Verifying the energy savings
Options overview – Option A – Option B – Option C – Option D
The primary difference between Options A and B is that Option A uses one-time baseline and post-installation “snap-shot” capacity, power measurements, or stipulated energy use, whereas Option B involves portable monitoring equipment installed in a facility for a period deemed sufficient to characterize lighting system performance during all operational periods, i.e., weekday, weekend, etc. Post-installation, the measurements are repeated to develop similar 24-hour profiles of lighting system energy consumption. Continuous post-installation measurements can also be taken.
Electricity savings due to reduced lighting energy consumption are calculated by analyzing the difference between measured 24-hour consumption profiles for the baseline and post-installation periods, and then projecting these savings to an annual calculated savings. Care should be taken to adequately capture the correct number of day-type profiles to accurately represent the facility’s baseline electricity use during weekday, weekend and holiday periods. In some cases, additional profiles may be needed to capture lighting energy use during secondary schedules. For example, educational facility loads often vary between school year and summer vacation periods. In some instances baseline, weekday/weekend profile measurements may be necessary during both of these times. Electric demand reductions can also be analyzed provided representative baseline and post-installation demand measurements have been taken. Post-installation measurements can either be taken continuously throughout the payback period or for a representative sample period. Savings can be projected with the appropriate statistical method.
Measurement accuracy is completely dependent on how well representative profiles match actual baseline and/or post-installation lighting profiles in the facility. Additionally, savings resulting from lighting efficiency and/or lighting controls projects that are calculated using Option B can be adversely affected by the same four factors which affect lighting projects evaluated with Option A