Integrating Submeters w/Building Management Systems for Energy Efficiency/Cost Savings
As a key element of today's sustainable building management system (BMS), submeters acquire and transmit a variety of energy data parameters for analysis and reporting through the BMS for common area cost allocation, fair and accurate tenant or department billing and other energy-saving capabilities of tangible value to the bottom line. This white paper overviews some of the key issues relative to integrating cost-effective metering technology into today's building management system protocols.
It wasn't that long ago that the only way you could access information from your electric submeter was to walk up to it and transcribe the reading onto a sheet of paper. What were jokingly referred to as "sneaker reads" probably provided an exercise benefit to the meter reader, but had some negatives like dog bites and a good soaking in inclement weather. But now, thanks to a variety of communication options, electric meters are easy to talk to-and you don't necessarily have to go to them to have the conversation! Indeed, a big advantage of today's electric submeter, the frontline energy data gathering tool used by many Building Management Systems (BMS), is that you can now communicate with it in different ways, which makes integrating meter data into the BMS much quicker and easier to accomplish.
The two classic ways of talking to submeters are (1) through proprietary energy analysis software and protocols or (2) through a pulse output into an energy management system. In both cases, the software resides on the user’s PC and communications are accomplished through a “hard-wired” system or a phone modem.
In the case of the former, the hard-wired system works through dedicated RS-485 cabling or through an Ethernet connection that uses an existing network. Ethernet communications do require an optional module and an Internet Protocol (IP) address. Using the RS-485 approach allows up to 4,000 feet of cabling to be run in the building. The manufacturer’s software is happy to use all of these methods simultaneously and is easily set up to do this. One important thing to remember is that pulse-output electric, water, gas, steam and other similar meter types have to be used with an IDR (Interval Data Recorder) to provide communication (Figure 1).
Figure 1. Unlike meters which continuously read energy usage as it occurs, IDRs collect and store consumption (kWh) and demand (kW) meter information at user-specified time periods from five to 60 minutes, allowing for profiling of energy data and more detailed comparative analysis or billing and other uses. Data can be collected from up to 8 or 16 separate meters/channels of information, and up to 36 days of 15-minute interval data can be stored in onboard memory. the IDR interval meter data can be accessed via telephone modem, Ethernet, ModBus, Internet Protocol (IP), LonWorks TP or MV-90. Data can be used to interface with E-Mon Energy Automatic Meter Reading & Billing software, building management systems or other energy software.
On the other hand, if a telephone modem is used, the meters and IDRs can be “daisy-chained” with the RS-485 cabling and then converted to RS-232 to connect to the modem. This provides access to the whole system with only one modem. Literally hundreds of meters at a location can be read from a single modem through IDRs collecting and storing data from E-Mon D-Mon meters and others.
One great advantage of the Ethernet communication method is that it’s good on both intranet and Internet systems. When tied to the Internet, for example, meters anywhere in the world can be read without bearing long distance charges, as would be the case using a telephone modem. Moreover, Internet access time is very quick, which is especially valuable if “real-time” access to the meter data is desired.
Modbus, another language used for meter communications, is prevalent in the controls industry. Individual meters typically offer three dozen or more data points for use with BMS or industrial controls. These include delivered power, received power, Volts, Amps, power factor, frequency, kW, kVAR, kVA, etc. With Modbus, the meters act as “slave” units to the BMS master. Data is exported from the meter on request and the automation or control system processes the raw data for its use. If the IDR is used through Modbus, the data is typically limited to kWh (consumption) and kW (demand). Modbus-compatible meters usually come in two flavors: Modbus RTU which communicates through RS-485 cabling, and Modbus TCP which is used when Ethernet is the form of communication required by the user. IDRs are also available with Modbus (Figure 2).
Figure 2. Block diagram showing the parallel operation of a facility's BMS and the submetering system for utility metering and tenant billing from a single hardware/software platform. Operating in parallel to the BMS, a facility-wide network of E-Mon D-Mon electric submeters accepts energy data from the BMS and imports it into E-Mon Energy software. This PC-based energy intelligence software analyzes and converts the raw meter data into monthly utility billing statements for the building's tenants. This particular real-world example includes some 205 Class 3000 E-Mon D-Mons, 91 BTU meters, seven steam meters, 17 water meters, eight gas meters and 58 air flow meters. This does not include utility meters, of which two steam, and one each gas and water meter are also part of the system. The airflow meter data is imported into E-Mon Energy software from the BMS.
BACnet is yet another language that's useful for talking with submeters. The HVAC industry seems to have standardized on BACnet as its language of choice for data and controls. As with Modbus, BACnet-compatible meters communicate over an RS-485 cable system or utilize Ethernet cabling. When used with RS-485, the BACnet MS/TP protocol is utilized. When Ethernet is the choice of communication, BACnet IP is the protocol.
As an open protocol, Lonworks has its own specialized form of communication and does not use either RS-485 or Ethernet cabling. Lon TP (twisted pair) is used with this meter and communicates over a twisted-pair of wires, making it somewhat unique in its application and installation.
Finally, we will consider wireless mesh networks where the data is transferred to a host Wireless Data Collector (WDC) by hopping from meter to meter wirelessly and then being received by the collector. The collector stores and communicates the pulse (kWh, kW) data that is received from the submeters. External wireless modules (Figure 3) can be used to collect data from pulse output water, gas and BTU meters. They can even be plugged into previously installed “legacy” submeters to integrate existing units into the wireless system. The final transmission from the WDC to a computer is through its Ethernet connection, using either the Internet or a local intranet system.
