[esp-r] Mean Radiant Temperature

[francesco.frontini at polimi.it]

Dear All,
I have a question about MRT.

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). 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.
Could you please send me the formula that ESP-r uses for the MRT  
calculation? Is there any approximation that would not be appropriate  
for low-emissivity surfaces?

I model the double glazing façade with the internal blind like a  
single construction (no air-ventilation between the glass and the  
blind). I set the U-value for each façade construction (it is similar  
but not identical for the two different solutions, U=0,985+-0,005,  
obtained from the WIS calculation), and the g-value. What changes in  
the model is the emissivity of the indoor-facing surface of the blind  
(e=0,9 for the first case and e=0,5 for the second one!), whereas the  
solar-optical properties remain the same for the two blinds. In the  
WIS model, the emissivity of the two blind surfaces is specified  
separately.  For both blinds, the emissivity of the outdoor-facing  
surface in the WIS model is 0.9.


Looking forward to your answer and thanking you for your help.
Any advice and help on this will be much appreciated.

Francesco Frontini