Integrated Combined Heat and Power and Gas Cooling

Fully dedicated on-site combined heat and power (CHP) systems present both challenges and opportunities for large multi-building projects; particularly when employing a combined cycle approach in the 3–20 MW range1. While some distributed power generation systems hedge their bets through reliance on both the sale and export of power (e.g., paralleling with a serving utility to achieve favorable economics), disappointing de-regulation benefits and the failure of energy trading to smooth out power supply vs. demand cost uncertainty has been a sobering experience for many California customers. Recent rethinking by concerned CHP designers has focused on exploring smaller footprint alternatives to use of higher cost heat-recovery- steam-generators (HRSGs). One such approach involves the use of prefabricated and fully integrated steam generators, complete with associated heat exchangers, controls and pumping systems, employing low pressure, non-volatile, recirculating heat transfer fluids (HTF) capable of direct heat extraction of turbine exhaust gas waste heat to generate steam and allow cascading the remaining captured waste heat to drive absorption chiller(s), and space and domestic hot water heating systems enabling greater utilization of available heat reclamation potentials in satisfying highly variable annual building power, heating and cooling load demands. This is achieved through maintaining favorable log-mean-temperature- differentials (LMTDs) at the turbine gas extraction coil also resulting in a lower exhaust gas temperature discharge to ambient. Various examples of such alternative HRSG cycles will be presented for gas turbine driven chiller and/or generator application, as well as gas turbine combined cycle operation to demonstrate the operational versatility and life cycle benefits of this approach for the above referenced range of commercially available gas turbines.