Power Management

Submetering Is More Important Than Ever in California’s Updated Title 24

The 2013 edition of the California Energy Commission’s Title 24 energy code incorporates a new emphasis on metering. Section 130.5(a) adds new requirements for whole-building metering. In addition, the code requires planning for more comprehensive metering of how individual systems use energy in its Section 130.5(b).

Under Section 130.5(b), electrical power distribution systems need to be designed to permit the measurement of “disaggregated” loads downstream from the service meter. This means system designs need to enable the ability to measure the use of individual building systems, such as lighting and HVAC loads – or, in multi-tenant buildings, separate areas, such as lobbies and tenant-controlled spaces.

The Section’s requirements are complicated. First, system designers need to understand several exemptions. The provisions apply to new services only rated higher than 50 kVA, not additions to existing equipment. And alterations where ALL of the following conditions exist are excluded from compliance:

The following existing equipment remains in place:

– Service distribution switchboards or panel boards, AND

– Feeders, AND

– Motor control centers or panel boards

The existing equipment listed above remains unaltered, except changes to:

– Load circuit connections, OR

– Quantity of outgoing overcurrent protection devices, OR

– Ampacity of outgoing overcurrent protection devices

Determining what is needed for new installations in which Section 130.5(b) applies requires careful study of the related table, “Minimum Requirements for Separation of Electrical Load.”As the table shows, provisions become more demanding as the size of the electrical service grows.

MinimumRequirements

The section’s language doesn’t specifically require metering equipment to be installed to measure the separate loads; instead, it says that each electrical system shall be designed to “permit” measurement of these loads. It takes careful reading of 130.5(b) and understanding of the allowed methods therein to understand exactly what was intended by the authors when they used the word “permit”. Fortunately, there is a companion Compliance Manual that illustrates this intent.

Title24_CTABannerSo, what does “permit” mean? The compliance manual explains, “Above a minimum threshold that varies by load type, electrical power systems must be designed and built such that the TOTAL load of specific building load types can be measured. The intent is to have a single feeder or breaker with each type of load (such as lighting) on it, such that a meter could be placed on the feeder to report energy use by that load type.” The manual provides several illustrations to further aid understanding.

To be consistent with the code’s intent, then, the designer needs to envision the measurement point to understand the correct application of sub panels. Subpanels need to be of the same type as the feeder or upstream panel. For example, a lighting subpanel can only be fed from another lighting panel or from the lighting feeder circuit. This way all of the lighting panels can be measured in total from one common point.

Example8.4

The compliance manual illustrates a split-bus panel in which the same panel serves different load types (Example 8-5). In this example, each section is fed separately from the combined feeder such that each split provides a separate point for measuring each type of load. Take care when specifying a split-bus panel for this application. Split-bus is not an industry standard term and the designs of split-bus panels can vary. Some split-bus panel designs may not maintain the required separation of electrical loads by type.

Example8.5

Although a split-bus panelboard may be used to save space, any design seeking to save space by consolidating loads without the use of separately fed splits must incorporate a means of metering the loads per Exception 1: “Buildings for which a complete metering and measurement system is provided.” A metering system can take measurements from individual breakers, then add or subtract to provide the total measurement for a particular load type to meet the code. Although this approach requires the metering system to be permanently installed at time of construction, this alternative frees the designer from the constraints of providing strictly segregated circuits.

We will describe some the options for meeting the section’s allowed options in the next post of the series, Branch Circuit Design. For more help, check out Schneider Electric’s Professional Engineer Portal for additional information and for access to experts you can call on for advice.

 


No Responses

Leave a Reply

  • (will not be published)