Development of a Component Based Simulation Tool for the Steady State and Transient Analysis of Vapor Compression Systems

Abstract

Computer simulations have become a commonly used tool to aid engineers design and optimize vapor compression systems. Generally, the simulation of vapor compression heat pump systems falls into one of two categories; steady state and transient. Steady state simulations are typically very accurate and highly detailed, and used for design and optimization of vapor compression systems and components. Transient simulations generally utilize more assumptions to reduce complexity and computational time, and are used to design and evaluate control strategies. However, utilizing two separate simulation tools to perform steady state and transient simulations presents the challenge and burden of increased software development and maintenance effort and inconsistency in the predicted results. This thesis presents a simulation tool that simultaneously serves the industry needs of an integrated steady state and transient vapor compression simulation tool. The tool is developed using a component-based architecture allowing for the users to incorporate in-house component models into the simulation and the component-based framework is discussed in detail. Particular emphasis is placed on transient heat exchanger simulation; resulting in an algorithm that reduces complex and detailed heat exchanger models into simplified, faster versions that still have sufficient accuracy so that transient and steady state results converge to the same performance under steady state conditions. Thus, consistency in the results between the steady state and transient simulations is preserved.

Nearly all pre-existing vapor compression system simulation tools are limited to the standard four component cycle. However, for enhanced efficiency and thermal comfort, multi-component systems are gaining in popularity. The component-based framework implemented by the simulation tool allows for the simulation of cycles with additional components.

During the development of the simulation tool, the need of a faster, more robust solution algorithm to solve a steady state vapor compression system became evident. Thus, a new solution algorithm was developed, thoroughly tested, and compared with existing solution techniques in the literature. An improvement of 50% was achieved in the solution algorithm's robustness. A more advanced method to determining initial guess values for steady simulations was developed and reduced the number of component evaluations by approximately 40%.