Abstract

The application of superinsulation materials (SIM) reaching thermal conductivities far below 20 mW/(mK) allows the construction of relatively thin building envelopes while still maintaining a high thermal resistance, which also increases the architectural design possibilities for both new buildings and refurbishment of existing ones. To accomplish such a task without applying vacuum solutions and their inherit weaknesses may be possible from theoretical principles by utilizing the Knudsen effect for reduced thermal gas conductance in nanopores.
This study presents the attempts to develop nano insulation materials (NIM) through the synthesis of hollow silica nanospheres (HSNS), indicating that HSNS may represent a promising candidate or stepping-stone for achieving SIM. Furthermore, initial experiments with aerogel-incorporated concrete and the conceptual work concerning NanoCon are presented.

ABSTRACT

The path toward energy-efficient buildings with a low or zero carbon footprint, e.g. zero energy and zero emission buildings, involves the development of high-performance thermal insulation, aiming at reaching thermal conductivities far below 20 mW/(mK). Applying such superinsulation will allow the construction of relatively thin building envelopes yet maintaining a high thermal resistance, thus also increasing the architectural design possibilities. A vacuum insulation panel (VIP) represents a stateof-the-art thermal insulation solution with a thermal conductivity of typical 4 mW/(mK) in the pristine and non-aged condition. However, the VIPs have issues with fragility, perforation vulnerability, increasing thermal conductivity during time and lack of building site adaption by cutting as four cardinal weaknesses, in addition to heat bridge effects and relatively high costs. Therefore, the VIPs of today do not represent a robust solution. Hence, our aim is from theoretical principles, utilizing the Knudsen effect for reduced thermal gas conductance in nanopores, to develop experimentally a high-performance nano insulation material (NIM). This work presents the current status of the development of NIM as hollow silica nanospheres (HSNS) in our laboratories, from the experimental synthesis to the material characterization by e.g. thermal conductivity measurements. One attempted approach for tailor-making HSNS is the sacrificial template method and optimization of the sphere diameter and shell thickness with respect to low thermal conductivity. The results so far indicate that HSNS represent a promising candidate for achieving the high-performance thermal superinsulation for application in the buildings of tomorrow.

Abstract

The application of traditional thermal insulation materials requires thicker building envelopes in order to satisfy the requirements of the emerging zero energy and zero emission buildings. This work summarizes the steps from the state-of-theart thermal insulation materials and solutions, like vacuum insulation panels (VIP), gas-filled panels (GFP) and aerogels which all have various drawbacks, to our concepts and experimental investigations for making superinsulation materials (SIM) like e.g. nano insulation materials (NIM).

A simple, mild, and effective template approach has been used to produce hollow silica nanospheres with controlled sizes ranging from 40 to 150 nanometers. The obtained powders showed systematic variations in measured thermal conductivity, with values down to 0.024 W/(mK) so far, with en expressed goal to reach below 0.020 W/(mK). Surface hydrophobization was successfully performed. Thus, hollow silica nanospheres are considered to be promising building blocks for new hydrophobic, superinsulating materials.