.Buildings.DHC.Plants.Combined.Subsystems.ChillerHeatRecoveryGroup

Information

This model represents a set of identical heat recovery chillers that are piped in parallel. Modulating isolation valves and modulating switchover valves are included on condenser and evaporator side. The switchover valves allow indexing the condenser (resp. the evaporator) either to the CWC loop or to the HW loop (resp. to the CWE loop or to the CHW loop). Modulating valves are used to allow for sequences of operation that bleed CWE into the HW return flow to modulate the condenser entering temperature.

Control points

The following input and output points are available.

• On/Off command y1: DO signal dedicated to each unit, with a dimensionality of one
• Cooling switchover command y1Coo: DO signal dedicated to each unit, with a dimensionality of one
• Supply temperature setpoint TSet: AO signal dedicated to each unit, with a dimensionality of one
  The signal corresponds either to the HW supply temperature setpoint when the unit operates in heating mode, or to the CHW supply temperature setpoint when the unit operates in cooling mode.
• Condenser and evaporator isolation valve commanded position yVal(Con|Eva): AO signal dedicated to each unit, with a dimensionality of one
• Condenser and evaporator switchover valve commanded position yVal(Con|Eva)Swi: AO signal dedicated to each unit, with a dimensionality of one
• Condenser and evaporator leaving temperature T(Con|Eva)Lvg: AI signal dedicated to each unit, with a dimensionality of one
• Condenser entering temperature TConEnt: AI signal dedicated to each unit, with a dimensionality of one
• Condenser and evaporator mass flow rate m(Con|Eva)_flow: AI signal dedicated to each unit, with a dimensionality of one

Details

HRC performance data

The performance data should cover the HRC lift envelope, that is when the HRC is operating in direct heat recovery mode, producing CHW and HW at their setpoint value at full load. In this case, and to allow for cascading heat recovery where a third fluid circuit is used to generate a cascade of thermodynamic cycles, two additional parameters TCasEntCoo_nominal and TCasEntHea_nominal are exposed to specify the entering temperature of the third fluid circuit when the HRC is operating in cooling mode and in heating mode, respectively. In cooling mode the third fluid circuit is connected to the condenser barrel. In heating mode, the third fluid circuit is connected to the evaporator barrel. The parameters TCasEnt*_nominal are then used to assess the design capacity in heating and cooling mode, respectively.

Actuators

By default, linear valve models are used. Those are configured with a pressure drop varying linearly with the flow rate, as opposed to the quadratic dependency usually considered for a turbulent flow regime. This is because the whole plant model contains large nonlinear systems of equations and this configuration limits the risk of solver failure while reducing the time to solution. This has no significant impact on the operating point of the circulation pumps when a control loop is used to modulate the valve opening and maintain the flow rate or the leaving temperature at setpoint. Then, whatever the modeling assumptions for the valve, the control loop ensures that the valve creates the adequate pressure drop and flow, which will simply be reached at a different valve opening with the above simplification.

Contents

Name	Description
Medium	Medium model for all four fluid circuits

Revisions

• February 24, 2023, by Antoine Gautier:
  First implementation.