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

[Joe Huang]

Sorry, there was a typo in the link to the ISD.  It should be 
www.ncdc.noaa.gov/oa/climate/isd/  (I tested it this time :-) )

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 10:50 AM, 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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