Client here in Laredo is enrolled in AEP Texas demand response program but having coordination issues with their HVAC controls. When AEP calls a DR event, the building automatically sheds HVAC load as programmed. Problem is when the event ends, all the HVAC comes back online at once creating a massive demand spike. Last month this caused a 380kW peak right after a DR event ended, which negated most of the DR payment benefits. The DR payment was $1,850 but the demand charge increase was about $2,200. Anyone dealt with similar post-DR demand spikes? Seems like poor program design if participating actually costs more than the payments.
AEP Texas demand response vs HVAC coordination
Emily, that's a classic problem with demand response programs that don't have proper load restoration controls. MLGW's DR program here in Memphis has staged restoration built in - loads come back online over 15-20 minutes instead of all at once. You need to talk to AEP about modifying the program controls or adding a restoration delay to your HVAC systems. The whole point of DR is to save money, not create bigger demand charges.
Arizona has had this exact issue with APS demand response programs. The solution was adding a "restoration sequencing" feature to the DR controls. Instead of all HVAC coming back at the DR event end time, units restart every 2-3 minutes in predetermined sequence. Reduced post-event demand spikes by about 60%. APS actually helped pay for the control modifications since it benefits the grid too. See if AEP Texas has similar support available.
We've seen this with Duke Energy programs in South Carolina. The key is distinguishing between "emergency" DR events where fast restoration might be needed versus "economic" events where staged restoration is fine. Most DR programs are economic, so staged restoration shouldn't be a problem. What type of DR program is your client in? Curtailable load, real-time pricing, or emergency response?
It's AEP's "4CP" demand response program - they call events during the four coincident peak hours each summer. These are economic events, not emergency, so staged restoration should definitely be acceptable. The building has about 200 tons of cooling across eight rooftop units. When DR ends, all eight units restart immediately to bring temperatures back down. I'm going to contact AEP about modification options and see if they'll help fund control upgrades.
Tennessee utilities have been pretty good about helping with DR program modifications. For 4CP programs especially, staged restoration makes total sense since you're just trying to avoid system peaks, not respond to emergencies. Eight 25-ton units all starting at once is about 200kW of inrush - definitely enough to create a demand problem. The control modification should be pretty straightforward for most BMS systems.
Ivan's right about the control modification being straightforward. Most modern BMS systems can handle staged startup sequences easily. The trick is coordinating with the DR program signals. You want the HVAC to stay off during the event, then start up in sequence maybe 5 minutes after the "event end" signal. That gives time for the grid to stabilize and prevents the demand spike your client is seeing.
Another option is pre-cooling before DR events. If you know an event is likely (like hot afternoon in summer), cool the building extra before the event starts. Then when HVAC shuts off during DR, the building stays comfortable longer. When systems restart after the event, they don't all need to run at full capacity immediately. Reduces both the DR load shed impact and the post-event demand spike.
Pre-cooling is a great idea Sarah. The building envelope is pretty good so it holds temperature well. We could probably pre-cool by 2-3 degrees before DR events without comfort complaints. Combined with staged restoration, that should solve the demand spike problem. I've got a call scheduled with AEP's DR program manager next week to discuss modification options and any available incentives.
Make sure to get any modification agreements in writing. Some utilities will verbally agree to control changes but then have problems if something goes wrong during an actual DR event. Document exactly what the staged restoration sequence will be, how long the delays are, and what happens if there's a true emergency that requires immediate HVAC restoration.
Good point Marcus about getting everything documented. DR programs can be great money savers but they need to be set up properly. The fact that Emily's client is actually losing money on the program shows something's wrong with the implementation. With proper staging and pre-cooling, they should be able to capture the DR payments without the demand charge penalty.
Exactly Randy. The whole point is to make money, not lose it. I'll update this thread after my call with AEP next week. Hopefully they'll be cooperative about the control modifications. If this works out well, might be worth sharing the details since I'm sure other DR participants have similar issues with post-event demand spikes.
Please do update us Emily. These DR program coordination issues are becoming more common as more facilities enroll. Having documented solutions that work with different utilities would be valuable for everyone. Good luck with the AEP call!