In a previous post titled "DES Energy Cost" dating back to May 13, 2013, my interpretation of the responses in the thread is that a project can choose to either follow 90.1 or the DES Guidance from LEED for determining energy rates applied in a project that is served by a district system. Up until finding this comment thread, my understanding had been that if a project was served by a DES it was required to follow the district guidance document published by LEED. Does anyone know if it is still the case that applying the DES Guidance is optional and a project team could instead choose to follow rules in 90.1? If so, what section of documentation or what LEED Interpretation would one use to come to this conclusion?