HVAC multivariable system modelling and control
Date
2022
Journal Title
Journal ISSN
Volume Title
Publisher
Sage journals
Abstract
Heating, Ventilation and Air Conditioning (HVAC) is a multivariable process where any alteration with one system
input affects most or all of the system’s outputs simultaneously. Owing to its comprehensiveness, a readily derived
multivariable HVAC mathematical model is selected for this work, mainly a hybrid distributed-lumped parameters
model. As the transfer function matrix was not established in the selected HVAC model, it was exclusively developed
in this study, using the time domain graphical responses of the chosen model. Based on the developed transfer function
matrix, a conceptual two-step approach was followed to control HVAC model performance. The first was decoupling
the interactions that affect all the system outputs, and the second was designing proper PID controllers for each
decoupled loop similar to those used for single input single output (SISO) systems. A direct Nyquist Array (DNA)
multivariable control strategy was used for this purpose and successfully decoupled the HVAC system into three
separate (SISO) loops. Three PID controllers afterwards were applied for each decoupled loop. The results showed
quite decoupled system outputs with a minor coupling percentage so that any change in a system input only affected
the corresponding system output. The output responses are also underdamped with almost zero steady-state error
confirming the effectiveness of the selected PID parameters. The values of steady-state responses are obtained in (10–
15) s compared with (200–600) s of open-loop response time. However, various overshoot percentages in the
responses are encountered but are relatively small, with a short settling time, so they don’t affect the thermal comfort
of the ventilated volume. System stability using the Nyquist criterion has also been examined and found to satisfy the
criterion. The multivariable DNA control technique and the SISO closed-loop PID controllers have shown the
capability to suppress external disturbances and restore the system to its original functional steady-state values.
Description
Keywords
HVAC, transfer function matrix, multivariable control, Direct Nyquist Array, loops decoupling
Citation
Touqan Basim, Abdul-Ameer, A. and Salameh Muna (2023) “HVAC multivariable system modelling and control,” Proceedings of the Institution of Mechanical Engineers, 237(9), pp. 2049–2061.