The Research Of Wall With Adjustable Heat Transfer Coefficient

Because of the constant heat transfer coefficient for traditional building wall,it is not effective for buildings using outdoor air for cooling or heating indoor air timely in large temperature daily range areas.In order to effectively use the outdoor air as natural cold/heat source to cooling/heating the building indoor air and reduce building energy consumption in these areas,this paper puts forward the concept of the wall with adjustable heat transfer coefficient varied with outdoor temperature.The main characteristic of the wall with adjustable heat transfer coefficient is the automatic adjusting for heat transfer coefficient according to the change of outdoor temperature that increases "good" heat transfer and reduces "bad" heat transfer.While the essence for energy saving of the wall with adjustable heat transfer coefficient is the use of natural outdoor cold/heat source,mainly the energy contained in outdoor air.This article introduces the principle of this new wall for adjusting its heat transfer coefficient and gives a form of the real utilization.Then sets up a heat transfer performance test-bed to test and analyze heat transfer coefficient of the control layer.This study also testes the heat flux density and temperature difference of the left test layer by analyzing the changing relationship and its influence on the heat transfer coefficient adjusting layer,which in the condition of changing the water filling height percentage of the layer total height from 0%(for all air heat transfer stage)to 25%,50%,75%and 100%(for all water heat transfer stage)in the stable temperature conditions of 30?,40? and 50? at the same time.The test results show that the equivalent heat conductivity coefficient of the control layer of heat transfer coefficient range from 0.024W/m ·K to 0.102W/m-K with stable temperature at 30?,the heat transfer coefficient range from 0.026W/m·K to 0.127W/m ·K with stable temperature at 40? and 0.038W/m·K to 0.180W/m·K at 50?.The change multiple of the equivalent heat conductivity coefficient can reach 4-5 times in the condition of high and low thermal resistance.By analyzing the heat transfer theory this paper proposed,we established a mathematical model of the new wall,and analyzed the influence of the heat transfer characteristics under different water filling height and thickness of cavity.Theoretical calculation results show that the equivalent heat conductivity coefficient increases with the increasing of cavity thickness.The equivalent heat conductivity coefficient?e of the cavity ranges from 0.048W/m-K to 0.336W/m-K at high heat transfer coefficient working condition(for all air heat transfer stage)with the water filling height increasing while the thickness of cavity range from 0.003-0.039m,it ranges from 0.655W/m·K to 12.641 W/m·K at low heat transfer coefficient working condition(for all water heat transfer stage).The change multiple of the equivalent heat conductivity coefficient can reach 2-35 times of the cavity.At the same time,we analyze energy conserving potential of the wall with adjustable heat transfer coefficient,which in the different partition of typical city in winter and summer climate in China.Calculation results show that the energy saving effect is more significant by using the wall with adjustable heat transfer coefficient as building exterior insulation materials compared with general materials under the condition of regional outdoor meteorological parameters,especially in the summer,the energy saving rate ?t can be as high as 66%,59%and 66%respectively in Harbin,Lan Zhou and Kun Ming.It also puts forward the other possible structures of this new wall and the application which combined with the sunlight greenhouse drip irrigation system in the end of this article.