I/A Series R2 Optimum Start Stop program object may improperly calculate start time when outdoor air temperature compensation is used.

Issue

I/A Series R2 Optimum Start Stop program object may improperly calculate start time when outdoor air temperature compensation is used.

Product Line

TAC I/A Series

Environment

I/A Series R2 (all versions)

Cause

Optimum start / stop compensation is performed through the use of a program object. The object could calculate a negative start lead time when outdoor air temperature compensation was used.

Resolution

A check was added to the program object to prevent a calculated negative start leadTime due to outdoor air temperature compensation.  The revised object is available for download from The Exchange Download Center. Download the file >> OSS for Niagara 08_03_11.zip

In addition, the object includes the following change history.

10-Nov-00  Moved the parameter reset control to an external stimulus

16-Aug-01  Changed reset input from BooleanPriority to DateTime

20-Dec-02  Added check for command time > next event time to account for a large leadtime calculation that results in a start time prior to midnight

14-Sep-05  Added safety check to prevent dynamically adjusted runtime factors from becoming too large

25-Apr-06  Corrected the following stop-time issues:
           1) stop-time calculation when earliestStopTime is after schedule stop time
           2) stop-time calculation when start/stop times span midnight
           3) determining when to perform stop-time analysis
  
05-Nov-08  Added changes from 2002 and 2003
           Added prestart (maxStartLimits) and comfortLimit inputs 18 Nov 02
           Added the ability to use OA temperature for OSS calculation 24 Feb 03

12-Dec-08  Added OA temperature to message strings.  Added output for calculated command time.

19-Feb-09  Corrected issues with stop-time analysis:
           1) lastStartTime was being used for stop-time calculation
           2) analysis for heating was adjusting drift time for cooling
           3) analysis for cooling was adjusting drift time for heating

           Corrected issues with stop time calculation:
           1) heating mode failed to drift when > upper comfort limit
           2) cooling mode failed to drift when < lower comfort limit
           3) stop mode calculation always reflected the next event time

15-Oct-09  Added properties and check to prevent dynamically adjusted drift time factors from exceeding a specified maximum value.

03-Aug-11  Added check to prevent calculated negative start leadTime due to outdoor air temperature compensation.