Abstract
The exhaust/return-split configuration is regarded as an important upgrade of traditional under-floor-air-distribution (UFAD) systems due to its higher energy efficiency. Moreover, existing studies are mostly focused on the effect of the return vent height on the performance of an UFAD system under cooling conditions. Knowledge of the performance under heating conditions is sorely lacking. This paper presents a numerical evaluation of the performance characteristics of an UFAD system with six different heights of the return vents in heating operation by comprehensively considering thermal comfort, air quality, and energy consumption. The results show that, in the heating mode, the general thermal comfort (predicted mean vote-predicted percentage dissatisfied (PMV-PPD) values) and indoor air quality indices (mean age of air and volatile organic compounds (VOCs) concentration) were greatly improved and energy consumption was slightly reduced with a lower return vent height. Although these were opposite to the findings of our previous study regarding the performance in cooling mode, an optimal return vent height in terms of the comprehensive all-year performance can be recommended. This method provides insight into the design and optimization of the return vent height of UFAD for space heating and cooling.
Highlights
In recent decades, an underfloor air distribution (UFAD) system has been spotlighted as a cooling terminal system, due to its energy efficiency and high ventilation performance [1,2,3]
The performance characteristics of the UFAD system with the various heights of the return vents under heating conditions were numerically investigated by focusing on the thermal comfort, the air quality, and the energy consumption simultaneously
The effects of the return vent height on the overall performance of this system for two modes were taken into account to obtain a good UFAD system with exhaust/return-split configuration for both heating and cooling
Summary
An underfloor air distribution (UFAD) system has been spotlighted as a cooling terminal system, due to its energy efficiency and high ventilation performance [1,2,3]. UFAD produces a stratified air flow pattern that takes advantage of the thermal buoyancy that is produced in cooling mode. UFAD removes heat loads and contaminants from the space more efficiently when compared with conventional overhead mixing ventilation (MV) [4]. Some studies have been conducted to investigate the performance of UFAD for heating mode. Tae et al [5] used Energyplus to evaluate the energy performance of the UFAD and MV systems for heating and cooling in the interior zone of an theatre complex. Hazim and Gan [6] employed the CFD
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