Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
(I'm not quite sure about all this "@Joe Huang" twitter stuff, but I did get an e-mail message from UnmetHours informing me of this question :-) )
In answer to the original question, i.e.., "the best way to find the type of sky (whether it is overcast, sunny clear, clear, uniform cloudy) in EnergyPlus", I have the following comments and suggestions: 1) EnergyPlus *.epw is just a derivative file format, so that the data contained depends entirely on the original provider of the weather file, such as NREL for the US TMYs , ASHRAE for the international IWECs, etc. 2) 99% of the weather files currently available are processed from standard weather station reports, although they don't carry over all the reported data, and also calculate a number of parameters, i.e., solar radiation and illuminances, that are not reported but needed for simulation programs. 3) Standard weather station reports contain a field called "Present Weather", which uses a 2-number code for the weather conditions that hour (00 = clear, 01 = clouds dissolving, 04 = haze, etc.). Unfortunately, most processed weather files do not include Present Weather, and even when they do (TMYs, IWECs) I'm not sure if they are retained when converted to epw. 4) I'm not familiar what is "Daylighting Model Sky Clearness". There is no such term in either the source or processed weather data of which I'm aware. 5) The closest weather fields I can think of are the TotalSkyCover or OpaqueSkyCover (always missing in my experience), which range from 0 to 10 as tenths of the sky dome covered by clouds. This field (TotalSkyCover) is almost always reported, as well as retained in most *.epw files, since it's a primary component used to calculate Solar Radiation. 6)Although there's clearly some correlation between TotalSkyCover and PresentWeather, it's not an exact match (e.g., does 5 indicate that half the sky is covered, or the whole sky is covered to 50% opacity?) and I don't know of anyone who's attempted to correlate the two.
| | 2 | No.2 Revision |
(I'm not quite sure about all this "@Joe Huang" twitter stuff, but I did get an e-mail message from UnmetHours informing me of this question :-) )
In answer to the original question, i.e.., "the best way to find the type of sky (whether it is overcast, sunny clear, clear, uniform cloudy) in EnergyPlus", I have the following comments and suggestions:
suggestions:
1) EnergyPlus *.epw is just a derivative file format, so that the data contained depends entirely on the original provider of the weather file, such as NREL for the US TMYs , ASHRAE for the international IWECs, etc.
2) 99% of the weather files currently available are processed from standard weather station reports, although they don't carry over all the reported data, and also calculate a number of parameters, i.e., solar radiation and illuminances, that are not reported but needed for simulation programs.
programs.
3) Standard weather station reports contain a field called "Present Weather", which uses a 2-number code for the weather conditions that hour (00 = clear, 01 = clouds dissolving, 04 = haze, etc.). Unfortunately, most processed weather files do not include Present Weather, and even when they do (TMYs, IWECs) I'm not sure if they are retained when converted to epw.
epw.
4) I'm not familiar what is "Daylighting Model Sky Clearness". There is no such term in either the source or processed weather data of which I'm aware.
aware.
5) The closest weather fields I can think of are the TotalSkyCover or OpaqueSkyCover (always missing in my experience), which range from 0 to 10 as tenths of the sky dome covered by clouds. This field (TotalSkyCover) is almost always reported, as well as retained in most *.epw files, since it's a primary component used to calculate Solar Radiation.
6)Although
6) Although there's clearly some correlation between TotalSkyCover and PresentWeather, it's not an exact match (e.g., does 5 indicate that half the sky is covered, or the whole sky is covered to 50% opacity?) and I don't know of anyone who's attempted to correlate the two.
I don't want to venture any suggestions, as I'm not sure of the objective or need for the weather condition.
| | 3 | No.3 Revision |
(I'm not quite sure about all this "@Joe Huang" twitter stuff, but I did get an e-mail message from UnmetHours informing me of this question :-) )
In answer to the original question, i.e.., "the best way to find the type of sky (whether it is overcast, sunny clear, clear, uniform cloudy) in EnergyPlus", I have the following comments and suggestions:comments:
1) EnergyPlus *.epw is just a derivative file format, so that the data contained depends entirely on the original provider of the weather file, such as NREL for the US TMYs , ASHRAE for the international IWECs, etc.
2) 99% of the weather files currently available are processed from standard weather station reports, although they don't carry over all the reported data, and also calculate a number of parameters, i.e., solar radiation and illuminances, that are not reported but needed for simulation programs.
3) Standard weather station reports contain a field called "Present Weather", which uses a 2-number code for the weather conditions that hour (00 = clear, 01 = clouds dissolving, 04 = haze, etc.). Unfortunately, most processed weather files do not include Present Weather, and even when they do (TMYs, IWECs) I'm not sure if they are retained when converted to epw.
4) I'm not familiar what is "Daylighting Model Sky Clearness". There is no such term in either the source or processed weather data of which I'm aware.
5) The closest weather fields I can think of are the TotalSkyCover or OpaqueSkyCover (always missing in my experience), which range from 0 to 10 as tenths of the sky dome covered by clouds. This field (TotalSkyCover) is almost always reported, as well as retained in most *.epw files, since it's a primary component used to calculate Solar Radiation.
6) Although there's clearly some correlation between TotalSkyCover and PresentWeather, it's not an exact match (e.g., does 5 indicate that half the sky is covered, or the whole sky is covered to 50% opacity?) and I don't know of anyone who's attempted to correlate the two.
I don't want to venture any suggestions, as I'm not sure of the objective or need for the weather condition.
