First and Second Law Thermodynamic Analysis of a Domestic Scale Trigeneration System

The potential use of small-scale trigeneration systems in domestic homes, especially for emergency use in the event of a hurricane or natural disaster where electricity and useful power are at a premium, is increasing. They have the ability to produce both useful thermal energy and electricity from a single source of fuel such as gasoline, natural gas, or other alternate fuel. However, small-scale systems present some technological challenges in order to achieve a significant increase in efficiency over conventional systems. This paper addresses the fundamental question of the splitting of a hot exhaust into two heat recovery heat exchangers that are part of a trigeneration system. We consider a system which produces electricity, refrigeration, and hot water by recovering waste energy from a reciprocating internal combustion engine. First and second law analyses were performed on the refrigerator and water heating heat exchangers and on the overall system. An optimal splitting of the available hot exhaust stream between the refrigerator and the hot water heat exchangers is identified. The thermodynamic optima is sharp and robust with respect to the variation of refrigerant and water inlet temperatures.