Design optimization, modelling, and performance evaluation of active chilled beam terminal units
Date of Issue2016-02-10
School of Electrical and Electronic Engineering
In recent years, the concept of green building enjoys a great popularity throughout the world. Energy conservation and Indoor Environmental Quality (IEQ) improvement in buildings receive consistent attentions from all walks of life. As the core element to create comfortable and healthy indoor environmental conditions for human beings, Heating, Ventilation, and Air-Conditioning (HVAC) systems which are also the largest source of energy consumption are necessary to be well studied and developed. Among various HVAC schemes, using active chilled beam terminal units is a very superior option for next generation HVAC solutions, which was listed as one of the 15 most promising HVAC related technologies by American Council for Energy Efficient Economy (ACEEE) in 2009. Active chilled beam terminal units based HVAC systems originate in Scandinavia and have been adopted widely in Europe and to some extent in Australia. More recently, the systems are penetrating into North America and Asia. However, in depth investigations on the systems are still inadequate. Some technical difficulties have emerged in the existing engineering application and need to be resolved for a wider acceptance, especially in the emerging markets. Therefore, this thesis tries to put some effort on this front, with the focus on the design optimization, modeling, and performance evaluation of active chilled beam terminal units for the tropical climate. The contributions of the thesis are briefly summarized as below: 1. As a core part of active chilled beam terminal units, the secondary heat exchanger should not be a standard “off the shelf” product as it used to be. In order to ma ximize t he coo ling capac it y w hile min im ize t he e ne r gy cons umpt io n, t he c irc uit a rra nge me nt is opt im ized. A n e xpe r ime nta l comparison study of four fin-tube heat exchangers with different circuit numbers is conducted to determine the optimal circuit number. Then, tube connecting sequences of the circuits are investigated. Though a series of experiment-aided simulations taking the in-situ secondary air velocity profile into consideration, optimal tube connecting sequences are proposed. With the optimized circuit arrangement, the performance of the secondary heat exchanger, as well as the terminal unit is substantially enhanced. More importantly, the findings and used methods will have significant effects on the design of future active chilled beam terminal units. 2. An appropriate model of active chilled beam terminal units is indispensable in the system design, simulation, performance evaluation, as well as development of advanced control and optimization strategies. However, the issue has been so far overlooked by the research communities. In this work, a hybrid dynamic model of the terminal units with few unknown parameters is established by deriving the model using first principles and estimating the parameters experimentally. Through this approach, a reasonable compromise is made between capturing the exact underlying physics and suitability for engineering applications. Static and dynamic performances of the model are verified. As the first reported model of active chilled beam terminal units, it is expected to have a wide range of applications in the aforementioned aspects. In addition, the modeling technique can be extended to the other terminal units. 3. When promoting the application of active chilled beam terminal units in different climates, inappropriate understanding of operating characteristics and efficiencies of the terminal units has probably been the essential obstacle. For example, in tropical regions, not only the sensible cooling capacity but also the latent cooling capacity of the terminal units should be matched with the counterparts of conditioned spaces to strictly avoid condensation. Nevertheless, the latent cooling capacity has never been involved in any studies. In order to address this issue, a series of simulations are carried out. The operating characteristics and efficiencies of the terminal units under variable air volume mode are revealed for the first time. The obtained result will be fundamental in designing and operating active chilled beam systems.