Thermal Comfort Analysis for Overhead and Underfloor Air Distribution Systems

Underfloor and overhead air distributions are two types of Heating Ventilating and Air Conditioning (HVAC) system in which both differs in term of channelling the supplied air into a space. Underfloor air distribution (UFAD) system channels the supplied air from the underfloor plenum and goes to the return vent at the ceiling. On the other hand, the overhead air distribution (OHAD) system utilizes the ceiling-to-ceiling air pathway approach. In this study, A developed HVAC model was proposed. Ansys Fluent program was used to numerically investigate the best thermal comfort of the proposed model in terms of occupant satisfaction by referring to ASHRAE Standard. Two scenarios were designed and adopted in the computational investigation which is OHAD and UFAD. Three heat-generating parameters were involved which are a room lamp, personal computer and occupant. The attained computational fluid dynamic (CFD) simulation results were validated. Generally, the attained CFD results showed that the UFAD system could perform better compare to the OHAD system even though the OHAD system could have some benefits. Specifically, the UFAD system provided the best thermal performance whereas the OHAD system was found to be less efficient in providing thermal comfort to the occupant and consumed a greater amount of energy because it was required to cool down the whole room instead of being cooled partly. The CFD results confirmed that the UFAD system was capable of maintaining the room temperature at 26°C at a height below 2.0 m compared to 1.2 m of the OHAD system. In conclusion, the UFAD system could provide better indoor air quality, and it could have superior performance for the tropic weather regions such as Malaysia compared to that of the OHAD system. Besides, using the UFAD system could be represented a preventive action that could be proposed to solve the mould growth inside any occupied room.

Indoor air distribution in a room with underfloor air distribution and chilled ceiling: Effect of ceiling surface temperature and supply air velocity

An underfloor air distribution (UFAD) system integrated with a chilled ceiling (CC) cooling system may be a potential advanced heating, ventilation and air conditioning system in modern non-residential buildings with high sensible cooling loads. This article presents an experimental study concerning the effect of ceiling surface temperature and supply air velocity on the indoor air distribution in a room with UFAD as the internal and external sensible cooling loads change. The vertical distributions of indoor air temperature, air velocity and contaminant (CO2) concentration were evaluated by vertical air temperature difference (VATD), turbulence intensity (TI) and contaminant removal effectiveness (CRE), respectively. The results showed that the average VATD, TI and CRE levels were 0.5°C–1.0°C, 31%–41% and 0.85–1.06 when both internal and external sensible cooling loads were 41.5 W/m2. These evaluation indices varied clearly when the external sensible cooling load increased from 41.5 W/m2 to 69.5 W/m2, whereas they remained almost the same when the internal sensible cooling load increased from 41.5 W/m2 to 69.5 W/m2. The maximum TI coincided with the minimum CRE under the condition of a constant sensible cooling load. Moreover, an air diffusion performance index clearly reduced with an increase in the heat removal effectiveness. It is recommended that it is important to balance the indoor air quality and energy consumption in a room with UFAD + CC.