Energy-saving Effect of VAV・VWV・CO₂ Concentration Control of Air Conditioning System Considering Automatic Control Logic and Parameters

<p>Variable air volume (VAV), variable water volume (VWV) control, and CO₂ concentration control are expected to contribute to energy conservation in heating ventilating and air conditioning (HVAC) systems, and various attempts have been made to quantify their energy-saving effects. In the case of VAV and VWV control, studies have not yet set detailed control parameters or considered the control behavior of a system under various operating conditions, including intermediate periods. Although CO₂ concentration control has been studied through actual measurements and simulations, issues remain in the experimental conditions and calculation conditions of the simulation. In general, VAV control, VWV control, and CO₂ concentration control combine various control logics to control the thermal environment and air quality of the room, and many detailed control parameters are incorporated, such as the integration time in the demand airflow calculation equation, and the proportional gain of PI control. In contrast, these control logics are designed by assuming the maximum load, and they may not be able to achieve proper control in some operating conditions such as low load during the intermediate periods. In our previous paper, we developed a simulation program that modeled the physical model, equipment model, and control logic in as detailed a manner as possible for a HVAC system and building envelope and quantified the energy-saving effect of both VAV and VWV control. Therefore, in this study, we use the same system simulation program as in the previous study and aim to investigate the effect of changing the detailed control parameters on the energy-saving effect and control behavior of VAV, VWV, and CO₂ concentration control. At this time, not only the energy consumption but also the controllability of the room temperature was also considered. First, we calculated the annual impact of the parameter changes, and then we analyzed the characteristics and control behavior on a monthly basis and on a representative day. The target parameters are related to the demand airflow calculation equation, supply air temperature control, damper opening control, supply fan frequency control, exhaust fan, chilled/hot water pump, bypass valve control, and CO₂ concentration control. In this study, a system simulation in which the physical model and control logic are constructed in as much detail as possible was performed, which enabled case studies for the detailed control parameters, and their influence could be calculated at the system level. When analyzed on a monthly basis, the effect of changing the parameters on the energy consumption and controllability was small in the intermediate period when the heat load was small; however, the effect was more observable in winter and summer when the load was large. It was also shown that the change in the proportional gain of the damper opening PI control also affected the air supply fan frequency and air temperature control. It was confirmed that a single parameter change can affect the entire system. Understanding the effect of parameter changes on the system behavior will be an important knowledge for data analysis and system design of VAV/VWV systems. </p>