modern buildings due to its advantages in terms of aesthetics,noise protection,permeability and so forth.It is comprised of two glass layers,a ventilated air cavity,and a venetian blind installed in the cavity.However,there are many unknowns of the thermal and energy performance for its complex heat transfer process,especially in the hot summer and cold winter zone in China.In other words,it is necessary to develop a systematic approach to dynamically model and calculate the energy consumption of the DSF quickly and meet the requirements of engineering application.In this thesis,dynamic modeling approaches are proposed to evaluate the thermal performance and calculate the annual energy consumption for the natural ventilated DSF with and without venetian blinds,and mechanical ventilated DSF.Economic evaluation of the DSF is performed.Optical properties of the DSF is calculated based on the net radiat ion method to establish the energy balance equations of the glass and/or blind layers with the beam and diffuse radiation separation.Meanwhile,a mixed methd combining ray tracing and radiosity method is proposed to calculate the optical properties of the venetian blind in the DSF.In this method,a shining factor is introducted to describe scattering and specular characteristics of the blind slats.The beam-beam radiation is calculated by the ray tracing method.While beam-diffuse and diffuse-diffuse radiation are calculated by the radiosity method.Numerical results are compared with the optical properties of venetian blind calculated by the radiosity method and the experimental results.It is found that the proposed model results fit better with the expe rimental results and it can be used to predict the solar heat gains of the DSF.Combined with the proposed optical method,an improved zonal model is proposed to model the natural ventilated DSF without blind dynamically.And the air flow rate in the cavity is calculated based on the airflow network and Bernoulli equation.At the same time,a simplified method is used to calculate the view factors and emissivity for the long-wave radiation.The model is validated by experiment.Moreover,some important parameters including DSF height,DSF width,and aera of the vent are analyzed.Similarly,an improved zonal approach is developed to model the natural ventilated DSF with venetian blind dynamically.The airflow in the cavity is calculated based on the natural ventilation rule and power law considering the cross air flow.The model is validated by the experiment,and the results show that the simulated results have good agreement with the experimental one.The proposed method can not only meet the requirements of engineering application,but also spend less computational time.Finally,some parameter are studied including the DSF width,the position of the blind,and the slat angle of the blind,which have great influence on the thermal performance of the natural ventilated DSF with venetian blind.An improved zonal approach of the mechanical ventilated DSF is developed to evaluate the thermal performance of it.The airflow network method is employed to describe the airflow in the cavity both considering the bl ind position and slat angle.The total pressure in the cavity is the sum of the pressure caused by the thermal buoyancy and the pressure caused by the exhaust fan.Experimental validation results show that simulation results fit well with the experimental results,and the compute speed is fast compared to the CFD method,that is,it can be used to calculate the annual energy consumption.Also the effect of the ventilation rate and the slat angle of the blind are studied.An experimental study is conducted t o compare the thermal performance of the natural and mechanical ventilated DSF.The results show that the thermal performance of the latter one is better.Thermal performance of two different types of the DSF(the double glazing is installed at the exterior and interior side of the DSF,respectively)are compared in both summer and winter season based on the proposed dynamic model.It is found that when the double glazing is installed at the interior side of the DSF has better thermal performance and it is used to simulate the subsequent annual energy consumption.Annual energy consumptions for six common building envelops of six typical cities in hot summer and cold winter zone are simulated.These envelopes are solid brick wall with double glazing window,porous brick wall with EPS external thermal insulation and double glazing window,reinforced concrete wall with EPS external thermal insulation and double glazing window,aerated concrete block wall with extruded polystyrene insulation board and double gla zing window,double glazing facade with external venetian blind,and double skin facade.The economic evaluations of these envelopes are performed.And the conclusion can be given out that the DSF has energy saving potential,but the application of DSF is economically infeasible.The proposed approach is an easy and fast method for the dynamic modeling of the DSF.Also it can be used to calculate the annual energy consumption with less computational time.