[Radiance-general] Meaning of EPW file's minute field and why is it 60 in TMY2-based EPW and 0 in TMY3-based EPW?

[Tim Perry]

If you take a look at the tmy2 man page, you'll see that illuminance is for
the 60 minutes preceding the time. Thus, the values for a time of "10:60"
maps to the hour starting 10:00:00 and ending at 10:59:59.
From: http://rredc.nrel.gov/solar/pubs/tmy2/pdfs/tmy2man.pdf

Field Position

Element
[image: page26image4992] [image: page26image5312]

Values
[image: page26image6240] [image: page26image6560] [image: page26image7032]

Definition
[image: page26image8224]

030 - 035

030 - 033 034
035

Diffuse Horizontal Radiation Data Value
Flag for Data Source
Flag for Data Uncertainty

0 - 700 A - H, ?

0-9
[image: page26image14200] [image: page26image14520]

Amount of solar radiation in Wh/m2 received from the sky (excluding the
solar disk) on a horizontal surface* during the 60 minutes preceding the
hour indicated *
[image: page26image17168]

036 - 041

036 - 039 040
041

Global Horiz. Illuminance Data Value
Flag for Data Source
Flag for Data Uncertainty

0 - 1300 I, ?

0-9

Average total amount of direct and diffuse illuminance in hundreds of lux
received on a horizontal surface *during the 60 minutes preceding the hour
indicated.*
0 to 1300 = 0 to 130,000 lux

042 - 047

042 - 045 046
047

Direct Normal Illuminance Data Value
Flag for Data Source
Flag for Data Uncertainty
[image: page26image28000] [image: page26image28320]

0 - 1100 I, ?

0-9
[image: page26image30064]

Average amount of direct normal illuminance in hundreds of lux received
within a 5.7 degree field of view centered on the sun *during the 60
minutes preceding the hour indicated*. 0 to 1100 = 0 to 110,000 lux

048 - 053

048 - 051 052
053

Diffuse Horiz. Illuminance Data Value
Flag for Data Source
Flag for Data Uncertainty
[image: page26image36608] [image: page26image36928]

0 - 800 I, ?

0-9
[image: page26image38672]

Average amount of illuminance in hundreds of lux received from the sky
(excluding the solar disk) on a horizontal surface *during the 60 minutes
preceding the hour indicated.*
0 to 800 = 0 to 80,000 lux



On Tue, Apr 4, 2017 at 3:06 AM, Philip Schwarz <
philip.johann.schwarz at googlemail.com> wrote:

> Hello everyone,
>
> I am new to EnergyPlus, Daysim and Radiance. I am looking at the process
> of converting EPW files to WEA files.
>
> I am trying to understand the meaning of the minute field in an EPW file.
>
> I read in http://www.radiance-online.org/pipermail/radiance-
> general/2012-October/008968.html that the minutes field does not relate
> to '*the time when the measurement was recorded, but to the **recording
> interval'.*
>
> The EPW Data Dictionary (http://bigladdersoftware.com/epx/
> docs/8-3/auxiliary-programs/energyplus-weather-file-epw-
> data-dictionary.html#field-minute) is not useful for understanding the
> meaning of the minutes field, as it simply says:
>
> * Field: Hour - This is the hour of the data. (1 - 24). Hour 1 is 00:01
> to 01:00. Cannot be missing.
>
> * Field: Minute - This is the minute field. (1..60)
>
> If I take the EPW file for Gatwick Airport in London (
> https://energyplus.net/weather-location/europe_wmo_
> region_6/GBR//GBR_London.Gatwick.037760_IWEC) I see that its minute
> fields are set to 60 (hours and minutes in bold):
>
> ...
>
> DATA PERIODS,1,1,Data,Sunday, 1/ 1,12/31
>
> 1991,1,1,*1,60*,...
>
> 1991,1,1,*2,60*,...
>
> ...
>
> If instead I take the TMY3-based EPW file for Central Park in New York (
> https://energyplus.net/weather-location/north_and_
> central_america_wmo_region_4/USA/NY/USA_NY_New.York-
> Central.Park.725033_TMY3), I see that its minute fields are set to 0 :
>
> ...
>
> DATA PERIODS,1,1,Data,Sunday, 1/ 1,12/31
>
> 1976,1,1,*1,0*,...
>
> 1976,1,1,*2,0*,...
>
> ...
>
> Yet if I take the TMY2-based EPW file for Central Park in New York (
> https://energyplus.net/weather-location/north_and_
> central_america_wmo_region_4/USA/NY/USA_NY_New.York.City-
> Central.Park.744860_TMY2), I see that its minute fields are set to 0:
>
> ...
>
> DATA PERIODS,1,1,Data,Sunday, 1/ 1,12/31
>
> 1976,1,1,*1,60*,...
>
> 1976,1,1,*2,60*,...
>
> ...
>
> Can someone please explain in simple terms what the meaning is of the
> minutes field?
>
> Why is there a difference in the value of the minutes fields in the
> IWEC-based EPW file for Gatwick (value is 0) and in the TMY3-based EPW file
> for Central Park (value is 60)? What is the minutes field telling me about
> the data?
>
> Why is there a difference in the value of the minutes fields in the EPW
> file for Central Park depending on whether it is TMY2-based (in which case
> the value is 60) or TMY3 based (in which case the value is 0)?
>
> Thank you in advance for your help,
>
> Philip Schwarz
>
>
> _______________________________________________
> Radiance-general mailing list
> Radiance-general at radiance-online.org
> http://www.radiance-online.org/mailman/listinfo/radiance-general
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.radiance-online.org/pipermail/radiance-general/attachments/20170405/3e28d3a4/attachment.html>