By: Allan Evora
Many different considerations can affect the overall cost of submeter installation.
One size does not fit all when it comes to submeter specification. In part 2 of the series, we’ll be talking about installation concerns, or problems that may arise during installation that could change the price, style, and type of submeter originally specified.
When speaking with customers, my submeter selection process is influenced by three parts, which I have outlined in this three-part series:
Once I understand a customer’s goals (see part 1), I can ask questions that help me continue to narrow down the best submeter to recommend. I like to keep price in mind too, as some installation costs associated with submetering often make it unaffordable for most owners.
The following considerations should be well-thought-out during submeter specification to ensure maximum ease and minimum cost of installation.
New Construction vs. Retrofit
There are two crucial considerations when it comes to submeter installation: new construction or retrofit environments.
For example, the environment will determine the type of current transformer (CT) needed as part of installation. Many owners and even some control systems integrators make the crucial mistake of specifying a CT without first thinking if it would fit in a retrofit environment, wasting valuable time and costs allocated to the project.
In general, new construction projects are a lot easier to install submeters at for two reasons:
- No shutdown: Because these sites don’t yet have power, no shutdown of service is required, indicating higher flexibility.
- Low cost CTs: Because submeters can be installed in concurrence with panels during construction, solid core CTs are the obvious choice. A solid core has no break in it, making it a lower cost, yet very accurate alternative to split-core CTs.
Retrofit projects are more difficult and costly for the following two reasons:
- Safety: Although OSHA requirements make our lives as installers safer, they have made pre-planning around installing submeters more difficult. To determine existing conditions within a retrofit environment, it often requires the power be turned off to that panel, and/or suiting in appropriate electrical personal protective equipment (PPE). Oftentimes this represents cost and time that the owner or project cannot afford.
- Split core CT determination: Retrofit projects take a bit more time when determining CT window size and style, based on existing conditions. A split core CT breaks apart and comes back together for retrofit installation, but its moving parts are reflective in its cost and accuracy. Of the two types of split core CTs (i.e., hard shell, rope) rope CTs are very popular in retrofit environments due to flexibility and no significant cost increase for larger window sizes. Installing a rope CT reduces the risk of selecting a CT that won’t fit around large groups of conductors, and decreases installation time in tight areas.
Accuracy vs. Safety
CTs are either offered in millivolt or amp output. Amp CTs have been the industry standard for a very long time, and many perceive millivolts as amateur in comparison. True, millivolts aren’t as accurate, but there are many technologies only built around millivolt CTs (like rope CTs.)
In addition, milivolts are much safer to work with and can be installed in advance of the submeter because a shorting terminal block is not required (which makes them great for retrofit projects.) Because amp CTs require a shorting terminal block for personnel safety and instrument protection, higher labors costs are associated with amp CTs.
High Density Submetering
If you’re thinking of measuring usage of multiple systems or multiple tenants, you must understand how the measure points are geographically located. There’s often significant cost savings if measurement points are in close proximity to one another, because you can utilize a high-density (multi-circuit) submeter.
In a retrofit environment, you can’t do much to change the geographic location of points you wish to measure, but in new construction, you can purposely design your space to allow for lower-cost high density submeters.
Submeter Display Types
Another decision you must be prepared to discuss is if you want a faceless submeter, or a submeter with a graphical display on the front.
A lot of owners don’t even know they have the option of a faceless submeter. In my opinion, a submeter face is a leftover from the days of manual meter reading. Now that SCADA or building automation systems monitor for us, they’re not necessary in most environments. Of course, there are instances when a local display would make sense (e.g., when standing in front of an emergency generator.)
Pros of a faceless submeter
- Less expensive (you’re not paying for the graphical interface or labor to cut a hole in your panel.)
- Has the ability to plug in to an external face, if local monitoring is occasionally required
Cons of a faceless submeter
- Requires a SCADA/building automation system to read and record data.
- Can make third party integration more difficult. For example, if Affinity Energy was asked to install submeters that communicate with a SCADA system integrated by a different vendor, that vendor now has to work directly with an installed submeter they may not be familiar with to verify their readings.
Pros of a submeter with display
- Operator can still see data even if SCADA/building automation system is offline.
- Eliminates doubts with third party SCADA integration that submeters are configured properly (eliminates finger pointing.)
Cons of a submeter with display
- Require you to cut a hole in an enclosure This is easily done in a new construction project, but in a retrofit project, it’s more complicated. (Power shut down, metal shavings everywhere, etc.)
- More expensive
In retrofit situations, I usually recommend a faceless submeter (if you have a SCADA system). If the meter is in a location that can be readily accessed, I will consider a submeter with a remote display option (such as a Schneider-Electric PM-8000) that has the ability to plug into a remote face if you ever need to read the submeter locally. It’s the best of both worlds. You get a safer, faster, and lower-cost installation.
As an alternative solution, Affinity Energy can provide cost-effective local HMI solutions, such as the RedLion G3 and Advantech WebOp to allow centralized viewing of meters that are all located in close proximity to one another, such as an electrical room.
Stay tuned for Submetering Specification Part 3: Rate Structures! Here’s a link to Submetering Specification Part 1: Understanding Your Goals.
Allan D. Evora is a leading expert in control systems integration and president of Affinity Energy with over 20 years of industry experience working in every capacity of the power automation project life cycle. With a background at Boeing Company and General Electric, Allan made the decision to establish Affinity Energy in 2002. Allan is an alumnus of Syracuse University with a B.S. in Aerospace Engineering, graduate of the NC State Energy Management program, and qualified as a Certified Measurement & Verification Professional (CMVP).
Throughout his career, Allan has demonstrated his passion for providing solutions. In 1990, he developed FIRST (Fast InfraRed Signature Technique), a preliminary design software tool used to rapidly assess rotary craft infrared signatures. In 2008, Allan was the driving force behind the development of Affinity Energy's Utilitrend; a commercially available, cloud-based utility resource trending, tracking, and reporting software.
Allan has been instrumental on large scale integration projects for utilities, universities, airports, financial institutions, medical campus utility plants, and manufacturing corporations, and has worked with SCADA systems since the early ‘90s. A passion for data acquisition, specialty networks, and custom software drives him to incorporate openness, simplicity, and integrity into every design in which he is involved.