Verifying the energy savings
Options overview – Option A – Option B – Option C – Option D
Option D is intended for energy conservation retrofits where calibrated simulations of the baseline energy use and/or calibrated simulations of the post-installation energy consumption are used to measure savings from the energy conservation retrofit. Option D can involve measurements of energy use both before and after the retrofit for specific equipment or energy end use as needed to calibrate the simulation program.
To measure electricity savings and thermal take-back from lighting/controls projects: i) create a baseline simulation model of the building, ii) calibrate the baseline model to either monthly data supplemented with snap-shop measurements or hourly data for the whole-building, iii) retrofit the building, iv) make changes to the input file that accurately reflect the retrofit, v) create a calibrated post-installation simulation model, and vi) measure the savings by comparing the calibrated baseline model to the calibrated post-installation simulation model.
Calculating Electricity Savings. These savings are calculated by analyzing the difference between the calibrated baseline and post-installation simulation. Care should be taken to adequately capture the correct number of day-type profiles which accurately represent baseline electricity use during weekday, weekend and holiday periods and to verify that these daytypes have been input properly into the simulation program. Annual savings projections are then calculated by comparing the baseline simulation to the post-installation simulation. Savings are significant if the difference between the model-predicted baseline and post-installation energy use is greater than model error as determined by the RMSE.
Calculating Peak Electric Demand Reductions. Electric demand reductions can also be analyzed provided representative baseline and post-installation measurements have been taken and used to calibrate the simulation programs. Both the owner and contractor/ESCO should understand that this analysis provides an hourly demand savings estimate which may not represent actual demand savings from the lighting project, especially if 15-minute or less than hourly demand intervals are in effect.
Calculating Interactive Heating/Cooling Savings. Interactive heating/cooling savings estimates can be calculated by the calibrated simulation program providing other changes are not made to the baseline and post-installation simulation programs. The owner and contractor/ESCO should agree in advance which type of weather file will be used to perform comparative calculations. Measured weather data corresponding to the post-installation period will yield the most accurate results. In cases where this data is not available, average-year weather data may be used.
Limitations Of Calculating Retrofit Savings From Lighting Efficiency and/or Controls Projects Using Option D. These calculations can be adversely affected by the following factors:
Demand savings may not match buildings where actual demand intervals of less than 60 minutes are used.
Simulated savings using Option D may not match actual savings because the simulations use average operation profiles and specified equipment performance parameters. If operating profiles change or equipment performance changes, simulation programs will need to be modified to reflect these changes.
Savings estimates may vary if there is a significant number of lamp outages or if the actual operating schedule varies significantly from the stipulated operating schedule.
Thermal savings predicted by Option D are only as good as the simulation program’s representation of the actual building envelope and HVAC systems.
Thermal savings are limited to how well the lights-to-space assumptions match actual building configuration.