Dual-source TES system

[hcasperfu]

This issue is to develop a dual-source TES system for district cooling.
Below is a simplified diagram of the said system.

System Description

• The district CHW network has a linear architecture (i.e. no loops or meshes).
• The sources and the users can be connected at any point of the network.
• The first source has one chiller.
• The second source has one chiller and one stratified cold water tank.
  • This tank can be charged by its local chiller or remotely by the chiller in the other source. To allow this the flow direction of this source is partially reversible.
• The sources, collaboratively,
  • Need to overcome the network's hydraulic resistance;
  • Need to satisfy the energy demand of the network.

Control
Source with Chiller Only

• P1 tracks a set point for dp at the most distant user (may be more than one).
  • P2 has its own control objectives (below) and can compensate the pressure when needed.
  • P1 then needs to be controlled faster than P2 so that it can reject disturbances before P2 compensates for it.

Source with Chiller and Tank

• When charging the tank from the remote chiller (chiller 1):
  P2 off, V1 closed, modulate V2 so that m_t tracks a mass flow set point.
• When charging the tank from the local chiller (chiller 2) without providing cooling to the network (e.g. storing energy when cheap):
  P2 off, V1 & V2 closed.
• When providing cooling to the network, from either the chiller or the tank or both:
  V1 open, V2 closed,
  P2 tracks m_t setpoint:
  • Chiller only: m_t = 0
  • Tank discharging: m_t > 0
  • Tank charging: m_t < 0
• When the most open valve of all consumers is 95% closed (i.e. there is no load), shut off cooling to avoid P2 producing
  too much pressure and issue an alarm. Enable cooling only only from supervisory control (which ensures there is load).
  There should also be a supervisory control that determines m_t and enables/disables the tank.