Single-crystalline sodium tungsten bronze (Na-WO3) nanorods with typical diameters of 10–200 nm and lengths of several of microns were prepared via hydrothermal synthesis. X-ray diffraction data showed that the as-prepared Na-WO3 nanorods crystallize in a hexagonal structure (space group P6 / mmm) with unit cell parameters a = 7.3166(8) Å and c = 3.8990(8) Å, and elongate along the <001> direction. The Na-WO3 nanorods had a mean chemical composition of Na0.18WO3.09·0.5H2O. The Na-WO3 nanorods exhibited a typical cathodic coloration related to proton insertion, indicating their potentials in electrochromic smart window applications.

Published in Conference papers

The Research Centre on Zero Emission Buildings - Annual Report 2012

Published in Reports

Net zero energy buildings (nZEBs) are understood as grid-connected buildings which do not require net inputs of non-renewable energy over a defined period of their life cycle. Energy requirements of nZEBs have until now been assessed based on the impact buildings have on the existing energy system. This paper introduces a new approach to nZEB energy balance that takes into account the actual amount of energy nZEBs require.

Energy balance methods previously proposed for nZEBs are illustrated in a new way and expressed in a series of equations based on a common terminology. Taking a different standpoint on the very logic that lies behind energy calculations; this article presents a new approach to energy balance in nZEBs. The paper highlights the important difference between preventing an increase in the demand for grid energy and ensuring that a building requires no net non-renewable energy. The authors argue that an energy payback approach constitute a more adequate way to tackle the environmental challenges nZEBs are meant to help solving, and to abide to a definition which stipulates that nZEBs should require no net non-renewable energy

Published in Journal papers

Monodisperse polystyrene (PS) spheres with controllable size have been synthesized by a straight forward and simple procedure. The as-synthesized PS spheres have a typical diameter ranging from ~180nm to ~900nm, where a reduced sphere size is obtained by increasing the polyvinylpyrrolidone (PVP)/styrene weight ratio. The PS spheres function as sacrificial templates for the fabrication of hollow silica nanospheres (HSNSs) for thermal insulation applications. By modifying the silica coating process, HSNSs with different surface roughness are obtained. All resulting HSNSs show typically a thermal conductivity of about 20mW/(mK), indicating that the surface phonon scattering is probably not significant in these HSNS samples.

Published in Journal papers

One of the most effective actions for reduction of energy loss through the building envelope is to optimize the thermal performance, area and localization of the transparent components in the façade in order to obtain minimal heat losses and optimal solar gains.

When considering the thermal performance of these transparent components, one should consider, not only heat loss (or gains) caused by thermal transmission, but also the beneficial effects of incident solar radiation and hence reduced demand for heating and artificial lighting.

This study presents calculations for a range of windows as part of a building where the coupled effects of incident solar radiation and thermal transmission heat losses are accounted for in terms of a net energy balance for the various solutions. Effects of varying thermal transmittance values (U-values) are studied in connection with solar heat gain coefficients.

Three different rating methods have been proposed and applied to assess the energy performance of several window configurations. It has been found that various rating methods give different energy saving potentials in terms of absolute figures. Furthermore, it has been found that windows, even with existing technology, might outperform an opaque wall in terms of heating and cooling demands.

Published in Journal papers

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