Developing Next Generation Building Envelope Insulation

In 2020, an average of 67% of the total household energy consumption within the EU was used for space heating in buildings.^[1] Thermal insulation is crucial to improving the thermal efficiency of buildings by reducing the heat lost through the building envelope to the outside environment.^[2] Organic based materials such as polyisocyanurate (PIR) foams are the current industry leading thermal insulation material for buildings due to their low density (&lt; 45 kgm^-3), suitable structural properties, and low thermal conductivity (0.024 Wm^-1K^-1). But, despite these advantageous properties, PIR is classified as combustible, with a fire rating class of B-s2 according to the European fire classification system.^[3] The Grenfell Tower disaster in London in 2017 demonstrated a fire propagating in a building envelope through combustible insulation.^[4] Following this fire, the UK government banned combustible materials from the exterior of buildings taller than 18m.^[5] According to the European fire classification, all new insulation materials must now be classed as A1, non-combustible or A2-s1, a limited combustible material (i.e. must self-extinguish &lt; 10 s after ignition).^[6] Stone wool an inorganic thermal insulation material with excellent fire resistance (A1 rating) but, a density up to 180 kgm^-3 which is not ideal for building insulation.^[7] Therefore, the study of low-density inorganic materials is a new concept to improve the fire ratings.<br/>This work studies adding expanded perlite (EP) and powdered aerogel into PIR foam system. Both EP and aerogel provide a low-density cellular structure with a high surface area, and a low thermal conductivity, along with heat resistance and the necessary structural properties. EP and aerogel have previously been used as insulating materials in seldom, making them ideal materials to add to the existing PIR system.^[8][9]<br/>The experiments focused on three foam formulations, a low weight addition of either EP, aerogel or a 50/50 mix of EP and aerogel, to explore the feasibility of adding solid-state materials into a liquid-based material. All foams exhibit low thermal conductivity, an average at 0.021 Wm^-1K^-1, densities below 45 kgm^-3, but slightly higher compression values versus PIR. Foams were also studied using two different heat sources for visual and quantitative data. First, a radiant heat furnace was ramped from ambient to 600°C with samples (25x35x20mm) removed every 50°C. Mass and dimensions were recorded at each step to quantify mass loss and expansion/shrinkage. At 600°C, masses remaining were PIR (4%), EP (15%), aerogel (12%) and 50/50 mixture (5%), respectively. Secondly, a propane flame placed below the foam to study thermal heat transfer throughout the foam by thermography with data calibrated for foam emissivity to plot temperature against time. The data suggest that inorganic particles absorb and scatter heat (IR light) causing an average decrease in temperature across the foam, when compared with pure PIR.<br/><br/><b>References</b><br/>[1] National Statistics, <i>Energy Trends March 2020</i>, <b>2020</b>.<br/>[2] M. Khoukhi, A. Hassan, S. Abdelbaqi, <i>Case Studies in Thermal Engineering</i> <b>2019</b>,16, 100562<br/>[3] Tata Steel UK Ltd, <b>2015</b>, 10.<br/>[4] T. Grenfell, T. Inquiry, <i>Grenfell Tower Inquiry: Phase 1 Report, Report of the Public Inquiry into the Fire at Grenfell Tower on 14 June 2017, Volume 2</i>, <b>2019</b>.<br/>[5] C. & L. G. Ministry of Housing, <i>The Building Regulations 2010</i> <b>2010</b>, <i>1</i>, 77.<br/>[6] M. R. Hall, in <i>Materials for Energy Efficiency and Thermal Comfort in Buildings</i>, Elsevier Science & Technology, <b>2010</b>, pp. 201–206.<br/>[7] A. A. Stec, T. R. Hull, <i>Energy Build</i> <b>2011</b>, DOI 10.1016/j.enbuild.2010.10.015.<br/>[8] A. M. Rashad, <i>Constr Build Mater</i> <b>2016</b>, <i>121</i>, 338.<br/>[9] J. L. Gurav, A. V. Rao, A. P. Rao, D. Y. Nadargi, S. D. Bhagat, <i>J Alloys Compd</i> <b>2009</b>, <i>476</i>, 397.