.Buildings.DHC.ETS.Combined.Controls.WatersideEconomizer

Information

This block implements the control logic for the waterside economizer.

The system is enabled if

• it has been disabled for more than 20 minutes, and
• the "cooling enabled" input signal is true, and
• the evaporator isolation valve is closed (i.e., the system is not in cold rejection mode), and
• the predicted leaving water temperature is lower than the entering water temperature minus dTEna.

The system is disabled if

• it has been enabled for more than 20 minutes, and
• the "cooling enabled" input signal is false, or
• the evaporator isolation valve is open, or
• the leaving water temperature is higher than the entering water temperature minus dTDis.

When the system is enabled

• the primary side is controlled so that the primary flow rate varies linearly with the secondary flow rate, and
• the bypass valve on the secondary side is fully closed.

When the system is disabled

• if the "cooling enabled" input signal is true and the evaporator isolation valve is closed, the primary pump (resp. valve) is operated at its minimum speed (resp. opening), otherwise it is switched off (resp. fully closed): this is needed to yield a representative measurement of the service water entering temperature, and
• the bypass valve on the secondary side is fully open.

Revisions

• March 7, 2025, by Michael Wetter:
  Increased, and added where missing, hysteresis, as the input signal is the output of the PID controller.
• July 14, 2021, by Antoine Gautier:
  First implementation.