8.3   Separation of Electrical Circuits for Electrical Energy Monitoring

The purpose of the Separation of Electrical Circuits requirement is to set up a backbone for monitoring the specific contributions of separate loads to the overall energy use of the building. By designing the electrical distribution system with separation of electrical loads in mind, energy monitoring can be readily setup and implemented without significant physical changes to the electrical installations. The end goal is to be able to monitor the electrical energy usage of each load type specified in Table 130.5-B of the Energy Standards: building owners, facility management, and others can make use of such energy usage information to better understand how much energy has been used by each building system during a certain period of time. Further analysis of such energy information can help facilitate energy efficiency measures to improve building energy performance for building owners and operators.

8.3.1    Compliance Methods

Electrical power distribution systems shall be designed so that measurement devices can monitor the electrical energy usage of load types according to Table 130.5-B. However, for each separate load type, up to 10 percent of the connected load may be of any other load type. Also, note that the 2016 requirements have moved to become more flexible than the 2013 requirements: where the 2013 Energy Standards prescribed specific methods for ensuring separation of electrical loads, the 2016 Energy Standards allow any approach that provides the ability to measure the separate loads of the building.

The separation of electrical circuit requirement of §130.5(b) , may be accomplished by any of the following example methods:

A.  Method 1: Switchboards, motor control centers, or panelboards loads can be disaggregated for each load type, allowing their independent energy measurement. This method must permit permanent measurement and determination of actual interval demand load value for each disaggregated load in the system.

This is a straightforward approach, as each distribution equipment serves a single load type. Summation of the kVA measurement of the distribution equipment in accordance with the respective load type can result in the energy usage of each load type. This method is simple and straightforward in terms of the effort required in compiling the measurement data.

B.  Method 2: Switchboards, motor control centers, or panelboards may supply other distribution equipment with their loads disaggregated for each load type. The measured interval demand load for each piece of distribution equipment must be able to be added or subtracted from other distribution equipment supplying them. This method must permit permanent measurement and determination of actual interval demand load value for each disaggregated load in the system.

This method allows distribution equipment to serve more than one load type while still allowing the separate energy use of each load to be determined. More effort may be required in terms of treatment of the measured energy data in order to obtain the energy usage of each load type.

C.  Method 3: Buildings for which a complete metering and measurement system is provided that at a minimum, measures and reports the loads by type.

This method allows a complete metering system to be used to meet the requirements of §130.5(b), provided that at a minimum measures and reports the loads called for in Table 130.5-B of the Energy Standards. Such an installation goes beyond the requirement of the Energy Standards as it meters and measures the power and energy usage of each load type.

8.3.2    Application Considerations

The Energy Standards envision the use of conventional panelboards, motor control centers, panelboards, and other standard wiring methods for meeting the requirement to separate electrical loads. The requirement may also achieved by a well-planned wiring approach, such as connecting all HVAC units to a single feeder from the service using a combination of through feeds and taps. The regulations are intentionally written to specify the “what” without prescribing the “how”, and thus provide as much flexibility as possible.

In a “typical” small building with a service less than 50kVA, separation of electrical loads is not required at all. Slightly larger buildings are able to comply by using carefully laid-out panelboards.

In larger buildings, separate risers for lighting, receptacles/equipment, and HVAC are allowed to be used for meeting the separation of electrical circuits requirement.  Single large loads or groups of loads, such as an elevator machine room, or a commercial kitchen, may be connected to panelboards or motor control centers served by a dedicated feeder and the electrical power and energy of the entire group of loads can be measured by metering the feeder.

For services rated more than 250 kVA, lighting and plug loads are required to be separated “by floor, type or area”. So, in a single-story building, all the lighting loads could be fed from a single panel, and all the plug loads could be fed from another panel (or, alternatively, both types of loads could be fed from one panel with a split bus).

In a multi-story building, a simple way to comply would be to install a separate lighting panel and a separate plug-load panel for each floor of the building. However, it would be equally acceptable (and may be more useful) to divide the load according to which area of the building it serves (office, warehouse, corridors etc.), or by the type of light fixture (metal halide vs. fluorescent, dimmable vs. fixed output, etc.). So, for instance, both the first and second floor office lights could be fed from the same panel, while the warehouse lights would be fed from a second panel. Dividing the load by area or by type instead of by floor is more likely to yield useful information when the loads are analyzed in an energy audit. All of these approaches are available to designers and installers, and are acceptable methods of complying with the Energy Standards.