kitControl-ElectricalDemandLimit

ElectricalDemandLimit provides load shedding calculations based upon a projected electrical demand averaging using a configurable sliding window interval.

To use the ElectricalDemandLimit component, as a minimum, you need to do the following:

configure the component properties
setup any Power Input links
setup the output links
enable the EDL component

The Shed Out slot (output) is typically linked to a ShedControl object, which actually performs the equipment shed and restoration control. Based on how you have configured the EDL component, the calculations direct that load shedding, load restoration, or no action be taken. With each calculation, the projected average demand is updated and displayed. Execution of this object can be enabled or disabled (default) either by linking or manually setting the Prediction Enabled property value.

ElectricalDemandLimit is available in the Energy folder of the kitControl palette, along with related objects SetpointOffset and ShedControl.

The following sections provide an overview and description of this component:

Overview of the Electrical Demand Limit component

Electrical Demand Limiting (EDL) is an energy management tool that allows you to level-out fluctuations that may occur in daily energy demand levels. Energy providers often set billing rates based on periodic maximum demand levels, so it is possible that a single day (anomaly) could dramatically increase a monthly billing rate. Reducing peak demand levels can significantly lower energy costs - even if the total energy consumption does not change. The ElectricalDemandLimit component is used to monitor and control building or enterprise energy usage in order to avoid costly spikes in demand level.

The EDL component monitors instantaneous electrical power, calculates a “projected demand average over a specified demand interval, and directs the shedding of specified loads whenever the projected demand average is higher than a specified demand limit. As projected demand levels recede, the component invokes a prioritized restoration of loads. Also, the EDL component records and saves peak demand times, dates, and values for both the current month and the previous month.

Projected Demand Average

The EDL component logic executes at a minimum of once per minute using a single Power Input value collected at the current time to calculate a “projected demand average”. It totalizes the Power Input every time the Power Input property value changes, but it only calculates projected demand average and Shed Level once a minute. This projected average is calculated using a combination of projected and historical samplings that are averaged over a specified interval (configurable in the EDL property sheet view). You can influence the value of the Projected Demand Average by using the Demand Interval and the Percent Interval Elapsed properties.
- Demand Interval
  
  You can set the demand interval time window using the EDL Demand Interval property. This property value sets the length (in minutes) of the demand window that is used for calculating the average. The default demand interval value is 15 minutes and may be set to 30 minutes—any other entry results in 15 minutes being used. The larger demand interval has more data points (one per minute) than the smaller interval. Depending on the value of the Percent Interval Elapsed property, these data points may be comprised of mostly sampled historical demand values, mostly values that are projected (based on current demand), or half and half.
- Percent Interval Elapsed
  
  You can control the weighting of projected demand data usage versus historical demand data usage by setting the Percent Interval Elapsed property value. A Percent Interval Elapsed value of “50” uses half of the actual sampled (or historical) values and half of the projected values in a demand interval to calculate the projected demand average. The projected demand value that is used to figure the “projected” data is the current energy demand.
Figure 21 shows how actual historical data and projected data are proportionally used across a 15 minute demand interval by setting the Percent Interval Elapsed property. In this example, the Percent Interval Elapsed property is set to 67, so the actual “minutes elapsed” over the 15 minute demand interval equals 10 minutes and the “minutes remaining” equals 5 minutes. The actual historical demand data is averaged over 10 minutes and the instantaneous demand (taken at the 11 minute point) is used to calculate an average “Projected Data” value. These two numbers are then used to calculate the Projected Demand Average.

Figure 21. Demand Interval Illustration
Demand Periods and Demand Limits

A day may be divided into three periods, based on time-of-day, with each period having a specific demand limit value. The Projected Demand Average is compared to the Demand Limit value that is set for the current time-of-day to determine whether “shedding” or “restoring” loads is appropriate. If the projected demand is higher than the demand limit for the current time of day, shedding is invoked. If shedding is active and the projected demand is lower than the demand limit for the current time of day, then the restoring is invoked.
Power Shed Levels

There are 32 Power Shed Level properties available in the EDL component. You can set a value on one or more of these properties to make them available for shedding calculations. Each shed level property value represents an amount of power that is dropped when that shed level is active. These values must be entered manually in the property sheet and are estimates, not “live” data.

