[Bldg-sim] EnergyPlus - Meant Radiant Temperature & Direct Solar Gain

[Cheney]

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
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