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

[Joe Huang]

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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