Submetering is becoming more important, and the technology for submetering systems is becoming more sophisticated and flexible. As the focus on saving energy grows, it is crucial to be able to pinpoint where and how energy is being used. With the meters that are now available, measurements can be made and displayed in real time, and the detailed records can be stored and recalled for analysis. Meters that can interface with flexible communication systems and dedicated software are necessary to do this job. The following are some fairly typical submetering products.
National Meter Industries (NMI) (www.national-meter.com) offers the K3000 single-phase series and the K4000 three-phase series of kilowatt-hour meters designed for submetering. They are microprocessor-based and have accuracy guaranteed to ANSI C12.16. Communications through RS-485 Modbus is standard. The liquid crystal display (LCD) indicates kilowatt-hours in six digits, with scrolling displays alternating every five seconds between kilowatt-hours and maximum demand. Maximum demand is the basis of utility billing for commercial tenants. It is also of great interest to utilities that want to decrease peak demand because it limits their ability to deliver power during periods of peak loading. In addition, the meter can display volts, amps, real-time kilowatts per phase, and correct/incorrect wiring. Up to 255 meters can be interconnected through Modbus, using 18/2 twisted pair or Category 5 cable. Every meter has a unique serial number, which the software uses to poll and identify each meter on the bus. Also provided is an Ethernet converter to access a LAN and/or a computer running the reading and billing software.
The Schneider/Square D sub metering products are categorized as PowerLogic energy-analysis software and metering products (www.powerlogic.com). As the name implies, it’s an integrated system of meters and software. The advantage is that the system can easily be tailored to the user’s needs and budget. At the low-cost end is a basic meter connected to an EGX300 gateway device, which can accept data from up to 64 PowerLogic system devices using a standard serial string. The device is tied into the building’s Ethernet network, so a user can access the data anywhere through a PC on the same network.
PowerLogic’s system ranges from the simple to the complex, which offers user advantages. For example, PowerLogic Powerview is entry-level software, which includes automatic device detect and provides preconfiguration of real-time and historical data displays that retrieve onboard data logs from connected devices. It also performs PC-based logging for devices without onboard memory. The software also features time-of-use capabilities for reporting energy and demand values over user-specified time periods, which satisfies special billing requirements and predefined reports for analysis of energy usage, peak demand power and more.
E-Mon LLC (www.emon.com) was a pioneer in the submetering business and is still at it, now as a subsidiary of Honeywell. The company’s 3000 class meters display kilowatt-hours, power factor, volts and amps per phase, real-time load in kilowatts, demand, and power factor. E-Mon also provides a range of communication options—RS-485 for up to 52 devices for use by E-Mon’s energy software—or Modbus, BACnet and LONworks options for integration into existing building-systems networks.
GE’s (www.gedigitalenergy.com) submeters, such as the EPM 1000 and 4000 series, have LCD readouts that can display up to 50 electrical parameters in real-time or as historical data. They come packaged with power line communication (PLC) capability in which the alternating-current power lines act as the communication medium. This can be really helpful in a retrofit application because the installer doesn’t have to pull extra wires for communication. GE also provides optional RS-485 Modbus open- protocol communication for integrating with other building systems, including data from water and gas meters that have pulse outputs.
The Integrated Metering Systems Inc. (IMS) (www.imsmeters.com) series 3000 provides the bells and whistles similar to high-end meters of the other manufacturers: kilowatt-hours, demand, instantaneous power and a clock with battery backup for a time-stamped record, which is stored at the meter and can be accessed remotely. Communication is by means of an RS-485 two-way serial port for Modbus and BACnet. The company’s meters are compatible with third-party automatic meter reading (AMR) software, which is available from many sources. IMS stresses the importance of using solid-core current transformers (CTs) for accuracy even though, for all but new installations, they can be very cumbersome to install. Second best, however, the company’s split-core transformers come with attached clamps, which help seat the two halves. Proper alignment and clamping of the CT is necessary in order to achieve the specified accuracy.
Other companies, including Eaton Corp., Siemens Industry Inc. and Veris Industries, manufacture submeters.
A contractor who understands submetering will be able to offer valuable tools to multitenant and multibuilding occupancies. Especially in tight economic times, the ability to closely monitor energy use and to accurately bill subtenants can be sold as valuable money (and energy) saving strategies.
BROWN is an electrical engineer, technical writer and editor. For many years, he designed high-power electronics systems for industry, research laboratories and government. Reach him at firstname.lastname@example.org or at www.writingengineer.com, an independent professional writing service.