[TRNSYS-users] Sebha Weather Generation

Michaël Kummert kummert at engr.wisc.edu
Fri Nov 5 08:28:44 PST 2004


> I used Type 54a to generate meteorological year depending on average 
> meteorological data of weather records at Sebha city at the south of 
> Libya as shown below:
> ...
> I got two questionable results:
> 1^st - *higher than normal daily ambient temperatures*, and my question 
> here is regarding, what average of daily monthly ambient temperatures I 
> should use in table 1 above, is it the average of Maximum daily monthly 
> ambient temperature or the average of Minimum daily monthly ambient 
> temperatures or the average of both such as:
> Average daily monthly ambient Temp. = (Average Tmax + Average Tmin)/2    ……?

The values you need to provide are monthly averaged temperatures, so it 
is none of the options you propose if I am right. The last option would 
be the closest to what you need if you assume the average temperature 
during a day is the same as (Tmin+Tmax)/2.
The concept of Monthly average daily "something" is only used for 
radiation in Type 54 (because you average the daily sum of irradiation 

> 2^nd – *the sum of Beam and Diffuse Irradiation give not the Global 
> Irradiation as it must be…? and* *The values of Beam (direct) 
> irradiation are higher than the values of Global irradiation during 
> summer months ( the Table 3 below contains the resulted monthly 
> integrated values of Solar Irradiation),* my question is where is the 
> mistake…..? since :
> /G_h must equal (G_bh + G_dh ), where: G_h is the Global Horizontal 
> Irradiance, G_bh is the Beam Horizontal Irradiance and G_dh is the 
> Diffuse Horizontal Irradiance./

I am assuming you are using outputs 7-9 of Type 54. Output 7 is the 
direct normal radiation (Gbn), not the direct (beam) horizontal 
radiation (Gb). So it should not be equal to (global horizontal - 
diffuse horizontal). If you want the beam horizontal radiation (Gb) you 
have to substract output 9 (Gd, diffuse horizontal) from output 7 (G, 
global horizontal). Or you can use Type 16, which you always need to do 
if you want to use sub-hourly time steps or calculate the radiation on a 
tilted surface.

Kind regards,

Michaël Kummert


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

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