Integration of phase change materials in hollow-core reinforced concrete roof slabs: A 3E approach for passive building design

The building sector in developing countries is experiencing a rapid rise in energy demand, particularly for space conditioning. Roofs, as primary recipients of solar radiation, offer significant potential for passive thermal regulation. This study experimentally investigates the thermal, energy, exergy, and economic (3E) performance of concrete roof slabs integrated with macroencapsulated phase change material (PCM) under real subtropical conditions in Rupnagar, India. A commercial paraffin-based PCM (OM37, melting point 37°C) was selected through a parametric analysis and encapsulated in symmetrical voided formers embedded within the roof slab. Two identical test rooms were constructed, one with a conventional slab and the other with the PCM-integrated slab (2 m × 2 m × 0.15 m). Results show that the PCM slab reduced indoor air temperature by up to 7.3°C during peak solar hours and decreased heat flux by 51.35%, enhancing thermal resistance. Discomfort hours were reduced by 4.5%, with maximum heat gain reductions of 36.07% (cooling) and 63.63% (heating), owing to the bidirectional buffering capacity of PCM. The system demonstrated a time lag of 2.3 h and a decrement factor of 0.77. Maximum energy and exergy outputs were 258.06 and 167.48 kJ, respectively. Economic analysis showed cooling cost savings of up to 0.05 USD/kWh/m² and daily average savings of 0.08 USD/kWh/m² for combined heating and cooling, with a simple payback period of 5.7 years, demonstrating its viability as a passive thermal energy management strategy.