The tomographic method for measuring 3-D temperature distribution based on measurement of resistance of linear resistive converters

: pp. 66-73
Lviv Polytechnic National University
Lviv Polytechnic National University

The application of infrared thermography as a method of estimation of heat losses of building structures is becoming more popular within the resolve the issues of power resources economy, determination of energy efficiency and increasing of buildings thermal protection. It should be remembered that the output result of buildings thermal imaging research is thermal temperature distribution of the investigated surface on the thermogram. Other information, including the value of the heat losses from the surface of the building envelopes, is gotten by analytical method, which involves the construction of certain algorithm. As the results of the review of recent researches and publications we can conclude that the usage of thermal imaging research is mainly limited by finding places with thermal field deviations from basic values and recognition that they are defective. Quantitative processing of heat losses that are related with it is missing out. Therefore, in the article the brief overview of current methods of heat losses calculation is provided, their features and weaknesses are identified and the method of calculating of heat losses of the building envelopes surface, that is based on the results of thermal imaging research depending on resistance of the thermal transmittance and temperature gradient of the basic and defect areas, is developed. Methods, that are provided by acting normative documents of Ukraine, optimally satisfy the conditions of complex heat exchange because they take into account within the usage of the resulted and subjunctive thermal transmittance coefficients all three types of heat exchange, namely conductivity (through heat conductivity of material), convection (through heat transmission) and radiation (through heat emission). Thus, if we can find all unknown values in the methods formulas such algorithms give us possibility to determine the basic value of building envelope heat losses for a specific rooms and building in general. The negative aspect of the usage of these algorithms is proximity of calculation (for example, as a result of surface heterogeneity of the building envelopes) and the reference to table values of most variables, which can significantly vary from the actual values as a result of the building exploitation, the influence of climatic conditions, the repairs etc. In addition, the awkwardness of the calculations and the need of the simultaneous availability of a large number of normative documents increase the time that is required to their realization, respectively the cost of such work, as well as the growth of subjective component of calculations error. Therefore we propose to add to the normative methods method of heat losses calculation of building that is based on the results of thermal imaging research. The first algorithm involves the determining of the value of resulted resistance of thermal transmittance of defective area using its basic value from formula of the surface temperature distribution of the building envelopes. The second algorithm allows to determining the growth of heat losses compared to its value of the basic area using the identified quantity of the relative resistance of thermal transmittance. The disadvantage of these two algorithms is that to calculate the heat losses we must have information about the structure of the building envelope (its basic area) to determine the resulted resistance of the thermal transmittance of the construction. The effectiveness of these two algorithms is justified in the case of simulation of potential thermal characteristics of the building on the results of the implementation of the recommendations for building thermomodernization, when the resulted resistance of building thermal transmittance is predetermined. The third algorithm allows to consider that in practice in real conditions operators have to work with the buildings of long time exploitation, for which its thermal characteristics are changed due to influence of various factors or data of these characteristics are absent. In this case, in calculating of heat losses we have to be limited only by the data of thermogram and the results of accounting of the research conditions to determine the resulted resistances of basic and defective areas. For this we provide the creation of the system of two equations based on the formula of surface temperature distribution of the building envelopes. Creation of such system is possible in three variants. Selection of each of them depends on the thermograms information of building and the possibility of second thermal imaging research, because each of the options makes its own budget of uncertainty in the resulting value of the resulted resistance of thermal transmittance. The following algorithm for determination of the heat losses suggests their definition only in the radiative component of heat flux. It allows to limit the minimum number of input variables, whose values are provided exclusively by thermal imager and technical documentation on it. It should be remembered that such losses are always smaller than losses that are determined by the total heat flux. On the basis of the calculation of building heat losses increase their monetary evaluation is conducted. It helps to estimate the recoupment of work to eliminate the sources of such heat losses.

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