Cogen Gas Rates

Hello all, We are attempting to model a cogen system (using gas to create electricity and using waste heat for domestic water heating). My questions are as follows: 1. Normally you have to use the same energy rates in the baseline as well as the proposed. However, since we have a cogen system, I assume that we can use a different rate. The gas company gives much better rates for cogen than standard gas supply. Does this sound accurate? 2. We are using Trane Trace for the model, and have to input the domestic water as a supplementary purchased hot water in order to alter the rates. Does this sound acceptable, or would there be another way o input the altered rate? Thanks in advance all. We are hoping to get this right the first time around in order to minimize back and forth with the USGBC.