[Equest-users] Temperature in weather data

[Joe Huang]

Ralph, others,

I think it all depends on the purpose of the simulation. Leaving aside the issue of design 
sizing for the moment, use of energy simulations to predict, or more often, match observed 
energy usage is typically concerned with annual or long-term energy usage.  In that case, 
stochastic variations around a mean doesn't provide much useful information, because the 
concern is not variability, but bias, in the results. It reminds me of when I saw that the 
uncertainty given for the modeled solar illuminance in the TMY2 weather files was less 
than 3%. That seemed wrong to me, since I know that for any particular hour the 
differences between modeled and measured solar could be quite large.  However, when I read 
the documentation, it made sense because the uncertainty indicates not the stochastic 
variability, but the "mean bias error", i.e., systematic variations, between the modeled 
and measured solar.

How does that relate to the value of stochastic modeling?  If we're only concerned in 
getting the annual totals to match, then whether or not we capture the stochastic 
variations from hour to hour seems to be minor importance.  I'm also having difficulties 
in understand what
additional information is output from "stochastic modeling", except having error bars on 
each hour, which undoubtedly will be large.

My last comment is that although weather patterns are stochastic, the data on the weather 
files is quite deterministic, if we allow that the weather stations are doing a reasonably 
good job in measuring temperatures, wind speeds, etc.  The question of adding precision to 
the DOE-2 weather files is not an issue of stochastic behavior, but simply that of 
round-off errors.

Joe

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
yjhuang at whiteboxtechnologies.com
www.whiteboxtechnologies.com
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"


