Experimental Investigation of PCM System Improved with Nighttime Ventilation for Enhanced Solidification

Abstract

It is predicted that in EU-buildings by 2030, the energy used for cooling will increase by 72%. Simultaneously, the energy needed for heating will drop by 30%. Thermally well-insulated lightweight framed buildings prevent heat losses through their envelope and reduce the energy demand over the heating season. However, the heat capacity of the lightweight wall is relatively low, and in summer, the building lacks thermal stability and overheats. Phase change materials (PCM) are broadly investigated for their well-known benefits of improving indoor thermal comfort by decreasing indoor temperatures while reducing the energy needed for space cooling when melting. One of the possible application methods is to encapsulate the material and place it in the 'building's building assemblies, such as walls and ceilings. However, due to a low material density (insulation effect) and high indoor temperatures on summer nights, the material does not completely solidify in the night cycle, and does not fully perform (melt) in the day-cycle. Thus, the nighttime outdoor air ventilation has to accelerate the solidification. The system is investigated in an experimental chamber divided into two units (reference and PCM modified). Each unit represents an office located in a South-Eastern Europe region with an above-average sun hours. Both units are equipped with a ventilation inlet (on the bottom of the wall) and outlet (in the middle of the ceiling). The internal wall and ceiling are entirely covered by macro-encapsulated PCM plates (SP24E) placed in the wooden frame. The original wall and ceiling are forming the airtight ventilation gap. In the nighttime cycle, the plates are being solidified with the linear diffuser (placed at the bottom of the wall), distributing the airflow behind the plates upwards (direction wall-ceiling). The results show that under the current configuration, the active-passive system decreases the indoor cell air temperatures in the hottest daily scenario up to 5 °C. Also, the complete PCM plates solidification may be accomplished within the nighttime cycle (12 h), when the air-gap is ventilated, average inlet air temperatures of 15 °C and 16 °C at a flowrate of 500 m3/h.