Demand charges, and why your bill is not just about how much you use
Residential customers pay for how much electricity they use. Commercial customers pay for that and for how hard they pull at their peak — which means a single afternoon can shape a bill for a whole month.
- Charged on
- Peak, not total
- Measured in
- kW
- Set by
- Your worst interval
What a demand charge is
A charge based on the highest rate of electricity draw your building hit during the billing period, measured over a short interval, rather than on the total energy consumed over the month.
Consumption is measured in kilowatt-hours and answers how much. Demand is measured in kilowatts and answers how fast. The utility has to build and maintain infrastructure capable of serving your peak whether you hit it once or continuously, and the demand charge is how that capacity gets billed.
The practical consequence is that the peak is set by a short window. If every chiller, rooftop unit and compressor in the building happens to run simultaneously on the hottest afternoon of the month, that moment can set a charge that applies across the entire billing period.
Why old equipment makes it worse
Aging plant tends to run harder, longer, and less selectively. Equipment that has lost efficiency compensates by running more of itself for more of the time, and that lifts the peak as well as the total.
A seized economizer is a clean example. On a mild day a working economizer cools with outside air and the compressors stay largely idle. With the economizer stuck shut, the same building runs mechanical cooling instead — so both consumption and peak demand rise on days that should have been nearly free.
Constant-speed equipment has the same problem in a different form. A constant-speed chiller or fan runs at full draw regardless of how much of its capacity the building actually needs, where variable-speed equipment throttles down and pulls a fraction of the power at partial load.
How a retrofit affects it
Replacing end-of-life plant with modern staged or variable-speed equipment reduces both what the building consumes and how hard it pulls at peak. The second effect is the one most owners do not anticipate.
Modern equipment stages. Several smaller boilers that bring capacity on as load rises, or a chiller that modulates rather than cycling on and off at full power, both flatten the demand curve rather than spiking it.
It is worth being straight about how this interacts with incentives: New Jersey utility programs model energy savings, and the demand reduction is generally a benefit that lands on your bill rather than a separate payment. It shows up in the operating cost, not in the incentive.
Common questions
What is a demand charge?
A charge based on the highest rate at which your building drew electricity during the billing period, measured in kilowatts, as distinct from the total kilowatt-hours consumed.
Why is my bill high when my usage looks normal?
Often because the demand component is high rather than the consumption component. A short period of simultaneous equipment operation can set a peak that is billed across the whole period even though total usage was unremarkable.
Do all commercial customers pay demand charges?
It depends on the rate class the account sits in, which is generally driven by the size of the service. The bill itself is the reliable place to check — it is one of the things we look at during a survey.
Will new equipment reduce my demand charge?
Usually, because staged and variable-speed equipment flattens peaks rather than spiking to full draw. How much depends on the building and the equipment being replaced, which is what the energy model establishes.
Related equipment
More guides
- A2L refrigerants and the R-410A phase-outYour existing equipment is not illegal, and you are not required to replace it. What actually changed, and what it means for a planned retrofit.
- HVAC economizersThe most expensive failure in commercial HVAC produces no service call, no complaint and no alarm. It just quietly doubles what cooling costs.
- Commercial energy auditsThe survey and the energy model are not paperwork. The model is what sets your incentive, which is why it comes before any pricing conversation.
- Steam vs hot water boilersA great deal of New Jersey's prewar apartment stock still heats with steam. What that means when the plant reaches end of life.
- VRF systemsVariable refrigerant flow is not a premium version of a split system. It solves a specific problem, and in the wrong building it is the wrong answer.
Find out what your building qualifies for
A survey and an energy model tell you the real number. That is a phone call, not a commitment.