Most commercial building operators understand energy charges: you pay a certain amount per kilowatt-hour for the electricity you consume. Far fewer understand demand charges, and yet demand charges can represent 30 to 50 percent of a commercial electric bill. A single 15-minute spike in your building's electrical load can set your demand charge for the entire billing month, costing thousands of dollars for what might have been a brief, avoidable event.
Demand charges exist because the utility must maintain enough infrastructure, transformers, substations, power lines, and generation capacity, to serve your building at its maximum electrical draw. Even if your building only hits its peak demand for 15 minutes each month, the utility still needs all that infrastructure available for those 15 minutes. The demand charge is how the utility recovers the cost of maintaining that capacity.
Understanding how demand charges work, what drives them in your buildings, and how to reduce them is one of the highest-return activities a building operator can undertake. Unlike energy efficiency projects that require capital investment, many demand reduction strategies can be implemented through operational changes alone, with immediate payback.
How Demand Charges Work
Your utility measures your building's electrical demand in kilowatts (kW) at 15-minute intervals throughout the billing period. The single highest 15-minute interval becomes your peak demand for the month. You are then charged a per-kW rate multiplied by that peak demand value. In most commercial rate schedules, the demand charge ranges from $8 to $25 per kW per month, depending on the utility and rate schedule.
To illustrate: a building with a peak demand of 500 kW at a demand rate of $15 per kW pays $7,500 per month in demand charges, regardless of how much total energy (kWh) the building consumed. If that 500 kW peak was caused by a single event, such as all HVAC units starting simultaneously on a hot morning, and the building typically operates at 350 kW, then 150 kW of that demand charge, or $2,250 per month, is being driven by a brief, avoidable spike. Annualized, that single spike costs $27,000.
Time-of-Use Demand Charges
Many commercial rate schedules include time-differentiated demand charges, meaning the per-kW rate is higher during peak hours than during off-peak hours. In these schedules, you may see two separate demand charges on your bill: a facilities demand charge based on your overall maximum demand at any time, and a time-related demand charge based on your maximum demand during peak hours only. This structure is common in California, New York, and other states with TOU rate designs.
Under a TOU demand structure, reducing your peak-hour demand is worth significantly more than reducing your off-peak demand. A building that drops its on-peak demand by 100 kW might save $20 to $25 per kW in combined facilities and time-related demand charges, while the same reduction off-peak might save only $8 to $12 per kW.
Ratchet Clauses
Some commercial rate schedules include a ratchet clause, which sets a minimum demand charge based on a percentage of the highest peak demand recorded in the previous 12 months. A common ratchet is 80 percent, meaning if your building hit 600 kW at any point in the past year, your minimum billed demand is 480 kW (80 percent of 600) for every subsequent month, even if your actual demand never exceeds 400 kW. Ratchet clauses make a single demand spike extremely expensive because its impact persists for up to 12 months.
Common Causes of Demand Spikes
Demand spikes rarely come from a single large piece of equipment. Instead, they typically result from the simultaneous operation of multiple loads that individually are manageable but collectively push the building past its typical operating range.
Morning startup. The most common cause of demand spikes in commercial buildings is the morning startup sequence. When a building management system turns on all HVAC units, lighting circuits, elevators, and plug loads simultaneously at 6 or 7 AM, the building's demand can spike 30 to 50 percent above its normal operating level. This spike lasts only 15 to 30 minutes as the building reaches steady state, but that 15-minute interval is enough to set the demand charge for the entire month.
Compressor staging. Large HVAC systems with multiple compressor stages can create demand spikes when multiple stages engage simultaneously. This often occurs during rapid temperature recovery after a setback period, or when the building transitions from economizer mode to mechanical cooling as outdoor temperatures rise during the morning.
Electric vehicle charging. As commercial buildings add EV charging infrastructure, unmanaged chargers can contribute significantly to demand spikes. A bank of ten Level 2 chargers drawing simultaneously adds 70 to 190 kW to the building's demand. If this coincides with the morning HVAC startup, the combined demand spike can be substantial.
Kitchen and food service equipment. In mixed-use buildings, commercial kitchen equipment such as electric ovens, fryers, and dishwashers can draw significant power. Restaurant tenants that start their equipment simultaneously during lunch or dinner prep can create demand spikes that affect the entire building's meter.
Backup generator testing. Monthly backup generator tests often involve transferring building load to the generator and back. The retransfer to grid power, when all building loads reconnect simultaneously, creates a demand spike that many operators do not realize is setting their monthly peak.
