Performance assessment of hybrid chiller systems for combined cooling, heating and power production

Hybrid chiller systems that combine electric and absorption chillers can play critical roles in performances of a combined cooling, heating, and power (CCHP) or trigeneration system. The objective of the present study is to investigate a new strategy for hybrid chiller-based CCHP systems that can optimize electric power production while achieving zero-excess electricity generation for a given building. Using this operation strategy, energy and environmental performances were examined for two U.S. Department of Energy reference buildings (large office and hospital) located in two climates (San Francisco, CA and Long Island, NY). The results show that the hybrid chiller-based CCHP systems can save the primary energy consumption up to 5.8 GWh/y for the large office building and 13.6 GWh/y for the hospital compared to the conventional reference system that utilizes a central grid. More significant energy savings are realized for the hospital than the large office mainly due to high electric and thermal loads throughout the year. Carbon dioxide emission associated with a CCHP system highly varies with the emission factor of a local grid. In case of using the hybrid chiller system in Long Island, NY, the carbon dioxide emission is 0.2-1.5 kton/y lower than the reference system, whereas it is 1.1-1.5 kton/y higher in San Francisco. However, compared to traditional CCHP systems that utilize only absorption chillers, the hybrid chiller-based CCHP systems can reduce carbon dioxide emission by 0.7 kton/y for the large office and 3.5 kton/y for the hospital. When comparing the effects of building types and local climates, building types have more significant effects on the energy performance, while local grid conditions have larger impacts on carbon dioxide emission of a hybrid chiller-based CCHP system. Overall, the study results suggest that the hybrid chiller-based CCHP systems can reduce more energy and carbon dioxide emission for commercial buildings or districts with high thermal and electric loads during the cooling season.