The pervasive use of LANs in school and campus environments, and also in multi-facility commercial, industrial and residential sites, is good news for building managers, electrical personnel and maintenance engineers tasked with cutting operating costs. Installed after the master meter in a building or facility, submeters are used to define the energy usage of a specific location, user or circuit. The data obtained through submeters can be used to implement demand side energy management programs, load shedding and other cost cutting measures that can really impact the facility bottom line. In that role, they are relatively inexpensive and very well suited.
LAN-based Automatic Meter Reading
In facilities that are not already wired for LANs, the submeter data must be carried back to the central monitoring point via home cabling runs. However, in a high percentage of applications, the fact that the data highway is already in place makes installation of the distributed submeter network much faster and a lot less expensive.
Comprising more than 80 per cent of the worldwide installed base, Ethernet's popularity as the LAN technology of choice is due mainly to its low cost and industry-wide support. Using a facility's existing LAN backbone as the submeter data highway can dramatically reduce submetering installation costs by eliminating cable runs between hardware elements and by eliminating the need for a modem and telephone line back to the central monitoring location.
Submetering hardware is now available for both star and bus topology Ethernet, particularly 10Base-T and 10Base-2 (Figure 1). Inexpensive switches and interfaces are also available for Fast Ethernet and fiber media, thus extending submetering's usefulness to whichever Ethernet medium may be encountered.
Note that not only electric, but gas, water, steam, BTU and other pulse output meters can be read on the network. This allows facility personnel to view total energy usage, not just electrical.
The data accumulator hardware interface between the submeter network elements and the LAN provides an RJ-45 connection that may be hooked into the LAN wherever a connection can be found. The data accumulator records energy profiles with a data and time stamp every fifteen minutes for rolling periods of up to 36 days. Battery-backed memory protects the data in the event of a power outage, and it can be stored in the accumulator for later retrieval or uploaded to a central monitoring location at any node on the network.
Online Monitoring Capability
Online services have recently come into play to help users track and analyze their 'big picture' electrical consumption and demand -- from a single circuit in one facility, to multiple sites all over the world -- using the convenience of the Internet. The metered data is transmitted to the data accumulator hardware interface and then sent via modem to the online server. The information is posted daily to the subscriber's password-protected folder where it may be accessed using standard Internet browsers.
Graphical and statistical presentations of peak demand load profiles and energy usage help users identify energy savings opportunities and areas where efficiency can be improved. Multi-site and aggregated load profiles enhance the user's ability to proactively negotiate the best possible rates in the deregulated utility marketplace. Typical monitoring functions include the ability to:
- Track facility energy use of electricity, water, natural gas, oil, steam
- Obtain seven-day energy, weather/degree day forecasts
- Profile detailed hourly and daily load shapes
- Monthly/year-to-date budget status
- Set budgetary and energy-usage level alarms
- Determine length of use and time of use.
Conclusion
Recently introduced Ethernet-compatible submetering equipment makes it even easier and less expensive than ever to implement a distributed submetering network in any facility where a LAN is already in place.
It also speeds up an already rapid system payback by increasing the utility and value of the LAN and by making critical information more easily accessible from any point on the information superhighway.
Don Millstein is president of E-MON Corp of Langhorne, PA. He may be reached at (800) 334-3666 or by e-mail at dmilstn@emon.com ET