THERMOCHROMIC COMPLEX-COMPOUNDS IN PHASE-CHANGE MATERIALS - POSSIBLE APPLICATION IN AN AGRICULTURAL GREENHOUSE

The possibility to combine two physico-chemical phenomena is studied i n this work in order to attain simultaneous control of temperature and light intensity in a greenhouse: (a) isothermal heat storage in phase change materials and (b) thermochromic behavior of complex compounds dissolved in the phase change materials. Two binary mixtures melting n ear the ambient temperature were studied: (a) 0.925 Ca(NO3)(2) . 4.06 H2O + 0.075 CaCl2 . 6.11 H2O melting at 35.6 degrees C and (b) 0.9 CH3 CONH2 + 0.1 Ca(NO3)(2) . 4 H2O, melting at 27.7 degrees C. The melting temperature, the enthalpy of fusion and the heat capacity of both mix tures were determined from DSC measurements. Both mixtures showed to b e suitable solvents for the formation of consecutive cobalt(II) chlori de complexes. The compositions of the complex compounds were adjusted in each mixture so that the absorption spectra in visible spectral ran ge exhibited low absorbance at the melting temperature and a pronounce d increase of the absorbance and/or change of color with the increase of temperature in the range relevant for passive solar energy receiver s. The combined latent heat storage and the outstanding reversible cha nge of the optical properties of the dissolved complex compounds with temperature is proposed to be applied in solar heated agricultural gre enhouses in areas with fluctuating climate conditions. The increase of absorbance with temperature acts as an auto-regulated shading protect ion from overheating. (C) 1998 Elsevier Science B.V. All rights reserv ed.