Outdoor comfort - Solar Adjusted MRT - Issue with contect

Replies to This Discussion

Permalink Reply by Chris Mackey on November 8, 2014 at 3:20pm

Greetings Fellow Solar MRT Adjustors,

I am pleased to announce that the solar adjusting component now outputs radiant temperature in degrees Celsius instead of radiation flux.  This includes both a legend for the colored mannequin that is in perceived radiant temperature and an output of the perceived radiant temperature of each mannequin mesh face from the component.  This radiant temperature mesh face list corresponds to a list of mesh face areas that are also output from the component such that you can perform statistical analysis on radiant asymmetry over the mannequin to gauge whether a certain temperature difference across the mannequin is of concern.  An important limitation to recognize if you do this type of analysis is that it is assumed that every part of the mannequin has the same clothingAbsorptivity or albedo and, in reality, the absorptivity is likely to differ across articles of clothing and between clothing and skin color so the radiant temperature difference between mesh faces might be much greater.

Furthermore, I have changed the analysisPeriod_ input to analysisPeriodOrHOY_ and this input can now accept specific hours of the year, which should make it easier to do point-in-time studies.  Reiner, I hope this helps with the studies that I saw you setting up and let me know if you experience any bugs or difficulties.

Lastly, I wanted to make a note relating to something that Bernardo asked, which was about the differences between the CBE method used in this component and its application to outdoor solar temperature adjustment.  I have realized that there is an important assumed factor in the CBE method, which is that the radiant heat transfer coefficient is about half of that of the convective heat transfer coefficient.  This is an ok assumption for most indoor conditions when you typically have low wind speeds and people lose about half of their heat to the radiant environment.  This assumption should also be ok if your final measure of comfort is with the PMV, Adaptive, or UTCI components, which will account for wind speed and air temperature in the heat balance.  However, if you are using this component and the CBE method to look at radiant asymmetry in the outdoors resulting from solar radiation, be aware that the MRT delta might not be as large as it seems because the wind speed can be much higher outdoors such that people lose much more heat to the air than the radiant environment.  I summary, I guess that there isn't much of a standard for radiant asymmetry outdoors anyway but I would caution using this component for outdoor radiant asymmetry studies.

You can find the new component in the attached GH file and you can get it in your LB toolbar by syncing with the github.

Enjoy!

-Chris

Permalink Reply by Abraham Yezioro on November 8, 2014 at 11:52pm

Hi Chris,

Just for the sake of trying the component, i did it for the whole year. It is supposed to get results like this? Something strange with the scale legend, isn't it?

-A.

Attachments:

• Capture.PNG, 118 KB

Permalink Reply by Chris Mackey on November 9, 2014 at 2:18pm

Ah.  I know what's happening.  I forgot to average the temperature for longer analysis periods.  Thank you for reporting and I will fix it right now.  I assure you that the comfort mannequin is not feeling radiant temperatures as hot as the surface of the sun.  Although, I guess this is saying that, if all of the sun's energy of a year hit the occupant in a single hour, they would be completely vaporized :)

Permalink Reply by Chris Mackey on November 9, 2014 at 2:57pm

Ok.  It's all fixed.

You can find the fixed component in the attached GH file and on the github.  I deleted the last GH definition so that people don't download the buggy one by accident.  Let me know if you find any other issues.

-Chris

Attachments:

• SolarAdjustedMRT4.gh, 369 KB

Permalink Reply by Reinier Zeldenrust on November 10, 2014 at 7:31am

Thanks Chris, this works well! Both the posture, the MRT, everything! 

Thanks a bunch!

Permalink Reply by Abraham Yezioro on November 10, 2014 at 11:57am

Hmmmmm ... Not so fast. Sorry.

Just opened and run the file you uploaded and the results are not making good sense.

Try month 12 and see the numbers. The scale goes from 20 to over 150 C. But you can try any other date.  I suppose the average process is not fixed yet.

The yearly simulation seems to be ok, though.

-A.

Permalink Reply by Chris Mackey on November 10, 2014 at 6:21pm

Abraham,

As crazy as those numbers seem, they are accurate.  Remember that this number is not surface temperature but is the perceived radiant temperature of the sun from the perspective of the person.

As a point of comparison, imagine taking a thermal camera and pointing it at the sun.  The camera is probably going to give you incredibly high values in excess of 100C and it is this value that is being measured here.

The perceived radiant temperature delta only reaches 130C for a very small portion of the mannequins body (where the camera is pointing directly at the sun), and over the whole person, it's only about an increase of 42 C at noon on the winter solstice (when the sun is most perpendicular to the standing person and the most radiation falls on the body).  Considering that radiant temperature is only half of the total perceived temperature and the air accounts for the other half, the sun is really only helping the person feel about 21C warmer.  So, really all that this is saying is that a person standing outside in 0C weather at noon on the solstice will probably feel fine if they stand in direct sun since this will cause them to experience a total perceived temperature of about 21C.  Let me know if this makes sense.

-Chris

Permalink Reply by Chris Mackey on November 10, 2014 at 7:09pm

An important addendum to my previous comment: I say that a person standing out in the sun at noon on the solstice in 0C weather will be comfortable but it is important to stress that this comfort is only thermal.  As you would see in the file, when the mannequin is in its default position at this hour, it is basically staring directly into the sun and there is no doubt that there would be some serious glare issues.  If you rotate the mannequin 90 degrees (as any normal human being would probably do in this case) the mean radiant temperature delta drops substantially.

Permalink Reply by Abraham Yezioro on November 11, 2014 at 12:03am

Hi Chris,

I'll take a look at the paper you referenced in the component.

I'm thinking about what will be the better way (or any way) to test the results ...

By now i'll give it a rest.

Thanks for your explanations!!

-A.

Permalink Reply by Berardo Matalucci on November 11, 2014 at 7:13am

Thank you Chris. I really appreciate your efforts to improve this great tool.

ber

Permalink Reply by Chris Mackey on November 14, 2014 at 6:38pm

Glad you're finding it useful, Bernardo!

Abraham, if this would put you a bit at ease, I did a quick 2-minute validation of those december conditions against the CBE's online SolarCal tool (http://smap.cbe.berkeley.edu/comforttool):

As you can see in the image, I got an MRT Delta of 40.2 C, which is pretty close to the ~42 C MRT Delta that we were getting over the whole mannequin in the outdoor conditions of noon on the NYC solstice.  I'm going to do a more in-depth validation of the tool for a conference paper this weekend and I'll post the link to the paper here once it gets past peer review in another few weeks.  For now, feel free to check your MRT values against the CBE Tool if you would like another source to ease your skepticism.

-Chris

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