[Bldg-sim] Precipitation value in stat extension file.
Joe Huang
yjhuang at whiteboxtechnologies.com
Fri Aug 29 13:13:52 PDT 2014
Mayank,
It would help if I knew the extent and purpose of your investigation into
precipitation/rainfall data. For example, what are the location(s)? Is it related to
assessing building energy performance, like for a green roof, etc. Is it a hypothetical
study for average conditions or a specific study of an actual building, time, and place ?
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 8/29/2014 8:13 AM, Mayank Bhatnagar wrote:
>
> 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
> <mailto: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
> <mailto: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
>> <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 <mailto: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/ <http://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 <mailto: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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