Sensitivity Analysis of a Biomass Fired Stirling Engine Combined Cooling, Heating, and Power System for a Small Office Building

Abstract

Over the past decade, rising energy demand and cost have created a surge of interest in alternative methods of power generation. As a result, the implementation of combined cooling, heating, and power (CCHP) systems has become a potential candidate for substitution in conventional power generation. The evaluation of a CCHP system must be based on its potential for savings in cost and primary energy reduction. In general, a CCHP system includes several components to satisfy the electric and thermal demands of the facility. These components include the prime mover, heat recovery system, auxiliary boiler, absorption chiller, heating coil unit, and hot water system unit. In practice, the most common prime mover used in CCHP technology is the internal combustion engine, which is limited by low thermal efficiency and poor emissions. Hence, this paper proposes the use of a Stirling engine prime mover that makes use of waste wood chips for fuel. In addition to the standard CCHP components, the Stirling engine houses heat exchangers to aid heat addition and rejection processes. These heat exchangers must be considered along with the other components when analyzing energy requirements. The goal of this study is to determine how the operational characteristics of a constant output biomass-fired Stirling CCHP system are affected by the performance of the individual CCHP system components. The results of this sensitivity analysis are useful in determining the most important parameters to be considered when implementing and designing the system. Results suggest that fuel cost, engine efficiency, engine size, chiller efficiency, and the Stirling engine’s hot side heat exchanger play the most important roles in the CCHP system operational cost. For example, the results show that increasing the engine size leads to increases in primary energy. In addition, an optimum engine size is suggested for cost savings, with smaller and larger engines both leading to increases in operational cost.