DS0602 -

In-situ measurement of thermal resistance of building envelopes – RESBATI

The objective of RESBATI project is to develop an experimental device for the in-situ measurement of the thermal resistance of building walls.

The initial objective of the RESBATI project was identified bacause at this time, there is no universal method allowing this kind of measurement in in-situ conditions, whereas successive thermal regulations define higher and higher levels of thermal performance of building envelopes. Moreover, existing methods are not useful for in-situ characterization of walls with high insulation level, i.e. in conformity with the active french thermal regulation.

The main challenge is to develop a portable device that can be used simply by professionals at several stages of the construction of a building.

The measuring equipment developed within the framework of project RESBATI will involve changes of practice of the professionals of the building guaranteeing a satisfactory thermal performance of the opaque walls. It will contribute to the lawful transition from an obligation of means to a warranty of results concerning the losses of the envelope of the renovated and new buildings. It will make it possible to sensitize the professionals with the importance of the implementation of increasingly powerful insulations. <br /> <br />The device which will be developed will have to respect operational requirements on site in order to allow a broad use by the professionals: ease of use (installation, transport, treatment of the results…), reasonable cost of acquisition and coherence with the economic issues, duration of measurement the shortest possible (according to the typology of the wall). The applications concerned are: the diagnosis of walls of existing buildings, self-checking on building site, control with reception of work (new building or renovation). <br /> <br />The consortium of project RESBATI was built so as to be able to treat all the scientific and technical aspects related to the project: modeling of the heat transfers and inverse methods, metrology, onboard instrumentation, thermal material characterization, normative aspects. The repercussions expected at the conclusion of project RESBATI will also make it possible to diversify the use of infrared thermography in buildings. This one will be extended to a quantitative tool for the thermal diagnosis. That will contribute to make offers of formations adapted to all the types of users: craftsmen, research departments, experts, diagnostician, manufacturers, etc... Thus, a new trade centered on the quantitative diagnosis of the buildings might be developped thanks to techniques more powerful than the tools of the current DPE.

The metrological tool privileged in this project is the infrared thermography in active approach. This technique consists in producing a thermal excitation artificially so as to create a variation of the temperature in the studied wall and recording a sequence of thermal images. Various techniques of thermal analysis (image processing, modeling, inverse methods) can then be applied so as to obtain characteristic quantitative information on the thermal resistance of the wall to be diagnosed. RESBATI project will try to show the advantages of the active approach: control must be able to be carried out whatever the weather conditions, for any type of building and use (occupied or not).

The robustness of the identification methods is tested thanks to a benchmark carried out between the various partners of the project. A prototype of device will be tested on instrumented test-walls thanks to the climatic rooms of partners (LNE (Cell REBECCA), CEREMA and IFSTTAR). The walls tested will be preliminary characterized by the CSTB by using the standardized method of the Guarded Hot Box. An evaluation of measurment uncertainties will be carried out by the LNE in order to determine the errors of measurement according to typologies of walls considered: Insulation brought back by interior (ITI) or outside (ITE), mono-wall (multi-alveolar brick), wooden wall framework.

The final product which will be developed at the conclusion of the project will include:
- a measuring equipment made up of various components allowing the implementation of infrared thermography in active mode (thermal camera, system of excitation, onboard computing) and additional sensors;
- an instrumentation and a methodology adapted to any type of use;
- a modeling and a robust identification of parameters;
- the display of the result of measurement and associated uncertainty.

A state of the art of the methods of diagnosis of building walls was carried out during the first phase of the project. A synthesis of this document will be written in English and submitted for publication as a Review Article at the end of 2018; a publication in the form of book of the complete state of the art will be considered at the end of the project (French and/or English version).

A benchmark of numerical methods for the estimation of parameters was carried out between four of the partners of project (CSTB, IFSTTAR, LNE and CERTES). The purpose is to perform a blind test of various methods of estimation of the thermal resistance of buildings walls in order to check their robustness. This work was the object of an intermediate report and an oral communication at the scientific workshop of the SFT (METTI group) on May 2nd, 2018. Various publications and communications in congress could be realized starting from this work over the academic year 2018-2019.

The choice of the walls to be tested and the conditions of tests led to the definition of the optimal tests to perform in test facilities of the partners concerned (IFSTTAR, Cerema, CSTB and LNE). This choice also led to define an optimal instrumentation of the walls which will allow to test the models of identification of walls thermal resistance.

