Design optimization and energy performance evaluation of a dedicated outdoor air system with dual cooling sources

Abstract

Dedicated outdoor air systems can save cooling energy and improve thermal comfort compared to conventional air-conditioning systems. Although many studies have investigated the energy performance of dedicated outdoor air systems for a certain application, there is a lack of a modeling resource to investigate with how the designs of the system are coordinated with control strategies aiming to improve its energy efficiency. This paper aims to optimize dedicated outdoor air system designs and develop a flexible model to evaluate the performance of the system. First, two innovative energy-saving designs of dedicated outdoor air system with dual cooling sources were proposed. Alternative design 1 optimizes the structure of the fresh air unit, while alternative design 2 builds on alternative design 1 by coupling it with a heat recovery system. Then, the two innovative systems and a baseline design were modeled using the equation-based Modelica tool. Finally, the energy performance of the three systems was evaluated under a hot and humid climate. Results showed that the Modelica-based models are able to capture the transient control strategy details. Alternative design 2 was found to be the optimal design among the three designs, with the highest energy efficiency ratio of chiller plants at 5.3. Moreover, it can reduce the cooling load supply by 9.3% and save about 7.4% on the energy consumption of chiller plants compared to the baseline design. In addition, alternative design 2 has a payback period of only 2.7 years, compared to the baseline design. It reveals the benefit of the heat recovery system in reducing the energy consumption and the cost of the cooling system. The developed dedicated outdoor air system simulation model can provide an evaluation for further improving the system optimization design, control strategy, and equipment configuration in engineering applications.