Influences of different operational configurations on combined effects of room air stratification and thermal decay in UFAD system

Byeong Ho Yu, Byeong Mo Seo, Sung Hyup Hong, Sanghun Yeon, Kwang Ho Lee

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)


The non-insulated underfloor supply plenum and the heat gain of the cool supply air into supply plenum results in significant magnitude of thermal decay defined as the supply air temperature rise. Eventually, these changes have influence on the room air stratification, causing negative effects throughout whole system. Therefore, for the optimization of UFAD system, it is important to understand these fundamentals and relevant effects on the overall system operation. In this study, comparative analysis was conducted during cooling period using validated EnergyPlus model, after employing different operational configurations related to room air stratification and thermal decay. The thermal behavior and cooling energy performance were analyzed by observing the convective heat transfer, thermal decay, airflow, stratification among different operational configurations. As a result, it was observed that the existence of non-insulated supply plenum have influences on the thermal behavior in occupied zone, and the corresponding heat transfer has load reduction effect of the space by about 40%. However, there were still significant amounts of cooling energy consumption in the form of thermal decay despite the reduced cooling load, indicating that unintended and additional energy consumption was occurred in supply plenum. In addition, return air temperature rise by the room air stratification increased the cooling coil load. Eventually, these effects canceled each other out. As a result, compared to CBAD system, standard UFAD system consumed more electric energy by approximately 30%, and for fully-insulated UFAD system, 6% energy saving could be achieved.

Original languageEnglish
Pages (from-to)262-274
Number of pages13
JournalEnergy and Buildings
Publication statusPublished - 2018 Oct 1
Externally publishedYes


  • Energy modeling
  • EnergyPlus
  • Room air stratification
  • Thermal decay
  • Underfloor air distribution
  • Underfloor supply plenum

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Building and Construction
  • Mechanical Engineering
  • Electrical and Electronic Engineering


Dive into the research topics of 'Influences of different operational configurations on combined effects of room air stratification and thermal decay in UFAD system'. Together they form a unique fingerprint.

Cite this