# [TRNSYS-users] Sebha Weather Generation

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

```Gassem,

> 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
levels).

> 2^nd – *the sum of Beam and Diffuse Irradiation give not the Global
> Irradiation as it must be…? and* *The values of Beam (direct)
> 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

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

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_________________________________________________________

Michaël Kummert

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