.Buildings.Applications.DataCenters.ChillerCooled.Examples.IntegratedPrimarySecondaryEconomizer

Information

System Configuration

This example demonstrates the implementation of a chiller plant with water-side economizer (WSE) to cool a data center. The system schematics is as shown below.

The system is a primary-secondary chiller plant with two chillers and an integrated WSE.

Control Logic

This section describes the detailed control logic used in this chilled water plant system.

Cooling Mode Control

The chilled water system with integrated waterside economizer can run in three modes: free cooling (FC) mode, partially mechanical cooling (PMC) mode and fully mechanical cooling (FMC) mode. The detailed control logics about how to switch among these three cooling modes are described in Buildings.Applications.DataCenters.ChillerCooled.Controls.CoolingMode. Details on how the valves are operated under different cooling modes are presented in Buildings.Applications.DataCenters.ChillerCooled.Equipment.IntegratedPrimarySecondary.

Chiller Staging Control

The staging sequence of multiple chillers are descibed as below:

• The chillers are all off when cooling mode is FC.
• One chiller is commanded on when cooling mode is not FC.
• Two chillers are commanded on when cooling mode is not FC and the cooling load addressed by chillers is larger than a critical value.

The detailed implementation is shown in Buildings.Applications.DataCenters.ChillerCooled.Controls.ChillerStage.

Pump Staging Control

For constant speed pumps, the number of running pumps equals to the number of running chillers.

For variable speed pumps, the number of running pumps is controlled by the speed signal and the mass flow rate. Details are shown in Buildings.Applications.BaseClasses.Controls.VariableSpeedPumpStage. And the speed is controlled by maintaining a fixed differential pressure between the outlet and inlet on the waterside of the Computer Room Air Handler (CRAH).

Cooling Tower Speed Control

The control logic for cooling tower fan speed is described as:

• When in FMC mode, the cooling tower speed is controlled to maintain the condenser water supply temperature (CWST) at its setpoint.
• When in PMC mode, the fan is enabled to run at 100% speed to make the condenser water as cold as possible and maximize the WSE output.
• When in FC mode, the fan speed is modulated to maintain chilled water supply temperature at its setpoint.

Detailed implementation of cooling tower speed control can be found in Buildings.Applications.DataCenters.ChillerCooled.Controls.CoolingTowerSpeed.

Room temperature control

The room temperature is controlled by adjusting the fan speed of the AHU using a PI controller.

Note that for simplicity, the chilled water supply temperature and differential pressure reset control are not implemented in this example.

Revisions

• November 16, 2022, by Michael Wetter:
  Corrected control to avoid cooling tower pumps to operate when plant is off, because shut-off valves are off when plant is off.
• November 1, 2021, by Michael Wetter:
  Corrected weather data bus connection which was structurally incorrect and did not parse in OpenModelica.
  This is for issue 2706.
• November 29, 2017, by Michael Wetter:
  Corrected conversion of enumeration.
  This is for issue 1083.
• July 30, 2017, by Yangyang Fu:
  First implementation.