Description:

New systems that integrate sensors and analytics are simplifying the submetering process and driving costs down. Single-circuit submeters provide the ability to monitor individual circuits within an electrical panel in a building, providing detailed power and energy consumption data at a much more granular level than was previously achievable in a cost-effective manner.

GSA's Green Proving Ground program found that single-circuit submeters are easy to install; integrate with existing GSA enterprise systems, such as GSA Link; and can provide insightful high-resolution data allowing building managers to identify energy conservation measures (ECMs) leading to measurable savings. Single-circuit submeters with voltage taps provide the accuracy needed for tenant billing (<2% average measurement error). Wireless current transformers (CTs) that clip onto circuit-panel electric wires and measure the current flowing through the wire are even easier to install but they lack the accuracy needed for tenant billing, (7% average measurement error with -10% to + 25% total error). Wireless CTs do accurately capture on/off states of equipment and can support fault detection and diagnostics (FDD) and identification of energy conservation measures (ECMs).

Special Considerations

• High-accuracy current transformers (CTs) with a phase angle shift of <0.5° are necessary to support tenant billing.
• Size CTs to estimated power levels, as opposed to rated breaker values. An ammeter can estimate amperage draw.
• It is critical to independently verify the installation and configuration of CTs to ensure the intended operation.
• If using a single CT on three-phase equipment, the load should be well balanced.
• Tracing loads to individual circuits can be challenging due to inaccurate panel schedules, obscure naming conventions, or lack of circuit tracing. Tracing loads may be an expensive process in locations with many low-load receptacles. Define monitoring goals prior to deployment.
• A registered electrician is required to install the system. A spare breaker for the voltage tap will facilitate system installation.

See GSA’s Green Proving Ground for more details on the field demonstration findings: wireless current transformers and single-circuit meters.