R-value estimation by local thermographic analysis

IR thermography applied in a proper way is able to detect very accurately temperature difference between air and surfaces. By means of this tool is now possible to analyse the local instantaneous heat flux through the surface of a building. In case of steady thermal state, this gives the thermal performance evaluation of the building envelope. In case of a transient condition an averaging process or a system identification algorithm must be applied on time-series of such a data. In any case, it is demonstrated that a standard technique based on thermal flux meter for the thermal resistance (R-value) measurements is more affected by errors than thermographic measurements using this new approach. The method is illustrated with experimental results obtained into a residential building. A dedicated thermographic apparatus is used to map the temperature of the indoor surface of an internal wall and to measure in same positions the air temperature at 10 cm from the surface. From these data the local heat flux is detected at any point of the internal surface. A conventional thermogram of the corresponding outside surface or the outdoor air temperature history allows an easy way to achieve both thermal conductance and transmittance of the investigated wall. In this way it is possible the evaluation of both radiative and convective heat flux on a local basis with a space resolution of 1 cm. The results are here presented within a comparison with the local measurement with a thermal flux-meter device. These results are important in order to enhance energy efficiency and comfort in buildings.

[1]  Ermanno G. Grinzato,et al.  Quantitative infrared thermography in buildings , 1998 .

[2]  Ralph Greif,et al.  Natural Convection in Undivided and Partially Divided Rectangular Enclosures , 1981 .

[3]  Hazim B. Awbi,et al.  Calculation of convective heat transfer coefficients of room surfaces for natural convection , 1998 .

[4]  Emanuele Menegatti,et al.  Automatic Indoor Environmental Conditions Monitoring by IR Thermography , 2009 .

[5]  P. Brunello,et al.  Energy performance of heating/cooling panels in large enclosures , 1997 .

[6]  M. Bohn,et al.  Temperature and Heat Flux Distribution in a Natural Convection Enclosure Flow , 1986 .

[7]  Christian Inard,et al.  Thermal experiments of full-scale dwelling cells in artificial climatic conditions , 1987 .

[8]  Fred Bauman,et al.  Correlations for convective heat transfer from room surfaces , 1982 .

[9]  R. H. Marshall,et al.  Validation of heat transfer coefficients on interior building surfaces using a real-sized indoor test cell , 1990 .

[10]  Filippo de Monte,et al.  Determination of the thermal resistance of walls through a dynamic analysis of in-situ data , 2004 .

[11]  Geoffrey P. Hammond,et al.  Improved data correlations for buoyancy-driven convection in rooms , 1983 .

[12]  Ermanno G. Grinzato,et al.  Automatic air and surface temperature measure by IR thermography with perspective correction , 1993, Other Conferences.

[13]  Ermanno G. Grinzato.  Humidity and air temperature measurement by quantitative infrared thermography , 2010 .

[14]  A. Bejan.  Convection Heat Transfer , 1984 .