Heat flow control and energy recovery using CO₂ in double glass arrangements

The interaction of gases such as carbon dioxide (CO₂) and other so-called participating gases with thermal infra-red (TIR) radiation is one of the mechanisms behind global warming and climate change. The noticeable effect this apparently gives at atmospheric concentrations of around 400 ppmv can be made use of in technical systems where pure (and pressurized) CO₂ is confined in, for example, a double glass arrangement. Depending on pressure, temperature, gas composition and path length a certain "optical thickness" for TIR radiation is obtained that can be used to decrease or increase heat flows, or create temperature differences. The latter would allow for power production using, for example, a Stirling engine. Of great importance also is the temperature difference between ground-level surroundings and the sky. With significant amounts of electric power being used for air-conditioning, heating or cooling purposes a smart window set-up that makes use of the interference of TIR radiation with participating gases may result in significant reductions in energy use and costs. Typical applications can be found in residential and office building windows or a glass roof that covers large building structures like railway stations or parking areas. Besides glass, plastics may be used as window material. The purpose of this paper is to present the potential of energy recovery from TIR radiation using most importantly earth-to-space radiation of long wavelengths (> 4 μm), to be distinguished from incoming solar radiation at shorter wavelengths (< 4 μm). Most relevant here is the TIR absorption band for CO₂ around a wavelength of 15 μm. Note also that unlike solar irradiation the earth-to-space radiation is not limited to daytime and cloudless skies. Finally, some examples for technical system lay-out and performance are given. This gives an introduction by the paper by Fält and Zevenhoven submitted to this conference (Fält and Zevenhoven, 2010).