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<p class="MsoNormal">Note that EnergyPlus v9.3 (May 2020) introduced the Carroll MRT model as an alternate interior radiant heat exchange algorithm.<o:p></o:p></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">Input:
<a href="https://bigladdersoftware.com/epx/docs/22-2/input-output-reference/group-simulation-parameters.html#zone-radiant-exchange-algorithm">
https://bigladdersoftware.com/epx/docs/22-2/input-output-reference/group-simulation-parameters.html#zone-radiant-exchange-algorithm</a><o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">Engineering description:
<a href="https://bigladdersoftware.com/epx/docs/22-2/engineering-reference/inside-heat-balance.html#carrollmrt">
https://bigladdersoftware.com/epx/docs/22-2/engineering-reference/inside-heat-balance.html#carrollmrt</a><o:p></o:p></li></ul>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">That said, I can’t speak to whether the model captures all effects we’re talking about here.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Scott<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b>From:</b> Bldg-sim <bldg-sim-bounces@lists.onebuilding.org>
<b>On Behalf Of </b>Chris Yates via Bldg-sim<br>
<b>Sent:</b> Friday, July 14, 2023 8:10 AM<br>
<b>To:</b> bldg-sim@lists.onebuilding.org<br>
<b>Subject:</b> Re: [Bldg-sim] emissivity of air<o:p></o:p></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p style="background:orange"><b><span lang="EN-GB" style="font-size:12.0pt;color:black">CAUTION:
</span></b><span lang="EN-GB" style="font-size:10.0pt;color:black">This email originated from outside of NREL. Do not click links or open attachments unless you recognize the sender and know the content is safe.</span><span lang="EN-GB"><o:p></o:p></span></p>
<div>
<p class="MsoNormal"><i><span lang="EN-GB">In this episode of throwback Friday, we’ll revisit the subject of water vapor’s damping effect on radiant temperatures!<o:p></o:p></span></i></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">To my knowledge, only IES, the CSE as described by Chip, and possibly ESP-r model this effect within the zone model. E+ version 9 certainly doesn’t.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">I recently revisited some IES simulations with the Riyad weather file with and without the effect enabled. It had up to 1.5 Celsius effect on MRT for a large space with direct adiabatic spray cooling in the AHU.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Comfort was still pretty bad (that’s why the contractor went for chillers and fan coils instead
</span><span lang="EN-GB" style="font-family:"Segoe UI Emoji",sans-serif">😊</span><span lang="EN-GB">). However, it might not be such an insignificant effect that it can be ignored especially in locations such as atria and warehousing.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Also, interestingly, this is essentially a greenhouse effect – water vapor being a greenhouse gas.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">For those wishing to know more, the write-up in IES apache methods succinctly describes the effect.
<a href="https://help.iesve.com/ve2021/long_wave_radiation_heat_transfer.htm">https://help.iesve.com/ve2021/long_wave_radiation_heat_transfer.htm</a><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Chris<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b>From:</b> Chris Yates <<a href="mailto:chris.malcolm.yates@gmail.com">chris.malcolm.yates@gmail.com</a>>
<br>
<b>Sent:</b> Tuesday, April 4, 2017 12:05 PM<br>
<b>Cc:</b> <a href="mailto:bldg-sim@lists.onebuilding.org">bldg-sim@lists.onebuilding.org</a><br>
<b>Subject:</b> Re: [Bldg-sim] emissivity of air<o:p></o:p></p>
</div>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB">Thanks Chip<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB">Isn't the sky in essence modelled as a 'superdome' in most models? I guess there may be similar algorithms in climate processors.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB">This is a longstanding concern of mine. MRT models are very popular, especially when considering 'less traditional' modes of cooling such as chilled beams or night cooling thermally massive buildings. However, there are
issues the models. For example, my understanding is that the further a zone departs from simple convex geometry, the less valid they become. Modelling exact (i.e. non convex) geometries has become quite popular in the UK, but engineers don't realise they could
be invalidating MRT calcs.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB">I'm fairly certain that I experienced a marked difference in results between IES with internal air emissivity on and off for a building that wasn't a 'superdome'. It was in actual fact 'a dome' - three storey's within
a glazed barrel vault! I presented the more onerous set of results ultimately!<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB">Don't be surprised if I revive this post in the months to come after I've had the opportunity to do some digging!<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB">Many thanks<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB">Chris<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB">On Mon, Apr 3, 2017 at 4:58 PM, Chip Barnaby via Bldg-sim <<a href="mailto:bldg-sim@lists.onebuilding.org" target="_blank">bldg-sim@lists.onebuilding.org</a>> wrote:<o:p></o:p></span></p>
<blockquote style="border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-top:5.0pt;margin-right:0in;margin-bottom:5.0pt">
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<p class="MsoNormal"><span lang="EN-GB">Chris / all --<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB">IES is not alone -- CSE (California Simulation Engine) accounts for this effect. CSE performs the simulations for CBECC-Res, the Title 24 residential compliance tool.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<div>
