.Buildings.DHC.ETS.Combined.BaseClasses.PartialHeatPumpHeatExchanger

Information

This model represents an energy transfer station based on that described in Sommer (2020), with some additioinal details:

The cooling function is provided in a compressor-less mode by a heat exchanger connected to the district supply line.

• The cooling heat exchanger primary pump is modulated based on a PI control loop tracking the chilled water supply temperature at the outlet of the heat exchanger secondary side.
• The chilled water is typically produced at high temperature and distributed to radiant cooling systems, for instance at 19°C.

The space heating heating function is provided by a water-to-water heat pump Buildings.DHC.ETS.Combined.Subsystems.HeatPump.

• By default, the condenser loop is operated with a variable mass flow rate to maintain a difference between supply and return water of dT_nominal, with a lower limit of mass flow specified by the ratio ratFloMin. The control logic is implemented and described in Buildings.DHC.ETS.Combined.Controls.PrimaryVariableFlow. The model can also represent a constant flow condenser loop by setting have_varFloCon to false.
• The evaporator loop is controlled according to the documentation in Buildings.DHC.ETS.Combined.Subsystems.HeatPump. Evaporator water is supplied by mixing flow directly from the district line with flow leaving the district side of the cooling heat exchanger. The hydronic arrangement modeled in Buildings.DHC.ETS.Combined.Subsystems.SwitchBox ensures that the resulting fluid stream in the district line always flows in the same direction.
• The space heating hot water is typically produced at low temperature, for instance 40°C.

Space Heating and Cooling Enable/Disable

Heating (resp. cooling) is enabled based on the input signal uHea (resp. uCoo) which is held for 15 minutes, meaning that, when enabled, the mode remains active for at least 15 minutes and, when disabled, the mode cannot be enabled again for at least 15 minutes. The heating and cooling enable signals should be computed externally based on a schedule (to lock out the system during off-hours), ideally in conjunction with the number of requests yielded by the terminal unit controllers, or any other signal representative of the load.

Modeling considerations

There is a control volume at each of the two fluid ports that serve as inlet and outlet of the heating and cooling systems. These approximate the dynamics of the substation, and they also generally avoid nonlinear systems of equations if multiple substations are connected to each other.

References

Sommer T., Sulzer M., Wetter M., Sotnikov A., Mennel S., Stettler C. The reservoir network: A new network topology for district heating and cooling. Energy, Volume 199, 15 May 2020, 117418.

Revisions

• February 15, 2024, by Ettore Zanetti:
  Switch box SwiFlo valve pressure drop reduced to zero.
• October 2, 2023, by Michael Wetter:
  Renamed input loaSHW to QReqHotWat_flow.
• May 17, 2023, by David Blum:
  Assigned dp_nominal to pum1HexChi.
  Corrected calculation of heat pump evaporator mass flow control.
  This is for issue 3379.
• February 23, 2021, by Antoine Gautier:
  Refactored with subsystem models and partial ETS base class.
  This is for issue 1769.
• December 12, 2017, by Michael Wetter:
  Removed call to Modelica.Utilities.Files.loadResource.
  This is for issue 1097.