[TRNSYS-users] Type1288 IAM

Jeff Thornton thornton at tess-inc.com
Tue Dec 22 12:22:29 PST 2020


Two questions:

1) Did you look at the external data file you are using to confirm that 
the IAM at 0,0 is equal to one?

2) Are you looking at the overall IAM or the IAM for beam radiation?  It 
may be you are noticing the combined impact of a beam IAM and a diffuse 
IAM less than one.


Jeff Thornton
President - TESS LLC
3 N. Pinckney Street, Suite 202, Madison WI USA 53703
Office: (608) 274-2577  Fax: (608) 278-1475
E-Mail: thornton at tess-inc.com

On 12/22/2020 5:31 am, Maximilian Stahlhut via TRNSYS-users wrote:
> Hey,
> I am using Type1288 for modeling a Parabolic Trough Collector with
> single-axis tracking.
> In Type 1288, the IAM values are read from an external data file which
>  contains the biaxial IAMs of the collector. For reading this data
> file, the longitudinal and transversal incident angle are needed. As
> far as I know, they are calculated by:
> Tranverse = ATAN(SIN(Zenith
> angle)*SIN(ABS(Azimuth-SolarAzimuth))/COS(IncidentAngle_Beam))
> Longitudinal = ABS(ATAN(TAN(Zenith
> angle)*COS(Azimuth-SolarAzimuth))-CollectorSlope)
> For Tranverse=0° and Longitudinal=0° I would have expected an IAM of
> 1. However, Type1288 calculates a smaller one at this timestep.
> Does anyone has experience using this Type or using a different type
> with a biaxial IAM input file and a similar problem occurred? Or have
> I missed something in my calculations?
> Regards,
> Maximilian
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