Create new cooling tower model

[JayHuLBL]

@wehuang16
This issue is to develop new cooling tower models, including dry cooler model and wet cooler model.

Stage 1: function based model

For the dry cooler model:

• Inputs:
  • Inlet water temperature
  • Outlet water temperature
  • Inlet air dry bulb temperature
  • Fan speed (0~1)
• Outputs:
  • Fan power

For the wet cooler model, with the calculation of water level, and potentially the basin heating:

• Inputs:
  • Inlet water temperature
  • Outlet water temperature
  • Inlet air wet bulb temperature
  • Fan speed (0~1)
  • Refill water (Boolean input)
• Outputs:
  • Fan power
  • Water level (0~1)
  • Water consumption
  • with the heat port, for basin heating

[Vbraciszewski]

Thank you for the interest in new cooling tower models. Please include option for including water consumption as an output as part of new cooling tower models. Water use is of particular interest for data center cooling. Also, some jurisdictions have banned evaporative cooling due to water scarcity so it is an issue generally as well.

[justnielsen]

A year ago we made a model of a seawater-based forced-draft cooling tower to be integrated in a larger district heating/cooling system model. Our focus was proces integration, study of the dynamic behaviour of cooling towers, and, particularly, control system design. We needed some features that were not available with the existing Modelica Buildings Library (MBL) cooling tower models.

Requirements for our cooling tower model:

• Extraction of the condensed water to be collected in one or more shared/interconnected basins.
• Dynamic, discretized design
• Reversible air flow direction for occasional heat treatment of the lower part of the cooling tower (Legionella mitigation).
• Parameterization from nominal values (like it is usually done in MBL)
• Basin makeup/blowdown to control salinity of the basin water
• Mechanistic design approach, based on well-tested components from MBL

Controller design

The cooling tower system controller controls

• Temperature approach using fan speed (air flow)
• Salinity (blowdown valve)
• Basin level (makeup pump)
• Cooling tower seawater temperature to limit Legionella growth (circulation pump)
• DH water inlet temperature to heat exchanger (seawater/DH water) to minimize SW-side scaling (DH shunt pump).

Missing features

We haven't implemented the seawater medium properties in Modelica yet (IAPWS R13-08) and, thus, the tower segment models don't support it yet (evaporated water = fresh. Condensed water = salty).

Documentation

If this work has any interest or if you need some inspiration, we put a short article on our website: https://en.addedvalues.eu/c/knowledge-hub/modeling-and-simulation-of-cooling-towers.

Since the model is designed in a commercial company (Added Values P/S), unfortunately, I can't share out model code (and all its dependencies), but I think some of the figures in the article will make sense anyway. Also, I'll be happy to answer questions about the model. Feel free to reach out!

[AntoineGautier]

@JayHuLBL For open-circuit cooling towers, it may be worth considering also the static (elevation) head between the basin and the top distribution header – currently, the CT models in MBL only include a fixed flow resistance to represent the flow-friction pressure drop.
For closed-circuit cooling towers: are both wet-cooling and adiabatic pre-cooling in scope? Is the spray pump included in the model?

[JayHuLBL]

@justnielsen Thanks for the detailed information about your models. The shared article is very helpful.