Generally, conventional controllers for comfort are designed by using on/off
control or proportional-integral (PI) control, with little consideration of energy
consumption of the system. This paper presents a multi-input-multi-output
(MIMO) model predictive control (MPC) for a direct expansion (DX) air conditioning
(A/C) system to improve both indoor thermal comfort and air quality,
whereas the energy consumption is minimised. The DX A/C system is modelled
into a nonlinear system, with a varying speed of compressor and varying
speed of supply fan and volume flow rate of supply air being regarded as inputs.
We first propose an open loop controller based on an optimisation of energy
consumption with the advantage of a unique set of steady states. The MPC
controller is proposed to optimise the transient processes reaching the steady
state. To facilitate the MPC design, the nonlinear model is linearised around its
steady state. MPC is designed for the linearised model. The advantages of the
proposed energy-optimised open loop controller and the closed-loop regulation
of the MIMO MPC scheme are verified by simulation results.