Scenario: Campus new construction projects which are connecting to an existing central plant for heating and cooling. The reference guide and DES guideline are clear that you must consider the refrigerant in the central plant (or District Energy System) when doing the calculation. One of the variables in the EAc4 calculation is service Life of equipment. These values are provided for new equipment by the ref guide and ASHRAE.

Question: For the existing central plant equipment, should the service life be the full rated service life as published by ASHRAE or a prorated life accounting for the current age of the equipment (since it is not new)?