It used to be that a building utilized an electricity meter, which recorded how much electricity was entering the building during a month (billing cycle), it would be recorded, and the building owner would be charged for that electricity used (in kilowatt-hours). Simple: the more usage, the more one would pay. But some time ago that changed for many utilities. As the economy grew and technology grew, electricity demand rose greatly. However, keeping up with the growth in demand became a challenge due to more farflung buildings and infrastructure upgrades to provide power. For many utilities, it is possible that they cannot deliver electricity to all users in an area, especially during peak demand, which is a hot, summer afternoon when there is maximum usage of air conditioning. Technology has made this worse. For example, people can be comfortable and well air conditioned in their offices and with their smart phones, at the same time, start their air conditioners at home, so the house is comfortable when they walk in.

Being thus challenged, utilities began to confer an additional charge to certain customers for peak demand in addition to the electric usage charge. Having a very high demand (in kilowatts) for a short period – even for just 15 minutes – in a one-month cycle can become very costly. In fact, utilities often charge for peak demand on a sliding scale, with the highest such charges being conferred in the summer. Therefore, while a robust energy audit to reduce usage is a good thing, such an audit should reveal opportunities to also reduce that peak demand, as well.

To address the issue of peak demand, first study your electric bills and see for yourself what your peak demand charges are. How high are they? What rates does your utility use? What has been your historic peak electric rate (peak kW) and how does it vary by season? Once that is better understood, here are some inexpensive, but effective strategies to reduce the peak energy costs, yet still serve your building power needs.

Let’s use an actual example. A large building’s July electric bill indicates a peak demand of 136 kW during one short period due to several rooftop air conditioning units cooling most of the building, many rooms being lit, and a number of laptops, flatscreen TVs, and other plug load operating. The building owner pays $35 per peak kW, a very high rate

Reduce Usage – Reducing usage, of course, not only reduces that charge, but also your peak demand and charge. Simple example: a building replaces 100 fluorescents of 40 watts each with 100 LEDs of 16 watts each. Assuming 50 hours/week of operation, the reduction is 2.4 kW in peak demand and 520 kWh in usage per month. At $35/kW and $0.08/kWh, savings is over $125/month, with three-quarters of this from reducing peak demand. If building can de-lamp fixtures or dim LEDs, savings would be greater.

Modify Scheduling – This building is incurring this high peak demand cost because it is operating many energy intensive processes simultaneously. Modifying the schedule can alleviate this problem of multiple equipment operating, if certain equipment can cycle off during peak hours. Can the rooftop units be rotated such that there is no period when all are operating simultaneously? In other words, operate a couple of them earlier in the day and have them turned off during a particular hot period, but the rooms have been cooled sufficiently for comfort. A building management system (BMS) can be programmed to effect such a solution, such as turning off certain rooftop units during peak times and dimming certain lights, especially those near windows receiving sunlight. For example, a “typical” 20-ton rooftop unit has a demand of 24 kW of power (the actual number depends on its efficiency). If a BMS can ensure that 2 units are not operating at all times, then that peak demand of every unit being on would be reduced by 48 kW. At $35/kW, this would reduce the peak charge by $1,680, well worth the effort. And this is for one month, although the rate represents the summer months, so over one year, the savings would not be this figure times 12.

A related example of scheduling to reduce peak demand is to implement an HVAC scheduling program taking into account the predicted weather to turn on certain units during the night, even if the building is unoccupied, instead of a custodian turning on all of the units at the start of the day. This is applicable to both cooling (air conditioning) and to electric heating. Operating an electric heating unit when it may be very cold at night and the building is not occupied may increase usage slightly, but will reduce the need to use it during occupancy, and, thus, given high demand rates, will reduce peak demand and thus, reduce overall electric costs, even if overall usage rises slightly.

Peak Shaving – Another way to reduce electric demand in a peak period is to create electricity during other time periods to use during what would normally be your peak demand. During periods of low electricity demand, the building can charge batteries with electricity from the grid. Then during times of high electric demand, the building can use the stored electricity instead of having it provided then. Between the capital costs of the batteries and the loss of some electricity in time, this can be a costly option, but it may be economical if the building pays a high peak demand rate. This can also be applied specifically to cooling. Chillers can create ice at night, which is a cooling energy storage. Air can then flow through the ice to provide cooling for the building during a period of peak use, while using little electricity (just for the fans, not to make the cool air).

Alternative Energy – Renewable power, such as solar PV and wind can help reduce peak demand charges, as such sources of power does not require electricity from the grid. Whatever electricity is produced by the solar array is less to be supplied by the utility. Two negatives. One, such systems are expensive to install. Also, they depend on the presence of sun (or wind). If there is a hot day calling for a high cooling demand, but it is also cloudy, then the solar panels cannot produce the needed electricity to meet the basic building demand. Thus, there is no reduction in peak demand from the utility, and the building owner pays the same high demand charge as before.

CCES has the expertise to help your building or company reduce your energy costs, whether it be the usage or the demand portion. We can help you devise strategies to fit your needs for reliable power, while minimizing those high demand costs. Contact us today at karell@CCESWorld.com or at 914-584-6720.