Thermal performance of brick and stone masonry: Cumulative heat flux dataset for main orientations and under diverse seasonal conditions

This dataset consists of the hourly heat flux for four seasons and orientations of 15 different construction configurations of brick and stone masonry combined with insulation system solutions. The analysis was conducted with the use of Finite Element Modelling (FEM). The development of the models and the investigation of their thermal performance was conducted with the use of thermal modelling and numerical simulation analysis with COMSOL Multiphysics. For this purpose, a transient 2D multi- dimensional, time- dependent simulation model on finite elements was developed. The governing equations of heat transfer were considered as well as the convection and radiation heat transfer coefficients in accordance to the ISO 6946:2017 [1].


Specifications
Energy Engineering, Building Physics Specific subject area Heat transfer, Heat flux, Finite Elements Modeling (FEM), Masonry, Insulation Type of data Tables; Figures  How data were acquired Solar radiation tool (PVGIS) [2] for boundary conditions Finite elements modelling tool (COMSOL Multiphysics) for heat flux Data format Processed data Parameters for data collection Data collection for the development of the numerical simulation model was performed using experimental building elements. Geometric parameters and thermophysical properties were obtained experimentally. Data collection for the development of the temperatures profiles, imposed on the surfaces of the masonry, were obtained with the use of PVGIS. Description of data collection The thermophysical properties of the brick and stone masonry were defined using experimental methods. In particular, their thermal properties have been measured based on the analysis of the temperature response of each masonry test specimen to heat flow impulses with the use of a measuring instrument for direct measurement of heat transfer properties. The exterior boundary data for the numerical models was defined using climatic conditions data extracted from the PVGIS tool for the calendar months January (winter), April (spring), July (summer), and October (

Value of the Data
• The data provided in this work may be used as a guideline for building element configurations to improve the overall thermal and energy performance of buildings. • These data can be used for other scientific studies that are correlating brick and stone masonry configurations with insulation system solutions for the improvement of building energy performance. • The data set will support researchers to correlate the heat losses resulting from heat transfer in various building construction configurations. • By providing the data of the energy performance of widely-used building elements in the construction sector, researchers can exploit the annual total loads to develop novel energy optimisation approaches.

Data Description
In Figs. 1 and 2 , the building elements which were investigated in terms of this work are provided. The investigated configurations are described in detail in  The results of this work have been summarized and are presented in this section. Fig. 3 illustrates the cumulative heat flux values and the monthly cumulative heat flux values for the months under study for the brick and stone masonries. Summary tables of cumulative   The Supplementary Material contains the transient 2D numerical simulation models, developed in Comsol Multiphysics, which delivered the results provided in this work. The numerical simulation models include all the input information and values used for their development. For each configuration, the geometry and the thermophysical properties of the materials (density, thermal conductivity, heat capacity, diffusion coefficient) are defined. The heat transfer tab contains the equations used for the time-dependent study and provides detailed information for the physical model, the dependent variables, the heat transfer mechanisms and the thermodynamics. Furthermore, the initial values, the thermal insulation and internal and external temperatures/ temperature profiles are also provided in this tab. The mesh settings, element size and element size parameters used for each simulation study are also defined. The numerical simulation models also provide information of the study settings, including the input for physics and variables selection, values of dependent variables, as well as the mesh selection solver configurations such as absolute tolerance and time stepping. The results tab of the simulation models also contain the heat flux tables, which are presented in this work.

Experimental Design, Materials and Methods
A transient 2D numerical model based on finite elements was developed with the use of a FEM tool (Comsol Multiphysics 5.0). The parameter based on which the alternative building elements were evaluated was the total heat flux. Information on the examined meshes, the domains, the calculation physics as well as the boundary conditions is provided below, while the specific input information and values used can be found in the numerical simulation models, found in the Supplementary Material: Concerning the physics of the finite element analysis, the fundamental law governing all heat transfer is the first law of thermodynamics, commonly referred to as the principle of conservation of energy.
The assumptions made for simplification of the solved equation are the following: • Heat transfer interfaces use Fourier's law of heat conduction • Mass conservation, ie density and the velocity are related through equation • Viscous heating and pressure work negligible • Heat transfer in solids (velocity = 0) Concerning the computational domain, two-dimensional rectangular multi-layer geometries, simulating 15 different construction alternatives of brick and rock masonries were developed. Triangular meshing was employed, of which the maximum and minimum element size were 0.0064 and 1.28E-5 meter, respectively. The maximum element growth rate was 1.1, and the curvature factor 0.2 with the resolution of narrow regions being 1. The preset for the mesh quality was chosen to be extremely fine, with the purpose of the accuracy of the results being directly proportional to the mesh size.
The boundary conditions were set in the form of a temperature profile for the external surface of the wall and constant temperature for the internal surface of the wall. Regarding the exterior wall boundary conditions, the use of the sol-air temperature was employed. Sol-air temperature T_(sol-air) is defined as The analysis was conducted for four calendar months, delivering representative results for the entire calendar year (January -Winter, April -Spring, July -Summer, October -Autumn), as well as for the four main orientations (azimuths 0 °, 90 °, 180 °, and 270 °). The ambient temperature values and the total solar irradiation for Nicosia, Cyprus, were retrieved from the PVGIS [2] tool of JRC, making use of also two reanalysis-based solar radiation datasets, namely ECMWF [3] ERA-5 and COSMO-REA [4] . Post-processing of the Tsol-air values was conducted, to define the most representative day of the month, to be used for the analysis. For the overall heat transfer coefficient h o , the convection and radiation heat transfer coefficients were considered according to the EN standard 6946:2007 [1] . The heat exchange with the sky dome was neglected. Regarding interior boundary conditions, the internal temperature was assumed to be 20 °C.

Ethics Statement
No ethical issues are associated with this work.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships whichhave, or could be perceived to have,influenced the work reported in this article. 20 cm thick exterior brick masonry wall with two layers of XPS insulation installed on either side and 4 layers of the repair cement mortar hereby developed S1 55 cm thick two-leaf exterior stone masonry wall without thermal insulation or coating (reference case) S2 55 cm thick two-leaf exterior stone masonry wall without thermal insulation and 1 layer of the NHL repair mortar hereby developed S3 55 cm thick two-leaf exterior stone masonry wall without thermal insulation and 2 layers of the NHL repair mortar hereby developed applied on one side of the wall S4 55 cm thick two-leaf exterior stone masonry wall without thermal insulation and 2 layers of the NHL repair mortar hereby developed applied on either side of the wall S5 55 cm thick two-leaf exterior stone masonry wall with XPS thermal insulation and 2 layers of the NHL repair mortar hereby developed S6 55 cm thick two-leaf exterior stone masonry wall with XPS thermal insulation and 2 layers of the NHL repair mortar hereby developed S7 55 cm thick two-leaf exterior stone masonry wall with XPS thermal insulation and 3 layers of the NHL repair mortar hereby developed S8 55 cm thick two-leaf exterior stone masonry wall with XPS thermal insulation and 3 layers of the NHL repair mortar hereby developed * B: Brick Case: S: Stone Case.