Solar water, residential - Rated system size incorretly calculated

SAM help says the field "Rated system size" is calculated using the formula:
Nameplate Capacity = Total Collector Area × FRta - FRUL × 30/1000

I input:
Total Collector Area = 8.968
FRta = 0.057
FRUL = 2.7

and calculate answer to be 0.430176.

SAM calculates -0.215232 and fails to run simulation. I get error messages. Please fix.
Thank you.

Hello,
Would you mind [url=mailto:sam.support@nrel.gov?subject=Question%20from%20Support%20Forum t=_self]emailing me[/url] your .sam file so I can see exactly what your inputs look like?
Best regards,

Paul.

Hi Paul,

I am having the same issue. I sent a .zsam file to upper mentioned email address. I hope I did not break any rules with this.

Here are user defined collector specifications I used:

Area: 2.5 m2
FRta: 0.7
FRUL: 4

SAM calculates the "Nameplate thermal capacity" to be: 1.45 kWt.

Whereas if one would use the upper mentioned formula from the help file (Nameplate Capacity = Total Collector Area × FRta - FRUL × 30/1000): 1.63 kWt.

I also tried a couple of more examples, and in some cases SAM even outputs a negative value for "Nameplate thermal capacity", the same like in upper reply by gisraelson.

Why is this happening?

Hi Paul.

I have just tested the same custom collector specifications (Area: 2.5 m2,FRta: 0.7, FRUL: 4) on the latest SAM version: "Version 2015.6.30, 64 bit, updated to revision 4". And it calculates the same "Rated system size": 1.45 kW.
Here is the file:
www.dropbox.com/s/5rufduh6atl93ga/swh_rating.sam?dl=0

Does this mean that the mentioned formula from the help file:

Nameplate Capacity = Total Collector Area × FRta - FRUL × 30/1000

is incorrect?
Because it outputs 1.63 kW for the same upper custom collector specifications (Area: 2.5 m2,FRta: 0.7, FRUL: 4).

wat this ever answered?

Hi Russ,

I don't think it was. This is about a very old version of SAM before some improvements were made to the solar water heating model.

Best regards,
Paul.