A numerical study on the thermal performance of night ventilated hollow core slabs cast with micro-encapsulated PCM concrete

• A numerical procedure for predicting the thermal performance of VHCSs is developed.
• Use of mPCMs (up to 20%) in VHCSs for building cooling applications is studied.
• Ideal room temperature cases for high & low thermal mass buildings are considered.
• For the ideal cases, effects of using various mPCMs & ventilation rates are studied.

This paper presents a numerical procedure for predicting the thermal performance of ventilated hollow core slabs (VHCS). The proposed approach is validated against experimental measurements available in the literature and then applied to study the effects of incorporating micro-encapsulated phase change materials (mPCM) in VHCSs for the cooling of office buildings. In particular, the impact of mPCM content, mPCM type (i.e. phase change temperature) and hollow core ventilation rates uin on the slab’s cooling potential is evaluated under two ideal room temperature cases. The first case reflects the behaviour of a high thermal mass building in which the high thermal mass enforces room temperature variations to be negligible. The second case imitates a low thermal mass building in which the room temperature is significantly affected by external temperature variations. It is assumed that the temperature responses within typical offices would fall between these two scenarios. The results indicate that, with the VHCS placed in a high thermal mass building, the use of the mPCM with a phase changing temperature of 20 °C (denoted by mPCM20) improves the cooling potential of the slab, regardless of the mPCM content (up to 20% incorporation) and the ventilation rate (up to uin = 5 m/s). However in the low thermal mass building case, the best performing mPCM type depends on the ventilation rate (i.e. mPCM20 when uin ≤ 2 m/s, and mPCM19 – the mPCM with a phase changing temperature of 19 °C when uin = 5 m/s) and is independent of the mPCM content.