Ecmweb 6508 Energy Management Systems Pr
Ecmweb 6508 Energy Management Systems Pr
Ecmweb 6508 Energy Management Systems Pr
Ecmweb 6508 Energy Management Systems Pr
Ecmweb 6508 Energy Management Systems Pr

Energy Management Systems and the NEC

July 16, 2014
The NEC now restricts the types of loads an energy management system can control.

Not that long ago, it took some doing to convince a building owner to pay for even low-cost energy-saving measures. Many factors have converged to produce a very different situation today. Consequently, installing an energy management system (EMS) is often part of a building construction or renovation project. A few simple strategies for reducing energy waste with an EMS can reap big savings (Photo 1).

Photo 1. HGA Architects and Engineers not only designs EMS applications, but also uses them in its own offices. For example, the HGA Milwaukee office uses automated strategies for HVAC control, automated lighting, and daylight harvesting (Photo courtesy of HGA Architects and Engineers).

New with the 2014 NEC is Art. 750, which provides the minimum electrical requirements for these systems. Running slightly less than a page and a half, Art. 750 has only five small sections. The way these are numbered, however, provides room for a much larger Article in a future NEC revision.

What’s an EMS?

The NEC gives a very flexible definition. It says an EMS is a system that monitors and/or controls an electrical load or a power production or storage source [750.2]. The definition gives a few examples of the types of devices used for this purpose, such as timers, controllers, and communications equipment.

Not everything related to energy savings falls under the umbrella of EMS. While automated blinds that close to block sunlight on the west-facing windows on summer afternoons fit the definition of energy-saving equipment, they don’t fit the definition of an EMS because there’s no control or monitoring of the actual load (the HVAC).

Photo 2. HGA Senior Electrical Engineer Krista McDonald Biason, who served as an alternate on the Code Making Panel for Art. 750, helps this client understand some finer points of interacting with the EMS (Photo courtesy of HGA Architects and Engineers).

You can think of EMS in the generic sense and be technically correct. For example, a bank of lights that automatically dim based on the sunlight coming in through the windows does control an electrical load to save energy. But it’s more common to think of an EMS as an engineered product (Photo 2) that enables an engineered solution. Common characteristics include:

Affordable to install. The fact these can be modularized and packaged into standard designs is one factor that has driven costs way down from what they were when each such system was a custom design from the ground up. This means low price points for entry-level systems.

Affordable for the tenant. Where the EMS involves a monitoring contract or other service, the monthly fees for basic service are low. The model is similar to that for intrusion alarm monitoring services.

Customizable. The specifier can customize a particular mix of control elements, communications devices, control panels, and other components.

Remote control capability. On-site control is great if you have the resources on-site to oversee the system. But in many cases, the facility manager doesn’t have a technical background and there’s very limited technical staff available. In commercial buildings, this is nearly always the case. Outsourcing the oversight and response to a contractor makes sense when the system has remote controls.

Touch panel interface. This type of user interface (UI) along with dashboards, on-demand reports, historical archives, trending, and configurable alarms have made these systems usable by the typical tenant, whether a restaurant or a bank branch office. Users can easily see what’s going on — in real time — with their energy consumption just by tapping their fingers on the display. That can help users make immediate adjustments to reap significant savings.

These systems reduce energy costs through such means as:

Undervoltage mitigation. Shut down selected loads as undervoltage conditions emerge.

Power factor penalty minimization. Control (or monitor and alert) which inductive loads run at any given time to keep power factor within preset parameters.

Peak shaving. Control specific loads to avoid peak usage penalties. For example, the system might do the following during peak load hours: dim warehouse lighting, lock scrap grinders out of use, lock garbage compactors out of use, adjust some thermostats by a few degrees, and lock out specific chillers entirely. Or, it may run the generator so all loads are still available to operations (Photo 3).

Photo 3. Using an EMS to remove some loads is one strategy for peak shaving, but that can impair operations. Another is to kick in a generator to reduce the amount of load supplied by the utility so that operations aren’t affected by peak shaving (Photo courtesy of HGA Architects and Engineers).

Waste monitoring. It sure would have been nice to know Chiller B (or the air compressor or some other large load) never shut off last month rather than have to figure out this month why that electric bill was so high.

These are just some examples of how an EMS can reduce the energy load costs for a given facility. If you have on-site generation, an EMS can manage that for energy savings, too. The takeaway here is an EMS isn’t just shutting off the bathroom lights with occupancy sensors to save a few bucks on that electric bill. It can do much more.

