By Andrei Moldoveanu, NEMA Technical Fellow, Building Infrastructure
SM31000 Series standards from NEMA form the cornerstone for proper design and testing of new sub-metering technology entering the market. This was regardless of each tenant’s individual use. There are no specific submetering standards for qualifying a sub-meter today until the advent of these NEMA standards. If you really want to know what you consume you need to measure at your own suite level. Do you read by candlelight, or do you run a small bakery out of your unit? If each unit gets a flat rate, in this case, you’re likely paying a share of your neighbor’s electricity bill!
Utility Master Meter
- Many commercial and residential buildings use a single “master meter,” also known as main meter. Electricity comes into a building at bulk rate prices from the utility, and landlords bill tenants for electricity based on flat fees or formulas derived from the space they occupy. Occupants pay for electricity as part of a monthly bill, but their energy use is not individually monitored or tracked.
- Typical construction comprises the meter and its related current sensors (current transformers) in one enclosure (single point meter).
- Utility mostly requires meters that are designed to be mounted outdoors, directly connected to the grid.
Sub-Meter
- Electrical submetering is the measurement of energy consumption after the master meter. Submeters (also referred to as power meters, electrical meters, and energy monitors) are installed after the master meter to measure individual electrical loads.
- Typical submeter system involves the meter and separately connected current sensors
- Submeters are installed indoors, after the entrance service panel, thus benefitting of less stringent design requirements
The Benefits of Electrical Submetering
Submeters allow for the granular measurement of energy, right down to the individual circuit. Building owners and property managers can pinpoint energy use, identify failing equipment, and allocate costs fairly by installing submeters. Tenants pay only for the electricity they use, are accountable for their consumption, use less energy, and lower their electricity bills.
Submeters are more flexible in economically addressing a variety of loads within a building structure.
Reduce Energy Use, Save Money
There are several strategies for reducing energy costs, but few are as compelling and fundamental as submetering. Many studies have shown that using submeters to allocate charges based on actual energy use is one of the most effective ways to reduce consumption.
One of the most exhaustive examinations of applying electrical submetering to commercial buildings was undertaken by the U.S. Department of Energy as part of the Federal Energy Management Program (FEMP) in 2007. This study showed that merely installing meters resulted in a 2% reduction in energy use through the Hawthorne Effect.1
But that was just the start. FEMP found that submetering as part of a coherent, continuous commissioning program of benchmarking, analysis, and remediation can result in 15% to 45% savings.2
Single or Multi-Circuit Meters?
Single-circuit meters are useful for measuring specific points of interest in a building and have long been used in building management applications. But to gain enough knowledge to make successful energy management decisions, more granularity is required.
Doing this using single-circuit meters would require a tremendous number of them. In these situations, multi-circuit meters offer several advantages over single-circuit meters related to hardware cost and deployment.
Multi-circuit meters can instrument one or more breaker panels. These have a much smaller footprint than multiple banks of single-circuit meters, and lower per meter-point deployment and maintenance costs. Additionally, in commercial settings where building configurations often change, tenant moves are more easily accommodated when multi-circuit meters are deployed.
- The Hawthorne Effect refers to how people modify their behavior when being observed or measured (Source: https://en.wikipedia.org/wiki/Hawthorne_effect).
↩︎ - Making the Case for Energy Metering (Source: ASHRAE) ↩︎