How to Measure Peak Demand with Set and Rolling Averages

How to Measure Peak Demand with Set and Rolling Averages


Knowing how your utility company measures demand is important because it can affect how you minimize peak demand charges. Utility companies use two common methods to measure peak demand, rolling average and set average. A rolling average calculates a new demand value every minute for a set time frame (eg. 15 min). With this method, you’ll see a new 15-minute demand value every minute. The other method, set average, measures peak demand once at the end of an interval. You can see the difference below; rolling average (green) results in a higher peak demand value during this time period than the set average demand (purple). Additionally, the rolling average demand was calculated 30 times between 9:30 am and 10:30 am while the set average demand was only calculated twice.


You can configure your eGauge to measure either type of peak demand using formula registers. Here’s how:

Note: To measure average demand correctly when back-feeding energy to the utility, it is important to create a “grid” register that records only positive values. If you do not, the average demand register may sometimes show a negative value, which is inaccurate.


How to Add Rolling Demand (updates every minute)
Go to your eGauge interface, click on Settings and then Installation. Then find the section titled “Registers” and click the button that says “Add Register”. Name your register, select the “=” option in the drop-down menu and enter this formula: ravg(REGISTER_NAME, INTERVAL). In the example below, we measure the rolling average demand from the whole building with a 15-minute interval. The same formula could be used to measure individual circuits or equipment.


How to Add Set Demand (updates once per interval)
Go to your eGauge interface, click on Settings and then Installation. Then find the section titled “Registers” and click the button that says “Add Register”. Name your register, select the “=” option in the drop-down menu, “power [W]” in the next drop-down, and enter this formula: savg(REGISTER_NAME, INTERVAL). In the example below, we measure the set average demand from the whole building with a 30-minute interval.