We've got a retail client in Charlotte with 12 rooftop units that keep creating demand spikes under Duke's Schedule SGS. The building automation system is supposed to stage them every 5 minutes but something's not working right. Last month hit 380 kW when normal peak should be around 250 kW. That's an extra $1,950 in demand charges. Has anyone dealt with Trane Tracer systems having staging problems? The contractor swears the programming is correct but the interval data tells a different story.
Duke Energy demand charges killing us - rooftop unit staging issues
Sam, I've seen this with Trane systems when the communication bus gets overloaded. Had a Grand Rapids client with similar issues - 8 RTUs all starting simultaneously despite proper staging settings. Problem was the BAS was trying to poll too many points too frequently, causing communication delays. When a zone called for cooling, the delay made the system think the first unit wasn't responding, so it started the next one immediately. Fixed it by reducing polling frequency and adding communication delays between unit starts.
Tina's right about communication issues. Here in Memphis with MLGW, I've found that older Tracer systems sometimes lose their staging timers after power outages or system resets. The units revert to default settings which is usually simultaneous start. Check if your client had any power quality issues or BAS maintenance recently. You might need to reprogram the staging sequences from scratch. I keep backup copies of all critical BAS programs now after learning this lesson the hard way.
Chris brings up a good point about power outages resetting BAS parameters. Here at MLGW we've seen this pattern with several commercial accounts after summer storms. The staging logic gets wiped but everything else appears normal, so building operators don't realize there's a problem until the next big demand bill arrives. I always recommend monthly staging tests now - manually cycle through the sequence during off-peak hours to verify proper delays. Takes 30 minutes but can save thousands in demand charges.