[esp-r] R: Mean Radiant Temperature

[Francesco Frontini]

Dear Achim
Yes I have obtained a MRT, close to the blind, higher for the solution with
low-e blind (that has a higer surface temperature). But for my opinion the
MRT has to take into account not only the view factor and the temperature of
the surface but also the emissivity. For that reason I'm also supposing that
with a low emmissivity also the MRT should be low (for exemple if the view
factor is the same: 43,88°x0,9>48.21°x0,5! Where the formula is
(T1(°C)blind)*(emissivity(1))>(T2(°C)blind)*(emissivity(2))!!!). It's not
correct?

Best regards,
Francesco

-----Messaggio originale-----
Da: Geissler Achim [mailto:Achim.Geissler at josef-gartner.ch] 
Inviato: martedì 20 maggio 2008 9.23
A: francesco.frontini at polimi.it; esp-r at lists.strath.ac.uk
Oggetto: RE: [esp-r] Mean Radiant Temperature

Dear Francesco,

> We want to assess the impact on the operative temperature in an office 
> if we use an internal blind with a low-emissivity coating (0,5 
> emissivity for indoor-facing surface) instead of 0.9 emissivity.
> We made two different simulation: static (with WIS program) and 
> Dynamic (ESP-r).

> The results from WIS and from ESP-R for the blind surface temperature 
> are consistent (blind temperature about 5K higher for the 
> low-emissivity blind).
That is good news.

> However, the mean radiant temperature at a position close to the blind 
> (0.5 m in ESP-R) is lower for the high-emissivity blind than the 
> low-emissivity blind with the ESP-R calculation.

As the mean radiant temperature is defined by view factors and surface
temperature, only, all is well, no? The low-e blind has a higher
temperature, thus I would expect the mean radiant temperature close to the
blind to be higher. That is what you seem to have obtained as result?

Best regards,
Achim