Error in SAM/Help contents

Hi Paul,

Something isn't adding for the piping losses for molten salt SPT. 

In the tower and receiver input page the piping heat loss coefficient is weirdly given in units of Wt/2K. These units are either incorrect or the equation stated further down is incorrect:
"The calculated thermal energy loss due to header piping, applied whenever the receiver is operating.Total Piping Loss (kWt) = Piping Length (m) × Piping Heat Loss Coefficient (Wt/m) ÷ 1000 (kW/W)"

Which is it? Surely it is the latter, but then if it is and you use the default value of 2, the value you calculate manually and that calculated in SAM are TOTALLY different. 

If I have a tower height of 90m, use a pipe length multiplier of 2.6, pipe constant of 0 and the default value of 2 (units???) then following the equation I should get an answer in SAM of :
90*2.6*2/1000 = 0.468 kW.

However this doesn't happen, instead I get a value of 367.2 kW within SAM, so something is reeeally off here. 

Please could you help urgently?

Thank you

Harry

Hi Harry,

Sorry for late reply. The input is in units of W/m2-K. The equation for Total Piping Loss in the Help is outdated - we will fix it.

Hi Ty, Paul,

It doesn't look like this issue has been fixed in the help notes in the March update. Are you able to provide a quick break down of the updated equation here for the time being, please? It would be really useful!

Kind regard

Harry

Hi Harry,

Sorry about that.

Here's the correct equation:

Total piping loss (Wt) = Piping length (m) * Pipe circumference (m) * Piping heat loss coefficient (W/m2-K) *  (T_pipe – T_ambient)

We fix that in Help for SAM 2023.12.17 Revision 2.

Best regards,
Paul.

Hi Paul,

No problem and thank you for providing the correction, I'm just wondering what SAM uses for the pipe circumference as there is no input field for this in the user interface. 

I'm also assuming the following formula for piping length still applies:Piping Length (m) = Piping Length Multiplier × Tower Height (m) + Piping Length Constant
 

Hello,

SAM runs a special simulation for a "design case" to calculate these values in the user interface -- they are pre-processed inputs that are then passed to the actual performance simulation. Variables like the pipe circumferences are internal ones that are not displayed in the user interface. To get an idea of how the calculations work, you can see the equations in the C++ source code here:

github.com/NREL/ssc/blob/a80f94ba2dee81f9b1ebcae0bd6ed220b91fa68b/tcs/sam_csp_util.cpp#L1199

Best regards,
Paul.