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Erik,<br>
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.<br>
Best,<br>
David<br>
<br>
<br>
On 11/11/2011 00:32, Erik Boschek wrote:
<blockquote
cite="mid:1320993124.86767.YahooMailNeo@web120219.mail.ne1.yahoo.com"
type="cite">
<div style="color:#000; background-color:#fff; font-family:arial,
helvetica, sans-serif;font-size:12pt">
<div><br>
</div>
<div>Dear TRNSYS users,</div>
<div><br>
</div>
<div>I have a simple question regarding weather reading and
interpolating direct normal radiation (DNI) values for time
steps less than an hour.</div>
<div><br>
</div>
<div>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):</div>
<div><br>
</div>
<div>1.) Do not interpolate, using Type 15 with output DNR (not
interpolated): you end up with a "steppy" profile</div>
<div>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</div>
<div>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.<br>
</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>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.<br>
</div>
<div><br>
</div>
<div>Thanks,</div>
<div><br>
</div>
<div>Erik Boschek<br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
</div>
<br>
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<br>
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</pre>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
***************************
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
<a class="moz-txt-link-abbreviated" href="mailto:d.bradley@tess-inc.com">d.bradley@tess-inc.com</a>
<a class="moz-txt-link-freetext" href="http://www.tess-inc.com">http://www.tess-inc.com</a>
<a class="moz-txt-link-freetext" href="http://www.trnsys.com">http://www.trnsys.com</a></pre>
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