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Development of an instrument for measuring and controlling the thermal resistance of building walls for direct on-site use

In an effort to improve the energy efficiency of buildings, performances of construction materials are currently being verified based on samples extracted and tested in the laboratory under a set of very specific conditions. In response to the need for in situ controls to obtain more representative results of real-world responses, an instrument for measuring the coefficient of thermal transmission on an external building wall will be developed through use of an active method coupled with an uncertainty estimation.

Background, challenges and objectives

The extent of thermal insulation used on solid walls remains critical to improving the energy efficiency of buildings. The thermal performance of all insulation introduced must be easily controlled as part of any anticipated building renovation, during construction, upon delivery and throughout its useful life. The need for an in situ wall control method is thus more pressing than ever. Such full-scale wall measurements offer an attractive complement to the more comprehensive, holistic building energy assessment methods (e.g. co-heating).

The physical parameter representing the quality of a structural shell from a thermal insulation standpoint is thermal resistance. Methods presently exist to measure this magnitude, whether in the form of laboratory or exploratory measurements, or as part of international standards or draft standards. None of these methods however actually fulfills the condition of guaranteeing a universal measurement, i.e. one that is: applied to any type of wall or building, conducted any time of year, measured over a short duration, easy to use, available at a modest cost price, and able to limit uncertainty.

An in situ measurement device meeting these underlying specifications and based on infrared thermography, all within an active approach, will be developed within the scope of the RESBATI Project. The uncertainties associated with results output by the instrument will then be evaluated by both introducing a Bayesian approach and identifying its application limitations.

The implementation strategy will consist of determining the thermal resistance of several types of solid walls at various scales:

  • reference methods using a guarded hot plate (basic LNE instrument) will serve to characterize this parameter at the material level under laboratory conditions;
  • the use of climate-controlled chambers (i.e. REBECCA at the LNE facility) and guarded hot boxes, for which environmental conditions and thermal constraints are perfectly controlled and known, will yield the thermal resistance of building walls at the laboratory scale;
  • measurements at actual instrumented sites will facilitate conducting field qualifications.

The prototype, based on infrared thermography in an active mode (as developed by the Themacs Engineering company), can thus be qualified through use of many installations made available by project partners and by performing numerical simulations of heat transfers based on various configurations (COMSOL model). LNE has contributed its array of skills and resources to this project in the area of thermal characterizations over a range of scales, in addition to its high level of expertise in uncertainty evaluation methodologies aimed at enhancing the reliability of data output. LNE's network of contacts (including FBE and ALEC) will help improve the system to better meet future users' expectations.

Scientific and industrial impacts

Measurement instrument prototype featuring an implemented thermal data processing model, along with development of a corresponding uncertainty evaluation model.


CERTES / IFSTTAR / CEREMA / CSTB / Themacs Engineering / AFNOR


Associated projects

ANR RESBATI - In situ thermal resistance measurement of building walls – Coordination provided by CERTES (Study and Research Center focusing on Thermodynamics, the Environment and Systems)