Human comfort is the main goal of the different air conditioning systems. In modern systems, the method chosen to deliver and to distribute the conditioned air to the space is strongly associated with increasing concerns about thermal comfort and energy saving. In the underfloor air distribution (UFAD) system, air is directly supplied from the base of the occupied zone, which causes temperature stratification from the lower to the upper layer of the zone. This flow pattern gives UFAD the advantage of using less energy while providing better thermal comfort than overhead mixing air distribution (OHAD) system. Previous studies showed that for facilities with high ceilings, a UFAD system would be more strongly appropriate to enhance thermal comfort and energy saving by distribution of air only to occupied zones.
In the present study a computational fluid dynamics (CFD) numerical investigation of air flow and temperature distribution in a theater of high ceiling and air conditioned by UFAD is presented for different operating and geometric conditions. The turbulent flow was solved by using realizable k-ε turbulent model. Numerical experiments were conducted to parametrically study the effects of supply air temperature, supply velocity, space height and number of supply diffusers on the performance of the air conditioning system including air flow velocity and temperature distribution characteristics as well as the thermal comfort measuring parameters. The results showed that (i) the used numerical technique could accurately predict the flow and temperature distribution in the conditioned space, (ii) the supply air velocity, supply air temperature, number of supply air diffusers and height of the theater have a significant impact on air velocity and temperature distribution, thermal comfort and energy consumption in the air conditioning system using UFAD system, (iii) Using
IV
supply air temperature of 18 °C, supply air velocity of 0.8 m/s and increasing the number of air diffusers have the appropriate performance of the UFAD system, especially the thermal comfort measuring parameters, and (iv) the energy saving of the UFAD system compared to the OHAD system increases with increasing the ceiling height of the air conditioned space and three diffusers. Comparing with overhead mixing air distribution (OHAD), UFAD system shows more comfortable environment and smaller vertical variations of air temperature as well as low energy consumptions. |
