Using PMDs (Power Metering & Monitoring Devices) to Measure and Manage Energy Costs

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Electricity meters have been critical components in facility electrical design since utility customers began paying for the commodity. However, while traditional meters at service-entrance points provide utilities with the consumption data they need for billing, they aren’t very helpful for facility owners and managers, who are more interested in how electricity is used, once it enters the building. Now, power metering and monitoring devices (PMDs) can help meet a range of needs, from monitoring the accuracy of the utility’s revenue meter. This post outlines three valuable applications for PMDs.

IEC TR 63213 is defining the meaning of “cost allocation” and “sub-billing” applications in opposition to a “billing” application (reference this post), see below Table 1:

Cost allocation

Owners of multi-building campuses, industrial plants, and other facilities with multiple cost centers can benefit from access to clear information on each operation’s energy use. For example, such verified data can help owners better allocate energy expenses against specific revenues, as well as aid in establishing benchmarks and tracking the impact of efficiency upgrades, over time.

As Figure 1 shows, PMDs in this application are installed for each cost center to be tracked. Software systems compile the data from the PMDs and main revenue meter to determine each cost center’s contribution (as a percentage) to the facility’s total monthly electricity bill.

Sub-billing (also called tenant metering)

Similar to their use for cost allocation, PMDs in this application can help building owners allocate electricity costs by use – in this case, by the use of individual tenants in a larger commercial office or retail facility. As shown in Figure 2, these costs are usually combined with those for other services in tenants’ monthly facility bills. PMDs complying with the International Electrotechnical Commission’s Standard 61557-12 can be used for sub-billing purposes, as permitted by local regulations.

Figure 3 is providing an example within a mall.

Bill checking

Electric utility bills often are simply accepted, as is, but that can be a big mistake for facility owners and managers because revenue meters aren’t infallible. For example, rate tariffs established years ago might no longer be accurate, thanks to efficiency upgrades installed over time. Additionally, billing intervals might be too long or too short, which can skew demand charges. Even mistakes in the building owner’s favor can be expensive in the long run, because supply contracts can allow the utility to recover missed charges months or years after an error occurs. For a commercial building owner, this could mean costs aren’t recoverable if tenants have moved out.

Figure 4 illustrates the relationship of a PMD to the utility’s revenue meter in a bill-auditing (also called “shadow metering” or “shadow billing”) application. As the figure shows, the PMD in this application is installed in parallel with the utility meter to calculate an accurate “shadow bill” that includes all expected energy and demand charges. This bill can then be compared to the utility bill to identify any inconsistencies. Note that the data in this use remains facility-wide.

Legal metrology requirements usually apply to billing applications for the measurement of active energy, in the framework of a commercial transaction between an energy supplier and a final consumer.

For other applications, PMD compliance with IEC 61557-12 is recommended.

In some countries, IEC 62053-2x may be also be recommended even though this set of standards specifies requirements only for active and reactive energy measurement. IEC 61557-12 provides requirements for all electrical measurements (U, I, P, PF, THD, etc.).

Compliance to IEC 61557-12 is a minimum requirement for all cost-allocation, bill checking, and sub-billing applications. For even greater assurance of durability and measurement accuracy, Schneider Electric recommends specifiers call for devices that have been third-party certified.

If you are looking for more details, you can check out the following documents:

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