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Re: [TRNSYS-users] Incident Angle Modifier - With only one value oflongit IAM
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@unisa.edu.au]
> Sent: Tuesday, 05 February, 2008 01:17
> To: trnsys-users@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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