6 An Optimal Control Strategy for Water-Cooled Direct Expansion System in Real-World Application

In this paper, the optimization-simulation approach based on Lagrange multiplier method is proposed to investigate energy saving potential of a water-cooled direct expansion (DX) cooling plant by refining the model of the HVAC system components and deriving optimal conditions for their operation subject to technical constraints. An actual water-cooled DX rooftop package of a real-world commercial building in hot and dry climate conditions is used for experimental data collection, modeling and strategy testing. Both inputs and outputs are measured from the field monitoring in one summer month. Based on the mathematical models and using collected data, modules incorporating the proposed optimal control strategy for the water-cooled DX air conditioning system with variable refrigerant flow rate are developed and embedded in a transient simulation software package. Simulation results are provided to show possibility of significant energy saving and comfort enhancement by implementing proposed optimal control strategy.