Freeze Protection Energy Increase with new version

I have just ran a simulation of my beta version case with the new SAM version.
I am studying a Physical Parabolic Trough CSP Model.
First of all the Annual Energy output decreased 28%, mainly because the freeze protection energy is much higher than before.

How does the model calculate the required freeze protection energy?

Thanks,
Pietro

Dear Pietro,

The physical trough reference manual describes the freeze protection calculations. You can download the manual here:

sam.nrel.gov/webfm_send/106

Please see Section 2.2.2 on p 16 for field freeze protection, and 4.1.3 p 85 for storage freeze protection.

For a description of changes to the model in the current version and their potential impact on results, please see the release notes, which you can open from the Help menu in SAM.

Do those documents help answer your question?

Best regards,
Paul.

Concerning freeze protection in the version 2012.12.02 it is possible to know the freeze protection energy which is needed when the temperature at the hot header outlet is less than the freeze protection temperature. However, for SAM version 2011.06.30, there isn’t any output variable for freeze protection energy and I don´t know how to calculate it. I have been considering that when the temperature decrease below the HTF minimum design temperature the energy for freeze protection is equal to the thermal losses in the solar field, is it right?.

Another question is that using the Empirical Model, we obtain results for ‘Solar Field Thermal Output’. Following the hourly results, I see that in the morning, at the plant starting up, energy from solar output is used for warming up the fluid. However, at the first hour, only a part of the ‘solar thermal output’ is available for this purpose. It seems as if the model assumes some operational losses during the first operation hour. Is it right?

Thanks,

Earlier versions of the SAM (including 2011.6.30) CSP models report fewer hourly variables on the Results page. To see more hourly variables in those versions, on the Results menu, click View Hourly Time Series (DView). That opens the DView data viewer where you can display the freeze protection energy (Q_freeze_prot for the physical trough model). You can right click the graphs in DView to export the data.

I'm not sure I completely understand your question about warmup energy. SAM accounts for the thermal energy absorbed by the solar field as it warms up to its design point temperature and reports that energy as "Solar Field Warmup Energy." You can use the following hourly variables to investigate what is happening during this time period:

Solar Field Energy Before Thermal Losses
Solar Field Thermal Output
Receiver Thermal Loss
Total Header Piping Loss
Solar Field Warmup Energy

Best regards,
Paul.

Dear Paul,

Thanks a lot for answer my questions. I have another one regarding Freeze protection for CSP trough empirical. In the empirical model, freeze protection behaves as an electric heater system. Are you planning, like in the physical trough model, to model freeze protection like a central heater?

Thanks,
Lupa

Dear Lupa,

We do not have any plans to make changes to the empirical trough model, aside from bug fixes as they come up. However, I will add your request to our list of feature requests in case that changes.

Best regards,
Paul.