[TRNSYS-users] meteo data files

Michaël Kummert kummert at engr.wisc.edu
Mon Dec 6 08:46:43 PST 2004

Ruut, Werner,

My understanding is also (like Ruut) that Meteonorm generates hourly 
data using measured (or spatially interpolated) monthly average values. 
The first volume of the Meteonorm documentation (theroy_1.pdf) explains 
the generation of hourly values.
I am not certain that real data hourly is not used for some stations in 
Europe (so I am not really contradicting Werner ;-), but if you use 
Meteonorm to generate data in the US, it will use the long-term averages 
from the US-TMY data but it will NOT reproduce recorded hourly data 

The US-TMY2 files compiled by NREL (which are distributed with TRNSYS 
16) consist of 12 actual months that were selected to match the 
long-term statistical properties of the data. On the other hand, 
Meteonorm files for the US are generated using the same long-term 
average values but do not represent actual hourly data.

Based on the situation for the US, my understanding is that Meteonorm 
always uses monthly averages to generate hourly data. In a majority of 
cases, the stations selected in the TRNSYS database are the ones were 
(monthly?) recorded solar radiation data was available, but we also had 
to include a certain number of stations for which even the monthly 
average values are spatially interpolated between locations where data 
is available. For that reason, Meteonorm files should always be used 
with care and they should probably not be used if you are looking for 
more than an estimation of the monthly/yearly performance of your system.

This being said, Meteonorm is one of the most complete databases that I 
know of. From what I know its quality is comparable to the IWEC database 
from ASHRAE, for example (but it has far more stations). If you do have 
actual hourly data from a national weather service (such as the US-TMY2 
database), it is still better to use those files in my opinion.

If some users have further questions on the Meteonorm data, please send 
them to me (no need to use the list). I will compile them, ask them to 
Meteotest and report the answers to this list.

