The Heat Exchange Model And Experimental Study For The Hollow Block Ventilated Wall

The continuous increase of building energy consumption makes people aware of the urgency and importance of using new technologies and new methods to realize energy saving. A new building envelope named the hollow block ventilated wall is proposed based on the purpose and requirement of building energy saving in this paper. The ventilated wall is built using the hollow blocks, the cold air in summer and hot air in winter is used to flow through the cavity of hollow block, in order to carry away the cool and heat stored in walls. This technology combines the heat recovery or renewable energy use with the reduction of cool and heat stored in walls, the effect of climate on indoor environment can be decreased, temperature fluctuation of internal surface of wall can be reduced, and thus human comfort can be improved. This paper focuses on the research of the heat transfer characteristic and the experimental test of the hollow block ventilated wall. The main content of the paper is as follows:(1) A simplified dynamic thermal network model(RC model) of the hollow block ventilated wall is presented and the parameters are optimized by using genetic algorithm(GA). How to accurately determine the parameters(thermal resistances and capacitance) are very difficult, but these parameters are very important to the accuracy of the simplified model. For the parameter identification of the RC model, the frequency characteristic of the hollow block ventilation wall which is calculated by the frequency-domain finite-difference(FDFD) model(theoretical model) is as a reference to optimize the parameters of the RC model by using the genetic algorithm(GA). The results show that using genetic algorithm to identify the parameters of the simplified model of the hollow block ventilated wall is very reliable.(2) A heat exchange model of the hollow block ventilated wall which is a coupled model by the RC model and the NTU model(Number of Transfer Units model)is developed. The heat transfer characteristic in the height direction of the hollow block ventilated wall can be taken through this model. Using the heat exchange model can calculate the outlet air temperature of the ventilated wall, the heat flux of the internal and external surface of the wall and the heat carried away by the air in the cavity. The results show that the heat exchange model can well predict the heat transfer characteristic in the height direction of this new structure.(3) An experiment platform of the hollow block ventilated wall is established in this paper. The construction process and the important equipment of the experiment platform are mainly introduced. To validate the accuracy of the heat exchange model, three typical experimental conditions are selected. The outlet air temperature of the ventilated wall which is calculated by the heat exchange model and from the experimental data is chosen as a compared object. The comparison shows the two results match well, the relative error is less than 5.0% under the three test conditions. This indicates the heat exchange model of the hollow block ventilated wall is very well.