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How Power Meters Work


September 22, 2020

Power meters are used in a wide variety of applications to measure electricity use on a more granular level than the main utility meter. Power meters, or submeters as they can sometimes be referred to as, can tell you where, how, and how much electricity is being used in the building.

Building owners can choose specific systems to be submetered. Examples include:

  • Lighting
  • Air Handling Units (AHU’s)
  • Chillers
  • Refrigeration
  • Tenant spaces

How Does a Power Meter Work?

Submeters are intended to measure a specific point of energy usage within the building to give the building owner, facilities manager, or other personnel a look at how much energy that point is using in real-time. A submeter needs two main inputs to accurately measure and perform calculations for the user. The first is a voltage (typically VAC) input and the second is a current measurement by way of current transformers (CTs) or Rogowski coils. Once a power meter is mounted, the voltage inputs and CTs or Rogowski coils must be wired in safely by a qualified professional. Then, once the power to the meter is turned on, powerful software in the meter can interpret all the energy parameter data coming in for calculations.

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Parameters a power meter can monitor include:

  • Volts
  • Amps
  • kW
  • kVAR
  • kVA
  • aPF
  • dPF
  • kW peak demand
  • Import/Export kWh
  • Net kWh
  • Import/Export kVAh
  • Net kVAh
  • Import/Export kVARh
  • Net kVARh
  • THD
  • Phase angle
  • Frequency

Getting the Data

Submeters can communicate with building management systems through advanced protocols like BACnet and Modbus. From there data can then be sent directly to building owners or facility managers to act on this real-time information. Some web-enabled meters and applications allow for instant access on cell phones, tablets or direct to email. This easy access to data allows for proactive monitoring of energy consumption instead of reacting to a large utility bill at the end of the month.

Topics: Energy Management