Exergetic analysis for improving the operation of building mechanical systems: results and recommendations

A review of past research reveals that while exergetic analysis has been performed on various building mechanical systems, there has not been extensive efforts in the areas of retrocommissioning air distribution systems or fault detection for cooling plants. Motivations for this new work include demonstrating the merits of exergetic analysis in association with retrocommissioning (RCX) an existing building air handling unit (AHU), as well as conducting an advanced analysis on an existing chiller for the purposes of health monitoring. The following research demonstrates the benefits of including a second law analysis in order to improve equipment operation based on lowered energy consumption and improved operation, and as a means for system health monitoring. Particularly, exergetic analysis is not often performed in the context of RCX, therefore this research will provide insight to those considering incorporating exergetic analysis in their RCX assessments. A previously developed RCX test for assessing an AHU on a college campus, as well as data collected from the testing is utilized for an advanced thermodynamic analysis. The operating data is analyzed using the first and second laws of thermodynamics and subsequent recommendations are made for retrofit design solutions to improve the system performance. The second law analysis provides beneficial information for determining retrofit solutions with minimal additional data collection and calculations. The thermodynamic methodology is then extended to a building's cooling plant which utilizes a vapor compression refrigeration cycle (VCRC) chiller. Existing chiller operational data is processed and extracted for use in this analysis. As with the air handling unit analysis, the second law analysis of the VCRC chiller provides insight on irreversibility locations that would not necessarily be determined from a first law analysis. The VCRC chiller data, originally collected several years ago for the design of an automated fault detection and diagnosis methodology, is utilized. Chiller plant data representing normal operation, as well as faulty operation is used to develop a chiller model for assessing component performance and health monitoring. Normal operation and faulty operation data is analyzed to determining the viability of using existing data and performing an exergy analysis for the purposes of health monitoring. Based on RCX activities and thermodynamic analyses, conclusions are drawn on the utility of using exergetic analysis in energy intensive building mechanical systems in order to improve system operation. The results show the utility of the analysis and illustrate system performance.