Research On Thermal Calculation Model Of Ventilated Double Skin Facde In Hot Summer Cold Winter Zone

As ventilated double skin fa ade (DSF) are widely used in newly constructions,its thermal performance attracted wide interest among the HVAC specialists aroundthe world. Being one of the Translucent building envelopes, the heat transfer processof ventilated double skin fa ade is fluctuant and unsteady, this feature is particularlyprominent in hot-summer and cold-winter zone of China. How to calculate thedynamic thermal parameters of ventilated double skin fa ade quickly and accurately isthe most important thing in engineering field and theoretical research.In this article, firstly we have studied the transient heat transfer process of DSFand then established a mathematical model to calculate the dynamic thermalperformance of the DSF in typical summer conditions.The solar radiation and surface incidence angle have a great influence on the heatloads which pass through DSF and get into the occupied places. Its value varied withseason, site location even times. The optical parameters of glasses also varied with theincident angle of the beam solar radiation. In order to get those critical parameters, asolar-radiation and an optical model were built.Most of the ventilated double skin fa ade have venetian blinds inside the cavity;it can prevent the beam solar radiation directly into the interior. In general, thespectral properties of the blind were assumed to be isotropic. Some researchers takethe slat as a perfect scatters, consider all the reflective solar radiation was diffused.This assumption is useful to simplify the calculating process of energy distribution,but will certainly lose some accuracy. In this article, we take the slat as partiallydiffuse and partially specular. A cell model that consists of two slats was applied tocalculate the energy distribution for specular and diffuse solar radiation respectively.Solar ray tracing algorithm was used to track the specular reflection between upperslat and lower slat. The diffused reflection part was calculated using the angle factor.Thus the energy distribution of the venetian blind could be determined separately.Instead of using complex software, a simple and explicit zone model is presented.This thermal model combines the control-volume method and the zone approach. Eachpart of the ventilated DSF system was divided into many sub-zones. Then we canestablish the energy and mass conservation equations for each sub-zone and using the finite difference method to iterate. Heat transfer coefficients and mass flow rate in thenatural ventilate DSF was discussed separately.A numerical simulation was done in typical summer conditions in Changsha. Theresults show that the whole DSF model was reliable for analyzing the dynamic heattransfer progress through the double-skin fa ade under the weather conditions inhot-summer and cold-winter zone in china.