[Bldg-sim] Precipitation value in stat extension file.

[Mayank Bhatnagar]

Thank you for your valuable suggestions.

Thank you joe, I am looking on source files for precipitation/ rainfall
data.

I hope, I will get your suggestions in future also.

Regards,
Mayank
On Aug 28, 2014 6:26 AM, "Joe Huang" <yjhuang at whiteboxtechnologies.com>
wrote:

> Sounds liked you're referring to Precipitable Water, which has no
> relationship to the actual liquid precipitation falling on the ground. PW
> is reported in the TMY2/3 weather files, mainly because it's used along
> with a few other arcane variables (aerosol optical depth, albedo) in
> modeling solar radiation. These are all echoed in the EPW, which
> content-wise is 99% identical to the TMY2/3s, but I can't think of any
> reason why any of these variables would be used in EnergyPlus.
>
> Another reason I'm doubtful of your explanation is that PW is typically
> reported in depth (0.1 cm in the TMYs) and not pressure.
>
> Sent from my IPad
>
> Joe Huang
>
>
> On Aug 27, 2014, at 3:59 PM, "Collinge, William Overton" <woc6 at pitt.edu>
> wrote:
>
>  The variable in kPa is probably showing the total column water vapor.
> kPa water vapor divided by atmospheric pressure (101.3 kPa or thereabouts
> at sea level) would be an aggregate measure of absolute humidity i.e. an
> average over the vertical profile at some specific location.
>
>
>
> Not sure what it is subsequently used for in E+?
>
>
>
> *From:* Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] *On
> Behalf Of *Michael J Witte
> *Sent:* Wednesday, August 27, 2014 3:52 PM
> *To:* bldg-sim at lists.onebuilding.org
> *Subject:* Re: [Bldg-sim] Precipitation value in stat extension file.
>
>
>
> Not sure what this section of the EnergyPlus stat file is reporting (will
> get this fixed or clarified)
>
>  - Monthly Indicators for Precipitation/Moisture (kPa)
>                     Jan    Feb    Mar    Apr    May    Jun    Jul
> Aug    Sep    Oct    Nov    Dec
>                     1.4      1.6      1.8      1.8      2.3      2.6
> 2.9      2.8      2.7      2.2      1.8      1.3
>
> But if you keep searching for "precipitation" you'll find what I think
> you're looking for
>
>  - Monthly Statistics for Liquid Precipitation mm
>                     Jan    Feb    Mar    Apr    May    Jun    Jul
> Aug    Sep    Oct    Nov    Dec
>        Total       117      43       97       0        0        83
> 0        0        0        0        0        31
>      Max Hourly    36       13       14       0        0        17
> 0        0        0        0        0        6
>
>
> That said, I would echo Joe's comments about using this information with
> caution.  Some data sources do not contain actual precip amounts but only a
> flag for raining or not raining.  The weather processor will fill in
> approximate precip amounts in that case.
>
> Mike
>
>
>
>  On 8/27/2014 12:50 PM, Joe Huang wrote:
>
> Mayank,
>
> You're right.  kPa is a unit of pressure, so somehow the header units
> you're using have been misaligned.  I won't comment on what you see in the
> EPW, but if you look at the source weather file, which probably uses a TMY3
> or TMY2/IWEC format (the only ones I know that contain precipitation data),
> there are two columns for liquid precipitation, one for depth in mm
> followed by one for duration in hr.
>
> Having said that, from my investigations in creating the IWEC2 weather
> files I've concluded that this way of reporting the liquid precipitation
> can lead to missing or double counting the amount of precipitation. The
> reason is that in the actual weather station reports, there may be multiple
> reports in one record, e.g.,
>    100mm over the past 1 hour and 500mm over the past 24 hours
> as well as reports that overlap in time, e.g.,
>    200mm over the past 4 hours
> followed several hours later by
>    400mm over the past 24 hours
>
> I've attached the brief-up about liquid precipitation from the IWEC2 final
> report with more details.
>
> The other thing to consider is that if you're using a "typical year"
> weather file, the liquid precipitation on that file are a random selection
> and may not represent long-range averages.  Depending on your level of
> interest, it's best to go back to the source historical weather files such
> as those available at NCDC:  www.ncdc.noaa/oa/climate/isd/
>
> Joe
>
>  Joe Huang
>
> White Box Technologies, Inc.
>
> 346 Rheem Blvd., Suite 205A
>
> Moraga CA 94556
>
> yjhuang at whiteboxtechnologies.com
>
> http://weather.whiteboxtechnologies.com for simulation-ready weather data
>
> (o) (925)388-0265
>
> (c) (510)928-2683
>
> "building energy simulations at your fingertips"
>
>
> On 8/27/2014 8:59 AM, Mayank Bhatnagar wrote:
>
>   Dear All,
>
> I am doing some analysis on weather file in which I need precipitation
> value in mm or  inches. However, when I look on stat extension file, there
> is monthly precipitation value in kPa. As I know 'kPa' is a unit of
> pressure. Please let me know if anyone has  conversion factor for monthly
> precipitation value from kPa to mm(inches).
>
> The epw extension file has hourly precipitation value in mm. However, all
> the weather files do not have hourly precipitation values.
>
> I'll be grateful if anyone can guide me on this. :)
>
>
>
> Regards,
>
> Mayank
>
>
>
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