Energy-exergy performance and indoor comfort of a radiant ceiling cooling system with air-to-air sensible heat exchanger in hot and humid climate

Abstract

Building energy use significantly contributes to global carbon emissions. Radiant ceiling panels (RCP) offer an energy-efficient alternative to traditional fan coil units (FCU) by utilizing low-grade thermal sources from low-lift heat pumps. However, the RCP lacks the dehumidification capability, requiring independent humidity control systems typically using dedicated outdoor air systems (DOAS) with high-lift chillers to cool the outdoor air to address latent loads. In hot and humid climates like Hong Kong with dense occupancy, ventilation demands dominate cooling loads, increasing reliance on high-lift chillers and undermining low-lift heat pump benefits. Additionally, overly cooled dehumidification air often causes occupant thermal discomfort. To address these challenges, this study proposed an RCP cooling system integrating an air-to-air sensible heat exchanger (AASHE) with a DOAS to pre-cool incoming outdoor air and reheat overly cooled supply air. Additionally, system performance was optimized by adjusting dehumidification temperature and implementing variable air volume (VAV) control. The proposed system was implemented in a high-humidity, FCU-based office building and evaluated through EnergyPlus and exergy analysis. Results showed that the proposed system reduced indoor discomfort ratios from 54.0 % to under 0.8 %. In addition, the RCP with VAV system reduced energy use by 8.0 % through fan savings with minimal cooling energy impact. The proposed RCP with AASHE system further reduced total energy use by 19.8 % and improved exergy efficiency from 16.1 % to 21.1 % compared to the original FCU system. These findings demonstrate the significant potential of the proposed system for high-density occupancy buildings in hot and humid climates.