Just finished analyzing 15-minute interval data for a Rochester client on RG&E Rate 8 (>300kW). Their December demand charges were about $3,200 higher than expected, so I dug into the interval data. Found the problem - HVAC sequencing controller failed in early December and all six rooftop units were cycling on/off together instead of in sequence. Created these nasty demand spikes every 45 minutes when the building called for heating. Peak went from normal 420kW to 547kW. Has anyone else seen HVAC sequencing failures create this kind of demand pattern? The interval data makes it crystal clear what happened.
RG&E interval data showing HVAC sequencing issues
Tom, that's a textbook case of why interval data analysis is so valuable. MLGW here in Memphis sees this all the time with older BMS systems. The 45-minute cycling pattern you described is classic sequencing failure - normal operations would show much smoother demand curves. Did the client have any indication the sequencing wasn't working properly? Sometimes facility managers don't notice because the building temperature stays comfortable.
Randy's right about the interval data being the smoking gun. We see similar patterns with SCE&G (now Dominion) customers down here. The facility manager probably had no idea anything was wrong until the electric bill showed up. Question is whether RG&E will work with you on this since it was equipment malfunction. Some utilities are more flexible than others about demand charge relief for documented equipment failures.
Client had no idea anything was wrong - building stayed comfortable because the total cooling/heating capacity was still adequate, just inefficient. The HVAC contractor found the failed sequencing module during routine maintenance in late December. I've got the work order showing the replacement and programming of proper staging delays. RG&E has a "special circumstances" provision in their Rate 8 tariff, so I'm preparing an appeal with all the interval data and repair documentation.
Arizona utilities have been pretty reasonable about equipment malfunction cases like this. APS approved a partial demand charge credit for a similar sequencing failure last year - they reduced the demand charge to what it would have been with proper sequencing based on the load profile analysis. The key was showing exactly when the malfunction started and that it was corrected. Your interval data should make that pretty straightforward.
What size are the rooftop units? Six units cycling together could create a significant inrush current spike on top of the demand issue. We had a case where simultaneous startup damaged some facility equipment due to voltage drop. Might be worth checking if there were any other electrical issues during that period - could strengthen your case that this was clearly abnormal operation.
They're six 15-ton units, so yeah, significant load when they all kick on together. Good point about checking for other electrical issues - I'll ask the facility manager if they noticed any lights flickering or equipment problems during December. That could be additional evidence of abnormal operation. The interval data shows some pretty sharp load swings that definitely weren't happening in November before the sequencing failed.
Those 15-ton units all starting together would definitely cause voltage fluctuations. That's about 180kW of additional load hitting the system simultaneously every 45 minutes. The interval data should show very distinct step changes versus the gradual load ramps you'd see with proper sequencing. Make sure to highlight that difference in your appeal - the visual comparison between November and December data should be pretty compelling.
Oklahoma utilities have been hit-or-miss on equipment malfunction appeals, but your documentation sounds solid. One thing that helped us with OG&E was getting a letter from the HVAC contractor explaining exactly what failed and confirming the dates of malfunction and repair. Sometimes utilities want third-party verification that it was truly equipment failure and not operator error or poor maintenance.
Great suggestion about the contractor letter. I'll get something from them documenting the failed sequencing module and confirming the repair dates. The interval data comparison is definitely compelling - November shows nice smooth load curves with staged startup, December looks like a seismograph during an earthquake. Filed the appeal yesterday, RG&E has 30 days to respond.
Perfect analogy about the seismograph! That's exactly what uncontrolled HVAC cycling looks like on interval data. Hope RG&E sees reason and provides some relief. Keep us posted on the outcome - these cases help establish precedents for future appeals with various utilities.