.Buildings.Controls.OBC.ASHRAE.G36.Generic.TrimAndRespond

Information

This block implements the trim and respond logic according to Section 5.1.14.3 and 5.1.14.4 of ASHRAE Guideline 36, May 2020.

For each upstream system or plant set point being controlled by a trim and respond loop, define the initial values in system or plant sequences. Values for trim, respond, time step, etc. shall be tuned to provide stable control.

The trim and respond logic shall reset setpoint within the range minSet to maxSet. When the associated device is off (uDevSta=false), the setpoint shall be iniSet. The reset logic shall be active while the associated device is proven on (uDevSta=true), starting delTim after initial device start command. When active, every time step samplePeriod, trim the setpoint by triAmo. If there are more than numIgnReq requests, respond by changing the setpoint by resAmo*(numOfReq-numIgnReq), i.e., the number of requests minus the number of ignored requests, but no more than maxRes.

In other words, every time step samplePeriod:

• Change setpoint by triAmo;
• If numOfReq > numIgnReq, also change setpoint by resAmo*(numOfReq -numIgnReq) but no more than maxRes.

Hold and release loop output

Optionally, if the parameter have_hol is set to true, an additional input signal uHol allows for holding the trim and respond loop output at a fixed value for the longer of the time the input uHol remains true and the duration specified by the parameter dtHol. When uHol switches back to false, the hold is released and resetting continues from the previously held value (without reinitializing to iniSet or going through a delay time of delTim).

This is typically used in control sequences to freeze the reset logic during the plant staging process. Consider for example the following specification:
"When a plant stage change is initiated, the reset logic shall be disabled and value fixed at its last value for the longer of 15 minutes and the time it takes for the plant to successfully stage."
Using this block with have_hol=true and dtHol=15*60 yields the following sequence of events.

• 0:00 - Stage change is initiated. T&R loop output is at 50 %.
• 0:12 - Stage change is completed. T&R loop output remains at 50 % since < 15 minutes have elapsed.
• 0:15 - T&R is released and continues resetting from 50 %.

Examples

The figure below illustrates the trim and respond logic with a negative trim amount, comparing scenarios with and without holding the loop output.

The figure below illustrates the trim and respond logic with a positive trim amount.

The figure below illustrates the trim and respond logic with a negative trim amount, in a scenario where the equipment switches on and off.

Revisions

• June 6, 2024, by Antoine Gautier:
  Added logic to hold trim and respond loop output. This is for #3761.
• June 3, 2020, by Jianjun Hu:
  Upgraded according to G36 official release.
• April 13, 2020, by Jianjun Hu:
  Corrected to delay the true initial device status. This is for #1876.
• August 28, 2019, by Jianjun Hu:
  Added assertions and corrected implementation when response amount is negative. This is for #1503.
• July 10, 2017, by Jianjun Hu:
  First implementation.