Peak Demand Management Principles for Industry

When developing a strategy to minimize peak electricity demand, there are several key elements of consider.

1) Gathering electricity meter data

Today’s utility meters typically have a variety of information available to the user, however getting at that information can be a bit tricky, especially when you need it in real time to make decisions regarding peak demand. Lets look at some different ways of getting information out of your main incoming utility meters.

a) Communication port

Many modern meters have communication ports that allow customers to “talk” to the meter in real time. Data within the meter is held in registers and can be retreived by software that uses the right “protocol” to talk to the meter and request the right information. Registers within the meter can contain kW, kWh, kVAh, KVA, kVarPower Factor, volts, amps, current, and other data relating to harmonics. For peak demand calculations, we’re interested in the kW and kVa registers primarily. By accessing data from these registers on a minute by minute basis, we can calculate the peak demand based on kW or kVA load.

b) Reading Pulse Outputs

Some meters only have pulses available and don’t have a way to “talk” to the meter. In this case the pulses need to be collected in an accumulator that can then talk to the compute software. Each pulse from the meter is equal to a pre-determined amount of electricity consumed. By taking the pulses and multiplying them by the meter multiplier, you can calculate the kW demand, kWh consumption and where kVA pulses are available, you can calculate the reactive load demand. The computer software typically reads data in the accumulator every minute and then turns the number of pulses received in that minute into a real energy consumption number.

2) Time is of the essence

Your utility calculates peak demand charges based on energy used over specific periods of time. In accordance with approved billing methods and alogithms. Some utilities calculate peak demand over a 15 minute window, while others use 30 or 60 minutes. In some rare cases, some utilities use sliding windows in their peak demand calculations, for example a utility may calculate demand over 30 minutes with a 5 minute rolling window, thereby always calculating the highest 30 minute window ever 5 minutes. The peak demand control software you choose to use to minimize your demand must be configurable to allow for a variety of different billing scenarios. The software must also be able to stay in sync with the utilities time window, in other words, the software must know when the 15 or 30 minute period ends to calculate demand correctly. Even being off by a minute can lead to unnacceptable inaccuracies and make controlling demand accurately impossible.

3) Real Time Information

The demand control software must collect data from the utility meters on a minute by minute basis and have the ability to predict the peak demand at the end of the current time window. For example if your utility calculates demand on a 15 minute window and you are 5 minutes into that window, the software must be calculating (based on 1 minute data) where you will end up as a peak at the end of the the 15 minutes. By calculating this on a ongoing basis the software can then determine when load needs to be shed to meet the desired peak demand target.

4) Setting a Target

The peak demand control software must have the ability to set a DEMAND TARGET either based on kW demand or kVA. Many utilities bill for peak demand based on Kilowatts, however some bill based on kVA or a percentage of kVA. Ideally, your demand control system should be configurable for either type of scenario.

5) Load Shedding Strategy

Once you have the ability to get the metering data into the software and predict the demand, you’ll need to know exactly what you’re going to shed when you need to reduce the load. How and what you decide to control will be based on whether individual equipment has variable power supplies or must be ON or OFF. The ideal strategy is to select some smaller loads for the first level of shedding and then add larger loads to the second and third levels. You can then configure the software to shed each level based on a percentage of the peak demand target. For example, you’re strategy could be that at 90% of the demand target, you’ll turn off 3 selected loads that can be turned off at any time. Should the demand prediction get to 95% of the demand target you could then turn off the next “bank” of load(s) that would be a bit more of an aggressive cut. Should you still need more shedding and the load reaches say 98% of the target, you could then shed additional loads and be very aggresive in doing so to ensure a significant cut to the overall demand. The end result is that you only need to shed what is necessary to achieve the target and can therefore assign more critical loads to higher levels and thereby shed them less often.

Ideal loads for peak demand control include heaters, induction furnaces, arc furnaces, variable voltage power supplies and other non-essential loads. Furnaces and heaters are excellent because they can usually be backed off in various degrees and have a thermal curve that makes controlling them for a short period of time relatively unnoticeable.

What type of savings can be expected from implementing advanced demand control software? Typically 15-25% of the demand portion of the electricity bill. However the side benefit is that you will be now running the facility to a management set target level of load and when you start doing this, you become more aware of waste and inefficiencies that can be corrected to deliver additional savings.

Lastly, we are often asked the question of what to set the peak demand target at initially. This requires a bit of knowledge about your loads and the peak demand that you currently are hitting on your bills. If you have a peak of 2mw and you only go to 2mw 3 times a month, then you will need to determine the next lowest peak and how often you hit that. For example you may hit 2mw 3 times a month, 1.9mw 12 times a month and 1.7mw 15 times a month, but most of the time your facility runs at 1.5 mw. You could then set a peak demand of say 1.6megawatts and then reduce the target slightly each month based on reports from the peak control software.

For more information regarding your own specific needs, please feel free to email us at info@energysoftware.com