Error in thermal storage system while calculating the heat exchanger derate in v2017

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saurabh.suman
Error in thermal storage system while calculating the heat exchanger derate in v2017

I was doing one to one analysis of a particular case file from SAM v2014 to SAM v2017 and I found out the following error:
1. While calculating the HX derate in v2014, a different formula has been used than in v2017 (Please check that)due to which storage parameters are coming out to be different.
2. For the same hot side and cold side HX approach temperature in v2014, the HX derate value is coming out to be different in v2017.
3. While changing the design loop inlet temperature thermal storage exergetic efficiency is not changing much as it should as per the formula given but the storage volume is changing significantly in v2017 but the same thing does not occur in v2014.
Please share your thoughts and suggestion on the above queries.

Paul Gilman

Dear Saurabh,

1 and 2. The "HX derate" in older versions of SAM is not the same as the "Exergetic efficiency" in the newer versions. Please see this post for a description of the equations and a link to a spreadsheet that replicates them:

https://sam.nrel.gov/node/70868

3. The equation for the storage volume in Help is wrong. It should be:

Storage volume equation

Where:

C is the TES thermal capacity

ρHTF is the HTF flud density

cHTF is the HTF flud specific heat

μhx is the exergetic efficiency

We will fix this error in the Help system. Thank you for bringing it to our attention.

Best regards,
Paul.

saurabh.suman

Dear Paul,
Thank you so much for your quick response. I just had one more query that, can you please share the formula of exergetic efficiency in v2017 and HX derate in v2014? The formula that you have shared on the link below is not the same as it is mentioned in the help section of v2017 (as I am using SAM version 2017.1.17).
https://sam.nrel.gov/node/70868
So please make the changes appropriately. I think that would be very helpful for the further understanding.
Thanks,

Regards,
Saurabh Suman

Paul Gilman

Dear Saurabh,

Yes, as I mentioned above, I will correct the storage volume equation in Help for the next update to the current version of SAM. We do not maintain older versions of SAM, so the mistake will remain in the Help system for SAM 2017.1.7 and older.

The equation for the heat exchanger derate for the 2014 version of SAM is:

heat_exchanger_derate = 1 - ( T_hot_approach + T_cold_approach ) / ( T_solar_field_outlet - T_solar_field_inlet )

Best regards,
Paul.

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