Innovating solutions of onboard instrumentation were proposed to design the prototype of the measuring equipment. This work was the object of a communication to the European congress of the EGU in Vienna in April 2018. The prototype will be tested on site at the end of 2018 and one version will be made available to voluntary professionals in order to obtain an experience feedback.

A survey “Questionnaire Utilisateur” was drawn up by THEMACS Engineering company in collaboration with the other partners of the project. It was then addressed in electronic form to building professionals. The diffusion of this questionnaire was carried out by the members of the follow-up committee of the project (ADEME, ALEC St Quentin in Yvelines, French federation of the Building industry). The examination of this survey will be carried out before the summer 2018. The results of this survey will make it possible to better target the user expectations in order to prepare the preproduction of devices which will be tested in the last phase of the project (during 2019). This will also make it possible to specify the outlets for trade of the device and the situations of control to be privileged (self-checking on building site, diagnosis of the existing frame, diagnosis with reception of work).

«Problématique de l'estimation de la résistance thermique de parois courantes de bâtiments par thermographie infrarouge: apport et limitations de la réduction de modèles«, Authors: L. IBOS, Thanh-Tung HA, V. FEUILLET (CERTES), J. WAEYTENS, Z. DJATOUTI, J.

Thermal insulation of opaque walls remains an essential point for improving the energy efficiency in buildings. Indeed, the number of badly insulated buildings in France is still very important. In addition, current thermal regulations set high requirements in terms of thermal insulation and will continue to be more rigorous as new building will be energy-positive with the French RT2020. However, there is no systematic method for measuring the thermal insulation level of the building walls. Their thermal performance must be controlled for renovation of the building, during its construction, for its delivery or during use. The need of a method of in-situ control of walls is more relevant than ever. Such a measurement at the wall level is an interesting complement to global methods (co-heating, etc.) that concern the whole building energy balance.

The physical parameter representing the quality of the wall thermal insulation is its thermal resistance. Currently, methods for measuring this parameter exist, either in the form of laboratory or exploratory methods, or in the form of international standards or draft standards. However, each of these methods does not meet all the conditions guaranteeing a general measurement: use on any type of wall and at any time of the year, low measurement duration, ease of use, moderate cost. The RESBATI project (in-situ measurement of the thermal resistance of building walls) aims at developing an in-situ measurement device that respects these specifications. The measuring means is infrared thermography in active approach. The uncertainty and the limitations of the measurement will be identified during the project.

Infrared thermography in passive mode has demonstrated for many years its ability to reveal the presence of insulation defects in buildings. However, it is essentially a qualitative tool. The active approach of infrared thermography is not very used for building investigation and is a promising way for obtaining quantitative information such as the thermal resistance of the wall to investigate. Indeed research results have already shown that this approach could be used to obtain quantitative estimations of the thermal resistance of opaque building walls. The RESBATI project will demonstrate the potential of the active approach so that control can be performed in any season, for any type of building and any use (occupied or not) and quickly. The passive approach might nevertheless be used as a complement because it does not require the use of additional equipment ensuring the thermal load of the wall to diagnose and provides access to larger wall surfaces to analyze.

The consortium brings complementary partners together working at different levels of the building: research laboratories, technical center, national metrology laboratory, company and standards organization. The advanced knowledge and past achievements of the various partners on the subject make it possible to develop such a method with measurement uncertainty and the associated prototypes. Many facilities will be available for qualification of prototypes: climate rooms for laboratory testing, existing buildings for in-situ qualifications. Thus, a wide variety of walls (structure and isolation level) can be tested. Moreover, these buildings have different uses (residential or service buildings). In conclusion of the project, measurements will be carried out by future end-users of the device.

Project coordinator

Monsieur Laurent IBOS (Centre d’Études et de Recherche en Thermique, Environnement et Systèmes)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

CERTES Centre d’Études et de Recherche en Thermique, Environnement et Systèmes
IFSTTAR IFSTTAR
CEREMA CEREMA-DTerEst
LNE LABORATOIRE NATIONAL DE METROLOGIE ET D'ESSAIS
CSTB Centre Scientifique et Technique du Bâtiment
THEMACS INGENIERIE
AFNOR AFNOR

Help of the ANR 724,000 euros
Beginning and duration of the scientific project: September 2016 - 36 Months

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