Kind regards,

Michaël Kummert

Werner Keilholz wrote:
> Ruut,
> is it possible that you are not looking at the latest version of 
> Meteonorm ?
> The latest version is 5.1
>  Brief description
> * Features METEONORM 5.0*
>    * Climatological data of 7 400 weather stations. 4 500 new stations
>      added. /Updated/
>    * Measured parameters: radiation, temperature, humidity,
>      precipitation, days with precipitation, wind speed and direction,
>      sunshine duration.
>    * New derived parameters: driving rain, spectral UVA/B and erythemal
>      radiation. /New/
>    * Use of satellite data for areas with low density of weather
>      stations. /New/
>    * Complete coverage of the globe, including polar regions. /New/
>    * Interpolation model for parameters for any site in the world. Updated
>    * Inclusion of current monthly radiation and temperature data by
>      internet. /New/
>    * Import of user data.
>    * Calculation of radiation for inclined surfaces.
>    * Effects of high horizon considered in radiation calculations. High
>      horizon calculated automatically for Switzerland, based on digital
>      terrain model. /Updated/
>    * Adaptation of algorithms to latest results of EU Research Program
>      FP5. /Updated/
>    * Calculation of daily sunrise and sunset.
>    * Graphical interface: Site selection on map. Data output displayed
>      graphically.
>    * 18 different predefined output formats as well user-definable
>      output format. /Updated/
>    * Low price: data and models on one CD-ROM for the price of a few
>      hours of work.
> Detailed description of METEONORM 5.0: Download 
> <http://www.meteotest.ch/pdf/am/mn_description.pdf> 439 kB
> http://software.cstb.fr/soft/present.asp?context=Meteonorm&langue=us&cd=n
> Ruut Brandsma wrote:
>> As far as I know MeteoNorm version 5.0 still works with hourly 
>> generated data based on measured monthly data.
>> A quote from the MeteoNorm v5.0 manual:
>> ----------- BEGIN OF QUOTE -----------
>> What is Meteonorm?
>> METEONORM is a comprehensive climatological database for solar energy 
>> applications:
>> -    a meteorological database containing comprehensive climatological 
>> data for solar engineering applications at every location of the globe.
>> -    a computer program for climatological calculations.
>> -    a data source for engineering design programs in the passive, 
>> active and photovoltaic application of solar energy with comprehensive 
>> data interfaces.
>> a standardization tool permitting developers and users of engineering 
>> design programs access to a comprehensive, uniform data basis.
>> meteorological reference for environmental research, agriculture, 
>> forestry and anyone else interested in meteorology and solar energy.
>> What is it based on?
>> METEONORM's orderly facade conceals not only numerous databases from 
>> all parts of the world but also a large number of computational models 
>> developed in international research programs.
>> METEONORM is primarily a method for the calculation of solar radiation 
>> on arbitrarily orientated surfaces at any desired location. The method 
>> is based on databases and algorithms coupled according to a 
>> predetermined scheme. It commences with the user specifying a 
>> particular location for which meteorological data are required, and 
>> terminates with the delivery of data of the desired structure and in 
>> the required format.
>> Depending on user requirements, the calculation procedure employs 
>> between one and four computation models):
>> The table shows the sequence in which the computational models are 
>> coupled in generating hourly radiation data on an arbitrarily 
>> orientated surface at a site for which no measurements are available.
>> ------- BEGIN TABLE ---------
>> Interpolation with monthly average value model Gh, Ta:
>> Space dependent interpolation of horizontal radiation and temperature 
>> based on weather data taking altitude, topography, region, etc. into 
>> account
>> Hourly value generator Gh, Ta:
>> Stochastic generation of time dependent global horizontal radiation 
>> and temperature data having a quasi-natural distribution and an 
>> average monthly value equal to the average value over 10 years
>> Radiation resolution Gh ® Dh, Bn:
>> Resolution of global radiation into diffuse and direct components
>> Radiation on inclined surface with skyline effect, hourly value model Gk:
>> Calculation of hemispherical radiation on arbitrarily orientated 
>> surfaces taking the reduction due to skyline profile into account 
>> ------- END TABLE ---------
>> In addition to the monthly values, METEONORM provides maximum 
>> radiation values under clear sky conditions. For Switzerland, 
>> standardized data (design reference years) for building simulation 
>> purposes are available for a number of locations.
>> Which data for what problem?
>> Depending on his/her specific requirements, the user must choose the 
>> most suitable method from among the numerous procedures available in 
>> METEONORM. To provide the user with the best possible service, a whole 
>> series of dependent parameters in addition to the measured data are 
>> available. In choosing the data, the quality and relevance of the 
>> basis data sets must be considered. The following criteria should be 
>> applied:
>> Measured and interpolated monthly values are of similar precision. 
>> Although measured data reflect the specific characteristics of a local 
>> site, they are always subject to measurement errors, and these tend to 
>> be compensated by the interpolation process. Interpolated data should 
>> therefore be used at sites with no weather station in the vicinity 
>> (approx. 20 km distance).
>> Dependent parameters such as diffuse radiation, celestial radiation, 
