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

It is well-known that on-site measurements are suitable for verifying the actual thermal performance of buildings. Performance assessed in situ, under actual thermal conditions, can substantially vary from the theoretical values. Therefore, experimental measurements are essential for better comprehending the thermal behavior of building components, by applying measurement systems and methods suitable to acquire data related to temperatures, heat flows and air speeds both related to the internal and external environments. These data can then be processed to compute performance indicators, such as the well-known thermal transmittance (U-value). This review aims at focusing on two experimental techniques: the widely used and standardized heat flow meter (HFM) method and the quite new thermometric (THM) method. Several scientific papers were analyzed to provide an overview on the latest advances related to these techniques, thus providing a focused critical review. This paper aims to be a valuable resource for academics and practitioners as it covers basic theory, in situ measurement equipment and criteria for sensor installation, errors, and new data post-processing methods.

Active Thermal Method Applied to the In Situ Characterization of Insulating Materials in a Wall

An in situ estimation of the thermal properties of bio-sourced building wall insulation components is of critical importance in improving both the energy efficiency of buildings and the development of construction materials with a smaller environmental footprint. Depending on weather conditions, passive methods are not always feasible; they require time to conduct lengthy testing and may lead to significant uncertainties. This article presents an active method based on power dissipation via flat electrical resistance. The method can be implemented regardless of outdoor weather conditions and is suitable for walls with high overall thermal resistance for which the small average component of the through flow is difficult to estimate. Measurements are conducted of both wall input flows and temperatures. An inverse method, derived from a finite difference model of 1D transfers along with a multi-objective approach, enables the characteristics of a two-material assembly to be identified. A multi-objective method was chosen to solve the problems of high correlation between the thermal parameters of the model. However, the method requires the use of two temperature sensors integrated inside the wall. Following a laboratory validation phase on a PVC/plasterboard assembly, the method is implemented on an actual wall. A coating/hemp concrete assembly is also characterized as part of this work program. The thermal conductivity of the hemp concrete block was estimated at 0.12 W m−1 K−1 and is consistent with values found in the literature.

Heat transfer through brick walls for designing the building fabric

The main aim of the study is to analyze the heat transfer through the clay brick walls of the residential building to find out the dominant mode of heat transfer and incorporate various materials in the wall to reduce heat loss and increase energy efficiency. The transient thermal analysis was performed using the finite element method, and by employing a CFD program focused on heat transfer processes. Later, two models of building wall fragments incorporating the Phase change materials were developed to identify the optimal position of the PCM layer inside the wall and to investigate the role of PCM on the heat transfer rate. Insulation was done with the different types of plywood and finite element simulation was performed to study the change in heat transfer rate. Inserting plywood into the sandwich material with Chinese plywood can reduce the heat transfer content.

Heat transfer through brick walls for designing the building fabric

The main aim of the study is to analyze the heat transfer through the clay brick walls of the residential building to find out the dominant mode of heat transfer and incorporate various materials in the wall to reduce heat loss and increase energy efficiency. The transient thermal analysis was performed using the finite element method, and by employing a CFD program focused on heat transfer processes. Later, two models of building wall fragments incorporating the Phase change materials were developed to identify the optimal position of the PCM layer inside the wall and to investigate the role of PCM on the heat transfer rate. Insulation was done with the different types of plywood and finite element simulation was performed to study the change in heat transfer rate. Inserting plywood into the sandwich material with Chinese plywood can reduce the heat transfer content.

Faience Waste for the Production of Wall Products

Increasing the efficiency of using gypsum binders can be carried out by using not natural gypsum raw materials, but calcium sulfate-containing waste from various industries (phosphogypsum, borogypsum, citrogypsum, etc.). As the main source material in the work, we used gypsum-containing waste from a faience factory in the form of waste molds for casting dishes, souvenirs and plumbing fixtures. It has been established that the optimal binding system is formed by mixing powders of dihydrate technogenic gypsum from a coarse and fine earthenware factory with average particle diameters of 3.473 microns and 3.065 microns in a percentage ratio of 30:70, respectively. Using a computer software developed by the authors, which makes it possible to simulate the microstructure of a raw mixture taking into account the contact interaction of particles and calculate the average coordination number, models of binary packing of particles were constructed at various ratios of their diameters. Studies of the strength of composites obtained on the basis of bidisperse systems have shown the presence of an extremum in the region of mixtures containing 30% coarse powder. With optimal packing, a large number of phase contacts are formed due to the regulation of the grain composition of the bidisperse system. It was revealed that a brick based on the waste of two-water gypsum from earthenware production has 2.5–5 times better characteristics of compressive strength than traditional building wall products based on natural gypsum. At the same time, the strength immediately after molding is more than 3 times higher than that of traditional gypsum products. Even higher indicators are achieved when adding microcalcite in addition to the waste of earthenware production, in this case, the compressive strength is 3–6 times higher, and the strength immediately after molding is almost 3 times higher than that of traditional gypsum products.