Hygrothermal and environmental performance of a perlite-based insulating plaster for the energy retrofit of buildings
Introduction
Most of the building stock in Italy was built before 1970 [1], during years in which no laws concerning energy savings in buildings were inforced. Moreover, the primary causes of energy consumption were related to civil use, and space heating/cooling represented the most significant part of the final energy demand [2]. The most critical elements were the installed opaque components, which contributed to a higher energy loss of the building [3]. Therefore, the energy retrofitting of existing buildings should be considered a good approach to reduce the overall building energy consumption. Since most of the building stock is made up of masonry, thermal insulating plasters can be considered suitable materials for energy retrofitting. These materials are made up in the same way as traditional plasters, but sand is replaced by different types of lightweight aggregates (LWA) that contribute to reducing the thermal conductivity. This retrofitting technique is preferable to the current solutions, due to the higher hygrothermal compatibility and easier application to irregular supports that can be achieved. Thanks to the good thermal properties achievable using LWA to produce plasters, several studies have analysed the variations in the thermal and mechanical behaviour as a function of the LWA content [4].
The aims of this study have been:
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to assess the thermal and environmental performance variations of a set of thermal insulating plasters that have been improved by the addition of variuos percentages of perlite;
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to analyse the variation of the actual thermal performance of thermal insulating plaster exposed to real operating conditions and compare the resultswith the results of laboratory tests.
To achieve the above-metioned objectives, a series of thermal conductivity measurments was carried out together with embodied energy and embodied carbon analyses to determine the influence of the perlite content on both the thermal conductivity and the environmental behaviour of the plasters; in addition, the thermal conductivity tests were repeated under water saturated conditions on a previously chosen mixture.
This formulation was also applied to the interior side of the external vertical walls of a XIX century rural house in Italy that had been selected as a case study and which was monitored to determine the thermal performance of the thermal plaster at a component scale. The insulated walls were monitored and compared with non-insulated walls in the building (the unheated rooms were not insulated), to identify the benefits achievable through the application of thermal plaster. The monitored data were then used to calibrate an HMT simulation model in WUFI Pro software [5], and the model was used to evaluate the changes in the hygrothermal behaviour of the wall over the long term. Analyses of the embodied energy and embodied carbon were conducted to assess how the perlite content can affect the environmental behaviour of the materials.
Attention was in particular focused on the conductivity relation as a function of the moisture content. A similar study was developed in 2014 [6], but no evaluation or simulation of the moisture content was reported.
Section snippets
State of the art on mineral-based thermal plasters
Thermal insulating plasters are made by adding various types of Light Weight Aggregates (LWA) to a matrix, which can be made of cement, gypsum, natural hydraulic lime or hydraulic lime. A widely diffused type of LWA is mineral aggregates, including perlite, vermiculite, diatomite, zeolite and pumice. Different studies have been developed on plasters made up of these different types of aggregates.
In 2009, L.M. Silva et al. [7] developed a study on a series of plaster mixtures packed with perlite
Methodology
The analyses reported in this study were conducted at the material and component scales.
A first series of laboratory test was conducted, at a material scale, by means of heat flux meter apparatus, to determine the thermal properties of plaster mixtures containing different quantities of a lightweight aggregate (perlite).
The environmental impact indicators (i.e. embodied energy and embodied carbon) were determined for each plaster mixture.
Two different analyses were carried out at a component
The effect of the perlite content on the thermal properties of plasters
The laboratory analyses were aimed, at a material level, at identifying the thermal conductivity of the different plaster mixtures, each of which was characterised by a different LWA content and a different dry bulk density. Table 1 reports the influence of the perlite content on the material density. It is possible to observe that an increase in the perlite content (from 25% to 40%) determined a relevant decrease in the density, that is, from ∼600 kg/m3 to ∼250 kg/m3.
A roughly linear increment
Conclusions
In this study, the thermal conductivity of a lime-based thermal insulating plaster has been assessed for different concentrations of Light Weight Aggregates (LWA). The HFM measurements show a decrease in the thermal conductivity as a function of the increase in the perlite content; the results range from between 0.118 W/mK (25% of perlite) to 0.059 W/mK (40% of perlite). Nevertheless, the reduction in λ obtained by increasing the perlite concentration from 25% to 30% is almost the same as the
Acknowledgements
The authors would like to thank Vimark Srl for providing the necessary data for the environmental analyses. Marco Dutto and Cinzia Ferrua are kindly acknowledged for their support during the preparation of the specimens. Francesco Isaia and Ylenia Cascone helped during the experimental and the simulations phase, Mr. Maurizio Cappa and Mrs. Elena Cappa made the case study building available for the experimental tests and Mrs. Manuela Bassi (ARPA Piemonte) supplied the climate data. The authors
References (41)
- et al.
Lightweight plaster materials with enhanced thermal properties made with polyurethane foam wastes
Constr. Build. Mater.
(2012) - et al.
Thermal insulating plaster as a solution for refurbishing historic building envelopes: First experimental results
Energy Build.
(2015) - et al.
Role of lightweight fillers on the properties of a mixed-binder mortar
Cement Concrete Composit.
(2010) - et al.
Impact of perlite, vermiculite and cement on the thermal conductivity of a plaster composite material: Experimental and numerical approaches
Composit.
(2015) - et al.
Properties of gypsum composites containing vermiculite and polypropylene fibers: Numerical and experimental results
Energy Build.
(2014) - et al.
A novel lightweight gypsum composite with diatomite and polypropylene fibers
Constr. Build. Mater.
(2016) - et al.
An integrated design approach to the development of a vegetal-based thermal plaster for the energy retrofit of buildings
Energy Build.
(2016) The benefits of using aerogel-enhanced systems in building retrofits
Energy Procedia
(2017)- et al.
Long-term thermal conductivity of aerogel-enhanced insulating materials under different laboratory aging conditions
Energy
(2018) - et al.
Long-term performance of aerogel-enhanced materials
Energy Procedia
(2017)
Hygrothermal performance of exterior walls covered with aerogel-based insulating rendering
Energy Build.
Temperature and moisture evolution beneath an aerogel based rendering applied to a historic building
J. Build. Eng.
Insulating coat to prevent mold growth in thermal bridges
Energy Procedia
Energy efficient retrofit of a prefabricated concrete panel building (Plattenbau) in Berlin by applying an aerogel based rendering to its façades
Energy Build.
Embodied energy in residential buildings towards the nearly zero energy building: A literature review
Build. Environ.
Need for an embodied energy measurement protocol for buildings: A review paper
Renewable Sustainable Energy Rev.
Energy assessment of a PCM–embedded plaster: embodied energy versus operational energy
Effect of expanded perlite on the mechanical properties and thermal conductivity, of lightweight concrete
Energy Build.
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