Adding a steam pressure regulating valve model with the URBANopt Project

[SaranyaAnbarasu]

Pressure regulating valve (PRV) for Steam District Heating with the URBANopt Project

@bravache: Hi Baptiste, could you please open a new branch for the steam PRV models as described below? If you have any questions or comments, please let us know. Thank you!

(@mwetter: Dr. Wetter, we're mentioning you here as well in case you would like to provide any particular input. Thanks!) (@khinkelman, mentioning you for your reference).

The existing Buildings.Fluid.Actuators.Valves.TwoWayLinear are specific to incompressible media and do not include density to compute the pressure drop across valves. Whereas steam is a compressible medium, so the pressure drop varies with changes in density (density of the steam medium is considered variable over the range of pressure conditions seen in real systems). The existing valve models do not capture this thermodynamic property.

This valve model will be essential for district heating applications on the demand side (reducing the high-pressure steam from boilers before passing through the heat exchangers).

Our proposed solution

To capture the correct performance, we are proposing new steam valves: (1) SteamTwoWayValve – Two-way valve with opening y input, similar to Buildings.Fluid.Actuators.Valves.TwoWayLinear

(2) SteamTwoWayValveSelfActing - SteamTwoWayValve with a PI controller to maintain the outlet pressure to the required setpoint. From testing, this seems to be the most numerically efficient way to mimic the self-actuating (damped springs) in the physical valves.

The implementation is similar to Buildings.Fluid.Actuators.Valves.TwoWayLinear, extended from the base class SteamValveParameters and PartialSteamTwoWayValveKv. The valve parameters are implemented based on ISA 75.01.01/IEC 60534 steam (compressible medium). The instantaneous inlet density is used in the calculation of pressure drop across the valve.

We had earlier proposed the steam valve models in the DHC package (https://docs.google.com/document/d/12GaIloYaMds4USyhZt1W_s2hB2W2_GWR/edit), but Buildings.Fluid.Actuators.Valve package seems to be a better fit. Please let us know your thoughts on the package structure below:

Buildings.Fluid.Actuators
•   Valves
    •   SteamTwoWayValve
    •   SteamTwoWayValveSelfActuating
    •   Examples
        •   SteamTwoWayValve
        •   SteamTWoWayValveSelfActing
    •   Validation
        •   SteamTwoWayValveParameterization
    •   BaseClasses
        •   PartialStreamTwoWayValve
        •   SteamValveParameters

Potential alternates We believe it could be possible to reuse some of the existing base classes (such as Buildings.Fluid.Actuators.BaseClasses.PartialTwoWayValve and/or Buildings.Fluid.Actuators.BaseClasses.ValveParameters) if they are modified, but we are unsure about the best way to do this. If you would like us to reuse base classes, please advise on your preferred methodology.

Some additional context Valve models with density (W_rho) and without density (Wo_rho) in the computation of pressure drop are exhibited below. A constant mass flow rate of 0.5kg/s is passed through the valve, with a constant valve opening of y=0.5. In typical steam systems, the inlet pressure of steam served at the building side fluctuates between +/- 0.5 to 3 bar. Thus, we varied the inlet pressure from 9 bar to 7.5 bar in this example case.

• For compressible medium, with the decrease in steam inlet pressure, its density decreases, and its specific volume increases. This should result in an increased pressure drop (observed in W_rho case).
• Incase of incompressible media, the pressure drop will be maintained constant and does not get impacted by the inlet pressure, which is observed in Wo_rho case.

Thank you

[bravache]

@SaranyaAnbarasu Thank you for the detailed description.

I opened the following branch for these changes: https://github.com/lbl-srg/modelica-buildings/tree/issue2848_steamvalve

Is that what you needed? If not, can you clarify your request?

Regarding the detail of the steam pressure regulating valve, this looks good at first glance. I believe there will likely be opportunities to reuse/extend the existing PartialTwoWayValve and ValveParameters, but I would have to look at the implementation to give any suggestion on changes that would be required.

[SaranyaAnbarasu]

@bravache Thank you for opening the branch. In an earlier technical meeting, Dr. Wetter suggested a few changes to the SteamTwoWayValveSelfActuating and the model location. We are currently working on those changes and we will update the revised models into the branch for your review.

Suggested changes:

• Remove the PI controller in the SteamTwoWayValveSelfActuating model and simplify the implementation similar to the Buildings.Fluid.Movers.BaseClasses.IdealSource model (Users may find it difficult to tune the k and Ti in the controller).
• The steam valves can be added to the DHC package as proposed earlier (https://docs.google.com/document/d/12GaIloYaMds4USyhZt1W_s2hB2W2_GWR/edit).

[SaranyaAnbarasu]

Hi @bravache

We have simplified the self-acting steam valve model based on the discussion with Dr. Wetter (GED meeting, 02.28.2022) and addressed the suggestions on PR #2908

• The earlier proposed self-acting valve SteamTwoWayValveSelfActing, has dependency with SteamTwoWayValve which extends from the baseclass SteamValveParameters (uses complex dependencies of Kv, m_flow and dp based on ISA 75.01.01/IEC).

• We have dropped this earlier approach completely and have simplified the self-acting valve model by using Buildings.Fluid.Movers.BaseClasses.IdealSource, that allows the pressure drop to be prescribed independently of mass flow rate. The valve maintains the user specified downstream pressure value (pb_nominal) and asserts a warning when the pb_nominal is set larger than the upstream (inlet) pressure.

With this revision, we now would like to propose one self-acting valve model and an example to demonstrate its performance. Proposed models:

Experimental.DHC.Loads.Steam
  BaseClasses
  • ValveSelfActing
        Examples 
          • ValveSelfActing

Please review the PR and let us know if you have any questions. Thank you

[SaranyaAnbarasu]

Hi @bravache

Dr. Wetter suggested a few minor changes to the PRV models during the GED discussion and we are working on the revisions. We saw that you have merged the Boiler PR and would start reviewing the next ones (Networks and Valves). Please keep PR #2908 on hold, until we update the changes (expected early next week).

Thanks.