[TRNSYS-users] Windows shading coefficients

[Michaël Kummert]

Maurizio,
>  
> 1) In my project there are two adjacent buildings but the contact is not 
> direct (air gap of 30 cm) so I need to define a radiation to 2 wall 
> which are always shaded. In PREBID (or TRNBuild) there aren't shading 
> coefficient to reduce the direct solar radiation for the wall (as for 
> the windows), so I think is necessary to modify the radiation in IISiBat 
> (or TRNSYS Studio).
> Type 68 (Shading Masks) seems the correct tool, but I need a external 
> file with the angular obstruction data. Maybe I can use type 34 
> (Overhang and Wingwall shading) in which the dimensions of the 
> obstruction are set to a very high value. Is it exact? Do simpler ways 
> exist to proceed?

You can define a special orientation for completely shaded external 
walls and leave the corresponding radiation inputs unconnected (i.e. 
constant to 0). For the sake of completeness, please note that this will 
not take into account longwave radiation heat exchange between the two 
walls (which I think is OK in your case). However, you should set their 
view factor to the sky to 0.0 since the walls will not have any longwave 
radiation exchange with the sky.

> 2) Last week I have tried to transfer my old Trnsys 15 projects in 
> Trnsys 16. I have a problem with type 16e (Radiation processor) when I 
> try to calculate beam and diffuse radiation for a vertical surface with 
> azimut among 225 (NE) and 315 (SE). The simulation is annual but stop 
> with warnings and error at time 994 with the following notice:
>  
> /TRNSYS Message 450: The maximum number of warnings allowed per 
> simulation has been exceeded. Please fix these warnings or increase the 
> limti on the number of warnings allowed per simulazion (LIMITS command)/
> // 
> The same climatic data return the expected results when I use TRNSYS 
> 15's radiator processor. Non running project is attached.

The problem comes from the new definition of the simulation start time 
in TRNSYS 16: The start time is now really the time at the beginning of 
the simulation (not the time at the end of the first time step). TRNSYS 
16 components are called once (no iterations) during that initialization 
time step and they output their initial values.
That change requires you to handle data files carefully: The first line 
of your data file corresponds to the average values between 00:00 and 
01:00 on January 1st (or the instantaneous values at 01:00). The mode 
you have chosen for Type 9 (mode 2) assumes that initial values ARE 
provided so all values are shifted by one hour, hence the numerous 
warnings that lead to the error message.
You can easily fix the problems by adding a line at the top of the file 
for January 1st at 00:00, or by changing to mode 3 which assumes no 
initial values are provided (using the Type9e proforma, "expert mode"). 
Finally, you might want to use mode 5 or 6 (instead of 2 or 3) since 
your file includes data for a full year. With modes 5 and 6 the 
appropriate number of lines will be skipped in the data file if your 
simulation does not cover a full year (remember to change the start day 
in Type 16!).

Another error I noticed in your file: you have set the data reader to 
interpolate values of solar radiation. Radiation values should never be 
interpolated in Type 9 (the solar radiation processor will interpolate 
them later). Also, you should pay attention to the "instantaneous or 
average" parameters for each column in your file. Typically radiation 
values are averages over the time step but temperature and humidity are 
instantaneous values at the hour.


I hope this helps,

Michaël Kummert

PS. For those of you who might be worried, please note that all standard 
weather files are handled correctly by Type 89 and 109 in TRNSYS 16 
without having to change any setting. You just have to worry about Type 
9 modes if you use custom files.


-- 
_________________________________________________________

Michaël Kummert

Solar Energy Laboratory - University of Wisconsin-Madison
1303 Engr Res Bldg, 1500 Engineering Drive
Madison, WI 53706

Tel: +1 (608) 263-1589
Fax: +1 (608) 262-8464
E-mail: kummert at engr.wisc.edu

SEL Web Site: http://sel.me.wisc.edu
TRNSYS Web Site: http://sel.me.wisc.edu/trnsys