Optimization Design of a District Heating and a District Cooling System Using Waste Heat Recovery from Power Plants on Isolated Island and Feasibility Assessment of Energy Savings Performance Contracts
Date Issued
2015
Date
2015
Author(s)
Lai, Ching-Hsien
Abstract
This dissertation numerically investigates the optimization design of a district heating and cooling system using waste heat recovery from the diesel generators of power plants on an isolated island and the feasibility assessment of energy savings performance contracts (ESPC) with energy-savings project. Firstly, the mathematical models of the hourly available waste heat for systems and the power consumption of systems are developed. In consideration of both parties, the power company and the energy service company (ESCO), the ESPC of energy-savings project is planned. This study then compares the performances of four updating rules of the particle swarm optimization (PSO) through applying four mathematical problems. The linear-decayed inertia weight method is favorable for this study because stability is the target solution. The objective function of the optimization design includes the initial cost and the running cost during the life-cycle period. In this study, the PSO method is adopted to acquire the minimum value of the objective function, where the constraints include the conservation of energy between absorption chiller and chilled water storage tank of district cooling system (DCS). The optimization result of the DCS is achieved with a 380 kW absorption chiller and a storage tank with a capacity of 1,500 kW-hr. Furthermore, the study compares energy-saving efficiency with and without the district heating and cooling system. In district heating system (DHS), it has been proved that the yearly average energy conservation rate, electricity consumption, diesel consumption, and CO2 emissions can be reduced by 95.1%, 9,237.6 MWh, 23,220 L, and 168 ton respectively. In district cooling system, it has been shown that the yearly average energy conservation rate is approximately 75.7%, whereas the yearly electricity consumption, diesel consumption and CO2 emissions can be reduced by 955.8 MWh, 32,566 L and 228 ton respectively. Setting the project period of 10 years, and the project lending rates of 2.25%, the results show that the energy-savings project combining DHS and DCS yield maximum income. For the power company, operation without ESPC results in the most income. The payback period and the income with ten-years of timespan are six years and 21,758,719 TWD respectively. Moreover, the return on investment is 54.9%. For ESCO, the contract type of shared savings has maximum income. The payback period and the receipts of ten-years are six years and 19,912,488 TWD respectively. Additionally, the return on investment is 48.3%. According to the current interest rate of this energy-saving project, the discounted interest rate for isolated islands’ constructions lower than 2.25 % would provide incentive for the execution of this project. Otherwise, the execution of this project would be hindered due to higher costs and longer payback periods.
Subjects
district heating system
district cooling system
waste heat recovery
particle swarm optimization
energy savings performance contracts
Type
thesis