Trigeneration system, which produces heat, cold and electricity simultaneously, is generally designed based on the nominal condition. However, the utility demands are seldom. fixed and they are usually changing in periodical manner with the climate and the human activities. These demand changes make the system design difficult. To ensure operability, the system should be feasible and flexible to tackle such demand variations. Over-sizing, thermal storage and. flexibility re-allocation can be used to improve a trigeneration system's feasibility and. flexibility. These techniques may enlarge the feasible operating region, change and shift the expected utility production demands and interchange between different generation capabilities according to the demand requirements. As a result, the process feasibility and. flexibility can be improved. With feasible operation ensured, process. flexibility can be considered under economic trade-offs. A. flexible design with reasonable investment and operating costs provides additional benefits to cater demand changes in the future. In this study, process. flexibility and feasibility characteristics are proposed and evaluated from a new perspective. These are demonstrated in the trigeneration system design with a pre-defined structure to handle periodical utility demand deviations in a commercial building complex. (C) 2009 Elsevier Ltd. All rights reserved.