The world is moving towards inexpensive but efficient passive solutions to increase operational energy efficiency in the building sector as a result of the increased energy demand for active space cooling inside modern buildings. In this current work, seven novel biocomposite PCM have been developed. Finally, W-PCM, with a melting point of 31.5oC, made from OM35 and water hyacinth biochar, has been selected for further application. W-PCM showed stability in terms of structural, chemical and thermal properties up to 500 cycles, tested with the help of a low-cost developed thermal cycling chamber. Clay brick and AAC brick are modified in the middle section with a 20mm thickness of W-PCM. A maximum temperature reduction of 7.98oC has been found for PCM clay bricks as compared to standard clay bricks. Based on strength analysis, PCM clay bricks come under grade 7.5 as per the IS 1077:1992 standards. Two prototype rooms have been constructed for outdoor experimentation with PCM clay bricks.