In the course of any metering exercise, there will be challenges that arise – these may occur in planning, specifying, purchasing, installing, or in the maintaining of the metering system.
This technical article focuses on five common metering challenges with the hope that identifying these early in the process mitigates potential impact //
- Metering planning
• Best information
• Under/Overestimating breadth of project
• Management buy-in and support
• Milestone development
- Equipment specification
• Operating range
• Cost of ownership
- Purchasing of metering equipment
• Manufacturer standardization
The planning step of the metering process is critical to program success. Some of the challenges in the planning process include //
1.1 Best Information
Good information drives good planning and decision making. It is incumbent on the planners to make sure the best available information is accessed and used. In metering of existing buildings, access to electrical plans, one-line diagrams and panel schedules is critical.
However, as is often the case, these documents (when available) are incomplete, outdated or are not considered “as-built”.
A recommended step in the planning process is the access and verification (possibly confirming with field inspection and spot measurement) of all technical documents.
1.2 Under/Overestimating Breadth of Project
A key to metering planning resides with an ability to estimate current and future needs. While it is difficult to accurately predict future needs, efforts to plan for future system expansion are critical to the economic success of the system.
1.3 Management Buy-in and Support
Obtaining and maintaining management support for project planning and implementation is an often overlooked activity.
Providing management with regular updates on activities and successes is one way to keep the project visible and maintaining this support.
1.4 Milestone Development
While many plans focus on the “what,” effective plans also focus on the “how”. Developing how and when the steps of the process will be implemented are critical to assuring a successful metering program.
The identification of the correct equipment is crucial to the project’s success and longevity. This requires an ability to distinguish the necessary parameters for proper function.
2.1 Operating range
When selecting metering equipment, understand the operating range of the expected measurements.
As defined, the accuracy of a metering system is the difference between the measured value and the actual value. While overall system accuracy is important and often reported for standard operating ranges, accuracy should be addressed for each component of the system and, importantly, over the entire range of expected values.
Current transformers (CTs) and fluid meters present good examples of this need.
CTs are usually accurate over a broad range. Basic CTs provide high accuracy from 10% to 110% of the rated current. Higher quality CTs, however, can provide high accuracy from 1% to 120% of the rated current.
CT sizing should be done with care and full knowledge of the expected measurement range, paying particular attention to the low end of the range.
Fluid meters are often specified on average and maximum flow rates. In systems with a wide range, and including low flows, accuracy can suffer. In these cases, compound meters can be specified to accommodate the two different flow rate regimes to achieve desired accuracy.
Prior to the identification and procurement it is important to understand the metering equipment. That is, its function, operation, and maintenance needs. This step must involve input from those who will be using the equipment.
Parameters to consider include //
- Meter installation and setup, paying particular attention to spatial constraints and code requirements
- Flow meters may require strainers or filters, straight pipe runs or flow conditioners and isolation valves for ease of maintenance.
- Software configuration and ease of use.
- Process and schedules for maintenance of system, sensors, and battery needs.
- Data synchronization for various meters and data acquisition systems.
Meters from different vendors or product lines can have different data sampling rates, sampling intervals, and communicate and transmit data using different protocols and formats (ACEEE 2010).
To mitigate any potential issues with communication consider the following guidance //
Standardization on manufacturer and/or data protocols -There are a number of established and developing protocols (e.g., BACnet, LonWorks, Modbus, pulse); make certain that the meters specified have a common protocol or can be converted for proper communication.
Data collection intervals – To assure accurate data processing, meters should be set to a universal time stamp (i.e., time-series records reference the same time stamp) and be collecting and integrating over the same interval (e.g., a 15-minute interval).
Data interoperability – Depending on how data are collected and processed, routines may need to be employed that pre-condition or consolidate the data for final processing.
2.5 Cost of Ownership
An important metric in specification is total cost of ownership over the metering equipment’s life. Identifying what the defined life of the system is the first step. It is important to determine the recurring cost, including any periodic calibration, needs for part/sensor replacement, or upgrades to system software or licensing.
All of these parameters should be readily available from equipment vendors and should be received in writing.
Most important, weigh the real benefit of additional features and options. Do not “over buy” metering equipment by adding features and options that add costs without corresponding savings.
The details and specifications of items procured are very important when purchasing metering equipment and accompanying sensors.
3.1 Manufacturer Standardization
While it is not always possible, there are some advantages to standardizing on one equipment manufacturer. These include //
- Single source of information and product
- Minimization of finger pointing when “system” problems occur
- Volume procurement/discount opportunities.
Following all manufacturers’ guidelines and relevant code requirements is essential to proper and safe installation. Additional recommendations to consider include the following //
Recommendation #1 Offer an explicit instruction set for all installations, provide relevant contacts for installation questions, and develop checklists for installation check out. Typical installation faults include //
- CT directionality or flow direction
- Voltage and phase consistency
- Meter constants, inputs, and programming
- Maximum output signal communication distances
- Meter power supply
Recommendation #2 Develop installation commissioning protocols. Verify each meter individually.
- Develop “expected” values for each meter
- Compare output against “expected” values and spot measurements
Recommendation #3 In multi-meter installations verify that the sum of the parts equals the whole.
- Individual end use, distribution centers, and building-level
Recommendation #4 Develop communication commissioning protocols.
- Verify each meter individually
- Confirm time series output received at endpoint/data center
- Confirm summed data received over duration (week/month) are accurate and expected
Once installed and operating, facility staff must focus on keeping metering systems productively functional. Meter/sensor calibration, data receipt, and accuracy are the key meter maintenance parameters most often neglected.
To prevent these issues from arising, the following are suggested //
#1 Consider developing time-based checklists of manufacturer’s maintenance recommendations and including these in regular maintenance activities.
#2 If the site uses a computerized maintenance management system (CMMS), all relevant metering information (manufacturer, model, date of installation, size, and procedures) should be entered into the CMMS from where automated work orders will be generated.
Reference // Metering Best Practices Guide by U.S. Department of Energy