LIFE CYCLE ENERGY AND EXERGY ANALYSIS FOR BUILDING COOLING SYSTEMS - A COMPARISON BETWEEN A SOLAR DRIVEN ABSORPTION CHILLER AND AN ELECTRIC DRIVEN CHILLER

Buildings in the United States utilize 39% of the primary energy, and more than 60% of that energy consumption is provided for heating and cooling in buildings. Most of the heating and cooling systems commercially available in the market today are driven by electricity and natural gas, which are high exergy resources, while the operating temperature in the building from a year-round perspective is closer to the reference environmental temperature. Thus, from a thermodynamic point of view, there exists a gap between the high exergy resources/supply and low exergy application/demand in buildings. This paper extends the traditional means of energy comparison between solar driven absorption chillers and electric driven chillers. A life cycle energy and exergy analysis is developed with the assumption that the fossil fuel for electricity generation is a different form of storing solar energy in the long run. Thus, both the systems are driven by solar energy, and the only difference is that the solar absorption chiller is an instantaneous solar energy utilization, while the electricity chiller utilizes the stored solar energy. A simple absorption chiller model is developed, and is calibrated using a paper published by the Center for Building Performance and Diagnostics in Carnegie Mellon University, using a 4-ton 2-stage absorption chiller provided by Broad Air Conditioning. The energy and exergetic efficiencies in each process are analyzed and provided in the two systems. This paper is useful in understanding the fundamental life cycle energy and exergy in chiller applications for building cooling.