Analysis of the characteristics of bimetallic and semiconductor heat flux sensors for in-situ measurements of envelope element thermal resistance
Oleksandra Hotra, Svitlana Kovtun, Олег Декуша
Abstract
Monitoring of the thermal resistance of building envelopes for assessing their energy efficiency is carried out through in-situ measurements of the heat flux. It is therefore necessary to take into account not only the heat transfer conditions of the studied object but also the characteristics of the measuring instruments, which may depend on these conditions. This paper presents the results of a study of the characteristics of heat flux sensors of two types —bimetallic and semiconductor — which are the most common in the control of building envelopes. The case studies were focused on the characteristics of the sensors, such as the conversion coefficient (inversely proportional to sensitivity to the heat flux), the temperature dependence of the conversion coefficient, the response time of the sensors, and the emissivity of the sensor surface. The conversion coefficient of a bimetallic sensor was determined under the conditions of conduction and radiation supply of heat energy, which revealed the dependence of the conversion coefficient on the heat transfer conditions of the sensor surface. The value of the emissivity of the semiconductor sensor surface is lower than that of bimetallic sensors, and the time constant of bi-metallic sensors is two times less than that of semiconductor sensors. Verification of the obtained results was carried out by studying the metrological characteristics of the multi-channel thermal resistance control system, which included bimetallic heat flux sensors as sensitive elements. Thus, we suppose that the results of our study could be used to improve the accuracy in measuring the thermal resistance of building envelopes by the correct selection of heat flow sensors, or by making corrections to the measurement results that take into account the influence of experimental conditions on the characteristics of the sensors.