Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Mago, J. Pedro

Committee Member

Hodge, B. Keith

Committee Member

Srinivasan, K. Kaylan

Committee Member

Luck, Rogelio

Date of Degree

5-1-2010

Document Type

Dissertation - Open Access

Major

Mechanical Engineering

Degree Name

Doctor of Philosophy

College

James Worth Bagley College of Engineering

Department

Department of Mechanical Engineering

Abstract

Increased demand for energy, rising energy costs, and heightened environmental concerns are driving forces that continually press for the improvement and development of new technologies to promote energy savings and emissions reduction. Combined heating and power (CHP), combined cooling, heating, and power (CCHP), and organic Rankine cycles (ORC) are a few of the technologies that promise to reduce primary energy consumption (PEC), cost, and emissions. CHP systems generate electricity at or near the place of consumption using a prime mover, e.g. a combustion engine or a turbine, and utilize the accompanying exhaust heat that would otherwise be wasted to satisfy the building’s thermal demand. In the case of CCHP systems, exhaust heat also goes to satisfy a cooling load. An organic Rankine cycle (ORC) combined with a CHP or CCHP system can generate electricity from any surplus low-grade heat, thereby reducing the total primary energy, cost, and emissions. This research first presents a review of the economical, energetic, and environmental benefits of CHP and CHP-ORC systems for a small office in various climates. Operating the systems 24 hours a day is compared to operating the system during typical office hours and benefits of the CHP system in terms of the EnergyStar and LEED programs are presented. Another objective of this dissertation is to study the critical role of the prime mover on the performance of CHP, CCHP, CHP-ORC, and CCHP-ORC systems under different pricing structures. Three different size natural gas engines are simulated for a small office under different operational strategies such as: follow the facility's electric demand, follow the facility's thermal demand, and follow a constant load. Simple optimizations were carried out to improve the system's performance. Using real prices for electricity and fuel to compute operational costs was compared to using the building's average prices without a CCHP system. Finally, a CCHP system using a load-share turbine for a large office building was examined while considering the source of carbon dioxide emissions, carbon offsetting through purchasing carbon credits, and available capital costs.

URI

https://hdl.handle.net/11668/15069

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