Study On Optimal Control Strategy Of VRF-rooftop Units Combining Air Conditioning System

Variable Refrigerant Flow (VRF) air conditioning systems have beenwidely used in buildings because of its energy-efficient features. However,fresh air can’t be introduced into the system, which is a big drawback. Inrecent years, many scholars focus on the study of simulation modelbuilding and components control strategy, but few on the fresh air. Asindoor air quality (IAQ) and energy saving are widely concerned, controlstrategies on the VRF and fresh air handling units are worth discussing.Simulation model of the VRF-Rooftop Units combining airconditioning system is built. Optimal control strategies are studied.Components model and refrigeration cycle algorithm are developed, anddynamic simulator is built. Simulation results show that the model can beused for the study of the control strategies.Thirdly, the optimal control strategies are studied. In terms of acertain amount of cooling load, the optimal control strategies studied theload ratio between the VRF part and the rooftop part to minimize thewhole energy consumption of the system. The objective function issolved based on the coefficient of performance (COP) prediction model.The load ratio is translated into the supply air temperature set point toachieve the optimal operation of the system. The optimization controllersare the core of the system. They are responsible for the cooling loadallocation. The local controllers are responsible for the optimal operationof the components under the load allocation by theoptimization controllers.Lastly, simulation experiments of the variable air volume, variableair supply temperature system under the control strategies are made. Results show that the indoor air conditions meet the design requirements.The system operation is stable and energy-efficient.