modelStoragePlant

Information

This model encompasses the components of a chilled water storage plant. It includes a flow-controlled primary pump, a stratefied storage tank, a reversible connection with the district network, and related controls to coordinate charging and discharging of the tank. The chiller is intentionally excluded in this component so that it can be otherwise chosen and configured. The tank in this plant can be charged by its local chiller or by a remote chiller on the same CHW district network.

System Concept Example

An example usage of this model within a district network is implemented in Buildings.DHC.Plants.Cooling.Examples.StoragePlantDualSource. Shown in the schematic below, it has two CHW plants and three users.

• Plant 1 only has a chiller. The supply pump, P1, is controlled to ensure that all users have enough pressure head. This represents a remote chiller plant, referenced above.
• Plant 2 has a chiller and a stratified CHW tank and is represented by this model. The storage plant has a reversible connection to the district network that can either pump water to the network from the plant using the pump P_sec, or throttle water from the pressurised network to charge the tank.

Control Signals

The plants are controlled as follows:

• In plant 1, for the sake of this discussion, assume the chiller is always on. The speed-controlled pump ensures that the users have enough pressure head at all times. This includes plant 2 when its tank is charged remotely by plant 1 and it acts like an energy consumer.
• For plant 2:
  • In the chiller loop, chiller 2 and its primary pump P_pri are on whenever needed (for charging the tank or producing CHW to the network). Otherwise, they are commanded off.
  • The system receives one of the following three commands regarding the tank: charge, discharge, or no action. The tank controller returns status signals. It can be empty, charged, or in-between. 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. See the Implementation section for details.
  • The reversible connection between plant 2 and the district network modulates the flow rate needed by plant 2.
    • When the storage plant produces CHW, P_sec receives a speed control signal from the same PI controller as P1 in plant 1.
    • When the storage plant is charged remotely, the pressure-independent valve is controlled to maintain a constant flow from the pressurised network to the storage tank.
    • Otherwise, the connection cuts off flow to isolate plant 2 from the district network.

Implementation

The flow control of the storage plant is implemented as a state graph in Buildings.DHC.Plants.Cooling.Controls.FlowControl.

Parameters

Connectors

Components

Contents

Name	Description
Medium	Medium package

Revisions

• April 28, 2023 by Hongxiang Fu:
  First implementation. This is for #2859.