Modeling Method and Assumptions

Hybrid Degree Day Analysis: Innovative method for computation of energy usage and savings:

• If utility data is available, OptiMiser calculates baseline energy usage from the bills. Then, a weather-normalized load is calculated from the baseline using the Princeton Scorekeeping Method (PRISM) regression modeling technique.
• All savings in OptiMiser are computed relative to this empirical baseline, not from the difference between two theoretical energy use models.
• OptiMiser computes ground coupling heat loss using possibly the best system available for this problematic area of calculation: BASECALC as implemented through BASEIMP which was developed for the HOT 3K modeling project of the Canadian Government.
• OptiMiser’s capacity to simultaneously model all improvements requires that over 40 complete variable base temp-HDD & CDD models are calculated simultaneously with each change in a control.
• Impacts from each improvement affect the variable base temperature and BLC through mechanisms that are estimated using traditional modeling techniques.
• Hourly models are used to model heat pumps, whole house fans, infiltration, and setback thermostats. All of these require hourly modeling to accurately estimate their impact.
• Solar gains through windows are modeled using hourly sun angle positions and hourly TMY3 insolation data. Solar gain computed by this hourly model modifies the base temperature in the OptiMiser analysis.
• By modifying the base temp, OptiMiser takes advantage of the computationally efficient adjustment for usability provided by standard degree day analyses. In contrast, hourly iterative modeling requires much greater computational resources.

Attached is OptiMiser’s original DOE Waiver Application, which contains many technical modeling specifications.