Detection Method Of Thermal Properties Inverse Analysis Of Exterior Wall By Using Infrared Technology

The building energy consumption accounts for a relatively high proportion in China.In order to improve energy efficiency and implement a sustainable development strategy,in addition to promulgating building energy conservation regulations and energy efficiency standards to guide building energy efficiency,the country also conducts thermal performance tests on existing building walls and provides assistance for building energy efficiency renovation through these methods.Existing testing methods mainly involve three aspects: energy-saving assessment of external walls of buildings,detection of thermal defects and construction quality.Commonly used detection methods are heat flow meter method,hot box method and infrared method.The infrared method is non-contact measurement.Compared with the first two contact measurement methods,it has the advantages of large detection range and fast speed.At the same time,with the use of drones,it can detect the external walls of buildings more efficiently and make the infrared method more suitable for the energy-saving renovation of existing buildings.As a temperature measurement method,the infrared method still has the defect of low accuracy,which leads to the inability to accurately calculate the thermal properties of the wall.In engineering,infrared method is usually used for qualitative analysis.In this paper,the principle of heat transfer and infrared temperature measurement is used to quantify the infrared qualitative detection in engineering applications,and a method for detecting thermal performance of external walls that is more suitable for practical engineering applications has been developed.To a certain extent,it solves the problem that the detection efficiency of the thermal property parameters of the external wall is too low or it is difficult to detect due to conditions during the energy-saving renovation of the building.In order to realize this detection method,this paper mainly conducted two aspects of research.The first aspect is the establishment of a theoretical model for the calculation of thermal properties of building exterior walls.The main purpose is to convert the infrared temperature measurement results into the thermal properties of the wall,so that the infrared detection method can quantitatively analyze the wall.Aiming at the practical problems corresponding to the three temperature laws of quasi-steady state,step heat flow response and periodic change,three reverse calculation models are established and combined with each other to solve the wall thermal properties.The three models are the inverse calculation model of the quasi-steady heat transfer of the wall,the inverse calculation model of the unsteady heat transfer under the wall step heat flow,and the genetic algorithm inversion model of the unsteady heat transfer of the wall.It is verified that the error of the three models is controlled at about 15% through experiments,and the overall error can meet the requirements of engineering applications.The research content of the second aspect of this article is to combine the infrared measurement method with the drones and improve the accuracy of infrared temperature measurement using drones.Firstly,the method of checking various parameters is improved by analyzing the error of infrared measurement.Then researches the difficult point that the long shooting distance and large deflection in infrared shooting with drones lead to many interference factors.Under the premise that the existing conventional infrared temperature measurement methods cannot exclude the influence of these interference factors,the operation procedure of checking parameters and shooting a large area before calculating the real temperature is proposed,which greatly improves the infrared temperature measurement accuracy and makes it close to the temperature measurement accuracy of the contact sensor.This detection method can effectively solve several existing practical problems,including the thermal performance test of the external wall of old buildings,the weak part of the thermal performance of the external wall of the building to be transformed,and the evaluation of whether the thermal performance of the newly built building can meet the standards.