RE: how to use incident angle modifiers

[Michaël Kummert <kummert@xxxxxxxxxxxxx>]

Dear Timo,

First, I must say that I am not sure how K_diff is assessed in experimental tests according to EN 12975. I suspect it is the value of KTauAlpha for an "equivalent angle" close to 60°. Hopefully someone will correct me if I am wrong!

For the flat-plate collector (Type 1), optical modes 2 and 3 allow you to take into account experimental data.

Mode 2 requires b0 and b1, the two parameters of an equation giving KTauAlpha vs. Theta: 
K = 1-bo*(1/cos(Theta)-1)-b1*(1/cos(Theta)-1)^2
b1 can often be neglected so you could fit a b0 value using only the value of K for 50°. If my assumption about K_Diff is right, you can use a second data point in your regression (K_diff for 60°). 

Mode 3 allows you to enter data in a file. In this case, you would have at least 3 data points:
(Theta, KTauAlpha)
(0 , 1.0)
(50 , your value KTauAlpha50°)
(90 , 0.0)
(you could add (60 , K_diff) if my assumption on K_diff is correct). Note that the subroutine DATA will interpolate linearly between these values.

I would suggest to use Mode 2 with a fitted b0 value but I don't think you would notice a big difference between the two options.

For the vacuum tube collector, you have to give data in a file (see section 4.2.3 of the main manual). You can enter the 3 (or 4) data points I mentioned here above for each direction (longitudinal & transversal). I don't think it would be a good idea to fit a "b0" parameter for this type of collector. Be careful not to mix transversal and longitudinal IAM's.

I hope this helps,

Michaël Kummert
_________________________________________________

Michaël Kummert

Solar Energy Laboratory - University of Wisconsin-Madison
1303 Engr Res Bldg, 1500 Engineering Drive
Madison, WI 53706

Tel: +1 (608) 263-1589
Fax: +1 (608) 262-8464
E-mail: kummert@engr.wisc.edu (NEW!)

SEL Web Site: http://sel.me.wisc.edu
TRNSYS Web Site: http://sel.me.wisc.edu/trnsys



> -----Original Message-----
> From: owner-trnsys@relay.doit.wisc.edu
> [mailto:owner-trnsys@relay.doit.wisc.edu] On Behalf Of Timo Sengewald
> Sent: Monday, January 06, 2003 04:32
> To: TRNSYS group
> Subject: how to use incident angle modifiers
>
>
> Hello!
>
> I have got the test protocol (according to DIN EN 12975) of
> the german ISFH for two different solar collectors: a flate
> plate and a evacuated tube collector. Can I use the given
> incident angle modifiers with Type 1 and Type 71? For the
> flat plate collector the IAMs are called K_taualpha_dir(45°)
> and K_taualpha_dif. The IAMs for the tube collector are
> K_long(50°) and K_rad(50°). Which values do I have to provide
> by the IAM files?
>
> Thanks a lot,
>
> Timo Sengewald
>
>
>
> ------------------------------------------
> Phönix Sonnenwärme AG
> Am Treptower Park 28-30
> D-12435 Berlin, Germany
> e-mail: timo.sengewald@sonnenwaerme-ag.de
> www.sonnenwaerme.ag
> Tel.: +49-(0)30-53 00 07-237
> Fax.: +49-(0)30-53 00 07-17
> ------------------------------------------
>