IPMVP Option D uses a calibrated thermal simulation model (eQUEST, EnergyPlus, IES-VE or equivalent) when baseline or reporting data are unavailable or unreliable, for example in new construction or full system replacements.

Option D is the 'model' method. Typical cases include new construction with no real baseline, full system replacement where the baseline is not comparable, absence of metering, and hypothetical/what-if audits. Calibration is critical: the model must reproduce measured consumption under verifiable conditions either before or after the ECM. ASHRAE Guideline 14 sets the calibration thresholds (NMBE <= 5 % and CV(RMSE) <= 15 % on a monthly basis).

Document every input assumption — auditors will challenge any unverifiable input long before they challenge the simulation engine itself.