Brenda from Phoenix. Client is very upset. Demand charges jumped about 40 percent from one month to the next with no change in operations. The client runs a hotel and swears nothing changed. What are the most common causes of an unexplained demand spike?
Demand charge jumped 40 percent — no change in operations
Paul from Minneapolis. Most common causes in my experience: a new large appliance or HVAC unit turned on for the first time or coming out of service, a demand meter that was recently replaced and is calibrated differently, a rate change that changed how billing demand is calculated, or a change in the demand interval by the utility.
Paul, how would I know if the demand interval changed? Would the utility notify the client?
Paul again. Not necessarily. Interval changes sometimes happen with meter replacements or system upgrades with little customer notice. Check the bill for any notation about a new meter or service change. Also look at whether the demand reading itself changed or whether the demand charge per kW changed — those tell very different stories.
Mark from Houston. In a hotel specifically, common culprits are large HVAC compressors starting after coming out of a maintenance lockout, the kitchen adding equipment, or conference center systems being activated. Hotels have a lot of large equipment that cycles in and out of use.
Brenda here. The hotel's chiller plant was serviced the month before the spike. The service technician may have reset the staging schedule.
Mark again. There it is. If the staging schedule was reset incorrectly the chillers may be starting simultaneously rather than staggered. A staggered start might bring up one 150 kW chiller at a time. Simultaneous start brings all three up at once and the inrush currents overlap in the same 15-minute demand window.