Influence of HFM Thermal Contact on the Accuracy of In Situ Measurements of Façades’ U-Value in Operational Stage

Abstract

Accurate information on the actual thermal transmittance of walls is vital to select appropriate energy-saving measures in existing buildings to meet the commitments of the European Green Deal. To obtain accurate results using the heat flow meter (HFM) method, good thermal contact must be made between the heat flow meter plate and the wall surface. This paper aimed to assess the influence of the non-perfect thermal contact of heat flow meter plates on the accuracy of in situ measurement of the façades’ U-value when a film was applied to avoid damage to the wall surface. Given the fact that to avoid harm to the wall surface, the laying of a film is a usual procedure in the installation of equipment during the building’s operational stage. The findings show that deviations between measured U-values when an HFM was installed directly on the wall surface and when an HFM was installed with a PVC film were found to differ significantly from the theoretical effect of including a PVC film during the monitoring process.

Comparison between Heat Flow Meter (HFM) and Thermometric (THM) Method for Building Wall Thermal Characterization: Latest Advances and Critical Review

“…Non-one-dimensional heat flows can contribute with uncertainties in the range of 1-5% [20]. Moreover, practices for protecting wall surfaces during in situ measurements (such as installing a PVC film) can cause U-value deviations ranging from 19% to 21% [41]. Different heights between the heat flow plate and the internal air temperature sensor can affect the results with inaccuracies ranging between 17% and 22% [24].…”

Non-Destructive Testing in Civil Engineering

“…For reliable testing using the heat meter method (HFM), good thermal contact should be provided between the heat meter plate and the surface of the wall. The aim of the article [16] was to assess the effect of an imperfect thermal contact of the heat meter plates on the accuracy of the in-situ measurements of the U value of the facade after applying foil. The foil was applied in order to avoid damage to the surface of the wall, which is a normal procedure during the operational phase of a building.…”

Combining Deep Learning and the Heat Flux Method for In-Situ Thermal-Transmittance Measurement Improvement

“…Policy measures often limit the U-values of building elements, but when we solve a problem of great importance, it is better to analyze the problem with numerical methods, since dynamic parameters such as heat storage are included in the analysis, so that we can, for example, optimize the thickness of the insulation layer so that we have a larger U-value but better energy efficiency when considered all year round [44]. All results are compared with the U-value defined in this subsection, since the analyzed specimens from the experimental research have known layers and it is common in the literature ( [23,27,33,[45][46][47]) to compare the analyzed solution with the theoretical U-value defined in this way.…”

“…It must have low thermal resistance to ensure that it does not have a large effect on the heat flux, and high sensitivity so that it can register a sufficient signal value at low heat-flux rates. When installing the sensor on the measuring element, it is recommended that no material be used between the element and the sensor, because even though this is theoretically permissible; in reality, it will result in relative differences by more than 20% when comparing the measured U-value with the expected [45]. In addition to the heat-flux sensor, the device for standardized U-value measurement contains two temperature sensors for measuring outdoor and indoor temperatures.…”