[Bldg-sim] EnergyPlus - Meant Radiant Temperature & DirectSolar Gain

Mon Dec 6 18:28:28 PST 2010

Ross and all,

The one tool I'm aware of that does account for solar radiation (direct,
diffuse, and, if I recall, reflected) striking occupants within a
building is the Advanced Human Thermal Comfort Model from the Center for
the Built Environment at UC Berkeley. The following web page on the CBE
site has information regarding this tool, its development, and a number
of related topics:

http://www.cbe.berkeley.edu/research/briefs-thermmodel.htm

This tool was used in developing a method that may form the basis for a
future National Fenestration Rating Council (NFRC) window comfort rating
method, useful to designers, manufacturers, and consumers. Information
regarding this project and a detailed 91-page technical paper on the
topic are available from the CBE on the following page:

http://www.cbe.berkeley.edu/research/facade_comfort.htm

I highly recommend the technical papers on the page and the previous
one. I hope you find this helpful.

Regards,

Timothy

Timothy Moore 
Special Projects 

timothy.moore at iesve.com <mailto:timothy.moore at iesve.com> 
www.iesve.com <http://www.iesve.com/> 

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From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Cheney
Sent: Monday, December 06, 2010 10:59 AM
To: Harding, Ross
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] EnergyPlus - Meant Radiant Temperature &
DirectSolar Gain

Hi Ross, 

According to Energy Plus engineeringreference " There are three options
to calculate mean radiant temperature in the thermal comfort models. One
is the zone averaged MRT, another is the surface weighted MRT, and the
other is angle factor MRT. The zone averaged MRT is calculated on the
assumption that a person is in the center of a space, whereas the
surface weighted MRT is calculated in consideration of the surface that
a person is closest to, and the angle factor MRT is calculated based on
angle factors between a person and the different surfaces in a space.
Here, the surface weighted MRT is the average temperature of the
selected surface and zone averaged MRT and is intended to represent
conditions in the limit as a person gets closer and closer to a
particular surface. In that limit, half of the person's radiant field
will be dominated by that surface and the other half will be exposed to
the rest of the zone. Note that the surface weighted MRT is only an
approximation. The angle factor MRT is the mean temperature of the
surrounding surface temperatures weighted according to the magnitude of
the respective angle factors and allows the user to more accurately
predict thermal comfort at a particular location within a space." 

Meanwhile, the effective temperature of the screen/glazing combination
that is used to calculate the window's contribution to the zone's mean
radiant temperature (MRT) is calculated with respect only to long wave
radiation. Therefore I believe the mean radiant temperature calculation
for energy + does not take into account direct solar radiation through
the window. 

To my understanding, "a person standing near a window" is the
exceptional case when indoor thermal comfort calculation, such as
Fanger's model, is implemented. Please bear in mind, those indoor
thermal comfort equations are normally based upon extensive indoor
survey results and the survey were unlikely carried out in extreme
conditions, such as under direct solar radiation. Fortunately. many
outdoor thermal models are developing recently (i.e. 
http://www.urbanclimate.net/matzarakis/papers/Radiation_6hellenic.pdf).
You may try to explain your scenario with respect to these models. 

A good paper regarding calculation of MRT outdoors can be found at 
http://www.gvc2.gu.se/Ngeo/bjorn/pdf/referee/12%20-%20Thorsson%20et%20al
%202007.pdf

Regards, 

Cheney Chen 

LinkedIN @ http://ca.linkedin.com/pub/yu-cheney-chen/27/637/72b 

On Mon, Dec 6, 2010 at 9:20 AM, Harding, Ross <
ross.harding at built-ecology.com> wrote:

	Hi All,

	Does anyone know if the for mean radiant temperature calculation
for energy plus has the ability to take into account direct solar gain
(ie not indirectly from surfaces)? 

	If not, how could this be accounted for in thermal comfort?
Results from a person standing near a window could be quite misleading
if the direct solar gain is not taken into account.

	Kind Regards

Ross Harding

Built Ecology Specialist

WSP House

70 Chancery Lane

London WC2A 1AF 

T. +44 20 7314 5000

F. +44 20 7314 5111

M.+44 7795 256 549

E. ross.harding at built-ecology.com
<mailto:joshua.kates at built-ecology.com> 

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