[Bldg-sim] Errors in TMY3 Files

[Joe Huang]

Interesting to see my work described by someone who was never involved. The original 
driver for doing that work was to correct the decimal mistake in some of the illuminance 
data that NREL had noted in 2005 but never corrected because the original developers had 
retired. The reporting of precipitation was an additional improvement I offered to NREL, 
and actually ended up the lion's share of the work because it required reprocessing all 
the source weather files.  Neither of these corrections/improvements should affect any 
other weather set developed from scratch.  i have always been careful to not infringe on 
NREL's branding of TMY for a number of reasons, one of which has just been shown that all 
TMYs are assumed to be related.

Joe

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
yjhuang at whiteboxtechnologies.com
http://weather.whiteboxtechnologies.com for simulation-ready weather data
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"

On 12/21/2020 3:04 PM, Linda Lawrie via Bldg-sim wrote:
> the TMY3 files on climate.onebuilding.org have been corrected from the document posted 
> by Joe Huang on the tmy3 site. But I think that was for precipitation.
>
> the TMYx files would never have had this problem as they come from a different source of 
> our creation for the TMYx files.
>
> And, as I remember, the illuminance problem was corrected by NREL at some point after 
> their first post.
>
> ------
> Linda
>
> FIBPSA, FASHRAE
> http://climate.onebuilding.org <http://climate.onebuilding.org/> - free repository of 
> climate data for building simulation
> Climate.onebuilding is a FREE service not supported by any outside organization or 
> government agency.
>
>
>
>> Does anyone know if the errors described in TMY3 files in this post from Joe Huang on 
>> Jan 14 2015 still exist in files on the http://climate.onebuilding.org/ 
>> <http://climate.onebuilding.org/> website? And were these errors also fixed in TMYx files?
>>
>> Specifically I’m interested in this issue:
>>
>>
>> 1) Illuminance. The TMY3s contain values for Global Horizontal, Direct Normal, Diffuse
>> Horizontal, and Zenith Illuminance that are calculated based on the sun position and solar
>> radiation. Although the documentation states that the units are 100 lux for the first
>> three illuminances, and 10 candela/m2 for the Zenith Illuminance, all the TMY3 files used
>> these units only for the period Jan. 2-31, and for the rest of the year used units of lux
>> and candela/m2, respectively. NREL put out a notice in August 2008 (see the link listed
>> earlier) informing users of this discrepancy and promising a corrected version that didn't
>> make it out until now! In this revision, we've decided to keep the units in the original
>> TMY3 documentation, i.e., 100 lux or 10 candela/m2, which is the same as what was in the
>> TMY2, and avoids the superfluous five-digit precision.
>>
>> If I use a TMY3 or TMYx file from the climate.onebuilding.org website, am I getting a 
>> TMY3 or TMYx version in which these issues are corrected?
>
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