[TRNSYS-users] Error found in STEC-Lib components for parabolic trough

[Jochen Doell]

Dear TRNSYS users,

While working and modifying type 396 (trough) of the TESSlib, I found an 
inconsistency between the way the type calculates its thermal efficiency 
and the formula in which the loss coefficients are given in the sources 
[2] and [8] in the manual:

In sources [2] and [8], the thermal efficiency is always given as
Ceff=K*(A+B*(DTo+DTi)/2) + (C+Cw*WS)*(DTo+DTi)/(2*Ieff) 
+D/(Ieff)*((DTo+DTi)/2)**2)

where K is the IAM, A,B,C,Cw and D are collector specific coefficients 
and (DTo+DTi)/2 the average temperature difference collector to ambient.

In the type, the equation is
Ceff=K*M*Sh*[(A+B*(DTo+DTi)/2)+(C+Cw*WS)*(DTo+DTi)/(2*I)+D/I*(DTo*DTi+(DTo-DTi)**2/3)]
while the same coefficients as in the sources are said to be used.

(M & Sh are calculated coefficients for end losses and shading)

The IAM factor K (as well as M and Sh) is multiplied with the complete 
equation instead of only the first term. Additionally, the use of the 
temperature difference in the last term seems to be not correct. Both 
differences will affect the "behavior" of the collector in the simulation.


If I am not mistaken, the type should be corrected before use.

Best regards,
Jochen

-- 
_________________________________________________

Dipl.-Ing. (FH) Jochen Döll
Dept. Thermal Systems and Buildings

Fraunhofer-Institut für Solare Energiesysteme ISE
Heidenhofstrasse 2, 79110 Freiburg, Germany

Phone:	+49 (761) 4588-5527
Fax:	+49 (761) 4588-9000
Mail:	jochen.doell at ise.fraunhofer.de
Web:	www.ise.fraunhofer.de
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