[TRNSYS-users] Incident Angle Modifier - With only one value oflongit IAM

[Michaël Kummert]

Edward,

For typical designs (e.g. evacuated tube collectors) the longitudinal IAM is
usually close to a "standard flat-plate" IAM, so I believe the usual ASHRAE
equation would give a reasonable approximation:
IAM = 1-b0 (1/cos(theta)-1)
So in your case you could fit the b0 parameter to match the one value you
have and then use the equation to generate longitudinal IAM values to fill
in your matrix.
I have to say, however, that your only value for the longitudinal IAM (0.85
at 40°) seems low compared to what I am used to see (typically the value at
50° is provided, and it is around 0.9). If that value is correct it might
indicate that the simple ASHRAE equation is not adapted at all to your
collector design.

I hope this helps,

Michaël Kummert
ESRU - University of Strathclyde  


> -----Original Message-----
> From: Edward Halawa [mailto:Edward.Halawa at unisa.edu.au] 
> Sent: Tuesday, 05 February, 2008 01:17
> To: trnsys-users at engr.wisc.edu
> Subject: [TRNSYS-users] Incident Angle Modifier - With only 
> one value oflongit IAM
> 
> Dear All,
> 
> I read Michael's explanation on how to create IAM matrix 
> values for Type 71. See link below:
> http://sel.me.wisc.edu/trnsys/mailinglist/archive2003/msg00021.html
> 
> My question is, how should I deal with IAMs data with only 1 
> IAM value for longitudinal angle?
> 
> Suppose I have the following data:
> Dir.      |0    | 20   | 40   | 60   | 90   |
> Trans IAM | 1.0 | 1.1  | 1.3  | 1.4  | 0.00 |
> Long. IAM |            | 0.85 |             |
> 
> Is the following reasonable:
> 0 20 40 60 90
> 40
> 0.85
> 0.94 (=1.1 * 0.85)
> 1.11 (=1.3 * 0.85)
> 1.19 (=1.4 * 0.85)
> 0
> 
> Or, should I assume the IAM values for other longitudinal angles ?
> 
> I appreciate your help.
> 
> ehalawa
> 
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