>> dew point temperature, etc., which are determined from calculated as 
>> opposed to measured data, are subject to greater inaccuracy owing to 
>> error propagation.
>> Design reference year - DRY - data (for Switzerland only) should 
>> preferably be used in situations for which they were generated and 
>> tested, i.e. for building simulations. This is because, like generated 
>> data, they are produced from original data via a data transformation 
>> procedure.
>> What has changed since the last edition?
>> The new version 5.0 includes much more data and many additional features:
>> First of all the climatological mean values of approx. 4'500 Stations 
>> all around the world were added. These mainly contain monthly values 
>> of air temperature, wind speed, humidity, precipitation and days with 
>> rain. In version 5.0 about 7'000 stations are directly accessible.
>> Use of satellite pictures for radiation measurements for areas with 
>> low density of radiation network.
>> Inclusion of current data (monthly means) for control of systems. The 
>> current data are accessible by internet.
>> Automatic calculation of high horizons. In Switzerland high horizons 
>> can be calculated automatically based on a digital terrain model.
>> Adaptation of the algorithms to the latest results found in the 
>> European Union Information Society Technology research project SODA 
>> and addition of more parameters (driving rain, UV).
>> Enhanced temperature generation based on measured distributions. Mean 
>> minimum design temperatures (1 and 4 day minimum temperatures) now 
>> included (e.g. output format sia 380/1).
>> The new edition includes 4 new output formats for TRY/WUFI (German 
>> test reference years, WUFI import format), Spectral (UVA/B and 
>> erythemal radiation), Meteo Matrix (TISO) and PVS.
>> The on-line-help has been enhanced.
>> The polar regions were added. METEONORM can now really covers the 
>> whole world.
>> The monthly radiation model - a relict of 1992 METEONORM Version 1.0 - 
>> was removed.
>> How precise is METEONORM?
>> Owing to the comprehensive framework chosen for the present edition, 
>> certain inconsistencies could not be avoided. However, it is always 
>> possible to establish which data basis and algorithms were used. 
>> Differences between the various data bases and algorithms may be 
>> summarized as follows:
>> Quality of basis data:    The radiation data was subjected to 
>> extensive tests. The error in interpolating the monthly radiation 
>> values was 15%, and for temperature 1.3°C.
>> Climatic variations:    The METEONORM radiation data base is based on 
>> 10-year measurement periods, the other parameters mainly on 1961-90 
>> means. Comparisons with longer term measurements show that the 
>> discrepancy in average total radiation due to choice of time period is 
>> less than 2% for all weather stations.
>> Computational models:    The models used in METEONORM are designed to 
>> calculate radiation on inclined surfaces and additional parameters. 
>> One or more models are used depending on data basis. If the results 
>> are to be passed on for further processing, the data basis and models 
>> used should be specified to ensure that the results are correctly 
>> interpreted.
>> In general, the hourly model tends to overestimate slightly the total 
>> radiation on inclined surfaces by 1%. The discrepancy compared to 
>> measured values is ±6% for individual months and ±3% for yearly sums.
>> It is important for users of METEONORM to be aware that the data basis 
>> and computational models only approximate the real situation. 
>> Notwithstanding this, the variation in measured total radiation 
>> between one year and another is greater than the inaccuracy in the 
>> models. ----------- END OF QUOTE -----------
>> Regards, Ruut Brandsma
>> -----Original Message-----
>> From: trnsys-users-admin at engr.wisc.edu
>> [mailto:trnsys-users-admin at engr.wisc.edu]On Behalf Of Werner Keilholz
>> Sent: donderdag, december 02, 2004 13:01
>> To: trnsys-users at engr.wisc.edu
>> Subject: Re: [TRNSYS-users] meteo data files
>> Hi Isabelle,
>> The data is based on hourly data.
>> In the present version, most of the data is taken from the GEBA 
>> (Global Energy
>> Balance Archive), from the World Meteorological Organization (WMO/OMM) 
>> Climato-logical Normals 1961-1990 and from the Swiss database compiled 
>> by MeteoSwiss.
>> Interpolations are made for certain variables which are not available 
>> at a given site.
>> If you install the additional French weather data distributed by CSTB
>> (in \Trnsys16\Weather\Meteonorm\Europe\France)
>> you will find a readme.htm file which explains which parameters are 
>> measured
>> for each site.
>> You find details about meteonorm at
>> http://software.cstb.fr/soft/present.asp?langue=us&m=lpr&context=Meteonorm 
>> Werner
>> Isabelle BRUYERE wrote:
>>> Hi everybody,
>>> Can anyone tell me how the meteo files available for Europe in TRNSYS 
>>> 16 were built ? I've read in the documentation that
>>> "All files were generated using default options in Meteonorm 
>>> V5.0.13". Does that mean that data sets of hourly  values were built 
>>> using mean daily values ? Or is it derived from real hourly mesures 
>>> for many years (like the US-TMY2 data) ?
>>> Thanks a lot already.
>>> Best regards,
>>> Isabelle Bruyère
>>> *Isabelle Bruyère                                                
>>> *Université Catholique de Louvain                        Place du 
>>> Levant, 1 à 1348 Louvain-la-Neuve
>>> Unité d'architecture - Architecture et Climat           Tél : 010/47 
>>> 21 38 - Fax : 010/47 21 50
>>> http://www-climat.arch.ucl.ac.be/


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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