Elsevier

Energy and Buildings

Volume 179, 15 November 2018, Pages 26-38
Energy and Buildings

Hygrothermal and environmental performance of a perlite-based insulating plaster for the energy retrofit of buildings

https://doi.org/10.1016/j.enbuild.2018.08.017Get rights and content

Highlights

  • An experimental assessment of the impact of the perlite content on the thermal performance of plaster is here presented.

  • Analyses have been carried out through laboratory, in-situ measurements and heat and moisture transfer simulations on a real case study.

  • The embodied energy and embodied carbon have been assessed for different percentages of perlite content.

Abstract

In the last few years, thermal insulating plasters have started to be an attractive solution for the insulation of already existing wall structures, especially old masonry ones, where refurbishment interventions can involve the replacement of damaged plasters.

Intensive research efforts are being made to reduce the thermal conductivity and the environmental impact of these materials by optimizing their mixtures (combination of lightweight aggregates, binders and additives).

In the present study, the hygrothermal performance and environmental impact of the different perlite-based plasters that are currently being developed have been investigated.

A series of analyses has been carried out, at a material scale, by means of heat flow meter apparatus, to determine the relationship between the perlite content and the thermal properties. Moreover, the effect of the moisture content on λ has been analyzed, and the embodied energy and embodied carbon of the four mixtures have been assessed using both the cradle-to-gate and the cradle-to-site approaches.

Furthermore, in-situ measurements have been conducted at a demonstration site, at a component scale, and a series of heat and moisture transfer simulations has been carried out to evaluate the actual thermal behaviour of the plaster under real operating conditions.

The thermal conductivity values of the four plaster mixtures ranged from between 0.118 W/mK and 0.059 W/mK, thus demonstrating that the perlite concentration had a significant impact on the reduction of thermal conductivity and that the embodied energy of the applied material (5 cm thickness) decreased as the perlite content increased. Moreover, the results of the measurements on the demonstration building and the hygrothermal simulations have revealed that the thermal insulating plaster is able to reduce the U-value of the wall. However, an increase of 26–30% of the actual thermal conductivity should be considered when the material is exposed to real operating conditions.

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:

  • 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;

  • 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)

  • M. Ibrahim et al.

    Hygrothermal performance of exterior walls covered with aerogel-based insulating rendering

    Energy Build.

    (2014)
  • T. Stahl et al.

    Temperature and moisture evolution beneath an aerogel based rendering applied to a historic building

    J. Build. Eng.

    (2017)
  • S. Fantucci et al.

    Insulating coat to prevent mold growth in thermal bridges

    Energy Procedia

    (2017)
  • K. Ghazi Wakili et al.

    Energy efficient retrofit of a prefabricated concrete panel building (Plattenbau) in Berlin by applying an aerogel based rendering to its façades

    Energy Build.

    (2018)
  • P. Chastas et al.

    Embodied energy in residential buildings towards the nearly zero energy building: A literature review

    Build. Environ.

    (2016)
  • MK Dixit et al.

    Need for an embodied energy measurement protocol for buildings: A review paper

    Renewable Sustainable Energy Rev.

    (2012)
  • C. Carbonaro et al.

    Energy assessment of a PCM–embedded plaster: embodied energy versus operational energy

    (2015)
  • O. Sengul et al.

    Effect of expanded perlite on the mechanical properties and thermal conductivity, of lightweight concrete

    Energy Build.

    (2011)
  • A.N.C.E., Lo stock abitativo in Italia,...
  • E.N.E.A., Rapporto annuale efficienza energetica (RAEE) 2017: analisi e risultati delle policy di efficienza energetica...
  • Cited by (33)

    • Review of methods for the combined assessment of seismic resilience and energy efficiency towards sustainable retrofitting of existing European buildings

      2022, Sustainable Cities and Society
      Citation Excerpt :

      From the discussion above, it is clear that the overall benefits in terms of cost-effectiveness, optimisation of resources, time saving, and logistics management are achievable only if the retrofit intervention is conceived as ‘integrated’ at the design stage and, at the same time, if properly combined technologies are implemented. For instance, it is desirable to improve the energy efficiency of the building by enhancing the thermal insulation of the strengthening materials (Fenoglio, Fantucci, Serra, Carbonaro & Pollo, 2018), thus generating an economic advantage that can partly return the investment for the integrated energy-structural renovation; similarly, it is important that energy and seismic retrofit measures are applied at a consistent dimensional scale (e.g. structural walls, envelope, etc.) to take advantage of common labour operations (Bournas, 2018). To this end, combined solutions have been recently developed for the renovation of existing structures.

    • A critical review of methods for the performance evaluation of passive thermal retrofits in residential buildings

      2020, Journal of Cleaner Production
      Citation Excerpt :

      Typical thermal bridges are found at external wall corners, junctions between building elements (e.g. floor and wall junctions), and in windows frames. A common audit tool to identify thermal bridges is thermography (James and Ambrose, 2017; Byrne et al., 2016; Gupta and Gregg, 2016; Synnefa et al., 2017; Morelli et al., 2012; Haverinen-Shaughnessy et al., 2018; Tong et al., 2018; Ćukovićgnjatović et al., 2016; Leardini et al., 2015; Fenoglio et al., 2018; Sdei et al., 2015; Campbell et al., 2017; Liu et al., 2014; Hurnik et al., 2018; Gagliano et al., 2013; Parker et al., 2019; Jankovic, 2019; Guiterman and Krarti, 2011; Miller et al., 2018). Miller et al. (2018) applied thermal imaging to identify retrofit strategies on an owner-led renovation project in Australia.

    • Characterisation of a multilayer external wall thermal insulation system. Application in a Mediterranean climate

      2020, Journal of Building Engineering
      Citation Excerpt :

      However, their thermal conductivities (λ) are, in general, relatively high (0.050 ≤ λ ≤ 0.200 W m−1 K−1 [8]), although within class T2 of EN 998-1 [9], underperforming classic thermal insulation materials. Various research works have been incorporating different lightweight thermal insulation aggregates in renders [10–17], but with both relatively high thermal conductivity and mechanical strength. Further efforts have been made, based on the use of nanotechnology [18–22], contributing to better thermal insulation of buildings’ envelopes, minimising their energy consumption [23,24], and, at the same time, trying to improve their sustainability [25,26].

    View all citing articles on Scopus
    View full text