In a single duct variable air volume (SDVAV) system, the supply air temperature is usually set as a constant value. Since this constant setpoint is selected to satisfy the maximum cooling load conditions, significant reheat will occur once the airflow reaches the minimum and the heating load increases. Resetting the supply air temperature (SAT) higher during the heating season can reduce the reheat. However, air flow will increase when the SAT is higher which consume extra fan power. Therefore, to minimize the total operating cost of a SDVAV system, the supply air temperature is typically reset based on outside air temperature (OAT) with a linear reset schedule. However, the linear reset schedule is often determined based on the engineer’s experience and it may not represent the optimal reset schedule for each building. This thesis documents a study to determine the optimized supply air temperature reset schedule for SDVAV systems and analyzes the influencing factors under different operation scenarios. The study was divided into five main sections. The first section introduces the research background and objective. Literature review is documented after the introduction. The third section describes the methodology used in this study and the fourth section develops an in-depth discussion and analysis of the impact of the key influencing factors: minimum air flow ratio; ratio of exterior zone area to total floor area (i.e., exterior area ratio); internal load and the prices of the electricity; the cooling and the heating energy. The simulation results using EnergyPlus Version 2.1.0 for various operation scenarios are investigated in this section. The last section is a conclusion of the whole study. The optimized supply air temperature can be set with respect to the OAT. The study found that instead of a simple linear relationship, the optimal reset schedule has several distinctive segments. Moreover, it is found that the optimal supply air temperature reset schedule should be modified with the change of operation conditions (e.g., different minimum flow ratios and internal loads). Minimum air flow ratio has a significant impact on energy consumption in a SDVAV system. Exterior area ratio determines zone load distribution and will change system load indirectly. For buildings with small internal load, a more aggressive supply air temperature reset tactic can be implemented. In addition, the cost of electricity, cooling and heating energy can determine which end use energy (i.e., reheat energy and fan power) should take the priority.

Single Duct Variable Air Volume (SDVAV) systems use series and parallel Fan Powered Terminal Units to control the air flow in conditioned spaces. This research developed a laboratory verified model of SDVAV systems that used series and parallel fan terminal units where the fan speeds were controlled by either Silicon Controlled Rectifiers (SCR) or Electronically Commutated Motors (ECM) motors. As part of the research, the model was used to compare the performance of the systems and to predict the harmonics generated by ECM systems. All research objectives were achieved. The CFD model, which was verified with laboratory measurements, showed the potential to identify opportunities for improvement in the design of the FPTU and accurately predicted the static pressure drop as air passed through the unit over the full operating range of the FPTU. Computational fluid dynamics (CFD) models of typical a FPTU were developed and used to investigate opportunities for optimizing the design of FPTUs. The CFD model identified key parameters required to conduct numerical simulations of FPTU and some of the internal components used to manufacture the units. One key internal component was a porous baffle used to enhance mixing when primary air and induced air entered the mixing chamber. The CFD analysis showed that a pressure-drop based on face velocity model could be used to accurately predict the performance of the FPTU. The SDVAV simulation results showed that parallel FPTUs used less energy overall than series systems that used SCR motors as long as primary air leakage was not considered. Simulation results also showed that series ECM FPTUs used about the same amount of energy, within 3 percent, of parallel FPTU even when leakage was not considered. A leakage rate of 10 percent was enough to reduce the performance of the parallel FPTU to the level of the series SCR system and the series ECM FPTUs outperformed the parallel FPTUs at all weather locations used in the study.