[TRNSYS-users] Basic help about Type16i

[thornton at tess-inc.com]

On 2022-05-12 08:56, Nicolas Heijmans via TRNSYS-users wrote:

> I check other models and I guess know that it's not a mistake of mine
> but something inherent to Type16.

All that Type 16 knows is that the total integrated radiation for the 
hour is X.  It doesn't know if it was really cloudy for half the hour 
then sunny for the second hour, partly cloudy for the entire hour, etc.  
So it assumes that the radiation profile mirrors that of the 
extraterrestrial radiation profile over that hour and scales it to match 
the integrated total.  That answer is as defendable as any other 
possible solution.  It does introduce discontinuities at the hourly 
boundaries if you have hourly data.

As for your questions about a "fix"

 From our documentation:

"There are several possible methods of interpolating radiation data. One 
fairly simple method is to linearly
interpolate hourly data to obtain estimates of radiation over shorter 
time intervals. This approach, which
was used in TRNSYS prior to Version 10.1, has several drawbacks. The 
most readily apparent problem is
that positive radiation values are produced before sunrise and after 
sunset. If sunrise is at 6:30 a.m., then
an hourly radiation data file may have a value of zero at 6:00 and 40 
watts/m2 at 7:00. Linear interpolation
will give 10 watts/m2 at 6:15, fifteen minutes before sunrise. This 
problem is compounded by the fact that
the ratio of beam radiation on a tilted surface to that on a horizontal, 
Rb, may become very large near
sunrise and sunset. If the estimate of radiation on the horizontal is 
too large near sunrise, the calculated
radiation on a tilted surface will be immense. Another method uses the 
curve for extraterrestrial radiation
to interpolate radiation data. While this seems to relieve the problems 
encountered with linear
interpolation, it does introduce a characteristic saw-tooth pattern in 
the radiation. With TRNSYS 18 a new
method that uses future values of radiation to produce a smoother curve 
to the sub-data intervals while
still preserving the values from the data file was introduced in Type15 
and a new mode was added to
GetHorizontalRadiation where no interpolation of the horizontal data 
will be performed."


Jeff

-- 
Jeff W. Thornton
President
Thermal Energy System Specialists LLC
3 N. Pinckney Street, Suite 202
Madison WI 53703 USA
(608) 274-2577
www.tess-inc.com