Tri-generation is a novel application of energy technologies which simultaneously produces heat, refrigeration and electricity. An expression for the calculation of the thermodynamic performance of a generic tri-generation scheme is presented. A brief first-law analysis involving an energy conversion ratio and newly defined heating-to-cooling and electric-to-cooling load ratios to usual system component thermodynamic parameters (such as coefficient of performance or prime mover thermal efficiency) was carried out. To illustrate the usefulness of the criterion, a tri-generation pilot plant set up in an office building was studied. (C) 2010 Elsevier B.V. All rights reserved.