TYM2 weather data

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Dear All,


I have already converted TYM2 data for Poznan (PL-Poznan-Lawica-123300) from
text file to excel using:

Some of meteorological data, which are there, have additional columns named
Flag of Data Source. Dry bulb temperature is one of these data. In my file
is written that data source for dry bub temperature is E, and in TYM2 manual
(http://rredc.nrel.gov/solar/pubs/tmy2/PDFs/tmy2man.pdf) I have read that it

Modeled or estimated, except: precipitable water, calculated from

radiosonde data; dew point temperature calculated from dry bulb

temperature and relative humidity; and relative humidity

calculated from dry bulb temperature and dew point temperature

Could you explain me what it is mean? I expected that temperature is


The second issue is that I would like to create my own TYM2 file to run
TRNSYS simulation with my own meteorological data. How should I model e.g.
illuminance. of maybe I don't need this value if I use in simulation only:

. Dry bulb temperature,

. Effective sky temperature,

. Humidity,

. Wind velocity and direction,

. Atmospheric pressure,

. Solar zenith and azimuth angle,

. Total surface radiation,

. Beam surface radiation,

. Angle of incidence for surface,

. Ground reflectance.

Which data (columns) do I need in TYM2 file to get above values?

I will be grateful for any tips!!!


Karol Bandurski MSc.

Karol Bandurski's picture
Joined: 2012-03-29
Reputation: 0

Without knowing the specifics of which data file you are using, its
hard to give a definitive answer. My understanding is that the original
set of TMY2 weather files are a series of files that were developed at
NREL for 230 or so sites in the US based on something called the Solmet
data base. Only 30 sites actually had measured data; the rest were
modeled, correlated, statistically processed, etc. The original set of
TMY2 data files for those US cities should not, I think, be confused
with the use of the TMY2 file format for weather files from other cities.

As for your other question, there is no particular need to create a
file that has the TMY2 format if you don't want to. Type9 is designed to
read an interpolate data files. Radiation data read by Type9 can then be
passed to Type16 for processing and calculation of radiation falling on
other surfaces. This saves you the trouble of having to figure out where
to obtain data values for the fields that you don't need in the TMY2
format. Type15 (the weather reader/processor) is really just a
combination of Type9 and Type16 glued together internally and given the
ability to read a series of standard file formats (TMY, TMY2, TMY3, E+,
Kind regards,


David BRADLEY2's picture
Joined: 2011-10-02
Reputation: 0

The only TMY2 files I'm aware are 239 files for US locations. What is the source for the
Poznan file that you mentioned? Are you referring to the IWEC or IMGW file available in
EPW format on the EnergyPlus web site?

It seems you're referring to TMY2 as a format, not a weather file type. The TMY2 format
was developed by NREL, and as in your quote below, it has both measured as well as
calculated data. To explain what the excerpt says,
the TMY2 data format contains dry-bulb, dew-point, and relative humidity. However,
weather stations typically measure only two, mostly dry-bulb and dew-point, in which case
the RH is calculated. On the other hand, if the weather station measurements are dry-bulb
and RH, then the dew-point temperature is calculated.

If you're trying to get your measurements into the TMY2 format, please note that you will
have to calculate quite a bit of information, such as extraterrestrial radiation, three
types of illuminances, precipitable moisture, RH, etc.
If the simulation program you're using (TRNSYS ?) doesn't read those, you could leave them
as empty data fields.

It sounds like you're trying to strip out information from the Poznan TMY2(?) weather file
and then combine that with your measured data. I wouldn't recommend that because the time
sequence is wrong, so I don't know what you'll get in the end.

I've had a lot of experience working with various weather file formats, including TMY2.
Let me know if you have more questions about this.

Joe Huang

Joe Huang's picture
Joined: 2011-09-30
Reputation: 406