If the designer is serious about lowering energy bills, the EMS controls circuit breakers at the feeder level, which means it could potentially shut down any load at the facility. That potential is one reason Art. 750 was needed.

Suck it up

Consider a particular type of load (to be named in a moment). It’s a big motor that starts across the line. And it starts under load, which means it calls for a huge inrush current. The load is such that, temporarily, there’s low voltage on that service and a consequent rise in current demand by all other loads.

Obviously, this is bad for the electric bill. Putting this load on the EMS so it at least doesn’t come on during peak load time seems like a no-brainer. In addition, it might be nice to just block that load whenever power factor is getting close to the allowable limit. Everyone in the facility agrees that they don’t need this load to even run for them to do their normal jobs. You checked the log and found this load hasn’t run for the past three weeks.

However, there’s a small problem with locking that load out. It just happens to be the fire pump that’s responsible for providing the fire suppression system with as much water as it needs. The fire pump is one of the four loads you cannot shed [750.30]. The other three are:

1. Emergency systems.

2. Legally required standby systems.

3. Critical operations power systems.

In fact, the fire pump is so important that you can’t use the EMS to override any control necessary to ensure continuity of its alternate power source either [750.20]. This also applies to the three other types of loads we listed as “cannot shed” and health care facilities.

The EMS can monitor these loads — it just can’t interfere with them. Why would you monitor a load but not control it? Let’s stick with the fire pump as an example.

A fire pump system consists of at least two pumps. You have the big main pump and a smaller jockey pump. You can turn this jockey pump on and off all day long with negligible effect on your power distribution system. But if it’s going on and off with much frequency, there’s a problem. The purpose of this pump is to maintain pressure in the fire suppression system piping. Why are you losing pressure such that this pump is engaging so much?

That’s one angle. Another is this. Suppose the main pump needs to start. Your EMS can monitor that and immediately shed less critical loads. This has several benefits, such as reducing the strain on the system while the fire pump is starting. And think of this. If your EMS shuts down all loads systematically in the event of a fire, first responders won’t waste time doing that upon arriving, and they won’t be opening breakers that are carrying a load.

The EMS can’t disconnect power to any of the following five types of loads [750.30(C)]:

1. Elevators and other systems for moving people.

2. Positive mechanical ventilation for hazardous locations.

3. Ventilation for hazardous gas or area reclassification.

4. Emergency lighting.

5. Essential systems in health care facilities.

A couple more rules

In addition to the “don’t touch these loads” rules for EMS, Art. 750 provides two other rules:

1. The EMS can’t cause an overload on any branch circuit, feeder, or service.

2. Where the EMS has remote control over power, you must post a directory identifying the controlled device(s) and circuit(s).

While the first rule falls into the category of “common sense” — and the second just echoes similar requirements elsewhere in the NEC — they are now explicitly stated for EMS.

Taking EMS to the next level

Going beyond the core EMS functionality can benefit both the contractor and the owner or tenant. The usual reason for installing an EMS is to save energy. But because of how it does that, you can use the EMS to achieve more.

You can turn the Art. 750 restrictions on their head to get an overall improvement in critical system performance and reliability. Preserve the restricted loads, but under specified conditions shed the others just as in our fire pump example.

If an EMS is part of the construction specifications, make a list of all the types of loads (create a load profile) of the facility. Then think beyond which loads the NEC says you can’t shed to which ones you should shed and why.  

Lamendola is an electrical consultant located in Merriam, Kan. He can be reached at [email protected].

About the Author

Mark Lamendola

Mark is an expert in maintenance management, having racked up an impressive track record during his time working in the field. He also has extensive knowledge of, and practical expertise with, the National Electrical Code (NEC). Through his consulting business, he provides articles and training materials on electrical topics, specializing in making difficult subjects easy to understand and focusing on the practical aspects of electrical work.

Prior to starting his own business, Mark served as the Technical Editor on EC&M for six years, worked three years in nuclear maintenance, six years as a contract project engineer/project manager, three years as a systems engineer, and three years in plant maintenance management.

Mark earned an AAS degree from Rock Valley College, a BSEET from Columbia Pacific University, and an MBA from Lake Erie College. He’s also completed several related certifications over the years and even was formerly licensed as a Master Electrician. He is a Senior Member of the IEEE and past Chairman of the Kansas City Chapters of both the IEEE and the IEEE Computer Society. Mark also served as the program director for, a board member of, and webmaster of, the Midwest Chapter of the 7x24 Exchange. He has also held memberships with the following organizations: NETA, NFPA, International Association of Webmasters, and Institute of Certified Professional Managers.

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