Negandhi, Vanita K (2015-08). Modeling and Control of Passive Chilled Beams with Underfloor Air Distribution of Ventilation in Office Buildings in Humid Climates. Doctoral Dissertation.
Thesis
This dissertation presents the results of a study to determine the operational control, energy performance and comfort conditions associated with passive chilled beams for office buildings in a humid climate and to develop a method for the modeling of passive chilled beams with a ventilation system and underfloor air distribution (UFAD). For the analysis, a 606,900 ft2 commercial office building in ASHRAE climate zone 3A with passive chilled beams and a ventilation system with UFAD was selected as the case-study building. In the first step, measured data from the building was used to develop a calibrated whole-building energy analysis model in EnergyPlus 8.1. The energy model also implemented methods to model the controls found in a passive chilled beam system with underfloor air distribution. A simplified steady-state energy model was also developed for the validation of the EnergyPlus model and for energy use prediction. In the second step, two methods of optimization for the operational control strategies were tested: a simplified rule-based optimization and a model-based predictive control optimization. The influence of these two approaches to optimization on HVAC energy savings and thermal comfort were found to be within 2% of each other. Finally, summertime stratification measurements were taken in the offices and were combined with a CFD model of a single zone in Star CCM+ 9.04 to establish temperature and airflow profiles in the zones. These comfort studies were conducted for the cooling season only and showed that the thermostat setpoints are not fulfilled in the exterior zones in summer and chilled beam and ventilation system interact with each other and have an adverse effect on the overall system energy efficiency. The results of the research show that if properly controlled, a passive chilled beam system with a parallel ventilation system has the potential for HVAC savings of 14-24% over standard VAV systems in office buildings in humid climates. All of the HVAC energy savings come from fan and reheat energy. Energy savings are affected by latent loads and ventilation requirements in the zones and the potential for the use of an economizer. Indoor humidity levels are also higher with a passive chilled beam system than a standard VAV system. Independent control of the volume of air supplied by the ventilation system and the supply air temperature is necessary to achieve the predicted energy savings. Lastly, the summertime zone comfort studies reveal that the presence of the UFAD ventilation system hinders the natural downward plumes from the chilled beams and the presence of the chilled beam system inhibits stratification in the zones. Because of the lower ventilation flow rates associated with the chilled beams, there is significant increase in the temperatures in the supply plenums.
