Piping heat losses

I have a question about CSP Parabolic through (empirical) model. Why does the model use a value of 10 W/m^2 for the Piping Heat Loss at Design Temp for default? I also want to know if the Piping Heat Loss Coefficients (1-3) values are universal for any plant configuration and if not, what they depend on?
Specifically I want to model a plant with Molten Salt as HTF

Dear Fernando,

SAM's Empirical Trough model was originally developed as a spreadsheet model, and its results were compared to measured performance data for the SEGS VI system. Please see the Empirical Trough model paper referenced on the SAM website's performance model documentation page for more details:

sam.nrel.gov/performance

In general, SAM's Physical Trough model is better for systems that have different configurations. The Empirical Trough model works best for systems that have configurations similar to the SEGS systems. Please see the descriptions of the Physical Trough model and Empirical Trough models in SAM's help system for a discussion for more about the two models.

Best regards,
Paul.

Thank you Paul,
Fernando