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Francois,<br>
This wasn't as straightforward to figure out as I would have thought.
<br>
<br>
First, there are two different sky temperature correlations that are
available in TRNSYS. One such correlation comes from <br>
<br>
M. Martin, P. Berdahl, Characteristics of Infrared Sky Radiation in the
United States, Lawrence<br>
Berkeley Laboratory, University of California - Berkeley, Solar Energy
Vol. 33, No. 3/4, pp. 321-<br>
336, 1984.<br>
<br>
and is implemented in Type69. The other is from ASHRAE (I believe) and
is implemented in Type575 (in the TESS Utility Library). As a side
note, there is at least one other sky temperature model out there that
is being used in EnergyPlus. The correlation that is built into Type15
is the correlation from Type575. <br>
<br>
There are actually two modes of Type69 available: one in which the
opaque cloud cover is read as an input and one in which the opaque
cloud cover is estimated from the ratio of diffuse to total radiation.
The mode used in Type15 is the one in which the opaque cloud cover is
read from the data file. I would recommend plotting out the opaque sky
cover output from Type15 and looking at it to make sure that it looks
reasonable and hasn't been set arbitrarily. In the comparison you
performed, you selected the mode of Type69 in which the opaque cloud
cover is estimated, which does indeed cause some differences in the sky
temperature. A more appropriate comparison would have been between
Type15 and the mode of Type69 in which the cloud cover is read from
Type15. Make sure that in doing this, you select the "opaque cloud
cover" output and not the "total cloud cover" output.<br>
<br>
My recommendation would be that if the opaque cloud cover data from
your meteonorm data file looks reasonable, use the effective sky
temperature from type15. If it does not, then use Type69's ability to
estimate the cloud cover based on solar radiation.<br>
Kind regards,<br>
David<br>
<br>
<br>
Francois Badinier wrote:
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<p class="MsoNormal">Dear TRNSYS community,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">It seems that there are some differences between
the “
Effective sky temperature” available in the weather component (e.g.
Type 15-6)
and the “fictive sky temperature” calculated with the Type69b. The
differences
are quite important and I would like to know which one I should “trust”
to
calculate some IR-emissions towards the sky.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I attached a simple testing project in which I
plotted
the following graphs:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoListParagraph" style="text-indent: -18pt;"><!--[if !supportLists]--><span
style="">1.<span
style="font-family: "Times New Roman"; font-style: normal; font-variant: normal; font-weight: normal; font-size: 7pt; line-height: normal; font-size-adjust: none; font-stretch: normal;">
</span></span><!--[endif]-->The <u>“effective sky temperature”</u> ,
straight from
the weather component <o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent: -18pt;"><!--[if !supportLists]--><span
style="">2.<span
style="font-family: "Times New Roman"; font-style: normal; font-variant: normal; font-weight: normal; font-size: 7pt; line-height: normal; font-size-adjust: none; font-stretch: normal;">
</span></span><!--[endif]-->The <u>ambient (dry-bulb) temperature</u><o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent: -18pt;"><!--[if !supportLists]--><span
style="">3.<span
style="font-family: "Times New Roman"; font-style: normal; font-variant: normal; font-weight: normal; font-size: 7pt; line-height: normal; font-size-adjust: none; font-stretch: normal;">
</span></span><!--[endif]-->The <u>average</u> between “effective
sky temperature”
and “ambient temperature”<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent: -18pt;"><!--[if !supportLists]--><span
style="">4.<span
style="font-family: "Times New Roman"; font-style: normal; font-variant: normal; font-weight: normal; font-size: 7pt; line-height: normal; font-size-adjust: none; font-stretch: normal;">
</span></span><!--[endif]-->The <u>“fictive sky temperature”</u>
calculated by the
Type69b (using “<b>total diffuse</b> <b>radiation</b>” as an input)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">What comes out of this graph is that the
“average
temperature” is quite close to the “fictive sky temperature” calculated
by
Type69b. <o:p></o:p></p>
<p class="MsoNormal">So where do the differences come from and which
temperature
should I use?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thank you for your help.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">François Badinier<o:p></o:p></p>
<p class="MsoNormal"><span style="color: rgb(192, 80, 77);">Development
Engineer<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(0, 176, 80);">ICAX Ltd<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 9pt; color: rgb(0, 176, 80);">1 Hatfield House
<o:p></o:p></span></p>
<p class="MsoNormal"><span
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<p class="MsoNormal"><span
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<p class="MsoNormal"><span
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lang="FR"><a moz-do-not-send="true" href="mailto:alan.kiff@icax.co.uk"><span
lang="EN-GB">francois.badinier@icax.co.uk</span></a></span><span
style="font-size: 8pt; font-family: "Courier New"; color: black;"><o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 8pt; font-family: "Courier New"; color: black;"
lang="FR"><a moz-do-not-send="true" href="http://www.icax.co.uk"><span
lang="EN-GB">www.icax.co.uk</span></a></span><span
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<p class="MsoNormal"><o:p> </o:p></p>
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<br>
<pre class="moz-signature" cols="72">--
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