Simplified calculation method for design cooling loads in underfloor air distribution (UFAD) systems

Stefano Schiavon, Kwang Ho Lee, Fred Bauman, Tom Webster

Research output: Contribution to journalArticle

48 Citations (Scopus)

Abstract

This paper describes the development of a simplified calculation method for design cooling loads in underfloor air distribution (UFAD) systems. The simplified design tool is able to account for key differences between UFAD and traditional mixing overhead (OH) systems. These include: (1) difference between design day cooling load profiles, (2) impact of a thermally stratified environment for UFAD versus well-mixed for OH, and (3) impact of heat transfer (temperature gain) in underfloor air supply plenums. The new design tool allows the use of a familiar load calculation procedure for OH mixing systems as input to the UFAD design tool. Based on 87 EnergyPlus simulations, four regression models have been developed to transform the OH cooling load into the UFAD cooling load, and then to split this total load between the supply plenum, zone (room), and return plenum. The regression models mainly depend on floor level, and position (interior or perimeter) and orientation of the zone under analysis. Although considered in the analysis, supply air temperature, window-to-wall ratio, internal heat gain, plenum configuration, climate, presence of the carpet and structure type do not strongly influence the developed models. The results show that, generally, UFAD has a peak cooling load 19% higher than an overhead cooling load and 22% and 37% of the total zone UFAD cooling load goes to the supply plenum in the perimeter and interior, respectively.

Original languageEnglish
Pages (from-to)517-528
Number of pages12
JournalEnergy and Buildings
Volume43
Issue number2-3
DOIs
Publication statusPublished - 2011 Feb

Keywords

  • Cooling load
  • HVAC sizing
  • Mixing ventilation
  • Overhead air distribution (OH)
  • Underfloor air distribution (UFAD)

ASJC Scopus subject areas

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

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