The other day, I was sent an indoor ice arena’s electricity bill that hit me like a lightning bolt. It was for one of the two “shut-down” months this facility has each year.
The lights were off, no one was home… but if you saw the cost of their electricity bill, you’d think otherwise.
Cost per Kilowatt Hour ($/kWh)
Most people understand that kilowatt hours are the currency of electricity – the amount of kilowatt hours used, multiplied by the rate ($/kWh). To find the blended rate of electricity that this particular facility was paying, I took the total cost of this bill and divided it by the number of kilowatt hours they’d used that month. That came to 37¢/kWh — light years away from the 16¢/kWh they thought they were paying.
Cost per Kilowatt ($/kW)
I know what you’re going to say: that I need to look at the distribution demand being charged (and you would be right!). The number of kilowatt hours used is one factor determining your bill, but the distribution demand charges are another. Those are ongoing and they make a tremendous impact to your bill — even when the lights are out and nobody’s home as was the case here. The distribution demand charges are based on peak — on the highest number of kilowatts your facility has hit over, usually, a 15-minute period in the previous year. If, tomorrow, you happen to beat that number, when, for example, putting in your ice during an extra-hot week in November, that rate will be used for determining your distribution demand charges going forward for the ENTIRE NEXT YEAR. Paying attention to the weather, your scheduling — and understanding what electricity demands that all the folks in your community might be requiring may be difficult to imagine, but bucking the trend can help you keep your peak down. Here’s an excerpt from the SunPower website that puts capacity and distribution demand charges into perspective:
For utilities, the real challenge comes in maintaining enough capacity to satisfy your and all their customers’ electricity needs (for instance, on a hot day when everyone’s running their AC at the same time). To do that, utilities must keep all sorts of expensive equipment on constant standby “just in case,” including substations, transformers and generating stations. This capacity is extremely expensive to build and maintain, and commercial electricity demand charges are used to help pay those costs.
– SunPower – “A closer look at commercial electricity demand charges and how to lower them“
How to Control Your Peak
So, how do you control your peak? There are a few different ways. One is permanent peak control and the example below is from Maple Run Unified School District’s Collins Perley Sports and Fitness Center in Saint Albans, VT, where their peak has been purposely limited to 165 kw.
Collins Perley’s 165 kW Max
I didn’t realize it back then when I wrote about what Dave Kimel did at the “CP” (see “An Energy Use Approach to an Arena Retrofit“) how important and, seriously, how absolutely genius this particular approach was, but I do now. Kimel is the Director of the CP. He’s got a business background, and is bottom-line driven, so when the arena needed replacement refrigeration equipment, he put a limit on the load, wanting to run the entire facility on no more than 165 kW — ever! That is a pretty slim number for a 70,000 square foot indoor facility with 45 acres of lit fields.
Kimel calculated that by keeping his peak under 165 kW, he’d be able to control his utility spend. That number was, Kimel says, “a reasonable limit” based on the demands of the facility.
“The highest amount of electricity used in any 15-minute period in a year is the rate we’re charged for the next 12 months. That’s critical. Not only do I want to reduce my kilowatt hours, but I also want to reduce my peak.”
He was able to achieve his no-more-than-165 kW target by installing an indirect system (Ice3 from Emerald Environmental Technologies) which he compares with grocery store compressors.
“At 47 kW needed for each “Cube” (they have four), they take about a quarter as much kW as what an industrial compressor would (150 kW), and a third as much as what a commercial compressor does (70 kW). The other advantage to these kind of compressors is you can buy off-the-shelf replacement parts for them from local plumbing and heating retailers – which is a great advantage.”
CP’s Cubes go on one at a time, and only when they’re needed.
“I’m also turning on pumps, so my actual load is higher than that, but after I’ve got one on, I can add another one, and another one — but most of the time it’s just one that’s running,” he says.
Ten years post-installation, Kimel is happy with the decisions made.
“I know of single sheets of ice that don’t have stadium fields with lights like we do that can’t run on 165 kW,” he says.
So… does he ever burst his 165 kW bubble?
“Yes,” Kimel says. “But because our electric utility has a 5-minute grace period, our control system is usually able to shut down components that would add to the load, to bring it back down within that time. And, in the rare cases when we have blown the 165 kw limit outside of that 5-minute threshold, the utility has graciously waived it. We’re a school and they understand our commitment to running it as efficiently as possible. We’re grateful to have such a good relationship.”
“We can predict when we’re going to have a problem,” Kimel says, “and when we expect we might be close to our limit, we have someone in front of the computer screen, monitoring the situation.” Last Friday night, for example, they had a lot of activities going on and they needed to take action.
“We shut off all our compressors for about an hour to make sure we didn’t go over our limit. That’s not an issue: the ice can go without refrigeration for an hour without any problems.” Kimel explains they had a lot of activities going on — a football game outside, under the lights, a big wellness class with big amplifiers pushing the music and running 18 special-effects lights, people playing tennis — and other activities.
“In the kitchen in my house, I can turn on one light above the kitchen table, but if I want more light, I’ve also got 8 recessed lights in the ceiling that I can turn on too. The problem is that with that system, I’m limited. I can’t just turn on two of those recessed lights or 4 or 6 of them — all 8 come on at the same time and if I want more light than that single light, it’s all or nothing. With the Ice3 system, I can turn on the amount of power I need — one, or two, or three or four compressors, or turn them off.”
Kimel says it’s rare that they have three running to keep their rink operating.
“The flexibility is just terrific – it’s a beautiful system,” he says.
Keeping the Distribution Demand Charges Down on the Fly
Replacing your refrigeration equipment is a long-term, permanent solution, but you can also make changes to reduce the distribution demand charges on the fly. One way is by looking at your scheduling, which Kimel says is also key for them. At CP, they try hard to not schedule a high school football game on the outdoor fields at the same time as a big hockey game in the indoor ice arena because they would need all the field lights on as well as cooling capacity. But as we’ve seen, making scheduling changes isn’t always possible.
Another way is to always be cognizant of hot weather and finding ways to work around it. Know what your utility considers to be peak hours and try to avoid building ice or doing ice maintenance during those times. Instead of building your ice from scratch during the day, consider moving that task to the night time, when the demand for electricity is low. Changing your team’s work schedule to build your ice during off-peak times won’t make a difference to the quality of your ice, but it MAY make a difference to the distribution demand charges your indoor ice arena will get charged for the entire year ahead, especially if the outdoor temperatures are unseasonably high.
For other ideas of how you can control your distribution demand charges, check out this post by SunPower. SunPower, a San Jose, CA-based company, “designs, manufactures and delivers the planet’s most powerful solar technology broadly available today”. Their recommendations include investing in a solar energy system and implementing an energy storage solution using batteries.