Fixed 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 Fixed 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. The following constants are used:

fSafety = safety factor which reduces the calculated demand limit by 5% before its value is used in the Fixed Window algorithm.

TSample = fixed one minute constant that is used between two samples of the power meter.

The following inputs are used in the algorithm:

T (Interval_Length) = interval length (minute).

PLimit (Active_Limit) = user specified demand limit (kW).

fElevation (Active_Elevation) = demand limit elevation (%) in use for current interval.

P(I) (Meter_Value) = metered demand at time I (kW).

St = current amount shed.

The following interim results are used in the algorithm:

TSinceEOI (Time_Since_EOI) = elapsed time since the latest EOI pulse (minute).

WSinceEOI (Energy_Since_EOI) = consumed energy since the latest EOI pulse (kWh).

PSinceEOI (Demand_Since_EOI) = average power since the latest EOI pulse (kW).

PProfile (Profile_Limit) = current value of the demand profile at time TSinceEOI (kW).

PMax (Max_Demand) = maximum allowed average power until the next EOI pulse (kW).

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

Procedure

  1. Calculate the current demand limit profile value in kW:
  2. Calculate the amount of energy consumed since the latest EOI pulse in kWh. P(I) is the first measured instantaneous demand during the currently elapsing interval.
  3. Calculate the average power since the latest EOI pulse in kW:
  4. Calculate the maximum allowed average power until the EOI pulse in kW:
  5. Calculate the amount of power to shed this minute to meet the demand limiting goal, using the current meter reading (P(t)) and the maximum allowed average power until the EOI (PMax) pulse as follows:

    DL to Shed = P(t) - PMax