Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
To answer your second question, Section G3.1.2.2 of ASHRAE Standard 90.1-2007 is where the 15% number comes from and says:
G3.1.2.2 Equipment Capacities. The equipment capacities for the baseline building design shall be based on sizing runs for each orientation (per Table G3.1, No. 5a) and shall be oversized by 15% for cooling and 25% for heating, i.e., the ratio between the capacities used in the annual simulations and the capacities determined by the sizing runs shall be 1.15 for cooling and 1.25 for heating.
So this applies to the baseline only. The proposed design should use the actual capacities for the design.
