gendaylit and epw weather files, minutes field

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.




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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