Need some advice from the veterans here. Client in Mesa got absolutely destroyed by APS demand charges last month. Their 400-ton chiller went down during a heat wave (118°F outside) and when it came back online, the restart procedure pulled 1,240kW for about 18 minutes. Normal peak is around 650kW. APS Schedule E-32 demand charge is $21.30/kW so that's an extra $12,567 for one bad day. The chiller manufacturer says the restart sequence was normal but this seems excessive.
APS Schedule E-32: Massive demand hit from chiller restart
Christie - that restart current sounds way too high for a 400-ton unit. Normal inrush should be maybe 300-400A per compressor, not whatever pulled 1,240kW. Was this a screw chiller or centrifugal? Might have had multiple compressors trying to start simultaneously or a stuck bypass valve. I'd push back on the manufacturer's explanation.
AEP here in Ohio has similar rates. We always recommend soft starters on anything over 200 tons. Also, most newer chillers have built-in demand limiting features - did they check if that was enabled? Sometimes factory settings disable it and techs forget to turn it back on during commissioning.
Randy - it's a Trane RTAC screw chiller, dual compressor setup. The service tech said both compressors tried to start at the same time instead of staging. Ruth - I'll check on the demand limiting settings. The building engineer mentioned something about factory defaults but I didn't dig into it. This is a relatively new installation, maybe 14 months old.
Georgia Power customer here - had the exact same issue with a Trane RTAC last year. Turned out the staging timer was set to zero seconds instead of the recommended 60 seconds. One simple programming change saved the client about $8K per year in demand charges. Check the controller settings before assuming it's a hardware problem.
NorthWestern Energy isn't as brutal on demand charges but we still see this issue. The Trane units have a "rapid restart" feature that's supposed to get the building cool faster after an outage. Problem is it overrides normal staging protocols. You can disable it in the advanced settings menu.
Marilyn's right about the rapid restart feature. It's designed for comfort but ignores demand management. Christie, I'd also recommend installing a separate demand controller that can override the chiller controls if needed. Something like a Schneider Electric ION or Honeywell system that monitors real-time demand and can delay equipment starts.
Entergy Arkansas recently changed their demand billing to include a 12-month ratchet. One bad month like this and you're paying elevated demand charges for a full year. We're pushing all our chiller clients to install demand monitoring systems. The technology has gotten much cheaper and more reliable over the past few years.
Thanks everyone - this is exactly the kind of insight I was hoping for. Going to check the staging timer settings first, then look into disabling rapid restart. Greg's point about the 12-month ratchet is scary - APS does the same thing. Client is definitely interested in demand monitoring now that they've been burned once.
Duke Energy here in South Carolina - we just had new demand charges kick in this year. $24.80/kW in summer months. These chiller restart issues are becoming much more expensive. I tell all my clients that demand management isn't optional anymore, it's basic cost control. The days of ignoring electrical demand are over.
George is absolutely right. AEP just announced another rate increase for 2025. We're seeing demand charges become the dominant cost factor for many commercial buildings. Christie, once you get this chiller situation sorted out, I'd recommend a comprehensive demand audit of the entire facility. There are probably other opportunities for optimization.