<p class="MsoNormal"><span lang="EN-GB">The CSE zone model is based on (underappreciated) work by Joe Carroll from the 1980s. See <a href="http://www.ibpsa.org/proceedings/BS2013/p_2487.pdf" target="_blank">http://www.ibpsa.org/proceedings/BS2013/p_2487.pdf</a> and
papers referenced therein. In particular,<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-GB">Carroll, J. A., 1980. An ‘MRT Method’ of Computing Radiant Energy Exchange in Rooms, Proc. Second Systems Simulation and Economic Analysis Conference, San Diego, CA.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<div>
<p class="MsoNormal"><span lang="EN-GB">At thermal wavelengths, air (especially humid air) is hazy. Depending on space size, some/most of the thermal radiant will be absorbed before it reaches other surfaces. But it takes a big space (read "SuperDome") for
the effect to be very significant.<o:p></o:p></span></p>
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<div>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-GB">CSE creates a virtual surface that participates in the long-wave radiant network. For an example 2850 ft2 zone with 24528 ft2 surface area (including partitions) exposed to the room air, the air "surface" area is 1784
ft2 or about 7%. So the effect is modest but not entirely negligible.<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-GB">Common comfort assessment methods (PMV / PPD) use MRT that is generally calculated directly from surface temperatures (in other words, ignoring the shielding effect of intervening air). That method introduces an error
for large spaces but is generally a reasonable approximation.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB">I don't think there would be much effect on small scales that would be seen within cooling equipment.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB">AFAIK, EnergyPlus does not represent this effect, although I may be wrong. It certainly could, given that it uses a first-principles heat balance zone model.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
</div>
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<p class="MsoNormal"><span lang="EN-GB">Chip Barnaby<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
</div>
<div id="m_3861706110741405111sig30953961">
<div>
<p class="MsoNormal"><span lang="EN-GB">--<o:p></o:p></span></p>
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<div>
<p class="MsoNormal"><span lang="EN-GB">Charles S. "Chip" Barnaby, FIBPSA / FASHRAE<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-GB"><a href="mailto:chipbarnaby@gmail.com" target="_blank">chipbarnaby@gmail.com</a><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-GB">879 Bean Rd, Moultonborough, NH 03254 USA<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-GB">(o) <a href="tel:(603)%20253-4593" target="_blank">
+1 603 253 4593</a> or <a href="tel:(603)%20253-4400" target="_blank">+1 603 253 4400</a> (m)
<a href="tel:(781)%20883-4593" target="_blank">+1 781 883 4593</a><o:p></o:p></span></p>
</div>
</div>
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<div>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<div>
<p class="MsoNormal"><span lang="EN-GB">----- Original message -----<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-GB">From: "Chris Yates via Bldg-sim" <<a href="mailto:bldg-sim@lists.onebuilding.org" target="_blank">bldg-sim@lists.onebuilding.org</a>><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-GB">To: "<a href="mailto:bldg-sim@lists.onebuilding.org" target="_blank">bldg-sim@lists.onebuilding.org</a>" <<a href="mailto:bldg-sim@lists.onebuilding.org" target="_blank">bldg-sim@lists.onebuilding.org</a>><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-GB">Subject: [Bldg-sim] emissivity of air<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-GB">Date: Mon, 3 Apr 2017 13:34:31 +0100<o:p></o:p></span></p>
</div>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB">Dear all,<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<div>
<p class="MsoNormal"><span lang="EN-GB">In IES apache 'simulation options' there is a setting called 'Internal air emissivity model'. This model has the effect of moist air dampening higher radiant temperatures. Apparently, this effect is more pronounced in
large spaces - though I haven't tested this.<o:p></o:p></span></p>
</div>
</div>
<div>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-GB">IES seems to be quite unique in implementing the 'emissivity of air'.<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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<div>
<p class="MsoNormal"><span lang="EN-GB">The concept seems a little unusual to me. So, I was wondering what experiences the simulation community has of this phenomenon? Where else it may be implemented in simulation tools? And, how does it feature for common
comfort temperature assessments involving some combination of radiant temperatures (e.g. operative)?<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
</div>
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<p class="MsoNormal"><span lang="EN-GB">Also, might it also demonstate enhanced comfort for systems with direct adiabatic cooling in dry climates (e.g. spray bar in supply side of AHU)?<o:p></o:p></span></p>
</div>
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<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
</div>
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<p class="MsoNormal"><span lang="EN-GB">Best regards<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-GB">Chris<o:p></o:p></span></p>
</div>
<p><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><u><span lang="EN-GB">_______________________________________________</span></u><span lang="EN-GB"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-GB">Bldg-sim mailing list<o:p></o:p></span></p>
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