Hello,
In SAM 2015.1.30, the outputs relating to the heat rejection system include:
* Condenser pressure (Pa)
* Condenser fraction of operating bays
* Parasitic power condenser operation (MWe)
* Cycle cooling water mass flow rate - makeup (kg/hr)
* Cycle efficiency (gross)
The cycle shown in the reference manual is used to determine the off-design performance scaling of the power cycle. SAM's model uses input that you provide to specify:
* design-point power cycle gross efficiency,
* inlet and outlet HTF temperature from the steam generator,
* design gross power output,
* design point ambient temperature, and
* design point condenser temperature rise (ITD at design point for air-cooling, Ref. condenser dT + Approach temperature for evap-coolint).
With these inputs, the cycle performance -- including mass flow rates -- is fully constrained for design point operation. Note that we don't actually model a particular turbine configuration, feedwater heating sequence, etc. -- rather we use the design-point data that you provide to make an inference about how the cycle operates under the specified conditions and then scale performance with non-dimensional curves.
The EES power cycle model is used to generate the curves that represent scaling in power production and heat absorption by the cycle (i.e. cycle efficiency) as a function of 3 variables: HTF mass flow rate, HTF inlet temperature, and condenser temperature. As these 3 variables deviate from their design point value, the curves correct cycle performance accordingly. These curves are non-dimensionalized, so they operate on the design point configuration without requiring specific knowledge of the design point settings.
If you reproduce the EES cycle model, you will likely notice that the efficiency of that cycle is substantially lower than the design-point value that we assume as the default value in SAM. The default of 0.3774 comes from the expected cycle efficiency of current trough systems, not from the EES scaling model.
Regarding the mass flow discrepancy, I would recommend that you replicate the cycles published by Lippke (see -- Lippke, F. W. (1995). Simulation of the part-load behavior of a 30MW SEGS plant. Sandia National Laboratory.
www.osti.gov/scitech/biblio/95571). His report provides detailed information regarding thermodynamic states and equipment sizing that you might find helpful in resolving your questions.
Finally, regarding your inquiry on investigating cooling methods in more depth, it is difficult to provide good guidance without knowing which issues or questions you specifically have in mind. A few points to consider: (1) Three cooling technologies are available in SAM - dry, evaporative, and hybrid. Each option is described in the technical manual. These three models capture a large share of proposed cooling methods. (2) You can manipulate the sizing of the cooling system by adjusting the design point temperature rises in the Cooling System settings. (3) The performance of each system depends on the climate in which it operates. Hopefully this helps.
Best,
Mike Wagner
NREL
