Maybe some minor SAM bugs, please check

Hello Paul,

(SAM 2013.9.20, parabolic trough empirical)

I was setting up the "calculated values" for usage in parametric SamUL calculations
and came across the following issues:

- SCA/HCE: SamUL input variable browser does not show "HCE percentage of solar field 1-4"

- SCA/HCE Type 3 Optical efficency: the value shown in the text box is not correct, too large.
In my case it has to be multiplied by 0.98, which might be the "dust on envelope" factor.
HCE Type 1,2,4 seem to be correct

- SCA/HCE Heat losses Type 1-4: something seems to be wrong here. I calculated the values using the
formula in the documentation (QHCEHLD,...) and I don't get the numbers shown in the
text boxes.
The value in the boxes are all times ~0.97 of what my SamUL calculation shows.

I calculated them twice, first using SamUL and then a calculator,
and yielded the same numbers. But they are different from the ones in the textboxes.
Could you please check this? Maybe the formula in the documentation was changed.

Could you please take a look at this. I hope that I am not wasting your time...

Kind regards,
Joe

Hi Joe,

1. Unfortunately, some input variables are missing from the SamUL variable list. The names of the HCE "Percent of Solar Field Variable" for Receivers 1-4 are:

csp.tr.hce.unit1_frac
csp.tr.hce.unit2_frac
csp.tr.hce.unit3_frac
csp.tr.hce.unit4_frac

Note that the label in the SAM user interface is misleading: The values are fractions, where 1 is 100% of the solar field, not percentages as the label would suggest.

2. I confirmed that the Optical Efficiency (HCE) value for Receiver 3 seems to exclude the Dust on Envelope factor, although in my review of the code, I can't see why it is not working. I'll let the developers know about that issue. That should only affect the value in the user interface, not the actual calculations during simulation.

3. Here is the equation taken right from the SAM user interface that calculates the HCE Heat Losses (W/m) value for Receiver 1:

=${csp.tr.hce.heatlossf1}*(
(${csp.tr.hce.a0_1}+${csp.tr.hce.a5_1}*${csp.tr.hce.hlterm1})
+ (${csp.tr.hce.a1_1}+${csp.tr.hce.a6_1}*${csp.tr.hce.hlterm1}) * ${csp.tr.hce.hlterm2}
+ (${csp.tr.hce.a2_1}+${csp.tr.hce.a4_1}*${csp.tr.solf.dp.dniradiation})* ${csp.tr.hce.hlterm3}
+ ${csp.tr.hce.a3_1}*${csp.tr.hce.hlterm4} )

Best regards,
Paul.

Hello Paul,

thanks for your quick reply.

On 3.:

I checked the equations and compared them to the documentary and
assume that the problem is in ${csp.tr.hce.hlterm2}.

The documentary states that it should be
( solarfield_temp_outlet + solarfield_temp_inlet - ambient_temp_reference_SM1) / 2

I guess there is a factor 2 on the ambient temperature and the equation used is

( solarfield_temp_outlet + solarfield_temp_inlet - 2 * ambient_temp_reference_SM1) / 2

Well, I don't know which one is correct...
Can you confirm this?

I also have another question about a missing variable, this time in the
Physical Trough model. Page Solar field - Single Loop configuration:
"Number of SCA/HCE assemblies per loop"

Kind regards,
Joe

Hello Paul,

yet another question I that just came up.

Using the Physical Trough model, I could not figure out how to calculate
the "Total loop conversion efficiency" as the equation needs the variable
"Receiver Heat Loss Efficiency" which I could not find mentioned elsewhere.
Not even in "Technical Manual for the SAM Physical Trough Model"

I tried some ideas but can't find the correct equation.

Kind regards,
Joe

Hi Joe,

On Item 2, it turns out that the optical efficiency value on the SCA/HCE page is correct. There is a hidden term in the calculation that depends on whether the receiver parameters are for one with broken glass. For receivers with broken glass, SAM excludes the "dust on envelope" loss from the receiver's optical efficiency calculation. In the default case, Receiver 3 is "2008 Schott PTR 70, Broken Glass."

On Item 3, I guess that equation does not make any sense without the definitions of hlterm1..4. Let's try this (HCE heat losses for Receiver 1):

HCE Heat Losses W/m =
Heat Loss Factor * {
( A0 + A5*WS^2 ) +
( A1 + A6*WS^2 ) * [ 0.5*(Tout + Tin) - Tamb ] +
( A2 + A4*DNI ) * [ (Tout^2 + Tout*Tin + Tin^2)/3 ] +
( A3 * [ (Tout^2 + Tin^2) * (Tout+Tin) / 4 ] }

Where Tamb, DNI, and WS are the "Solar Multiple Reference Conditions," and Tin and Tout are the Solar Field Inlet Temp and Outlet Temp, respectively, all from the Solar Field page.

For the physical trough model, the name of the "Number of SCA/HCE assemblies per loop" variable is csp.dtr.solf.loop. It is an array, and I'm not sure exactly how it works. Its default value is [8,1,1,8,1,1,7,1,1,6,1,1,5,1,1,4,1,1,3,1,1,2,1,1,1]. My guess is that the first element is the number of assemblies, and that the remaining elements are in groups of three for each assembly: SCA type, HCE type, Defocus order. If my hunch is correct, for a single loop, the array would look like [1,1,1,1]. You will have to experiment a little with that array in SamUL to see if you can make it work.

Best regards,
Paul.

Hello Paul,

thanks for your response.

On Item 2:
Ok, makes sense now.

On Item 3:
Ok, this equation leads to the correct result.
Now that I take a closer look at it, it also makes more sense
Then the equation in the documentary is incorrect.
There the ambient temperature is also multiplied by 0.5 .

Maybe you missed my other question from the previous comment:

Using the Physical Trough model, I could not figure out how to calculate
the "Total loop conversion efficiency" as the equation needs the variable
"Receiver Heat Loss Efficiency" which I could not find mentioned elsewhere.
Not even in "Technical Manual for the SAM Physical Trough Model"
I tried various approaches but can't find the correct equation.

A copy of the relevant source code should do it

Kind regards,
Joe