Can I Calculate Plug Load Energy Savings Without the Exact Number of Devices or the Standby Loads?

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Energy Saving Calculation

Yes, it’s possible to calculate potential plug load energy savings without having detailed device information using an automated savings calculator. While the estimate will be less accurate than an estimate using actual device counts and standby load data, it is often sufficient to determine whether to proceed with a detailed audit, especially given the fact most energy managers do not have the tools or enough information to confidently estimate potential savings on their own.

Rule of Thumb Estimate

Lacking specifics about devices and loads, the following rule of thumb can be used to gauge potential energy savings;

The yearly cost to power an uncontrolled kW load is roughly $1,000. Powering the load off nights and weekends saves nearly $700 each year since commercial buildings are only occupied about 30 percent of the time.

Here’s the math:

Annual Cost Uncontrolled kW MEL at $.11 kWh
Devices are on all day, every day

8,760 hours on x $.11 kWh rate = $ 963.60

Annual Savings Controlled kW MEL at $.11 kWh
Devices on weekdays and off nights and weekends

6,132 hours off x $.11 kWh rate = $ 674.52

Use Plug Load Energy Savings Calculator To Estimate Savings

A more accurate and detailed plug load energy savings estimate can be created using an automated savings calculator like Bert’s Preliminary Savings Sheet, which models the expected number of common plug loads for buildings based on the type of building and its size.  Bert uses exclusive data about the number of devices per square foot and average hourly standby loads from earlier projects to estimate savings.

Minimal building data is needed for an estimate. For example, Bert’s model only needs the following data: building types, square footages and kWh rates. These tools are an easy way to determine whether projects make sense. Estimates should include kWh and $ savings for the project as well as savings calculations broken out by device type and building.

Contact Bert for a Preliminary Savings estimate.

Audit Every Building For A More Accurate Estimate

For the most accurate savings estimate, a physical inventory of all plug and hardwired loads is necessary. Without this level of detail, it is simply not possible to accurately calculate plug load energy savings.

Record the location, quantity and device type of all MELs. Ideally, the audit data is captured electronically and automatically entered into the savings calculator. Besides improving the accuracy of the savings estimate, data can be shared between energy service companies, installation partners and the end user.

At the same time, the standby loads for each device type should be determined. Once all the data is collected, the savings model is re-run, using the actual audit counts and standby load data.

Compare Measured Overnight Load to Savings Estimate

Once control and measurement devices, such as the Bert Smart Plug and Inline Series, are installed the savings model should be run again using the ‘as-built” quantities and measured standby loads. kWh and $ savings can be compared to earlier savings estimates.

Overnight Loads Make Up 30% to 50% of Baseline Loads

Finally, compare the proportion of the Overnight Load to the Baseline Load to calculate the energy savings as a percentage of the total Baseline Load. In most projects, Overnight Load represents somewhere between 30% and 50% of the Baseline Load.

This percentage varies greatly between projects, depending on occupancy hours, kinds of devices controlled and the daytime energy usage patterns.

In buildings with heavy daytime device usage, the daytime load represents a larger proportion of the overall load, so the savings percentage will be smaller.

In buildings where devices are used fewer hours, the daytime and overnight loads are closer to the same size, meaning the savings percentage could be close to 50 percent.

As you look at the savings percentage, it’s important to note that the percentage reduction is not directly related to total kWh or $ savings. A lower percentage does not mean that a project is saving less money or fewer kWh than a project with a higher percentage. It just means that, on a relative basis, it’s likely the project with the smaller percentage has devices that are used more frequently during the week.

Breakdown of the Baseline Load

Baseline Load: kWh recorded during baseline data collection
Includes all devices and circuits that will be controlled. Devices run with no schedules, while hourly measurement data for each load is captured. Baseline Load is split into two categories for savings calculations: Daytime Load and Overnight Load.

Daytime Load: kWh while the building is occupied
This load varies from week-to-week and can differ from the load recorded during baseline data collection. Devices are scheduled on during daytime hours. Measurement data is collected.

Building operators seeking detailed information about daytime device usage should use an administrative dashboard like Bert Analysis to analyze and compare daytime energy usage.

Overnight Load: kWh while the building is empty
Also called Standby Load. This load is eliminated once devices are scheduled, meaning total kWh and $ savings are equal to the size of this load.