Low-emissivity materials for building applications: A state-of-the-art review and future research perspectives

Abstract

Low-emissivity (low-e) materials can be used in order to reduce energy usage in both opaque and transparent areas of a building. The main focus for low-e materials is to reduce the heat transfer through thermal radiation. Furthermore, low-e materials will also influence on the daylight and total solar radiation energy throughput in windows, the latter one often characterized as the solar heat gain coefficient (SHGC). This work reviews low-e materials and products found on the market, and their possible implementations and benefits when used in buildings. The SHGC is often left out by many countries in energy labellings of windows. With opaque materials, research is still ongoing to correctly calculate the effect with regard to thermal performance when applied in buildings. Future research perspectives on where low-e technologies may develop are explored. To the authors' knowledge, there seems to be little available literature on how ageing affects low-e materials and products. As this is of large significance when calculating energy usage over the lifetime of a building, ageing effects of low-e materials should be addressed by manufacturers and the scientific community.

A thermal model for energy loss through walls behind radiators

“…Regardless, as with Eq. (19), Eq. (18) gives expected magnitudes of h conv,wi for the driving temperature differentials anticipated.…”

“…Reflector panels would have emissivity values in the region of =0.03-0.1 whilst, what are called low-e paints, would be in the range of =0.3-0.5 [19]. Fig.…”

Building Integrated Photovoltaics: A Concise Description of the Current State of the Art and Possible Research Pathways

“…"Future solar cell materials may also be envisioned as thin laminate or paint layers, hence also enabling application by paint brush or spray" [7]. A development towards higher solar cell efficiencies and building envelopes utilizing building integrated photovoltaics, smart window technologies [7,57,[101][102][103][104][105][139][140][141], better thermal insulation [44,[193][194][195][196][197][198][199][200], low-emissivity materials [201] and phase change materials [202], among others, may increase the energy efficiency and shorten the payback time of buildings and their applied technologies. We may end this with the following vision from Richard Lunt at Michigan State University: "Ultimately, we want to make solar harvesting surfaces that you don't even know are there."…”

ITO and AZO films for low emissivity coatings in hybrid photovoltaic-thermal applications

“…TCOs are widely used in architecture for energy efficient windows, either as static films to control thermal emissivity [5] or in smart windows [6], to control the solar gain. The use of TCOs in solar energy extends also to solar thermal collectors, where the purpose is to allow all sunlight to enter in the collector and prevent radiative heat loss.…”