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Metering: The Hows & The Whys
Campus-wide metering project pays dividends
In 2009 my company embarked on a large project on the campus of a
university located in the city limits of Chicago. The project consisted
of fitting upwards of 65 buildings with meters. Yes, meters. Primarily
electrical meters, but other types as well. The intent of the project
was to be able to accurately measure and monitor energy consumption on
a campus-wide scale. Pretty lofty goal, and not one that was to be
accomplished overnight, but over time (three years and counting, to be
First, some background and statistics. To monitor the energy consumption of each and every building on campus, the utilities serving each building would need to be individually monitored. No easy task, as each building is served by several utilities (electricity, gas, water, etc.), and many buildings have more than one feed per utility, be it multiple electrical power feeds, more than one gas feed, what have you.
Specifically, the utilities monitored include the following: electricity, natural gas, city water, steam consumption, and BTU (hot and/or chilled water) consumption. The first three (electricity, gas, and water), are provided from outside the campus. Steam, hot water, and chilled water are generated within the campus, and utilize all three of the first mentioned, to differing extents. To monitor all utilities serving a given building would therefore introduce some overlap, as would need to be handled through software calculations in order to come up with an accurate representation of total energy usage per building (and not an overestimate).
Of the 62 or so buildings monitored, all buildings were fitted with at least one electrical meter, and several required more than one, anywhere from two to seven total! From there, most (but not all) were fitted with natural gas and city water meters, which was easier said than done. As for steam, the campus generates steam from a central plant, and distributes it throughout the campus, to maybe half the buildings. These buildings were fitted with steam consumption meters. Other buildings have local hot water boilers and/or chillers, and many of these buildings were fitted with BTU consumption meters.
For each meter installed, we monitor the pulse output of the meter, which gives us energy consumption. Through software we then totalize and calculate total energy consumption on an ongoing basis. Just like your electrical, gas, and water meters at home, where the dude comes and takes readings on a periodic basis so the utility companies can bill you, these meters do the same, however the information is not necessarily locally viewable, but viewable and “processable” through the hierarchical monitoring system that we installed (more on that later).
What follows is a brief, simplified description on each metering scenario and an overview of the monitoring system, from both a hardware and software viewpoint:
An electrical meter designed to monitor three-phase power has several connections required to be made to it. First there are the voltage connections, where each leg is “tapped” and connected to the appropriate inputs on the meter. Then there are the current connections. These are a bit more involved. A current transformer is required for each power leg. Current transformers consist of a doughnut-shaped magnetic core with wire wrapped around it, and covered with an insulated outer jacket. They’re installed so that they surround the power leg. In other words, the leg goes through the doughnut. As a transformer, they convert the electrical current on one side, the side being measured (primary), to a linearly related current on the other side. This “other side” (secondary) is manifested in a two-wire connection that connects to the appropriate current input on the meter. The current range may be scalable, or more likely fixed at one or five amps.
We installed electrical meters wherever the main feeds were for each building. This work required a shutdown of the power into the building, such that we were able to tap the power legs for the voltage connections, and install the current transformers for the current connections.
For those buildings that were fed by the campus steam-generating plant, we installed vortex flow meters that had integral RTD temperature sensors. These self-contained meters required our contracting team to cut away some existing steam piping to make them fit, and weld some new flanges to the pipe in order to permanently install them. Each meter came equipped with a side mounted “main brain” that offered several different types of output signals, including the pulse signal that we required for our purposes.
For those buildings that had their own hot or chilled water plants, we installed BTU meters, of which consisted of several separate components. Central to the meter was the flow meter itself, an insertion type meter with a turbine or “pinwheel” at the end of the insertion probe. Then there were the immersion temperature sensors required, one for the supply and one for the return. Lastly, the “brainbox”, which was a microprocessor-based wall-mounted unit that the flow meter and temperature sensors wired into. The brainbox provided our pulse signal.
Gas & Water
Old campus, old buildings, and therefore old gas and water meters. Some of the newer structures have utility (natural gas and city water) meters that embrace relatively modern technology, and were able to be retrofitted with a purpose-built add-on that would allow us to pull a pulse signal from the existing meter. Unfortunately, too often was the case that this was not feasible, and so we had to install our own meters. This again, as with the steam meters, required some piping modifications, but when all was said and done, we got our pulses and were able to monitor these utilities.
In each building, we installed a digital controller, one with enough inputs to accept the pulse signals of all meters installed in the particular building. That’s the “short” story anyway. The controllers were networked together, from building to building, by tying on to the campus-wide Ethernet.
On paper, the hardware installation was the “easy” part, for now came the hard part: making sense of all those pulses through software. Remember that the purpose of this project was to be able to accurately monitor energy consumption, campus-wide. That presented some interesting and complicated situations, of which I’ll not go into detail here (runnin’ out of room, that’s my excuse!). That said, you can imagine that with all that data from all those meters, there was a fair amount of overlap, by which we needed to employ “subtractive metering”, which is an easy way to say that we removed the overlap (per building) through elaborate software calculations.
Beside the main goal being accomplished, many other side benefits presented themselves throughout the course of this project. For instance, several of the buildings are residence buildings (frat houses, dorms, etc.). These buildings need to be billed individually for energy usage. Now there is a streamlined process in place, via integration with the campus enterprise accounting system and software. In addition, these residential buildings were challenged, in contest form, to reduce energy consumption and operate more efficiently. I can picture it…college kids actually aware and concerned about conserving energy in their dorms! Granted this is an engineering school and so I would imagine, being one of them myself and remembering my college experience (barely!), there’s maybe more of a “buy-in” to the proposition of “saving energy as a form of competition”.
Other benefits, to name just a couple, are an overall campus awareness of energy consumption and conservation, via dashboards located throughout campus that show energy statistics and other “green” initiatives and objectives, and, maybe in the near-term, a kickback to the students for helping to lower campus energy costs, in the form of a reduced tuition or room & board fee (hey, why not??).
Tip of the Month: Seek out metering opportunities with your current and prospective customers. The old adage “you can’t control what you can’t measure” goes a long way in this day and age, especially given the technology now at our fingertips that was virtually unavailable just a generation ago. Ask your customers to provide you with several months of past electrical bills, and propose to reduce those monthly bills simply by installing meters. There’s more to it on your end, and you know that, but human nature alone helps you out with that, for simply knowing what you’re consuming gives you incentive alone to reduce that consumption, whereas not knowing does nothing!
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