[TRNSYS-users] (no subject)

[David BRADLEY]

Erik,
  You are right on with all three of your points. For reference, we 
discontinued use of Type109 in Trnsys17 in favor of option 2 (Type15), 
which is correct from an energy perspective even though it isn't a 
smooth curve. In gernal think that a control strategy that relies only 
on the instantaneous DNI as its input might run into trouble not only in 
simulation but also in the real world; clouds pass in front of the sun 
rapidly sometimes. While I won't pretend that the "spiky" profile that 
Type15 generates is totally realistic, I think it is a fairly accurate 
representation of DNI. Bear in mind that Type15 is trying to reconstruct 
a minute by minute radiation profile based only on 1 number and to do so 
correctly for all possible climate types. You might consider a control 
strategy that uses the output of Type15 but put through a 
running-average component so that your control decisions are based on a 
somewhat more stable (smoother) profile.
Best,
  David


On 11/11/2011 00:32, Erik Boschek wrote:
>
> Dear TRNSYS users,
>
> I have a simple question regarding weather reading and interpolating 
> direct normal radiation (DNI) values for time steps less than an hour.
>
> As long as I have been using TRNSYS (using TRNSYS 16.1) I have 
> understood this can be done in a few ways as follows, including the 
> consequence for an example TM2 file (see attached screen shot for 
> clarification):
>
> 1.) Do not interpolate, using Type 15 with output DNR (not 
> interpolated): you end up with a "steppy" profile
> 2.) Using Type 15, but with 2-axis tracking and the output "Beam 
> radiation for surface": you get a discontinuous "spikey" profile, but 
> the integration of energy across the hour is respected
> 3.) Same as 2, but using Type109-TMY2: You get a smooth profile, but 
> often there appear inexplicable spikes at the beginning or end of the 
> day. The one in the plot obviously is an extreme case.
>
> For reference: I just used the Daggett profile 
> "US-CA-Daggett-23161.tm2" which came with TRNSYS, but the behavior is 
> not specific to this file.
>
> Generally, I have been using 2, but it can cause problems if there is, 
> for example, some triggering function based on DNI and the DNI hovers 
> around the threshold. Is there another option for getting a smoother 
> profile or is it best just to not interpolate? Any opinions? Feel free 
> to point me to an earlier post on this topic in case I missed it.
>
> Thanks,
>
> Erik Boschek
>
>
>
>
>
>
>
>
> _______________________________________________
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> TRNSYS-users at cae.wisc.edu
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-- 
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI  53703 USA

P:+1.608.274.2577
F:+1.608.278.1475
d.bradley at tess-inc.com

http://www.tess-inc.com
http://www.trnsys.com

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