Understanding LED inrush current and the financial impact on your lighting design
As more growers around the world implement LED lighting technology in their greenhouses, project managers and lighting strategists are encouraging them to gather all the facts about a fixture before making a short-term decision on price that could cost more in the long run. A problem can arise if an electrical contractor designs a lighting project based around a specific LED fixture. If a grower finds a different LED fixture for the contractor to install, a redesign may be required to ensure compatibility between the facility design and the selected LEDs.
“Growers may end up paying more in total project costs because the specifications of the product purchased for the installation deviated from the product for which the project was designed. Perhaps they saw the lower price of a fixture and ran with it,” says Mark Pedersen, President/CEO, Climatrol Solutions Ltd., Surrey, British Columbia. “We want everything to run seamlessly, and it is very important with a lighting fixture that we have the complete information, just like any other component purchased for their facility. We need to be sure it is going to work for their greenhouse and not cause an issue to their electrical or hydro-electrical system.”
Complete fixture specifications are crucial
An important first step in a new facility design or redesign is to ensure your electrical contractor has a complete fixture specification sheet and application guide. This information will enable the project engineer to properly design the system. LED lighting manufacturers should make published specifications readily available that include operating voltage range, full load current at common operating voltages, rated input power, power factor, total harmonic distortion, operating frequency, and inrush current on startup. Often, growers assume that engineers can assess wattage and other technical factors simply based on fixture name or sight, which is not the case. Or a grower may not fully grasp the importance to the electrical design, of lesser-known technical specs.
Knowing these details from the beginning of the project ensures engineers can specify the proper cables, panels, high voltage sub feeds and transformers, among other components. Without exact specifications, small deviations from the initial plan can add up to huge expenses and long delays during installation.
“Just the difference between 800 or 805 watts affects everything, and the more fixtures you have in your installation, the more it affects the design including how many circuits are required or how far away the fixture is from the panel,” says Pedersen. “What I really value here is for companies like Signify, with their Philips brand LED lighting, who have the team, and the engineers, to design where those features go.” While a difference of 5 watts may not seem like much, when you are installing 1,000, 10,000 or 25,000 fixtures, the “minor” wattage difference creates a significant deviation and major complications in a system.
Make sure to know the instantaneous power demand
“Matching the inrush current is particularly important”, says Evann Seney, Master Electrician, Honey Electric, Chatham, Ontario. Put simply, the inrush current value informs the electrician about the instantaneous power demand from a light. Inrush current has implications at the time of startup, in the event of power failure and on the number of fixtures that can be switched on at the same time.
A fixture that has a very high inrush current can cause extensive issues in a lighting system, particularly if the circuits, cables, and transformers aren’t built to handle that load. A greenhouse system could have 150 to 200 lighting panels, all of which may have to be adapted – at significant expense – if the inrush current is higher than specified.
Certain LED fixture drivers will actively manage the fixture inrush current at startup. In these cases, the inrush current is negligible. “All of our products are designed with our own drivers,” says Chris Strom, Application Engineer for Signify North America, manufacturer of Phillips LED products. “One of the big things we designed into the drivers was a low inrush current. Many off-the-shelf drivers and even advanced drivers have a high inrush current, and that impacts the load on the lighting system.”
It is important to consider the effect that the inrush profile will have on system protection (such as circuit breakers and fuses). A circuit sized properly for a fixture with a negligible or nominal load may trip at startup if not built for higher inrush.
The wrong inrush current between fixture and panel also means that each time power flickers or there is a loss of power throughout the electrical grid, the controls shut off individual panels. That in turn, blows fuses. When power is restored and all the fixtures come back on at once, more issues may occur.
Seney says. “If the lights are shut off in the event of a power flicker, when the power comes back on, a timer in each panel would stagger it so that you would turn on one panel at a time.”
In addition, if the inrush current on a fixture is significantly higher than expected, the contractor may have to install up to four timers to then turn that lighting panel on in four sections, as opposed to one. “The electrician and the engineer should know this ahead of time so you’re not having this come up after you've installed everything,” he says. “That is a huge cost.”
Do not spend unnecessary money on your transformer
In the same way, missing or incorrect information or specifications on fixtures could also lead to unnecessary expense on transformers. For example, if an engineer accounts for a fixture drawing 848 watts, and the grower opts for a fixture that draws 840 watts, the greenhouse could be installing one more transformer than they need, or a higher voltage transformer than necessary.
“This could mean you have designed your transformer to have 80% load on it, and it has only 70% load,” Seney explains. “So, if you look at the entire facility, you could have saved one 2.5 mva transformers instead of a 2.75 mva transformer. The difference from a 2.5 mva transformer to a 2.75 mva transformer is around $20,000 Canadian dollars.”
The cost is in turn multiplied by accompanying costs including cables, concrete pads, and electric panels. “The installation costs more. It is a heavier cable; it adds more weight, which means you need more supports in the structure to carry the weight of the load on the superstructure,” Pedersen says.
Both experts emphasize that it’s critical to be able to receive the proper specifications on inrush current and other key technical factors, or the project risks unplanned costs. “It is a domino effect because everything else now must be larger. It is all for nothing at the end of the day as no one wants the expense of having to go back and add more light fixtures,” Seney says. “These are phantom costs as a result of not having the proper data in the first place.”
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