CPS Energy in San Antonio uses 15-minute demand intervals like most utilities. But I just picked up a client served by LCRA wholesale through a local distribution co-op and they use 30-minute demand intervals. The exact same load profile produces significantly different peak demand readings depending on whether the interval is 15 or 30 minutes. A short spike that averages out over 30 minutes gets captured at full intensity in a 15-minute window. Has anyone quantified the billing impact of interval length?
Demand window ? 15 minutes vs 30 minutes makes a huge difference
Michelle ? the interval length matters enormously for clients with spiky load profiles. A 200 kW spike lasting 5 minutes registers as 200 kW in a 15-minute interval but only about 100 kW averaged across a 30-minute interval. For clients with motor starting transients, compressor cycling, or batch processing loads, the 30-minute interval is significantly more favorable. I had a printing plant in Chicago where switching from ComEd 15-minute to an alternate supply arrangement with 30-minute metering reduced billed demand by 18%.
From the engineering side ? the demand interval length is a function of the meter programming, which is determined by the tariff. You cant choose your interval. But if a client has the option between two rate schedules and one uses 15-minute intervals and the other uses 30-minute, and the client has a spiky load profile, the 30-minute rate could save substantial demand charges even if other rate components are slightly higher.
Hector ? agreed you cant choose the interval on a given tariff. But the point about comparing total bill impact between tariff options is important. I modeled my co-op clients load profile under both 15-minute and 30-minute intervals. The 15-minute peak was 520 kW. The 30-minute peak for the same period was 445 kW. At their demand rate of $12.50 per kW thats $937.50 per month or $11,250 annually difference from interval length alone.
In Wisconsin, WPS and Alliant both use 15-minute intervals on their standard commercial tariffs. But Madison Gas & Electric uses 30-minute intervals on their Cg-2 rate. I have a manufacturing client who was considering relocating within the Madison metro area. The choice between MG&E territory and Alliant territory could mean $15,000+ annually in demand charges from interval differences alone. Location decisions should factor in utility tariff structure.
Vernon ? hourly demand integration? Thats remarkably favorable for spiky loads. A 5-minute spike averaged over 60 minutes is barely a blip on the demand reading. Do any non-TVA utilities use hourly integration?
Im not aware of any standard commercial tariff using hourly demand integration. But some industrial interruptible tariffs use 60-minute integration as an incentive. In Albuquerque PNM has an experimental rate for large interruptible customers that uses 60-minute integration as part of the incentive package. Very limited availability.
Important thread. Demand interval length is often overlooked in auditing. Key points to remember: 1) 15-minute intervals penalize spiky loads more than 30-minute intervals 2) When comparing rate options, model the actual load profile under each intervals measurement method 3) The billing impact of interval length can exceed other tariff cost differences 4) Always check whether alternative tariffs use different demand intervals before comparing demand charges directly.
TVA uses 30-minute demand intervals for directly served industrial customers. All the local power companies that distribute TVA power use 30-minute intervals too. But some large customers metered at transmission voltage use integrated hourly demand for certain rate riders. Three different interval lengths within the same TVA system depending on the specific rate component and service level.