Abstract
This article addresses different duct static pressure control strategies which could be implemented in variable air volume air-conditioning systems (VAV). Two pressure reset control strategies are compared to the commonly used control solution based on the “Constant static pressure” method. First pressure reset control strategy, known as PID Control, uses signals from VAV boxes controllers to reset duct static pressure in a way that one of the VAV dampers is maintained almost entirely open. Second strategy decreases static pressure setpoint until an adjustable number of pressure requests occur. As a response to the certain amount of requests, static pressure setpoint is increased. This strategy is called Trim & Respond. Both static pressure reset control strategies described in this paper are considered to have more significant potential for energy savings than the “Constant static pressure” method. In order to validate this potential, several simulations for different control strategies were carried out and the obtained results are compared and analysed. The theoretical limit of the energy savings - set of the optimal control actions, was estimated with Nelder-Mead algorithm and also presented in this article. General description of the static pressure control strategies Constant static pressure, PID Control and Trim & Respond is given.
Highlights
Variable air volume systems have been applied since the end of the World War II [1], while the term variable air volume airconditioning systems (VAV), was formulated and first used almost two decades later in the sixties of the last century [2]
In order to investigate the impact of the duct static pressure reset control strategy on the energy consumption by HVAC system, PID Control and Trim & Respond strategies were described and compared to the "Constant static pressure" method
If there are no further requests from the zones' VAV boxes, Trim and Respond (T&R) strategy starts to decrease the static pressure setpoint
Summary
Variable air volume systems have been applied since the end of the World War II [1], while the term VAV (variable air volume), was formulated and first used almost two decades later in the sixties of the last century [2]. In continental Europe, VAVs gained their popularity in the eighties They are commonly applied and implemented in the modern HVAC installations. A typical VAV system consists of variable air volume zone boxes with dampers and variable speed fans. In response to varying loads in the ventilating zones, VAV damper's position changes in order to maintain required airflow. A fan responds by adjusting its speed to the point which allows to maintain static pressure at a given setpoint. At the same time fan reduces its speed to maintain constant duct static pressure. In order to investigate the impact of the duct static pressure reset control strategy on the energy consumption by HVAC system, PID Control and Trim & Respond strategies were described and compared to the "Constant static pressure" method. Optimal control actions were estimated using Nelder-Mead algorithm and used as a benchmark for other presented strategies (Fig. 1)
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