Figure 3. External Wireless Modules (EWM) provide an easy upgrade path to wireless mesh capability for new or existing meters. The module's plug-and-play installation self-configures the meter to interface with the wireless mesh network system for automatic meter reading & energy analysis with energy intelligence software.
How submeters facilitate BMS performance
The level of profiling needed by high-volume energy consumers, including commercial, industrial and institutional facilities, is simply unobtainable using the standard utility meter found at the building's main electrical service entrance. It is one of the primary reasons that growing numbers of engineering firms, along with facility owners and operators, are deploying submeters to help save literally thousands of dollars in reduced energy costs through:
- Usage analysis and peak demand identification;
- Time-of-use metering of electricity, gas, water, steam, BTUs and other energy sources;
- Cost allocation for tenant billing;
- Measurement, verification and benchmarking for energy initiatives, including LEED Energy & Atmosphere (EA) and Water Efficiency (WE) credits;
- Load comparisons;
- Threshold alarming and notification;
- Multi-site load aggregation and real-time historical monitoring of energy consumption patterns for negotiating lower energy rates, and more.
Of the three main submeter types shown in Table 1, the first two - feed-through and current transformer (CT)-based - are socket-type meters. CT-style socket meters are used with loads of 400A and above. In commercial applications, they may be specified but will take up a lot of space in the electrical room due to the need for CT cabinets and the meter bases. The extra space requirement cuts into the available rental space, which is undesirable in the commercial marketplace. Another major disadvantage in many jurisdictions - socket meters are not UL listed. The third type is the electronic submeter, a non-socket device (Figure 4) that provides clear advantages over the previous two, as shown in Table 1.
Table 1. Non-socket type electronic submeters are less expensive initially, quicker and easier to install and offer superior performance and options compared to other types of meters.
Figure 4. Voltage and current connection diagram of an electronic (non-socket type) submeter into a typical subpanel. For a close up of the current sensor connections, see Figure 5.
Since their introduction, submeters have grown dramatically in functionality and usefulness, providing great value to facility owners and operators as “front-line” energy data gathering tools in an era of rising utility costs and tightening budgets (by scannevin). Today submeters are coming out of the electrical room onto the factory floor and into building lobbies to give users, tenants, employees and others visibility on actual energy usage and its impact in terms of CO2 emissions, kWh dollars and other parameters easily understood by laymen. Submeters not only improve the facility bottom line, but facilitate implementation of building retro-commissioning projects and other energy initiatives while also encouraging every level of the enterprise to become a stakeholder in the energy management and conservation process.
In response to EPAct 2005, EISA 2007 and other federal energy mandates impacting the facility landscape, E-Mon and other manufacturers have developed advanced hardware and software tools that specifically address the needs of the sustainability market. Certified to ANSI C12.1 & C12.16 national accuracy standards, new-generation advanced meters like E-Mon's Green Class meter (Figure 6) offers a number of important functions and capabilities for new construction or retrofit applications, including:
- Scrolling LCD display of kilowatt-hour (kWh) usage;
- kWh in dollars;
- Current demand load (kW);
- Cost per hour, based on current load;
- Estimated CO2 emissions in pounds, based on DOE standards;
- Estimated hourly CO2 emissions based on current load;
- Net metering, including utility-delivered vs. user-received power and net usage;
- Compatibility with pulse-output utility meters, including water, gas, BTU, steam, etc.
Meter dashboards for BMS energy data presentment
By importing data from electric submeters and other metering devices into Web-based communications, interval data may be cost-effectively collected, analyzed and displayed in near real-time. Referred to as meter or energy dashboards (Figure 7), typical displays may include:
- Automobile-style gauges showing how power, fuel and energy budgets are being consumed on a real-time basis;
- 24-hour load profiles for power, chilled water, steam or other building systems;
- Historical comparisons of current usage versus previous time periods under similar conditions (time, day of week, temperature);
- Automated carbon foot-print calculations;
- Tenant- or consumer-level information about energy use and efficiency efforts.
Figure 7. Internet-based meter dashboards like E-Mon's Web-Mon family allows users to automatically integrate their distributed metering infrastructure into real-time meter dashboards via open-architecture Modbus IP-compatible LAN/WANs. Dashboards are available for single-facility as well as multi-facility campus-style applications to provide real-time and historical presentment of electricity, gas, water, steam, BTU and other metered parameters.
Bottom line considerations
A key element of today's sustainable building management system, submeters acquire and transmit a variety of energy data parameters for analysis and reporting through the BMS for common area cost allocation, fair and accurate tenant or department billing, power factor penalty identification, utility meter shadowing and other energy-saving capabilities of tangible value to the facility bottom line.
For the engineering firm, the contractor and others, there is no question that green building construction and retrofit projects will continue to be a major trend across the facility landscape. An enabling technology, submeters can help facilities improve their bottom lines by benchmarking, measuring and verifying compliance with major energy initiative guidelines, while also encouraging every level of the enterprise to become a stakeholder in the energy management and conservation process. As today's sustainability-minded facility operators face ever-tightening operational challenges, new technologies and strategies will be needed to keep pace with rising costs while, at the same time, maintaining or improving service quality levels.
One such energy strategy, performance-based contracting, can result in major cost savings with little or no up-front investment. Utilizing project-related savings to underwrite energy improvements on a pay-as-you-go basis, submetering technology can be used to identify inefficiently operating equipment, allowing repair or replacement. The cost savings realized from reducing operational inefficiencies can then be applied to other areas, including deferred maintenance or installing other energy-saving equipment or services.
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