When the projected demand exceeds the Demand Limit for the current demand period, a calculation is performed to determine home many loads to shed. The Power Shed Level properties should be set to a demand value that is based on loads that are controlled by the specific shed group. The load shed logic calculates how much demand is required to be reduced, and then uses the Power Shed Level values to determine how many of the loads to shed.

Shedding or restoring loads occurs in a fixed priority that sheds Power Shed Level1 first and restores it last.

Following, are examples that illustrate how Projected Demand Average calculation can vary.

Example 4. Projected demand average using mostly Projected Values

Assuming that the Demand Interval is set to 15 minutes and the Percent Interval Elapsed property is set to “7” (7%), then the Projected Data (calculated demand) is based on the current minutes demand reading being projected for the remaining minutes in the Demand Interval window. The following example assumes that the Power Input value is 400.

minutesElapsed = 15 * 6.67 / 100 = 1

minutesRemaining = 15 - 1 = 14

calculated total = (current Power Input * minutesRemaining) + Power
Input from each minutesElapsed interval

calculated total = (400 * 14) + 400 = 6000

projectedDemand = calculated total / (minutesElapsed + minutesRemaining)

projectedDemand = 6000 / (1 + 14) = 400

Note the following about this example:

By setting the Percent Interval Elapsed property to a value that corresponds to the first minute of the demand window, the calculated demand is based almost entirely on a projected data value.
In this case the projected demand calculation uses the Power Input value at minute “2” and averages that demand across the remaining 14 minutes.

Example 5. Projected demand average using all Recorded Values

Assuming that the Demand Interval property is set to 15 minutes and the Percent Interval Elapsed property is set to 93%, then the calculated demand is based completely on recorded demand readings for the current minute and the 14 previous minutes. Following, is an example of using all “recorded” values and no “projected” values.

minutesElapsed = 15 * 93.33 / 100 = 14

minutesRemaining = 15 - 14 = 1

calculated total = (current Power Input * minutesRemaining) + Power
Input from each minutesElapsed interval

calculated total = (600 * 1) + 600 + 600 + 600 + 600 + 600 + 600 + 600 + 600 + 600 + 400 + 400 +400 + 400 + 400 = 8000

projectedDemand = calculated total / (minutesElapsed + minutesRemaining)

projectedDemand = 8000 / (14 + 1) = 533

There would be no actual “projected” demand in this case.
This example assumes that the Power Input is currently 600 and has been at that value for the previous 9 minutes, prior to that the value was 400.
By setting the Percent Interval Elapsed to a value that corresponds to the last minute of the Demand Interval, the projected output is a sliding window average of the minutely recorded Power Input values.
In this case actual demand is used in the calculation as opposed to projected demand.

Example 6. Projected demand average using Recorded and Projected Values

The default operation of the EDL component uses a Percent Interval Elapsed property value of 75%. The calculated demand is then based 75% on actual recorded Power Input property values and 25% on a projection that assumes the demand will remain at the current value for the remaining minutes in the Demand Interval.

Determining shed levels

When Projected Demand Average exceeds the Demand Limit value for the current Demand Interval, a calculation is performed to determine home many loads to shed. All available (or desired) Power Shed Level properties (1-32) should be set to a demand value based on the loads that are controlled by the specific shed group. The load-shed logic calculates how much demand is required to be reduced, and then uses the Power Shed Level property values to determine how many the loads to shed.

