Abstract
Buildings account for a large portion of the total energy use in the US; therefore, improving the operation of typical variable-air-volume (VAV) systems in buildings can provide a tremendous economic opportunity. ASHRAE Guideline 36 recommends a resetting strategy for supply air temperature (SAT) for VAV systems based on outside air temperature. However, this strategy may not produce optimal performance, particularly when simultaneous cooling and heating occurs in zones. In addition, there is no strategy recommended in the Guideline to reset the zone minimum airflow set point in a single-duct VAV terminal unit with reheat, although this setpoint has a great impact on zone reheat requirements and ventilation efficiency. Thus, this paper introduces new strategies to reset both the SAT and zone minimum airflow rate set points to improve the efficiency of typical VAV systems. The strategies were tested under various conditions through experiments performed in fully instrumented VAV systems located in the HVAC lab at the University of Cincinnati. The experiments were conducted on a chilled-water VAV system that serves three controlled zones with hot-water reheat VAV boxes controlled by a typical commercial BACnet web-based building automation system BAS. The simulation studies were performed using the building energy simulation software EnergyPlus to evaluate the strategies at a larger scale in various locations. The simulation results show that the proposed resetting strategies can provide fan energy savings between 1.6% and 5.7% and heating load savings between 7.7% to 33.7%, depending on the location. The laboratory testing shows that the proposed strategies can provide stable control performance in actual systems as well as achieving the anticipated reheat and fan energy savings. The result offers significant improvements that can be implemented in the Guideline for single-duct VAV system operation and control.
Highlights
Wang and Song proposed the optimization of the supply air temperature during the economizer cycles, which can minimize energy costs [7]
Nassif et al proposed a new resetting method for the minimum zone airflow rate set point, but the study assumed that the supply air temperature was constant, and the study overlooked the interaction between the SAT and the zone minimum airflow rate setpoints [21]
Integrated SAT and minimum airflow rate resetting strategies are introduced in this Integrated SAT and minimum airflow rate resetting strategies are introduced in this and minimum minimum airflow rate strategies introduced paperIntegrated in order to achieve better energy efficiency in buildings
Summary
Buildings are among the major consumers of global energy. As a matter of fact, this sector accounts for approximately 40 percent of the energy consumed in the United. Nassif et al proposed a new resetting method for the minimum zone airflow rate set point, but the study assumed that the supply air temperature was constant, and the study overlooked the interaction between the SAT and the zone minimum airflow rate setpoints [21] To address these challenges, this paper introduces integrated two control strategies that reset both the SAT and the minimum airflow rate set point for a single-duct multi-zone VAV system and evaluate the methods in simulation and real control systems. These strategies are easy to implement in real systems and can improve the efficiency of typical VAV systems
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