[Radiance-general] gendaylit and epw weather files, minutes field

[Jan Wienold]

Hi Lars,

usually radiation data in weather files is the sum for one hour and not 
the current irradiation for a given time-stamp.

That means e.g. hour no. 8 is the hour between 7:00 and 8:00, the value 
is usually the total sum in Wh between 7 and 8..

Daysim is using the sun position of the middle of the time step, in 
that case would be 7:30.

Be careful about sunset and sunrise!

In case the sunrise would be at 7:40 you run into trouble regarding sun 
position, in that case you might use the middle between sunrise and next 
time step (in that case 7:50). This is also implemented into Daysim.

Cheers,

Jan


Am 16.10.2012 09:26, schrieb Lars O. Grobe:
> Hi all,
>
> while working around reading in values from an epw file for gendaylit
> for climate based simulation, I found some really weird time values 
> in
> my data. The epw file should contain hourly data from 01:00 to 24:00.
> However, I found that the "minutes" field was set to 60 for every
> record, so the last record was 24:60. I tried to figure out what this
> could mean (I was first guessing that the timezone may have been
> applied by adding 60 minutes).
>
> In the end, I got an answer that was rather surprising to me, and
> that I would like to share. The value "60" in the minutes field does
> NOT refer to the time when the measurement was recorded, but to the
> recording interval (hourly). In other words, it has nothing to do 
> with
> the time stamp, but is an integration time. So 24:60 is the value for
> 00:00, and, if I understand this correctly, the values of the record
> should be the average of measurements from 23:30 to 00:30.
>
> For using the data with gendaylit, this means that I sed the minutes
> fields and set it to zero (without incrementing the hours field). Did
> anyone else get stuck with this before? I hope I got it right now...
>
> Cheers, Lars.
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