Sliding Window Algorithm Details - Metasys - LIT-12011288 - Software Application - Metasys Building Automation System - 6

DLLR Technical Bulletin

Product
Building Automation Systems > Building Automation Systems > Metasys Building Automation System
Document type
Technical Bulletin
Document number
LIT-12011288
Version
6
Revision date
2013-10-15

About this task

The Sliding Window algorithm uses the sequence of calculations described in this section to determine the amount of energy to shed for the current minute to meet the user specified target. These values are used:

et = forecast error

elimit = user specified Error Limit

Pt = measured demand at time t

St = amount shed at time t

Ut-1 = total uncontrolled demand last minute

= smoothed absolute error

= smoothed absolute error last minute

MAXt = maximum smoothed absolute error

K = exponential smoothing constant (0.01)

n = prediction time in minutes; one minute shorter than interval length

z = selected sensitivity factor (high: 3.30; medium: 2.58; low: 1.96)

T = interval length

Tsample = time between two samples of the current metered power; fixed at one minute

Plimit = user specified demand limit

Alimit = active demand limit (DL target this minute)

DL to Shed = how much energy to shed this minute to meet the demand target

Note: Ut and St are determined after handling the Load Rolling algorithm.

The necessary amount of power to shed is calculated as follows:

Procedure

  1. Calculate forecast error (et). If this is the first time the algorithm is calculated, set the forecast error to zero. If not the first time, use the following equation:

    et = Pt + St - Ut-1
  2. Calculate the new smoothed absolute error (t), and compare it to the maximum smoothed absolute error (MAXt):
  3. Calculate the total uncontrolled demand (Ut):

    Ut = Pt + St
  4. Calculate the projected total uncontrolled demand amounts (Ut+1, Ut+2, ... , Ut+n):
    where I = 1 to n
  5. Calculate the projected shed values (St+1, St+2, ... , St+n):
    where I = 1 to n
  6. Determine the worst-case projected shed value (STotal):

    STotal = MAX (St+1, St+2, ... , St+n)
  7. Calculate the amount of energy to shed this minute to meet the demand limiting goal, using the worst case total amount to shed (STotal) and the amount already shed (St) as follows:

    DL to Shed = STotal - St