Determine severity of supply air temperature control loop error

Applicable Systems

  • Primary: AHU, RTU, MUA, ERV

Objective/Method/Outcome

  • Objective: Determine the performance index of a supply air temperature control system using amount of time and total deviation the SAT is not within the desired set point.
  • Method: Calculate the performance metric based on the total time and absolute difference between the SAT and the desired set point during occupied hours.
  • Outcome: An insight is generated if the weekly index is more than 4 centigrade-hours per week.

Logic

  • This rule integrates the error of a control loop outside of its range over the course of a week. This rule sums the difference between the PV and SP, above an acceptable threshold. This means the magnitude of error is just as important as the time of error.
If(abs(SAT-SP) > Threshold) { Sum over course of a week(abs(SAT-SP) - Threshold) }
Determine severity of supply air temperature control loop error

Inputs

  • Supply Air Temperature [°C] {sensor, discharge, air, temp} (Real Trend Log)
  • Supply Air Temperature Setpoint [°C] {sp, discharge, air, temp} (Real Trend Log)
  • Status {cmd|status|occupied} (Binary Trend Log)

Parameters

ParameterSeries NumberDescriptionDefault Value (Units)
Primary Air
Temperature Threshold75The acceptable temperature deviation from set point that is considered normal. This is generally a bit tighter than on the PV vs SP and PV vs SP KPI rules.1 (C)
Acceptable Values Outside Range76The number of centigrade-hours per week that is considered acceptable for the unit. Anything more than that time is considered a fault.4 (centigrade-hours)

Calculated Trend Logs

Control LoopNameDescription
Primary Air (SAT)SAT_INTG_ERRRecords the amount of centigrade-hours the SAT has been outside of an acceptable range of its set point

Other Information

This rule is primarily used to generate a calculated TL for sake of reports. The insight itself is not as valuable as the report, as the reports grade systems against each other. Thus, the insight is often hidden by choosing the Zero logic series (logic series ID 74) as the trigger block and selecting the Trigger Type as “Active High”.

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