Example 7. Estimating the Power Shed Level values

An estimate of the demand associated with a group of equipment can be calculated if the operating voltage and current draw are known for the loads. For example:

Single Phase Loads

W = V * A

W = 120 Volts * 30 Amps = 3600
Watts = 3.6 kW
Three Phase Loads (use square root of 3)

W = V * A * 1.73

W = 480 Volts * 30 Amps * 1.73 = 24919
Watts = 24.9 kW

Example 8. Shed calculation

Using the following list of property values, this example shows a calculation that uses an EDL component configured with three power shed levels. For this example, assume that the current Demand Limit Period is Demand Limit Period1.

calculated total = 7625 kW
Projected Demand Average = 533 kW
Demand Interval = 15
Percent Interval Elapsed: = 75
Demand Limit Period1: = 500 kW
Demand Limiting Deadband = 5 kW
Power Shed Level: = 20 kW
Power Shed Leve2: = 15 kW
Power Shed Leve3: = 30 kW

The following equations show example calculations:

targetIntervalTotal = demandLimit * (minutesElapsed + minutesRemaining)

targetIntervalTotal = 500 * (11.25 + 3.75) = 7500

powerChange = (calculated total - targetIntervalTotal) / minutesRemaining

powerChange = (7625 - 7500) / 3.75 = 33.33
KW that needs to be shed

Note the following about this example:

Since Power Shed Level1 is only expected to reduce the demand by 20 kW, both Power Shed Level1 and Power Shed Level2 must be shed to reduce the demand by an expected 35 kW combined.
The necessary loads are shed in sequential order during the same execution cycle, without evaluating the actual impact on demand.
The load shed determination is based on the projected reduction in demand for each group.
Subsequent executions of the object may result in additional load shedding if the actual demand is not reduced below the demand limit.

The following properties are available in the Electrical Demand Limit component property sheet view.

Prediction Enabled

This property allows you to enable or disable the EDL component by choosing true or false, respectively. Choosing the null option (by selecting the null checkbox from the property sheet view) leaves the “enabled” status in its current state. For example, if this property is currently set to true then choosing the null option does not stop the execution of the EDL component. This value must be set to true for the component to work.
Power Input

This property is a writable field that allows you to link in a numeric value that represents the actual power demand (kW) rate. This property monitors the demand rate and averages it over every minute in order to use the value for comparison to the Projected Demand Average. This property should always represent the total actual demand rate — the total of all meters that are on the energy network being monitored by this component. Whenever a shed or restoration is invoked, this value is expected to change in relation to the estimated values that are set in the Power Shed Level properties.
Message

This property displays information that relates to the status of the shed, restoration, or projected demand values. It also may indicate the status of the EDL component, itself.
Shed Out

This property displays a value that indicates the number of shed levels that are to be shed. For example, a Shed Out value of 3 specifies that a Power Shed Level of 3 is being shed.
Billing Start Delay

This property specifies the first billing day of the month for utility billing. This allows you to align your data with actual energy company billing periods. Each month, on the day specified by this property, the “current month” data moves to “Previous Month” and the current month data becomes “This Month”.
Demand Interval

This property represents the length of time, in minutes, that is used for the demand window portion of the Projected Demand Average calculation. The default value is 15 minutes and may also be set to 30 minutes.

If any value other than 15 or 30 minutes is entered in this field, the value automatically reverts to 15.
Percent Interval Elapsed

This property is used to determine how much of the calculated demand is based on actual demand as opposed to how much is based on projected demand. This integer value is used to set where in the demand window the “current minute” is. In a 15 minute demand window, a value of 67 would mean that the “current minute” is at 10. Larger numbers in this property increase the amount of historical data that is used and decrease the amount of data that is based on the “current minute” demand.
Rotate Level

This property specifies the maximum Shed Level that may be used. For example, a Rotate Level value of 3 limits load shedding to Shed Level 3.
Demand Limiting Deadband

This property allows you to set a deadband value that is used when activating restoration levels. The deadband value is used only in determining whether or not to invoke a restoration action; it is not used for invoking shed actions.
Demand Period (1, 2, and 3) Start

These three properties allow you to split-up a 24 hour day into three different time-periods in order to assign a separate demand limit for each distinct time.
Demand Limit Period (1,2,3)

These three property fields allow you to set a desired demand limit value to correspond to each of the three demand periods. When the Demand Limit value for a period is exceeded, load shedding is invoked.
Power Shed Level (1-32)

These properties allow you to set up to 32 estimated power shed levels. Each property represents the amount of demand that you expect to shed when the associated shed level is invoked. The numbers in these properties are used to calculate how many shed levels need to be invoked in order to lower the demand level below the current Demand Period limit. Once a shed level is invoked, the actual power drop is evaluated at the next minute to determine the actual effects of the shed action. If the initial load shed does not actually bring down the demand to below the demand limit level, the next shed level (if any) is invoked.

