Ventilation Control and Ventilation Performance of Multi-zone Air Conditioning Systems

The indoor air quality (IAQ) and energy consumption of buildings have received increasing concern over the last twenty years. The optimal ventilation control of multi- zone VAV Air-conditioning (HVAC) systems provides great potential in reducing energy consumption while ensuring acceptable IAQ and satisfactory thermal comfort. However, most of them cannot always maintain satisfying ventilation performance due to variable indoor thermal comfort and pollution sources of different ventilation zones. Another important issue is that the modeling of the space ventilation usually uses perfect mixing models in conventional dynamic ventilation simulations to test and evaluate the control of air-conditioning systems. However, the complete-mixing air model fails to consider the impact of non-uniform air temperature stratifications on the ventilation performance.;Therefore, the aim of this study is to develop an online ventilation optimal control strategies for multi-zone air-conditioning systems to minimize the overall system energy consumption while maintaining satisfactory IAQ. A CFD-based virtual ventilation test system is also developed to evaluate the dynamic ventilation performance by taking account of indoor air stratification phenomena using a CFD-based space temperature offset model. The aim is achieved through addressing the following objectives. (1) Develop a CO2-based adaptive Demand Controlled Ventilation (DCV) strategy, (2) Develop an indoor air temperature set point reset strategy for critical zones, (3) Develop a model-based indoor air temperature set point resetting strategy for critical zones, and (4) Develop a model-based outdoor air flow rate optimal control strategy for a full air system with primary air handling units. In addition, a CFD-based ventilation test method is developed for control and optimization of the indoor environment by combining a ventilated room with a ventilation control system in a simulated environment.;A simulation package developed on the Transient Simulation Program (TRNSYS) is used as the simulation platform to validate and evaluate the performance of the proposed different ventilation optimal control strategies. The test results showed that about 1.01%∼17.7% energy in the system under investigation can be saved when using these optimal control strategies when compared with the conventional ventilation control strategies.