Comparing the Eco-Footprint of On-Site CHP vs. EPGS Systems

This paper compares the Eco-Footprint of three (3) sustainable on-site CHP system alternatives vs. a representative 30% thermally efficient conventionally designed remote electric utility/merchant power generation station (EPGS) serving a 3.5 MW gas turbine installation proposed for a central California university campus. It has been demonstrated (ASHRAE Transactions # DA-07-009) that sustainable on-site cooling-heating-power (CHP) systems for large multi-building projects employing a simplified design approach from that of a conventionally designed mini-utility-type CHP systems employing large volume/footprint, costly, high thermal mass heat-recovery steam-generators (HRSG’s), and 24/7 stationary engineers, can result in lower annual owning and operating costs. The above peer-reviewed 2007 paper illustrated the use of prefabricated, skid-mounted hybrid steam generators with internal headers, fully integrated with a low-pressure drop heat extraction coil (in lieu of a HRSG) located in the combustion gas turbine (CGT) exhaust. Subject CGT extraction coil utilized environmentally benign heat transfer fluid to redistribute extracted CGT exhaust waste to serve campus multi-building annual space cooling, heating, and domestic hot water loads with system thermal balance facilitated via maintenance of a high year-round log-mean-temperature-differential at the CGT extraction coil, also resulting in a lower CGT back-pressure, and significant life-cycle cost savings. This paper also takes an alternative look at the above referenced CHP plant designs for greater operating economies along with a third CHP alternative employing a direct CGT exhaust gas fired 2-stage absorption chiller, and then compare the Eco Footprint and life cycle cost for each of the three CHP options with the above referenced EPGS supplying comparable annual electric power requirements. Finally, using the Eco Footprint of the EPGS as a baseline, the most promising CHP alternative of the above three will also be explored as a potential “cap and trade” candidate to further reduce its first cost and therefore enhance its sustainability from both an energy with greenhouse gas emissions standpoint.