Economic Optimization of a Combined Heat and Power System for an Office Building

The determination of a prime mover’s characteristics is important in ascertaining its suitability for combined heat and power (CHP) applications. By definition, its operation affects the operation of all heat recovery equipment downstream. The correct balance between component electrical efficiency and waste heat is needed if the electric power producing equipment is to be used in a CHP application in a cost effective manner. Understanding the relationship between electric efficiency and exhaust stream energy content for different prime movers systems is a first step in an overall CHP system optimization. The goals of this work are to determine the potential financial benefit of utilizing waste heat from various prime mover configurations as well as establish the relationship between the two types of energy generation and costs. An economic optimization was performed to determine the system with the lowest average product (electricity and thermal energy) generation cost. The prime mover system was required to meet the electrical load demand of a typical 9290 m² (100,000 ft²) office building in New York, NY, USA. The composition of the most cost effective prime mover system, when considering both electrical and thermal energy generation, was shown to be a single microturbine. When comparing the electrical and thermal energy generation of all systems studied with product generation cost, the more cost effective systems had either high electrical efficiency with a low thermal energy generation or high amounts of waste heat with low electrical efficiency. Each installation site and load demand is unique. The results of this study, along with others, can be used to help determine a cost effective system for a particular application.