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

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

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.

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

···

From: http://rredc.nrel.gov/solar/pubs/tmy2/pdfs/tmy2man.pdf

On Tue, Apr 4, 2017 at 3:06 AM, Philip Schwarz < [email protected]> 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
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

Sorry, that sent before I was ready. Similar verbiage is found for TMY3 on
http://www.nrel.gov/docs/fy08osti/43156.pdf. My best guess for why there is
a zero in the minutes for Gatwick in the TMY3 and a 60 in the TMY2 is that
someone made a mistake. But I'm sure a more precise answer will emerge on
this list.

Table 1-3. TMY3 data fields (lines 3-8762)

Field

Element

Unit or Range

Resolution
[image: page11image5464]

Description

1

Date

MM/DD/YYYY

···

--

Date of data record

2

Time

HH:MM

--

Time of data record (local standard time)

3

Hourly extraterrestrial radiation on a horizontal surface

Watt-hour per square meter

1 Wh/m2

Amount of solar radiation received on a horizontal surface at the top of
the atmosphere during the 60-minute period ending at the timestamp

4

Hourly extraterrestrial radiation normal to the sun

Watt-hour per square meter

1 Wh/m2

Amount of solar radiation received on a surface normal to the sun at the
top of the atmosphere during the 60- minute period ending at the timestamp

5

Global horizontal irradiance

Watt-hour per square meter

1 Wh/m2

Total amount of direct and diffuse solar radiation received on a horizontal
surface during the 60-minute period ending at the timestamp

On Wed, Apr 5, 2017 at 12:24 PM, Tim Perry <[email protected]> wrote:

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@ > 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_cent
ral_america_wmo_region_4/USA/NY/USA_NY_New.York.City-Centra
l.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
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

A bit more info...

The minute field in the EPW has little meaning (ever) for hourly based
files. Frankly the TMY2 should have been 00 rather than 60. They have some
meaning for subhourly files but aren't ever parsed for EnergyPlus usage.

Note that the TMY3 files on EnergyPlus.net are not updated to the latest
version (TMY3a) from January 2015 (correcting illuminance, precipitation
and a few other issues).

Up to date TMY3a data are available from http://climate.onebuilding.org .
The zips there also include .WEA (Daysim format) as well as EPW, CLM (ESP-r
format) along with substantially expanded statistics. Climate.OneBuilding
has more than 2,200 locations throughout the world -- many not available on
EnergyPlus.net.

···

On Wed, Apr 5, 2017 at 3:27 PM, Tim Perry <[email protected]> wrote:

Sorry, that sent before I was ready. Similar verbiage is found for TMY3 on
http://www.nrel.gov/docs/fy08osti/43156.pdf. My best guess for why there
is a zero in the minutes for Gatwick in the TMY3 and a 60 in the TMY2 is
that someone made a mistake. But I'm sure a more precise answer will emerge
on this list.

Table 1-3. TMY3 data fields (lines 3-8762)

Field

Element

Unit or Range

Resolution
[image: page11image5464]

Description

1

Date

MM/DD/YYYY

--

Date of data record

2

Time

HH:MM

--

Time of data record (local standard time)

3

Hourly extraterrestrial radiation on a horizontal surface

Watt-hour per square meter

1 Wh/m2

Amount of solar radiation received on a horizontal surface at the top of
the atmosphere during the 60-minute period ending at the timestamp

4

Hourly extraterrestrial radiation normal to the sun

Watt-hour per square meter

1 Wh/m2

Amount of solar radiation received on a surface normal to the sun at the
top of the atmosphere during the 60- minute period ending at the timestamp

5

Global horizontal irradiance

Watt-hour per square meter

1 Wh/m2

Total amount of direct and diffuse solar radiation received on a
horizontal surface during the 60-minute period ending at the timestamp

On Wed, Apr 5, 2017 at 12:24 PM, Tim Perry <[email protected]> wrote:

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 < >> [email protected]> 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://bigladderso
ftware.com/epx/docs/8-3/auxiliary-programs/energyplus-weathe
r-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_a
merica_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_cent
ral_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
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general