Elsevier

Energy and Buildings

Volume 210, 1 March 2020, 109742
Energy and Buildings

Laboratory study on hygrothermal behavior of three external thermal insulation systems

https://doi.org/10.1016/j.enbuild.2019.109742Get rights and content

Highlights

  • Adhesive used for ETICS provides moisture within the wall and increases moisture transfer resistance.

  • Simulated temperature and relative humidity profiles agree with the measured ones.

  • Using bio-based insulation may reduce the condensation risk.

  • The ventilated cladding system design is of high importance regarding the condensation risk.

Abstract

This work focuses on the hygrothermal behavior of three external thermal insulation systems: one ETICS including EPS insulation and two ventilated cladding systems including either mineral or biobased insulation. These systems were applied on a rendered hollow concrete wall and tested simultaneously between two climatic chambers. Thermocouples, humidity sensors and heat flux sensors allow investigating the hygrothermal behavior of the retrofitted wall at different stages: just after the application of insulations systems, during safe and critical use. The measured data are compared to numerical results obtained by solving a heat and moisture transfer model.

Results highlight the key role of adhesive on ETICS, which provides a significant moisture source during the application and forms an additional moisture transfer resistance within the wall. Results on ventilated cladding systems show that using biobased insulation may delay and even prevent the risk of interstitial condensation. The comparison between numerical and experimental results is satisfying for temperature and heat flow density, but underline the sensitivity of relative humidity to the sorption capacity of hygroscopic building materials. In addition, the systems design has a great influence on the condensation risks.

Introduction

In France, dwellings built between 1950 and 2000 represent around 50% of residential building stock. They are made mainly with masonry and are characterized by low or inexistent thermal insulation [1]. In the view of achieving high energy performance, safe and efficient refurbishment of external walls have to be undertaken. For now, External Thermal Insulation Composite Systems (ETICS) and ventilated cladding systems are widespread techniques. Depending on the building types and the climatic conditions, they are designed to fulfill minimal thermal and acoustic performance and fire resistance. Examples of building renovation with external thermal insulation can be found in [2], [3], [4].

Nevertheless, one of the major concerns with external thermal insulation is moisture performance and its consequences [5]. For instance, ETICS wetting occurs obviously by driving rain [6], but also by surface condensation when wall external surface temperature drops below the dew point of the air in consequence of long-wave radiation exchanges [7]. If the drying is not sufficiently fast, high moisture content on surfaces may reduce service-life and durability of ETICS. In this view, numerous numerical studies aimed to evaluate short-term risk of surface condensation [8], [9], [10], [11], [12] and long-term risk of carbonation and corrosion of reinforcement of ETICS [13,14]. Recently, it was expected that installing a cladding instead of a rendering may reduce the risks [15]. However, the validation of this conclusion is rather difficult: when available, the experimental data are monitored on real buildings over years and their comparison with numerical results underline the great influence of building orientation, radiative properties, but also hygric properties of thermal insulation layer and exterior plaster.

To limit the influence of unknown or hazardous phenomenon, like weather, there is therefore a need to collect experimental data in well-controlled conditions i.e. in climatic chambers or specially built test facilities like hot-box [16]. To date, temperature profiles, thermal resistance (or U-value) and thermal behavior were evaluated mainly for ETICS [17], [18], [19], [20], [21], [22], [23] under static and dynamic climate [17,[21], [22], [23]], under accelerated ageing [18] or even under high temperature-rain simulation test [19,20]. In most of these studies, moisture is expected to influence the thermal behavior. Unfortunately, none of them focused on the hygrothermal behavior of the walls in the hygroscopic range. On the other hand, hygric behavior in the capillary range was studied by Hens and Carmeliet [24] and Barreira et al. [25] by monitoring mass changes during the drying stage: Hens and Carmeliet [24] noted that a wet massive brick wall may take a considerable time before drying all its built-in moisture, while Barreira et al. [25] observed a rather fast drying kinetic of ETICS itself. Regarding ventilated cladding systems, their hygrothermal behavior was investigated experimentally in a context of lightweight building as reviewed by Busser et al. [26]. However, no laboratory experiments in a context of external thermal insulation was found in the literature.

Therefore, the current paper proposes a laboratory investigation of thermal and hygrothermal behavior of two ventilated cladding systems applied on a rendered hollow concrete block wall. For comparison purpose, ETICS is also studied. Particularly, the performances of these three external thermal insulation systems are evaluated during different stage of their service-life: during the application of thermal insulation, the consequences in terms of humidity are evaluated; in normal use, thermal resistances are estimated and compared to theoretical ones, while the hygrothermal behavior is measured in the view of validating heat and moisture transfer model; last, risk of condensation is investigated for ventilated cladding systems and the design of the systems is questioned. In this view, the paper is divided as follows: Section 2 presents the three external thermal insulation systems studied, their instrumentation and the hygrothermal model; in Section 3, experimental evidences are pointed out during the application of the insulation systems and under steady state; Section 4 deals with the transient hygrothermal behavior and the numerical results for ventilated cladding systems.

Section snippets

External thermal insulation systems

Three External Thermal Insulation (ETI) systems are applied on a wall with dimensions of 2 × 2.1 × 0.21 m made of hollow concrete block and cement mortar and rendered on its outer face with a lime-based render (VPI Monolor ZF).

The first system is an ETICS made of double EPS panels, a 10 mm thick coarse hydraulic plaster layer (Parexlanko EHI GM) and a 5 mm thick siloxane finishing plaster layer on its outer face (Parexlanko Revlane+ siloxané Ignifugé TF). ETICS is bonded to the wall substrate

Consequences of the application of ETI systems

The RHCB wall is built 4 months before the application of ETI systems and conditioned under different temperature and humidity conditions until hygrothermal equilibrium is reached [38]. ETI systems are applied at t = 0 (see Fig. 3): Glass Wool and Biobased are completely build while only EPS panels are installed for ETICS, the plaster layers being applied 65 days later. Then, the walls are subjected to constant temperature and relative humidity for 160 days: regulation set points are fixed to

Hygrothermal behavior of ventilated cladding systems

This section aims to compare the measured and simulated hygrothermal behavior of the systems. Since ETICS has not reached hygrothermal equilibrium, its transient simulation is rather difficult, particularly due to the uncertainties in the initial conditions. Therefore, this section focuses only on Glass Wool and Biobased walls. Two experiments are performed: the first one lead to hygrothermal safe conditions within the walls, while the second ones should lead to interstitial condensation.

Conclusions

This work focused on the hygrothermal behavior of three external thermal insulation systems. Experimentally, a rendered hollow concrete wall was insulated with one ETICS and two ventilated cladding systems among which one includes biobased insulation. The walls were tested in a biclimatic chamber in which temperature and relative-humidity are controlled. Simultaneously, their hygrothermal behavior were simulated with a heat and moisture transfer model under steady and transient states.

Regarding

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