Variations of Stratification and Cooling Energy Performance According to Diffuser Condition in UFAD System

Sang Hun Yeon, Byeongho Yu, Jong Man Lee, Sung Lok Do, Minjae Shin, Kwang Ho Lee

Research output: Contribution to journalArticlepeer-review


The underfloor air distribution (UFAD) system, which is a building energy-saving technology, is an air-conditioning system that enables maintenance of the indoor temperature with a relatively low supply air flow rate. UFAD has advantages compared to the conventional overhead system, which improves occupants' comfort, health, and work efficiency, decreases life cycle cost, and improves indoor air quality, ventilation efficiency, and lay-out flexibility related to building services. Also, the floor height is reduced because a duct is unnecessary. The stratification of the UFAD system is a key factor to the system, which refers to the inconsistent vertical temperature distribution from the floor to the ceiling due to the buoyant effect of air. It plays a critical role in determining the thermal, ventilation, and energy performance. However, based on the comprehensive literature review, study on the stratification of UFAD is insufficient due to lack of understanding and actual measurement facilities related to UFAD. Therefore, this study, by using the EnergyPlus simulation and phi-gamma formula, aims to assess the stratification according to the variation of a diffuser condition. As a result, stratification of the perimeter zone was improved by diffuser condition but the energy savings was not noticeable. The floor area of the interior zone accounts for 75% of the total floor area but stratification of the interior zone was not nearly changed by diffuser condition. Also, as the stratification was improved, the wall convection heat gain increased in the interior zone. Therefore, it is considered that the cooling load was increased and the decrease of energy consumption is insignificant.

Original languageEnglish
Article number04020017
JournalJournal of Energy Engineering
Issue number4
Publication statusPublished - 2020 Aug 1

Bibliographical note

Funding Information:
This study was supported by a Korea University Grant and supported by the Human Resources Development of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea Government Ministry of Trade, Industry, and Energy (No. 20184030201900). This study was supported by a Korea University Grant (No. K1909671).

Publisher Copyright:
© 2020 American Society of Civil Engineers.


  • Cooling energy
  • Diffuser
  • Discharge angle
  • Effective diffuser area
  • EnergyPlus
  • Stratification
  • Underfloor air distribution (UFAD)

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Renewable Energy, Sustainability and the Environment
  • Nuclear Energy and Engineering
  • Energy Engineering and Power Technology
  • Waste Management and Disposal


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