USA weather data

[Michael Hurd]

I can find no source of weather data in the USA that includes all of the data that WUFI needs to perform calculations. I have been told that NCDC has the data but to my knowledge this is incorrect. The NCDC data lacks the global and diffuse radiaton data. Can you tell me the source of weather data for the US cities that are currently included in WUFI? Perhaps we could contact that source for additional weather data for cities not included in WUFI.

[Thomas]

Dear Mr. Hurd,

the US weather data were provided by Dr. Karagiozis from ORNL (karagiozisan@ornl.gov) who obtained them from ASHRAE. If you cannot find measured weather data for the location of interest you may be able to create a weather data file with the METEONORM software which creates synthetic hourly weather data for any location, based on a global database of monthly mean values. Those files appear to work well for hygrothermal simulations, one of the available file formats can be read by WUFI.

Regards,
Thomas

[Michael Hurd]

Thanks again Thomas!

[Michael Hurd]

Is it necessary that the global and diffuse radiation data be from the same year as the balance of the other weather data required for WUFI? I have found a source for the radiation data but it does not have the temperature, wind, rain, etc. I have a separate source for the other data but it is for a different set of years.

[Thomas]

There may be applications for which mixing weather elements from different years might work, but in general I would not recommend this.

For example, if the wall surface is wet from rain and you have strong sunshine on the surface, the high vapor pressure of the heated moisture will drive a strong vapor flow into the wall, and if the outer wall layers are permeable enough, this may contribute to the moisture load on the construction ("reverse condensation" or "summer condensation"). In reality this happens, for example, after a thunderstorm in summer when after a short but intense rain the clouds depart and the summer sun can shine on the facade. If rain and sunshine in the weather file do not correspond to each other you may have intense sunshine even during rain, which would make the condensation problem in the calculation worse than it actually is.

Another concern might be the vapor pressure of the exterior air. Dull days tend to have high relative humidity, sunny days tend to have low relative humidity. If the sunshine data come from a clear day and result in a warm facade, while the air temperature and humidity data imply high humidity, then this high humidity and the high surface temperature combined imply unrealistically high vapor pressure at the surface, which may again give rise to unrealistic vapor flows.

If your construction happens to be insensitive to these meteorological inconsistenies, you can combine the weather data; otherwise you should not. We are aware that it is often difficult to find appropriate data sets, but I'm afraid we cannot yet offer an easy way out. In many cases, the constructions under investigations are more or less insensitive to rain (e.g. if they have hydrophobic facades or if the cladding is impermeable to rain). So rain is a weather element that can occasionally be neglected, and in these cases it may be easier to find a dataset which is complete except the rain.

Regards,
Thomas

[Ned Lyon]

I would be careful with Meteonorm. While evaluating it I compared a calculated Boston to a WUFI Boston file. Solar was good match, rain amount was reasonable, wind speed was good but direction was about 180 degrees off. Our northeasters became southwesters...may work for some of you....

[Peter Vander Heide]

Ned, which version of Meteonorm did you look at? I'm just thinking about it now, and it looks like a real time saver, if the data is usable.