Plug Load Reduction Using ASHRAE - 2010

The issue you will run into is what is your Baseline assumption regarding what was left on. This potentially reduces run time but only if your Baseline assumption is that all or a portion of this load was left on. I think you would need to find data to support this assumption if you are claiming savings.

Is there any reason to believe that the rationale from LEED Interpretation ID# 10462 could be used to assume that a LEED v3 project could assume a 20% energy reduction in plug loads for the proposed case model when the design meets the requirements of 90.1-2010 section 8.4.2?

Makes sense to me. I would think you this is sufficient justification for a 20% savings.

The comment from Marcus is spot on, I have provided a calculation for a couple of project with the same justification without any problems for GBCI reviewers.  My baseline is based on the energy calculations with the same schedule as the other systems for the occupied space (i.e. HVAC, lighting, etc.)  These controls are tied into the lighting controls (occupancy/vacancy sensors), so the same schedule you utilize for the lighting has to be applied.  I has justified the % savings using ASHRAE table G3.2. This table applies to Power Adjustment Percentages that are above and beyond that required by the Mandatory Measures.  I do not think you can justify anything beyond what a bunch of engineers came up over lengthy discussions at their committee meetings.  So anything above 10% - 15%, depending on the specific case you have on your project might not get approved or may get you a question from the reviewer.  If you try to achieve 20% you are going to have to explain the rational behind the assumption, since it is assuming more savings than on Table G2.3.