[TRNSYS-users] Type 109 weather processor

[Michaël Kummert]

Rémi,

> Does anyone know if and how Type109 manipulates the data that it reads?  I
> am using Type109 to read the CA-QC-Montreal-716270.tm2 that comes with
> TRNSYS.  The output values from type 109 don't match the data that is in the
> file.  It seems to only be right on the first hour of the year. 
> 
> Also doesn't wind direction in TMY give N=0?  TRNSYS output is supposed to
> be N=180, but it doesn't seem to be changed from the input data.

What you are observing is just a difference between instantaneous values 
and hourly averages. In TRNSYS, all variables are average values over 
the simulation time step (and the convention is that values are reported 
at the end of the time step). So if TRNSYS outputs an ambient 
temperature of 2.32 at TIME=2, it means the average temperature between 
01:00 and 02:00 on January 1st was 2.32.
Weather data files typically include instantaneous values for 
temperature, humidity, etc. so all data readers in TRNSYS calculate the 
average value from 2 instantaneous values. Type 109 also applies a 
spline interpolation to Temperature, which explains that the average is 
not the exact mean value between 2.4 and 2.2. Note that solar radiation 
is usually provided as an average value in weather data files so that 
variable is not modified when you use an hourly time step (it is 
interpolated "intelligently" by Type 109 or Type 16 if you use a shorter 
time step).

There are several threads about this in the TRNSYS Mailing list archive, 
e.g: 
http://sel.me.wisc.edu/trnsys/mailinglist/archive1999-2002/msg00735.html

The reason I tried to beat the new TRNSYS engineer in answering you is 
that we noticed a problem in the Meteonorm-generated TMY2 file for 
Montréal (if you plot the temperature you will see what I mean). 
Meteotest has confirmed that this was a bug in the Meteonorm version 
that was used at the time TRNSYS files were generated and they have 
fixed it in Version 5.102. I will send you the corrected file in a 
separate email.

The TRNSYS convention for azimuth angles is indeed to have South = 0 in 
the Northern hemisphere (North = 0 in the Southern hemisphere) and 
positive values towards the West (i.e. East = -90). This convention 
applies to sun angles, walls, windows, solar collectors, etc. but not to 
the wind direction because weather files typically use 0 for North and 
positive towards East. To my knowledge the components that really care 
about wind direction are consistent with this convention (e.g. TRNFLow, 
the version of Type 56 with multizone airflow calculation).

Kind regards,

Michaël Kummert

-- 
_________________________________________________________________

Michaël Kummert

École Polytechnique de Montréal - Génie Mécanique
Case Postale 6079, succursale Centre-Ville
Montréal   QC   H3C 3A7
Canada

Tel: +1 (514) 340-4711, Ext. 3367
Fax: +1 (514) 340-5917
Email : michael.kummert à polymtl.ca