Our project is a college residence hall in downtown Boston. Energy for heating will be purchased from a steam utility company, so the project will not include boilers. In calculating the energy performance of this building above the minimum requirements of ASHRAE 90.1-1999, can we compare a standard efficiency steam boiler as our base case (Energy Cost Budget)and a higher efficiency boiler (reflecting the higher efficiencies of the district steam boilers) as the design case (Design Energy Cost)? For example: To calculate the Energy Cost Budget: A building with an 80% efficient standard steam boiler (as per ASHRAE 90.1 1999, Table 6.2.1F). To calculate the Design Energy Cost: A building with a high efficiency steam boiler with equivalent efficiency as the district steam boilers(typical efficiency 85 to 88 %). We will document the exact efficiency of district steam boilers with a letter from the utility as part of the project LEED documentation.
The appropriate HVAC system selection for the budget building is described in ASHRAE 90.1-1999 Section 11.4.3. The budget systems descriptions in table 11.4.3A include note 6, which indicates that for systems using purchased steam the boilers are not explicitly modeled. The comparison as described is not permitted by the Standard.