Control and energy simulation of variable refrigerant flow air conditioning system combined with outdoor air processing unit

A variable refrigerant flow (VRF) unit and outdoor air (OA) processing unit combined air conditioning system is proposed as a solution for ventilation problems in VRF systems. System structure and control strategies are addressed. Simulation platform is established based on component and sub-system models developed. Control and energy performances analysis are then put forward under various conditions. It is found that the combined system could maintain all the zones at their specific set-points within small errors no matter set-points of the zones are the same or different. In addition, indoor air quality can be ensured. Energy efficiency characteristics of the combined system are greatly affected by the OA supply temperature of the OA processing unit, which opens up the opportunity of minimizing the energy consumption of the combined system through optimal control strategy. Results reveal that the best OA supply temperature can be obtained through optimizing part load ratio of the OA processing unit to a range in which the system operates with high efficiency. - Highlights: •A VRF and ventilation combined system is proposed to take merits of both parts. •A simulation platform is developed for the combined system. •The combined system could maintain thermal comfort and indoor air quality. •Characteristics of system energy efficiency are revealed for further optimal control