You can limit the maximum number of shed levels that may be invoked by using the Rotate Level property.
This Month Demand Period (1,2, or 3) Peak

This historical data property displays the value of the highest demand (minute) that has occurred (so far) in the current month.
This Month Demand Period (1,2, or 3) Time

This property is associated with the “This Month Demand Period (1,2, or 3) Peak and displays the time and date that the current month’s peak demand occurred.
Previous Month Demand (1,2, or 3) Period Peak

This historical data property displays the value of the highest demand (minute) that occurred in the previous month.
Previous Month Demand (1,2, or 3) Period Time

This property is associated with the “Previous Month Demand Period (1,2, or 3) property and displays the time and date that the previous month’s peak demand occurred.
Projected Demand Average

This is the read-only display of the average demand that is predicted to occur for the current demand interval. Calculations occur to update this value every minute.
Max Shed Level

This property displays the maximum shed level that has been used in the current month.

The following example illustrates using the Electrical Demand Limit component.

Example 9. Setting EDL component links and properties

The following example shows a partial wiresheet view of an EDL component configured for shedding energy loads. The current time period in this example is Demand Period2.

Figure 22. Wiresheet view of EDL example application

Note the following about this example:

EDL Configuration
- Power Input
  
  Total demand is linked into the EDL component Power Input property. This is a single input property, therefore the power sources need to be totaled before linking because there is more than one meter supplying actual electrical demand data. This demand level value is expected to change in response to load shedding.
- Demand Interval
  
  This property is set to the default value of 15 minutes.
- Percent Interval Elapsed
  
  This property is set to 25 percent, which adds more weight to the “current demand” and less weight to “historical demand” for each calculation of the Projected Demand Average.
- Demand Limit
  
  Demand limits are shown for Period1 and Period2, as 1000 and 2000, respectively. These are the values that specify the demand levels that initiate power shedding.
- Demand Period
  
  Demand period start times are shown for Period1 and Period2, as 0000 (midnight) and 0800 (8:00 am), respectively. Demand Period3 start time is not shown. These values specify the start time for each of the three Demand Periods.
- Power Shed levels
  
  In this example, it is estimated that by shedding loads associated with Power Shed Level1, that the amount of demand will decrease by 900 kW. Power Shed Levels 2 and 3 are set at 910 and 920, respectively. These properties are only the estimated amount of demand that is reduced by shedding at each respective level. If they are exactly correct, then shedding at level 3 reduces demand by the sum of all three shed levels: (900+910+920)=27030kW.
- Projected Demand Average
  
  The current value for this property is shown as 2051, so shedding is initiated, as shown in the message property “SHEDDING REQUIRED! Projected demand is 2051” and in the Shed Out property value of “1.0” (Shed Level 1).
EDL Linking
- Shed Out
  
  The EDL Shed Out property value is linked to a Shed Control component that allows you to set specific Shed Level(1-16) links into boolean controls. In the example, these controls are configured to shut off power to “Plant_A”, “Plant_B”, and “Plant_C”, with Shed Level(1, 2, and 3), respectively. In addition, the Shed Control component “out1” value is linked to a SetpointLoadShed component that uses a configurable setpoint offset to reduce power usage.
  
  You can also link from the Shed Out property to other energy components, such as a Setpoint Offset component (also shown here).
- Power Input
  
  In the example, with a Shed Level1 in effect, Power Input is at 2100, and the Projected Average Demand value is 2051, still greater than the Demand Limit Period2 value of 2000. The Power Shed Level2 value (estimate) indicates that invoking a Power Shed Level2 will yield a decrease of 910kW and bring the demand down below the limit. If this estimate is fairly accurate, actual power usage should drop and the Power Input value lower to below the Demand Limit Period2 value.