基于热成像技术的牛舍围护结构传热阻测试方法

Evaluation on measure method of heat transfer resistance for enveloped structure of cattle barn based on infrared imaging method

针对传统的接触式传热阻测试方法对测试场合要求高、操作复杂、操作时间相对较长等难以应用于环境较为恶劣的畜禽舍问题,该文引入热成像技术,开展了黑龙江地区2种不同类型牛舍的围护结构热特性参数现场测试,获得了基于热成像法和传统接触式测试法下牛舍墙体、屋面、门窗的特征温度值。在此基础上,计算了牛舍围护结构材料的传热阻,并与相应建筑材料的传热阻理论计算值进行了对比分析。结果表明,对于墙体、屋面等围护结构,2种方法所获得的传热阻测试值与理论计算值的偏差小于15%;对于围护结构窗体和门,2种方法所获得的传热阻测试值与理论计算值的偏差在20%~30%之间;虽然热成像法和接触式测试法现场实测值与理论计算值之间都存在偏差,但因现场测试能综合材料老化、脱落、受潮和施工质量等实际情况,相对而言实测值的可信度更高;但综合考虑2种方法,热成像法的操作简单、便捷,可以很好地用于畜禽舍围护结构的热工性能评价。

The heat transfer resistance of enveloped building structure plays an important role in the heat gain and heat loss of building environment.It is also a crucial index related to building thermal comfort.Compared with the housing conditions of residents,those conditions of housings for animals are more complex,which are filled with heavy moisture,highly toxic gases,and high-level dust.The accumulation of these factors can have a negative effect on the thermal performance on the surface material of building structure.For minimizing the heat loss of material,it is vital to accurately measure the material heat transfer resistance in the field environment.In recent years,the infrared imaging method,an advanced technology in the area of fault diagnosis and detection,has been widely used in various industries,such as the thermal performance test of enveloped structures on industrial and civil building.It has the distinct advantage on the portable and prompt detection of surface temperatures with the visualized thermal image.This article mainly focuses on the application of infrared thermal image technology in2different forms of cattle barns in northeast region.To determine heat transfer resistance of enveloped structure,the derivation of related heat transfer equation would be taken into account.Compared with the traditional method,the infrared imaging method is more reliable to evaluate the heat transfer resistance of the enveloped structure in the cattle barn.The hand-held infrared thermal imager was used to measure the surface temperature of enveloped structure with setting the view from center passageway towards the wall of the barn.The instrument was carefully calibrated to ensure the setting parameters(emissivity,reflection temperature,humidity,and so on)to be in the optimal conditions before the measurement.For the validation of the infrared image method,the environment temperature was also recorded by the T&RH sensors with6testing points in the north and south sides of the barn.The T thermocouples were installed at the height of1.5m(the same level as standing cattle)and automatically measured the enveloped structure temperature.A data acquisition system(Agilent34972A)was applied for continuous data collection.The results showed that the thermal imaging method could be used for the detection of thermal properties in some places unavailable for the contact measurement,such as side walls,roof,and shutter.Compared with the theoretical value obtained from the theoretical calculation,these2methods both had a high agreement(absolute deviation percentage was basically within15%).However,the detection of heat transfer resistance in windows and doors by these methods was not consistent(deviation percentage was between20%and30%).Thermal imaging technology made comprehensive use of the site environment parameters and the actual heat value of enveloped structures,which was affected by materials aging,falling off,damp air conditions,scene construction quality,and so on.Therefore,the result from infrared imaging method on the detection of the heat transfer resistance is acceptable and reliable.The results of heat transfer resistance with some conventional methods,such as formula deduction and correlation equations,were significantly influenced by the precision of the measuring instrument,some accidental errors,and limitation on the defects detection.Therefore,the infrared image technology can be an alternative method for the detection of thermal properties in the housing system for animal.