On 7/27/2012 1:42 PM, Ralph Muehleisen wrote:
> Chris, Joe, others,
>
> The dramatic effects of simply rounding off/ceiling the temperature data in weather 
> files is a perfect example of why we need to, as an industry, move from deterministic 
> energy predictions to stochastic energy predictions.
>
> Weather and occupancy are inherently stochastic and when we couple 
> that stochasticity with our uncertainty in so many of the actual building parameters (at 
> least uncertainty as to their what their values will be when installed), it seems to me 
> that far more meaningful energy predictions could be made using stochastic methods.
>
> While you wouldn't necessarily want to use stochastic methods during much of the design 
> iteration, stochastic estimation should be a standard procedure for comparing major 
> iterations and for final energy predictions.
>
> For all us researchers, there is plenty of work to be done in properly quantifying the 
> stochasticity of weather, occupancy and other stochastic parameters and in developing 
> uncertainty profiles for important parameters that are not stochastic.  There is also 
> opportunities for industry to develop the wrappers to take the info and create the DOE2 
> wrappers.
>
> Am I alone on this or do others feel the same way?
>
> Ralph T Muehleisen
> PhD, PE, LEED AP, INCE Board Certified, FASA
> Principal Building Scientist
> Argonne National Lab
> 9700 S. Cass Ave, Bldg 221
> 630-252-2547, rmuehleisen at anl.gov <mailto:rmuehleisen at anl.gov>
>
>
>
> On Thu, Jul 26, 2012 at 2:31 PM, Joe Huang <yjhuang at whiteboxtechnologies.com 
> <mailto:yjhuang at whiteboxtechnologies.com>> wrote:
>
>     Chris, others,
>
>     Since as you've raised the question of how significant would be adding extra
>     precision to the weather data in DOE-2, I was sent a copy of a recent paper by
>     Annie-Claude Lachapelle of the Univ. of Calgary given at eSim Canada 2012 on this
>     exact topic, "DOE2 Dry-Bulb Temperature Precision Level Impact on Sensible
>     Economizer Performance".   With the author's permission, I've attached the paper
>     with this post.
>
>     Joe
>
>     Joe Huang
>     White Box Technologies, Inc.
>     346 Rheem Blvd., Suite 108D
>     Moraga CA 94556
>     yjhuang at whiteboxtechnologies.com  <mailto:yjhuang at whiteboxtechnologies.com>
>     www.whiteboxtechnologies.com  <http://www.whiteboxtechnologies.com>
>     (o)(925)388-0265  <tel:%28925%29388-0265>
>     (c)(510)928-2683  <tel:%28510%29928-2683>
>     "building energy simulations at your fingertips"
>
>
>     On 7/25/2012 10:45 AM, Joe Huang wrote:
>>     Chris,
>>
>>     My attention on this issue was first raised about 15 years ago when I was working
>>     with non-US weather data , i.e., the rest of the world, that are all reported in
>>     0.1 C. I've noticed since that US stations have also moved to the use of metric
>>     units, i.e., 0.1 C for temperature. The DOE-2 weather format is still in integer F,
>>     which leads to three unfortunate effects: (a) hourly records can be off by as much
>>     as 0.5 F, (b) clumping of the temperature distribution, and (c) statistics such as
>>     degree-days will be off by a percent or two compared to the original data. Now, one
>>     can say that all this is immaterial in the bigger picture of things, which has been
>>     the default attitude so far, but since it's really quite simple to fix, why not get
>>     it right, i.e., doesn't it feel much better to see the same temperatures in the
>>     DOE-2 outputs as in the original weather data?
>>
>>     BTW, all the weather data that I've looked at are records of conditions on the
>>     hour, not the average over the hour, except for solar radiation.
>>
>>     Joe
>>
>>
>>     On 7/25/2012 9:53 AM, Chris Jones wrote:
>>>     Joe
>>>     Given that the time steps are an hour, and the fact that weather data is averaged
>>>     over an hour, plus the fact that the building local will have variations from the
>>>     weather station local, would an extra decimal point provide more useful information?
>>>
>>>
>>>     At 07:43 AM 25/07/2012, Joe Huang wrote:
>>>>     This is not possible at present without changing the DOE-2.2 source code to read
>>>>     a weather input file with decimal values. When DOE-2 was first designed in the
>>>>     early 1980's, memory was a big concern, so the weather data was reduced to
>>>>     integers and then packed, which is why the DOE-2 *.BIN file is so small (146K). I
>>>>     have actually developed a modified file format for *.BIN where I save an extra
>>>>     digit of precision, i.e., temperatures to 0.1F instead of 1 F, but the source
>>>>     code would also need to be changed slightly to read this extra information. I've
>>>>     mentioned this to the developer of eQUEST/DOE-2.2 and will be experimenting with
>>>>     making this change to the source code. If and when it's proven to work and gets
>>>>     incorporated into DOE-2.2, I'll let everyone know. I welcome anyone who thinks
>>>>     this is a useful modification to send me an e-mail. It might spur me on to do
>>>>     something! Joe On 7/23/2012 2:44 AM, è”¡æ˜€èŠ wrote: > Hi, everyone: > > We know
>>>>     that eQUEST can edit personal weather data. > But the dry-bulb and wet-bulb
>>>>     temperature in weather data can only > enter integers. > Is it possible to have
>>>>     more precise temperature to decimal place? > Thank you very much. > > >
>>>>     _______________________________________________ > Equest-users mailing list >
>>>>     http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org > To
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>>>>     EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG
>>>>     <mailto:EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG> > -- Joe Huang White Box
>>>>     Technologies, Inc. 346 Rheem Blvd., Suite 108D Moraga, CA 94556 (o) (925)388-0265
>>>>     <tel:%28925%29388-0265> (c) (510)928-2683 <tel:%28510%29928-2683>
>>>>     www.whiteboxtechnologies.com <http://www.whiteboxtechnologies.com> "Building
>>>>     energy simulations at your fingertips"
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>>>
>>>     >>
>>>     Christopher Jones, P.Eng.
>>>     Suite 1801, 1 Yonge Street
>>>     Toronto, ON M5E1W7
>>>     Tel. 416-203-7465 <tel:416-203-7465>
>>>     Fax. 416-946-1005 <tel:416-946-1005>
>>>     email cj at enersave.ca <mailto:cj at enersave.ca>
>>>
>>>
>>
>>
>>
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