Evaluation of CCHP systems performance based on operational cost, primary energy consumption, and carbon dioxide emission by utilizing an optimal operation scheme Heejin Cho, Pedro J. Mago * , Rogelio Luck, Louay M. Chamra Department of Mechanical Engineering, Mississippi State University, 210 Carpenter Engineering Building, P.O. Box ME, Mississippi State, MS 39762-5925, USA article info Article history: Received 13 November 2008 Received in revised form 13 April 2009 Accepted 15 April 2009 Available online 13 May 2009 Keywords: CCHP systems Optimal energy dispatch algorithm Primary energy consumption abstract Optimization of combined cooling, heating, and power (CCHP) systems operation commonly focuses only on energy cost. Different algorithms have been developed to attain optimal utilization of CCHP units by minimizing the energy cost in CCHP systems operation. However, other outcomes resulting from CCHP operation such as primary energy consumption and emission of pollutants should also be considered dur- ing CCHP systems evaluation as one would expect these outcomes can be subject to regulation. This paper presents an optimization of the operation of CCHP systems for different climate conditions based on oper- ational cost, primary energy consumption (PEC), and carbon dioxide emissions (CDE) using an optimal energy dispatch algorithm. The results for the selected cities demonstrate that in general there is not a common trend among the three optimization modes presented in this paper since optimizing one param- eter may reduce or increase the other two parameters. The only cities that show reduction of PEC while also reducing the CDE are Columbus, MS; Minneapolis, MN; and Miami, FL. For these cities the opera- tional cost always increases when compared to the reference case consisting of using a vapor/compres- sion cycle for cooling and natural gas for heating. On the other hand, for San Francisco and Boston, CCHP systems increase the CDE. In general, if CCHP systems increase the cost of operation, as long as energy savings and reduction of emissions are guaranteed, the implementation of these systems should be considered. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Traditional power plants convert about 30% of the fuel’s avail- able energy into electric power. The majority of the energy content of the fuel is lost at the power plant through the discharge of waste heat. Further energy losses occur in the transmission and distribu- tion of electric power to the individual user. Inefficiencies and pol- lution issues associated with conventional power plants provide the impetus for developments in ‘‘onsite and near-site” power gen- eration. Combined cooling, heating, and power (CCHP) systems have the potential to reduce carbon and air pollutant emissions and to increase resource energy efficiency dramatically. These sys- tems use reciprocating internal combustion engines, turbine en- gines, and even fuel cells to generate electrical power while recovering waste heat for heating or cooling (through absorption chillers) purposes. CCHP systems produce both electric and useable thermal energy onsite or near site, converting as much as 80% of the fuel into useable energy. A typical CCHP system consists of a power generation unit (PGU) interacting with thermally-activated components, such as absorption chillers, cooling towers, and air handling units (AHUs). A variety of PGUs can be used in CCHP systems: micro-turbines, internal combustion (IC) engines, fuel cells, etc. Fig. 1 illustrates a schematic of a CCHP system. As shown in this figure, Fuel (F pgu ) is supplied to the PGU, and it produces electric energy (E pgu ) and rejects heat as byproduct that is normally wasted in many applica- tions. This electric energy is used to power appliances and lights in the building (E building ) and operate auxiliary cooling and heating components (E comp ). If the PGU does not produce enough electric energy to satisfy the electric demand, the difference (E grid ) can be imported from the electric grid (EG). If there is excess electricity (E excess ), it can be exported or sold to the EG. The recovered waste heat (Q rcv ) from the PGU is used to produce cooling or heating (Q cool or Q heat ) to satisfy the building cooling and heating loads. If the heat recovered from the PGU is not enough to fulfill the thermal energy requirement for building space cooling and heating, a boiler is used to provide the remaining required heat (Q boiler ). Design of CCHP and CHP systems involves selection of the type and size of components (power generator, heat exchanger, absorption chiller, etc.). The selection process must take into 0306-2619/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2009.04.012 * Corresponding author. Tel.: +1 662 325 6602; fax: +1 662 325 7223. E-mail address: mago@me.msstate.edu (P.J. Mago). Applied Energy 86 (2009) 2540–2549 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy