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Research Papers

Efficient Operation of Air-Side Economizer Using Extremum Seeking Control

[+] Author and Article Information
Pengfei Li

Department of Mechanical Engineering, University of Wisconsin-Milwaukee, Milwaukee, WI 53211pli@uwm.edu

Yaoyu Li

Department of Mechanical Engineering, University of Wisconsin-Milwaukee, Milwaukee, WI 53211yyli@uwm.edu

John E. Seem

Building Efficiency Research Group, Johnson Controls, Inc., Milwaukee, WI 53209john.seem@gmail.com

J. Dyn. Sys., Meas., Control 132(3), 031009 (Apr 27, 2010) (10 pages) doi:10.1115/1.4001216 History: Received March 28, 2009; Revised October 19, 2009; Published April 27, 2010; Online April 27, 2010

As the heating, ventilating, and air conditioning (HVAC) systems accounts for a major sector of energy consumption for commercial buildings, there has been a greater demand for improving the efficiency of such systems. The air-side economizers have been developed as a class of energy-saving HVAC devices that may increase the energy efficiency by taking advantage of outdoor air during cool or cold weather. However, many economizers do not operate in the expected manner and waste even more energy than before installation, mostly due to the unreliable sensors and actuators in practice. Better control strategy is needed for optimal and robust operation. In this paper, an extremum-seeking control (ESC) based self-optimizing strategy is proposed to minimize the energy consumption, with the feedback of chilled water supply command rather than the temperature and humidity measurements. The mechanical cooling load is minimized by seeking the optimal outdoor air damper opening in real time. Such scheme does not need temperature and humidity sensors, and depends much less on the knowledge of the economizer model. Simulation was performed on a MODELICA based transient model of a single-duct air-handling unit developed with DYMOLA and AIRCONDITIONING LIBRARY . The simulation results demonstrated the potential of using ESC to achieve the minimal mechanical cooling load in a self-optimizing manner. In addition, an antiwindup ESC scheme is proposed to handle the ESC windup issue due to actuator (damper) saturation. The simulation results validated the effectiveness of the proposed antiwindup ESC.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Single-duct air-handling unit

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Figure 2

State transition diagram for the proposed control strategy

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Figure 3

Control states for different outside air conditions for an ideal coil with return conditions of 75°F and 50% RH

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Figure 4

DYMOLA layout of the air-handling unit model

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Figure 5

Damper characteristic curve

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Figure 6

Comparison of the pressure drops due to wall friction in the ducts

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Figure 7

Block diagram of ESC: (a) detailed block diagram; (b) simplified block diagram

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Figure 8

ESC based economizer control

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Figure 9

Block diagram of the antiwindup ESC

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Figure 10

Static map from OAD opening to the chilled water flow rate

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Figure 11

Tuning results of the standard ESC design based on 30% initial OAD opening

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Figure 12

Tuning results of the standard ESC design based on 20% initial OAD opening

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Figure 13

Tuning results of the standard ESC design based on 25% initial OAD opening

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Figure 14

Tuning results of the standard ESC design based on 40% initial OAD opening

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Figure 15

Tuning results of the standard ESC design based on 65% initial OAD opening

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Figure 16

Tuning results of the standard ESC design based on 75% initial OAD opening

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Figure 17

Tuning results of the standard ESC design based on 85% initial OAD opening

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Figure 18

Change in the outdoor air conditions on the psychrometric chart

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Figure 19

Ramp change in the outdoor air conditions at 5000 s and 8000 s

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Figure 20

Static map from the OAD opening to chilled water flow rate (state 2)

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Figure 21

Integral windup of the standard ESC under actuator saturation

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Figure 22

Antiwindup ESC under actuator saturation

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