SIMULATION STUDY ON ENERGY CONSUMPTION AND INDOOR AIR DISTRIBUTION OF AN INTEGRATED PERSONALIZED VENTILATION AND ACTIVE CHILLED BEAM AIR CONDITIONING SYSTEM FOR OFFICE BUILDING IN SINGAPORE

Abstract

Integrated personalized ventilation and active chilled beam (PV-ACB) air conditioning system may provide excellent indoor air quality and thermal comfort and simultaneously save significant energy. In this study, both indoor air distribution and energy consumption of this novel air conditioning system are investigated for office buildings in Singapore. Indoor air distribution analysis is conducted by applying Computational Fluid Dynamics (CFD) simulation tool, Ansys Fluent; Integrated Environment Solutions (IES) is used for simulating energy consumption and analyzing energy performance. A twenty-storey office building with full glazing is built up and applied as the model for IES energy simulation, while the model for CFD simulation is based on one small-scaled modular working area with eight workstations at one level in this building. In order to quantify energy consumption and indoor air distribution, PV-ACB air conditioning system is compared to the baseline conventional variable air volume (VAV) air conditioning system. More specifically, indoor air distribution and energy consumption of PV-ACB air conditioning system are analyzed in the cases of peak load (100%) and part loads (75%, 50%, 25%). The IES energy simulation results illustrate that PV-ACB air conditioning system at peak load (100%) shows 16% annual energy savings. At part loads of 75%, 50% and 25%, PV-ACB air conditioning system may save 27%, 41% and 58% respectively, compared to conventional VAV air conditioning system, indicating a higher energy saving potential at part load. In particular, 59% of the annual energy savings is attributed to distribution fans while chillers, distribution pumps and heat rejection fans/pumps account for respectively 32%, 4% and 5% of the annual energy savings. In terms of CFD simulation results on indoor air distribution, the baseline, conventional VAV air conditioning system, provides a uniform indoor air distribution of approximately 24oC in the case of peak load (100%). For the PV-ACB air conditioning system, thermal stratification is observed at peak load (100%); the results reveal that the average temperature range of the occupant level (0-2m) locates at 23-24oC with the higher background temperature of 26-27oC in the upper zone (2-4m). Horizontal temperature difference at the height of 1.2m is also found. The temperatures around occupants near workstations are about 22-23oC because of the conditioned outdoor air supplied by PV air terminal devices (ATDs), while the areas outside workstations keep a higher temperature of 26-27oC. Moreover, at part loads (75%, 50%, 25%), temperature differences in both the vertical and horizontal directions are obtained due to the merits of thermal stratification and spot cooling from PV-ACB air conditioning system. The temperatures around the occupied workstations are maintained around 23-24oC at various part loads (75%, 50%, 25%), although the temperatures of unoccupied workstations and upper zone are 2-4oC higher. In order to apply the PV-ACB air conditioning system in practice, the combination of the raised floor and PV ATDs is recommended to overcome the adverse impact of unsightly PV ATDs. On the other hand, the coupling of PV ATDs, ACBs and occupants should also be considered in the design stage of PV-ACB air conditioning system, in order to provide comfortable indoor built environment and desirable energy savings simultaneously. In this study, the combination of four PV ATDs, two ACBs and four occupants is proposed and applied for both energy and CFD simulations. The results indicate that this combination may achieve both pronounced energy savings (up to 58%) and impressive indoor air distribution.