Quantification of heat losses through building envelope thermal bridges influenced by wind velocity using the outdoor infrared thermography technique

Abstract

Improving the thermal performance of the existing building stock is essential to significantly reduce the overall energy consumption in the building sector. A key objective is the retrofitting of the existing building envelope. A necessary first step in the building envelope optimization process is the assessment of its actual thermal performance. This assessment should be repeated after retrofitting to clearly define the improvements that were made and the heat loss reduction that was achieved. In this study, an efficient, non-destructive, in-situ measurement method, based on an outdoor infrared thermographic survey, is developed to determine the thermal bridging performance. As wind velocity significantly influences the heat losses through the building envelope, this study includes quantification of the wind velocity impact on the Ψ-value. This was assessed by undertaking ITT of the same thermal bridge at various wind velocities, in a controlled environment, in a hot box device. The results showed that the Ψ-value is highly dependent on wind velocity so that measurement of the Ψ-value taken at different wind conditions cannot be directly compared. An adjustment procedure is proposed that can be used to convert the Ψ-value measured at any wind velocity to a standard value corresponding to a velocity of 4 m/s. From a practical point of view, this adjustment procedure makes the methodology widely applicable. Highlights• A method to assess thermal bridging heat loss using the outdoor ITT is developed • The ITT approach compared with measurements from hot box and numerical predictions • The wind velocity impact on thermal bridging is quantified • Adjusting procedure for the Ψ-value measured at different wind velocities is developed • This procedure allows measured and standard Ψ-value comparison

Quantification of heat energy losses through the building envelope: A state-of-the-art analysis with critical and comprehensive review on infrared thermography

“…On the basis of this approach, the research activities of working groups are still ongoing, aiming at refining the methodology, based on infrared thermography, for the evaluation of linear thermal transmittance and thermal bridge incident factor, based on an analysis pixel-by-pixel. The approach has been tested on glazing [71], in situ [210], with a hot box with different specimens [213] and under different convective solicitations [211], and with thermal images enhancement for more accurate results [215].…”

Patents Analysis of Thermal Bridges in Slab Fronts and Their Effect on Energy Demand

“…Regarding their quantification, the ISO standard 10211 [10] establishes a calculation procedure for two-dimensional and three-dimensional evaluations yielding adequate results [20]. In spite of the existence of software which calculates the linear thermal transmittance with a high accuracy (for example, THERM), the characterization of thermal bridges constitutes one of the main study gaps in the last years: (i) Asdrubali et al [21,22], Bianchi et al [23], Garrido et al [24], and O'Grady et al [25,26] presented different methodologies to detect automatically and quantify thermal bridges through thermographies; (ii) Zalewski et al [27] developed a methodology of characterization of thermal bridges by means of three-dimensional modelling, and compared the results with measurements using temperature probes and thermographies; (iii) Tadeu et al [28] proposed a special methodology of quantification of thermal bridges through a boundary element model; and (iv) Dilmac et al [29] suggested a particular method of two-dimensional evaluation of the thermal bridge slab, beam and wall.…”

Impact of point thermal bridges on thermal properties of building envelopes

“…According to references, the total impact of thermal bridges on the heating energy need is considerable and can vary from 5% to 42% [3][4][5][6]. This influence depends on weather conditions, level of insulation, the thermal bridges constructive solution, type of building (use and geometry) and of the method used to implement its effect within the calculation of the building energy demand [7][8][9][10][11][12].…”