Demand Reduction Strategies
Staggered Startup Sequences
The simplest and most effective demand reduction strategy is to stagger the morning startup sequence. Instead of starting all HVAC units simultaneously, program the BMS to start units in a sequential pattern with 5 to 10 minute delays between each unit or zone. This spreads the startup demand over 30 to 60 minutes, preventing the 15-minute demand peak from spiking. A building with six rooftop units that starts them all at 6:00 AM might peak at 500 kW. Starting them at 6:00, 6:10, 6:20, 6:30, 6:40, and 6:50 AM might cap the peak at 380 kW, saving $1,800 per month in demand charges at $15 per kW.
Demand Limiting Controls
Modern building management systems include demand-limiting algorithms that monitor real-time building demand against a configurable threshold. When demand approaches the threshold, the BMS automatically sheds non-critical loads: dimming parking garage lights, reducing ventilation in unoccupied zones, throttling cooling in common areas, or pausing EV chargers. The loads are restored once demand drops below the threshold. This creates a hard ceiling on peak demand that prevents spikes from setting an artificially high monthly charge.
Battery Peak Shaving
Behind-the-meter battery storage can be programmed specifically for demand peak shaving. The battery monitors the building's real-time demand and automatically discharges when demand exceeds a preset threshold, injecting power from the battery to reduce the building's net draw from the grid. A 100 kW/200 kWh battery system dedicated to peak shaving can reliably reduce peak demand by 80 to 100 kW, saving $1,200 to $2,500 per month in demand charges. At that savings level, the battery can achieve payback on the demand charge reduction alone within three to five years, before considering any energy arbitrage or demand response revenue.
EV Charger Load Management
Smart EV charging management systems can throttle or pause chargers when building demand approaches the target threshold. Rather than allowing all chargers to draw at full power simultaneously, the system allocates a maximum aggregate power budget to the charging bank and distributes it across active sessions. If the building's base load increases, the charging allocation automatically decreases. This approach allows buildings to offer EV charging without incurring demand charge penalties.
Measuring Demand Performance
The key metric for demand performance is the load factor, calculated as average demand divided by peak demand over a billing period. A building with a high load factor (0.70 to 0.85) has a relatively flat demand profile, meaning its peak is close to its average. A building with a low load factor (0.30 to 0.50) has significant demand spikes relative to its average, indicating substantial demand charge reduction opportunity.
Pull interval data from your utility and identify the specific 15-minute intervals that set your peak demand each month. Map those intervals to building operations to determine what caused the spike. Was it morning startup? An HVAC fault? Generator testing? EV charging? Once you identify the cause, you can implement the appropriate mitigation strategy.
Track your load factor monthly and set improvement targets. A building that improves its load factor from 0.45 to 0.65, meaning it reduces peak demand by approximately 30 percent relative to average, will typically save 15 to 25 percent on its total electric bill. This is one of the highest-return metrics in building energy management.
Demand Charges Across Rate Schedules
Not all rate schedules treat demand charges equally. Some utilities offer alternative rate schedules with lower demand charges but higher energy charges, or vice versa. Buildings with high load factors (flat demand profiles) typically benefit from schedules with higher demand charges and lower energy charges. Buildings with low load factors (spiky demand profiles) do better on schedules that minimize demand charges even if per-kWh energy rates are higher.
Request a rate comparison analysis from your utility to determine whether your current schedule is optimal for your building's demand profile. Many utilities will run this analysis at no charge. The potential savings from switching to a more favorable rate schedule can be 5 to 10 percent of your total bill with zero operational changes.
Portfolio-Level Demand Management
For operators managing multiple buildings, demand charge management should be prioritized at the portfolio level. Start by calculating the demand charge as a percentage of total electric cost for each building. Buildings where demand charges exceed 40 percent of the total bill are your highest-priority targets for intervention. These buildings have the lowest load factors and the most room for improvement.
Create a monthly dashboard that tracks peak demand, load factor, and demand charges for every building. Flag any building where peak demand increased more than 10 percent month-over-month, which could indicate an equipment issue, a BMS programming error, or a new load that was added without demand management consideration.
Standardize demand management protocols across the portfolio: staggered startup sequences should be standard BMS programming for every building, demand limiting should be configured with building-specific thresholds, and EV charger policies should include demand management requirements. These operational standards cost nothing to implement and can reduce portfolio-wide demand charges by 15 to 25 percent.
A single 15-minute demand spike can cost your building $1,000 to $3,000 in a single month. Over 12 months, that adds up to $12,000 to $36,000 in avoidable costs per building. For a portfolio, the aggregate impact can reach six or seven figures annually.