.Buildings.DHC.Plants.Cooling.Controls.FlowControl

Information

This block implements a state graph to control the flows of the storage plant. It receives two tank status Boolean signals indicating that the tank is charged or empty. These two signals can be both false indicating an in-between state. The block can receive one of the following commands:

  1. Charge tank,
  2. No command, and
  3. Discharge tank.

The command to tank may be disregarded. For example, if the tank is receiving a discharge command but it is already empty, it will not discharge which would let warm return water directly into the supply side.

The system transitions among the following states:

Step Description Transition in Transition out
All Off
(Initial Step)		 All off. This is the initial step. - -
Local Charging Charge the tank with the local chiller. "Charge tank" command
AND tank is not charged yet
AND chiller is enabled.
This transition takes priority
over the one below.1		 The in-transition condition becomes false.
Remote Charging Charge the tank with the remote chiller. Same as above except that
the chiller is not enabled.		 The in-transition condition becomes false.
Secondary Pump On Turn on the secondary pump.
This step is in parallel with the two below.2		 The district has load AND
the additional conditions of
either step below become true.		 Both steps below are no longer active (implicit).
Tank Producing The tank produces CHW to the district.
This step is in parallel with "secondary pump on".		 The district has load AND
"Discharge tank" command AND
tank not empty.
This transition takes priority
over the one below.		 To "chiller producing": The in-transition condition becomes false AND
The chiller is enabled.
This transition takes priority over the one below.
To initial step: No load OR the in-transition conditions
of "tank producing" and "chiller producing" are both false
(i.e. neither tank or chiller is available).
Chiller Producing The chiller produces CHW to the district.
This step is in parallel with "secondary pump on".		 The district has load AND
the chiller is enabled.		 To "tank producing": The condition for in-transition of
"tank producing" becomes true.
This transition takes priority over the one below.
To initial step: No load OR the in-transition conditions
of "tank producing" and "chiller producing" are both false.

Notes:

  1. Out-transitions from the same step have priorities. When the conditions of more than one of them become true, the transition connected by a connector with the lowest index in the array fires. For example, even when the in-transition condition of "chiller producing" becomes true, as long as the in-transition condition of "tank producing" is also true, the latter fires because of priority.
  2. Steps that are in parallel are and must be active at the same time. When "secondary pump on" is active, either "tank producing" or "chiller producing" is also active.

Revisions

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