blockMappingWithWSE

Information

Block that resets maximum cooling tower speed setpoint yMaxTowSpeSet, controls condenser water pump speed yConWatPumSpeSet, and head pressure control valve position yHeaPreConVal for plants with water side economizers and headered condenser water pumps. The development follows ASHRAE Guideline 36-2021, section 5.20.10 Head pressure control, part 5.20.10.5, 5.20.10.6, and 5.20.10.7.

1. For each chiller, when the waterside economizer is disabled (uWSE = false), map the chiller head pressure control loop signal uHeaPreCon as follows:

• When uHeaPreCon changes from 0 to 50%, reset the maximum cooling tower speed setpoint yMaxTowSpeSet from 100% to the minimum speed minTowSpe.
• When uHeaPreCon changes from 50% to 100%, reset condenser water pump speed yConWatPumSpeSet from design speed for the stage desConWatPumSpe to the minimum speed minConWatPumSpe.
• Each head pressure control valve yHeaPreConVal of the enabled chiller shall be 100% open, irrespective of the loop output.

2. When the waterside economizer is enabled (uWSE = true),

• The maximum cooling tower speed setpoint yMaxTowSpeSet shall be 100% irrespective of loop output.
• Condenser water pump speed yConWatPumSpeSet shall be equal to the design speed for the stage desConWatPumSpe, irrespective of loop output.
• Each enabled chiller head pressure control loop output uHeaPreCon shall reset the head pressure control valve position yHeaPreConVal from 100% open at 0% loop output to the minimum position minHeaPreValPos at 100% loop output.

3. When the head pressure control loop is disabled (uHeaPreEna = false), the head pressure control valve shall be closed; the maximum tower speed setpoint and the condenser water pump speed setpoints become 0.

Parameters

Connectors

Revisions

• January 30, 2019, by Jianjun Hu:
  First implementation.